Journal of Neurology, Neurosurgery, and Psychiatry 1987;50:971-975 Changes in cerebral blood flow during anaesthesia and surgery in the sitting position

SUMMARY Serial measurements of global cerebral blood flow (CBF) were made in 15 patients undergoing elective neurosurgical procedures in the sitting position, using a modified intravenous 133Xenon technique. ' The mean supine CBF rose from 43 (+/-3) ml/lOOg/min to 62 (+/-6) ml/1OOg/min in the sitting position and remained elevated at the end of surgery at 62 (+/-5) ml/1OOg/min. Both increases in CBF were statistically significant with respect to baseline supine values. The threat of cardiovascular instability and air embolism dissuades many neurosurgeons from using the sitting position.2 Even in the absence of these complications the cerebral perfusion pressure and cardiac output are known to fall when patients are sat up, and in these circumstances a reduction in CBF might be anticipated. A sustained peroperative fall in CBF could prejudice the outcome of an otherwise uncomplicated procedure. This study was undertake