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MAYO CLINIC CRITICAL AND

NEUROCRITICAL

CARE BOARD REVIEW

MAYO CLINIC SCIENTIFIC PRESS

Mayo Clinic Atlas of Regional Anesthesia and Ultrasound-Guided Nerve Blockade

Edited by James R. Hebl, MD, and Robert L. Lennon, DO

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MAYO CLINIC CRITICAL AND NEUROCRITICAL CARE BOARD REVIEW

EDITED BY

Eelco F. M. Wijdicks, MD, PhD

Chair, Division of Critical Care Neurology

Mayo Clinic, Rochester, Minnesota

Professor of Neurology

Mayo Clinic College of Medicine and Science

James Y. Findlay, MB, ChB

Consultant, Department of Anesthesiology and Perioperative Medicine

Mayo Clinic, Rochester, Minnesota

Associate Professor of Anesthesiology

Mayo Clinic College of Medicine and Science

William D. Freeman, MD

Consultant, Departments of Critical Care Medicine, Neurology, and Neurosurgery

Mayo Clinic, Jacksonville, Florida

Professor of Neurology and of Neurosurgery

Mayo Clinic College of Medicine and Science

Ayan Sen, MD

Chair, Department of Critical Care Medicine

Mayo Clinic Hospital, Phoenix, Arizona

Assistant Professor of Emergency Medicine and of Medicine

Mayo Clinic College of Medicine and Science

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Library of Congress Cataloging-in-Publication Data

Names: Wijdicks, Eelco F. M., 1954– editor. | Findlay, James Y., editor. | Freeman, William D., editor. | Sen, Ayan.

Title: Mayo Clinic critical and neurocritical care board review / [edited by] Eelco F. M. Wijdicks, James Y. Findlay, William D. Freeman, Ayan Sen.

Other titles: Critical and neurocritical care board review

Description: New York, NY : Oxford University Press, 2019. | Includes bibliographical references and index.

Identifiers: LCCN 2019005581| ISBN 9780190862923 (pbk.) | ISBN 9780190862930 (updf) | ISBN 9780190862947 (epub) | ISBN 9780190862954 (on-line)

Subjects: | MESH: Critical Care | Study Guide

Classification: LCC RC86.9 | NLM WX 18.2 | DDC 616.02/8076—dc23

LC record available at https://lccn.loc.gov/2019005581

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Preface

Physicians have cared for patients with acute illnesses throughout history. The terminology related to these patients has changed. Sick patients became critically ill patients, and all needed intensive care. After the devastating poliomyelitis epidemics of the 1950s, a new specialty of critical care medicine emerged. Initially, respiratory care units were created for the patients affected by this severe illness, but soon they were transformed into intensive care units. Trauma units and transplant units soon followed. Specialized care for patients with acute neurologic or neurosurgical disease was established in parallel with these developments, but many of the early neuroscience intensive care units were redesigned wards. Specialized physicians and nursing staff delivered multidisciplinary care, recognizing that no one group could function well alone. Inevitably, critical care for the sickest patients was the only option to give them a fighting chance to survive.

In the United States, the Society of Critical Care Medicine brought the specialty clearly into focus in the early 1970s, and training program guidelines soon were developed in the United States and abroad. The Neurocritical Care Society was founded in 2002, and accreditation was established through the American Academy of Neurology (United Council of Neurologic Subspecialties). Most importantly, the American Board of Medical Specialties has approved creation of a neurocritical care subspecialty, and Accreditation Council for Graduate Medical Education–accredited fellowships and a new board examination are planned.

Currently, the neurocritical care board examination combines neurocritical care with general intensive care, and questions are equally divided between the 2 subjects. Accordingly, combining both areas of expertise in a single volume is appropriate.

The chapters in this book correspond with the key disorders suggested by the United Council of

Neurologic Subspecialties to be studied in preparation for the examination and to assist with the critical care board examination. The book is not only detailed in basic pathophysiologic content but also describes major disorders and syndromes and their management. Because of its unprecedented complete coverage of acute neurologic disorders, it is equally useful as preparation for the critical care medicine board examination.

The success of board review books hinges on clarity of the presented information, and we focused on conciseness and readability. Readers find tables, explanatory drawings, and bullet points useful, and thus we included them throughout while keeping the text specific and informative. We edited the entire text, and we sought expert advise to fill in our gaps in knowledge or to verify our additions. All chapters were written and closely edited by Mayo Clinic faculty. The references are up-to-date and include many guidelines.

Board review books have multiple disclaimers, as does this one. Use of this book alone will not guarantee passing the examination(s), and additional texts should be consulted. The book has more than 500 multiplechoice practice questions and answers. References are included with each answer. The questions are of the type used on the board examination. Reviewing the questions may improve one’s ability to take the board examination, but we all appreciate that (in essence) passing an examination is directly related to sufficient knowledge of the topics. We hope you will benefit from studying this text. It should appeal to any aspiring intensivist in training. We enjoyed selecting the material for you, and we definitely learned a few things along the way. We hope this book will help you pass the examination.

EFM WIJDICKS

JY FINDLAY

WD FREEMAN

SEN

Contributors xiii

Section I: Fundamentals of Critical Care

1 • Respiratory Physiology in Critical Illness 3

Minkyung Kwon, MD and Jose L. Diaz-Gomez, MD

2 • Mechanical Ventilation: Basic Modes 10

Amelia A. Lowell, RRT, RCP

3 • Mechanical Ventilation: Advanced Modes 17

Amelia A. Lowell, RRT, RCP and Bhavesh M. Patel, MD

• Cardiovascular System in the Critically Ill Patient 26

Juan G. Ripoll Sanz, MD; Norlalak Jiramethee, MD; and Jose L. Diaz-Gomez, MD

5 • Renal Function in Critically Ill Patients 35

Pramod K. Guru, MBBS, MD

6 • Nutrition in Critical Illness 42

Angela N. Vizzini, RDN, LD/N and Mireille H. Hamdan, RDN, LD/N

Section I: Questions and Answers 50

Section II: Fundamentals of Neurocritical Care

7 • Neurologic Examination in Neurocritical Illness 61

Eelco F. M. Wijdicks, MD, PhD

8 • Intracranial Pressure 69

Eelco F. M. Wijdicks, MD, PhD and William D. Freeman, MD

9 • Cerebrospinal Physiology 74

Joseph Zachariah, MD

• Cerebral Circulation and Cerebral Blood Flow 79

Arnoley S. Abcejo, MD and Jeffrey J. Pasternak, MD

• Consequences of Anoxia and Ischemia to the Brain 86

Jennifer E. Fugate, DO

• Consequences of Acute Metabolic Changes to the Brain 92

Sherri A. Braksick, MD and Sara E. Hocker, MD

• Consequences of Acute Hypertension to the Brain 97

Katherine M. Oshel, MD and Hani M. Wadei, MD

14 • Coma and Other Altered States of Consciousness 101

Eelco F. M. Wijdicks, MD, PhD

15 • Neuromuscular Respiratory Failure 109

Maximiliano A. Hawkes, MD and Eelco F. M. Wijdicks, MD, PhD

16 • Neurogenic Breathing Patterns 115

Eelco F. M. Wijdicks, MD, PhD

17 • Neurogenic Cardiac Manifestations 118

Sherri A. Braksick, MD and Eelco F. M. Wijdicks, MD, PhD

18 • Paroxysmal Sympathetic Hyperactivity 122

Kevin T. Gobeske, MD, PhD

Section II: Questions and Answers 125

Section III: Critical Care Disorders

Pulmonary Disorders

19 • Acute Respiratory Distress Syndrome 137

Richard K. Patch III, MD and James Y. Findlay, MB, ChB

• Pulmonary Embolism: An Overview 142

Brandon T. Nokes, MD and Rodrigo Cartin-Ceba, MD

• Asthma in the Critically Ill Patient 150

Jonathan J. Danaraj, DO and Augustine S. Lee, MD

• Chronic Obstructive Pulmonary Disease

Exacerbation 157

Isabel Mira-Avendano, MD and Minkyung Kwon, MD

• Pleural Diseases in Critical Care Medicine 161

Karthika R. Linga, MBBS and Neal M. Patel, MD

• Pulmonary Malignancy 166

Ali A. Zaied, MD and Margaret M. Johnson, MD

• Pulmonary Hypertension and Right-Sided Heart Failure in the Critically Ill 171

Charles D. Burger, MD

Circulatory and Cardiovascular Disorders

• Anaphylaxis and Anaphylactic Shock 179

Megan S. Motosue, MD and Gerald W. Volcheck, MD

• Cardiogenic Shock 183

Robert A. Ratzlaff, DO and Jason L. Siegel, MD

• Acute Coronary Syndrome 190

Siva S. Ketha, MD and Juan Carlos Leoni Moreno, MD

• Cardiac Rhythm and Conduction Disturbances 197

Yahaira Ortiz Gonzalez, MD and Fred Kusumoto, MD

• Hypertensive Emergencies 207

Denzil R. Hill, MD and James A. Onigkeit, MD

• Cardiopulmonary Resuscitation 211

Richard K. Patch III, MD

32 • Vascular Emergencies of the Aorta 216

Tariq Almerey, MD; January F. Moore; and Houssam Farres, MD

Acute Endocrine Disorders

33 • Pituitary Apoplexy 225

Sherri A. Braksick, MD

34 • Diabetes Insipidus 229

Dana Erickson, MD

35 • Panhypopituitarism 234

Diane Donegan, MB, BCh and Irina Bancos, MD

36 • Thyroid Disorders in the Intensive Care Unit 239

John E. Moss, MD

37 • Glycemic Control in Neurocritically Ill Patients 241

Carla P. Venegas-Borsellino, MD; Michael A. Pizzi, DO, PhD; and Santiago Naranjo-Sierra, MD

