Low flow anaesthesia with isoflurane and sevoflurane in the dog

The aim of the present study was to compare the safety and efficacy of sevoflurane and isoflurane during low flow anaesthesia (fresh gas flow (FGF) 14 ml/kg/min) as well as to compare the consumption of both anaesthetics. Data were gathered from 60 dogs assigned for surgery under general anaesthesia with an expected duration of 75 minutes or longer. All dogs were induced with 0.6 mg/kg (maximum 25 mg) l-methadone and 1 mg/kg (maximum 25 mg) diazepam i.v.. Anaesthesia was maintained with isoflurane (group 1) or sevoflurane (group 2) in a mixture with 50% O2 and 50% N2O as carrier gases, under controlled ventilation. Monitoring included electrocardiogram, body temperature, the temperature of in- and exspired gases, arterial oxygen saturation, arterial blood pressure as well as a continuous monitoring of inhaled and exhaled gas concentrations (O2, N2O, CO2, isoflurane, sevoflurane). The consumption of isoflurane and sevoflurane as well as the dogs' recovery times were evaluated for both groups. In all groups the inspired oxygen concentrations ranged above the minimum value of 30 Vol% during low flow anaesthesia, with an arterial oxygen saturation above 97%. End tidal concentration of CO2, heart rate and arterial blood pressure were within the physiological ranges and showed no differences between the two groups. Recovery time was significantly shorter after sevoflurane compared to isoflurane anaesthesia, whilst the consumption of sevoflurane was higher than that of isoflurane. Sevoflurane appears to be as clinically safe as isoflurane in low flow anaesthesia. Even considering that sevoflurane is more expensive than isoflurane, the use of the low flow technique decreases the cost of anaesthesia due to the reduced volatile anaesthetic consumption.     

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.     

Clinical comparison of isoflurane and sevoflurane anaesthesia in the gerbil (Meriones unguiculatus)

The objective of this study was a comparison of the volatile anaesthetics isoflurane and sevoflurane in terms of their clinical effects in gerbils (Meriones unguiculatus) (n=12 each). Induction of anaesthesia was performed in a body chamber with an anaesthetic concentration of 4.0 Vol.% at an oxygen flow of 500 ml/min for isoflurane and 8.0 Vol.% at an oxygen flow of 1000 ml/min for sevoflurane, respectively. Anaesthesia was maintained via nose cone with an anaesthetic concentration of 2.8 to 3.2 Vol.% at an oxygen flow of 200 ml/min for isoflurane and 5.0 to 5.2 Vol.% at an oxygen flow of 400 ml/min for sevoflurane. Those anaesthetic concentrations ensured reflex status conform with surgical tolerance. In spite of its higher blood-gas coefficient induction time was slightly faster for isoflurane. Recovery time was significantly longer in the isoflurane group than it was in the sevoflurane group. Both inhalants caused respiratory depression. Respiratory rate was lower in sevoflurane animals compared to isoflurane. The animals were positioned on a heating pad immediately after induction, thus a decrease of the body temperature could be prevented. Both inhalants can be recommended for usage in gerbils. Sevoflurane showed no clinical benefit compared to isoflurane.     

Cardiopulmonary effects of three different anaesthesia protocols in cats.

