We compared the ability of 2 alpha2-adrenergic receptor antagonists, atipamezole and yohimbine, to reverse medetomidine-induced CNS depression and cardiorespiratory changes in lambs. Twenty lambs (7.8 +/- 2.6 kg) were randomly allotted to 4 treatment groups (n = 5). Each lamb was given medetomidine (30 micrograms/kg of body weight, IV), followed in 15 minutes by IV administration of atipamezole (30 or 60 micrograms/kg), yohimbine (1 mg/kg), or 0.9% NaCl (saline) solution. Medetomidine caused lateral recumbency in 1 to 2 minutes in all treated lambs. Medetomidine significantly (P < 0.05) decreased heart rate at 5 and 10 minutes after its administration. Heart rate remained above 120 beats/min, and severe bradycardia (< 70 beats/min) and other arrhythmias did not occur throughout the study. Medetomidine also induced tachypnea in all treated lambs. The tachypnea was abolished by atipamezole and yohimbine, but not by saline solution administration. The medetomidine-induced tachypnea did not significantly affect arterial pH and PaCO2. Arterial oxygen tension was within acceptable range (PaO2 = 71 to 62 mm of Hg), but was lower than expected. Administration of atipamezole, yohimbine, or saline solution did not change PaO2 significantly. Lambs treated with 30 or 60 micrograms of atipamezole/kg were able to walk unassisted in 2.4 +/- 0.4 and 2.3 +/- 0.7 minutes, respectively, whereas yohimbine-and saline-treated lambs did not walk unassisted until 15.6 +/- 2.7 and 73.0 +/- 6.8 minutes later, respectively. Results of this study indicated that medetomidine is a potent CNS depressant in lambs. Atipamezole at dosage of 30 or 60 micrograms/kg was equally effective, and was more effective in antagonizing medetomidine-induced CNS depression than was yohimbine.

Free, autogenous, full-thickness skin grafts were applied to 10 dogs; 5 dogs were given an iron chelator, deferoxamine-10% hydroxyethyl pentafraction starch (DEF-HES; 50 mg/kg of body weight, IV), and 5 dogs were given an equal volume of 10% hydroxyethyl pentafraction starch (HES) in 0.9% saline solution (5 ml/kg, IV). All dogs (DEF-HES/HBO- and HES/HBO-treated) were exposed to 60 minutes of hyperbaric oxygen (HBO) at 2 atmospheres absolute pressure twice daily for 10 days, beginning the day of surgery. The percentage of viable graft on day 10 was lower in HES/HBO-treated-dogs (mean +/- SD, 13.3 +/- 21.3%; median, 3.0%) than in DEF-HES/HBO-treated dogs (64.7 +/- 39.2%; 88.3%; P = 0.095, Mann-Whitney two-tailed test). There was a positive correlation between percentage of viable graft (on day 10) and percentage of haired skin on the graft site (on day 28) for all dogs (r = 0.91) and for HES/HBO-treated dogs (r = 0.97). The DEF-HES/HBO-treated dogs had less consistent correlation (r = 0.67). Perivascular aggregates of foamy cells were observed in the superficial and reticular portions of the dermis and in the subcutaneous tissue on both surfaces of the panniculus muscle in the graft sites of DEF-HES/HBO-treated dogs. These cells were also observed in the dermis, but not subcutaneous tissue of the control skin sections, and in some viscera of DEF-HES/HBO-treated dogs. Deferoxamine appears to attenuate the detrimental effect of HBO and HES on survival of free skin grafts. However, clinical use of HBO is not recommended as adjunct treatment for free skin grafts in dogs in the first 10 days after grafting. Administration of DEF-HES is not recommended because it has failed to improve the survival of free skin grafts, and the consequence of the cellular response seen in this study is undetermined.

Transcutaneous oxygen (PO2.TC) monitoring is commonly used in human medicine for evaluating skin viability. The application of transcutaneous monitoring for evaluating skin viability in dogs was investigated. The changes in PO2-TC values were measured from 16 avascular skin flaps created along the lateral hemithoraces of 4 dogs. Transcutaneous oxygen values were serially recorded from the vascular base and avascular apex of each flap for 12 hours after surgery. A single transcutaneous measurement was obtained from each flap base and apex 24 hours after surgery. Serial arterial blood gas analyses were obtained to compare central oxygen values with PO2-TC values. Full-thickness skin biopsy specimens were harvested from the base and apex of each flap 24 hours after surgery. The flaps were observed for 4 days and then excised for histologic examination. A subjective grading scale was used to assess histologic changes. Throughout the 12-hour period and at 24 hours, a statistically significant difference was found between the PO2-TC values for apices and bases of the flaps. The mean PO2-TC for all bases was 90.9 mm of Hg +/- 3.3 SEM, and the mean PO2-TC for all apices was 21.2 mm of Hg +/- 1.8 SEM. The mean regional perfusion index (apex PO2.TC/base PO2-TC) was 0.23 +/- 0.02. The subjective numbers assigned to the biopsy specimens were statistically evaluated by using a paired Student's t test and a Wilcoxon signed-rank test. A significant difference was found between the numbers for the collective bases and apices with both tests. A statistically significant difference was found between the numbers for the apex biopsy specimens taken 24 hours after creation of the skin flap and those taken when the flap was excised, whereas no difference was found between the numbers for the base biopsy specimens. On the basis of our findings, PO2-TC monitoring is a useful technique for assessing skin viability in dogs.

