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.     

A combination of methotrimeprazine, midazolam and guaiphenesin, with and without ketamine, in an anaesthetic procedure for horses.

A combination of 0.5 mg/kg of methotrimeprazine, 0.1 mg/kg of midazolam and 100 mg/kg of a 10 per cent guaiphenesin solution was investigated for the induction of recumbency in 15 horses; the addition of 1.6 mg/kg of ketamine was also evaluated in 15 horses and anaesthesia was maintained with halothane in oxygen. The horses became recumbent quickly and smoothly and they recovered quietly, with little ataxia. Tachycardia occurred after induction, but no other changes from pre-operative values were observed until halothane in oxygen had been given, when hypothermia, hypotension, bradypnoea, hyperoxaemia, respiratory acidosis and decreased respiratory minute volume developed. Horses given ketamine in addition to methotrimeprazine, midazolam and guaiphenesin were easier to intubate and recovered more quickly than horses receiving only methotrimeprazine, midazolam and guaiphenesin.     

Minimal alveolar concentration of desflurane in combination with an infusion of medetomidine for the anaesthesia of ponies

The minimum alveolar concentration of desflurane when combined with a continuous infusion of medetomidine at 3.5 microg/kg/hour was measured in seven ponies. Anaesthesia was induced with medetomidine (7 microg/kg intravenously) followed by ketamine (2 mg/kg intravenously) and maintained with desflurane in oxygen. The infusion of medetomidine was started 20 minutes after the induction of anaesthesia. The electrical test stimulus was applied at the coronary band (50 V, 10 ms bursts at 5 Hz for one minute), and heart rates and rhythms, arterial blood pressures, and arterial blood gas tensions were measured at intervals, just before the application of the stimulus. The mean (sd) minimum alveolar concentration of desflurane was 5.3 (1.04) per cent (range 3.2 to 6.4 per cent), 28 per cent less than the previously published value for desflurane alone after the induction of anaesthesia with xylazine and ketamine. The cardiopulmonary parameters remained stable throughout the period of anaesthesia. The mean (sd) time taken by the ponies to stand after the administration of desflurane ceased was 16.5 (6.17) (range 5.8 to 26) minutes, and the quality of recovery was good or excellent. However, one pony died shortly after standing; a postmortem examination revealed that it had chronic left atrial dilatation.     

Effects of a constant‐rate infusion of dexmedetomidine on the minimal alveolar concentration of sevoflurane in ponies

Reasons for performing study: Dexmedetomidine has been administered in the equine as a constant‐rate infusion (CRI) during inhalation anaesthesia, preserving optimal cardiopulmonary function with calm and coordinated recoveries. Inhalant anaesthetic sparing effects have been demonstrated in other species, but not in horses. Objectives: To determine the effects of a CRI of dexmedetomidine on the minimal alveolar concentration (MAC) of sevoflurane in ponies. Methods: Six healthy adult ponies were involved in this prospective, randomised, crossover, blinded, experimental study. Each pony was anaesthetised twice (3 weeks washout period). After induction with sevoflurane in oxygen (via nasotracheal tube), the ponies were positioned on a surgical table (T0), and anaesthesia was maintained with sevoflurane (expired sevoflurane fraction 2.5%) in 55% oxygen. The ponies were randomly allocated to treatment D (dexmedetomidine 3.5 µg/kg bwt i.v. [T10–T15] followed by a CRI of dexmedetomidine at 1.75 µg/kg bwt/h) or treatment S (bolus and CRI of saline at the same volume and rate as treatment D). After T60, MAC determination, using a classic bracketing technique, was initiated. Stimuli consisted of constant‐current electrical stimuli at the skin of the lateral pastern region. Triplicate MAC estimations were obtained and averaged in each pony. Monitoring included pulse oximetry, electrocardiography, anaesthetic gas monitoring, arterial blood pressure measurement and arterial blood gases. Normocapnia was maintained by mechanical ventilation. Analysis of variance (treatment and period as fixed factors) was used to detect differences between treatments (α= 0.05). Results: An intravenous (i.v.) dexmedetomidine CRI decreased mean ± s.d. sevoflurane MAC from 2.42 ± 0.55 to 1.07 ± 0.21% (mean MAC reduction 53 ± 15%). Conclusions and potential relevance: A dexmedetomidine CRI at the reported dose significantly reduces the MAC of sevoflurane.     

