Effects of enalaprilat on cardiorespiratory, hemodynamic, and hematologic variables in exercising horses.

OBJECTIVE: To determine the effects of IV administration of enalaprilat on cardiorespiratory and hematologic variables as well as inhibition of angiotensin converting enzyme (ACE) activity in exercising horses. ANIMALS: 6 adult horses. PROCEDURE: Horses were trained by running on a treadmill for 5 weeks. Training was continued throughout the study period, and each horse also ran 2 simulated races at 120% of maximum oxygen consumption. Three horses were randomly selected to receive treatment 1 (saline [0.9% NaCl] solution), and the remaining 3 horses received treatment 2 (enalaprilat; 0.5 mg/kg of body weight, IV) before each simulated race. Treatment groups were reversed for the second simulated race. Cardiorespiratory and hematologic data were obtained before, during, and throughout the 1-hour period after each simulated race. Inhibition of ACE activity was determined during and after each race in each horse. RESULTS: Exercise resulted in significant increases in all hemodynamic variables and respiratory rate. The pH and PO2 of arterial blood decreased during simulated races, whereas PCO2 remained unchanged. Systemic and pulmonary blood pressure measurements and arterial pH, PO2, and Pco2 returned to baseline values by 60 minutes after simulated races. Enalaprilat inhibited ACE activity to < 25% of baseline activity without changing cardiorespiratory or blood gas values, compared with horses administered saline solution. CONCLUSIONS AND CLINICAL RELEVANCE: Enalaprilat administration almost completely inhibited ACE activity in horses without changing the hemodynamic responses to intense exercise and is unlikely to be of value in preventing exercise-induced pulmonary hemorrhage.

Effects of intramuscular administration of low doses of medetomidine and medetomidine-butorphanol in middle-aged and old dogs.

OBJECTIVE: To determine effects of low doses of medetomidine administered with and without butorphanol and glycopyrrolate to middle-aged and old dogs. DESIGN: Prospective randomized clinical trial. ANIMALS: 88 healthy dogs > or = 5 years old. PROCEDURE: Dogs were assigned randomly to receive medetomidine (2, 5, or 10 micrograms/kg [0.9, 2.3, or 4.6 micrograms/lb] of body weight, i.m.) alone or with glycopyrrolate (0.01 mg/kg [0.005 mg/lb], s.c.), medetomidine (10 micrograms/kg) and butorphanol (0.2 mg/kg [0.1 mg/lb], i.m.), or medetomidine (10 micrograms/kg), butorphanol (0.2 mg/kg), and glycopyrrolate (0.01 mg/kg). Anesthesia was induced with thiopental sodium and maintained with isoflurane. Degree of sedation and analgesia were determined before and after medetomidine administration. Respiratory rate, heart rate, and mean arterial blood pressure were determined 10 and 30 minutes after medetomidine administration. Adverse effects and amounts of thiopental and isoflurane used were recorded. RESULTS: Sedation increased after medetomidine administration in 79 of 88 dogs, but decreased in 7 dogs that received 2 or 5 micrograms of medetomidine/kg. Mean postsedation analgesia score and amounts of thiopental and isoflurane used were less in dogs that received medetomidine and butorphanol, compared with other groups. Respiratory rate, heart rate, and blood pressure were not different among groups. Significantly more adverse effects developed in dogs that did not receive glycopyrrolate. CONCLUSIONS AND CLINICAL RELEVANCE: Administration of medetomidine (10 micrograms/kg, i.m.) and butorphanol (0.2 mg/kg, i.m.) induced sedation and analgesia and reduced amounts of thiopental and isoflurane required for anesthesia in middle-aged and old dogs. Glycopyrrolate decreased frequency of medetomidine-associated adverse effects.

Cardiorespiratory effects of a tiletamine/zolazepam-ketamine-detomidine combination in horses.

OBJECTIVE: To determine cardiorespiratory effects of a tiletamine/zolazepam-ketamine-detomidine (TZKD) combination in horses. ANIMALS: 8 healthy adult horses. PROCEDURE: Horses were instrumented for measurement of cardiorespiratory, acid-base, and electrolyte values. Each horse was given xylazine (0.44 mg/kg of body weight, IV) 10 to 15 minutes prior to induction of recumbency by administration of the TZKD combination. Cardiorespiratory, acid-base, and electrolyte values were measured at 5-minute intervals for > or =30 minutes. RESULTS: All horses became recumbent within 1 minute after IV administration of TZKD. Mean +/- SD duration of recumbency was 40+/-8 minutes. All horses regained standing position after < or =2 attempts. Quality of anesthesia and analgesia was determined to be satisfactory in all horses. Xylazine induced decreases in respiratory rate, heart rate, cardiac output, maximum rate of increase of right ventricular pressure, and rate pressure product. The PaCO2, right atrial pressure, and peripheral vascular resistance increased, whereas blood temperature, PO2, pHa, HCO3-, PCV, total solids, Na, and K values remained unchanged. Subsequent administration of TZKD caused right atrial pressure and PaCO2 to increase and PaO2 to decrease, compared with values obtained after xylazine administration. Remaining cardiorespiratory, acid-base, hematologic, and electrolyte values did not differ from those obtained after xylazine administration. CONCLUSION: IV administration of TZKD induces short-term anesthesia in horses. Potential advantages of this drug combination are the small volume of drug administered; minimal cardiorespiratory depression; quality of induction and maintenance of, and recovery from, anesthesia; and duration of drug effects.

