George F. Stegmann

Sedative-hypnotic effects of midazolam in goats after intravenous and intramuscular administration

OBJECTIVE To examine the effect of dose and route of administration on the sedative-hypnotic effects of midazolam. DESIGN Prospective randomized controlled study ANIMALS: Six indigenous, African bred goats. METHODS Pilot studies indicated that the optimum dose of midazolam for producing sedation was 0.6 mg kg-1 for intramuscular (IM) injection, while the optimum intravenous (IV) doses causing hypnosis without, and with loss of palpebral reflexes were 0.6 mg kg-1 and 1.2 mg kg-1, respectively. These doses and routes of administration were compared with a saline placebo in a randomized block design in the main experiment, and the sedative-hypnotic effects evaluated according to pre-determined scales. RESULTS Intramuscular midazolam produced sedation with or without sternal recumbency in all animals with the peak effect occurring 20 minutes after administration. The scores for IM sedation with midazolam were significantly different (p < 0.05) from placebo. Intravenous midazolam at 0.6 mg kg-1 resulted in hypnosis, and at 1.2 mg kg-1 increased reflex suppression was observed. The maximum scores for hypnosis at both doses were obtained 5 minutes after IV injection. The mean (± SD) duration of lateral recumbency was 10.8 (± 3.8) minutes after IV midazolam (0.6 mg kg-1) compared to 20 (± 5.2) minutes after midazolam at 1.2 mg kg-1. Compared to baseline, the heart rate increased significantly (p < 0.05) after high dose IV midazolam. CONCLUSION Intramuscular midazolam (0.6 mg kg-1) produced maximum sedation 20 minutes after injection. Intravenous injection produced maximum hypnosis within 5 minutes. Increasing the IV dose from 0.6 to 1.2 mg kg-1 resulted in increased reflex suppression and duration of hypnosis. CLINICAL RELEVANCE For a profound effect with rapid onset midazolam should be given IV in doses between 0.6 and 1.2 mg kg-1.

Effects of fentanyl on isoflurane minimum alveolar concentration and cardiovascular function in mechanically ventilated goats

The effects of fentanyl on the minimum alveolar concentration (MAC) of isoflurane and cardiovascular function in mechanically ventilated goats were evaluated using six healthy goats (three does and three wethers). Following induction of general anaesthesia with isoflurane delivered via a mask, endotracheal intubation was performed and anaesthesia was maintained with isoflurane. The baseline MAC of isoflurane (that is, the lowest alveolar concentration required to prevent gross purposeful movement) in response to clamping a claw with a vulsellum forceps was determined. Immediately after baseline isoflurane MAC determination, the goats received, on separate occasions, one of three fentanyl treatments, administered intravenously: a bolus of 0.005 mg/kg followed by constant rate infusion (CRI) of 0.005 mg/kg/hour (treatment LFENT), a bolus of 0.015 mg/kg followed by CRI of 0.015 mg/kg/hour (treatment MFENT) or a bolus of 0.03 mg/kg followed by CRI of 0.03 mg/kg/hour (treatment HFENT). Isoflurane MAC was redetermined during the fentanyl CRI treatments. Cardiopulmonary parameters were monitored. A four-week washout period was allowed between treatments. The observed baseline isoflurane MAC was 1.32 (1.29 to 1.36) per cent. Isoflurane MAC decreased to 0.98 (0.92 to 1.01) per cent, 0.75 (0.69 to 0.79) per cent and 0.58 (0.51 to 0.65) per cent following LFENT, MFENT and HFENT respectively. Cardiovascular function was not adversely affected. The quality of recovery from general anaesthesia was good, although exaggerated tail-wagging was observed in some goats following MFENT and HFENT.

