Doppler flow velocity and intra-cranial pressure: Responses to short-term mild hypocapnia help to assess the pressure-volume relationship after head injury

摘要

To anticipate an increase in intra-cranial pressure (ICP), information about pressure-volume (p/v) compliance is required. ICP monitoring often fails at this task after head injury. Could a test that transiently shifts intra-cranial blood volume produce consistent information about the p/v relationship? Doppler flow velocities inthe middle cerebral arteries (left: 80.8±34.7cm/s; right: 65.9±28.0cm/s) and ICP (16.4±6.7mm Hg) were measured in 29 patients with head injury, before and during moderate hypocapnia (4.4±3.0kPa). The ratio ofvasomotor response to change in ICP differed between those with high (left: 14.8±6.9, right: 14.4±6.6cm/s/kPa/mm Hg) and low (left: 1.8±0.6, right: 2.2±0.9cm/s/kPa/mm g) intra-cranial compliance. Additionally, the ratio identified 12 patients deviating from the classic non-linear p/v curve (left: 5.7±1.3, right: 5.8±1.0cm/s/kPa/mm Hg). They exhibited an almost proportional relationship between vasomotor and ICP responses (R=0.69, p<0.01). Results suggest that a test that combines the responses of two intra-cranial compartments may provide consistent information about intra-cranial p/v compliance, even if the parameters derived from ICP monitoring are inconclusive.