Cerebral and cardiovascular responses to changes in head elevation in patients with intracranial hypertension

Abstract

To establish if an optimum level of head elevation exists in patients with intracranial hypertension, the authors examined changes in intracranial pressure (ICP), systemic and pulmonary pressures, systemic flows, and intrapulmonary shunt fraction with the patient lying flat, and then with the head elevated at 15 degrees, 30 degrees, and 60 degrees. Cerebral perfusion pressure (CPP) was calculated. The lowest mean ICP was found with elevation of the head to 15 degrees (a fall of -4.5 +/- 1.6 mm Hg, p less than 0.001) and 30 degrees (a fall of -6.1 +/- 3.5 mm Hg, p less than 0.001); the CPP and cardiac output were maintained. With elevation of the head to 60 degrees, the mean ICP increased to -3.8 +/- 9.3 mm Hg of baseline, while the CPP decreased -7.9 +/- 9.3 mm Hg (p less than 0.02), and the cardiac index also fell -0.25 +/- 0.28 liters/min/sq m (p less than 0.01). No significant change in filling pressures, arterial oxygen content, or heart rate was encountered at any level of head elevation. Therefore, a moderate degree (15 degrees or 30 degrees) of head elevation provides a consistent reduction of ICP without concomitant compromise of cardiac function. Lower (0 degrees) or higher (60 degrees) degrees of head elevation may be detrimental to the patient because of changes in the ICP, CPP, and cardiac output.