To develop an alternative anaesthetic regimen for cats with cardiomyopathy, the cardiopulmonary effects of three different premedication-induction protocols, followed by one hour maintenance with isoflurane in oxygen: air were evaluated in six cats. Group I: acepromazine (10 microg/kg) + buprenorphine (10 microg/kg) IM, etomidate (1-2 mg/kg) IV induction. Group II: midazolam (1 mg/kg) + ketamine (10 mg/kg) IM induction. Group III: medetomidine (1.5 mg/m2 body surface) IM, propofol (1-2 mg/kg) IV induction. Heart rate, arterial blood pressure, arterial blood gases, respiration rate, and temperature were recorded for the duration of the experiment. In group I the sedative effect after premedication was limited. In the other groups the level of sedation was sufficient. In all groups premedication resulted in a reduced blood pressure which decreased further immediately following induction. The reduction in mean arterial pressure (MAP) reached statistical significance in group I (142+/-22 to 81+/-14 mmHg) and group II (153+/-28 to 98+/-20 mmHg) but not in group III (165+/-24 to 134+/-29 mmHg). Despite the decrease in blood pressure, MAP was judged to have remained within an acceptable range in all groups. During maintenance of anaesthesia, heart rate decreased significantly in group III (from 165+/-24 to 125+/-10 b.p.m. at t=80 min). During anaesthesia the PCO2 and PO2 values increased significantly in all groups. On the basis of the results, the combination acepromazine-buprenorphine is preferred because heart rate, MAP, and respiration are acceptable, it has a limited sedative effect but recovery is smooth.     

Effects of alpha-2 adrenoceptor agonists during recovery from isoflurane anaesthesia in horses

REASONS FOR PERFORMING STUDY: Recovery from inhalant anaesthesia in the horse is a critical and difficult period to manage; however, several factors could help to obtain a calm recovery period including choice of anaesthetic and analgesic procedure used and the conditions under which anaesthetic maintenance and recovery occur. OBJECTIVES: The objective of this study was to evaluate and compare the quality of recovery in horses administered saline, xylazine, detomidine or romifidine during recovery from isoflurane anaesthesia. METHODS: Six mature and healthy horses were premedicated with i.v. xylazine and butorphanol, and anaesthesia induced using ketamine. After 2 h of inhalant anaesthesia with isoflurane vaporised in oxygen, saline solution, xylazine (0.1 mg/kg bwt), detomidine (2 microg/kg bwt) or romifidine (8 pg/kg bwt) were administered. The quality of recovery of each horse and the degree of sedation and ataxia were evaluated. Cardiovascular and respiratory parameters were recorded, and arterial blood samples obtained and analysed for pH, PO2 and PCO2 during recovery. RESULTS: Quality of recovery was better in groups treated with alpha-2 adrenergic receptors agonists, showing less ataxia. Degree of sedation was greater in the romifidine group. CONCLUSIONS: We concluded that the administration of alpha-2 adrenoceptor agonists during recovery from isoflurane anaesthesia in horses prolonged and improved the quality of recovery without producing significant cardiorespiratory effects. POTENTIAL CLINICAL RELEVANCE: Administration of alpha-2 adrenoceptor agonists after inhalent anaesthesia could prevent complications during the recovery period.     

A clinical comparison of two anaesthetic protocols using lidocaine or medetomidine in horses

OBJECTIVE: To compare the effects of two balanced anaesthetic protocols on end-tidal isoflurane (Fe'ISO), cardiopulmonary performance and quality of recovery in horses. DESIGN: Prospective blinded randomized clinical study. ANIMALS: Sixty-nine client-owned horses, American Society of Anesthesiologists category I and II, undergoing elective surgery. METHODS: The horses were premedicated with acepromazine (0.03 mg kg(-1)) IM 30-60 minutes before induction of anaesthesia and were randomly assigned to one of two treatments: in group L (37 horses) xylazine (1 mg kg(-1)) and in group M (31 horses) medetomidine (7 microg kg(-1)) was administered IV for sedation. Anaesthesia was induced 5 minutes later with ketamine (2.2 mg kg(-1)) and diazepam (0.02 mg kg(-1)) IV and maintained with isoflurane in oxygen/air (initial FIO2 0.40-0.50) and a constant rate infusion (CRI) of either lidocaine (2 mg kg(-1)/15 minutes loading dose followed by 50 microg kg(-1) minute(-1)) (group L) or medetomidine (3.5 microg kg(-1) hour(-1)) (group M). If horses showed movement or nystagmus, additional thiopental or ketamine was administered. Heart rate, mean arterial pressure (MAP), Fe'ISO and arterial blood gases were measured. Cardiac output was measured with the lithium dilution method in 10 (group L) and 11 (group M) horses every 45 minutes. Recovery was scored. RESULTS: Heart rate and the cardiac index (CI) were significantly higher in group L with changes over time. In group M, MAP was significantly higher during the first 50 minutes. Group L needed more additional ketamine and thiopental to maintain a surgical plane of anaesthesia and Fe'ISO was significantly higher from 70 minutes. Recovery was longer in group M and of better quality. The significance level was set at p < 0.05. CONCLUSIONS AND CLINICAL RELEVANCE: In group M, maintenance of stable anaesthetic depth was easier and lower Fe'ISO was required to maintain a surgical plane of anaesthesia. Recoveries were longer but of better quality. The CI was higher in group L but cardiovascular function was generally well maintained in both groups.     