ETORPHINE–KETAMINE–MEDETOMIDINE TOTAL INTRAVENOUS ANESTHESIA IN WILD IMPALA (AEPYCEROS MELAMPUS) OF 120-MINUTE DURATION

Abstract:  There is a growing necessity to perform long-term anesthesia in wildlife, especially antelope. The costs and logistics of transporting wildlife to veterinary practices make surgical intervention a high-stakes operation. Thus there is a need for a field-ready total intravenous anesthesia (TIVA) infusion to maintain anesthesia in antelope. This study explored the feasibility of an etorphine–ketamine–medetomidine TIVA for field anesthesia. Ten wild-caught, adult impala (Aepyceros melampus) were enrolled in the study. Impala were immobilized with a standardized combination of etorphine (2 mg) and medetomidine (2.2 mg), which equated to a median (interquartile range [IQR]) etorphine and medetomidine dose of 50.1 (46.2–50.3) and 55.1 (50.8–55.4) μg/kg, respectively. Recumbency was attained in a median (IQR) time of 13.9 (12.0–16.5) min. Respiratory gas tensions, spirometry, and arterial blood gas were analyzed over a 120-min infusion. Once instrumented, the TIVA was infused as follows: etorphine at a variable rate initiated at 40 μg/kg per hour (adjusted according to intermittent deep-pain testing); ketamine and medetomidine at a fixed rate of 1.5 mg/kg per hour and 5 μg/kg per hour, respectively. The etorphine had an erratic titration to clinical effect in four impala. Arterial blood pressure and respiratory and heart rates were all within normal physiological ranges. However, arterial blood gas analysis revealed severe hypoxemia, hypercapnia, and acidosis. Oxygenation and ventilation indices were calculated and highlighted possible co-etiologies to the suspected etorphine-induced respiratory depression as the cause of the blood gas derangements. Impala recovered in the boma post atipamezole (13 mg) and naltrexone (42 mg) antagonism of medetomidine and etorphine, respectively. The etorphine–ketamine–medetomidine TIVA protocol for impala may be sufficient for field procedures of up to 120-min duration. However, hypoxemia and hypercapnia are of paramount concern and thus oxygen supplementation should be considered mandatory. Other TIVA combinations may be superior and warrant further investigation.

Preliminary investigation into the ventilatory effects of midazolam in isoflurane-anaesthetised goats

The ventilatory effects of intravenous midazolam (MDZ) were evaluated in isoflurane- anaesthetised goats. Eight female goats aged 2-3 years were fasted from food and water for 12 h. Anaesthesia was then induced using a face mask with isoflurane in oxygen, whilst the trachea was intubated with a cuffed tracheal tube and anaesthesia maintained with isoflurane at 1.5% end-tidal concentration. Ventilation was spontaneous. The goats were treated with either a saline placebo (PLC) or MDZ intravenously at 0.2 mg/kg. Analysis of variance for repeated measures was used for the analysis of data. Significance was taken at the 0.05 level. Differences between treatments were not statistically significant (p > 0.05) for tidal volume, ventilation rate, tidal volume/kg (VT/kg) and end-tidal carbon dioxide partial pressure. Within treatments, VT and VT/kg differed 5 min after MDZ administration; this was statistically significant (p < 0.05). The occurrence of apnoea in the MDZ-treated goats was statistically significant (p = 0.04) compared with the PLC treated goats. Intravenous MDZ at 0.2 mg/kg administered to isoflurane-anaesthetised goats may result in transient apnoea and a mild decrease in VT and VT/kg.

Single-Incision Laparoscopic Sterilization of the Cheetah (Acinonyx jubatus)

OBJECTIVE To describe laparoscopic ovariectomy and salpingectomy in the cheetah (Acinonyx jubatus) using single-incision laparoscopic surgery (SILS). STUDY DESIGN Prospective cohort. ANIMALS Female cheetahs (Acinonyx jubatus) (n = 21). METHODS Cheetahs were randomly divided to receive either ovariectomy (n = 11) or salpingectomy (n = 10). The use and complications of a SILS port was evaluated in all of cheetahs. Surgery duration and insufflation volumes of carbon dioxide (CO2 ) were recorded and compared across procedures. RESULTS Laparoscopic ovariectomy and salpingectomy were performed without complications using a SILS port. The poorly-developed mesosalpinx and ovarian bursa facilitated access to the uterine tube for salpingectomy in the cheetah. The median surgery duration for ovariectomy was 24 minutes (interquartile range 3) and for salpingectomy was 19.5 minutes (interquartile range 3) (P = .005). The median volume of CO2 used for ovariectomy was 11.25 L (interquartile range 3.08) and for salpingectomy was 4.90 L (interquartile range 2.52), (P = .001) CONCLUSIONS: Laparoscopic ovariectomy and salpingectomy can be performed in the cheetah using SILS without perioperative complications. Salpingectomy is faster than ovariectomy and requires less total CO2 for insufflation.

