Estimation of Cerebral Blood Flow at Bedside by Continuous Jugular Thermodilution

Abstract

The Kety-Schmidt technique can be regarded as the reference method for the measurement of cerebral blood flow (CBF). However, the method is somewhat cumbersome for routine use in the intensive care unit (ICU) at the beside. The continuous thermodilution technique developed many years ago for the measurement of coronary sinus blood flow can be applied for the measurement of jugular blood flow (JBF). However, the measurement of JBF by thermodilution has never been validated using the Kety-Schmidt reference method. We first validate the continuous thermodilution in vitro by comparison with a volumetric flow. The thermodilution method is accurate for flows between 50 and 900 ml min-1 with a mean difference volumetric-thermodilution flow of -1 +/- 18 ml min-1 (mean +/- SD), and precise with a coefficient of variability ranging between 1.21% and 2.50%. In vivo accuracy was assessed by comparing in 15 comatose patients CBF measured using the Kety-Schmidt (CBFKS) method and estimated from JBF measured by thermodilution (CBFTH) at four levels of arterial PaCO2 (25, 30, 35, and 40 mm Hg). The mean difference CBFKS-CBFTH is -0.9 +/- 3.6 ml min-1 100 g-1. In vivo precision of the method was good, with a coefficient of variability of 4.1% in mean. We conclude that jugular continuous thermodilution technique is a reliable method for estimating CBF at the bedside. This technique allows repeated measurements jugular bulb blood sampling for brain metabolic studies.