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Abstract

Objective

To evaluate selected hemodynamic, respiratory, and behavioral responses to propofol in horses premedicated with xylazine or detomidine.

Design

Xylazine (0.5 and 1.0 mg/kg of body weight) was administered IV on different days to each of 6 horses prior to IV administration of propofol (2 mg/ kg). In a second group of 6 horses, detomidine (15 and 30 µg/kg) was similarly studied.

Animals

2 groups of 6 mature healthy horses.

Procedure

Rectal temperature, heart and respiratory rates, arterial blood gas tensions, and direct arterial blood pressures were recorded before and at fixed intervals after drug administration. Induction and recovery events were quantitatively and qualitatively assessed. Cardiopulmonary and behavioral data to follow were statistically analyzed (P< 0.05).

Results

Heart rate decreased in dose-dependent manner from a mean (± SD) of 39.5 ± 5.1 beats/min after xylazine and detomidine. Second-degree atrioventricular dissociation was commonly seen at the higher drug doses. After propofol administration, heart rate either transiently increased or was less depressed early in recumbency, compared with predrug values. Direct arterial blood pressures varied inconsistently from predrug values. Mean arterial carbon dioxide tension tended to increase after drug administration (significance variable) from predrug values of 42 to 46 mm of Hg in both drug groups. After xylazine or detomidine administration, arterial oxygen tension decreased significantly from predrug values of 97 to 103 mm of Hg. The magnitude and duration of decrease was dose-dependent and greatest during recumbency.

Behavioral responses to anesthetic induction were variable, but horses were uniformly calm and coordinated during recovery. Recumbency time increased in reponse to the higher dose of either premedicant drug. Mean (± SD) times to standing were 25.02 ± 4.42 and 35.57 ± 6.83 minutes for the low and high doses of xylazine, respectively and 41.04 ± 11.21 and 52.64 ± 14.67 minutes for the low and high doses of detomidine, respectively.

Conclusion

Neither xylazine nor detomidine prevented excitation associated with propofol injection in horses.

Clinical Relevance

Xylazine- or detomidine-propofol combinations likely will not replace common anesthetic induction techniques for horses. However, recovery characteristics associated with propofol encourage further study in horses. (Am J Vet Res 1996;57:512–516)

Free access
in American Journal of Veterinary Research

SUMMARY

Cardiovascular and respiratory responses to variable Pao2 were measured in 6 horses anesthetized only with halothane during spontaneous (sv) and controlled (cv) ventilation. The minimal alveolar concentration (mac) for halothane in oxygen was determined in each spontaneously breathing horse prior to establishing Pao2 study conditions—mean ± sem,0.95 ± 0.03 vol%. The Pao2 conditions conditions of > 250, 120, 80, and 50 mm of Hg were studied in each horse anesthetized at 1.2 mac of halothane and positioned in left lateral recumbency. In response to a decrease in Pao2, total peripheral resistance and systolic and distolic arterial blood pressure decreased (P < 0.05) during sv. Cardiac output tended to increase because heart rate increased (P < 0.05) during these same conditions. During cv, cardiovascular function was usually less than it was at comparable Pao2 during sv (P < 0.05). Heart rate, cardiac output, and left ventricular work increased (P < 0.05) in response to a decrease in Pao2, whereas total peripheral resistance decreased (P < 0.05). During sv, cardiac output and stroke volume increased and arterial blood pressure and total peripheral resistance decreased with duration of anesthesia at Pao2 > 250 mm of Hg. During sv, minute expired volume increased (P < 0.05) because respiratory frequency tended to increase as Pao2 decreased. Decrease in Paco2 (P < 0.05) also accompanied these respiratory changes. Although oxygen utilization was nearly constant over all treatment periods, oxygen delivery decreased (P < 0.05) with decrease in Pao2, and was less (P < 0.05) during cv, compared with sv, for comparable Pao2 values. Muscle and hepatic-derived serum biochemical values were substantially increased and evidence of depressed renal function was observed in these horses immediately after anesthesia recovery. These serum biochemical changes exceeded values in horses previously studied during prolonged halothane anesthesia in the absence of low Pao2.

Free access
in American Journal of Veterinary Research

Abstract

Objective

To characterize responses associated with two 1-hour total intravenous anesthesia techniques in horses.