CONTINUOUS INTRAVENOUS INFUSION ANESTHESIA WITH MEDETOMIDINE, KETAMINE, AND MIDAZOLAM AFTER INDUCTION WITH A COMBINATION OF ETORPHINE, MEDETOMIDINE, AND MIDAZOLAM OR WITH MEDETOMIDINE, KETAMINE, AND BUTORPHANOL IN IMPALA (AEPYCEROS MELAMPUS)

Abstract In order to develop a long-term anesthesia for flighty antelope species in field situations, two different protocols for induction and maintenance with an intravenous infusion were evaluated in wild-caught impala (Aepyceros melampus). Ten adult female impala were induced with two induction protocols: one consisted of 0.2 mg/kg medetomidine, 4 mg/kg ketamine, and 0.15 mg/kg butorphanol (MKB) and one consisted of 0.375 mg/kg etorphine, 0.2 mg/kg medetomidine, and 0.2 mg/kg midazolam (EMM). In both treatments, anesthesia was maintained with a continuous intravenous infusion (CII) at an initial dose rate of 1.2 μg/kg per hr medetomidine, 2.4 mg/kg per hr ketaminen and 36 μg/kg per hr midazolam. Partial reversal was achieved with naltrexone (2 : 1 mg butorphanol; 20 : 1 mg etorphine) and atipamezole (5 : 1 mg medetomidine). Evaluation of anesthesia included respiratory rate, heart rate, rectal temperature, arterial blood pressure, oxygen saturation, end tidal carbon dioxide tension, and tidal volume at 5-min intervals, palpebral reflex and response to painful stimuli at 15-min intervals, and arterial blood gases at 30-min intervals. Plasma cortisol concentration was determined after induction and before reversal. Duration and quality of induction and recovery were evaluated. EMM caused a faster induction of 9.5 ± 2.9 min compared to 11.0 ± 6.4 min in MKB. Recovery was also quicker in EMM (EMM: 6.3 ± 5.4 min; MKB: 9.8 ± 6.0 min). However, EMM also produced more cardiopulmonary side effects, including hypoxemia and hypercapnia, and calculated oxygenation indices (PaCO2-PETCO2) were worse than in MKB. One animal died after induction with EMM. The CII provided surgical anesthesia in 7 of 10 animals in MKB and in 9 of 9 animals in EMM for 120 min. In conclusion, the MKB induction protocol had advantages for prolonged anesthesia in impala with significantly less cardiopulmonary depression compared to EMM. The comparably decreased anesthetic depth could easily be adjusted by an increase of the CII.

ACCURACY OF NONINVASIVE ANESTHETIC MONITORING IN THE ANESTHETIZED GIRAFFE (GIRAFFA CAMELOPARDALIS)

Abstract This study evaluated the accuracy of pulse oximetry, capnography, and oscillometric blood pressure during general anesthesia in giraffes (Giraffa camelopardalis). Thirty-two giraffes anesthetized for physiologic experiments were instrumented with a pulse oximeter transmittance probe positioned on the tongue and a capnograph sampling line placed at the oral end of the endotracheal tube. A human size 10 blood pressure cuff was placed around the base of the tail, and an indwelling arterial catheter in the auricular artery continuously measured blood pressure. Giraffes were intermittently ventilated using a Hudson demand valve throughout the procedures. Arterial blood for blood gas analysis was collected at multiple time points. Relationships between oxygen saturation as determined by pulse oximetry and arterial oxygen saturation, between arterial carbon dioxide partial pressure and end-tidal carbon dioxide, and between oscillometric pressure and invasive arterial blood pressure were assessed, and the accuracy of pulse oximetry, capnography, and oscillometric blood pressure monitoring evaluated using Bland-Altman analysis. All three noninvasive methods provided relatively poor estimates of the reference values. Receiver operating characteristic curve fitting was used to determine cut-off values for hypoxia, hypocapnia, hypercapnia, and hypotension for dichotomous decision-making. Applying these cut-off values, there was reasonable sensitivity for detection of hypocapnia, hypercapnia, and hypotension, but not for hypoxemia. Noninvasive anesthetic monitoring should be interpreted with caution in giraffes and, ideally, invasive monitoring should be employed.