The effects of spontaneous and mechanical ventilation on central cardiovascular function and peripheral perfusion during isoflurane anaesthesia in horses

OBJECTIVE: To compare the effects of spontaneous breathing and mechanical ventilation on haemodynamic variables, including muscle and skin perfusion measured with laser Doppler flowmetery, in horses anaesthetized with isoflurane. STUDY DESIGN: Prospective controlled study. ANIMALS: Ten warm-blood trotter horses (five males, five females). Mean mass was 492 kg (range 420-584 kg) and mean age was 5 years (range 4-8 years). MATERIALS AND METHODS: After pre-anaesthetic medication with detomidine (10 microg kg(-1)) anaesthesia was induced with intravenous (IV) guaifenesin and thiopental (4-5 mg kg(-1) IV) and maintained using isoflurane in oxygen. The horses were positioned in dorsal recumbency. In five animals breathing was initially spontaneous (SB) while the lungs of the other five were ventilated mechanically using intermittent positive pressure ventilation (IPPV). Total anaesthesia time was 4 hours with the ventilatory mode changed after 2 hours. During anaesthesia, heart rate (HR) cardiac output (Qt) stroke volume (SV) systemic arterial blood pressures (sAP), and pulmonary arterial pressure (pAP) were recorded. Peripheral perfusion was measured in the semimembranosus and gluteal muscles and on the tail skin using laser Doppler flowmetry. Arterial (a) and mixed venous (v) blood gases, pH, haemoglobin concentration [Hb], haematocrit (Hct), plasma lactate concentration and muscle temperature were measured. Oxygen content, venous admixture (s/Qt) oxygen delivery (DO(2)) and oxygen consumption (VO(2)) were calculated. RESULTS: During mechanical ventilation, HR, sAP, pAP, Qt, SV, Qs/Qt and PaCO(2) were lower and PaO(2) was higher compared with spontaneous breathing. There were no differences between the modes of ventilation in the level of perfusion, DO(2), VO(2), [Hb], (Hct), or plasma lactate concentration. After the change from IPPV to SB, left semimembranosus muscle and skin perfusion improved, while muscle perfusion tended to decrease when SB was changed to IPPV. Low-frequency flow motion was seen twice as frequently during IPPV compared with SB. CONCLUSIONS: Mechanical ventilation impaired cardiovascular function compared with SB in horses during isoflurane anaesthesia. Muscle and skin perfusion changes occurred with ventilation, although further studies are needed to elucidate the underlying mechanisms.     

Comparison of two combinations of sedatives before anaesthetising pigs with halothane and nitrous oxide

