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Original Study

Journal of Veterinary Emergency and Critical Care 12(4) 2002, pp 245±251

Comparison of unilateral versus bilateral nasal catheters for oxygen administration in dogs Elizabeth D. Dunphy, DVM, F. A. Mann, DVM, MS, DACVS, DACVECC, John R. Dodam, DVM, MS, PhD, DACVA, Keith R. Branson, DVM, MS, DACVA, Colette C. Wagner-Mann, DVM, PhD, Paula A. Johnson, DVM and Mark A. Brady, DVM

Abstract Objective: To determine the effect of bilateral nasal oxygen supplementation on tracheal airway and arterial blood gas parameters. Design: Original research. Setting: Research Laboratory. Animals: Eight normal dogs. Interventions: None. Measurements: Intra-tracheal oxygen concentration and arterial oxygen partial pressure at three different oxygen flow rates given through either unilateral or bilateral nasal catheters. Main results: FIO2 and PaO2 were significantly increased with higher total oxygen flow rates, but the increase was the same whether the higher flow was delivered through one nasal catheter or divided and administered though two nasal catheters. The use of bilateral nasal catheters allowed a tracheal FIO2 as high as 0.60 with minimal patient discomfort. Conclusions: The benefit of bilateral nasal catheters for oxygen supplementation is the ability to provide high total oxygen flows with decreased risk of patient discomfort. If the desired oxygen flow can be achieved with a unilateral nasal catheter, then the only benefit of bilateral catheters is increased patient comfort. The use of bilateral nasal oxygen catheters for oxygen supplementation can result in an FIO2 that is high enough to produce oxygen toxicity with prolonged administration. (J Vet Emerg Crit Care 2002; 12(4): 245±251) Keywords: canine, FIO2, fraction of inspired oxygen, nasal cannula(e), oxygen supplementation, oxygen toxicity

From the Department of Veterinary Medicine and Surgery, College of Veterinary Medicine, University of Missouri-Columbia, Columbia, MO (Dunphy, Mann, Branson, Johnson), Department of Veterinary Medicine and Surgery, Department of Veterinary Biomedical Sciences, College of Veterinary Medicine, University of Missouri-Columbia, Columbia, MO (Dodam), Department of Surgery, School of Medicine, University of Missouri-Columbia, Columbia, MO (Wagner-Mann), Veterinary Specialists of Kansas City, Overland Park, KS (Brady). Funding and Support: this study was partially funded by the Committee on Research, Department of Veterinary Medicine and Surgery, College of Veterinary Medicine, University of MissouriColumbia. Address correspondence and reprint requests to: Elizabeth D. Dunphy, DVM, University of Missouri-Columbia, College of Veterinary Medicine, 379 East Campus Drive, Columbia, MO 65211. Fax: 573-884-5444. E-mail: dunphye@missouri.edu ß Veterinary Emergency and Critical Care Society 2002

Introduction Supplemental oxygen is frequently used to increase oxygen content of the blood in animals that are hypoxemic. Among the available methods to deliver supplemental oxygen are oxygen cages, facemasks, hoods, nasal cannulae and transtracheal catheters. The efficacy, advantages and disadvantages of each of these methods have been reported.1±7 Oxygen is commonly delivered through a unilateral nasal catheter because of its ease of implementation, minimal discomfort, and cost effectiveness. Occasionally, oxygen delivered through a unilateral nasal catheter fails to adequately reverse hypoxemia due to its failure to adequately elevate the percent of inspired oxygen (FIO2) or the arterial partial pressure 245


