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.