Two groups of 21 three-month-old Landrace x Large White pigs were sedated with either azaperone (2 mg/kg), butorphanol (0.2 mg/kg) and ketamine (5 mg/kg) (group A), or detomidine (100 microg/kg), butorphanol (0.2 mg/kg) and ketamine (5 mg/kg) (group D) administered intramuscularly, before being anaesthetised with halothane, oxygen and nitrous oxide for a bilateral stifle arthrotomy. The pigs' heart rate, respiratory rate, mean arterial blood pressure, electrocardiogram, arterial oxygen saturation, arterial blood gases, and oesophageal and rectal temperature were measured while they were anaesthetised and five minutes after they were disconnected, and their recovery times and any complications were recorded. Both groups were well sedated. Their heart rate was unchanged during the period of anaesthesia but increased when they recovered. The respiratory rate, mean arterial blood pressure and rectal temperature were lower in group A than in group D (P<0.05). Mild respiratory acidosis developed during anaesthesia in both groups. Both groups recovered equally rapidly and complications were generally minor, though two pigs in group D appeared to develop malignant hyperthermia.     

Recovery times and evaluation of clinical hemodynamic parameters of sevoflurane, isoflurane and halothane anaesthesia in mongrel dogs

In the present study the influence of three volatile agents (halothane, isoflurane and sevoflurane) in oxygen at two concentrations [1.5 and 2 minimum alveolar concentration (MAC)] on non-invasive cardio-respiratory parameters (heart and respirators rates, non-invasive blood pressures at 15, 30, 60 min and after extubation) and on the recovery times (appearance of the first eyelid reflex, emergence time) after clinical anaesthesia was studied. After premedication with fentanyl-droperidol (5 microg/kg and 0.25 mg/kg, intramuscularly) and induction with propofol (5 mg/kg, intravenously) six dogs were randomly anaesthetized for 1 h for a standard neurologic stimulation test. A wide individual variation in respiration rate (induced by an initial hyperpnea) was observed in the 1.5 MAC protocols, without significant differences. Heart rate was significantly lower during 1.5 and 2 MAC halothane when compared to isoflurane and sevoflurane. An increase from 1.5 to 2 MAC induced significant decreases in diastolic (DAP) and mean arterial blood pressure in all groups without significant changes in the systolic arterial pressures. Only DAP in sevoflurane protocol was significantly different at 1.5 and 2 MAC compared to halothane. Time had no significant influences in the non-invasive blood pressures in all protocols. Extubation induced a significant increase of all parameters in all protocols. The time for a first eyelid reflex was significantly longer after 2 MAC compared to the 1.5 MAC protocol. There was no significant difference between the three anaesthetic agents. Although emergence time was longest for halothane at both anaesthetic concentrations, no significant difference in emergence time was observed for the three volatile agents.     

Effects of sevoflurane, isoflurane and halotane anaesthesia on fluorescein angiographic phases of dogs: a comparative study

A fluorescein angiography method was developed to compare the onset and the total duration of the fluorangiographic phases between three anaesthetic protocols in six healthy mixed-breed dogs. The animals were anaesthetized three times. Each dog received, as pre-anaesthetic protocol, atropine (10 micrograms/kg intramuscularly), and as a sedative, romifidine (80 micrograms/kg intravenously). Fifteen minutes later, induction of anaesthesia was delivered with propofol (1 mg/kg intravenously) and maintained either with sevoflurane (SEVO group), isoflurane (ISO group) or halothane (HAL group) for 30 min in all cases. Some angiographic, cardiovascular and respiratory variables were registered during the procedure. Recovery times were also registered. Angiographic variables recorded were: onset of the arterial phase (TA), onset of the arteriovenous phase (TAV), onset of the venous phase (TV), complete arterial phase duration (I1), complete arteriovenous phase duration (I2) and I1 plus I2 (I3). Mean heart rate, mean arterial pressure, systolic arterial pressure, diastolic arterial pressure, respiratory rate, tidal volume, arterial oxygen saturation and end-tidal CO2 during SEVO and ISO anaesthesia, were similar in dogs. Minute ventilation and rectal temperature were higher in dogs with SEVO than ISO. HAL produced higher arterial pressures and a lower arterial oxygen saturation than ISO and SEVO. Mean respiratory rate, rectal temperature and minute ventilation were higher in HAL. Pulse rate, end-tidal CO2 and tidal volume were similar in the dogs of the three groups. No differences in recovery times were found. The fluorescein angiographic times were within the normal range. There were no significant differences between protocols in I1, I2 or I3. HAL produced a significant increase of all temporal variables (TA, TAV and TV) when compared with ISO; TA was higher in HAL than SEVO-treated dogs. All protocols appear to be safe and effective for inducing and maintaining general anaesthesia in healthy dogs for performing fluorescein angiography.     