38 • Adrenal Insufficiency in Neurocritically Ill Patients 246

Carla P. Venegas-Borsellino, MD and Santiago Naranjo-Sierra, MD

Gastrointestinal Disorders

39 • Acute Gastrointestinal Hemorrhage 253

Pablo Moreno Franco, MD and Philip E. Lowman, MD

40 • Paralytic and Obstructive Ileus 259

Juan M. Canabal, MD

41 • Acute Liver Failure 264

James Y. Findlay, MB, ChB and Eelco F. M. Wijdicks, MD, PhD

42 • Acute Perforations of the Gastrointestinal Tract 270

Levan Tsamalaidze, MD and John A. Stauffer, MD

43 • Acute Vascular Disorders of the Intestine 276

Omar Y. Mousa, MBBS and Surakit Pungpapong, MD

44 • Abdominal Compartment Syndrome 281

Daniel J. Johnson, MD

Renal Disorders

45 • Acute Kidney Injury 287

Ankit Sakhuja, MBBS and Kianoush B. Kashani, MD

46 • Acid-Base Disorders 294

Onur Demirci, MD

47 • Drug Dosing in Renal Failure 299

Daniel A. Jackson, PharmD, RPh

48 • Principles of Renal Replacement Therapies 302

Peter M. Fitzpatrick, MD

49 • Disorders of Water and Electrolyte Balance 306 Yuzana Zaw, MBBS and Mira T. Keddis, MD

Hematologic and Inflammatory Disorders

50 • Anemia and Blood Transfusion 319

Joy D. Hughes, MD; Mariela Rivera, MD; and Myung S. Park, MD, MS

51 • Hematologic and Oncologic Complications in the Intensive Care Unit 325

Carl A. Ruthman, MD and Jose C. Yataco, MD

52 • Thrombocytopenia and Thrombocytopathy 331

Gretchen Johns, MD

53 • Disseminated Intravascular Coagulation: Clinical Diagnosis and Management 337

Prakash Vishnu, MBBS and Sikander Ailawadhi, MD

54 • Diagnosis and Management of Acquired Bleeding Disorders 345

Rajiv K. Pruthi, MBBS

55 • Anticoagulation Monitoring and Reversal 353

Theresa N. Kinard, MD

56 • Therapeutic Plasma Exchange for Acute Hematologic Disorders 359

Jill Adamski, MD, PhD

57 • Rheumatologic and Autoimmune Emergencies 363

Megan L. Krause, MD and Kevin G. Moder, MD

Sepsis and Other Infectious Diseases

58 • Infectious Diseases Complicating Critical Care 369

David A. Sotello Aviles, MD and Walter C. Hellinger, MD

59 • Antibiotics in the Intensive Care Unit 375

David A. Sotello Aviles, MD and Walter C. Hellinger, MD

60 • Sepsis and Septic Shock 381

Charles R. Sims III, MD and Thomas B. Comfere, MD

Dermatologic Concerns

61 • Dermatologic Emergencies in the Intensive Care Unit 391

Matthew R. Hall, MD

Trauma and Burns

62 • Initial Approach to the Management of Multisystem Trauma 397

David S. Morris, MD

63 • Chest and Abdominal Trauma 402

Joy D. Hughes, MD and David S. Morris, MD

64 • Skeletal Trauma 405

Joshua S. Bingham, MD and Kevin J. Renfree, MD

65 • Burns and Electrical Injuries 409

Brandon T. Nokes, MD and Ayan Sen, MD

Cardiothoracic Critical Care

66 • Cardiothoracic Surgery and Postoperative Intensive Care 417

Juan G. Ripoll Sanz, MD and Robert A. Ratzlaff, DO

67 • Mechanical Circulatory Assist Devices 424

Ayan Sen, MD and Bhavesh M. Patel, MD

68 • Extracorporeal Membrane Oxygenation 429

J. Kyle Bohman, MD and Gregory J. Schears, MD

69 • Cardiac Pacing in the Intensive Care Unit 435 J. William Schleifer, MD; Farouk Mookadam, MB, BCh; and Harish Ramakrishna, MD

Transplant Critical Care

• Clinical Management of Heart Transplant Recipients 443

Arzoo Sadiqi, BS and Jama Jahanyar, MD, PhD

• Critical Care of Heart-Lung and Lung Transplant Recipients 446

Ramachandra R. Sista, MD

• Clinical Management of Liver Transplant Recipients 453

Bhargavi Gali, MD

• Clinical Management of Kidney Transplant Recipients 457

James A. Onigkeit, MD

• Small Intestinal Transplant 460

Ayan Sen, MD

Toxicity and Toxins

75 • Serotonin Syndrome 467

Kevin T. Gobeske, MD, PhD and Eelco F. M. Wijdicks, MD, PhD

• Neuroleptic Malignant Syndrome and Hyperthermia 472

J. Ross Renew, MD and Monica Mordecai, MD

• Clinical Toxicology: Selected Drugs of Abuse and Chemical and Biological Warfare Agents 475

Matthew D. Sztajnkrycer, MD, PhD

Section III: Questions and Answers 483

Section IV: Neurocritical Illness

Acute Cerebrovascular Disorders

• Diagnosis and Management of Hemispheric Infarction 543

Sanjeet S. Grewal, MD and Benjamin L. Brown, MD

• Basilar Artery Occlusion 547

Michael R. Pichler, MD and Jennifer E. Fugate, DO

• Carotid Artery Disease 555 Nnenna Mbabuike, MD and Rabih G. Tawk, MD

• Adult Primary Central Nervous System Vasculitis 563

Carlo Salvarani, MD; Robert D. Brown Jr, MD, MPH; and Gene G. Hunder, MD

• Intracerebral and Intraventricular Hemorrhage 570 Oana Dumitrascu, MD and Maria I. Aguilar, MD

• Aneurysmal Subarachnoid Hemorrhage 577

Giuseppe Lanzino, MD and Biagia La Pira, MD

• Intracranial Arteriovenous Malformations 585

Kelly D. Flemming, MD and Michael J. Link, MD

• Cerebral Venous and Dural Sinus Thrombosis 594

Sara E. Hocker, MD

86 • Cervical Arterial Dissection 600

Bart M. Demaerschalk, MD

Traumatic Brain and Spine Injury

87 • Traumatic Brain Injury and Spinal Cord Injury 605

Maya A. Babu, MD

88 • Traumatic Epidural and Subdural Hematomas 614

Patrick R. Maloney, MD and Michelle J. Clarke, MD

89 • Unstable Spinal Fractures 621

William E. Clifton III, MD and Mark A. Pichelmann, MD

Acute Central Nervous System Infections

90 • Encephalitis 629

Allen J. Aksamit Jr, MD

91 • Acute Bacterial Meningitis 637

Eelco F. M. Wijdicks, MD, PhD

92 • Brain Abscess and Spinal Epidural Abscess 642

Selby G. Chen, MD

Acute Neuromuscular Disorders

93 • Myasthenia Gravis 651

Maximiliano A. Hawkes, MD and Eelco F. M. Wijdicks, MD, PhD

94 • Guillain-Barré Syndrome 658

Eelco F. M. Wijdicks, MD, PhD

95 • Amyotrophic Lateral Sclerosis 664

Jennifer M. Martinez-Thompson, MD and Nathan P. Staff, MD, PhD

96 • Rhabdomyolysis and Toxic Myopathies 670

Justin C. Kao, MB, ChB and Margherita Milone, MD, PhD

97 • Myopathy and Neuropathy Acquired in the Intensive Care Unit 677

Priya S. Dhawan, MD and Jennifer A. Tracy, MD

Miscellaneous Disorders of Acute Brain Injury

98 • Status Epilepticus 687

Christopher P. Robinson, DO, MS and Sara E. Hocker, MD

99 • Posterior Reversible Encephalopathy Syndrome 693

Sudhir V. Datar, MBBS and Jennifer E. Fugate, DO

100 • Demyelinating Disorders of the Central Nervous System 699

Aurelia A. Smith, MD and Brian G. Weinshenker, MD

101 • Rapidly Progressive Dementia and Coma 704

Prasuna Kamireddi, MBBS; Jason L. Siegel, MD; and Dennis W. Dickson, MD

Neuro-oncology

102 • Brain and Spine Tumors 715

Mithun Sattur, MBBS; Matthew E. Welz, MS; and Bernard R. Bendok, MD

103 • Neoplastic Meningitis 722

Alyx B. Porter, MD

104 • Autoimmune Encephalitis 726

Eslam Shosha, MB, BCh and Sean J. Pittock, MD

105 • Radiation Therapy 734

Sameer R. Keole, MD

Postoperative Neurosurgery

106 • Intensive Care After Spinal Surgery 739

Clarence B. Watridge, MD

107 • Intensive Care After Craniotomy 746

Kelly Gassie, MD; Belinda G. Bradley, APRN; Robert E. Wharen Jr, MD; and Betty Y. S. Kim, MD, PhD

108 • Intensive Care After Neuroendovascular Procedures 753

Mithun Sattur, MBBS; Chandan Krishna, MD; Bernard R. Bendok, MD; and Brian W. Chong, MD