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of oxygen (PaO2). One possible solution is to increase the flow rate of oxygen delivered through the unilateral nasal catheter. Unfortunately, high oxygen flow can cause increased discomfort for the patient, presumably due to trauma to the nasal mucosa from the pressurized stream of gas. Administration of additional oxygen through a second catheter placed in the alternate naris has been proposed to overcome this obstacle.1,3,6,8 However, the efficacy of bilateral nasal oxygen as it relates to increases in FIO2 or PaO2 has not been studied. The purpose of this study was to compare the use of bilateral and unilateral nasal catheters for administration of supplemental oxygen with respect to three specific aims: (1) to determine if a second nasal catheter for oxygen administration would increase the FIO2 and the PaO2; (2) to quantitate the magnitude of increases in FIO2 and PaO2 with the addition of a second nasal catheter at 3 different oxygen flow rates; and (3) to determine if FIO2 and PaO2 are different when a specific total oxygen flow is given through one nasal catheter or divided between two. Materials and Methods Animals: Eight conditioned hound-type dogs weighing 21.1 + 3.6 kg were used in this study. Four were intact males and 4 were intact females. Each dog was determined to be normal on physical examination prior to admission into the study. In addition, each dog was confirmed to be heartworm negativea. The research protocol was reviewed and approved by the University of Missouri-Columbia Institutional Animal Care and Use Committee. Instrumentation: Dogs were sedated with acepromazineb (0.05 mg/kg IM) and butorphanolc (0.5 mg/kg IM). After approximately 30 mins, the skin over the right or left metatarsus was aseptically prepared for catheter placement, and 0.5% bupivicaine HCld (0.5 mL) was injected subcutaneously to desensitize skin over the right or left dorsopedal artery. A 20-gauge over-theneedle cathetere was then placed in the dorsal pedal artery for arterial blood samples. The catheter was sutured in place, a 3-way stopcock attached, and a protective bandage applied. Dogs were then placed in dorsal recumbency and the ventral cervical region was aseptically prepared. The trachea was palpated and manually stabilized and 0.5% bupivicaine HCL (0.5 mL) was infiltrated at the cricothyroid membrane. A 5.0 French polyurethane catheterf was placed through the skin and cricothyroid membrane and into the trachea. Catheters were advanced to the level of the tracheal bifurcation 246

(approximately 15 cm). The position of each transtracheal catheter was confirmed using fluoroscopy. The catheters were then sutured in place and a protective bandage was placed. A temperature probe was inserted into the rectum and interfaced with a clinical vital signs monitorg. Rectal temperature values were used for arterial blood gas temperature correction. Bupivicaine HCL (0.5 mL) was then instilled into each nostril and an 8.0 French red rubber catheterh was passed into the ventral meatus to the level of the medial canthus of the eye. This procedure was performed bilaterally. The catheters were secured to the skin with skin staples and 2±0 nylon suture. The nasal catheters were fitted with adapters to provide leak-proof attachments to a humidified medical oxygen sourcei,j. Each nasal catheter was connected to a separate oxygen source and flow meterk. Data collection was delayed after instrumentation until the animals were able to voluntarily maintain sternal recumbency. Data Collection: Tracheal catheters were interfaced with an airway gas analyzerl via sampling tubing. Inspired (PICO2) and exhaled (PECO2), partial pressure of carbon dioxide, and inspired (FIO2) and exhaled (FEO2) oxygen concentration were obtained from gas aspirated through the tracheal catheters. The monitor was also equipped with a pulse oximeter to determine hemoglobin saturation (SPO2), and this parameter was monitored using an optical probe placed on the dog's upper lip. Blood gas samples were collected into heparinized syringes and immediately analyzed by a blood gas analyzerm using temperature correction. Each dog had simultaneous arterial blood and tracheal gas samples taken prior to oxygen supplementation, and for each of 3 oxygen flow rates: 50, 100, and 200 mL/kg/min/ nasal catheter. The order in which these flows were given was randomized such that the chronological order was 50-100-200 mL/kg/min/catheter for half the dogs (n ˆ 4) and 200-100-50 mL/kg/min/catheter for the remainder of the dogs (n ˆ 4). A tracheal gas analysis and arterial blood gas sample were obtained between different oxygen flows, while the dogs were spontaneously breathing room air to ensure there were no residual effects from the previous oxygen administration. A minimum of 3 minutes was allowed from the initiation of each new flow rate until the arterial sampling. All measurements were obtained in duplicate. Heart rates, respiratory rates, and body temperatures were taken simultaneously with each blood gas sample. After all samples for each oxygen flow rate were taken for the bilateral nasal catheter sampling, one intranasal catheter was removed. The entire sampling process described above was then repeated to obtain data for the unilateral nasal catheter sampling. Finally, all nasal cannulae were ß Veterinary Emergency and Critical Care Society 2002