Postadulticide pulmonary hypertension mechanisms and treatment with antihistamines and supplemental oxygen were studied in eight dogs with heartworm disease. To ensure severe postadulticide thromboembolism, additional heartworms (either 20 or 40 into 4 dogs each) were transplanted into naturally infected dogs before thiacetarsamide treatment. During pentobarbital anesthesia, 2 pulmonary hemodynamic studies were conducted on each dog with a sequence of baseline, hypoxia with FlO2 = 10%, hyperoxia with FlO2 = 100%, a second baseline, treatment with either diphenhydramine (D) or cimetidine (C), and another hypoxia. All dogs were pulmonary hypertensive, with each dog having a mean pulmonary arterial pressure (PPA) greater than 20 mm of Hg. Mean PPA increased from baseline conditions (25.0 +/- 4.5 SD for D and 24.3 +/- 4.4 for C) to hypoxia (28.5 +/- 4.7 for D and 28.4 +/- 3.7 for C), and decreased during hyperoxia (16.9 +/- 3.0 for D and 17.4 +/-3.0 for C), respectively. Neither antihistamine reduced PPA at normoxia. The degree of pulmonary hypertension when breathing room air increased even more during hypoxia, and this increase was not attenuated by either antihistamine. Histamine did not appear to mediate pulmonary hypertension during postadulticide thromboembolism, nor to modify the hypoxia-mediated pulmonary hypertension at this disease stage. Because baseline PO2 was low (66.6 +/- 11.7 mm of Hg for D and 69.4 +/- 14.2 for C) and because PPA decreased during administration of oxygen, the pulmonary hypertension was mostly hypoxia-induced. In addition to the arterial lesions, much of the pulmonary hypertensive mechanism was an active and reversible vasoconstriction in response to hypoxia caused by the secondary lung disease. Supplemental oxygen to dogs with pulmonary hypertension could reduce PPA and right ventricular afterload. This study supports the use of oxygen, but not antihistamine drugs, in the treatment of postadulticide heartworm disease in dogs that are hypoxic, with signs of congestive heart failure or dyspnea.

OBJECTIVE To determine the cardiopulmonary effects of IV administration of fentanyl to cats anesthetized with isoflurane and during anesthetic recovery with concurrent administration of acepromazine or dexmedetomidine. ANIMALS 6 healthy adult cats. PROCEDURES Cats received an IV bolus (5 μg/kg) followed by an IV infusion (5 μg/kg/h) of fentanyl for 120 minutes during isoflurane anesthesia and for 30 minutes after discontinuing isoflurane. Cats were randomly assigned in a crossover study to receive acepromazine (0.05 mg/kg) or dexmedetomidine (2.5 μg/kg), IV, when isoflurane was discontinued. Cardiopulmonary data were obtained during anesthesia and for 30 minutes during the anesthetic recovery period. RESULTS The administration of fentanyl during isoflurane anesthesia resulted in a transient increase in arterial blood pressure, mean pulmonary artery pressure, and oxygen delivery. Compared with values during isoflurane anesthesia, administration of dexmedetomidine during anesthetic recovery resulted in significant decreases in cardiac index, stroke index, and oxygen delivery and significant increases in arterial, central venous, and mean pulmonary artery pressures; systemic vascular resistance index; and oxygen extraction ratio. Administration of acepromazine resulted in increases in heart rate, cardiac index, oxygen uptake, and oxygen extraction ratio. Oxygen extraction ratio did not differ between acepromazine and dexmedetomidine. CONCLUSIONS AND CLINICAL RELEVANCE Fentanyl transiently improved indices of cardiopulmonary performance when administered to healthy cats anesthetized with isoflurane. The cardiovascular effects of acepromazine and dexmedetomidine in healthy cats receiving fentanyl during recovery from isoflurane anesthesia differed, but measured cardiopulmonary parameters remained within acceptable limits.

OBJECTIVE To evaluate the repeatability and accuracy of fingertip pulse oximeters (FPO) for measurement of hemoglobin oxygen saturation in arterial blood and pulse rate (PR) in anesthetized dogs breathing 100% O2. ANIMALS 29 healthy client-owned anesthetized dogs undergoing various surgical procedures. PROCEDURES In randomized order, each of 7 FPOs or a reference pulse oximeter (PO) was applied to the tongue of each intubated anesthetized dog breathing 100% O2. Duplicate measurements of oxygen saturation (Spo2) and PR were obtained within 60 seconds of applying an FPO or PO. A nonparametric version of Bland-Altman analysis was used. Coefficient of repeatability was the interval between the 5th and 95th percentiles of the differences between duplicate measurements. Bias was the median difference, and the limits of agreement were the 5th and 95th percentiles of the differences between each FPO and the PO. Acceptable values for the coefficient of repeatability of Spo2 were ≤ 6%. Agreements were accepted if the limits of agreement had an absolute difference of ≤ ± 3% in Spo2 and relative difference of ≤ ± 10% in PR. RESULTS Coefficient of repeatability for Spo2 was acceptable for 5 FPOs, but the limits of agreement for Spo2 were unacceptable for all FPOs. The limits of agreement for PR were acceptable for 2 FPOs. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that some FPOs may be suitable for accurately monitoring PRs of healthy anesthetized dogs breathing 100% O2, but mild underestimation of Spo2 was common.

