Complications of saffan anaesthesia in cats

Complications associated with Saffan anaesthesia were recorded following 100 administrations of the anaesthetic to cats. Hyperaemia or oedema of the pinnae or forepaws was recorded in 69 per cent of administrations. Other common complications included coughing and partial laryngean spasm at intubation, cyanosis, postoperative vomiting and opisthotonus. Suggestions are made for minimising the incidence of such complications.     

Propofol infusion anaesthesia in dogs pre-medicated with medetomidine

Ten laboratory beagles pre-medicated with medetomidine (40 μg/kg bodyweight [bwt]) were anaesthetised using a rapid injection of propofol, followed by propofol infusion. A loading dose of 4 mg/kg bwt of propofol was administered intravenously (iv) as a bolus and, immediately after, a 60 min iv propofol infusion (150 μg/kg bwt/min) was initiated. After a transient increase, mean arterial blood pressure decreased significantly below the pre-propofol level. However, the lowest values recorded (115 ± 11 mmHg) remained within the physiological limits. Heart rate increased significantly (from 41 ± 7.3 to 58 ± 11 beats/min) after initiation of the propofol infusion. No significant changes were seen in respiratory frequency; pO₂ decreased transiently; minimum values (10 ± 2.3 kPa) recorded 5 mins after initiation of the propofol infusion differed significantly from the starting level. pCO₂ increased significantly and the highest values recorded were 6.1 ± 0.35 kPa. Accordingly, pH decreased reaching the lowest level (pH 7.29) 15 mins after initiation of the propofol infusion. The analgesic effect of the present combination was not studied, but the absence of the palpebral and pedal reflexes suggested a surgical stage of anaesthesia. Therefore, propofol infusion in beagles pre-medicated with medetomidine proved to be a promising anaesthetic regimen but, if used clinically, oxygen-enriched inspired air should be used.     

Propofol anaesthesia for surgery in late gestation pony mares

Objective To characterize propofol anaesthesia in pregnant ponies. Animals Fourteen pony mares, at 256 ± 49 days gestation, undergoing abdominal surgery to implant fetal and maternal vascular catheters. Materials and methods Pre‐anaesthetic medication with intravenous (IV) acepromazine (20 µg kg^?1), butorphanol (20 µg kg^?1) and detomidine (10 µg kg^?1) was given 30 minutes before induction of anaesthesia with detomidine (10 µg kg^?1) and ketamine (2 mg kg^?1) IV Maternal arterial blood pressure was recorded (facial artery) throughout anaesthesia. Arterial blood gas values and plasma concentrations of glucose, lactate, cortisol and propofol were measured at 20‐minute intervals. Anaesthesia was maintained with propofol infused initially at 200 µg kg^?1 minute^?1, and at 130–180 µg kg^?1 minute^?1 after 60 minutes, ventilation was controlled with oxygen and nitrous oxide to maintain PaCO₂ between 5.0 and 6.0 kPa (37.6 and 45.1 mm Hg) and PaO₂ between 13.3 and 20.0 kPa (100 and 150.4 mm Hg). During anaesthesia flunixin (1 mg kg^?1), procaine penicillin (6 IU) and butorphanol 80 µg kg^?1 were given. Lactated Ringer's solution was infused at 10 mL kg^?1 hour^?1. Simultaneous fetal and maternal blood samples were withdrawn at 85–95 minutes. Recovery from anaesthesia was assisted. Results Arterial blood gas values remained within intended limits. Plasma propofol levels stabilized after 20 minutes (range 3.5–9.1 µg kg^?1); disposition estimates were clearance 6.13 ± 1.51 L minute^?1 (mean ± SD) and volume of distribution 117.1 ± 38.9 L (mean ± SD). Plasma cortisol increased from 193 ± 43 nmol L^?1 before anaesthesia to 421 ± 96 nmol L^?1 60 minutes after anaesthesia. Surgical conditions were excellent. Fetal umbilical venous pH, PO₂ and PCO₂ were 7.35 ± 0.04, 6.5 ± 0.5 kPa (49 ± 4 mm Hg) and 6.9 ± 0.5 kPa (52 ± 4 mm Hg); fetal arterial pH, PO₂ and PCO₂ were 7.29 ± 0.06, 3.3 ± 0.8 kPa (25 ± 6 mm Hg) and 8.7 ± 0.9 kPa (65 ± 7 mm Hg), respectively. Recovery to standing occurred at 46 ± 17 minutes, and was generally smooth. Ponies regained normal behaviour patterns immediately. Conclusions and clinical relevance Propofol anaesthesia was smooth with satisfactory cardiovascular function in both mare and fetus; we believe this to be a suitable anaesthetic technique for pregnant ponies.     