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removed, and the last blood gas and tracheal gas samples taken. Statistical Analysis: The study design was a continuous self-control trial with classic reversal or change-over. All continuous data are reported as mean + standard deviation. As two FIO2 and PaO2 measurements were taken at each sampling time to verify stability/validity of the measurements, means for PaO2 and FIO2 were calculated at each sampling time. Using these calculated sampling time means, a two-way (factor 1: unilateral/ bilateral cannulation; factor 2: oxygen flow rate) repeated measures analysis of variance was performed (a ˆ 0.05) to identify differences between levels for a given factor, and interactions between factors. When a significant F statistic was calculated, the Tukey posthoc or multiple comparison test was applied to identify significant differences between means. While not specifically targeted in this study, the baseline and equilibration-on-room-air FIO2 and PaO2 measurements were graphed against time to identify any trends over time for individual dogs and as an average of all dogs. Results There were no complications associated with the instrumentation or data collection. The only adverse effect

associated with the oxygen administration was seen at flow rates exceeding 100 mL/kg/min/catheter. Oxygen flow was audible and the dogs began shaking their heads and trying to paw at the nasal catheters. The descriptive statistics of the results are shown in Tables 1±4. The physical presence of the nasal catheters had no influence on respiratory rate, heart rate, body temperature, arterial blood gas or tracheal airway parameters. There were no differences in respiratory rate, heart rate or body temperature between dogs breathing room air and those receiving oxygen supplementation. The arterial partial pressure of carbon dioxide (PaCO2), bicarbonate (HCO3), total carbon dioxide (TCO2), base excess, and partial pressure of inspired carbon dioxide (PICO2) were unaffected by the administration of supplemental oxygen. There were statistically significant differences in PaO2, FIO2, partial pressure of expired carbon dioxide (PECO2), and pH when comparing room air versus oxygen supplementation and when comparing the different oxygen flow rates. Of these parameters, only the differences in FIO2 and PaO2 were statistically and clinically significant (Figures 1 and 2). Oxygen supplementation increased FIO2 and PaO2 in a total flow-rate dependent fashion; however, FIO2 and PaO2 were unaffected by the number of catheters. The FIO2 and PaO2 for a total flow rate of 100 mL/kg/min was

Table 1: Respiratory rate, body temperature and heart rate for dogs administered oxygen through unilateral and bilateral nasal

catheters at varying flow rates (mean + standard deviation). n ˆ 8 dogs

Parameter

No Catheter

Room Air *

Bilateral 50{

Bilateral 100{

Bilateral 200{

Unilateral 50{

Unilateral 100{

Unilateral 200{

Respiratory Rate Temperature Heart Rate

11.3 + 2.2 99.7 + 0.6 88.4 + 20.0

10.0 + 3.3 98.9 + 0.6 92.8 + 25.1

8.1 + 1.2 99.9 + 0.7 85.1 + 18.0

9.2 + 1.7 99.9 + 0.4 89.0 + 18.7

8.1 + 3.4 100.0 + 0.7 93.6 + 28.6

9.3 + 2.9 99.8 + 0.6 76.9 + 7.2

9.3 + 2.3 99.8 + 0.6 86.8 + 34.0

8.8 + 1.9 99.7 + 0.6 76.5 + 19.2

* Room air values were derived from all baselines, i.e. prior to and between different oxygen flow rates. { ml/kg/min/catheter of supplemental oxygen.

Table 2: Arterial blood gas parameters for dogs administered oxygen through unilateral and bilateral nasal catheters at varying

flow rates (mean + standard deviation). n ˆ 8 dogs

Parameter pH PaCO2 PaO2 HCO3 TCO2 BE SaO2

No Catheter

Room Air *

Bilateral 50{

Bilateral 100{

Bilateral 200{

Unilateral 50{

Unilateral 100{

Unilateral 200{

7.34 + 0.02 41.3 + 4.8 89.0 + 7.2c 21.8 + 3.0 23.0 + 3.1 2.9 + 2.9 95.7 + 1.4c

7.3 5 + 0.02 39.5 + 4.7 95.3 + 8.5c 21 + 3.0 22.2 + 3.0 3.6 + 3.0 96.5 + 0.8c

7.32 + 0.02 43.7 + 4.1 193.2 + 16.9 21.9 + 3.1 23.2 + 3.3 3.0 + 3.2 99.3 + 0.3

7.3 1 + 0.03 44.0 + 4.0 297.3 + 56.3b 21 + 2.6 22.9 + 2.7 3.4 + 2.5 100.0 + 0.0a

7.32 + 0.03 43.5 + 5.7 388.3 + 74.9a 21.7 + 2.8 22.9 + 3.1 3.3 + 2.9 100.0 + 0.0b

7.33 + 0.02 43.1 + 3.9 146.6 + 20.7 22.0 + 2.6 23.4 + 2.7 2.8 + 2.7 98.8 + 0.4a,b