Section IV: Questions and Answers 759

Section V: Imaging in Critical Illness

109 • Radiography and Computed Tomography of the Chest 785

Barbara L. McComb, MD

110 • Abdominal Radiography 797

Joseph G. Cernigliaro, MD and David J. DiSantis, MD

111 • Fluoroscopy: Principles and Safety 805

David M. Sella, MD; Glenn M. Sturchio, PhD; and Beth A. Schueler, PhD

112 • Ultrasonography 809

Santiago Naranjo-Sierra, MD and Lauren K. Ng Tucker, MD

113 • Transesophageal Echocardiography 816

Ryan C. Craner, MD; Farouk Mookadam, MB, BCh; and Harish Ramakrishna, MD

Section V: Questions and Answers 827

Section VI: Procedures

Airway Procedures and Modes of

Ventilation

114 • Basics of Airway and Oxygen Delivery Devices 835

Andrew W. Murray, MD

115 • Endotracheal Intubation Procedures 840

Matthew J. Ritter, MD

116

• Noninvasive Positive Pressure Ventilation 846

Karen W. Hampton, MS, RRT

117 • Tracheostomy 850

Saba Ghorab, MD and David G. Lott, MD

118 • Diagnostic and Interventional Bronchoscopy in the Intensive Care Unit 855

Cesar A. Keller, MD

Cardiovascular and Cardiopulmonary

Monitoring and Access

119 • Electrocardiographic Monitoring 865

Pragnesh P. Parikh, MD and K. L. Venkatachalam, MD

120 • Hemodynamic Monitoring 870

Hannelisa E. Callisen, PA-C;

Stacy L. Libricz, PA-C, MS; and Ayan Sen, MD

121

• Pulmonary Artery Catheterization 879

Philip E. Lowman, MD

122 • Thoracentesis and Chest Tubes 883

Staci E. Beamer, MD

123

• Central Line Placement 890

Nicholas D. Will, MD and W. Brian Beam, MD

124 • Interventional Radiology Procedures 892

Rahmi Oklu, MD, PhD

Neuromonitoring and Procedures

125 • Intracranial Pressure Monitoring and External Ventricular Drainage 899

Maya A. Babu, MD and John L. D. Atkinson, MD

126 • Lumbar Puncture 903

Christina C. Smith, APRN

127 • Lumbar Drain 907

Jamie J. Van Gompel, MD

128 • Intraventricular Drug Administration 912

William W. Horn Jr, APRN and Benjamin L. Brown, MD

129 • Transcranial Doppler Ultrasonography 914

Mark N. Rubin, MD

130 • Electroencephalography 918

Amy Z. Crepeau, MD

131 • Essentials of Multimodal Brain Monitoring 925

Jennifer E. Fugate, DO

132 • Essentials of Cranial Neuroimaging 932

E. Paul Lindell, MD

Section VI: Questions and Answers 941

Section VII: Pharmacotherapeutics

133 • Anticonvulsant Drugs 955

Anteneh M. Feyissa, MD and Jeffrey W. Britton, MD

134 • Effects of Targeted Temperature Management on Drugs 963

Lauren K. Ng Tucker, MD

135 • Sedation and Analgesia 967

Juan G. Ripoll Sanz, MD and Jose L. Diaz-Gomez, MD

136 • Inotropes, Vasopressors, and Antihypertensive Agents 972

Juan N. Pulido, MD

137 • Antibiotics, Antivirals, and Antifungals 981

David A. Sotello Aviles, MD and Walter C. Hellinger, MD

Section VII: Questions and Answers 990

Section VIII: Ethics in the Neurointensive Care Unit

138 • Palliative and End-of-Life Care in the Intensive Care Unit 997

Maisha T. Robinson, MD

139 • Communicating With Families 1001

Cory Ingram, MD

140 • Brain Death 1005

Eelco F. M. Wijdicks, MD, PhD

141 • Minimally Conscious State and Persistent Vegetative State 1008

David T. Jones, MD

142 • Ethical Concerns and Care Before Organ Donation 1012

Diane C. McLaughlin, APRN and

Lauren K. Ng Tucker, MD

Section VIII: Questions and Answers 1015

Index 1019

Contributors

Arnoley S. Abcejo, MD

Senior Associate Consultant, Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota; Assistant Professor of Anesthesiology, Mayo Clinic College of Medicine and Science

Jill Adamski, MD, PhD

Chair, Division of Laboratory Medicine, Mayo Clinic Hospital, Phoenix, Arizona; Associate Professor of Laboratory Medicine and Pathology, Mayo Clinic College of Medicine and Science

Maria I. Aguilar, MD

Consultant, Department of Neurology, Mayo Clinic, Scottsdale, Arizona; Associate Professor of Neurology, Mayo Clinic College of Medicine and Science

Sikander Ailawadhi, MD

Consultant, Division of Hematology and Oncology, Mayo Clinic, Jacksonville, Florida; Associate Professor of Medicine, Mayo Clinic College of Medicine and Science

Allen J. Aksamit Jr, MD

Consultant, Department of Neurology, Mayo Clinic, Rochester, Minnesota; Professor of Neurology, Mayo Clinic College of Medicine and Science

Tariq Almerey, MD

Research Fellow in Surgery, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Jacksonville, Florida

John L. D. Atkinson, MD

Consultant, Department of Neurologic Surgery, Mayo Clinic, Rochester, Minnesota; Professor of Neurosurgery, Mayo Clinic College of Medicine and Science

Maya A. Babu, MD

Resident in Neurosurgery, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Rochester, Minnesota

Present address: Harvard Medical School, Boston, Massachusetts

Irina Bancos, MD

Consultant, Division of Endocrinology, Diabetes, Metabolism, & Nutrition, Mayo Clinic, Rochester, Minnesota; Assistant Professor of Medicine, Mayo Clinic College of Medicine and Science

W. Brian Beam, MD

Consultant, Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota; Assistant Professor of Anesthesiology, Mayo Clinic College of Medicine and Science

Staci E. Beamer, MD

Senior Associate Consultant, Department of Cardiovascular and Thoracic Surgery, Mayo Clinic Hospital, Phoenix, Arizona; Assistant Professor of Surgery, Mayo Clinic College of Medicine and Science

Bernard R. Bendok, MD

Chair, Department of Neurologic Surgery, Mayo Clinic Hospital, Phoenix, Arizona; Professor of Neurosurgery, Mayo Clinic College of Medicine and Science

Joshua S. Bingham, MD

Fellow in Reconstructive Surgery, Mayo Clinic School of Graduate Medical Education and Instructor in Orthopedics, Mayo Clinic College of Medicine and Science, Scottsdale, Arizona

J. Kyle Bohman, MD

Consultant, Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota; Assistant Professor of Anesthesiology, Mayo Clinic College of Medicine and Science

Belinda G. Bradley, APRN

Lead Nurse Practicioner, Department of Neurologic Surgery, Mayo Clinic, Jacksonville, Florida

Sherri A. Braksick, MD

Fellow in Critical Care Neurology, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Rochester, Minnesota

Present address: University of Kansas Medical Center, Kansas City, Kansas

Jeffrey W. Britton, MD

Chair, Division of Epilepsy, Mayo Clinic, Rochester, Minnesota; Professor of Neurology, Mayo Clinic College of Medicine and Science

Benjamin L. Brown, MD

Senior Associate Consultant, Department of Neurologic Surgery, Mayo Clinic, Jacksonville, Florida; Assistant Professor of Neurosurgery, Mayo Clinic College of Medicine and Science

Robert D. Brown Jr, MD, MPH

Chair, Division of Stroke and Cerebrovascular Diseases, Mayo Clinic, Rochester, Minnesota; Professor of Neurology, Mayo Clinic College of Medicine and Science

Charles D. Burger, MD

Consultant, Division of Pulmonary, Allergy, and Sleep Medicine, Mayo Clinic, Jacksonville, Florida; Professor of Medicine, Mayo Clinic College of Medicine and Science

Hannelisa E. Callisen, PA-C

Physician Assistant, Department of Critical Care Medicine, Mayo Clinic Hospital, Phoenix, Arizona

Juan M. Canabal, MD

Senior Associate Consultant, Department of Transplantation, Mayo Clinic, Jacksonville, Florida; Assistant Professor of Medicine, Mayo Clinic College of Medicine and Science

Rodrigo Cartin-Ceba, MD

Consultant, Department of Critical Care Medicine, Mayo Clinic, Scottsdale, Arizona; Associate Professor of Medicine, Mayo Clinic College of Medicine and Science

Joseph G. Cernigliaro, MD

Chair, Division of Abdominal Imaging, Mayo Clinic, Jacksonville, Florida; Associate Professor of Radiology, Mayo Clinic College of Medicine and Science

Selby G. Chen, MD

Senior Associate Consultant, Department of Neurologic Surgery, Mayo Clinic, Jacksonville, Florida; Assistant Professor of Neurosurgery, Mayo Clinic College of Medicine and Science

Brian W. Chong, MD

Consultant, Department of Radiology, Mayo Clinic Hospital, Phoenix, Arizona; Associate Professor of Radiology, Mayo Clinic College of Medicine and Science

Michelle J. Clarke, MD

Consultant, Department of Neurologic Surgery, Mayo Clinic, Rochester, Minnesota; Professor of Neurosurgery and of Orthopedics, Mayo Clinic College of Medicine and Science

William E. Clifton III, MD

Resident in Neurologic Surgery, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Jacksonville, Florida

Thomas B. Comfere, MD

Consultant, Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota; Assistant Professor of Anesthesiology, Mayo Clinic College of Medicine and Science

Ryan C. Craner, MD

Consultant, Department of Anesthesiology and Perioperative Medicine, Mayo Clinic Hospital, Phoenix, Arizona; Assistant Professor of Anesthesiology, Mayo Clinic College of Medicine and Science