Animals

6 mature, healthy mares.

Procedure

Each horse was anesthetized 3 times. Treatment order was determined by a series of Latin squares. After baseline measurements and instrumentation, horses were given xylazine (XYL) IV; anesthesia was induced 5 minutes later with 10% guaifenesin given IV, then either ketamine (KET) or propofol (PRO) was given IV. After anesthesia induction, each horse received an infusion of XYL and either KET or a low or high dose of PRO. Cardiopulmonary variables were measured at 20, 40, and 60 minutes after the start of the infusion; arterial blood samples were collected prior to each set of measurements, and blood gas tensions and plasma drug concentration were determined. A noxious stimulus was applied after each of the 3 sets of measurements.

Results

Differences in measured cardiopulmonary variables were significant among all treatments at different times. Most notable differences were between KET and high PRO. Times to regaining sternal and standing posture were shortest for KET, and differed significantly from values for low and high PRO. Purposeful responses were not observed for high PRO in horses after noxious stimulation. In contrast, 4 horses given KET responded at all time points and 1 horse given low PRO responded.

Conclusion

None of the infusion techniques were flawless, but results support continued efforts at technique refinement and selected clinical use. (Am J Vet Res 1998;59:1292–1298)

Free access
in American Journal of Veterinary Research

Abstract

Objective—To characterize the effect of general anesthesia and minor surgery on renal function in horses.

Animals—9 mares with a mean (± SE) age and body weight of 9 ± 2 years and 492 ± 17 kg, respectively.

Procedure—The day before anesthesia, urine was collected (catheterization) for 3 hours to quantitate baseline values, and serum biochemical analysis was performed. The following day, xylazine (1.1 mg/kg, IV) was administered, and general anesthesia was induced 5 minutes later with diazepam (0.04 mg/kg, IV) and ketamine (2.2 mg/kg, IV). During 2 hours of anesthesia with isoflurane, PaCO2 was maintained between 48 and 52 mm Hg, and mean arterial blood pressure was between 70 and 80 mm Hg. Blood and urine were collected at 30, 60, and 120 minutes during and at 1 hour after anesthesia.

Results—Baseline urine flow was 0.92 ± 0.17 ml/kg/h and significantly increased at 30 and 60 minutes after xylazine administration (2.14 ± 0.59 and 2.86 ± 0.97 ml/kg/h respectively) but returned to baseline values by the end of anesthesia. Serum glucose concentration increased from 12 ± 4 to 167 ± 8 mg/dl at 30 minutes. Glucosuria was not observed.

Conclusions and Clinical Relevance—Transient hyperglycemia and an increase in rine production accompanies a commonly used anesthetic technique for horses. The increase in urine flow is not trivial and should be considered in anesthetic management decisions. With the exception of serum glucose concentration and urine production, the effect of general anesthesia on indices of renal function in clinically normal horses is likely of little consequence in most horses admitted for elective surgical procedures. (Am J Vet Res 2002;63:1061–1065)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To qualitatively and quantitatively evaluate the characteristics of desflurane with regard to the induction of and recovery from anesthesia in cats.

Animals—6 cats.

Procedure—Anesthesia was induced and maintained with desflurane in oxygen. Individual minimum alveolar concentration (MAC) values were determined; anesthesia was maintained at 1.25 × MAC for a total anesthesia time (including MAC determination) of 5 hours. Cats were allowed to recover from anesthesia. Induction and recovery periods were video recorded and later scored by use of a grading scale from 0 to 100 (100 being the best outcome). Timing of events was recorded.

Results—The MAC of desflurane was 10.27 ± 1.06%, and mean dose was 5.6 ± 0.2 MAC-hours. Times to loss of coordination, recumbency, and endotracheal intubation were 1.3 ± 0.4, 2.3 ± 0.3, and 6.4 ± 1.1 minutes, respectively. Median score for quality of anesthetic induction was 93 (range, 91 to 94). Times to first movement, extubation, standing, and ability to jump and land with coordination were 2.8 ± 1.0, 3.8 ± 0.5, 14.3 ± 3.9, and 26.4 ± 5.1 minutes, respectively. Alveolar washout of desflurane was rapid. Median score for quality of anesthetic recovery was 94 (range, 86 to 96).