7.32 + 0.02 45.0 + 2.8 206.8 + 24.4b 22.6 + 2.1 23.8 + 2.2 2.4 + 2.2 99.4 + 0.5

7.33 + 0.02 43.8 + 4.0 278.9 + 37.2a 22.0 + 2.4 23. 5 + 2.6 2.9 + 2.4 99.9 + 0.2

*Room air values were derived from all baselines, i.e. prior to and between different oxygen flow rates. {ml/kg/min/catheter of supplemental oxygen a,b: significantly different than each other c: significantly different than all other values for that parameter. ß Veterinary Emergency and Critical Care Society 2002

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E.D. Dunphy et al. Table 3: Transtracheal gas parameters for dogs administered oxygen through unilateral and bilateral nasal catheters at varying

flow rates (mean + standard deviation). n ˆ 8 dogs

Parameter

No Catheter

Room Air*

Bilateral 50{

Bilateral 100{

Bilateral 200{

Unilateral 50{

Unilateral 100{

Unilateral 200{

PECO2 FIO2 PICO2 SpO2

43.6 + 3.1 20.2 + 0.5a 2.8 + 1.4 95.8 + 3.3

45.0 + 3.8 20.2 + 0.4a 2.8 + 1.4 95.8 + 3.1

49.1 + 4.2 36.4 + 5.9b 2.6 + 1.2 97.9 + 2.2

47.8 + 3.3 56.0 + 11.9c 3.4 + 2.5 97.3 + 2.0

45.6 + 4.4 77.3 + 13.5d 3.0 + 2.8 97.7 + 2.1

46.3 + 3.4 29.8 + 5.6 3.4 + 2.1 96.2 + 2.7

47.7 + 3.8 37.3 + 5.7b 3.6 + 3.0 97.8 + 1.9

48.1 + 3.8 57.9 + 12.7c 3.6 + 2.4 97.4 + 1.3

*Room air values were derived from all baselines, i.e. prior to and between different oxygen flow rates. {mL/kg/min/catheter of supplemental oxygen. PECO2 ˆ partial pressure of expired carbon dioxide; PICO2 ˆ partial pressure of inspired carbon dioxide. a: not statistically different than each other, but significantly different than all others. b, c: not statistically different than each other. d: statistically different from all others for that parameter.

Table 4: Linear regression analysis results for the dogs administered oxygen through unilateral and bilateral nasal catheters at

varying flow rates. n ˆ 8 dogs

Bilateral Nasal Catheter Unilateral Nasal Catheter Bilateral Nasal Catheter Unilateral Nasal Catheter

Parameter

R-value

Derived Equation

P-value

F IO 2 FIO 2 PaO2 PaO2

0.990 0.998 0.979 0.993

FIO2 ˆ 22.42 ‡ (0.286  Oxygen Flow/Catheter) FIO2 ˆ 19.94 ‡ (0.187  Oxygen Flow/Catheter) PaO2 ˆ 116.92 ‡ (1.45  Oxygen Flow/Catheter) PaO2 ˆ 100.74 ‡ (0.924  Oxygen Flow/Catheter)

0.010 0.002 0.021 0.007

500

1.0 O2 partial pressure (mmHg)

Fraction of inspired oxygen

450 0.8

0.6

0.4

0.2

400 350 300 250 200 150 100 50

0.0 0

50

100 150 Oxygen flow (ml/kg/min/catheter)

200

0

50

100 150 Oxygen flow (ml/kg/min/catheter)

200

Figure 1: Fraction of inspired oxygen (FIO2) and linear regression lines for unilateral (!) and bilateral (.) nasal oxygen at room air and each of 3 different oxygen flow rates. Data presented as mean + standard deviation. FIO2 increased in a linear fashion with increasing total oxygen flow rates. There was no statistical difference in FIO2 for a given flow rate when comparing the flow given in one nasal catheter or divided between 2 catheters.

Figure 2: Arterial partial pressure of oxygen and linear regression lines for unilateral (!) and bilateral (.) nasal oxygen at room air and each of 3 different oxygen flow rates. Data presented as mean + standard deviation. PaO2 increased in a linear fashion with increasing total oxygen flow rates. There was no statistical difference in PaO2 for a given flow rate when comparing the flow given in one nasal catheter or divided between 2 catheters.

not statistically different whether that flow was administered as 50 mL/kg/min in each of two nasal catheters or administered as 100 mL/kg/min through one catheter. Likewise, a total flow of 200 mL/kg/min was also not significantly different when this flow was

administered as 100 mL/kg/min in each of the two nasal catheters or administered as 200 mL/kg/min through one catheter. There were no significant differences among baseline room air measurements for FIO2 or PaO2 and the

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measurements obtained between each level of oxygen supplementation (i.e. there were no residual effects of oxygen supplementation once the oxygen was discontinued).

