NEUROSURGICAL ANESTHESIA

Most emergencies that occur during neuroanaesthesia are the same as those that occur during any other anaesthetic (e.g. hypoxaemia, hypotension) and are treated in the usual way. Airway problems are a particular concern as access is usually limited. One must always consider the patient's airways, breathing and circulation before looking for specific neurosurgical problems. We are always interested in preventing vital organ damage but in neurosurgery the potential for cerebral damage is accentuated. Once the general causes have been eliminated, increases in ICP/brain swelling are most commonly due to the underlying process (e.g. head injuries) but specific anaesthetic and surgical problems must be identified and corrected. If no correctable cause is found then head-up tilt, hypocarbia, diuretics, intravenous anaesthetics and CSF drainage are used. Acute hypertension is dangerous because it may cause aneurysm rupture and increases in ICP/brain swelling. It is usually due to inadequate reflex depression resulting from failure to anticipate the stimuli. Acutely, it should be controlled with thiopentone and then by increasing the longer-term reflex depression either centrally (e.g. narcotics) or peripherally (e.g. labetalol). Cerebral vasodilators should be avoided. Hypotension is usually due to blood loss or drug effects. One must not forget spinal cord damage and non-intracranial sites of bleeding as causes. Sudden movement or coughing is treated with thiopentone and then either increasing the central reflex depression or paralysis. Cerebral oedema is an increase in brain parenchymal volume due to excess water; it is divided into vasogenic and cytotoxic types. These are best understood by considering the factors that determine water movement. Air embolus may occur at any tim that part of the venous system has both a subatmospheric pressure and has been breached. Air may either stay within the venous system or gain access to the arterial system. The consequences of the latter are much worse. Management is by preventing its occurrence or by early detection of its entry. Aneurysm rupture is best dealt with by preventing it happening! If it does, and the dura is closed, one needs to control the ICP and reduce the blood pressure to its usual levels with thiopentone and then clip the aneurysm as soon as possible. Induced hypotension should only be used to reduce the bleeding once the dura is opened. © 1993 Baillière Tindall.