Anaesthetic management of a 10-month-old white rhinoceros (Ceratotherium simum) calf for emergency exploratory celiotomy

A 10-month-old, 580 kg, hand-reared white rhinoceros (Ceratotherium simum) calf was presented for emergency exploratory celiotomy. Anaesthesia was safely induced with three successive intravenous (IV) boluses of diazepam (10 mg) and ketamine (100 mg) until the trachea could be intubated. Anaesthesia was adequately maintained with isoflurane-inoxygen (mean end-tidal isoflurane concentration of 1.1% ± 0.2%) on a circle anaesthetic machine with carbon dioxide absorption and an intravenous infusion of ketamine and medetomidine at a mean rate of 0.02 mg/kg/min and 0.02 µg/kg/min, respectively. Mean values recorded during anaesthesia and surgery were heart rate (56.9 ± 11 beats/min), mean arterial blood pressure (6.16 kPa ± 1.75 kPa), end-tidal carbon dioxide concentration (6.23 kPa ± 0.30 kPa). Abdominal gas distension contributed to hypoventilation that resulted in hypercapnoea, confirmed by arterial blood gas analysis (PaCO2 14.69 kPa), which required controlled ventilation for correction. Blood volume was maintained with the intravenous infusion of a balanced electrolyte solution at 10 mL/kg/h and blood pressure supported with a continuous infusion of dobutamine and phenylephrine. Duration of anaesthesia was 3.5 h. It was concluded that anaesthesia was safely induced in a compromised white rhinoceros calf with a combination of diazepam and ketamine. A constant-rate infusion of medetomidine and ketamine allowed for a reduction in the dose of isoflurane required during maintenance of anaesthesia and improved intra-operative blood pressure management.

Preliminary investigation of concurrent administration of phenylbutazone and romifidine in healthy horses

OBJECTIVE To characterize the cardiorespiratory and electrocardiographic effects of the combined administration of phenylbutazone and romifidine. STUDY DESIGN Prospective four-period, four-treatment, blinded, randomized, crossover trial. ANIMALS Five, healthy, mixed breed horses. METHODS Prior to treatment administration, a catheter was introduced into the intra-thoracic cranial vena cava via the jugular vein and a subcutaneously located carotid artery was catheterised. All treatments were administered intravenously (IV) and consisted of saline placebo (PLC), phenylbutazone (PBZ, 4.4 mg kg(-1) ) romifidine (ROM, 80 μg kg(-1) ) and a combination of phenylbutazone (4.4 mg kg(-1) ) and romifidine (80 μg kg(-1) ). There was at least a 1 week washout period between treatments. Heart rate (HR), respiratory rate (f(R) ), systolic (SAP), diastolic (DAP) and mean (MAP) arterial pressures and central venous pressure (CVP) were recorded for baseline (prior to drug administration) and at 5 minute intervals thereafter for 30 minutes. Electrocardiographic abnormalities were recorded. Data were analyzed by anova. RESULTS For the cardiovascular variables there were no statistically significant (p>0.05) differences between horses treated with ROM and PBZ_ROM. Statistically significant (p<0.05) differences only occurred between treatments with romifidine (ROM and PBZ_ROM) and without romifidine (PLC and PBZ). Within treatments, for ROM, changes over time were statistically significant (p<0.05) for HR, SAP, DAP, MAP and CVP. For PBZ_ROM, changes over time were statistically significant (p<0.05) for CVP. Sino-atrial and atrio-ventricular blocks occurred in horses treated with ROM and PBZ_ROM. CONCLUSIONS AND CLINICAL RELEVANCE The combined IV administration of phenylbutazone and romifidine had no statistically significant effect on cardiorespiratory variables. These limited data suggest no evidence why both agents should not be included in a preoperative medication protocol for healthy horses but do not exclude the possibility of interactions occurring in a larger population.

Xenotransfusion with packed bovine red blood cells to a wildebeest calf (Connochaetes taurinus)

A 4-month-old female blue wildebeest (Connochaetes taurinus) was presented for bilateral pelvic limb fracture repair. Clinical examination under anaesthesia revealed a water-hammer pulse and a haematocrit of 0.13. A xenotransfusion was performed using bovine (Bos taurus) erythrocytes because of inability to acquire a wildebeest donor. Clinical parameters improved following transfusion and the post-operative haematocrit value was 0.31. The wildebeest remained physiologically stable with a gradually declining haematocrit for the next three days. On the third post-operative day, the wildebeest refractured its femur and was humanely euthanised because of the poor prognosis for further fracture repair. Xenotransfusion using blood from domestic ruminants represents a life-saving short-term emergency treatment of anaemic hypoxia in wild ungulates. Domestic goats could be used as blood donors for rare ungulates where allodonors are not available.