Comparison of the cardiopulmonary effects of anesthesia maintained by continuous infusion of ketamine and propofol with anesthesia maintained by inhalation of sevoflurane in goats undergoing magnetic resonance imaging

OBJECTIVE: To compare the cardiopulmonary effects of anesthesia maintained by continuous infusion of ketamine and propofol with anesthesia maintained by inhalation of sevoflurane in goats undergoing magnetic resonance imaging. ANIMALS: 8 Saanen goats. PROCEDURES: Goats were anesthetized twice (1-month interval) following sedation with midazolam (0.4 mg/kg, IV). Anesthesia was induced via IV administration of ketamine (3 mg/kg) and propofol (1 mg/kg) and maintained with an IV infusion of ketamine (0.03 mg/kg/min) and propofol (0.3 mg/kg/min) and 100% inspired oxygen (K-P treatment) or induced via IV administration of propofol (4 mg/kg) and maintained via inhalation of sevoflurane in oxygen (end-expired concentration, 2.3%; 1X minimum alveolar concentration; SEVO treatment). Cardiopulmonary and blood gas variables were assessed at intervals after induction of anesthesia. RESULTS: Mean +/- SD end-expired sevoflurane was 2.24 +/- 0.2%; ketamine and propofol were infused at rates of 0.03 +/- 0.002 mg/kg/min and 0.29 +/- 0.02 mg/kg/min, respectively. Overall, administration of ketamine and propofol for total IV anesthesia was associated with a degree of immobility and effects on cardiopulmonary parameters that were comparable to those associated with anesthesia maintained by inhalation of sevoflurane. Compared with the K-P treatment group, mean and diastolic blood pressure values in the SEVO treatment group were significantly lower at most or all time points after induction of anesthesia. After both treatments, recovery from anesthesia was good or excellent. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that ketamine-propofol total IV anesthesia in goats breathing 100% oxygen is practical and safe for performance of magnetic resonance imaging procedures.     

Effects of four anaesthetic protocols on the neurological and cardiorespiratory variables of puppies born by caesarean section

Twenty-four bitches which had been in labour for less than 12 hours were randomly divided into four groups of six. They all received 0.5 mg/kg of chlorpromazine intravenously as premedication, followed 15 minutes later by either 8 mg/kg of thiopentone intravenously (group 1), 2 mg/kg of ketamine and 0.5 mg/kg of midazolam intravenously (group 2), 5 mg/kg of propofol intravenously (group 3), or 2.5 mg/kg of 2 per cent lidocaine with adrenaline and 0.625 mg/kg of 0.5 per cent bupivacaine with adrenaline epidurally (group 4). Except for group 4, the bitches were intubated and anaesthesia was maintained with enflurane. The puppies' heart and respiratory rates and their pain, sucking, anogenital, magnum and flexion reflexes were measured as they were removed from the uterus. The puppies' respiratory rate was higher after epidural anaesthesia. In general the puppies' neurological reflexes were most depressed after midazolam/ketamine, followed by thiopentone, propofol and epidural anaesthesia.     