Myocardial damage in cats that died after anaesthesia

Summary

The necropsy findings of 85 cats that died up to six weeks after administration of injectable anaesthetics are described The most obvious findings in these cats were degeneration and necrosis of heart muscle fibres followed and related to time after the administration of the anaesthetics, by infiltration of predominantly mononuclear cells and by an increase in collagenous connective tissue. The lesions were most obvious on the inner side of the myocardium, indicating that hypoxic injury occurred during anaesthesia. The possible mechanism of the damage to the heart and its role in the pathogenesis of cardiomyopathy in the cat is discussed.     

Myocardial damage in cats that died after anaesthesia.

The necropsy findings of 85 cats that died up to six weeks after administration of injectable anaesthetics are described. The most obvious findings in these cats were degeneration and necrosis of heart muscle fibres followed and related to time after the administration of the anaesthetics, by infiltration of predominantly mononuclear cells and by an increase in collagenous connective tissue. The lesions were most obvious on the inner side of the myocardium, indicating that hypoxic injury occurred during anaesthesia. The possible mechanism of the damage to the heart and its role in the pathogenesis of cardiomyopathy in the cat is discussed.     

Induction of anaesthesia in dogs and cats with propofol

Propofol was used to induce anaesthesia in 89 dogs and 13 cats of either sex, various breeds and of widely different ages and weights; they varied considerably in physical condition and were anaesthetised for a variety of investigations and surgical procedures. They were premedicated with acepromazine, papaveretum, diazepam, pethidine, atropine and scopolamine in different combinations. After induction with propofol, anaesthesia was maintained with halothane, isoflurane, methoxyflurane and enflurane and, or, nitrous oxide. The mean (+/- sd) induction doses of propofol in unpremedicated and premedicated animals were 5.2 +/- 2.3 mg/kg and 3.6 +/- 1.4 mg/kg respectively for dogs, and 5.0 +/- 2.8 mg/kg and 5.3 +/- 4.3 mg/kg for cats. There were no differences between the sexes. Premedication did not affect recovery times. The incidence of side effects was very low. One dog showed evidence of pain when propofol was injected. No incompatibility was observed between propofol and the premedicants and other anaesthetic agents used.     

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.     

Clinical use of dexmedetomidine as premedicant in cats undergoing propofol-sevoflurane anaesthesia

The purpose of this report was to evaluate the cardiorespiratory effects and efficacy of dexmedetomidine as a premedicant agent in cats undergoing ovariohysterectomy anaesthetized with propofol-sevoflurane. Cats were randomly divided into two groups of eight animals each. Dexmedetomidine (0.01 mg/kg) or 0.9% saline was administered intravenously (D and S, respectively). After 5 min, propofol was administered intravenously and anaesthesia was maintained with sevoflurane. Heart and respiratory rates, arterial blood pressure, oxygen saturation, rectal temperature and the amount of propofol needed for induction were measured. Premedication with dexmedetomidine reduced the requirement of propofol (6.7+/-3.8 mg/kg), but induced bradycardia, compared with the administration of saline (15.1+/-5.1 mg/kg). Recovery quality was significantly better in D but no significant difference in time to return of swallowing reflex was observed between groups (D=2.5+/-0.5 min; S=3.2+/-1.8 min). In conclusion, dexmedetomidine is a safe and effective agent for premedication in cats undergoing propofol-sevoflurane anaesthesia with minimal adverse effects.     

Mask induction of anaesthesia with isoflurane or sevoflurane in premedicated cats

A comparison was made of the time to and quality of induction of anaesthesia when sevoflurane (n=14) or isoflurane (n=14) was delivered by mask in premedicated healthy adult cats presented for elective surgery. Times to induction and intubation were significantly shorter with sevoflurane (210 +/- 57 seconds and 236 +/- 60 seconds, respectively) than with isoflurane (264 +/- 75 seconds and 292 +/- 73 seconds). The quality of induction was similar for both agents. Two cats in each group developed opisthotonus of less than 45 seconds' duration. Both sevoflurane and isoflurane produced mask induction of anaesthesia of a similar quality in this species. Sevoflurane provided more rapid induction of anaesthesia and establishment of a controlled airway than isoflurane.     

