Hematologic and serum biochemical alterations associated with multiple halothane anesthesia exposures and minor surgical trauma in horses

Five horses were anesthetized similarly by use of xylazine, guaifenesin, thiamylal sodium, and halothane in oxygen on 3 consecutive days, and minor surgical procedures were performed. For 1 to 10 days after the last anesthetic exposure, clinical, hematologic, and serum biochemical features were monitored, and after necropsy, histologic examination of major organ tissues was performed. Predominant hematologic changes from base-line values included leukocytosis (maximal at 27 hours, 10,500 +/- 1,750 cells/microliter), neutrophilia (maximal at 51 hours, 7,485 +/- 1,719 cells/microliter), and lymphopenia (minimal at 51 hours, 1,636 +/- 564 cells/microliter). Alterations observed in other clinicopathologic features were minor and indicative of mild renal disturbance and nonspecific cellular necrosis. Histopathologic lesions in the liver were mild.     

Effect of general anesthesia on plasma cardiac troponin I concentrations in healthy horses

Objective

To evaluate the effect of general anesthesia on plasma cTnI concentrations in horses.

Animals, materials and methods

Thirty-two horses undergoing general anesthesia and either elective surgery or MRI without surgery were prospectively studied. Twenty-nine horses (22 surgical, 7 imaging) completed the study. Plasma cTnI concentrations were determined prior to anesthesia and at 6, 12 and 24 h following discontinuation of the inhalant anesthetic.

Results

All horses had cTnI values within the reference range at all time points. Six horses (21%) developed detectable cTnI 6 or 12 h following anesthesia. Risk factors for detectable cTnI include increasing age and dorsal recumbency. Horses with detectable cTnI had significantly lower mean and diastolic arterial blood pressures than those without detectable cTnI.

Conclusion

Uncomplicated general anesthesia with or without surgery does not result in cardiac troponin I elevations above the reference range in the first 24 h postoperatively.     

Influence of general anesthesia on pharmacokinetics of intravenous lidocaine infusion in horses

OBJECTIVE: To compare the disposition of lidocaine administered IV in awake and anesthetized horses. ANIMALS: 16 horses. PROCEDURE: After instrumentation and collection of baseline data, lidocaine (loading infusion, 1.3 mg/kg administered during 15 minutes (87 microg/kg/min); constant rate infusion, 50 microg/kg/min) was administered IV to awake or anesthetized horses for a total of 105 minutes. Blood samples were collected at fixed times during the loading and maintenance infusion periods and after the infusion period for analysis of serum lidocaine concentrations by use of liquid chromatography with mass spectral detection. Selected cardiopulmonary parameters including heart rate (HR), mean arterial pressure (MAP), arterial pH, PaCO2, and PaO2 were also recorded at fixed time points during lidocaine administration. Serum lidocaine concentrations were evaluated by use of standard noncompartmental analysis. RESULTS: Serum lidocaine concentrations were higher in anesthetized than awake horses at all time points during lidocaine administration. Serum lidocaine concentrations reached peak values during the loading infusion in both groups (1,849 +/- 385 ng/mL and 3,348 +/- 602 ng/mL in awake and anesthetized horses, respectively). Most lidocaine pharmacokinetic variables also differed between groups. Differences in cardiopulmonary variables were predictable; for example, HR and MAP were lower and PaO2 was higher in anesthetized than awake horses but within reference ranges reported for horses under similar conditions. CONCLUSIONS AND CLINICAL RELEVANCE: Anesthesia has an influence on the disposition of lidocaine in horses, and a change in dosing during anesthesia should be considered.     

Effects of general anesthesia on myoelectric activity of the intestine in horses.

Myoelectric activity was monitored from the terminal ileum, cecum, and colonic pelvic flexure by use of AgpAgCl bipolar electrodes in 4 adult horses before, during, and after general anesthesia. Horses were anesthetized by way of 3 commonly used regimens, including xylazine (1.1 mg/kg of body weight) and ketamine hydrochloride (2.2 mg/kg); thiopental sodium (7.7 mg/kg), followed by halothane vaporized in oxygen; and thiopental sodium (2.5 g) in guaifenesin (100 mg/ml) solution given to effect, followed by halothane in oxygen. All 3 anesthetic regimens decreased intestinal spike-burst activity in the areas monitored. The slowest return to preanesthetic myoelectric activity was observed after xylazine and ketamine administration. After both of the barbiturate/halothane anesthetic regimens, there was a rebound increase in spike-burst frequency, without alteration in the proportion of propagative myoelectric events. All 3 anesthetic regimens appeared to reset the timing of the small and large intestinal migrating myoelectric complexes. By 9 hours after recovery from anesthesia, the effects of anesthesia, irrespective of regimen, had disappeared. Although anesthesia significantly (P less than 0.05) altered intestinal myoelectric activity, no particular anesthetic regimen had a prolonged effect. Results of our study indicate that the particular chosen regimen of general anesthesia is unimportant in development of motility disturbances in horses after anesthesia.     