Amy Z. Crepeau, MD

Consultant, Department of Neurology, Mayo Clinic Hospital, Phoenix, Arizona; Assistant Professor of Neurology, Mayo Clinic College of Medicine and Science

Jonathan J. Danaraj, DO

Resident in Pulmonary and Critical Care Medicine, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Jacksonville, Florida

Sudhir V. Datar, MBBS

Division of Critical Care Neurology, Wake Forest University Medical Center, Winston-Salem, North Carolina; Assistant Professor of Neurology and of Anesthesiology, Wake Forest School of Medicine

Bart M. Demaerschalk, MD

Consultant, Department of Neurology, Mayo Clinic Hospital, Phoenix, Arizona; Professor of Neurology, Mayo Clinic College of Medicine and Science

Onur Demirci, MD

Consultant, Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota; Assistant Professor of Anesthesiology, Mayo Clinic College of Medicine and Science

Priya S. Dhawan, MD

Resident in Neurology, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Rochester, Minnesota

Present address: University of British Columbia, Vancouver, British Columbia

Jose L. Diaz-Gomez, MD

Consultant, Departments of Critical Care Medicine, Anesthesiology, and Neurosurgery, Mayo Clinic, Jacksonville, Florida; Associate Professor of Anesthesiology, Mayo Clinic College of Medicine and Science

Present address: Private Practice

Dennis W. Dickson, MD

Consultant, Departments of Laboratory Medicine and Pathology and of Neuroscience, Mayo Clinic, Jacksonville, Florida; Professor of Laboratory Medicine and Pathology, Mayo Clinic College of Medicine and Science

David J. DiSantis, MD

Senior Associate Consultant, Department of Radiology, Mayo Clinic, Jacksonville, Florida; Professor of Radiology, Mayo Clinic College of Medicine and Science

Diane Donegan, MB, BCh

Research Collaborator in Endocrinology, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Rochester, Minnesota

Oana Dumitrascu, MD

Fellow in Vascular Neurology, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Scottsdale, Arizona

Dana Erickson, MD

Consultant, Division of Endocrinology, Diabetes, Metabolism, & Nutrition, Mayo Clinic, Rochester, Minnesota; Associate Professor of Medicine, Mayo Clinic College of Medicine and Science

Houssam Farres, MD

Consultant, Division of Vascular Surgery, Mayo Clinic, Jacksonville, Florida; Assistant Professor of Surgery, Mayo Clinic College of Medicine and Science

Anteneh M. Feyissa, MD

Senior Associate Consultant, Department of Neurology, Mayo Clinic, Jacksonville, Florida; Assistant Professor of Neurology, Mayo Clinic College of Medicine and Science

James Y. Findlay, MB, ChB

Consultant, Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota; Associate Professor of Anesthesiology, Mayo Clinic College of Medicine and Science

Peter M. Fitzpatrick, MD

Consultant, Division of Nephrology and Hypertension, Mayo Clinic, Jacksonville, Florida; Assistant Professor of Medicine, Mayo Clinic College of Medicine and Science

Kelly D. Flemming, MD

Consultant, Department of Neurology, Mayo Clinic, Rochester, Minnesota; Associate Professor of Neurology, Mayo Clinic College of Medicine and Science

William D. Freeman, MD

Consultant, Departments of Critical Care Medicine, Neurology, and Neurosurgery, Mayo Clinic, Jacksonville, Florida; Professor of Neurology and of Neurosurgery, Mayo Clinic College of Medicine and Science

Jennifer E. Fugate, DO

Consultant, Department of Neurology, Mayo Clinic, Rochester, Minnesota; Assistant Professor of Neurology, Mayo Clinic College of Medicine and Science

Bhargavi Gali, MD

Consultant, Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota; Assistant Professor of Anesthesiology, Mayo Clinic College of Medicine and Science

Kelly Gassie, MD

Resident in Neurologic Surgery, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Jacksonville, Florida

Saba Ghorab, MD

Resident in Otolaryngology, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Scottsdale, Arizona

Kevin T. Gobeske, MD, PhD

Resident in Critical Care Neurology, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Rochester, Minnesota

Sanjeet S. Grewal, MD

Resident in Neurologic Surgery, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Jacksonville, Florida

Pramod K. Guru, MBBS, MD

Senior Associate Consultant, Department of Critical Care Medicine, Mayo Clinic, Jacksonville, Florida; Assistant Professor of Medicine, Mayo Clinic College of Medicine and Science

Matthew R. Hall, MD

Consultant, Department of Dermatology, Mayo Clinic, Jacksonville, Florida; Assistant Professor of Dermatology, Mayo Clinic College of Medicine and Science

Mireille H. Hamdan, RDN, LD/N

Dietician, Clinical Nutrition Services, Mayo Clinic, Jacksonville, Florida; Instructor in Nutrition, Mayo Clinic College of Medicine and Science

Karen W. Hampton, MS, RRT

Respiratory Therapist, Respiratory Services, Mayo Clinic, Jacksonville, Florida

Maximiliano A. Hawkes, MD

Fellow in Critical Care Neurology, Mayo Clinic School of Graduate Medical Education and Assistant Professor of Neurology, Mayo Clinic College of Medicine and Science, Rochester, Minnesota

Walter C. Hellinger, MD

Chair, Division of Infectious Diseases, Mayo Clinic, Jacksonville, Florida; Associate Professor of Medicine, Mayo Clinic College of Medicine and Science

Denzil R. Hill, MD

Senior Associate Consultant, Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota; Instructor in Anesthesiology, Mayo Clinic College of Medicine and Science

Sara E. Hocker, MD

Consultant, Department of Neurology, Mayo Clinic, Rochester, Minnesota; Associate Professor of Neurology, Mayo Clinic College of Medicine and Science

William W. Horn Jr, APRN

Nurse Practitioner, Department of Neurologic Surgery, Mayo Clinic, Jacksonville, Florida

Joy D. Hughes, MD

Research Fellow in General Surgery, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Rochester, Minnesota

Gene G. Hunder, MD

Emeritus Professor of Neurology, Mayo Clinic College of Medicine and Science, Rochester, Minnesota

Cory Ingram, MD

Senior Associate Consultant, Division of Community Palliative Medicine, Mayo Clinic, Rochester, Minnesota; Assistant Professor of Family Medicine and of Palliative Medicine, Mayo Clinic College of Medicine and Science

Daniel A. Jackson, PharmD, RPh

Pharmacist, Pharmacy Services, Mayo Clinic, Jacksonville, Florida; Assistant Professor of Pharmacy, Mayo Clinic College of Medicine and Science

Jama Jahanyar, MD, PhD

Senior Associate Consultant, Department of Cardiovascular and Thoracic Surgery, Mayo Clinic Hospital, Phoenix, Arizona; Assistant Professor of Surgery, Mayo Clinic College of Medicine and Science

Norlalak Jiramethee, MD

Fellow in Critical Care Medicine, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Jacksonville, Florida

Gretchen Johns, MD

Consultant, Department of Laboratory Medicine and Pathology, Mayo Clinic, Jacksonville, Florida; Assistant Professor of Laboratory Medicine and Pathology, Mayo Clinic College of Medicine and Science

Daniel J. Johnson, MD

Chair, Department of Surgery, Mayo Clinic Hospital, Phoenix, Arizona; Associate Professor of Surgery, Mayo Clinic College of Medicine and Science

Margaret M. Johnson, MD

Consultant, Division of Pulmonary, Allergy and Sleep Medicine, Mayo Clinic, Jacksonville, Florida; Associate Professor of Medicine, Mayo Clinic College of Medicine and Science

David T. Jones, MD

Consultant, Department of Neurology, Mayo Clinic, Rochester, Minnesota; Assistant Professor of Neurology, Mayo Clinic College of Medicine and Science

Prasuna Kamireddi, MBBS

Research Trainee, Department of Neurology, Mayo Clinic, Jacksonville, Florida

Justin C. Kao, MB, ChB

Fellow in Advanced Clinical Neurology, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Rochester, Minnesota

Kianoush B. Kashani, MD

Consultant, Division of Nephrology and Hypertension, Mayo Clinic, Rochester, Minnesota; Professor of Medicine, Mayo Clinic College of Medicine and Science

Mira T. Keddis, MD

Consultant, Division of Nephrology, Mayo Clinic, Scottsdale, Arizona; Assistant Professor of Medicine, Mayo Clinic College of Medicine and Science

Cesar A. Keller, MD

Emeritus Professor of Medicine, Mayo Clinic College of Medicine and Science, Jacksonville, Florida

Sameer R. Keole, MD

Consultant, Department of Radiation Oncology, Mayo Clinic Hospital, Phoenix, Arizona; Assistant Professor of Radiation Oncology, Mayo Clinic College of Medicine and Science

Siva S. Ketha, MD

Research Collaborator, Mayo Clinic, Jacksonville, Florida; Assistant Professor of Medicine, Mayo Clinic College of Medicine and Science

Betty Y. S. Kim, MD, PhD

Consultant, Department of Neurologic Surgery, Mayo Clinic, Jacksonville, Florida; Associate Professor of Neurosurgery and Assistant Professor of Neuroscience, Mayo Clinic College of Medicine and Science

Theresa N. Kinard, MD

Consultant, Department of Laboratory Medicine, Mayo Clinic Hospital, Phoenix, Arizona; Assistant Professor of Laboratory Medicine and Pathology, Mayo Clinic College of Medicine and Science

Megan L. Krause, MD

Fellow in Rheumatology, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Rochester, Minnesota