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.     

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).     

Peri-operative body temperatures in isoflurane-anaesthetized rabbits following ketamine-midazolam or ketamine-medetomidine

OBJECTIVE: To investigate alterations in peri-operative body temperatures and oesophageal-skin temperatures in isoflurane-anaesthetized rabbits following either ketamine-midazolam or ketamine-medetomidine induction of anaesthesia. ANIMAL POPULATION: Fifty client-owned rabbits, (25 male, 25 female) of different breeds anaesthetized for elective neutering (age range: 3-42 months; mass range: 1.15-4.3 kg). STUDY DESIGN: Randomized, blinded clinical study. METHODS: Pre-anaesthetic rectal temperature was measured. A 24 SWG catheter was placed in a marginal ear vein after local anaesthesia. Ketamine (15 mg kg(-1)) with medetomidine (0.25 mg kg(-1)) (group KMT) or with midazolam (3 mg kg(-1)) (group KMZ) was injected intramuscularly (IM). Following endotracheal intubation anaesthesia was maintained with isoflurane in oxygen. Carprofen (3 mg kg(-1)) and glucose saline (5 mL kg(-1) hour(-1)) were administered through the intravenous catheter. Room temperature and humidity, skin temperature (from tip of pinna) and oesophageal temperature were measured during anaesthesia. Ovariohysterectomy or castration was performed. Rectal temperature was taken when isoflurane was discontinued (time zero) and 30, 60 and 120 minutes thereafter. Atipamezole (0.5 mg kg(-1)) was administered IM to rabbits in group KMT at zero plus 30 minutes. Mass, averaged room temperature and duration of anaesthesia data were compared using a two-tailed t-test. Age, averaged room humidity, rectal temperature decrease, oesophageal temperature decrease and oesophageal-skin difference data were compared using a Kruskal-Wallis test. p < 0.05 was considered significant. RESULTS: The averaged oesophageal-skin temperature difference was significantly greater in group KMT [median 9.85 degrees C (range 6.42-13.85 degrees C)] than in group KMZ [4.38 degrees C (2.83-10.43 degrees C)]. Rectal temperature decreased over the anaesthetic period was not significantly different between the two groups; however, oesophageal temperature decrease was significantly less in group KMT [1.1 degrees C (-0.1-+2.7 degrees C)] than in group KMZ [1.4 degrees C (0.6-3.1 degrees C)]. CONCLUSIONS: Oesophageal-skin temperature difference is larger in rabbits anaesthetized with ketamine-medetomidine combination than ketamine-midazolam. CLINICAL RELEVANCE: The oesophageal temperature in rabbits anaesthetized with ketamine-medetomidine and isoflurane decreases significantly less than in animals anaesthetized with ketamine-midazolam and isoflurane, during anaesthesia.     

Comparison of racemic ketamine and S-ketamine as agents for the induction of anaesthesia in goats

