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.

Cardiovascular effects of epidural morphine or ropivacaine in isoflurane-anaesthetised pigs during surgical devascularisation of the liver.

The cardiovascular effects of non-abdominal and abdominal surgery during isoflurane anaesthesia (A-group) or isoflurane anaesthesia supplemented with either epidural ropivacaine (AR-group; 0.75 % solution, 0.2 ml/kg) or morphine (AM-group; 0.1 mg/kg diluted in saline to 0.2 ml/kg) were evaluated in 28 healthy pigs with a mean body weight of 30.3 kg SD +/- 4.1 during surgical devascularisation of the liver. Anaesthesia was induced with the intramuscular injection of midazolam (0.3 mg/kg) and ketamine (10 mg/kg). Anaesthesia was deepened with intravenous propofol to enable tracheal intubation and maintained with isoflurane on a circle rebreathing circuit. The vaporiser was set at 2.5% for the A-group and 1.5% for the AR- and AM-groups. Differences between treatment groups were not statistically significant (P > 0.05) for any of the variables. Differences between AM- and AR-groups were marginally significant heart rate (HR) (P = 0.06) and mean arterial blood pressure (MAP) (P = 0.08). Within treatment groups, differences for the A-group were statistically significant (P < 0.05) between non-abdominal and abdominal surgery for HR, systolic blood pressure, diastolic blood pressure (DIA) and MAP. Within the AM-group differences were statistically significant (P < 0.05) for DIA and MAE and within the AR group differences for all variables were not statistically significant (P > 0.05). It was concluded that in isoflurane-anaesthetised pigs, the epidural administration of ropivacaine decreased heart rate and improved arterial blood pressure during surgery.

Sedative and cardiopulmonary effects of acepromazine, midazolam, butorphanol, acepromazine-butorphanol and midazolam-butorphanol on propofol anaesthesia in goats.

UNLABELLED: The sedative, propofol-sparing and cardiopulmonary effects of acepromazine, midazolam, butorphanol and combinations of butorphanol with acepromazine or midazolam in goats were evaluated. Six healthy Boer - Indigenous African crossbreed goats were by randomised cross-over designated to 6 groups: Group SAL that received saline, Group ACE that received acepromazine, Group MID that received midazolam, Group BUT that received butorphanol, Group ACEBUT that received acepromazine and butorphanol and Group MIDBUT that received midazolam and butorphanol as premedication agents intramuscularly on different occasions at least 3 weeks apart. The degree of sedation was assessed 20 minutes after administration of the premedication agents. Thirty minutes after premedication, the dose of propofol required for induction of anaesthesia adequate to allow placement of an endotracheal tube was determined. Cardiovascular, respiratory and arterial blood-gas parameters were assessed up to 30 minutes after induction of general anaesthesia. Acepromazine and midazolam produced significant sedation when administered alone, but premedication regimens incorporating butorphanol produced inconsistent results. The dose of propofol required for induction of anaesthesia was significantly reduced in goats that received midazolam alone, or midazolam combined with either acepromazine or butorphanol. The quality of induction of anaesthesia was good in all groups, including the control group. Cardiovascular, respiratory and blood-gas parameters were within normal limits in all groups and not significantly different between or within all groups. IN CONCLUSION: sedation with midazolam alone, or midazolam combined with either acepromazine or butorphanol significantly reduces the induction dose of propofol with minimal cardiopulmonary effects in goats.

Cardiovascular effects of lumbar epidural anaesthesia in isoflurane-anaesthetised pigs during surgical removal of the liver.

In humans the combined administration of epidural anaesthesia and inhalation anaesthesia may result in cardiovascular instability associated with decreases in heart rate and blood pressure. Anaesthesia was induced with a combination of midazolam/ketamine in 18 female pigs with a mean body weight of 24.9 +/- 5.9 kg scheduled for surgical removal of the liver. After tracheal intubation, anaesthesia was maintained on a circle rebreathing circuit with isoflurane. Epidural anaesthesia was administered with ropivacaine (AL-group, n = 8) at 0.2 ml/kg of a 7.5 mg/ml solution to the anaesthetised animals. The A-group (n = 10) received isoflurane anaesthesia only. The vaporiser was set at 2.5% for the A-group and 1.5% for the AL-group. Heart rate, invasive systolic, diastolic, and mean arterial blood pressure were monitored. Comparisons were made between treatments and within treatments comparing variables during surgical preparation and abdominal surgery. Differences between treatments were not statistically significant (P > 0.05) during surgical preparation or during abdominal surgery. For within treatment groups, the differences between surgical preparation and abdominal surgery were statistically significant (P < 0.05) for heart rate in the A-group, but not statistically significant (P > 0.05) for the other variables. It is concluded that abdominal surgery may be associated with statistically significant changes in heart rate in isoflurane-anaesthetised pigs and that the combined administration of epidural ropivacaine may prevent statistically significant changes in HR during abdominal surgery.

