Is Transcranial Doppler Ultrasonography (TCD) Good Enough in Determining CO₂ Reactivity and Pressure Autoregulation in Head-Injured Patients?

Summary

Disturbance of cerebral haemodynamic status, cerebral vasoreactivity (CVR) to carbon dioxide (CO₂) and pressure autoregulatory response (PAR) have been shown to be associated with severity of head injury and to correlate with neurological condition and clinical outcome. Information regarding impaired CVR and/or lost PAR has been shown to be of prognostic value in treating head-injured patients. The classic method of evaluating cerebral haemodynamic status requires an invasive measurement of cerebral blood flow (CBF) such as the technique of Kety and Schmidt or by the ¹³³Xe inhalation method. Transcranial Doppler ultrasonography (TCD) is a simple and non-invasive method for its assessment. In this study, cerebral haemodynamic status as determined by TCD was compared with that of stable xenon-enhanced cerebral blood flow (XeCBF) which is generally regarded as a gold standard in CBF measurement with minimal complication, suggesting that employing CO₂ and blood pressure challenge with TCD measurement to assess the CVR and PAR in head-injured patients, provides a relatively less invasive method and can be repeated at least daily to assess the cerebrovascular autoregulatory reserve.