ObjectiveTo compare racemic ketamine and S-ketamine as induction agents prior to isoflurane anaesthesia.Study designProspective, blinded, randomized experimental study.AnimalsThirty-one healthy adult goats weighing 39-86 kg.MethodsGoats were premedicated with xylazine (0.1 mg kg^?1) intravenously (IV) given over 5 minutes. Each goat was assigned randomly to one of two treatments for IV anaesthetic induction: group RK (15 goats) racemic ketamine (3 mg kg^?1) and group SK (16 goats) S-ketamine (1.5 mg kg^?1). Time from end-injection to recumbency was measured and quality of anaesthetic induction and condition for endotracheal intubation were scored. Anaesthesia was maintained with isoflurane in oxygen for 90 minutes. Heart rate, invasive arterial blood pressure, oxygen saturation, temperature, end-tidal carbon dioxide and isoflurane were recorded every 5 minutes. Arterial blood samples were taken for analysis every 30 minutes. Recovery time to recurrence of swallowing reflex, to first head movement and to standing were recorded and recovery quality was scored. Two-way repeated measures anova, Mann-Whitney and a Mantel-Cox tests were used for statistical analysis as relevant with a significance level set at p < 0.05.ResultsInduction of anaesthesia was smooth and uneventful in all goats. There was no statistical difference between groups in any measured parameter. Side effects following anaesthetic induction included slight head or limb twitching, moving forward and backward, salivation and nystagmus but were minimal. Endotracheal intubation was achieved in all goats at first or second attempt. Recovery was uneventful on all occasions. All goats were quiet and needed only one or two attempts to stand.Conclusions and clinical relevanceS-ketamine at half the dose rate of racemic ketamine in goats sedated with xylazine and thereafter anaesthetised with isoflurane induces the same clinically measurable effects.     

Stress responses in ponies during halothane or isoflurane anaesthesia after induction with thiopentone or xylazine/ketamine

Endocrine and metabolic responses to anaesthesia with three different anaesthetic regimes were examined in six ponies. All animals were anaesthetised with each protocol: acepromazine-thiopentone-isoflurane, xylazine-ketamine- halothane and xylazine-ketamine-isoflurane. Anaesthesia was maintained for 2 h. Pulse rate, respiratory rate, arterial blood pressure, arterial blood gases and pharyngeal and skin temperature were measured and blood was withdrawn for glucose, lactate, cortisol, insulin, liver and muscle enzymes and total protein assay. Measurements were made before anaesthesia, at 20 min intervals during anaesthesia and at 20 mins and 2, 4, 6 and 24 h after anaesthesia. The effects of anaesthesia were similar in all groups. Arterial blood pressure decreased and oxygen tension and plasma cortisol concentration increased in all groups. Arterial carbon dioxide tension increased and respiratory rate and pH decreased in all ponies anaesthetised with isoflurane. There was a tendency for increased glucose and lactate concentrations and decreased insulin concentration and packed cell volume, particularly in the xylazine-ketamine groups. There was no change in pulse rate except for a transient increase at induction with thiopentone. The results were compared with data reported by Taylor (1989), which were collected from the same animals during acepromazine-thiopentone-halothane anaesthesia, and were found to be similar. It was concluded that these commonly used anaesthetic protocols themselves constitute a considerable insult or stressor in horses. However, the stress response to all the regimes investigated was similar and the precise stimulus to this response has yet to be elucidated.     

A comparison of the haemodynamic effects of isoflurane and halothane anaesthesia in horses