Activation procedures in the electroencephalograms of healthy and epileptic cats under propofol anaesthesia

The current study evaluated the diagnostic value of electroencephalographic recordings (EEG) in cats with epilepsy under special consideration of photic stimulation and hyperventilation. EEGs in six healthy cats were recorded under light (mean dose of 0.23 mg/kg/min) and deep (mean dose of 0.7 mg/kg/min) propofol anaesthesia, whereas EEGs in 13 diseased cats were recorded under a propofol anaesthesia which was kept as light as possible (mean dose of 0.39 mg/kg/min). Paroxysmal discharges were detected in six of 13 cats suffering from seizures (two cats with idiopathic epilepsy and four cats with symptomatic epilepsy). Activation techniques did not enhance the diagnostic value of the EEGs. Photic driving was detected in one of six healthy cats under light, in five of six healthy cats under deep propofol anaesthesia and in 11 of 13 cats with seizures. Systematic use of activation techniques does not seem to increase the diagnostic yield of the recorded EEGs and should not be used in a clinical setting until future studies indicate value. Further investigations into the origin of photic driving under propofol anaesthesia are needed and could lead to the development of a reliable animal model to research into drug effects on the EEG.     

Cardiovascular changes associated with anaesthesia induced by medetomidine combined with ketamine in cats

SUMMARY Fifteen cats had anaesthesia induced by intramuscular injection of medetomidine combined with ketamine. By five minutes after drug administration, heart rate had decreased by 31 per cent, respiratory rate had decreased by 70 per cent and systolic blood pressure had increased by 69 per cent. Atipamezole administration was associated with a decrease in systolic blood pressure and an increase in heart and respiratory rates. Time to first head lift was eight minutes and to sternal recumbency 12 minutes after atipamezole administration. Postoperative analgesia was provided by methadone, administered when the cats adopted sternal recumbency.     

An evaluation of medetomidine/ketamine and other drug combinations for anaesthesia in cats

The anaesthesia induced by cyclohexylamine derivatives in cats was studied by comparing the effects induced by four pairs of agents: acepromazine/ketamine, xylazine/ketamine, zolazepam/tiletamine and medetomidine/ketamine. Acepromazine/ketamine was free of undesirable side effects but provided inadequate anaesthetic cover. The other combinations differed only in the dosage, the quality of the anaesthesia and the importance of the side effects. Medetomidine/ketamine was the best combination; it induced a good degree of anaesthesia with small doses and was free of major side effects.     

Comparison of the brainstem auditory evoked responses during sevoflurane or alfaxalone anaesthesia in adult cats

Objective

To compare the effects of general anaesthesia using sevoflurane or alfaxalone on the brainstem auditory evoked response (BAER) test in adult healthy cats.

A comparison of cardiorespiratory variables during isoflurane-fentanyl and propofol-fentanyl anaesthesia for surgery in injured cats

OBJECTIVE: To compare haemodynamic and respiratory variables during isoflurane-fentanyl (IF) and propofol-fentanyl (PF) anaesthesia for surgery in injured cats. STUDY DESIGN: Prospective, randomized, controlled clinical study. ANIMALS: Thirty-three client-owned injured cats undergoing orthopaedic surgery. MATERIALS AND METHODS: Pre-anaesthetic medication was intravenous midazolam 1 mg kg(-1), butorphanol 0.4 mg kg(-1) and ketamine 2 mg kg(-1). Anaesthesia was induced with propofol (P) and maintained with either: (a) a continuous rate infusion (CRI) of fentanyl (F) 0.02 mg kg(-1) hour(-1) and isoflurane (initial end-tidal concentration of 1%), (b) a fentanyl CRI (dose as before) and sevoflurane (initial end-tidal concentration of 2%) or (c) a CRI of propofol (12 mg kg(-1) hour(-1)). All three techniques were given to effect until surgical anaesthesia was achieved. Heart rate and rhythm (ECG), mean arterial blood pressure, respiratory rate, tidal volume and end-tidal CO(2) concentration were recorded. Venous blood gas analysis was performed before and after sedation, and at the end of anaesthesia. Blood chemistry and blood cell counts were assessed before, at the end of, and 24 hours after anaesthesia. The variables recorded from cats anaesthetized with IF and PF were compared. RESULTS: Mean end-expiratory isoflurane concentration was 1.19 +/- 0.19%. The propofol infusion rate was 11.4 +/- 0.8 mg kg(-1) hour(-1). No significant differences between the two groups in heart rate were identified; no cardiac dysrhythmias were recorded. Mean arterial blood pressure was significantly lower in IF cats during skin incision (p = 0.01), during surgery without intense surgical stimulation (p < 0.01) and during surgery with intense surgical stimulation (p = 0.01). Nine of 11 cats in the IF group were markedly hypotensive (34-49 mmHg) while seven of 11 cats in group PF were mildly hypotensive (49-59 mmHg). One of 11 cats in group IF and nine of 11 cats in group PF required intermittent positive pressure ventilation (IPPV) to maintain end-tidal CO(2) levels below 6.66 kPa (50 mmHg). CONCLUSION AND CLINICAL RELEVANCE: Despite the necessity to ventilate the lungs of cats in the PF group, arterial blood pressure was better maintained. Propofol-fentanyl anaesthesia is better for surgery in injured cats providing the means to impose IPPV are available.     

