Cerebrovascular responses to a 90° tilt in healthy neonates

Abstract

Background: Tilts can induce alterations in cerebral hemodynamics in healthy neonates, but prior studies have only examined systemic parameters or used small tilt angles (<90°). The healthy neonatal population, however, are commonly subjected to large tilt angles (≥90°). We sought to characterize the cerebrovascular response to a 90° tilt in healthy term neonates.

Methods: We performed a secondary descriptive analysis on 44 healthy term neonates. We measured cerebral oxygen saturation (rcSO₂), oxygen saturation (SpO₂), heart rate (HR), breathing rate (BR), and cerebral fractional tissue oxygen extraction (cFTOE) over three consecutive 90° tilts. These parameters were measured for 2-min while neonates were in a supine (0°) position and 2-min while tilted to a sitting (90°) position. We measured oscillometric mean blood pressure (MBP) at the start of each tilt.

Results: rcSO₂ and BR decreased significantly in the sitting position, whereas cFTOE, SpO₂, and MBP increased significantly in the sitting position. We detected a significant position-by-time interaction for all physiological parameters.

Conclusion: A 90° tilt induces a decline in rcSO₂ and an increase in cFTOE in healthy term neonates. Understanding the normal cerebrovascular response to a 90° tilt in healthy neonates will help clinicians to recognize abnormal responses in high-risk infant populations.

Impact: Healthy term neonates (≤14 days old) had decreased cerebral oxygen saturation (~1.1%) and increased cerebral oxygen extraction (~0.01) following a 90° tilt. We detected a significant position-by-time interaction with all physiological parameters measured, suggesting the effect of position varied across consecutive tilts. No prior study has characterized the cerebral oxygen saturation response to a 90° tilt in healthy term neonates.

Fig. 1. Position changes during the 90° tilt-test.

In our 90° tilt-test, neonates were first in a supine (0°) position (a) for 2-min and tilted (over 1–2 s) to a sitting (90°) position (b) for an additional 2-min. We ensured neonates were not slouched or hunched when being tilted. In the supine position, the heart and brain are of equal height from the ground. In the sitting position, the brain is higher than the heart, resulting in orthostatic stress from gravitational forces. c Image of an actual neonatal study participant in the “snuggle-up” during the supine position (permission obtained from the parents).

Fig. 2. Aggregated rcSO₂ time series of healthy term neonates.

rcSO₂ was measured at 5-s intervals during a 5-min period in both the supine and sitting positions for all 44 healthy term neonates in our sample. The data from each participant were then combined and aggregated into the above time series. We empirically verified our selection of a 2-min window to capture the cerebrovascular response to a 90° tilt through visual examination of all individual time series, including the above figure. Our aim in selecting a 2-min window was to accurately capture tilt-induced changes while removing the return to baseline.

Fig. 3. Study inclusion flow chart.

Forty-six neonates were screened for eligibility from July 2018 to May 2022. All 46 met study eligibility and underwent testing. Two neonates were excluded from the present analysis as three consecutive tilts were not conducted.

Fig. 4. Two-minute supine and sitting marginal means of physiological parameters.

Marginal means for each physiological parameter were estimated from the mixed-model repeated-measures analysis shown in Table 2. Error bars denote standard error. rcSO₂ = regional cerebral oxygen saturation (a); SpO₂ = arterial peripheral oxygen saturation (b); HR = heart rate (c); MBP = mean blood pressure (d); BR = breathing rate (e); cFTOE = cerebral fractional tissue oxygen extraction (f); bpm = beats per minute; mmHg (millimeters of mercury); BPM = breaths per minute. *2-sided p ≤ 0.05.