Rapid bedside determination of cerebral blood pressure autoregulation (AR) may improve clinical utility. We tested the hypothesis that cerebral Hb oxygenation (Hb Diff ) and cerebral Hb volume (Hb Total ) measured by near-infrared spectroscopy (NIRS) would correlate with cerebral blood flow (CBF) after single dose phenylephrine (PE). Critically ill patients requiring artificial ventilation and arterial lines were eligible. During rapid blood pressure rise induced by i.v. PE bolus, ⌬Hb Diff and ⌬Hb Total were calculated by subtracting values at baseline (normotension) from values at peak blood pressure elevation (hypertension). With the aid of NIRS and bolus injection of indocyanine green, relative measures of CBF, called blood flow index (BFI), were determined during normotension and during hypertension. BFI during hypertension was expressed as percentage from BFI during normotension (BFI%). Autoregulation indices (ARIs) were calculated by dividing BFI%, ⌬Hb Diff , and ⌬Hb Total by the concomitant change in blood pressure. In 24 patients (11 newborns and 13 children), significant correlations between BFI% and ⌬Hb Diff (or ⌬Hb Total ) were found. In addition, the associations between Hb-based ARI and BFI%-based ARI were significant with correlation coefficients of 0.73 (or 0.72). Rapid determination of dynamic AR with the aid of cerebral Hb signals and PE bolus seems to be reliable. (Pediatr Res 69: 436-441, 2011) I ntact cerebral blood pressure autoregulation (AR) describes the intrinsic ability of the brain to maintain cerebral blood flow (CBF) during changes in cerebral perfusion pressure. Diverse factors, such as age of patient, illness, injury, or vasoactive drugs, have been found to impair this ability-often to an unpredictable extent. Patients with impaired or even absent AR are at increased risk for inadequate CBF and consequently for cerebral ischemia. Measuring AR may provide clinically useful information and permit more individualized critical care. Several recent studies have demonstrated the potential of so-called dynamic AR to predict outcome in adult (1) or pediatric TBI (2) and in premature infants (3). In addition, monitoring of dynamic AR may allow determination of optimal cerebral perfusion pressure (4) and determination of treatment efficacy in controlling intracranial pressure (ICP) after head injury (5). Finally, AR-guided treatment of cerebral perfusion pressure in patients suffering severe head trauma carries the potential to improve outcome (6) and has therefore been recommended in the new adult guidelines (7). Nevertheless, further work is needed to delineate the clinical utility of AR determination in critical illness, especially for the child and newborn.Determination of the classic, steady state (or static) AR in intensive care medicine remains cumbersome and time consuming. In contrast, determination of the short-latency cerebrovascular response (or dynamic AR) to rapid perfusion pressure changes has been shown to be easily performed at the bedside and allows for repetitive...