Effect of pressure support ventilation during weaning on ventilation and oxygenation indices in healthy horses recovering from general anesthesia

ObjectiveTo determine if pressure support ventilation (PSV) weaning from general anesthesia affects ventilation or oxygenation in horses.Study designProspective randomized clinical study.AnimalsTwenty client‐owned healthy horses aged 5 ± 2 years, weighing 456 ± 90 kg.MethodsIn the control group (CG; n = 10) weaning was performed by a gradual decrease in respiratory rate (f_R) and in the PSV group (PSVG; n = 10) by a gradual decrease in f_R with PSV. The effect of weaning was considered suboptimal if PaCO₂ > 50 mmHg, arterial pH < 7.35 plus PaCO₂ > 50 mmHg or PaO₂ < 60 mmHg were observed at any time after disconnection from the ventilator until 30 minutes after the horse stood. Threshold values for each index were established and the predictive power of these values was tested.ResultsPressure support ventilation group (PSVG) had (mean ± SD) pH 7.36 ± 0.02 and PaCO₂ 41 ± 3 mmHg at weaning and the average lowest PaO₂ 69 ± 6 mmHg was observed 15 minutes post weaning. The CG had pH 7.32 ± 0.02 and PaCO₂ 57 ± 6 mmHg at weaning and the average lowest PaO₂ 48 ± 5 mmHg at 15 minutes post weaning. No accuracy in predicting weaning effect was observed for f_R (p = 0.3474), minute volume (p = 0.1153), SaO₂ (p = 0.1737) and PaO₂/PAO₂ (p = 0.1529). A high accuracy in predicting an optimal effect of weaning was observed for V_T > 10 L (p = 0.0001), f_R/V_T ratio ≤ 0.60 breaths minute^?1 L^?1 (p = 0.0001), V_T/bodyweight > 18.5 mL kg^?1 (p = 0.0001) and PaO₂/FiO₂ > 298 (p = 0.0002) at weaning. A high accuracy in predicting a suboptimal effect of weaning was observed for V_T < 10 L (p = 0.0001), f_R/V_T ratio ≥ 0.60 breaths minute^?1 L^?1 (p = 0.0001) and Pe′CO₂ ≥ 38 mmHg (p = 0.0001) at weaning.Conclusions and clinical relevancePressure support ventilation (PSV) weaning had a better respiratory outcome. A higher V_T, V_T/body weight, PaO₂/FiO₂ ratio and a lower f_R/V_T ratio and Pe′CO₂ were accurate in predicting the effect of weaning in healthy horses recovering from general anesthesia.     

隆朋麻醉及其手术下对犬儿茶酚胺的影响

应激反应是一种急性时相反应,常导致神经、内分泌系统的激素和炎性细胞因子的变化.神经系统的表达主要是通过交感-肾上腺髓质系统使儿茶酚胺水平发生改变,儿茶酚胺水平的改变是反映机体应激反应的重要指标之一.     

Recovery of horses from general anesthesia in a darkened or illuminated recovery stall

ObjectiveTo assess whether recovery from general anesthesia, in an illuminated or a darkened stall, has an effect on time to first movement, time to standing, and recovery score.Study designProspective randomized clinical study.AnimalsTwenty-nine healthy, 2- to 5-year-old horses undergoing surgical correction of dorsal displacement of the soft palate.MethodsEach horse was assigned randomly to recover in either an illuminated (n = 15) or a darkened stall (n = 14). For pre-anesthetic medication, all horses received intravenous (IV) xylazine (0.4 mg kg⁻¹) and butorphanol (0.02 mg kg⁻¹). Anesthesia was induced with midazolam (0.1 mg kg⁻¹) and ketamine (2.2 mg kg⁻¹) IV and maintained on isoflurane in oxygen. Vital parameters, end-tidal CO₂ and isoflurane were recorded at 5-minute intervals. At the conclusion of anesthesia, horses were placed in either an illuminated or a darkened stall and xylazine (0.2 mg kg⁻¹) IV was administered at extubation. Video cameras were used to record the horses while they were allowed to recover undisturbed. Video recordings were later viewed and recoveries were evaluated on a 100-point scale by three graders.ResultsHorses in illuminated and darkened recovery stalls were evaluated on total anesthesia time, minimum alveolar concentration hours of isoflurane, time to first movement, time to standing, and total recovery score. There were no significant differences between the two groups in any of the measured parameters.ConclusionRecovering horses in a darkened versus an illuminated recovery stall may provide no benefit.Clinical relevanceDarkening the recovery stalls for horses recovering from general anesthesia may be unnecessary.     