Recumbency affects respiratory mechanics and oxygenation in anesthetized horses. Changes in pleural and abdominal pressures that can impair ventilation have not been described in all recumbencies. The objective of this study was to determine the effects of patient positioning on transdiaphragmatic pressure and selected hemodynamic variables. Horses were maintained under total intravenous general anesthesia with nasal oxygen supplementation. Transnasal balloon catheters in the stomach and thoracic esophagus were used to measure intrathoracic and gastric pressures in standing horses and in anesthetized horses positioned in right and left lateral recumbency, dorsal recumbency, reverse Trendelenburg position, and Trendelenburg position. Transdiaphragmatic pressure was calculated as the difference between gastric and intrathoracic pressures. Measurements of oxygen saturation (SpO(2)), heart rate, systolic, diastolic and mean arterial pressures, and respiratory rate were obtained every 5 minutes. When compared to dorsal recumbency, gastric expiratory pressure is decreased in the standing position. Thoracic expiratory pressure is decreased in standing and reverse Trendelenburg. Transdiaphragmatic expiratory pressure and SpO(2) are decreased in Trendelenburg. Heart rate is increased in reverse Trendelenburg. Systolic, diastolic, and mean arterial pressures are decreased in reverse Trendelenburg and increased in left lateral and right lateral recumbency. We found that there is wide variation in respiratory pressures between horses and positions and they are not predictive of associated changes in hemodynamic variables.

The aim of this study was to evaluate the respiratory and hemodynamic effects of a low-dose dexmedetomidine infusion [1mg/kg body weight (BW) per hour], with or without a loading dose (1 mg/kg BW), in dogs under isoflurane anesthesia. Thirty dogs were premedicated with methadone [0.3 mg/kg BW intramuscular (IM)], induced with propofol intravenous (IV) and maintained with isoflurane (1.3% to 1.4%) under mechanical ventilation. Animals were randomly assigned to 3 intravenous (IV) treatments (n = 10): 1 mg/kg BW dexmedetomidine, followed by 1 mg/kg BW per hour (group BI); or saline solution bolus, followed by either an infusion of 1 mg/kg BW per hour dexmedetomidine (group I) or saline solution (group C). The infusions were interrupted after 30 minutes. Respiratory system static compliance (Cstat) and respiratory system resistance (Rrs), partial pressure of oxygen/fractional inspired oxygen ratio (PaO(2)/FIO(2)), intrapulmonary shunt (Fshunt), and cardiac output (CO) were determined 5 minutes before the bolus (BASELINE), at the end of the bolus (BOLUS), and at 15 (T15), 30 (T3(0)), and 45 minutes (T45) intervals. In group BI, Cstat and PaO(2)/FiO(2) were higher at T15 and T3(0) than at BASELINE in the same group and than group C at the same times. In group I, the same parameters at T30 were higher than at BASELINE and than group C at the same time. In group BI, Rrs and Fshunt were lower than at BASELINE and than group C at the same time. In group I, the same parameters at T30 were lower than at BASELINE and those of group C at the same time. Cardiac output (CO) at T30 was higher in groups BI and I than in group C. The results of this study showed that low-dose dexmedetomidine infusion improves oxygenation and respiratory system mechanics and has a stabilizing hemodynamic effect in dogs anesthetized with isoflurane and mechanically ventilated.

OBJECTIVE To assess effects of nitrogen and helium on efficacy of an alveolar recruitment maneuver (ARM) for improving pulmonary mechanics and oxygen exchange in anesthetized horses. ANIMALS 6 healthy adult horses. PROCEDURES Horses were anesthetized twice in a randomized crossover study. Isoflurane-anesthetized horses in dorsal recumbency were ventilated with 30% oxygen and 70% nitrogen (treatment N) or heliox (30% oxygen and 70% helium; treatment H) as carrier gas. After 60 minutes, an ARM was performed. Optimal positive end-expiratory pressure was identified and maintained for 120 minutes. Throughout the experiment, arterial blood pressures, heart rate, peak inspiratory pressure, dynamic compliance (C(dyn)), and Pao(2) were measured. Variables were compared with baseline values and between treatments by use of an ANOVA. RESULTS The ARM resulted in significant increases in Pao(2) and C(dyn) and decreases in the alveolar-arterial gradient in the partial pressure of oxygen in all horses. After the ARM and during the subsequent 120-minute phase, mean values were significantly lower for treatment N than treatment H for Pao2 and C(dyn). Optimal positive end-expiratory pressure was consistently 15 cm H(2)O for treatment N, but it was 10 cm H(2)O (4 horses) and 15 cm H(2)O (2 horses) for treatment H.