James R. Munis

Peripheral venous pressure as a hemodynamic variable in neurosurgical patients.

Neurosurgical patients undergoing either craniotomy or complex spine surgery are subject to wide variations in blood volume and vascular tone. The ratio of these variables yields a pressure that is traditionally mea-sured at the superior vena cava and referred to as “central venous pressure” (CVP). We have investigated an alternative to CVP by measuring peripheral venous pressure (PVP), which, in parallel animal studies, correlates highly with changes in absolute blood volume (r = 0.997). We tested the hypothesis that PVP trends parallel CVP trends and that their relationship is independent of patient position. We also tested and confirmed the hypothesis, during planned circulatory arrest, that PVP approximates mean systemic pressure (circulatory 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 surgery (prone, n = 7). Repeated-measures analysis of variance indicated a highly significant relationship between PVP and CVP (P < 0.001), with a Pearson correlation coefficient of 0.82. The correlation was best in cases with significant blood loss (estimated blood loss >1000 mL;r = 0.885) or hemodynamic instability (standard deviation of CVP > 2;r = 0.923). IMPLICATIONS In patients undergoing either elective craniotomy or complex spine surgery, peripheral venous pressure (PVP) trends correlated with central venous pressure (CVP) trends with a mean offset of 3 mm Hg (PVP > CVP). PVP trends provided equivalent physiological information to CVP trends in this subset of patients, especially during periods of hemodynamic instability. In addition, measurements made during a planned circulatory arrest support the hypothesis that PVP approximates mean systemic pressure (systemic arrest pressure), which is a direct index of patient volume status independent of cardiac or respiratory activity.