Effects of medetomidine-midazolam,midazolambutorphanol, or acepromazine-butorphanol as premedicants for mask induction of anesthesia with sevoflurane in dogs

OBJECTIVE: To characterize the effects of medetomidine-midazolam, midazolam-butorphanol, or acepromazine-butorphanol as premedicants for mask induction of anesthesia with sevoflurane in dogs. ANIMALS: 10 healthy Beagles. PROCEDURE: The following premedicants were administered intramuscularly: medetomidine-midazolam (20 microg/kg and 0.3 mg/kg, respectively), midazolam-butorphanol (0.1 and 0.2 mg/kg, respectively), and acepromazine-butorphanol (0.05 and 0.2 mg/kg, respectively). Saline (0.9% NaCI) solution (0.1 ml/kg) was administered intramuscularly as a control. Anesthesia was induced in each dog with sevoflurane in a 100% O2 at a flow rate of 4 L/min developed by a facemask. Vaporizer settings were increased by 0.8% at 15-second intervals until the value corresponding to 4.8% sevoflurane was achieved. Time to onset and cessation of involuntary movements, loss of the palpebral reflex, negative response to tail-clamp stimulation, and endotracheal intubation were recorded, and the cardiopulmonary variables were measured. RESULTS: Mask induction with sevoflurane in dogs that received each premedicant resulted in a shorter induction time and milder changes in heart rate, mean arterial blood pressure, cardiac output, and respiratory rate, compared with mask induction without premedicants. Treatment with medetomidine-midazolam resulted in a shorter and smoother induction, compared with acepromazine-butorphanol or midazolam-butorphanol treatment, whereas the cardiovascular changes were greater. Cardiopulmonary variables of dogs during induction following treatment with acepromazine-butorphanol or midazolam-butorphanol were maintained close to the anesthetic maintenance values for sevoflurane, with the exception of mild hypotension that was observed in dogs following acepromazine-butorphanol treatment. CONCLUSION AND CLINICAL RELEVANCE: In dogs use of premedicants provides a smoother and better quality mask induction with sevoflurane.     

Cardiopulmonary effects of sufentanil long acting on sevoflurane anaesthesia in dogs

OBJECTIVE: To evaluate the cardiopulmonary effects of sufentanil long acting (SLA) in sevoflurane-anaesthetized dogs. STUDY DESIGN: Randomized prospective study. Animals Forty female dogs (beagles) aged 1-2 years, weighing 11.97 +/- 1.40 kg. MATERIALS AND METHODS: The dogs were divided into five groups of eight. Two control groups were used: group A received intramuscular (IM), SLA (50 microg kg(-1)) alone, while group B received the SLA vehicle followed by sevoflurane anaesthesia for 90 minutes. In the other groups, SLA (50 microg kg(-1) IM) was given immediately before (group C(0)), 15 minutes before (group D(15)) or 30 minutes (group E(30)) before induction [with intravenous (IV) thiopental] of sevoflurane anaesthesia lasting for 90 minutes. Heart rate, arterial blood pressure, respiratory rate (f(r)), arterial oxygen haemoglobin saturation and end-tidal sevoflurane concentration (Fe'SEVO) were measured every 10 minutes during anaesthesia and at 2, 4 and 24 hours after induction (not Fe'SEVO). Acid-base and blood gas analyses were performed. RESULTS: Sufentanil LA reduced heart rate and increased arterial CO(2) tensions during anaesthesia. Respiratory depression was least in group E(30) compared with groups C(0) and D(15). Bradycardia was present for at least 24 hours. Respiratory rate was least in group B although arterial O(2) and CO(2) tension values were acceptable up to 24 hours after anaesthesia. CONCLUSIONS: Pre-anaesthetic medication with SLA moderately aggravated the cardiopulmonary effects of sevoflurane. CLINICAL RELEVANCE: In spite of a moderate depressant effect on cardiorespiratory parameters, SLA may be of use as pre-anaesthetic medication before sevoflurane anaesthesia in dogs. Intermittent positive pressure ventilation may occasionally be necessary.     

