VALUE OF TRANSCRANIAL DOPPLER ULTRASONOGR APHY IN HEAD-INJURED PATIENTS

Transcranial doppler ultrasonography (TCD) is a non invasive technique for the assessment of cerebral blood flow (CBF). The aim of this pros pective study was to evaluate the benefit of TCD for the monitoring of major head trauma patients. Therefore 10 of such patients, aged 17 to 37 years, had a TCD at admission and subsequently at least twice a da y. Following data were measured simultaneously at the site of the righ t and the left middle cerebral arteries : the systolic (SV), diastolic (DV) and mean (MV) blood velocity, the resistance index (RI) of Pourc elot (RI = SV - DV/SV) and the pulsatility index (PI) of Gosling (PI = SV - DV/MV). Simultaneously, the mean intracranial pressure (ICP) obt ained with a subarachnoid probe, the PaCO2 and the mean arterial press ure (Pa) were measured. The cerebral perfusion pressure (CPP) was calc ulated with the formula : CPP - Pa - ICP. A total of 132 measures were analysed. There was a linear relation between RI and CPP (r = 0.566; p < 0.001), between RI and ICP (r = 0.822; p < 0.001), as well as betw een PI and CPP (r = 0.563; p < 0.001) and between PI and ICP (r = 0.83 7; p < 0.001). In the opposite there was no statistically significant relation between ICP and MV (r = 0.18) nor between CPP and MV (r = 0.2 3). However, a MV over 100 cm . s-1 was regularly associated with a IC P over 60 mmHg. The close correlation between RI, PI and ICP allows to use RI or PI to estimate ICP. Since this evaluation can be obtained n on invasely, this possibility is important for the clinician, despite the lack of correlation between MV and ICP. The measurement of MV prov ides an estimated value of CBF in patients with steady Pa and steady P aco2. The TCD allows the allocation of head trauma patients with high ICP or RI into two groups : a first group with a low MV, in which hype rventilation and barbiturates may cause cerebral ischaemia by a furthe r decrease of CBF; a second group with a normal or increased MV and fo r which these treatments can be administered. Multimodal monitoring sh ould be used more and more in severely head injured patients, to allow such situations to be identified.