Chandan Krishna, MD

Senior Associate Consultant, Department of Neurologic Surgery, Mayo Clinic Hospital, Phoenix, Arizona; Assistant Professor of Neurosurgery, Mayo Clinic College of Medicine and Science

Fred Kusumoto, MD

Consultant, Department of Cardiovascular Diseases, Mayo Clinic, Jacksonville, Florida; Professor of Medicine, Mayo Clinic College of Medicine and Science

Minkyung Kwon, MD

Resident in Pulmonary and Critical Care Medicine, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Jacksonville, Florida

Giuseppe Lanzino, MD

Consultant, Departments of Neurologic Surgery and Radiology, Mayo Clinic, Rochester, Minnesota; Professor of Neurosurgery, Mayo Clinic College of Medicine and Science

Biagia La Pira, MD

Research Trainee, Department of Neurologic Surgery, Mayo Clinic, Rochester, Minnesota

Present address: Private Practice, Rome, Italy

Augustine S. Lee, MD

Chair, Division of Pulmonary, Allergy and Sleep Medicine, Mayo Clinic, Jacksonville, Florida; Associate Professor of Medicine, Mayo Clinic College of Medicine and Science

Juan Carlos Leoni Moreno, MD

Consultant, Department of Transplantation, Mayo Clinic, Jacksonville, Florida; Instructor in Medicine, Mayo Clinic College of Medicine and Science

Stacy L. Libricz, PA-C, MS

Physician Assistant, Department of Critical Care Medicine, Mayo Clinic Hospital, Phoenix, Arizona; Instructor in Medicine, Mayo Clinic College of Medicine and Science

E. Paul Lindell, MD

Consultant, Department of Radiology, Mayo Clinic, Rochester, Minnesota; Assistant Professor of Radiology, Mayo Clinic College of Medicine and Science

Karthika R. Linga, MBBS

Fellow in Pulmonary and Critical Care Medicine, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Jacksonville, Florida

Michael J. Link, MD

Consultant, Department of Neurologic Surgery, Mayo Clinic, Rochester, Minnesota; Professor of Neurosurgery, Mayo Clinic College of Medicine and Science

David G. Lott, MD

Consultant, Department of Otolaryngology-Head & Neck Surgery/Audiology, Mayo Clinic, Scottsdale, Arizona; Associate Professor of Otolaryngology, Mayo Clinic College of Medicine and Science

Amelia A. Lowell, RRT, RCP

Clinical Respiratory Care Specialist, Mayo Clinic Hospital, Phoenix, Arizona; Assistant Professor of Anesthesiology, Mayo Clinic College of Medicine and Science

Philip E. Lowman, MD

Consultant, Department of Critical Care Medicine, Mayo Clinic, Jacksonville, Florida; Instructor in Medicine, Mayo Clinic College of Medicine and Science

Patrick R. Maloney, MD

Research Collaborator, Department of Neurologic Surgery, Mayo Clinic, Rochester, Minnesota

Jennifer M. Martinez-Thompson, MD

Senior Associate Consultant, Department of Neurology, Mayo Clinic, Rochester, Minnesota; Assistant Professor of Neurology, Mayo Clinic College of Medicine and Science

Nnenna Mbabuike, MD

Fellow in Endovascular Neurosurgery, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Jacksonville, Florida

Present address: University of Pennsylvania Medical Center, Altoona, Pennsylvania

Barbara L. McComb, MD

Emeritus Associate Professor of Radiology, Mayo Clinic College of Medicine and Science, Jacksonville, Florida

Diane C. McLaughlin, APRN

Nurse Practitioner, Department of Neurology, Mayo Clinic, Jacksonville, Florida; Instructor in Neurology, Mayo Clinic College of Medicine and Science

Margherita Milone, MD, PhD

Consultant, Department of Neurology, Mayo Clinic, Rochester, Minnesota; Professor of Neurology, Mayo Clinic College of Medicine and Science

Isabel Mira-Avendano, MD

Consultant, Division of Pulmonary, Allergy and Sleep Medicine, Mayo Clinic, Jacksonville, Florida; Assistant Professor of Medicine, Mayo Clinic College of Medicine and Science

Kevin G. Moder, MD

Consultant, Division of Rheumatology, Mayo Clinic, Rochester, Minnesota; Associate Professor of Medicine, Mayo Clinic College of Medicine and Science

Farouk Mookadam, MB, BCh

Consultant, Department of Cardiovascular Diseases, Mayo Clinic Hospital, Phoenix, Arizona; Professor of Medicine, Mayo Clinic College of Medicine and Science

January F. Moore

Special Project Associate, Division of Vascular Surgery, Mayo Clinic, Jacksonville, Florida

Monica Mordecai, MD

Consultant, Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Jacksonville, Florida; Assistant Professor of Anesthesiology, Mayo Clinic College of Medicine and Science

Pablo Moreno Franco, MD

Consultant, Department of Transplantation, Mayo Clinic, Jacksonville, Florida; Assistant Professor of Medicine, Mayo Clinic College of Medicine and Science

David S. Morris, MD

Consultant, Division of Trauma, Critical Care, & General Surgery, Mayo Clinic, Rochester, Minnesota

Present address: Intermountain Medical Center, Murray, Utah

John E. Moss, MD

Consultant, Department of Critical Care Medicine, Mayo Clinic, Jacksonville, Florida; Assistant Professor of Medicine, Mayo Clinic College of Medicine and Science

Megan S. Motosue, MD

Resident in Allergy and Immunology, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Rochester, Minnesota

Omar Y. Mousa, MBBS

Fellow in Gastroenterology and Hepatology, Mayo Clinic School of Graduate Medical Education and Assistant Professor of Medicine, Mayo Clinic College of Medicine and Science, Jacksonville, Florida

Andrew W. Murray, MD

Consultant, Department of Anesthesiology and Perioperative Medicine, Mayo Clinic Hospital, Phoenix, Arizona; Assistant Professor of Anesthesiology, Mayo Clinic College of Medicine and Science

Santiago Naranjo-Sierra, MD

Visiting Research Fellow in Department of Critical Care Medicine, Mayo Clinic, Jacksonville, Florida

Present address: Hospital Pablo Tobon Uribe, Medellín, Colombia

Lauren K. Ng Tucker, MD

Consultant, Department of Critical Care Medicine, Mayo Clinic, Jacksonville, Florida; Assistant Professor of Medicine, Mayo Clinic College of Medicine and Science

Brandon T. Nokes, MD

Resident in Internal Medicine, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Scottsdale, Arizona

Rahmi Oklu, MD, PhD

Chair, Division of Interventional Radiology, Mayo Clinic Hospital, Phoenix, Arizona; Professor of Radiology, Mayo Clinic College of Medicine and Science

James A. Onigkeit, MD

Consultant, Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota; Assistant Professor of Anesthesiology, Mayo Clinic College of Medicine and Science

Yahaira Ortiz Gonzalez, MD

Resident in Cardiovascular Diseases, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Jacksonville, Florida

Katherine M. Oshel, MD

Consultant, Division of Nephrology and Hypertension, Mayo Clinic, Jacksonville, Florida; Instructor in Medicine, Mayo Clinic College of Medicine and Science

Pragnesh P. Parikh, MD

Consultant, Department of Cardiovascular Diseases, Mayo Clinic, Jacksonville, Florida; Assistant Professor of Medicine, Mayo Clinic College of Medicine and Science

Myung S. Park, MD, MS

Consultant, Department of Surgery, Mayo Clinic, Rochester, Minnesota; Associate Professor of Surgery, Mayo Clinic College of Medicine and Science

Jeffrey J. Pasternak, MD

Chair, Division of Neuroanesthesia, Mayo Clinic, Rochester, Minnesota; Associate Professor of Anesthesiology, Mayo Clinic College of Medicine and Science

Richard K. Patch III, MD

Consultant, Department of Anesthesiology and Perioperative Medicine and Division of Critical Care Medicine, Mayo Clinic, Rochester, Minnesota; Assistant Professor of Anesthesiology and of Medicine, Mayo Clinic College of Medicine and Science

Bhavesh M. Patel, MD

Consultant, Department of Critical Care Medicine, Mayo Clinic Hospital, Phoenix, Arizona; Assistant Professor of Anesthesiology, of Medicine, and of Neurology, Mayo Clinic College of Medicine and Science

Neal M. Patel, MD

Consultant, Department of Pulmonary and Critical Care Medicine, Mayo Clinic, Jacksonville, Florida; Instructor in Medicine, Mayo Clinic College of Medicine and Science

Mark A. Pichelmann, MD

Consultant, Department of Neurologic Surgery, Mayo Clinic, Jacksonville, Florida; Assistant Professor of Neurosurgery, Mayo Clinic College of Medicine and Science

Michael R. Pichler, MD

Fellow in Cerebrovascular Neurology, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Rochester, Minnesota

Sean J. Pittock, MD

Consultant, Department of Neurology, Mayo Clinic, Rochester, Minnesota; Professor of Neurology, Mayo Clinic College of Medicine and Science

Michael A. Pizzi, DO, PhD

Fellow in Critical Care Medicine, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Jacksonville, Florida

Alyx B. Porter, MD

Consultant, Department of Neurology, Mayo Clinic Hospital, Phoenix, Arizona; Assistant Professor of Neurology, Mayo Clinic College of Medicine and Science

Rajiv K. Pruthi, MBBS

Consultant, Divisions of Hematology, Hematopathology, and Laboratory Genetics and Genomics, Mayo Clinic, Rochester, Minnesota; Associate Professor of Medicine, Mayo Clinic College of Medicine and Science