Anaesthesia with midazolam/medetomidine/fentanyl in chinchillas (Chinchilla lanigera) compared to anaesthesia with xylazine/ketamine and medetomidine/ketamine

We studied four different drug regimes for anaesthetic management in chinchillas and evaluated and compared their cardiovascular and respiratory effects. In this randomized, cross-over experimental study, seven adult chinchillas, five females, two males [515 +/- 70 (SD) g] were randomly assigned to one of the following groups: group 1 [midazolam, medetomidine and fentanyl (MMF), flumazenil, atipamezole and naloxone (FAN); MMF-FAN] received 1.0 mg/kg midazolam, 0.05 mg/kg medetomidine and 0.02 mg/kg fentanyl i.m., and for reversal 0.1 mg/kg flumazenil, 0.5 mg/kg atipamezole and 0.05 mg/kg naloxone s.c. after 45 min; group 2 (MMF) 1.0 mg/kg midazolam, 0.05 mg/kg medetomidine and 0.02 mg/kg fentanyl i.m.; group 3 [xylazine/ketamine (X/K)] 2.0 mg/kg xylazine and 40.0 mg/kg ketamine i.m.; and group 4 [medetomidine/ketamine (M/K)] 0.06 mg/kg medetomidine and 5.0 mg/kg ketamine i.m. Reflexes were judged to determine anaesthetic stages and planes. Anaesthesia with X/K and M/K was associated with a prolonged surgical tolerance and recovery period. By reversing MMF, recovery period was significantly shortened (5 +/- 1.3 min versus 40 +/- 10.3 min in MMF without FAN, 73 +/- 15.0 min in X/K, and 31 +/- 8.5 min in M/K). Without reversal, MMF produced anaesthesia lasting 109 +/- 16.3 min. All combinations decreased respiratory and heart rate but compared with X/K and M/K, respiratory and cardiovascular complications were less in the MMF groups. Focussing on the clinical relevance of the tested combinations, completely reversible anaesthesia showed two major advantages: anaesthesia can be antagonized in case of emergency and routinely shortens recovery. In small animals particularly these advantages lead to less complications and discomfort and thus often can be lifesaving. As all analgesic components (medetomidine and fentanyl) are reversed, postoperative analgesia should be provided before reversal of anaesthesia.     

Maintenance of anaesthesia in sheep with isoflurane, desflurane or sevoflurane

Rapid recovery from anaesthesia is advantageous in small ruminants, to reduce the risk of regurgitation. Theoretically, the least soluble inhalation agents should result in the fastest recoveries, but using additional injectable agents may negate this advantage. This study compared three inhalation agents for the maintenance of anaesthesia in sheep. Eighteen ewes that were to undergo orthopaedic surgery were allocated to one of three groups. Each group was premedicated with xylazine (0.1 mg/kg intramuscularly), anaesthesia was induced using ketamine (2 mg/kg) and midazolam (0.03 mg/kg) intravenously and analgesia provided by buprenorphine (0.008 mg/kg intramuscularly). Anaesthesia was then maintained with either isoflurane, sevoflurane or desflurane. Cardiopulmonary parameters were monitored throughout. All three inhalation agents provided adequate stable anaesthesia and there was no significant difference between the groups in their cardiopulmonary parameters or their recovery times. The mead (sd) postanaesthetic times to first swallow, first chewing attempts and ability to maintain their head lifted for five minutes were, respectively, 3.95 (2.53), 6.37 (3.68) and 32.8 (18.1) minutes for isoflurane, 3.62 (0.98), 7.66 (0.78) and 38.8 (16.6) minutes for sevoflurane, and 4.37 (1.65), 6.95 (1.52) and 29.8 (11.5) minutes for desflurane. Two sheep had poor quality recoveries after the use of sevoflurane, but all the other sheep recovered uneventfully. All three inhalation agents were suitable for the maintenance of anaesthesia in sheep but, as used in this study, there were no differences between them in speed of recovery.     