Conclusions and Clinical Relevance—Desflurane was associated with rapid induction of and recovery from anesthesia in cats; assessors rated the overall quality of induction and recovery as excellent. Results appear to support the use of desflurane for induction and maintenance of anesthesia in healthy cats. (Am J Vet Res 2004;65:748–751)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine whether infusion of xylazine and ketamine or xylazine and propofol after sevoflurane administration in horses would improve the quality of recovery from anesthesia.

Animals—6 healthy adult horses.

Procedures—For each horse, anesthesia was induced by administration of xylazine, diazepam, and ketamine and maintained with sevoflurane for approximately 90 minutes (of which the last 60 minutes were under steady-state conditions) 3 times at 1-week intervals. For 1 anesthetic episode, each horse was allowed to recover from sevoflurane anesthesia; for the other 2 episodes, xylazine and ketamine or xylazine and propofol were infused for 30 or 15 minutes, respectively, after termination of sevoflurane administration. Selected cardiopulmonary variables were measured during anesthesia and recovery. Recovery events were monitored and subjectively scored.

Results—Cardiopulmonary variables differed minimally among treatments, although the xylazine-propofol infusion was associated with greater respiratory depression than was the xylazine-ketamine infusion. Interval from discontinuation of sevoflurane or infusion administration to standing did not differ significantly among treatments, but the number of attempts required to stand successfully was significantly lower after xylazine-propofol infusion, compared with the number of attempts after sevoflurane alone. Scores for recovery from anesthesia were significantly lower (ie, better recovery) after either infusion, compared with scores for sevoflurane administration alone.

Conclusions and Clinical Relevance—Xylazine-ketamine or xylazine-propofol infusion significantly improved quality of recovery from sevoflurane anesthesia in horses. Xylazine-ketamine or xylazine-propofol infusions may be of benefit during recovery from sevoflurane anesthesia in horses for which a smooth recovery is particularly critical. However, oxygenation and ventilation should be monitored carefully.

Full access
in American Journal of Veterinary Research

Abstract

Objective

To characterize isoflurane (ISO)-induced anesthesia in ferrets and rats.

Animals

8 ferrets (Mustela putorius furo) and 8 Sprague-Dawley rats.

Procedure

Ferrets and rats were anesthetized in a similar manner, using ISO in oxygen. Minimum alveolar concentration (MAC) was determined, using the tail-clamp method. Immediately thereafter, assessments were recorded for 0.8, 1.0, 1.5, and 2.0 MAC (order randomized) of ISO.

Results

MAC of ISO was (mean ± SEM) 1.74 ± 0.03 and 1.58 ± 0.05% for ferrets and rats, respectively. Mean arterial blood pressure (MAP) was 75.0 ± 4.3 and 107.9 ± 2.7 mm Hg at 0.8 MAC for ferrets and rats, respectively, and decreased in a parallel dose-dependent manner. Respiratory frequency decreased in rats as ISO dose increased; however, respiratory frequency increased in ferrets as ISO dose increased from 0.8 to 1.5 MAC but then decreased at 2.0 MAC. At 0.8 MAC, hypoventilation was much greater in ferrets (Paco2 = 71.4 ± 3.5 mm Hg), compared with rats (Paco2 = 57.7 ± 1.9 mm Hg). In both species, Paco2 progressively increased as anesthetic dose increased. Eyelid aperture of ferrets increased in a dose-dependent manner. Pupil diameter in ferrets and rats increased as ISO dose increased.

Conclusions and Clinical Relevance

The MAP and Paco2 in ferrets and rats and eyelid aperture in ferrets consistently and predictably changed in response to changes in anesthetic dose of ISO. Magnitude of respiratory depression was greater in ferrets than rats. Changes in MAP and Paco2 in ferrets and rats and eyelid aperture in ferrets are consistent guides to changes in depth of ISO-induced anesthesia. (Am J Vet Res 1999;60:1577–1583)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To characterize variables used to monitor rabbits during inhalation anesthesia.

Animals

8 male New Zealand White rabbits.

Procedure

Rabbits were similarly anesthetized with halothane (HAL) or isoflurane (ISO) in a crossover study; half received HAL followed by ISO, and the protocol was reversed for the remaining rabbits. After induction, minimum alveolar concentration (MAC) was determined for each agent, using the tail-clamp method, and variables were recorded at 0.8, 1.0, 1.5, and 2.0 MAC (order randomized).