Partial intravenous anaesthesia in 5 horses using ketamine, lidocaine, medetomidine and halothane.

A partial intravenous protocol was used successfully to maintain anaesthesia in 5 healthy horses. Horses were premedicated with acepromazine, romifidine and butorphanol, induced with guaifenesin and ketamine and maintained on a constant rate infusion of lidocaine, ketamine and medetomidine together with halothane inhalation anaesthesia. Mean end-tidal halothane concentration to maintain a surgical plane of anaesthesia was 0.8 +/- 0.2%. Mean dobutamine requirement to maintain mean arterial pressure above 9.31 kPa was 0.42 +/- 0.3 microg/kg/min. The administration of relatively low doses of lidocaine, ketamine and medetomidine together with halothane resulted in haemodynamically stable anaesthesia, followed by smooth recovery.

Limb fracture during recovery from general anaesthesia: an often tragic complication of equine anaesthesia.

A 10-year-old Thoroughbred mare was presented for lameness of the left hindlimb as a result of an apical fracture of the lateral proximal sesamoid bone. The mare was ultimately euthanased after suffering catastrophic fractures of the 3rd and 4th metatarsal bones of the contra-lateral hindlimb during an uncoordinated attempt to rise during recovery from general anaesthesia after undergoing arthroscopic surgery. The case report focuses mostly on horse anaesthesia-related mortality, anaesthetic procedure in the horse, possible causes of fractures in horses during recovery and ways in which rate of occurrence of these fractures can be minimised.

Cardiopulmonary effects of medetomidine or midazolam in combination with ketamine or tiletamine/zolazepam for the immobilisation of captive cheetahs (Acinonyx jubatus).

Captive cheetah (Acinonyx jubatus) scheduled for either general health examination or dental surgery were immobilised with combinations of medetomidine-ketamine (K/DET, n = 19), midazolam-ketamine (K/MID, n = 4) or medetomidine-tiletamine-zolazepam (Z/DET, n = 5). Induction time and arterial blood pressure was not statistically significantly (P > 0.05) different between treatment groups. Transient seizures were observed in the K/DET treated animals during induction. Hypertension was present in all groups during anaesthesia with mean (+/- SD) systolic pressure of 30.7 +/- 5.0 kPa for the K/DET group, 27.7 +/- 2.7 kPa for the K/MID group, and 33.1 +/- 4.6 kPa for the Z/DET group. Heart rate was statistically significantly (P < 0.05) lower in the K/DET group (69 +/- 13.2 beats/min) compared to the K/MID group (97 +/- 22.6 beats/min), and ventilation rate was statistically significantly (P < 0.05) lower in the K/MID group (15 +/- 0.0 breaths/min) compared with the K/DET group (21 +/- 4.6). A metabolic acidosis and hypoxia were observed during anaesthesia when breathing air. Oxygen (O2) administration resulted in a statistically significant (P < 0.05) increase in the arterial partial pressure of carbon dioxide (hypercapnoea), arterial partial pressure of O2, and % oxyhaemoglobin saturation.

Midazolam/ketamine induction and isoflurane maintenance of anaesthesia in a 2-month-old, hand-raised African buffalo (Syncerus caffer).

The use of a midazolam/ketamine combination for induction of anaesthesia in a 2-month-old, hand-raised buffalo calf (Syncerus caffer) is described to allow endotracheal intubation for the maintenance of anaesthesia with isoflurane and oxygen. Intraoperative complications were hypotension and hypothermia. For postoperative analgesia meloxicam and butorphanol was administered intramuscularly.

Some cardiopulmonary effects of midazolam premedication in clenbuterol-treated bitches during surgical endoscopic examination of the uterus and ovariohysterectomy.

Midazolam was administered intravenously to 8 bitches in a randomised, placebo-controlled clinical trial before propofol induction of surgical anaesthesia. Anaesthesia was maintained with isoflurane-in-oxygen during surgical endoscopic examination of the uterus and ovariohysterectomy. Clenbuterol was administered at the start of surgery to improve uterine muscle relaxation, and to facilitate endoscopic examination of the uterus. Ventilation was controlled. Induction of anaesthesia with propofol to obtain loss of the pedal reflex resulted in a statistically significant (P < 0.05) decrease in minute volume and arterial oxygen partial pressure in the midazolam group. Apnoea also occurred in 50% of dogs in the midazolam group. The dose for propofol in the midazolam group was 7.4 mg/kg compared to 9.5 mg/kg in the control. Minute volume was significantly (P < 0.05) higher in both groups during isoflurane maintenance, compared to the value after incremental propofol to obtain loss of the pedal reflex. Propofol induction resulted in a 25-26% reduction in the mean arterial blood pressure in both groups, and the administration of clenbuterol at the start of surgery resulted in a transient, but statistically significant (P < 0.05), decrease in mean arterial blood pressure in the midazolam group during isoflurane anaesthesia. It is concluded that intravenous midazolam premedication did not adversely affect cardiovascular function during propofol induction, but intra-operative clenbuterol during isoflurane maintenance of anaesthesia may result in transient hypotension. Midazolam premedication may increase adverse respiratory effects when administered before propofol induction of anaesthesia.

