BACKGROUND: Continuous monitoring of cerebral blood flow (CBF) may be valuable in critically ill patients with sepsis. In this study, we compared spatially resolved near-infrared spectroscopy (NIRS) to transcranial Doppler ultrasound (TCD)-derived estimates of noradrenaline-associated changes in CBF in such patients.

METHODS: Mean arterial blood pressure (MAP) was elevated by increasing the noradrenaline infusion rate in eight mechanically ventilated, critically ill patients diagnosed with severe sepsis or septic shock. The associated changes in CBF were assessed by simultaneous ipsilateral NIRS (ScO(2)) and TCD (middle cerebral artery blood flow velocity, MCAv) measurements.

RESULTS: A total of fifteen simultaneous NIRS- and TCD-derived assessments of noradrenaline-associated changes in CBF were obtained. MAP was increased from 74 (median; interquartile range (IQR), 71-90) to 100 (median; IQR, 93-115) mmHg (P<0·05), which was associated with an increase in MCAv of 14% (median; IQR, 2-22; P<0·05), whereas no changes were observed in ScO(2) ; 1% (median; IQR, [-4]-3; P = 0·96). A Bland-Altman plot was used to compare the two methods and showed a poor agreement between NIRS- and TCD-derived estimates with a relative bias of 14% and limits of agreement of -18% to 45% change in CBF.

CONCLUSION: Our findings stress that TCD and NIRS cannot be used interchangeably for monitoring changes in cerebral haemodynamics in critically ill patients with sepsis receiving vasopressor treatment with noradrenaline.