Ann E. Wagner

Complications and Mortality Associated With Anesthesia in Dogs and Cats

The complications and mortality associated with anesthesia of dogs and cats in a university teaching hospital were determined. During one year, 2,556 dogs and 683 cats were anesthetized by the anesthesia service. Hypotension occurred in 179 (7%) dogs and 58 (8.5%) cats. Cardiac dysrhythmias occurred in 64 (2.5%) dogs and 12 (1.8%) cats. Transfusions were required in 31 (1.2%) dogs. Hypercapnea occurred in 33 (1.3%) dogs and one (less than 1%) cat. Hypoxemia occurred in 14 (0.5%) dogs. Anesthetic complications, as defined, occurred in 12.0% of dogs and 10.5% of cats, while deaths associated with the perianesthetic period occurred in 0.43% of dogs and 0.43% of cats.

Clinical evaluation of perioperative administration of gabapentin as an adjunct for postoperative analgesia in dogs undergoing amputation of a forelimb.

OBJECTIVE To evaluate perioperative administration of gabapentin as an adjunct for analgesia in dogs undergoing amputation of a forelimb. DESIGN Randomized, controlled trial. ANIMALS 30 client-owned dogs. Procedures-On the day before surgery, a baseline pain evaluation was performed in each dog by use of multiple pain assessment methods. Dogs then received gabapentin (10 mg/kg [4.5 mg/lb], PO, once, followed by 5 mg/kg [2.3 mg/lb], PO, q 12 h for 3 additional days) or a placebo. On the day of surgery, dogs were anesthetized and forelimb amputation was performed. Fentanyl was infused after surgery for 18 to 24 hours; use of other analgesics was allowed. In-hospital pain evaluations were repeated at intervals for 18 hours after surgery, and owners were asked to evaluate daily their dogs activity, appetite, and wound soreness for the first 3 days after discharge from the hospital. Results were analyzed by use of a repeated-measures ANOVA. RESULTS Pain evaluation scores did not differ significantly between gabapentin and placebo groups in the hospital or at home after discharge. CONCLUSIONS AND CLINICAL RELEVANCE As an adjunct to other analgesics and anesthetics, gabapentin, at the dose and frequency used in this study, did not provide a significant benefit for the management of acute perioperative pain in dogs undergoing forelimb amputation. The small sample size and number of other confounding factors, such as aggressive use of other analgesics, limited the likelihood of detecting a benefit of gabapentin. Other gabapentin doses or dosing regimens warrant further study.

Complications in Equine Anesthesia

General anesthesia of horses entails considerable risk of morbidity and mortality. A large-scale, multicenter study reported that the death rate from non-colic-related anesthetics was 0.9%, while the perianesthetic mortality rate at a single, busy equine surgical practice was somewhat more favorable, at 0.12%. While any perianesthetic death is devastating, mortality figures alone do not reflect the overall morbidity of equine anesthesia in terms of nonterminal events or injuries related to recovery. In some circumstances, recognition of perianesthetic complications may allow appropriate intervention to prevent the complication from worsening or progressing to mortality. This article describes some of the complications that may occur during and after general anesthesia of horses, and suggests ways to prevent or mitigate them.

Multicenter, randomized controlled trial of pain-related behaviors following routine neutering in dogs

OBJECTIVE To evaluate the degree of postoperative pain in dogs undergoing elective castration or ovariohysterectomy (OHE); determine whether an association exists between surgeon experience, incision length, or surgery duration and degree of postoperative pain; and determine whether analgesic treatment decreases expression of postoperative pain behaviors. DESIGN Randomized controlled clinical trial. ANIMALS 426 client-owned dogs undergoing OHE or castration. PROCEDURES Dogs underwent OHE or castration performed by an experienced veterinarian or a fourth-year veterinary student. Dogs were randomly assigned to 1 of 4 treatment groups: no perioperative analgesic treatment (n = 44), preoperative administration of morphine (144), preoperative administration of nalbuphine (119), and postoperative administration of ketoprofen (119). Dogs were evaluated while in the hospital before anesthesia and for 4 hours after surgery and once a day at home for 3 days after surgery. RESULTS Dogs in all 4 groups had significant increases in overall pain scores after surgery, compared with baseline scores. There were significant differences among groups, with control dogs having significantly higher increases in overall pain scores than dogs in the other groups. Factors that did not influence the frequency or severity of pain-related behaviors included breed, individual hospital, anesthetic induction protocol, surgeon experience, and duration of surgery. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that dogs expressed behaviors suggestive of pain following OHE and castration, that analgesic treatment mitigated the expression of pain-related behaviors, and that surgeon experience and surgery duration did not have any effect on expression of pain-related behaviors.

Effects of intravenous administration of lidocaine on the minimum alveolar concentration of sevoflurane in horses

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.

Effects of stress on pain in horses and incorporating pain scales for equine practice.

The stress response represents an animals attempt to reestablish the bodys homeostasis after injury, intense physical activity, or psychological strain. Two different neuroendocrine pathways may be activated in stressful situations: the hypothalamic-pituitary-adrenocortical axis, leading to increased cortisol levels, and the sympathoadrenomedullar system, leading to increased catecholamine levels. By applying some of the evaluation methods described in this article in the appropriate clinical situations, equine veterinarians can almost certainly improve their ability to recognize and manage pain in horses.