Some clinical effects of midazolam premedication in propofol-induced and isoflurane-maintained anaesthesia in dogs during ovariohysterectomy.

In a randomised, placebo-controlled clinical trial, anaesthesia was induced with propofol (4 mg/kg) after intravenous premedication with or without midazolam (0.1 mg/kg), in a group of 8 dogs scheduled for ovariohysterectomy. Midazolam administration induced acute behavioural changes, and increased reflex suppression after propofol induction. Compared to the control group, the dose required to obtain loss of the pedal reflex was significantly reduced by 37%, and the end-tidal isoflurane concentration during maintenance, reduced by 23%.

Rectal prolapse associated with a healed pelvic fracture in a pregnant free-ranging African black rhinoceros (Diceros bicornis). Part 1: anaesthesia.

Anaesthesia was required in a heavily-pregnant, adult, free-ranging African black rhinoceros Diceros bicornis with a rectal prolapse for examination and possible treatment. The animal was immobilised with 4.5 mg etorphine and 60 mg azaperone. For continued observation, the immobilised animal was transported to a boma. Additional etorphine and azaperone were administered to keep the animal anaesthetised during treatment and transport. In addition, 15 mg nalorphine was administered during this time to improve ventilation and reduce muscle rigidity. Sixty hours later, in preparation for surgery, 2.5 mg etorphine and 40 mg azaperone were administered, followed by endotracheal intubation and halothane anaesthesia. During anaesthesia, a decrease in tidal volume was observed. Venous blood-gas analysis indicated a decrease in the oxygen partial pressure, and a mixed respiratory and metabolic acidosis. Cardiac arrest was preceded by an increase in heart rate and tidal volume after 80 min of inhalation anaesthesia.

Rectal prolapse associated with a healed pelvic fracture in a pregnant free-ranging African black rhinoceros (Diceros bicornis). Part 2: surgery and necropsy.

The oedematous and traumatised protruding section of the rectal tissue of an adult free-ranging female African black rhinoceros (Diceros bicornis) was surgically amputated. Immediately before completion of surgery, the rhinoceros died of anaesthetic-related cardiac arrest. At necropsy a deformed pelvis and sacrum associated with a healed fracture of the left ileal wing were noted. New bone formation in and around the left ventral sacral foramina may have resulted in neuropathy of particularly the 3rd and 4th left ventral sacral nerves, which (in the horse) supply the majority of the nerve fibres innervating the caudal rectum and anus. The cause of the injury is not known, although back injuries, presumably sustained during mating by bulls, have been recorded in white rhinoceros. An encounter with elephants could also have been responsible for the injury in this case.

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.

Hypoxaemia and suspected pulmonary oedema in a Dorper ewe after diazepam-ketamine induction of anaesthesia.

Anaesthesia was required in an 18-month-old Dorper ewe scheduled for surgical repair of an abdominal hernia. Anaesthesia was induced with diazepam (0.15 mg/kg) and ketamine (6 mg/kg), and maintained with halothane in oxygen on a circle anaesthetic machine. Hypotension, hypoxaemia, cyanosis and pulmonary oedema were observed from the start of surgery, but the symptoms improved towards the completion of the procedure. The aetiology of this condition could not be established. It is suggested that propylene glycol, the organic solvent in the diazepam formulation, may have stimulated the release of vasoactive substances that resulted in pulmonary oedema.

Effects of xylazine on acid-base balance and arterial blood-gas tensions in goats under different environmental temperature and humidity conditions.

The effects of acute exposure to 3 different temperature and humidity conditions on arterial blood-gas and acid-base balance in goats were investigated after intravenous bolus administration of xylazine at a dose of 0.1 mg/kg. Significant (P<0.05) changes in the variables occurred under all 3 environmental conditions. Decreases in pH, partial pressure of oxygen and oxyhaemoglobin saturation were observed, and the minimum values for oxygen tension and oxyhaemoglobin saturation were observed within 5 min of xylazine administration. The pH decreased to its minimum values between 5 and 15 min. Thereafter, the variables started to return towards baseline, but did not reach baseline values at the end of the 60 min observation period. Increases in the partial pressure of carbon dioxide, total carbon dioxide content, bicarbonate ion concentration, and the actual base excess were observed. The maximum increase in the carbon dioxide tension occurred within 5 min of xylazine administration. The increase in the actual base excess only became significant after 30 min in all 3 environments, and maximal increases were observed at 60 min. There were no significant differences between the variables in the 3 different environments. It was concluded that intravenous xylazine administration in goats resulted in significant changes in arterial blood-gas and acid-base balance that were associated with hypoxaemia and respiratory acidosis, followed by metabolic alkalosis that continued for the duration of the observation period. Acute exposure to different environmental temperature and humidity conditions after xylazine administration did not influence the changes in arterial blood-gas and acid-base balance.