Juan N. Pulido, MD

Consultant, Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota

Present address: Private practice, Seattle, Washington

Surakit Pungpapong, MD

Consultant, Department of Gastroenterology and Hepatology, Mayo Clinic, Jacksonville, Florida; Associate Professor of Medicine, Mayo Clinic College of Medicine and Science

Harish Ramakrishna, MD

Consultant, Department of Anesthesiology and Perioperative Medicine, Mayo Clinic Hospital, Phoenix, Arizona; Professor of Anesthesiology, Mayo Clinic College of Medicine and Science

Robert A. Ratzlaff, DO

Consultant, Departments of Critical Care Medicine and Anesthesiology and Perioperative Medicine, Mayo Clinic, Jacksonville, Florida; Assistant Professor of Anesthesiology, Mayo Clinic College of Medicine and Science

J. Ross Renew, MD

Consultant, Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Jacksonville, Florida; Assistant Professor of Anesthesiology, Mayo Clinic College of Medicine and Science

Kevin J. Renfree, MD

Consultant, Department of Orthopedic Surgery, Mayo Clinic Hospital, Phoenix, Arizona; Associate Professor of Orthopedics, Mayo Clinic College of Medicine and Science

Juan G. Ripoll Sanz, MD

Resident in Anesthesiology, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Jacksonville, Florida

Matthew J. Ritter, MD

Consultant, Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota; Assistant Professor of Anesthesiology, Mayo Clinic College of Medicine and Science

Mariela Rivera, MD

Consultant, Department of Surgery, Mayo Clinic, Rochester, Minnesota; Assistant Professor of Surgery, Mayo Clinic College of Medicine and Science

Christopher P. Robinson, DO, MS

Fellow in Neurocritical Care, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Rochester, Minnesota

Present address: Department of Neurology and Neurocritical Care Division, University of Florida, Gainesville, Florida

Maisha T. Robinson, MD

Consultant, Department of Neurology, Mayo Clinic, Jacksonville, Florida; Assistant Professor of Neurology, Mayo Clinic College of Medicine and Science

Mark N. Rubin, MD

Fellow in Vascular Neurology, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Scottsdale, Arizona

Present address: North Shore Neurological Institute, Glenview, Illinois

Carl A. Ruthman, MD

Resident in Pulmonary and Critical Care Medicine, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Jacksonville, Florida

Arzoo Sadiqi, BS

Research Trainee, Department of Cardiovascular and Thoracic Surgery, Mayo Clinic Hospital, Phoenix, Arizona

Ankit Sakhuja, MBBS

Fellow in Critical Care Medicine, Mayo Clinic School of Graduate Medical Education, and Assistant Professor of Medicine, Mayo Clinic College of Medicine and Science, Rochester, Minnesota

Carlo Salvarani, MD

Department of Rheumatology, Azienda Ospedaliera Arcispedale Sante Maria Nuova, Reggio Emilia, Italy

Mithun Sattur, MBBS

Resident in Neurologic Surgery, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Scottsdale, Arizona

Gregory J. Schears, MD

Consultant, Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota; Professor of Anesthesiology, Mayo Clinic College of Medicine and Science

J. William Schleifer, MD

Fellow in Cardiovascular Diseases, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Scottsdale, Arizona

Present address: Department of Internal Medicine, Division of Cardiology, University of Nebraska Medical Center, Omaha, Nebraska

Beth A. Schueler, PhD

Consultant, Department of Radiology, Mayo Clinic, Rochester, Minnesota; Associate Professor of Radiology and Professor of Medical Physics, Mayo Clinic College of Medicine and Science

David M. Sella, MD

Consultant, Department of Radiology, Mayo Clinic, Jacksonville, Florida; Assistant Professor of Radiology, Mayo Clinic College of Medicine and Science

Ayan Sen, MD

Chair, Department of Critical Care Medicine, Mayo Clinic Hospital, Phoenix, Arizona; Assistant Professor of Emergency Medicine and of Medicine, Mayo Clinic College of Medicine and Science

Eslam Shosha, MB, BCh

Research Fellow in Neurology, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Rochester, Minnesota

Jason L. Siegel, MD

Senior Associate Consultant, Department of Neurology, Mayo Clinic, Jacksonville, Florida; Assistant Professor of Neurology, Mayo Clinic College of Medicine and Science

Charles R. Sims III, MD

Senior Associate Consultant, Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota; Instructor in Anesthesiology, Mayo Clinic College of Medicine and Science

Ramachandra R. Sista, MD

Senior Associate Consultant, Division of Pulmonary Medicine, Mayo Clinic, Scottsdale, Arizona

Aurelia A. Smith, MD

Fellow in Multiple Sclerosis and Neuroimmunology, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Rochester, Minnesota

Christina C. Smith, APRN

Nurse Practitioner, Department of Neurologic Surgery, Mayo Clinic, Jacksonville, Florida; Assistant Professor of Neurosurgery, Mayo Clinic College of Medicine and Science

David A. Sotello Aviles, MD

Fellow in Infectious Diseases, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Jacksonville, Florida

Present address: Texas Tech University Health Sciences Center, Lubbock, Texas

Nathan P. Staff, MD, PhD

Consultant, Department of Neurology, Mayo Clinic, Rochester, Minnesota; Associate Professor of Neurology, Mayo Clinic College of Medicine and Science

John A. Stauffer, MD

Consultant, Department of Surgery, Mayo Clinic, Jacksonville, Florida; Associate Professor of Surgery, Mayo Clinic College of Medicine and Science

Glenn M. Sturchio, PhD

Consultant, Department of Radiology, Mayo Clinic, Jacksonville, Florida; Assistant Professor of Physiology, Mayo Clinic College of Medicine and Science

Matthew D. Sztajnkrycer, MD, PhD

Consultant, Department of Emergency Medicine, Mayo Clinic, Rochester, Minnesota; Professor of Emergency Medicine, Mayo Clinic College of Medicine and Science

Rabih G. Tawk, MD

Consultant, Department of Neurologic Surgery, Mayo Clinic, Jacksonville, Florida; Associate Professor of Neurosurgery, Mayo Clinic College of Medicine and Science

Jennifer A. Tracy, MD

Consultant, Department of Neurology, Mayo Clinic, Rochester, Minnesota; Assistant Professor of Neurology, Mayo Clinic College of Medicine and Science

Levan Tsamalaidze, MD

Visiting Research Fellow in Surgery, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Jacksonville, Florida

Jamie J. Van Gompel, MD

Consultant, Department of Neurologic Surgery, Mayo Clinic, Rochester, Minnesota; Associate Professor of Neurosurgery and Otorhinolaryngology, Mayo Clinic College of Medicine and Science

Carla P. Venegas-Borsellino, MD

Senior Associate Consultant, Department of Critical Care Medicine, Mayo Clinic, Jacksonville, Florida

K. L. Venkatachalam, MD

Consultant, Department of Cardiovascular Diseases, Mayo Clinic, Jacksonville, Florida; Associate Professor of Medicine, Mayo Clinic College of Medicine and Science

Prakash Vishnu, MBBS

Senior Associate Consultant, Division of Hematology and Oncology, Mayo Clinic, Jacksonville, Florida; Assistant Professor of Medicine, Mayo Clinic College of Medicine and Science

Angela N. Vizzini, RDN, LD/N

Director, Clinical Nutrition Services, Mayo Clinic, Jacksonville, Florida; Assistant Professor of Nutrition, Mayo Clinic College of Medicine and Science

Gerald W. Volcheck, MD

Chair, Division of Allergic Diseases, Mayo Clinic, Rochester, Minnesota; Associate Professor of Medicine, Mayo Clinic College of Medicine and Science

Hani M. Wadei, MD

Senior Associate Consultant, Division of Neurology and Hypertension, Mayo Clinic, Jacksonville, Florida; Associate Professor of Medicine, Mayo Clinic College of Medicine and Science

Clarence B. Watridge, MD

Associate Consultant, Department of Neurologic Surgery, Mayo Clinic, Jacksonville, Florida; Associate Professor of Neurosurgery, Mayo Clinic College of Medicine and Science

Present address: Ponte Vedra Beach, Florida

Brian G. Weinshenker, MD

Consultant, Department of Neurology, Mayo Clinic, Rochester, Minnesota; Professor of Neurology, Mayo Clinic College of Medicine and Science

Matthew E. Welz, MS

Research Technologist for Neurosurgery, Mayo Clinic Hospital, Phoenix, Arizona

Robert E. Wharen Jr, MD

Consultant, Department of Neurologic Surgery, Mayo Clinic, Jacksonville, Florida; Professor of Neurosurgery, Mayo Clinic College of Medicine and Science

Eelco F. M. Wijdicks, MD, PhD

Chair, Division of Critical Care Neurology, Mayo Clinic, Rochester, Minnesota; Professor of Neurology, Mayo Clinic College of Medicine and Science

Nicholas D. Will, MD

Resident in Anesthesiology, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Rochester, Minnesota

Jose C. Yataco, MD

Senior Associate Consultant, Department of Critical Care Medicine, Mayo Clinic, Jacksonville, Florida

Present address: Memphis, Tennessee

Joseph Zachariah, MD

Fellow in Critical Care Neurology, Mayo Clinic School of Graduate Medical Education, Mayo Clinic College of Medicine and Science, Rochester, Minnesota

Present address: Spectrum Hospital, Grand Rapids, Michigan

Ali A. Zaied, MD

Senior Associate Consultant, Department of Pulmonary, Critical Care, and Sleep Medicine, Mayo Clinic Health System—Northwest Wisconsin, Eau Claire, Wisconsin

Yuzana Zaw, MBBS

Fellow in Nephrology and Hypertension, Mayo Clinic School of Graduate Education, Mayo Clinic College of Medicine and Science, Scottsdale, Arizon

Fundamentals of Critical Care I Section

Goals

1 Respiratory Physiology in Critical Illness

MINKYUNG KWON, MD; JOSE L. DIAZ- GOMEZ, MD

• Describe the basic lung volumes and capacities and the fundamentals of breathing mechanics.

