Noninvasive continuous monitoring of the effects of head position on brain hemodynamics in ventilated infants.

摘要

HYPOTHESIS: Laying supine with the head in midline position improves cerebral venous return by preventing functional occlusion of the vessels of the neck. OBJECTIVES: To assess changes in cerebral blood volume (DeltaCBV) and cerebral blood flow (CBF) with the position of the head in ventilated patients using a noninvasive method. The influence of the type of ventilation and birth weight was evaluated. METHODS: Thirteen conventionally ventilated and 8 high-frequency oscillatory ventilated infants, with mean gestational ages and birth weights of 31 +/- 5 weeks (24--38) and 1575 +/- 803 g (560--3000), respectively, were studied 5.8 +/- 7.8 days (1--33) after birth. DeltaCBV (mL/100 g) and CBF (mL/100 g/min) were measured by near-infrared spectroscopy with the head in supine midline position (DeltaCBVs, CBFs) and rotated 90 to one side (DeltaCBVlat, CBFlat). Heart rate, peripheral saturation, transcutaneous PCO(2), and blood pressure were monitored continuously. Ventilatory settings remained constant throughout the study period. RESULTS: Mean DeltaCBVs was lower than mean DeltaCBVlat, although no changes in blood pressure, transcutaneous PCO(2), oxygenation, or heart rate occurred. This change in DeltaCBV was not associated with the type of ventilation or birth weight, but the differences tended to be greater (dDeltaCBV = DeltaCBVlat-DeltaCBVs) in the smallest infants (<1200 g). In contrast, CBF did not vary. CONCLUSION: The supine midline position of the head favors cerebral venous drainage and helps to prevent elevation of CBV. SPECULATION: This finding may be important in the first days of life, particularly in tiny preterm infants recovering from lung disease with improving lung compliance, in which functional obstruction of cerebral venous drainage should be avoided.