Elevation of the head of bed reduces splanchnic blood flow in patients with intra-abdominal hypertension.

BACKGROUND

Elevation of the head of bed (HOB) increases intra-abdominal pressure (IAP), but the effect of body position on abdominal splanchnic perfusion is not clear. The current study aimed to evaluate the effect of body position on the superior mesenteric artery (SMA) and the celiac artery (CA) blood flow by Doppler ultrasound in mechanically ventilated patients with intra-abdominal hypertension (IAH).

METHODS

This prospective cohort study included 53 mechanically ventilated patients with IAH. IAP, hemodynamic variables, and Doppler parameters of the SMA and CA were measured in the supine position. The measurements were repeated after the HOB angle was raised to 15° for 5 min and similarly at HOB angles of 30° and 45°. Finally, the patient was returned to the supine and these variables were re-measured.

RESULTS

The median (interquartile range, IQR) superior mesenteric artery blood flow (SMABF) decreased from 269 (244-322) to 204 (183-234) mL/min and the median (IQR) celiac artery blood flow (CABF) from 424 (368-483) to 376 (332-472) mL/min (both p<0.0001) while median (IQR) IAP increased from 14(13-16) to 16(14-18) mmHg (p<0.0001) when the HOB angle was changed from 0° to 15°. However, SMABF and CABF were maintained at similar levels from 15° to 30°, despite median (IQR) IAP increased to 17(15-18) mmHg (p = 0.0002). Elevation from 30° to 45° further reduced median (IQR) SMABF from 200(169-244) to 164(139-212) mL/min and CABF from 389(310-438) to 291(241-383) mL/min (both p<0.0001), Meanwhile, median (IQR) IAP increased to 19(18-21) mmHg (p<0.0001).

CONCLUSIONS

In mechanically ventilated patients with IAH, progressive elevation of the HOB from a supine to semi-recumbent position was associated with a gradual reduction in splanchnic blood flow. However, the results indicate that splanchnic blood flow is not further reduced when the HOB is elevated from 15° to 30°.This study confirms the influence of head-up angle on blood flow of the splanchnic organs and may contribute to the selection of the optimal position in patients with abdominal hypertension.