The effect of position on intracranial pressure

Abstract

The question as to whether the head and trunk of neurosurgery patients should be elevated remains controversial. This question is particularly important when intracranial hypertension is present. Head up position may have beneficial effects on intracranial pressure (ICP) via changes in mean arterial pressure (MAP), airway pressure, central venous pressure and cerebro spinal fluid displacement. However, in some circumstances, head up position may decrease MAP which in turn will result in a paradoxical rise in ICP through autoregulation mechanisms. Therefore, the degree of head elevation has to be titrated by evaluating the most adequate cerebral perfusion pressure (CPP) for each patient by means of transcranial Doppler or measurement of jugular venous blood oxygen saturation. Head elevation above 30 degrees should be avoided in all cases. In most patients with intracranial hypertension, head and trunk elevation up to 30 degrees is useful in helping to decrease ICP, providing that a safe CPP of at least 70 mmHg or even 80 mmHg is maintained. Patients in poor haemodynamic conditions are best nursed flat. CPP is thus the most important factor in assessment and monitoring when considering head elevation in patients with increased ICP.