Comparison of thiopentone/guaifenesin, ketamine/guaifenesin and ketamine/midazolam for the induction of horses to be anaesthetised with isoflurane

Forty-eight horses subjected to elective surgery were randomly assigned to three groups of 16 horses. After premedication with 0.1 mg/kg acepromazine intramuscularly and 0.6 mg/kg xylazine intravenously, anaesthesia was induced either with 2 g thiopentone in 500 ml of a 10 per cent guaifenesin solution, given intravenously at a dose of 1 ml/kg (group TG), or with 100 mg/kg guaifenesin and 2.2 mg/kg ketamine given intravenously (group KG), or with 0.06 mg/kg midazolam, and 2.2 mg/kg ketamine given intravenously (group KM). Anaesthesia was maintained with isoflurane. The mean (sd) end tidal isoflurane concentration (per cent) needed to maintain a light surgical anaesthesia (stage III, plane 2) was significantly lower in group KM (0.91 [0.03]) than in groups TG (1.11 [0.03]) and KG (1.14 [0.03]). The mean (sd) arterial pressure (mmHg) was significantly lower in group KG (67.4 [2.07]) than in groups TC (75.6 [2.23]) and KM (81.0 [2.16]). There were no significant differences in the logarithm of the heart rate, recovery time or quality of recovery between the three induction groups. However, pronounced ataxia was observed in the horses of group KM, especially after periods of anaesthesia lasting less than 75 minutes.     

Comparison of the arterial blood gas,arterial oxyhaemoglobin saturation and end-tidal carbon dioxide tension during sevoflurane or isoflurane anaesthesia in rabbits

The effects of sevoflurane or isoflurane on arterial blood gas, arterial oxyhaemoglobin saturation and end-tidal CO2 tension were monitored during induction and maintenance of anaesthesia in 10 premedicated New Zealand White (NZW) rabbits.For induction, the anaesthetic agents were delivered via a face-mask. After induction was completed, an endotracheal tube was introduced for maintenance of anaesthesia for a period of 90 minutes. Changes in heart rate, respiratory rate, arterial blood gas, arterial oxyhaemoglobin saturation, blood pH and end-tidal CO2 tension were recorded. Although sevoflurane and isoflurane produce similar cardiopulmonary effects in premedicated rabbits, sevoflurane provides a smoother and faster induction because of its lower blood/gas partition coefficient. Thus sevoflurane is probably a more suitable agent than isoflurane for mask induction and maintenance. Its lower blood solubility also makes sevoflurane more satisfactory than isoflurane for maintenance of anaesthesia because it allows the anaesthetist to change the depth of anaesthesia more rapidly.     

Anti-nociceptive and sedative effects of sufentanil long acting during and after sevoflurane anaesthesia in dogs

The purpose of the present study was to determine the most effective time interval between the administration of sufentanil long acting (LA) and the induction of sevoflurane anaesthesia in dogs. The occurrence of sedation, analgesia and other marked side-effects were evaluated in addition to the possible dosage-reducing effect of sufentanil on sevoflurane in dogs. Forty clinically normal beagles aged 1-2 years and weighing between 8.4 and 13.6 kg were included. Two control groups were used: one group of dogs (A) received sufentanil LA (50 microg/kg i.m.) and a second group (B) the sufentanil vehicle followed by standard inhalation anaesthesia of 90 min. After premedication with sufentanil LA immediately before (C0), 15 min (D15) or 30 min (E30) prior to induction with thiopental (i.v.) the dogs were anaesthetized for 90 min with sevoflurane in oxygen. Pain and sedation scores were evaluated every 10 min during sevoflurane anaesthesia and at 2 (T120), 4 (T240) and 24 h (T1440) after initiation of anaesthesia. The occurrence of adverse reactions such as hypothermia, lateral recumbency, ataxia, noise sensitivity, vomiting, defaecation, salivation, nystagmus and excitation was observed at the same time-points. During the recovery period pain scores were lower and sedation scores higher in the sufentanil LA groups. In many dogs acceptable pain and sedation scores persisted during 24 h. Several dogs showed ataxia, lateral recumbency, arousal on auditory stimulation, defaecation, salivation and excitation at several time-points after sufentanil LA administration. Sufentanil LA in addition to sevoflurane anaesthesia offered beneficial dosage-reducing analgesic effects up to 69.8% for thiopental and 78.3% for sevoflurane; although several typical opioid side-effects occurred. To achieve this advantageous dosage-reducing effect 15 min should be respected between sufentanil LA administration and induction of sevoflurane anaesthesia.     