• Describe airway resistance, lung compliance, and thoracic wall compliance as major components of pulmonary ventilation.

• Distinguish restrictive physiology from obstructive physiology.

• Describe common patterns of increased work of breathing and their associated factors.

• Describe the mechanisms of hypoxemia.

Introduction

The fundamental pillars of critical care medicine are the management of the lungs, heart, and kidneys and the provision of nutritional support. The practice of critical care medicine is often defined by abnormal respiratory physiology and requires detailed knowledge of lung mechanics, the mechanism of hypoxia, and the control of breathing. Therefore, laboratory assessment in pulmonary disorders is useful (Table 1.1; Box 1.1). Before the lungs can enable gas exchange, air must move from the upper airway down a series of branching small airways and reach the alveoli. In the walls of the alveoli, capillaries form a dense network and receive blood flowing from the pulmonary artery (from the right ventricle) before it flows to the pulmonary vein (and then to the left atrium). Between the capillary network and the alveoli lies a thin blood-gas barrier through which oxygen (O2) and carbon dioxide (CO2) move, chiefly by simple diffusion.

At rest, inspiration and expiration generate tidal volume. After the tidal volume is exhaled, further forceful expiration generates expiratory reserve volume. The volume of air remaining in the lung is the residual volume. After resting inspiration, forceful inspiration to maximal capacity

generates inspiratory reserve volume. Volume that can be generated by maximal inspiration to maximal expiration is called vital capacity (Figure 1.1). Normal vital capacity is around 3 to 5 L, and normal tidal volume is approximately 500 mL. Total minute ventilation is the product of the tidal volume times the respiratory rate per minute.

Mechanics of Breathing

During rest, inspiration is active and expiration is passive. The most important muscle of inspiration is the diaphragm. When it contracts, the abdominal contents are forced downward and forward, and the vertical dimension of the chest cavity is increased. The external thoracic muscles make the rib margins lift and move out, increasing the transverse diameter of the thorax during forceful inspiration. At functional residual capacity, the rib cage acts as an outward force that generates negative pleural pressure. At end-expiration, the diaphragm prevents the abdominal organs from encroaching on the thoracic space and influencing the lung in the supine or prone position. During spontaneous breathing, these muscles expand the lung, creating even more negative intrapleural pressure and resulting in inspiration. During mechanical ventilation, positive pressure from the ventilator expands the chest wall, but the intrapleural pressure is positive.

Airway Resistance and Lung Compliance

Pulmonary ventilation and the work of breathing depend on the airway resistance and compliance of the lungs and the thoracic cage. Airway resistance is the pressure difference between the alveoli and the mouth divided by the flow rate. Most airway resistance is produced in mediumsized bronchi rather than in small bronchioles. The bronchial smooth muscles, located in medium-sized bronchi, are innervated by the autonomic nervous system. Stimulation of β-adrenergic receptors causes bronchodilation;

Table 1.1 • Useful Laboratory Values in Pulmonary Disorders

Laboratory Value

Arterial blood gas

Hemoglobin, glucose, urea nitrogen, creatinine, electrolytes, calcium, phosphorus, thyrotropin

Plasma brain natriuretic peptide

Serum bicarbonate

Alpha1-antitrypsin

Eosinophils

Procalcitonin

C-reactive protein

Rheumatologic serology (ANA, RF, antisynthetase antibodies, CK, aldolase, SS-A/SS-B, Scl-70)

Anti-GBM antibody, ANCA

Polycythemia

Significance in Pulmonary Disorders

Hypoxia, hypercapnia, acidosis, alkalosis

Nonpulmonary causes of dyspnea

Pulmonary edema due to heart failure

Chronic hypercapnia in COPD or obesity-hypoventilation syndrome

Alpha1-antitrypsin deficiency, obstructive pattern

Allergic asthma, parasitic infection, drug reaction, syndromes of pulmonary infiltrates with eosinophilia

Bacterial pneumonia

Pneumonia

Interstitial lung disease

Pulmonary hemorrhage

Recurrent hypoventilation or obstructive sleep apnea–associated hypoxemia

Abbreviations: ANA, antinuclear antibody; ANCA, antineutrophil cytoplasmic autoantibody; CK, creatine kinase; COPD, chronic obstructive pulmonary disease; GBM, glomerular basement membrane; RF, rheumatoid factor.

parasympathetic activity causes bronchoconstriction and increased airway resistance. Lung volume has an important effect on airway resistance: As lung volume decreases, airway resistance increases. Small airways may even close completely at low lung volumes.

Lung compliance is defined by the volume change per unit pressure change. Furthermore, it has 2 components: static and dynamic lung compliance.

Static Lung Compliance

Lung tends to collapse at any degree of pulmonary inflation, whereas the chest wall tends to recoil outward. This natural trend represents compliance of both the lung and the chest wall in static pressure-volume curves (Figure 1.2).

Lung compliance changes with various nonparenchymal conditions. Patients with obesity, ascites, or intra-abdominal hypertension have a stiffer chest wall; the lung and total respiratory system compliance curves shift down and rightward. In contrast, massive aspiration, alveolar edema, or fibrotic lung disease decreases the lung and total respiratory system compliance. In a patient with acute respiratory distress syndrome (ARDS), lung volume is further reduced and compliance is decreased. In addition, the overall volume of tissue and chest wall may be affected by illness, so that in ARDS the net effect on pleural pressure is unpredictable.

Static airway pressure of the respiratory system correlates with plateau pressure during mechanical ventilation. Moreover, the plateau pressure also represents the intraalveolar pressure during use of an end-inspiratory hold.

In passive ventilation, such as when patients are deeply sedated or paralyzed, the chest wall compliance curve tracks the pleural pressure. Thus, pressure measured with an esophageal balloon can be used to approximate these measures.

Dynamic Lung Compliance

Dynamic pressure-volume curves during inspiration and expiration exhibit a different pattern. This phenomenon, hysteresis, can be explained by surface tension variation at the alveolar air-fluid interface during inspiration and expiration. Pulmonary surfactant, a natural substance produced by type II epithelial cells in the lung, reduces the surface tension of the fluid layer lining the alveoli. During inspiration, alveolar surface tension increases because pulmonary surfactant spreads over a wider alveolar surface. The reverse occurs during expiration, when pulmonary surfactant condenses over a smaller alveolar surface.

Work of Breathing

Work is required to move the lung and the chest wall. The area under the dynamic pressure-volume curve of the lungs is used to estimate the work of breathing (WOB). During inspiration, the elastic WOB is the work needed to overcome elastic forces of the chest wall, lung parenchyma, and alveolar surface tension. In addition, resistive WOB is needed during inspiration to overcome tissue and airway resistance. During expiration, only resistive WOB is needed. Hence, increased WOB occurs with higher breathing rates

Box 1.1 • Interpretation of Blood Gas Data

Step 1. Determine whether the primary condition is acidemia (pH <7.35) or alkalemia (pH >7.45).

Step 2. Determine whether the disorder is metabolic (pH and Paco2 changes are in the same direction) or respiratory (pH and Paco2 changes are in the opposite direction).

Step 3. Determine whether compensation is adequate.

Metabolic acidosis: Paco2 = (1.5 [HCO3–]) + 8 (Correction ± 2)

Acute respiratory acidosis: Increase in [HCO3–] = ∆Paco2/10 (Correction ± 3)

Chronic respiratory acidosis: Increase in [HCO3–] = 3.5 (∆Paco2/10)

Metabolic alkalosis: Increase in Paco2 = 40 + 0.6 (∆HCO3–)

Acute respiratory alkalosis: Decrease in [HCO3–] = 2 (∆Paco2/10)

Chronic respiratory alkalosis: Decrease in [HCO3–] = 5 (∆Paco2/10) to 7 (∆Paco2/10)

Step 4. Calculate the anion gap (AG):

AG Na Cl ]HCO 12 2. [] [] 3 =− +− ± +− [

If the AG is elevated (>12), calculate the osmolar (OSM) gap (normal is <10):

OSMGap =Measured OSM2 Na Glucose/ 18 SUN/ 2.8) ([ ]) ( +

Step 5. If an AG is present, calculate the delta-delta ratio:

Delta Delta Ratio AG HCO3 −= ∆∆/. []

If <1, a concurrent non-AG metabolic acidosis is likely present. If >2, a concurrent metabolic alkalosis is likely present.

Abbreviations: Cl–, chloride; ∆, change in; HCO3–, bicarbonate; Na+, sodium; SUN, serum urea nitrogen.

Data from Kaufman DA. Interpretation of arterial blood gases (ABGs) [Internet]. New York: American Thoracic Society. c2017 [cited 2017 Sep 5]. Available from: http://www.thoracic. org/professionals/clinical-resources/critical-care/clinicaleducation/abgs.php. Spirogram

and faster flow rates. With a larger tidal volume, the elastic WOB is larger. Patients with stiff lungs tend to take small rapid breaths, and patients with severe airway obstruction breathe more slowly.

