IS TRANSCRANIAL DOPPLER ULTRASONOGRAPHY (TCD) GOOD ENOUGH IN DETERMINING CO2 REACTIVITY AND PRESSURE AUTOREGULATION IN HEAD‐INJURED PATIENTS

Abstract

Objectives: Blood flow velocity (BFV) measurement by transcranial Doppler ultrasonography (TCD) has been shown to give accurate indication of changes in cerebral blood flow (CBF). Cerebral haemodynamic status [cerebral vasoreactivity (CVR) to carbon dioxide (CO2) and pressure autoregulatory response (PAR)] as determined by TCD was compared with that of stable xenon‐enhanced cerebral blood flow (XeCBF), generally regarded as gold standard in CBF measurement.Blood flow velocities (BFV) in both middle cerebral arteries were measured continuously by TCD. XeCBF measurement was performed after (1) moderate hyperventilation, (2) normocapnia and (3) normocapnia with induced increase in blood pressure (BP). Preserved CVR was defined as more than 1% change in XeCBF and BFV per mm Hg end‐tidal CO2 and intact PAR was defined as within 1% change in XeCBF and BFV per mmHg BP change.Results: Fourteen sedated and ventilated head‐injured patients (median G.C.S. score : 6.5, mean age: 44.2 ± 16.9 years) underwent 32 pairs of CVR and PAR tests. BFV and XeCBF were 74.4 ± 26.8 cm/s and 53.6 ± 22.6 mL/100 g/min (r = 0.49, P < 0.0005) respectively. In CVR test, correlation coefficient (r) of changes in BFV versus changes in XeCBF was 0.34 (P = 0.006). Sensitivity and specificity of detecting preserved and impaired CVR were 70.5% and 50.0%. In PAR test, changes in BFV correlated significantly with changes in XeCBF (r = 0.73, P < 0.0005). Sensitivity and specificity of detecting intact and loss of PAR were 73.0% and 59.3%.Conclusions: This study suggests BFV measurement using TCD is reliable to assess cerebral haemodynamic status. In ventilated head‐injured patients, correlation in pressure autoregulation was stronger in comparison with cerebral vasoreactivity.