Questionnaire on the process of recovering horses from general anesthesia and associated personnel injury in equine practice

ObjectiveTo collect data about the current practice of recovering horses from general anesthesia and recovery personnel safety.Study designOnline survey.MethodsAn online questionnaire, including questions on general demographic data, recovery drugs, modality and characteristics of equine recovery and morbidity and mortality, was designed and distributed via e-mail to equine practitioners worldwide.ResultsPractitioners from 22 countries completed 373 questionnaires; 53% of the participants were board-certified equine surgeons, and the remainder were board-certified anesthesiologists (18%), large animal residents (8%), general practitioners (7%), large animal interns (6%), anesthesia residents (4.5%) and veterinary technicians (1.6%). Respondents were employed by academia (58%) or private practice (42%). Of the respondents employed at a university, 93% had a board-certified anesthesiologist on staff compared with 7% of respondents employed at a private practice. Most of the respondents assist horses during recovery, with 23% assisting every recovery and 44% assisting recovery in the majority of cases. Reasons for choosing to assist horses during recovery were: orthopedic procedures (57%), neurological deficits (49%), bad health (47%), history of poor recovery (44%), foals (42%), draft breeds (30%), magnetic resonance imaging (17%) and computed tomography (16%). Unacceptable recoveries were reported by 77% of participants. Commonly reported complications during recovery with any method were: orthopedic injury (66%), myopathy (54%), skin abrasion (53%) and airway obstruction (37%). The incidences of unacceptable quality of recovery (p = 0.09) or personnel injury (p = 0.56) were not different between assisted and nonassisted recoveries; however, more equine fatalities were reported for assisted recoveries (p < 0.006). Practitioners in academia reported more unacceptable recoveries (p < 0.0007) and personnel injuries (p < 0.002) compared with those in private practice.ConclusionsThe method of recovery differs among hospitals. Recovery personnel injuries associated with assisting horses during recovery are an important and previously unreported finding.     

Analgesic and gastrointestinal effects of epidural morphine in horses after laparoscopic cryptorchidectomy under general anesthesia

ObjectiveTo evaluate the hypothesis that epidural morphine (0.1 mg kg^?1) decreases pain in horses after laparoscopic surgery without adversely affecting gastrointestinal (GI) motility.Study designRandomized clinical trial.AnimalsEighteen horses undergoing laparoscopic cryptorchidectomy under general anesthesia.MethodsHorses were randomly assigned to receive either epidural morphine (0.1 mg kg^?1) or no epidural before the start of surgery. Pain behaviors were assessed during the first two post-operative days using a numerical rating scale. Barium-filled spheres were administered through a nasogastric tube before anesthesia. GI motility was assessed by recording manure production, by quantitating the spheres in the manure, and by abdominal auscultation of intestinal sounds. Heart rates and cortisol concentrations were also measured during the post-operative period.ResultsPain scores increased for 12 hours after surgery in the control group and were significantly higher than in the morphine group for the first 6 hours. Pain scores remained unaltered in the morphine group throughout the observation period. Heart rate and plasma cortisol concentrations did not differ between groups or with time. No signs of colic were observed in any horse.Conclusion and clinical relevanceEpidural morphine (0.1 mg kg^?1) did not adversely affect GI motility in horses after laparoscopic surgery under general anesthesia.     

