Changes in cerebral blood flow during anaesthesia and surgery in the sitting position.

Abstract

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 undertaken to examine changes in CBF during anaesthesia and surgery in the sitting position and their relationship, if any, to outcome. Materials and methodsThe patients studied were undergoing elective surgery under the care of a single consultant neurosurgeon (JB) Following premedication with atropine 0-6 mg IM, general anaesthesia was induced using intravenous sodium thiopentone 250-500 mg, fentanyl 100-150 rg, and alcuronium or pancuronium and maintained with 60% nitrous oxide/-oxygen, fentanyl, alcuronium or pancuronium, supplemented by occasional use of 0-25-0 5% halothane or 0 2-0 5% trichloroethylene. In every case the electrocardiogram, radial arterial blood pressure and end tidal pCO2 were continuously monitored (Hewlett Packard; ECG-HP0300A, Pressure transducer-HP1290A, Capnometer-47210A). In 12 cases an oesophageal stethoscope and precordial Doppler probe (Sonicaid Doppler) were employed. A right atrial catheter was inserted in five cases. After endotracheal intubation the patients were mechanically ventilated using a Cape-Wayne Mk 111 ventilator, maintaining the end tidal pCO2 between 30 and 35 mm Hg.Positive and expiratory pressure (PEEP) was added at the discretion of the anaesthetist. All patients had compression bandages applied to their lower limbs and 400-500 ml crystalloid fluid were given intravenously before changing position. A standard neurosurgical chair was used in which the knees were kept flexed to avoid sciatic nerve traction and the head supported in a horseshoe headrest. Rigid cranial fixation was not used.The global cerebral blood flow was measured using a modified intravenous 1 33Xenon technique, deriving the data for cerebral and arterial clearance from single mid-frontal and apical chest probes as previously described from this centre.

Differences between Internal Jugular Vein and Vertebral Vein Flow Examined in Real Time with the Use of Multigate Ultrasound Color Doppler

“…11,18 Because the arterial BF passing from the supine to the sitting position is slightly reduced 19 or increased, 20 additional paths of cerebral outflow should be strongly considered.…”

The Effect of the Sitting Upright or ‘Beachchair’ Position on Cerebral Blood Flow during Anaesthesia for Shoulder Surgery

“…Other volatile agents are also reported to increase CBF. In an early study of sitting neurosurgical patients, halothane anaesthesia increased CBF by 50%, as measured with 113Xenon clearance gas technique 24 . Similarly, desflurane increases CBF by 11%, tends to maintain MAP, but impairs cerebral autoregulation at concentrations greater than 0.5 MAC 25 .…”