Results

Mean ± sem mac was 1.42 ± 0.05 and 2.07 ± 0.09% for hal and iso, respectively. Directly measured auricular mean arterial blood pressure was 52.8 ± 5.6 and 54.8 ± 6.1 mm Hg at 0.8 mac for hal and iso, respectively, and decreased from these values in a parallel dose-dependent manner. Respiratory frequency remained constant (range, 69 to 78 breaths/min) over the range of hal doses but incrementally decreased from a mean of 53 (at 0.8 mac) to 32 breaths/min (at 2.0 mac) for iso. The Paco2 was similar at 0.8 mac for hal and iso and progressively increased with increasing doses of both agents; Paco2 at 2.0 mac for iso was significantly greater than that at 2.0 mac for hal (79.8 ± 13.7 vs 54.9 ± 4.0 mm Hg, respectively). Eyelid aperture consistently increased in a dose-dependent manner for both anesthetics.

Conclusions

Arterial blood pressure, Paco2, and eyelid aperture consistently and predictably changed in rabbits in response to changes in anesthetic doses. The magnitude of respiratory depression was greater for iso than for hal. (Am J Vet Res 1999;60:1189–1195)

Free access
in American Journal of Veterinary Research

Summary

Eighteen healthy, pregnant mares scheduled for laparotomy and uterine manipulation were randomly allotted to 2 equal groups. After iv administration of xylazine hydrochloride and thiamylal sodium, general anesthesia was maintained with halothane (halo) or isoflurane (iso) in oxygen. Results of cardiovascular measurements were similar with both inhalant anesthetics; mean arterial blood pressure was 79 and 82 mm of Hg with halo and iso, respectively. Respiratory rate decreased most with iso (mean frequency was 4 and 9 breaths/min with iso and halo, respectively). Partial pressure of arterial CO2 was increased similarly with halo and iso. Partial pressure of arterial O2 varied greatly among mares and decreased with duration of use of both anesthetics. Recovery time from anesthesia was significantly (P < 0.05) shorter after use of iso vs halo. Minor superficial injuries were associated with recovery from both anesthetics (in 5 mares with iso and in 1 mare with halo). Physical signs of postanesthetic myopathy or vital-organ dysfunction were not associated with either agent.

Free access
in Journal of the American Veterinary Medical Association

Abstract

Objective—To determine effects of a continuous rate infusion of lidocaine on the minimum alveolar concentration (MAC) of sevoflurane in horses.

Animals—8 healthy adult horses.

Procedures—Horses were anesthetized via IV administration of xylazine, ketamine, and diazepam; anesthesia was maintained with sevoflurane in oxygen. Approximately 1 hour after induction, sevoflurane MAC determination was initiated via standard techniques. Following sevoflurane MAC determination, lidocaine was administered as a bolus (1.3 mg/kg, IV, over 15 minutes), followed by constant rate infusion at 50 μg/kg/min. Determination of MAC for the lidocaine-sevoflurane combination was started 30 minutes after lidocaine infusion was initiated. Arterial blood samples were collected after the lidocaine bolus, at 30-minute intervals, and at the end of the infusion for measurement of plasma lidocaine concentrations.

Results—IV administration of lidocaine decreased mean ± SD sevoflurane MAC from 2.42 ± 0.24% to 1.78 ± 0.38% (mean MAC reduction, 26.7 ± 12%). Plasma lidocaine concentrations were 2,589 ± 811 ng/mL at the end of the bolus; 2,065 ± 441 ng/mL, 2,243 ± 699 ng/mL, 2,168 ± 339 ng/mL, and 2,254 ± 215 ng/mL at 30, 60, 90, and 120 minutes of infusion, respectively; and 2,206 ± 329 ng/mL at the end of the infusion. Plasma concentrations did not differ significantly among time points.

Conclusions and Clinical Relevance—Lidocaine could be useful for providing a more balanced anesthetic technique in horses. A detailed cardiovascular study on the effects of IV infusion of lidocaine during anesthesia with sevoflurane is required before this combination can be recommended.

Full access
in American Journal of Veterinary Research