Neurological Disease and Anaesthesia

Introduction

Neurological disease can be intracranial, spinal or neuromuscular. Their presentations can be variable, ranging from a patient who appears otherwise healthy and normal, to one that is in a coma. These patients may require a general anaesthetic for diagnostic procedures, surgery or supportive therapy.

Intracranial

Intracranial neurological disease can include such conditions as head trama, epilepsy and neoplasia.

Intracranial Pressure

One of the biggest concerns with intracranial conditions is an increase in intracranial pressure (ICP). Clinical signs of increased ICP include depression, changes in pupils, and cardiovascular and respiratory changes. These increases in ICP can be avoided by using such agents as diuretics, positioning the patient to prevent jugular occulsion which may lead to an increase in central venous pressure which in itself should be avoided as can increase ICP and finally the use of IPPV to allow for normocapnia.

Preanaesthetic considerations in patients with elevated ICP include the use of diuretics and correction of any underlying electrolyte disturbances. The premedication choices are patient dependent as some patients may require no premedication. However, drugs which induce vomiting as these can exacerbate the increase in ICP. The patient should be preoxygenated and then at induction the patient should be sufficiently anaesthetised to avoid the patient coughing at intubation. As with any patient, extensive monitoring should be used throughout the procedure. The patient should ideally be kept anaesthestised until they are normothermic and good hydration status. Multimodal analgesia should be used and on recovery, sedation may be required to allow for a calm recovery. As with any neurological patient, they should be monitored for any seizure activity.

Epilepsy

It is important for antiepileptic therapy to continue for any epileptic patient undergoing a general anaesthetic. It is important to have IV access in these patients to allow for quick administration of anti-epileptic drugs if required. Ideally, masked induction should be avoided in these patients as it may induce seizure activity.

In status epilepticus, total intravenous anaethesia can be used to stop seizures until the patient can be stabilised via other means.

Spinal

As in any disease, severity ranges between patients. Spinal disease can affect any part of the spine, and each requires specific positioning. Analgesia should always be given as part of the premedication, and multimodal analgesia should be used. Fluid replacement is important in cases where haemorrhage is suspected. Post operatively, the patients should be restricted and so may require sedation to prevent too much movement. Animals that are recumbant require turning to prevent sores developing and many spinal patients need a urinary catheter placed.

Neuromuscular

Preoperatively, radiographs should be taken in patients suspected of having a neuromuscular disease to rule in/out megaoesophagus. Patients should be preoxygenated and rapid intravenous induction should be performed. Patients should be kept in sternal recumbancy to prevent aspiration of any regurgitation that may occur prior to intubation, and if available, suction should be used when necessary. Throughout the anaesthetic, patients should be closely monitored as IPPV may be necessary. Post operatively, a PEG tube may be required to feed patients with megaoesophagus and tracheostomy performed in those patients that may have ventilation difficulties.