Evaluation of a portable clinical analyzer in a veterinary hospital setting.

OBJECTIVE: Evaluation of a portable clinical analyzer for determination of blood gas tensions, electrolyte and glucose concentrations, and Hct in a hospital setting. DESIGN: Prospective study. ANIMALS: 50 dogs, 50 cats, and 28 horses, all clinically normal. PROCEDURE: Blood samples were analyzed on a portable clinical analyzer to determine concentrations of sodium, potassium, chloride, BUN, glucose, and ionized calcium and values of Hct, pH, PCO2, and PO2. Values obtained were compared with those obtained from the same blood samples, using a standard automatic analyzer (serum sodium, potassium, chloride, BUN, and glucose concentrations), a cell counter (Hct), a blood gas analyzer (pH, PCO2, PO2), and a calcium-pH analyzer (ionized calcium). Bias (mean difference between values obtained on the same sample by different methods) and variability (SD of differences) were determined for all values. Data were also subjected to Deming regression analysis. RESULTS: Correlation coefficients were > 0.90 for all values except potassium and ionized calcium concentrations. Bias and variability were within clinically acceptable limits (+/- 2 SD) for all but potassium, ionized calcium, and glucose concentrations and Hct. Species-dependent variability was observed for glucose concentration and Hct. CLINICAL IMPLICATIONS: Most differences between values obtained with the portable clinical analyzer and standard clinical laboratory systems could be accounted for by differences in type of sample tested (blood vs serum). The portable clinical analyzer is suitable for point-of-care analysis in critical care situations and for routine blood biochemical analysis when extensive laboratory support is unavailable.

Cardiorespiratory effects of low-flow and closed circuit inhalation anesthesia, using sevoflurane delivered with an in-circuit vaporizer and concentrations of compound A.

OBJECTIVES: To determine the concentrations of sevoflurane and compound A (a degradation product of sevoflurane) in the anesthetic circuit when sevoflurane was delivered with an in-circuit vaporizer, and to determine the cardiorespiratory effects of sevoflurane in dogs. ANIMALS: 6 mixed-breed dogs. PROCEDURE: In-circuit vaporizers were connected to the inspiratory limb of a circle rebreathing system connected to a ventilator. A reservoir bag was attached to the Y-piece connector to act as an artificial lung, and sevoflurane concentrations in the anesthetic circuit were measured at vaporizer settings of 1, 3, 5, 7, and 10 and oxygen flow rates of 250 and 500 ml/min. Cardiorespiratory effects of sevoflurane were determined in dogs while they were breathing spontaneously, during controlled ventilation, and during closed circuit anesthesia. Concentrations of compound A were determined by means of gas chromatography with flame ionization. RESULTS: The concentration of sevoflurane in the anesthetic circuit increased with vaporizer setting and time. For oxygen flow rates of 250 and 500 ml/min, vaporizer settings between 5 and 7 and between 7 and 10, respectively, produced sevoflurane concentrations closest to values reported to produce surgical anesthesia in dogs. Significant differences were not observed in cardiorespiratory variables with time or among anesthetic conditions. Concentrations of compound A in the anesthetic circuit were less than values reported to produce renal toxicoses and death in rats. CONCLUSION: Results suggested that sevoflurane can be administered to nonsurgically stimulated dogs, using an in-circuit vaporizer and low (< 15 ml/kg/min) oxygen flow rates, without causing significant cardiorespiratory depression or clinically important concentrations of compound A.

Respiratory depression and apnea induced by propofol in dogs.

OBJECTIVE: To determine the maximal i.v. administered dose of propofol that would not induce a serious adverse event in nonsedated dogs. ANIMALS: 6 clinically normal dogs (3 males and 3 females) between 8 and 12 months old and weighing between 8.8 and 11.3 kg. PROCEDURE: Propofol was administered i.v. at an initial dosage of 6.5 mg/kg of body weight at a rate of 20 mg/10 s. Subsequent doses were incrementally increased by 2.5 mg/kg (eg, second dose: 9 mg/kg) and separated by a minimum of 3 days. This procedure was repeated until a dose that induced a serious respiratory, cardiovascular, or neurologic adverse effect was determined. RESULTS: Apnea was determined to be the serious adverse effect for all dogs. Duration of apnea varied between dogs, but increased in a dose-dependent manner at dosages > 14 mg/kg. CONCLUSIONS: Respiratory depression and apnea are the most likely adverse effects induced by i.v. administration of propofol to dogs. Propofol administered i.v. at a rate of 20 mg/kg/10 s induces minimal cardiovascular depression at dosages in excess of the apneic dosage. CLINICAL RELEVANCE: Respiratory depression and apnea should be expected as potential adverse effects after i.v. administration of propofol to dogs, particularly when administered at rapid rates of infusion.