A comparison of equine recovery characteristics after isoflurane or isoflurane followed by a xylazine–ketamine infusion

OBJECTIVE To determine whether infusion of xylazine (XYL) and ketamine (KET) for 30 minutes after isoflurane administration in horses would result in improved quality of recovery from anesthesia, without detrimental cardiopulmonary changes. STUDY DESIGN Randomized, blinded experimental trial. ANIMALS Seven healthy adult horses aged 6.4 +/- 1.9 years and weighing 506 +/- 30 kg. METHODS Horses were anesthetized twice, at least 1 week apart. On both occasions, anesthesia was induced by the administration of XYL, diazepam, and KET, and maintained with isoflurane for approximately 90 minutes, the last 60 minutes of which were under steady-state conditions (1.2 times the minimum alveolar concentration isoflurane). On one occasion, horses were allowed to recover from isoflurane anesthesia, while on the other, XYL and KET were infused for 30 minutes after termination of isoflurane administration. Heart rate, respiratory rate, arterial blood pressure, pH, and blood-gases were measured and recorded at set intervals during steady-state isoflurane anesthesia and XYL-KET infusion. Recovery events were timed and subjectively scored by one nonblinded and two blinded observers. Data were analyzed using a restricted maximum likelihood-based mixed effect model repeated measures analysis. RESULTS Infusion of XYL and KET resulted in longer recovery times, but there was no significant improvement in recovery quality score. CONCLUSIONS Under the conditions of this study, infusion of XYL and KET does not positively influence recovery from isoflurane anesthesia in horses. CLINICAL RELEVANCE This study does not support the routine use of XYL and KET infusions in horses during the transition from isoflurane anesthesia to recovery.

Comparison of the cardiovascular effects of equipotent anesthetic doses of sevoflurane alone and sevoflurane plus an intravenous infusion of lidocaine in horses

OBJECTIVE To compare cardiovascular effects of sevoflurane alone and sevoflurane plus an IV infusion of lidocaine in horses. Animals-8 adult horses. PROCEDURES Each horse was anesthetized twice via IV administration of xylazine, diazepam, and ketamine. During 1 anesthetic episode, anesthesia was maintained by administration of sevoflurane in oxygen at 1.0 and 1.5 times the minimum alveolar concentration (MAC). During the other episode, anesthesia was maintained at the same MAC multiples via a reduced concentration of sevoflurane plus an IV infusion of lidocaine. Heart rate, arterial blood pressures, blood gas analyses, and cardiac output were measured during mechanical (controlled) ventilation at both 1.0 and 1.5 MAC for each anesthetic protocol and during spontaneous ventilation at 1 of the 2 MAC multiples. RESULTS Cardiorespiratory variables did not differ significantly between anesthetic protocols. Blood pressures were highest at 1.0 MAC during spontaneous ventilation and lowest at 1.5 MAC during controlled ventilation for either anesthetic protocol. Cardiac output was significantly higher during 1.0 MAC than during 1.5 MAC for sevoflurane plus lidocaine but was not affected by anesthetic protocol or mode of ventilation. Clinically important hypotension was detected at 1.5 MAC for both anesthetic protocols. CONCLUSIONS AND CLINICAL RELEVANCE Lidocaine infusion did not alter cardiorespiratory variables during anesthesia in horses, provided anesthetic depth was maintained constant. The IV administration of lidocaine to anesthetized nonstimulated horses should be used for reasons other than to improve cardiovascular performance. Severe hypotension can be expected in nonstimulated horses at 1.5 MAC sevoflurane, regardless of whether lidocaine is administered.

Behavioral responses following eight anesthetic induction protocols in horses

OBJECTIVE To compare behavioral characteristics of induction and recovery in horses anesthetized with eight anesthetic drug protocols. STUDY DESIGN Randomized prospective experimental study. ANIMALS Eight horses, 5.5 ± 2.4 years (mean ± SD) of age, and weighing 505 ± 31 kg. METHODS After xylazine pre-medication, each of eight horses was anesthetized on four occasions using one of eight different anesthetic induction protocols which incorporated various combinations of ketamine (KET), propofol (PRO), and thiopental (THIO): THIO 8 mg kg-1; THIO 6 mg kg-1 + PRO 0.5 mg kg-1; THIO 4 mg kg-1 + PRO 1 mg kg-1; THIO 2 mg kg-1 + PRO 1.5 mg kg-1; KET 2 mg kg-1; KET 1.5 mg kg-1 + PRO 0.5 mg kg-1; KET 1 mg kg-1 + PRO 1 mg kg-1; KET 0.5 mg kg-1 + PRO 1.5 mg kg-1. Quality of induction and recovery were scored from 1 (poor) to 5 (excellent), and time taken to achieve lateral recumbency, first movement, sternal recumbency, and standing were evaluated. RESULTS Time taken to achieve lateral recumbency after drug administration differed significantly (p < 0.0001) among the various combinations, being shortest in horses receiving THIO-8 (mean ± SD, 0.5 ± 0.3 minutes) and longest in horses receiving KET-2 (1.4 ± 0.2 minutes). The best scores for induction quality were associated with KET-1.5 + PRO-0.5, and the worst scores for induction quality were associated with KET-2, although the difference was not significant. Time to first movement varied significantly among drug protocols (p = 0.0133), being shortest in horses receiving KET-2 (12.7 ± 3.6 minutes) and longest in horses receiving THIO-8 (29.9 ± 1.5 minutes). Horses receiving THIO-8 made the greatest number of attempts to attain sternal posture (6.5 ± 4.7) and to stand (1.6 ± 0.8). Horses in the THIO-8 treatment also received the poorest recovery scores (3.3 ± 1.0 and 3.0 ± 0.7 for sternal and standing postures, respectively). The best recovery scores were associated with combinations comprised mainly of propofol. CONCLUSIONS Combining propofol with either ketamine or thiopental modifies behaviors associated with use of the individual drugs. CLINICAL RELEVANCE Quality of early anesthesia recovery in horses may be improved by some combinations of propofol with either thiopental or ketamine.

Evaluation of infusions of xylazine with ketamine or propofol to modulate recovery following sevoflurane anesthesia in horses

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.