Changes in cerebral interstitial glycerol concentration in head-injured patients; correlation with secondary events

To investigate the association between the occurrence of secondary events, clinical outcome and the interstitial glycerol levels as measured with cerebral microdialysis.

All patients received a ventriculostomy, a Camino pressure sensor and a CMA 70 microdialysis catheter. Intracranial pressure (ICP), cerebral perfusion pressure (CPP), blood pressure and arterial oxygen saturation (SaO2) were continuously monitored. Hourly microdialysis samples were collected and glycerol concentrations analyzed on-line. Glasgow Coma Score (GCS) scoring, blood gas and other laboratory analyses or investigations followed the routine of the intensive care unit. The Glasgow Outcome Scale (GOS) was assessed 6 months after injury.

Intensive Care Unit and Department of Neurosurgery, VU University Hospital.

Fifteen consecutive patients with severe traumatic brain injury and a GCS of 8 or less.

No association was found between low CPP, high ICP, low PaCO2, low SaO2 or rise in temperature and the level of interstitial glycerol. In patients with a favorable outcome, the glycerol concentration never reached a level above 150 micromol/l, whereas a peak glycerol level above 150 micromol/l had a positive predictive value of 100% for an unfavorable outcome. The average of the area under the curve during the first 24 h of monitoring was significantly higher in the group with an unfavorable outcome (Kolmogorov-Smirnov test, p=0.044).

Measuring interstitial glycerol for early detection of secondary adverse events, which possibly lead to secondary brain damage, does not seem useful. A peak level of interstitial glycerol above 150 micromol/l has a positive predictive value of 100% for an unfavorable outcome and hence indicates the severity of the parenchymal damage.