Peripheral venous pressure as a hemodynamic variable in neurosurgical patients

Neurosurgical patients undergoing either craniotomy or complex spine surger y are subject to wide variations in blood volume and vascular tone. The rat io of these variables yields a pressure that is traditionally measured at t he superior vena cava and referred to as "central venous pressure" (CVP). W e have investigated an alternative to CVP by measuring peripheral venous pr essure (PVP), which, in parallel animal studies, correlates highly with cha nges in absolute blood volume (r = 0.997). We tested the hypothesis that PV P trends parallel CVP trends and that their relationship is independent of patient position. We also tested and confirmed the hypothesis, during plann ed circulatory arrest, that PVP approximates mean systemic pressure (circul atory arrest pressure), which reflects volume status independent of cardiac function. PVP was compared with CVP across 1026 paired measurements in 15 patients undergoing either craniotomy (supine, n = 8) or complex spine surg ery (prone, n = 7). Repeated-measures analysis of variance indicated a high ly significant relationship between PVP and CVP (P < 0.001), with a Pearson correlation coefficient of 0.82. The correlation was best in cases with si gnificant blood loss (estimated blood loss >1000 mL; r = 0.885) or hemodyna mic instability (standard deviation of CVP > 2; r = 0.923).