Change in circulating blood volume following craniotomy

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Abstract
The importance of monitoring circulating blood volume (CBV) during perioperative management is widely recognized in critically ill patients. The purpose of this study was to investigate the change in CBV following craniotomy by using indocyanine-green pulse spectrophotometry. Circulating blood volume and plasma hormones related to stress and fluid regulation were measured five times: preoperatively, immediately postoperatively, and 1, 2, and 7 days after craniotomy was performed in 17 patients with a brain tumor or an unruptured aneurysm. The mean value of CBV preoperatively was 82 ml/kg, which decreased to 64 ml/kg (78%) immediately postoperatively and gradually recovered to 82 ml/kg on Day 7 postsurgery (p = 0.0069). The mean values of adrenaline, noradrenaline, arginine vasopressin, renin, and aldosterone were highest immediately postoperatively. The mean intraoperative balances of water and sodium were 1,090 ml and 113 mEq, respectively. Partial correlation coefficients of CBV to noradrenaline and serum sodium during the entire study were -0.430 (p = 0.0036) and 0.418 (p = 0.0048), respectively. Attention should be paid to decreased CBV following craniotomy, which is caused by the shift of fluid to interstitial spaces due to surgical stress. Hypovolemia can be suspected from a postoperative decrease in serum sodium.