Noninvasive Continuous BP Monitoring in Newborns Based on Pulsatile Signal Morphological Features Using NIRS

Continuous blood pressure monitoring is important for critically ill newborns to prevent brain injury caused by dysregulated changes in cerebral perfusion. In addition, continuous blood pressure monitoring is beneficial to management of many other conditions in neonates: including hypoxic-ischemic encephalopathy; for monitoring respiratory issues such as respiratory distress syndrome and pulmonary hypertension related to meconium aspiration syndrome; for managing the vascular resistance in conditions like patent ductus arteriosus and congenital heart failures; for ensuring adequate tissue perfusion during critical illness like sepsis and necrotizing enterocolitis (NEC); and for maintaining vascular tone when using inotropes or vasopressors.

The gold standard for continuous BP monitoring in newborns is via arterial line (A-line BP). However, it involves catheterization of the umbilical or a peripheral artery and can lead to complications such as vasospasm, nerve damage, ischemia, thrombosis, and, in severe cases, limb amputation. Due to these risks, A-line BP monitoring is only used when deemed necessary in critically ill neonates.

Existing noninvasive alternatives, including volume-clamp photoplethysmography cuffs, pulse-transit-time, and tonography, are problematic due to large error and safety concerns. They have been validated primarily for adults and are not tailored for neonates who pose unique challenges due to their fragile limbs, underdeveloped vasculature, immature cardiac function, and mean arterial BP often being less than a third of an adult's (30 mmHg).

To address this critical need for accurate, continuous, and noninvasive BP monitoring in newborns, the study team proposes employing a near-infrared spectroscopy (NIRS) technique on the head, focusing on pulsation tones and shapes in cerebral hemodynamics, which are sensitive to BP changes. The team has developed a wearable, battery-operated NIRS device, called FlexNIRS, capable of providing continuous photoplethysmogram (PPG) with a high temporal resolution of 266 Hz. In adults, the team has shown that the time derivative of its optical pulse waveforms d/dt(PPG) is related to pulsatile blood flow, and found strong correlations between specific features of d/dt(NIRS-PPG) and blood pressure changes. Based on these findings, it is hypothesized that NIRS-PPG collected in the brain is most ideal for neonates, especially given their fragile peripheries, and the head site allowing more robust measure of deep brain with less external factors, such as pressure from the sensor itself, room temperature, and extra arterial resistance that builds up in local peripheries. Importantly, the study team has tested the FlexNIRS in a preterm newborn and found pulsatile morphology patterns comparable to those in adults.

The current study aims to validate this novel technique for BP assessment in the newborn population from up to 80 newborns, divided evenly across Massachusetts General Hospital (MGH) and Brigham and Women's Hospital (BWH). Each measurement will involve monitoring infants with one or two FlexNIRS devices for 3-24 hours a day, for at least one day. This data will be used to refine the study team's FlexNIRS-based blood pressure estimation algorithms and correlate results with invasive A-line BP as the gold standard or periodic BP cuff readings performed by clinical staff. This research will provide invaluable data demonstrating method feasibility and initial clinical utility. The successful execution of this aim will guide the study team to a larger clinical study.