Effect of the knee-chest position on cerebral blood flow in patients undergoing lumbar spinal surgery.

Abstract

sumMARY The cerebral haemodynamic effect of the knee-chest position was evaluated in 15 anaesthetised patients undergoing elective lumbar disc surgery and divided into a control group (n = 8) where cerebral blood flow (CBF) was measured twice in the supine position and an experimental group (n = 7) where the first CBF was measured in the supine position and the second in the knee-chest position. CBF was measured by a modified intravenous "'xenon washout technique.Mean global CBF did not change in control group (56-1, SD 9-2 versus 52 8, SD 108 units) and was not significantly modified by the knee-chest posture, 51-8, SD 8-8 units versus 53-9, SD 7-4 units in the supine position. The results indicate that mean global CBF in the knee-chest position is not different from CBF in the supine position in healthy patients.The knee-chest position for lumbar intervertebral disc surgery has many advantages: excellent exposure of interlaminar spaces, avoidance of epidural venous engorgement with decreased blood loss, easy administration of intermittent positive pressure ventilation and decreased risk of injury to major prevertebral vessels and organs even in obese patients."' However, undesirable effects of the knee-chest position have been reported, such as persistent postoperative pain in the hip and the quadriceps area,5 deep vein thrombosis,' bilateral calf-muscle ischaemia with rhabdomyolysis and acute renal failure' due to the prolonged flexion of the lower limbs and systemic hypotension when the legs are straightened at the end of surgery.6The knee-chest position is not a physiological position. It could theoretically produce a significant decrease in CBF, especially in old arteriosclerotic patients,8 since the head is slightly downwards (fig 1). Furthermore in our practice, we have occasionally observed oedema and venous stasis of the face at the end ofsurgery. If similar stasis occurred in the cerebral veins, it could also increase intracranial pressure and possibly decrease CBF.The present study was designed to compare the effect of the knee-chest with the supine position on CBF in patients undergoing elective lumbar disc surgery. Methods PatientsAfter informed consent and institutional approval, sixteen patients scheduled for elective lumbar intervertebral disc surgery participated in the study. The patients were randomly divided into a control (n = 8) and an experimental group (n = 7). Patients more than 62 years old, or with cardiovascular, pulmonary, or neurological diseases, or under medication other than minor analgesics, were excluded from the study. Moreover, the patients enrolled in the study were immediately excluded from the investigation if they had cardiac arrhythmias or a decrease ofmore than 30% ofmean systemic arterial pressure (MAP) after induction of anaesthesia despite a rapid infusion of 500 ml of crystalloids. ProcedureThe effects of knee-chest position on cerebral haemo-

Hemodynamic effects of chest-knee position: comparison of perioperative propofol and sevoflurane anesthesia

“…The effect of positioning on hemodynamic parameters in anesthetized patients has been also evaluated in the literature (2,(11)(12)(13). No significant HR changes were demonstrated in anesthetized patients while moving the patient from the supine to the chest-knee position (13)(14)(15). The elevation of HR in GrS during the induction of anesthesia was thought to be a sort of stress response to intubation.…”

“…In the current study, although 2 different induction agents were used to compare the hemodynamic parameters, the alterations during the induction period in GrS could be related to thiopental, while perioperative changes in hemodynamic parameters might be related to sevoflurane because of the limited metabolic effect of the bolus dose of thiopental. The effect of positioning on hemodynamic parameters in anesthetized patients has been also evaluated in the literature (2,(11)(12)(13). No significant HR changes were demonstrated in anesthetized patients while moving the patient from the supine to the chest-knee position (13)(14)(15).…”