Determining cerebral perfusion pressure thresholds in severe head trauma

Laboratory studies suggest the pulsatile component of the transcranial doppler (TCD) waveform may be useful in determining lower autoregulatory threshold. This study aimed to assess the effect of increasing CPP on jugular bulb oximetry (SjO2) and middle cerebral artery (MCA) TCD flow velocities in the early management of severe head injury. 16 severely head injured patients (GCS < or = 8), had intracranial pressure (ICP), mean arterial pressure, SjO2 and MCA Doppler velocity monitored continuously. CPP was increased by intravenous fluids (right atrial pressure approximately equal to 10) and supplemented with adrenaline infusion until TCD pulsatility (Gosling pulsatility index [PI] reached a plateau. The mean CPP at which SjO2 surpassed 55% was 62 +/- 6.2 mm Hg. TCD PI did not plateau until a significantly higher mean CPP of 74 +/- 5.1 mm Hg was achieved (p < 0.01). In 8 cases, increased CPP was associated with a fall in ICP, ranging from 1 to 8 mm Hg. We conclude that a critically low level of SjO2 is a late indicator of failed autoregulation. CPP values associated with intact autoregulation identified by TCD assessment of MCA flow are significantly higher than those indicated by SjO2 monitoring. MCA Doppler flow assessment may be useful in determining the level of CPP at which therapy should be aimed in the early resuscitation of head trauma.