Closing Capacity

Lung cannot be completely empty because of airflowlimiting segments in the small airways. Hence, expiration

Figure 1.1. Standard Lung Volumes and Capacities. After resting inspiration, forceful inspiration to maximal capacity generates inspiratory reserve volume. The volume that can be generated by maximal inspiration to maximal expiration is the vital capacity (VC). ERV indicates expiratory reserve volume; FRC, functional residual capacity; IC, inspiratory capacity; IRV, inspiratory reserve volume; RV, residual volume; TLC, total lung capacity; TV, tidal volume.

after development of airflow-limiting segments is effort independent. What remains in the lungs when small airways start to close is called the closing capacity. Patients with airway disease (eg, asthma, chronic obstructive pulmonary disease [COPD], or cystic fibrosis) are predisposed to having a higher closing capacity, leaving a large residual volume. The volume of air expired between closing capacity and residual volume is called the closing volume

Changes in Lung Mechanics in Acute Respiratory Failure

In patients who are critically ill with respiratory failure, 2 types of physiologic derangement occur: obstructive and restrictive.

Obstructive Physiology

In obstructive lung diseases, pulmonary compliance is normal or increased, but airway resistance is increased, especially during expiration. As mentioned above, normal expiration is passive. However, with obstructive physiology, such as in patients with asthma or COPD, extra work is needed for adequate expiration.

Restrictive Physiology

Pneumonia and ARDS are examples of diseases with restrictive physiology in which compliance of the lung, or chest wall (or both) is decreased. The static pressurevolume curve of the lungs or chest wall (or both) is shifted rightward. The transpulmonary pressure (alveolar pressure minus pleural pressure) indicates the pressure across the alveolus and therefore across the pulmonary capillary bed. Decreased compliance of the lungs requires

Figure 1.2. Compliance Curves. Compliance curves for lung and chest are shown along with total lung compliance. At small lung volumes, the negative transmural pressure of chest compliance indicates the chest wall’s natural tendency to spring outward and expand. Lung compliance is high (ie, the slope of the curve is steep) at low lung volumes and decreases as the lung expands. Functional residual capacity is the summation of transmural pressures generated by the chest wall and lung when they are equal and opposing.

increased transpulmonary pressure for tidal inspiration. Further, the elastic WOB required for inspiration is increased and is usually compensated for by rapid shallow breathing. The intrinsic causes of restrictive physiology are interstitial lung diseases, pneumonia, and ARDS, and the extrinsic causes include respiratory muscle weakness, chest deformities, cardiomegaly, hemothorax, pneumothorax, empyema, and pleural effusion or thickening.

Respiratory Mechanics Affecting Circulation

Higher transpulmonary pressure leads to greater impedance to right ventricular outflow through the pulmonary vascular tree. A high right ventricular afterload decreases right ventricular output. Right ventricular preload depends on the degree of intrapleural pressure. With mechanical ventilation, intrapleural pressure increases during inspiration, further decreasing right ventricular preload. A stiffened chest wall increases intrapleural pressure, decreasing right ventricular preload further. Use of positive end-expiratory pressure and the prone position can also decrease right ventricular preload by increasing intrapleural pressure and stiffening the chest wall, respectively.

Neurogenic Pulmonary Edema

Acute central nervous system events such as acute head injury, seizure, tumors, and intracranial or subarachnoid

hemorrhages can induce acute pulmonary edema within minutes or as late as 12 to 24 hours after the event. Besides having acute shortness of breath from pulmonary edema, patients may have fever, tachycardia, hypertension, and leukocytosis from sympathetic surge. The proposed pathophysiology is that the neuronal damage increases sympathetic tone with a catecholamine surge, which subsequently increases systemic vascular resistance and decreases left ventricular contractility, causing alveolar capillary leakage and eventually leading to a severe increase in intracranial pressure. Management is primarily supportive. α-Blockers can be used, and excessive diuresis should be avoided. The key is to treat the underlying central nervous system insult and the increased intracranial pressure.

Physiology of Hypoxia

Changes in Diffusing Capacity in Critical Illness

Gases move across the blood-gas barrier by diffusion. The O2 diffusion reserve of the normal lung is enormous. However, in patients with alveolar hypoxia and thickening of the blood-gas barrier, O2 diffusion is challenged.

Pulmonary Vascular Resistance

Pulmonary vascular resistance is usually small and can further decrease by recruitment and distention of capillaries. Pulmonary vascular resistance increases at high and low lung volumes. Hypoxia, serotonin, histamine, thromboxane A2, and endothelin constrict pulmonary vasculature. Hypoxia constricts small pulmonary arteries probably by the direct effect of the low Po2 on vascular smooth muscle. This mechanism, called hypoxic pulmonary vasoconstriction, directs blood flow away from poorly ventilated areas of the diseased lung in the adult.

Nitric oxide, phophodiesterase inhibitors, calcium channel blockers, and prostacyclin dilate pulmonary vasculature. Inhaled pulmonary vasodilators such as nitric oxide or inhaled phophodiesterase inhibitors reduce vascular tone locally in the well-ventilated regions, causing a shift in blood flow away from unventilated regions toward betterventilated regions. Inhaled nitric oxide has been shown to reduce shunting and improve arterial oxygenation in patients with ARDS. Use of intravenous pulmonary vasodilators, such as prostacyclin, does not change Pao2 much in patients with ARDS and pulmonary hypertension, probably because of the mixed effects of reduced pulmonary arterial pressure, increased cardiac output, and worsened intrapulmonary shunt.

In contrast, systemic vasodilators can produce hypoxemia. Systemic vasodilators increase cardiac output, impair hypoxic vasoconstriction in both well-ventilated and poorly ventilated pulmonary vasculature, and change intracardiac pressure or pulmonary arterial pressure, thereby altering the distribution of pulmonary blood flow. Nitroprusside, hydralazine, nitroglycerine, nifedipine, dopamine, and dobutamine can produce this effect.

Physiology of Hypoxemia

The 5 mechanisms of hypoxemia are hypoventilation, diffusion limitation, shunt, ventilation-perfusion (V/Q ) mismatch, and low inspiratory O2 pressure.

Hypoventilation

Hypoventilation always increases the alveolar Pco2, which leads to lower alveolar Pao2 unless additional O2 is inspired. The treatment is to provide additional O2.

Diffusion Limitation

Diffusion of gases is limited when the blood-gas barrier is thickened.

Shunt

This refers to blood that enters the arterial system without going through ventilated areas of the lung. Hypoxemia resulting from a shunt does not improve after adding O2 If the shunt is caused by mixed venous blood, its size can be calculated from the shunt equation. Shunt is an

important cause of hypoxemia in patients with ARDS and pneumonia.

V/Q Mismatch

V/Q mismatch is the most common cause of hypoxemia, especially in the perioperative period after general anesthesia. A patient with V/Q mismatch has a problem with either ventilation (air going in and out of the lungs) or perfusion (O2 and CO2 diffusion at the alveoli and the pulmonary arteries). V/Q ratios compare the amount of air reaching the alveoli to the amount of blood reaching the alveoli. The V/Q ratio describes the gas exchange in any single lung unit. Regional differences in the V/Q ratio in the upright lung cause regional changes in gas exchange. The normal V/Q ratio is about 1, and decreases or increases in the ratio indicate changes in the alveolar gas and endcapillary blood composition. V/Q mismatch impairs the uptake or elimination of all gases by the lung. Although CO2 elimination is impaired by V/Q mismatch, it can be corrected by increasing the ventilation to the alveoli. In contrast, hypoxemia resulting from V/Q mismatch cannot be resolved by increased ventilation. The difference in the CO2 and O2 responses results from their own dissociation curve characteristics. Clinically, regions with low or high V/Q ratios cause hypoxemia, impaired CO2 elimination, and increased WOB in COPD patients.

Low Inspiratory O2 Pressure

Low inspiratory O2 pressure causes hypoxemia even with a normal alveolar-arterial difference in the partial pressure of O2.

Changes in Dead Space in Critical Illness

Dead space is the volume (not a space) that is ventilated but does not participate in perfusion. There are 2 types of dead space: anatomical dead space and physiologic dead space. Anatomical dead space, normally about 150 mL, is the volume of the conducting airways. Physiologic dead space is the volume of gas that does not eliminate CO2. Because physiologic dead space includes airway and alveolar dead space, it is increased in many lung diseases. Furthermore, increased V/Q mismatch and shunt are the most likely contributors to increased dead space in ARDS.

Supplemental O2 and CO2 Retention in COPD Patients

High fractional supplemental O2 may cause CO2 retention in COPD patients because supplemental O2 may increase the partial pressure of O2 in the alveoli (Pao2) in lung units with a low V/Q ratio, inhibiting regional hypoxic pulmonary vasoconstriction and increasing blood flow to these units. Consequently, blood is diverted away from better-ventilated regions, converting them to lung units with high V/Q ratios, which increases wasted ventilation.

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Preface

Table of Contents

Section V: Imaging in Critical Illness

Section VI: Procedures

Section VII: Pharmacotherapeutics

Contributors

Fundamentals of Critical Care I Section

1 Respiratory Physiology in Critical Illness

Mechanics of Breathing

Airway Resistance and Lung Compliance

Static Lung Compliance

Dynamic Lung Compliance

Work of Breathing

Box 1.1 • Interpretation of Blood Gas Data

Closing Capacity

Changes in Lung Mechanics in Acute Respiratory Failure

Obstructive Physiology

Restrictive Physiology

Physiology of Hypoxia

Pulmonary Vascular Resistance

Low Inspiratory O2 Pressure

Changes in Dead Space in Critical Illness

Supplemental O2 and CO2 Retention in COPD Patients