EVALUATION OF THE TRANSIENT HYPEREMIC RESPONSE TEST IN HEAD-INJURED PATIENTS

The transient hyperemic response test has been shown to provide an ind ex of cerebral autoregulation in healthy individuals and in patients w ho have suffered a subarachnoid hemorrhage. In this study, the test wa s applied to patients who had received a severe head injury, and the v alue of the test was assessed by comparing its result with the individ ual's clinical condition (Glasgow Coma Scale [GCS] score), cerebral pe rfusion pressure (CPP), transcranial Doppler wave form-derived index f or cerebral autoregulation (relationship between the CPP and the middl e cerebral artery flow velocity), and outcome (Glasgow Outcome Scale [ GOS] score). Forty-seven patients, aged 16 to 63 years, with head inju ries were included in the study. Signals of intracranial pressure, art erial blood pressure, flow velocity, and cortical microcirculatory flu x were digitized and recorded for a period of 30 minutes using special computer software. Two carotid compressions were performed at the beg inning of each recording. The transient hyperemic response ratio (THRR : the ratio of the hyperemic flow velocity recorded after carotid rele ase and the precompression baseline flow velocity) was calculated, as was the correlation coefficient Sr used to describe the relationship b etween slow fluctuations in the systolic flow velocity and CPP through out the period of recording. No significant changes in CPP were found during compression. There was a significant correlation between the TH RR and the Sr (r = 0.49, p < 0.0001). The hyperemic response proved to be lower in patients who exhibited a poor clinical grade at presentat ion (GCS scores < 6, p = 0.01) and lower in patients achieving a poor outcome (GOS scores of 3, 4, and 5, p = 0.003). Loss of postcompressio n hyperemia occurred when the CPP fell below 50 mm Hg. The carotid com pression test provides a simple index of cerebral autoregulation that is relevant to the clinical condition and outcome of the severely head injured patient.