The effect of pre-anaesthetic medication on the incidence of cardiac arrhythmias during halothane anaesthesia in cats

Objective To compare the incidence of arrhythmias in cats receiving either acepromazine or diazepam for pre-anaesthetic medication prior to halothane anaesthesia.
Study design A blinded, randomized clinical study.
Animals Forty-six healthy cats undergoing surgery.
Methods Animals were allocated to one of two groups for pre-anaesthetic medication. Group 1 received diazepam (0.2 mg kg⁻¹). Group 2 received acepromazine (0.02 mg kg⁻¹). The trial drug was administered intramuscularly in combination with buprenorphine (0.01 mg kg⁻¹) 30 minutes prior to induction of anaesthesia with propofol (approximately 5 mg kg⁻¹). Anaesthesia was maintained using halothane: delivered concentration was 1–2% carried in oxygen and nitrous oxide via an endotracheal tube attached to an Ayre's T-piece (with Jackson-Rees modification) breathing system. The incidence of cardiac arrhythmias was determined by continuously monitoring the electrocardiogram from the time of induction until recovery occurred. Demographical group characteristics were compared using analysis of variance. The incidence of cardiac arrhythmias was compared by the Chi squared test. Statistical significance was set at the 5% level.
Results The two groups were similar in weight, age, length and type of procedure undertaken. The incidence of arrhythmias was the same in each group (3/23 cases) ( p = 1.0).
Conclusions The incidence of cardiac arrhythmias in this study did not appear to be influenced by the nature of pre-anaesthetic medication.
Clinical relevance The incidence of cardiac arrhythmias under halothane anaesthesia was 13% in this study. Acepromazine did not appear to exert an anti-arrhythmic effect. This may not be the case in a larger scale study.     

Antagonistic activities of atipamezole, 4-aminopyridine and yohimbine against medetomidine/ketamine-induced anaesthesia in cats

The objectives of this trial were to determine the ability of atipamezole, 4-aminopyridine and yohimbine to reverse the anaesthetic effects of a combination of medetomidine and ketamine in cats. Forty healthy cats were anaesthetised with 80 micrograms/kg medetomidine combined with 5 mg/kg ketamine. Thirty minutes later atipamezole (200 or 500 micrograms/kg), 4-aminopyridine (500 or 1000 micrograms/kg) or yohimbine (250 or 500 micrograms/kg) were injected intramuscularly. The doses of antagonists were randomised, so that each dose was administered to five cats, and 10 cats were injected only with physiological saline. Atipamezole clearly reversed the anaesthesia and bradycardia induced by medetomidine and ketamine. The mean (+/- sd) arousal times were 28 (+/- 4.7), 5.8 (+/- 1.8) and 7 (+/- 2.1) minutes in the placebo group, and the groups receiving 200 and 500 micrograms/kg atipamezole, respectively. The heart rates of the cats receiving 200 micrograms/kg atipamezole rapidly returned to values close to the initial ones, but 15 minutes after the injection of 500 micrograms/kg atipamezole a significant tachycardia was observed. All the cats showed moderate signs of ataxia during the recovery period. A dose of 500 micrograms/kg yohimbine also clearly reversed the anaesthetic effects of medetomidine/ketamine but 250 micrograms/kg was not effective. The dose of 500 micrograms/kg allowed a smooth recovery with no particular side effects except for some signs of incomplete antagonism of the ketamine effects, ie, ataxia and muscular incoordination. With 4-aminopyridine there were no statistically significant effects on the recovery, or the heart and respiratory rates of the cats anaesthetised with medetomidine/ketamine.