Anaesthesia for neurosurgery in the sitting position: a practical approach.

Neurosurgery in the sitting position offers advantages for certain operations. However, the approach is associated with potential complications, in particular venous air embolism. As the venous pressure at wound level is usually negative, air can be entrained. This air may follow any of four pathways. Most commonly it passes through the right heart into the pulmonary circulation, diffuses through the alveolar-capillary membrane and appears in expelled gas. It may pass through a pulmonary-systemic shunt such as a probe patent foramen ovale (paradoxical air embolism); it may collect at the superior vena cava-right atrial junction. Rarely it may traverse through lung capillaries into the systemic circulation. Many monitors, such as the precordial Doppler; capnography, pulmonary artery catheter; transoesophageal echocardiography are useful for venous air embolism detection, with transoesophageal echocardiography being today's gold standard. Various manoeuvres, including neck compression and volume loading, are also useful in reducing the incidence of venous air embolism. Volume loading, in particular; is very helpful as it reduces the risk of hypotension. Other particular concerns to the anaesthetist are airway management, avoidance of pressure injuries, and the risk of pneumocephalus, oral trauma, and quadriplegia. Newer anaesthetic agents have made the choice of anaesthetic technique easier. An appreciation of the implications of neurosurgery in the sitting position can make the procedure safer

Neurosurgery in the sitting position: a case series.

Prospective data was collected on 58 patients having neurosurgery in the sitting position in one institution. The incidence of venous air embolism was 43% (25/58), of which the majority were small or moderate in size. There were no episodes of paradoxical air embolism. The incidence of other intraoperative and postoperative complications was low. There was no mortality or serious morbidity. With a proper understanding of the pathophysiology of venous air embolism and the use of sensitive monitoring, anaesthesia for sitting position neurosurgery can be provided safely.

The effect of selective brain cooling on intracerebral temperature during craniotomy.

In this study we investigated the effect of topical application of cool irrigation fluid on brain tissue temperature during craniotomy. Eight patients were given a standard general anaesthetic for craniotomy. Distal oesophageal and nasopharyngeal temperatures were measured continuously and systemic normothermia was maintained. A sterile needle temperature probe was inserted 18 mm into the cerebrum to measure brain temperature. Brain temperatures were recorded for five minutes while the brain was irrigated with 1000 ml of normal saline at a temperature of 30 degrees C. Measurement continued until the brain temperature returned to baseline. The mean maximum decrease in cerebralparenchymal temperaturefollowing irrigation was 1.6 +/- 0.5 degrees C (P<0.01). The average time to return to baseline temperature after cessation of irrigation was 5.3 +/- 1.5 minutes. Cooling the brain has a marked protective effect after brain injury, but systemic hypothermia can produce significant harmful effects. This study demonstrates that the use of cool irrigation fluid during neurosurgery is a simple and effective method of cooling the brain whilst minimizing the use of systemic hypothermia.

Pre-bypass myocardial ischaemia in patients undergoing coronary artery surgery.

One hundred patients undergoing elective coronary artery surgery were studied to determine the incidence of pre-bypass myocardial ischaemia. Leads II, aVF and V5 of the electrocardiogram (ECG) were recorded at five-minute intervals from arrival in the anaesthetic room until onset of cardiopulmonary bypass. Thirteen patients developed sixteen episodes of significant ST depression on the ECG during the study period. Three patients were diagnosed as having postoperative myocardial infarction by ECG criteria and creatine phosphokinase-MB rise above 80 units. None of these patients had pre-bypass ST depression. Comparisons of these results with similar studies are presented.

Radial artery cannulation--the influence of method on blood flow after decannulation.

A prospective randomised study of two hundred patients undergoing open-heart surgery was carried out to determine if the method of radial artery cannulation (direct threading or transfixion) had any influence on the incidence of abnormal flow after decannulation. A standard 20-gauge non-tapered teflon-coated cannula was used and the groups were well matched for age, sex, wrist circumference, duration of cannulation and haematoma formation, all of which have been postulated to influence thrombosis rate. We were unable to demonstrate a statistically significant difference between the two methods of cannulation. The overall abnormal flow rate at five days assessed by Doppler ultrasound was low at 5%.

Hypotensive effect of mannitol administered rapidly.

Mannitol is an osmotic diuretic commonly used to reduce intracranial pressure. While various side-effects, including hyperosmolar states, precipitate reduction in intracranial pressure, rebound phenomenon and hypervolaemia have been described, hypotension due to rapid administration has not been widely recognised.

Cardiovascular risk factors in patients for vascular surgery.

Various attempts have made been made to quantify the cardiovascular risk factors associated with anaesthesia and surgery. Two such schemes are the "Multifactorial Index of Cardiac Risk" developed by Goldman et al., and the one devised by Cooperman et al. The validity of these two schemes in relation to anaesthesia for vascular surgery was investigated by carrying out a prospective study of 100 patients. Cooperman's scheme was found to be much more accurate than Goldman's scheme in assessing patient risk. The study confirms the impression that the vascular patient falls into a higher risk group than most other surgical patients with regard to cardiovascular complications.

Pulmonary artery catheterisation. An assessment of risks and benefits in 220 surgical patients.

The benefits and risks of pulmonary artery catheterisation were assessed in 220 patients having cardiac or vascular surgery. Prior to induction of anaesthesia 20% of patients had pulmonary artery wedge pressure measurements which indicated the need for blood volume support, vasodilator therapy or modification of the anaesthetic induction technique. Of those patients for cardiac surgery, 38% had important changes before cardiopulmonary bypass requiring blood volume support or vasodilator therapy. These changes were not reflected by similar changes in the central venous pressure. The risks of the technique were minimal. Minor complications occurred in 25% of patients (transient arrhythmias) and more serious complications occurred in 3.6% of patients. There was no mortality or long-term sequelae. We conclude that the benefits of pulmonary artery catheterisation outweigh its risks in patients having major cardiac and vascular surgery.