Transcranial Doppler recordings in raised intracranial pressure

The pulsatility index (PI) registered by the transcranial doppler (TCD) was examined in relation to arterial pCO2 (paCO2) and epidural pressure (ICP). In 10 normal subjects PI was studied during variations in paCO2. In 10 neurosurgical patients with head injuries concomitant measurements of PI and ICP were obtained. The results showed a negative exponential correlation between PI and paCO2. PI changes with 3.2% pr mmHg paCO2. A positive exponential correlation between PI and ICP was observed. PI changed with 2.4% pr mmHg ICP. In the subgroup of patients with raised ICP (15 mmHg <) paCO2 was found not to influence the PI-reflection of the ICP, probably because paCO2-changes affected PI as well as ICP. The results suggest that the noninvasive bedside TCD-registration may be a useful marker of the ICP and probably replace the former invasive methods of measuring ICP.