The purpose of this study was to compare the haemodynamic effects of equipotent isoflurane and halothane anaesthesia. Six adult horses were investigated on two separate occasions at least 4 weeks apart. On both occasions anaesthesia was induced by ketamine 2.2 mg/kg bwt given 5 min after i.v. administration 100 microg/kg bwt romifidine. Anaesthesia was maintained either by halothane or isoflurane (end-tidal concentrations 0.9-1.0% and 1.3-1.4%, respectively). Horses were ventilated by intermittent positive pressure to maintain PaCO2 between 40-50 mmHg. Haemodynamic variables were measured using catheter-mounted strain gauge transducers in the left and right ventricle, aorta, and right atrium. Cardiac output (CO), velocity time integral (VTI), maximal aortic blood flow velocity (Vmax) and acceleration (dv/dt(max)), left ventricular pre-ejection period (PEP) and ejection time (ET) were measured from aortic blood flow velocity waveforms obtained by transoesophageal Doppler echocardiography. Flow velocity waveforms were recorded from the femoral arteries and veins using low pulse repetition frequency Doppler ultrasound. Time-averaged mean velocity (TAV), velocity of component a (TaVa), velocity of component b (TaVb) and early diastolic deceleration slope (EDDS) were measured. Pulsatility index (PI) and volumetric flow were calculated. Microvascular blood flow was measured in the left and right semimembranosus muscles by laser Doppler flowmetry. Maximal rate of rise of LV pressure (LVdp/dt(max)), CO, Vmax, dv/dt(max), ET, VTI were significantly higher at all time points during isoflurane anaesthesia compared to halothane anaesthesia. Pre-ejection period and diastolic aortic blood pressure were significantly less throughout isoflurane anaesthesia compared to halothane. Isoflurane anaesthesia was associated with significantly lower systemic vascular resistance than halothane anaesthesia. Femoral arterial and venous blood flow were significantly higher and EDDS and PI were significantly lower during isoflurane anaesthesia compared to halothane anaesthesia. In addition during both halothane and isoflurane anaesthesia, femoral arterial flow was higher and EDDS and PI lower in the left (dependent) artery compared to the right (nondependent) artery. This study supports previous work demonstrating improved left ventricular systolic function during isoflurane compared to halothane anaesthesia. This improvement was still evident after premedication with a potent-long acting alpha2-adrenoreceptor agonist, romifidine, and induction of anaesthesia with ketamine. There was also evidence of increased hindlimb blood flow during isoflurane anaesthesia. However, there were differences observed in flow between the left and right hindlimb during maintenance of anaesthesia with each agent, suggesting that there were differences in regional perfusion in anaesthetised horses caused by factors unrelated to agents administered.     

Effects of constant rate infusion of lidocaine and ketamine, with or without morphine, on isoflurane MAC in horses

REASONS FOR PERFORMING STUDY: Lidocaine and ketamine are administered to horses as a constant rate infusion (CRI) during inhalation anaesthesia to reduce anaesthetic requirements. Morphine decreases the minimum alveolar concentration (MAC) in some domestic animals; when administered as a CRI in horses, morphine does not promote haemodynamic and ventilatory changes and exerts a positive effect on recovery. Isoflurane-sparing effect of lidocaine, ketamine and morphine coadministration has been evaluated in small animals but not in horses. OBJECTIVES: To determine the reduction in isoflurane MAC produced by a CRI of lidocaine and ketamine, with or without morphine. HYPOTHESIS: Addition of morphine to a lidocaine-ketamine infusion reduces isoflurane requirement and morphine does not impair the anaesthetic recovery of horses. METHODS: Six healthy adult horses were anaesthetised 3 times with xylazine (1.1 mg/kg bwt i.v.), ketamine (3 mg/kg bwt i.v.) and isoflurane and received a CRI of lidocaine-ketamine (LK), morphine-lidocaine-ketamine (MLK) or saline (CTL). The loading doses of morphine and lidocaine were 0.15 mg/kg bwt i.v and 2 mg/kg bwt i.v. followed by a CRI at 0.1 mg/kg bwt/h and 3 mg/kg bwt/h, respectively. Ketamine was given as a CRI at 3 mg/kg bwt/h. Changes in MAC characterised the anaesthetic-sparing effect of the drug infusions under study and quality of recovery was assessed using a scoring system. Results: Mean isoflurane MAC (mean ± s.d.) in the CTL, LK and MLK groups was 1.25 ± 0.14%, 0.64 ± 0.20% and 0.59 ± 0.14%, respectively, with MAC reduction in the LK and MLK groups being 49 and 53% (P<0.001), respectively. No significant differences were observed between groups in recovery from anaesthesia. Conclusions and clinical relevance: Administration of lidocaine and ketamine via CRI decreases isoflurane requirements. Coadministration of morphine does not provide further reduction in anaesthetic requirements and does not impair recovery.     