Discussion The physical presence of the nasal catheters had no influence on arterial blood gas or tracheal airway parameters. There was no difference in FIO2 or PaO2 when comparing a specific flow rate given through one catheter to that same flow rate divided between 2 catheters. There was also no difference detected in FIO2 or PaO2 when comparing dogs breathing unsupplemented room air with or without nasal catheters in place. Increases in FIO2 and PaO2 observed in this investigation are a reflection of the increase in the amount of oxygen flow delivered to the animal, not the number of catheters through which this flow was delivered. It is likely that a portion of the increase seen in FIO2 was due to an increase in the concentration of oxygen in the oropharynx and nasopharynx because the nasal cavity, nasopharynx and oropharynx act as reservoirs for inspired air. During normal breathing, airflow is intermittent, but during oxygen supplementation, the airflow is continuous. During the interval between exhalation and the following inspiration, this anatomical space fills with supplemented oxygen. Because this anatomical space has a fixed volume, as the volume of oxygen increases, so must the overall concentration of oxygen in the reservoir, and therefore, the FIO2 increases. The time interval between exhalation and the next inhalation is usually quite short, and higher flow rates allow a larger total volume of oxygen to be delivered into the nasal cavity, nasopharynx and oropharynx during this short interval. Moreover, it is also likely that the increase in oxygen tension was due to an increase in oxygen flow from the catheters into the trachea during inhalation. The recommended initial therapeutic dose for unilateral nasal oxygen supplementation is approximately 50Âą100 mL/kg/min.2,11,12 Previous studies have shown that a tracheal FIO2 of approximately 50% can be achieved when oxygen is delivered at these flow rates through a unilateral nasal catheter.2,5,7 The results of this study confirm these previous findings. We allowed 3 minutes for the FIO2 to equilibrate at each new flow rate and to return to baseline between oxygen flows. In reality, the airway analyzer indicated that stabilization of FIO2 occurred within 30 seconds. Also, there were no residual effects from the previous flow rates and no differences detected between the original baseline and subsequent room air measurements. It is important to realize that the beneficial increases in Ă&#x; Veterinary Emergency and Critical Care Society 2002

FIO2 and PaO2 associated with oxygen administration diminish rapidly when oxygen is discontinued. As shown in Figures 1 and 2, there is a linear relationship between the increases seen in FIO2 and PaO2 with increasing total oxygen flow rates. Based on a linear regression analysis, it can be said with a high degree of confidence that increasing the flow rate beyond the maximum of 200 mL/kg/min/catheter used in this study would result in an even higher FIO2 and PaO2, although there will certainly be a plateau as FIO2 approaches 1.0. High gas flow rates can be administered through a unilateral nasal catheter but often are associated with patient discomfort. During this study, there was audible turbulent flow at 200 mL/kg/min/catheter and the dogs showed signs of discomfort. This discomfort has been subjectively noted in our clinical patients when an attempt is made to deliver flow rates higher than 100 mL/ kg/min through a single nasal catheter. Nasal mucosal irritation and erosion and gastric distension are recognized side-effects of increased oxygen flow rates delivered through nasal prongs in human beings. Similar side-effects are likely to be the cause of discomfort seen in veterinary patients when oxygen is delivered at higher flow rates. Gastric distension commonly occurs when nasal catheters are placed into the nasopharynx, allowing air to flow into the esophagus, but can also occur when very high flow rates are delivered into a catheter within the nasal cavity.7 By dividing higher flows between two catheters, the desired increase in FIO2 can be achieved with a decreased risk of sideeffects. Red rubber catheters were used in this study to deliver the oxygen, as these catheters are the most commonly used in the clinical setting. An alternative would be to use a catheter specifically made for oxygen delivery. These catheters have multiple small holes on the distal tip to more evenly disperse the pressurized gas. One such catheter is distributed by Allegiance Healthcaren and come in sizes 10 and 14 French. It is important to note that most conscious patients will not tolerate high flow rates through a unilateral nasal catheter. Therefore, it is difficult to achieve an FIO2 high enough to cause oxygen toxicity with this method of oxygen supplementation. But, by dividing that flow through two nasal catheters, FIO2 can be easily achieved with very little patient discomfort. At a flow rate of 100 mL/kg/min given in each of two catheters, a mean FIO2 of approximately 0.6 was achieved. At 200 mL/kg/min in each catheter, this mean rose to almost 0.8. These values are well within the range that has been shown to cause oxygen toxicity if used for a prolonged period of time.9,10 The current recommendations in both the veterinary and human literature is to keep the FIO2 below 0.6 if oxygen is to be administered for greater than 24 hours to prevent pulmonary changes 249