The influence of ventilation mode (spontaneous ventilation, IPPV and PEEP) on cardiopulmonary parameters in sevoflurane anaesthetized dogs

The purpose of this study was to investigate the cardiopulmonary influences of sevoflurane in oxygen at two anaesthetic concentrations (1.5 and 2 MAC) during spontaneous and controlled ventilation in dogs. After premedication with fentany-droperidol (5 microg/kg and 0.25 mg/kg intramuscularly) and induction with propofol (6 mg/kg intravenously) six dogs were anaesthetized for 3 h. Three types of ventilation were compared: spontaneous ventilation (SpV), intermittent positive pressure ventilation (IPPV), and positive end expiratory pressure ventilation (PEEP, 5 cm H2O). Heart rate, haemoglobin oxygen saturation, arterial blood pressures, right atrial and pulmonary arterial pressures, pulmonary capillary wedge pressure and cardiac output were measured. End tidal CO2%, inspiratory oxygen fraction, respiration rate and tidal volume were recorded using a multi-gas analyser and a respirometer. Acid-base and blood gas analyses were performed. Cardiac index, stroke volume, stroke index, systemic and pulmonary vascular resistance, left and right ventricular stroke work index were calculated. Increasing the MAC value during sevoflurane anaesthesia with spontaneous ventilation induced a marked cardiopulmonary depression; on the other hand, heart rate increased significantly, but the increases were not clinically relevant. The influences of artificial respiration on cardiopulmonary parameters during 1.5 MAC sevoflurane anaesthesia were minimal. In contrast, PEEP ventilation during 2 MAC concentration had more pronounced negative influences, especially on right cardiac parameters. In conclusion, at 1.5 MAC, a surgical anaesthesia level, sevoflurane can be used safely in healthy dogs during spontaneous and controlled ventilation (IPPV and PEEP of 5 cm H2O).     

Comparison of sevoflurane and isoflurane in dogs anaesthetised for clinical surgical or diagnostic procedures

OBJECTIVES: To assess attributes of sevoflurane for routine clinical anaesthesia in dogs by comparison with the established volatile anaesthetic isoflurane. METHODS: One hundred and eight dogs requiring anaesthesia for elective surgery or diagnostic procedures were studied. The majority was premedicated with 0.03 mg/kg of acepromazine and 0.01 mg/kg of buprenorphine or 0.3 mg/kg of methadone before induction of anaesthesia with 2 to 4 mg/kg of propofol and 0.5 mg/kg of diazepam. They were randomly assigned to receive either sevoflurane (group S, n=50) or isoflurane (group I, n=58) in oxygen and nitrous oxide for maintenance of anaesthesia. Heart rate, respiratory rate, indirect arterial blood pressure, haemoglobin saturation, vaporiser settings, end-tidal carbon dioxide and anaesthetic concentration and oesophageal temperature were measured. Recovery was timed. Data were analysed using analysis of variance and non-parametric tests. RESULTS: Heart rate (85 to 140/minute), respiratory rate (six to 27/minute) and systolic arterial blood pressure (80 to 150 mmHg) were similar in the two groups. End-tidal carbon dioxide between 30 and 60 minutes (group S 6.4 to 6.6 and group I 5.8 to 5.9 per cent) and vaporiser settings throughout (group S 2.1 to 2.9 and group I 1.5 to 1.5 per cent) were higher in group S. There was no difference in time to head lift (18+/-16 minutes), sternal recumbency (28+/-22 minutes) or standing (48+/-32 minutes). No adverse events occurred. CLINICAL SIGNIFICANCE: Sevoflurane appeared to be a suitable volatile anaesthetic for maintenance of routine clinical anaesthesia in dogs.     