Reversible anaesthesia of free-ranging lions (Panthera leo) in Zimbabwe

The combination of medetomidine-zolazepam-tiletamine with subsequent antagonism by atipamezole was evaluated for reversible anaesthesia of free-ranging lions (Panthera leo). Twenty-one anaesthetic events of 17 free-ranging lions (5 males and 12 females, body weight 105-211 kg) were studied in Zimbabwe. Medetomidine at 0.027-0.055 mg/kg (total dose 4-11 mg) and zolazepam-tiletamine at 0.38-1.32 mg/kg (total dose 50-275 mg) were administered i.m. by dart injection. The doses were gradually decreased to improve recovery. Respiratory and heart rates, rectal temperature and relative haemoglobin oxygen saturation (SpO2) were recorded every 15 min. Arterial blood samples were collected from 5 lions for analysis of blood gases and acid-base status. For anaesthetic reversal, atipamezole was administered i.m. at 2.5 or 5 times the medetomidine dose. Induction was smooth and all lions were anaesthetised with good muscle relaxation within 3.4-9.5 min after darting. The predictable working time was a minimum of 1 h and no additional drug doses were needed. Respiratory and heart rates and SpO2 were stable throughout anaesthesia, whereas rectal temperature changed significantly over time. Atipamezole at 2.5 times the medetomidine dose was sufficient for reversal and recoveries were smooth and calm in all lions independent of the atipamezole dose. First sign of recovery was observed 3-27 min after reversal. The animals were up walking 8-26 min after reversal when zolazepam-tiletamine doses < 1 mg/kg were used. In practice, a total dose of 6 mg medetomidine and 80 mg zolazepam-tiletamine and reversal with 15 mg atipamezole can be used for either sex of an adult or subadult lion. The drugs and doses used in this study provided a reliable, safe and reversible anaesthesia protocol for free-ranging lions.     

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.     

Hepatic effects of halothane, isoflurane or sevoflurane anaesthesia in dogs

The effects of halothane, isoflurane and sevoflurane anaesthesia on hepatic function and hepatocellular damage were investigated in dogs, comparing the activity of hepatic enzymes and bilirubin concentration in serum. An experimental study was designed. Twenty-one clinically normal mongrel dogs were divided into three groups and accordingly anaesthetized with halothane (n = 7), isoflurane (n = 7) and sevoflurane (n = 7). The dogs were 1-4 years old, and weighed between 13.5 and 27 kg (18.4 +/- 3.9). Xylazine HCI (1-2 mg/kg) i.m. was used as pre-anaesthetic medication. Anaesthesia was induced with propofol 2 mg/kg i.v. The trachea was intubated and anaesthesia maintained with halothane, isoflurane or sevoflurane in oxygen at concentrations of 1.35, 2 and 3%, respectively. Intermittent positive pressure ventilation (tidal volume, 15 ml/kg; respiration rate, 12-14/min) was started immediately after intubation and the anaesthesia lasted for 60 min. Venous blood samples were collected before pre-medication, 24 and 48 h, and 7 and 14 days after anaesthesia. Serum level of aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP) and gamma-glutamyltransferase (GGT), lactate dehydrogenase (LDH GGT) activities and bilirubin concentration were measured. Serum AST, ALT and GGT activities increased after anaesthesia in all groups. In the halothane group, serum AST and ALT activities significantly increased all the time after anaesthesia compared with baseline activities. But in the isoflurane group AST and ALT activities increased only between 2 and 7 days, and in the sevoflurane group 7 days after anaesthesia. GGT activity was increased in the halothane group between 2 and 7 days, and in the isoflurane and sevoflurane groups 7 days after anaesthesia. All dogs recovered from anaesthesia without complications and none developed clinical signs of hepatic damage within 14 days. The results suggest that the use of halothane anaesthesia induces an elevation of serum activities of liver enzymes more frequently than isoflurane or sevoflurane from 2 to 14 days after anaesthesia in dogs. The effects of isoflurane or sevoflurane anaesthesia on the liver in dogs is safer than halothane anaesthesia in dogs.