The effect of general anesthesia and abdominal surgery upon plasma thromboxane B concentrations in horses

OBJECTIVE: To compare the effect of anesthesia alone with anesthesia and abdominal surgery on plasma thromboxane B(2) concentrations in horses. STUDY DESIGN: Non-randomized experimental study. ANIMALS: Six male mixed-bred horses (5-12 years, 350 +/- 18 kg). METHODS: All horses were anesthetized for 2.5 hours using halothane, and a month later abdominal surgery was performed using the same anesthetic technique with a similar duration. The schedule of anesthesia included pre-medication with diazepam (0.1 mg kg(-1) IM), followed by xylazine (2.2 mg kg(-1) IV), and 10 minutes later anesthesia was induced with ketamine hydrochloride (2.2 mg kg(-1) IV). After orotracheal intubation, anesthesia was maintained with halothane. Blood samples for the determination of thromboxane B(2) (TXB(2)) were obtained before, at induction, at 60 minutes after halothane was first inspired, and at recovery from anesthesia as well as at the corresponding stages of the experimental abdominal surgery (before induction, prior to laparotomy, enterectomy, enteroanastomosis, abdominal wall closure). RESULTS: Baseline value for the anesthesia group was 76 +/- 12 pg mL(-1) and increased (p < 0.001) after 1 hour of anesthesia to 265 +/- 40 pg mL(-1). With surgery, the corresponding value was 285 +/- 21 pg mL(-1) (hour 1, p < 0.001) and 210 +/- 28 pg mL(-1) (hour 2, p < 0.001), respectively. These were not different from anesthesia alone. CONCLUSION: The increased concentrations of thromboxane B(2) between 1 and 2.5 hours of halothane anesthesia and during the corresponding stages of the surgical intervention suggested that the anesthetic technique caused a significant increase in thromboxane B(2) and that surgery did not appear to contribute to this response.     

Xylazine and tiletamine-zolazepam anesthesia in horses

The cardiopulmonary and anesthetic effects of xylazine in combination with a 1:1 mixture of tiletamine and zolazepam were determined in 6 horses. Each horse was given xylazine IV or IM, as well as tiletamine-zolazepam IV on 4 randomized occasions. Anesthetics were administered at the rate of 1.1 mg of xylazine/kg of body weight, IV, 1.1 mg of tiletamine-zolazepam/kg, IV (treatment 1); 1.1 mg of xylazine/kg, IV, 1.65 mg of tiletamine-zolazepam/kg, IV (treatment 2); 1.1 mg of xylazine/kg, IV, 2.2 mg of tiletamine-zolazepam/kg, IV (treatment 3); and 2.2 mg of xylazine/kg, IM, 1.65 mg of tiletamine-zolazepam/kg, IV (treatment 4). Tiletamine-zolazepam doses were the sum of tiletamine plus zolazepam. Xylazine, when given IV, was given 5 minutes before tiletamine-zolazepam. Xylazine, when given IM, was given 10 minutes before tiletamine-zolazepam. Tiletamine-zolazepam induced recumbency in all horses. Duration of recumbency in group 1 was 31.9 +/- 7.2 (mean +/- 1 SD) minutes. Increasing the dosage of tiletamine-zolazepam (treatments 2 and 3) significantly (P less than 0.05) increased the duration of recumbency. Xylazine caused significant (P less than 0.05) decreases in heart rate and cardiac output and significant (P less than 0.05) increases in central venous pressure and mean pulmonary artery pressure 5 minutes after administration. Respiratory rate was decreased. Arterial blood pressures increased significantly (P less than 0.05) after xylazine was administered IV in treatments 1 and 3, but the increases were not significant in treatment 2. Xylazine administered IM caused significant (P less than 0.05) increases in central venous pressure and significant (P less than 0.05) decreases in cardiac output.(ABSTRACT TRUNCATED AT 250 WORDS)     

Use of the Anderson Sling suspension system for recovery of horses from general anesthesia

OBJECTIVE: To describe a sling recovery system (Anderson Sling) for horses and to evaluate outcome of high-risk horses recovered from general anesthesia by a sling. STUDY DESIGN: Retrospective study. SAMPLE POPULATION: Horses (n=24) recovered from general anesthesia. METHODS: Complete medical and anesthetic records (1996-2003) for horses recovered from general anesthesia using the Anderson Sling system were evaluated retrospectively. Information retrieved included anesthetic protocol, surgical procedure, recovery protocol, recovery time, and quality of the recovery. Horses were recovered from anesthesia supported by the Anderson Sling in a standing position within a traditional padded equine recovery stall. RESULTS: Twenty-four horses had 32 assisted recoveries; 31 events were successful. No complications associated with the sling or recovery system protocol occurred. One horse was intolerant of the sling's support and was reanesthetized and recovered successfully using head and tail ropes. CONCLUSION: The Anderson Sling recovery system is an effective and safe way to recover horses that are at increased risk for injury associated with adverse events during recovery from general anesthesia. CLINICAL RELEVANCE: The Anderson Sling system should be considered for assisted recovery of equine patients from general anesthesia.