# A prospective observational study of head-of-bed adjustment for patients following elective craniotomy based on cerebral autoregulation

## TL;DR

This study examines how adjusting the head-of-bed angle affects brain function in patients after craniotomy, finding that a flat position worsens outcomes.

## Contribution

The study provides empirical evidence on optimal head-of-bed angles for cerebral autoregulation after craniotomy.

## Key findings

- A 0° head-of-bed position significantly increases intracranial pressure and decreases cerebral perfusion pressure.
- Baseline cerebral autoregulation status significantly influences hemodynamic responses to head-of-bed adjustments.
- Elevated intracranial pressure remains high regardless of head position, emphasizing the need for careful postoperative management.

## Abstract

While head-of-bed (HOB) elevation is standard in neurocritical care for managing intracranial hypertension, its optimal angle for patients after elective craniotomy remains undefined. This study aimed to evaluate the effects of different HOB angles on cerebral hemodynamics, oxygenation, and cerebral autoregulation (CA) in patients during the early postoperative period following elective craniotomy.

In a prospective observational study, 21 patients underwent sequential positioning at HOB 45°, 30°, 15°, and 0°. Each angle was maintained for 15 min, with multimodal data including intracranial pressure (ICP), cerebral perfusion pressure (CPP), mean flow velocity (mFV) and pulsatility index (PI) of the middle cerebral artery (MCA) M1 segment, tissue oxygenation index (TOI) and the mean flow index (Mx-a) for CA recorded during the final 5 min. Linear mixed-effects models assessed the main effects of HOB angle, baseline ICP status (Elevated: >15 mmHg vs. Normal), and baseline CA status (Impaired: Mx-a > 0.3 vs. Intact).

The 0° position significantly increased ICP (coefficient +8.95 mm Hg, 95% CI 7.02 to 10.88 p < 0.001) and decreased CPP (coefficient −7.65 mm Hg, 95% CI −13.13 to −2.17 p < 0.05). Conversely, 45° elevation significantly lowered ICP (coefficient−1.64 mm Hg, 95% CI −2.87 to −0.41). A significant reduction in Mx-a was observed at 0° (coefficient −0.13, 95% CI −0.25 to −0.007, p < 0.05). Both the 15° and 0° postures were associated with significant decreases in PI (coefficient −0.12, 95% CI −0.21 to −0.03, p < 0.05 and coefficient −0.13, 95% CI −0.23 to −0.03, p < 0.05, respectively). TOI remained unchanged across all positions. The Elevated ICP group maintained higher ICP and lower CPP throughout. Baseline impairment of CA (Mx-a > 0.3) was independently and significantly associated with an increase in the Mx-a index itself during the study period (coefficient +0.26, 95% CI 0.13 to 0.40, p < 0.001).

HOB significantly modulates cerebral hemodynamics after elective craniotomy. The 0° position is particularly detrimental, elevating ICP, reducing CPP, and potentially exhausting cerebrovascular regulatory reserve. Patient’s baseline ICP and CA status are key determinants of their hemodynamic response. Postoperative management must extend beyond the prevention of intracranial hypertension to also include the vigilant avoidance of CA impairment.