Effect of propofol at two injection rates or thiopentone on post-intubation apnoea in the dog

Ventilatory effects at induction of anaesthesia were studied following intubation in 66 dogs anaesthetised using thiopentone (10 mg/kg) or propofol (4 mg/kg, injected rapidly or 4 mg/kg, injected slowly). Acepromazine and morphine preanaesthetic medication was administered, and anaesthesia was maintained with halothane in nitrous oxide and oxygen. The time from connection of the breathing system to the first breath was measured. Apnoea was defined as cessation of spontaneous respiration for 15 seconds or longer. Respiratory rate and minute volume were measured for the first five minutes of anaesthesia. Propofol was associated with a greater incidence of apnoea than thiopentone (59 per cent and 64 per cent compared with 32 per cent), but this difference was not statistically significant. Time to first breath was significantly longer with propofol than thiopentone and longest with the slower injection of propofol (P<0.05) (median of four seconds for thiopentone, 19.5 seconds for the propofol rapid injection, and 28.8 seconds for the propofol slow injection). In conclusion, the induction agent and speed of injection affect the incidence and duration of post-intubation apnoea.     

Development of an opiate-based anaesthetic technique for use in dogs with cardiomyopathy.

An opiate-based anaesthetic technique has been developed for use in dogs with end-stage heart failure due to dilated cardiomyopathy. It has been used in dogs undergoing translocation of the left latissimus dorsi around the descending thoracic aorta to create an autologous counterpulsation system. Anaesthesia was induced with barbiturate (10 mg/kg thiopentone) and fentanyl (500 micrograms) and maintained by an infusion of fentanyl (0.5 micrograms/kg/minute) [corrected] in addition to halothane (0.1 to 0.5 per cent) and nitrous oxide (20 to 60 per cent). This technique provided safe anaesthesia for major intrathoracic surgery.     

The interaction of nitrous oxide and fentanyl on the minimum alveolar concentration of sevoflurane blocking motor movement (MACNM) in dogs

The study objective was to determine the effects of 70% nitrous oxide (N₂O) and fentanyl on the end-tidal concentration of sevoflurane necessary to prevent movement (MAC_NM) in response to noxious stimulation in dogs. Six healthy, adult, intact male, mixed-breed dogs were used on 3 occasions in a randomized crossover design. After induction of anesthesia with sevoflurane, each of the following treatments was randomly administered: fentanyl loading dose (Ld) of 15 μg/kg and infusion of 6 μg/kg per hour [treatment 1 (T1)], 70% N₂O (T2), or fentanyl (Ld of 15 μg/kg and infusion of 6 μg/kg per hour) combined with 70% N₂O (T3). Each dog received each of the 3 treatments once during the 3-week period. Determination of MAC_NM was initiated 90 min after the start of each treatment. The values were compared using the baseline MAC_NM, which had been determined in a previous study on the same group of dogs. Data were analyzed using a mixed-model analysis of variance (ANOVA) and Tukey-Kramer tests, and expressed as least squares mean ± SEM. The baseline MAC_NM decreased by 36.6 ± 4.0%, 15.0 ± 4.0%, and 46.0 ± 4.0% for T1, T2, and T3, respectively (P < 0.05), and differed (P < 0.05) among treatments. Mean fentanyl plasma concentrations did not differ (P ≥ 0.05) between T1 (3.70 ± 0.56 ng/mL) and T3 (3.50 ± 0.56 ng/mL). The combination of fentanyl and N₂O resulted in a greater sevoflurane MAC_NM sparing effect than either treatment alone.     

