Anaesthesia and central nervous system disease in small animals. Part I: General considerations

Total intravenous anaesthesia in a goat undergoing craniectomy

BACKGROUND

Cerebral coenurosis is a disease of the central nervous system in sheep and goats, and is usually fatal unless surgical relief is provided. Information regarding neuroanaesthesia in veterinary medicine in goats is scant.

CASE PRESENTATION

We describe anaesthetic management of an intact female goat (2 years; 16 kg) presented for craniectomy. The goat was sedated with xylazine (0.05 mg kg-1, i.m.) and morphine (0.05 mg kg-1, i.m.). General anaesthesia was induced 20 min later with propofol and maintained with a constant rate infusion of propofol (0.2 mg kg-1 min-1). A cuffed endotracheal tube was placed and connected to a rebreathing (circle) system and mechanical ventilation with 100% oxygen was initiated. A bolus of lidocaine (1 mg kg-1), midazolam (0.25 mg kg-1) and fentanyl 2.5 μg kg-1 was delivered via the intravenous route followed immediately by a constant rate infusion of lidocaine (50 μg kg-1 min-1), midazolam (0.15 mg kg-1 h-1) and fentanyl (6 μg kg-1 h-1) administered via the intravenous route throughout surgery. Craniectomy was undertaken and the goat recovered uneventfully.

CONCLUSION

Total intravenous anaesthesia with propofol, lidocaine, fentanyl and midazolam could be an acceptable option for anaesthesia during intracranial surgery in goats.

Evaluation of an anaesthetic technique used in dogs undergoing craniectomy for tumour resection

OBJECTIVE

To evaluate a total intravenous anaesthetic technique in dogs undergoing craniectomy.

STUDY DESIGN

Prospective clinical study.

ANIMALS

Ten dogs admitted for elective surgical resection of rostro-tentorial tumours.

METHODS

All dogs were premedicated with methadone, 0.2 mg kg(-1) intramuscularly 30 minutes prior to induction of anaesthesia. Anaesthesia was induced with propofol administered intravenously (IV) to effect, following administration of lidocaine 1 mg kg(-1) IV and maintained with a continuous infusion of propofol at < or =0.4 mg kg(-1) minute(-1) during instrumentation and preparation and during movement of the animals to recovery. During surgery, anaesthesia was maintained using a continuous infusion of propofol at <or =0.4 mg kg(-1) minute(-1) and alfentanil < or =1 microg kg(-1) minute(-1). Lidocaine was administered at 1 mg kg(-1) IV immediately prior to extubation. Arterial blood pressure and heart rate (HR) were recorded prior to induction and every 5 minutes throughout preparation and surgery. Central venous pressure was recorded every 5 minutes throughout surgery.

RESULTS

Administration of propofol and lidocaine prevented significant increases in mean arterial blood pressure (MAP) and HR during endotracheal intubation and extubation. Adequate MAP was maintained throughout anaesthesia. Recovery was smooth and excitement free. There was no association between duration of anaesthesia, total drugs administered, or severity of neurological disease and recovery times. Postoperatively there was no deterioration in neurological function in the immediate postoperative period with complete resolution of pre-existing neurological deficits within 7 days of surgery.

CONCLUSION

This technique provided minimal response to intubation and extubation, adequate arterial blood pressure and a smooth predictable recovery. All animals were neurologically improved by the time of discharge, suggesting that this technique had not caused significant neuronal damage.

CLINICAL RELEVANCE

Total intravenous anaesthesia with propofol and alfentanil appears to be a satisfactory anaesthetic technique for use in dogs undergoing surgery for debulking/removal of rostro-tentorial tumours.

Cardiac arrhythmias associated with acute major haemorrhage during craniectomy in a dog

An estimated 43% of total blood volume was lost during craniectomy in a 32-kg Labrador retriever. One episode of bradycardia, followed by ventricular tachycardia occurred during surgery when the rate of haemorrhage exceeded fluid replacement. Sinus rhythm was re-established with intravenous lidocaine (1.25 mg kg^-1). Twenty-four hours later, premature ventricular complexes appeared followed by episodes of ventricular tachycardia, some requiring lidocaine treatment. Myocardial hypoxia resulting either from hypovolaemia and/or air embolism (the right transverse venous sinus was damaged during surgery) may have caused the arrhythmias. Mild intracranial hypertension may have aggravated the problem.