E.D. Dunphy et al.

associated with oxygen toxicity. Therefore, caution must be used when utilizing bilateral nasal catheters at flow rates higher than 100 mL/kg/min/catheter for greater than 18±24 hours. This study was performed on healthy dogs with normal respiratory rate and effort. None of the dogs were panting or mouth breathing during data collection. It is certainly possible that the presence of pulmonary disease, such as that found in a clinical patient receiving oxygen supplementation, would affect these results. The next step in determining the benefits of bilateral nasal oxygen would be to repeat this study in animals with known pulmonary disease and hypoxia. We believe there are two clinical indications for bilateral nasal catheters. The first is in a patient that has an acceptable FIO2 and PaO2 but is uncomfortable as a result of the high flow rate. A second nasal catheter can be placed and the flow rate divided. This will not increase the FIO2 or PaO2, but should improve the patient's comfort level. The second indication is in a patient whose hypoxemia was not corrected with the use of a unilateral nasal catheter. A second catheter can be placed in order to increase the amount of oxygen flow and improve PaO2. If hypoxemia cannot be reversed by the placement of a second nasal catheter and/or the necessary flow rate results in an FIO2 greater than 0.5 for longer than 24 hours, than other measures such as mechanical ventilation should be pursued. If ventilation is not a possibility, the clinician needs to balance the individual patient's need for oxygen supplementation with the risk of oxygen toxicity and identify the minimum oxygen flow rate required to treat the hypoxemia as well as optimize other factors that contribute to oxygen delivery, such as hemoglobin content, body temperature, stress levels, etc. Conclusion The benefit of using bilateral nasal catheters for oxygen supplementation is the ability to provide high total oxygen flows with minimal risk of patient discomfort. If the desired oxygen flow can be achieved with the use of a unilateral nasal catheter, the only benefit in using bilateral catheters is increased patient comfort and presumed decreased nasal mucosal injury. The use of bilateral nasal oxygen catheters for oxygen supplementation can result in a FIO2 that could produce oxygen toxicity if given for prolonged periods. Acknowledgements The authors would like to thank Dr John Bonagura for the use of his laboratory, Dan Hatfield, Drs Julio 250

Toro, Heidi Hungerbuhler, and Brianne Strand for technical assistance. This project was partially funded by the University of Missouri-Columbia, College of Veterinary Medicine, Department of Veterinary Medicine and Surgery Committee on Research and Small Animal Emergency and Critical Care Department funds. Footnotes a b c d e f

g h i j k l m

n

K9 Heartworm Antigen Test, IDEXX Labs, Westbrook, ME Acepromazine Maleate, Fort Dodge, IA Butorphanol, Fort Dodge, IA Bupivicaine HCL 0.5%, Abbott Labs, North Chicago, IL Abbott Caths, Abbott Labs, North Chicago, IL Seldinger Central Venous Catheter, Cook Veterinary Products, Spencer, IN Pulse OX Plus, Heska Corp., Fort Collins, CO Sherwood Medical, St. Louis, MO Reusable humidifier, Hudson RCI, Temecula, CA Suction tubing, Con Med Corp, Utica, NY Timeter, Allied Healthcare Products, St. Louis, MO Ohmeda Rascal II, Ohmeda, Louisville, CO Radiometer ABL5 Blood Gas Analyzer, Radiometer Medical A/S, Bronshoj, Denmark Nasal cannula, Healthcare Allegiance, McGraw Park, IL

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10. Klein J. Normobaric pulmonary oxygen toxicity. Anesth Analg 1990; 70: 195±207. 11. Gibbons G. Respiratory Emergencies. In: Murtaugh RJ, Kaplan PM, eds. Veterinary Emergency and Critical Care Medicine. St. Louis: Mosby Year Book, 1992: pp. 399±419.

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12. Plunkett S, Emergency Procedures for the Small Animal Veterinarian. 1st edn. Philadelphia: W.B. Saunders, 1993: p. 248.

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Comparison of unilateral versus bilateral nasal catheters for oxygen administration in dogs