Total intravenous anaesthesia (TIVA) with propofol-fentanyl and propofol-midazolam combinations in spontaneously-breathing goats

ObjectiveTo compare the efficacy and cardiopulmonary effects of propofol and fentanyl, with propofol and midazolam for total intravenous anaesthesia.Study designProspective, randomized, crossover experimental study.AnimalsSix goats; three does and three wethers.MethodsGoats received either fentanyl 0.02 mg kg^?1 (treatment FP) or midazolam 0.3 mg kg^?1 (treatment MP) intravenously. One minute later anaesthesia was induced with propofol, then maintained by constant rate infusion of propofol 12.0 mg kg^?1 hour^?1 and fentanyl 0.02 mg kg^?1 hour^?1 (treatment FP) or propofol 12.0 mg kg^?1 hour^?1 and midazolam 0.3 mg kg^?1 hour^?1 (treatment MP) for 90 minutes. Response to noxious stimulus was tested every 10 minutes and propofol dose adjusted to prevent purposeful movement. Cardiopulmonary parameters were measured continuously, and arterial blood-gas analysis performed intermittently. Recovery was timed and quality scored. Results are presented as median (IQR).ResultsDifferences in the propofol induction dose [4.00 (3.96-4.01) and 3.97 (3.91-4.00) mg kg^?1 for treatments FP and MP, respectively] were not significant. Quality of induction in both groups was smooth. The median propofol dose for maintenance was less (p = 0.004) with treatment FP (12.0 mg kg^?1 hour^?1) than MP (18.0 mg kg^?1 hour^?1). Cardiopulmonary function was well maintained with both treatments. Recovery times in minutes from the end of anaesthetic infusion for treatments FP and MP respectively were; to extubation 3.0 (3.0-3.0) and 4.5 (3.3-5.0); to sternal position, 4.5 (3.3-5.0) and 5.0 (5.0-6.5) and to standing 13.0 (10.3-15.0) and 15.0 (11.3-17.3). Quality of recovery was acceptable in both groups, but abnormal behavioural signs were observed after treatment FP.Conclusions and clinical relevanceTotal intravenous anaesthesia with propofol and fentanyl or propofol and midazolam, at the doses studied, in spontaneously-breathing, oxygen-supplemented goats is practicable. Recovery from the fentanyl-propofol combination is not always smooth.     

The use of intraoperative fentanyl in spontaneously breathing dogs undergoing orthopaedic surgery

Nineteen dogs were assigned randomly to one of three groups. Animals in Group 1 were pre-medicated with acepromazine, 50 μg/kg bodyweight (bwt) intramuscularly (im) and received 10 ml of 0.9 per cent saline intravenously (iv) at the time of skin incision. Dogs in Group 2 were pre-medicated with acepromazine, 50 μg/kg bwt im, and received fentanyl 2 μg/kg bwt iv at skin incision. Dogs in Group 3 were pre-medicated with acepromazine, 50 μg/kg bwt and atropine, 30 to 40 μg/kg bwt, im and received fentanyl, 2 μg/kg bwt iv at skin incision. Pulse rate, mean arterial blood pressure, respiratory rate and end tidal carbon dioxide were measured before and after fentanyl or saline injection. Fentanyl caused a short-lived fall in arterial blood pressure that was significant in dogs premedicated with acepromazine, but not in dogs pre-medicated with acepromazine and atropine. A significant bradycardia was evident for 5 mins in both fentanyl treated groups. The effect on respiratory rate was most pronounced in Group 3, in which four of seven dogs required intermittent positive pressure ventilation (IPPV) for up to 14 mins. Two of six dogs in Group 2 required IPPV, whereas respiratory rate remained unaltered in the saline controls. The quality of anaesthesia was excellent in the fentanyl treated groups; however, caution is urged with the use of even low doses of fentanyl in spontaneously breathing dogs under halothane-nitrous oxide anaesthesia.