Baroreflex Dysfunction in Sick Newborns Makes Heart Rate an Unreliable Surrogate for Blood Pressure Changes

BACKGROUND: Cerebral pressure passivity (CPP) in sick newborns can be detected by evaluating coupling between mean arterial pressure (MAP) and cerebral blood flow measured by NIRS hemoglobin difference (HbD). However, continuous MAP monitoring requires invasive catheterization with its inherent risks. We tested whether heart rate (HR) could serve as a reliable surrogate for MAP in the detection of CPP in sick newborns. METHODS: Continuous measurements of MAP, HR, and HbD were made and partitioned into 10-minute epochs. Spectral coherence (COH) was computed between MAP and HbD (COH(MAP-HbD)) to detect CPP, between HR and HbD (COH(HR-HbD)) for comparison, and between MAP and HR (COH(MAP-HR)) to quantify baroreflex function (BRF). The agreement between COH(MAP-HbD) and COH(HR-HbD) was assessed using ROC analysis. RESULTS: We found poor agreement between COH(MAP-HbD) and COH(HR-HbD) in left hemisphere (area under the ROC curve (AUC) 0.68) and right hemisphere (AUC 0.71). Baroreflex failure (COH(MAP-HR) not significant) was present in 79% of epochs. Confining comparison to epochs with intact BRF showed an AUC of 0.85 for both hemispheres. CONCLUSIONS: In these sick newborns, HR was an unreliable surrogate for MAP required for the detection of CPP. This is likely due to the prevalence of BRF failure in these infants.