Isoflurane anaesthesia in an African wild dog, Lycaon pictus.

Anaesthesia was required in a captive female African wild dog (Lycaon pictus) for surgical wound treatment. After it was immobilised with a medetomidine-ketamine combination, bradycardia, hypothermia, systolic hypertension and metabolic acidosis were observed. Surgical anaesthesia was maintained with a 1% end-tidal isoflurane concentration. A decrease in the arterial blood pressure, rectal temperature and pH occurred during maintenance of anaesthesia.

Clinical, cardiopulmonary and haemocytological effects of xylazine in goats after acute exposure to different environmental temperature and humidity conditions.

This study was carried out to assess the influence of xylazine administration on clinical, cardiopulmonary and haemocytological variables after acute exposure to different environmental conditions. Xylazine hydrochloride was administered intravenously at 0.1 mg/kg body mass to 6 clinically healthy, castrated male goats. All animals were exposed for 60 min to 3 sets of climatic conditions: 14 degrees C, 33% relative humidity; 24 degrees C, 55% RH, and 34 degrees C, 65% RH. The variables that were measured for a period of 60 min after xylazine administration were sedation, analgesia, salivation, urination, ventilation rate, heart-rate, mean arterial blood pressure, oesophageal temperature, haematocrit, mean corpuscular volume and mean corpuscular haemoglobin concentration. Xylazine induced sedation, analgesia, salivation and urination independently of the 3 environmental conditions. Environment had no influence on the onset, duration and recovery from sedation. In the 14 degrees C environment, xylazine resulted in a significant decrease in ventilation and heart-rate from baseline values. Significant changes in mean arterial blood pressure, haemoglobin concentration, mean corpuscular volume, haematocrit and red cell count were observed in the 3 environments. Total plasma protein was significantly altered at 24 degrees C and 34 degrees C. Acute exposure of goats to different environmental conditions had no significant influence on the clinical, cardiopulmonary and haemocytological variables. Physiological changes induced by xylazine were therefore independent of the environment.

Observations on some cardiopulmonary effects of midazolam, xylazine and a midazolam/ketamine combination in the goat.

Xylazine, midazolam and a midazolam/ketamine combination were administered to 6 goats in a randomised 3-way block design. All goats received all treatments with at least a 7-day interval between treatments. Statistically significant (P < 0.05) changes were observed in some of the measured cardiopulmonary variables for xylazine and midazolam/ ketamine. Xylazine administration resulted in statistically significant decreases in minute volume, arterial partial pressure of oxygen, heart rate and mean arterial blood pressure. The increase in arterial partial pressure of carbon dioxide was not statistically significant. For the midazolam/ketamine combination, the decrease in tidal volume was statistically significant, but not the decrease in minute volume and increase in arterial partial pressure of carbon dioxide. The decrease in the arterial partial pressure of oxygen was also statistically significant. The mean arterial blood pressure for the combination was statistically significantly higher compared to xylazine. The changes in cardiopulmonary variables after midazolam administration were not statistically significant, such as tidal and minute volume, arterial partial pressure of oxygen and carbon dioxide. However, clinically significant effects such as hypoventilation and hypoxia were observed after its administration. The change in mean arterial blood pressure was minimal.

Etorphine-halothane anaesthesia in two five-year-old African elephants (Loxodonta africana).

Anaesthesia of 2 five-year-old female African elephants (Loxodonta africana) was required for dental surgery. The animals were each premedicated with 120 mg of azaperone 60 min before transportation to the hospital. Before offloading, 1 mg etorphine was administered intramuscularly (i.m.) to each elephant to facilitate walking them to the equine induction/recovery room. For induction, 2 mg etorphine was administered i.m. to each animal. Induction was complete within 6 min. Surgical anaesthesia was induced with halothane-in-oxygen after intubation of the trunk. During surgery the mean heart rate was 61 and 45 beats/min respectively. Systolic blood pressures increased to 27.5 and 25.6 kPa respectively, and were treated with intravenous azaperone. Blood pressure decreased thereafter to a mean systolic pressure of 18.1 and 19.8 kPa, respectively. Rectal temperature was 35.6 and 33.9 degrees C at the onset of surgery, and decreased to 35.3 and 33.5 degrees C, respectively, at the end of anaesthesia. Etorphine anaesthesia was reversed with 5 mg diprenorphine at the completion of 90 min of surgery.