Metabolic suppressive therapy as a treatment for intracranial hypertension--why it works and when it fails

Thirty years after its first description metabolic suppressive therapy is still controversial in patients with intractable intracranial hypertension. In this study high dose propofol was used to induce metabolic suppression. The effects on intracranial pressure (ICP) and the cerebral metabolic rates for oxygen and glucose (CMRO2 and CMRGlc) are reported. A total of 28 studies were performed on 14 head injured patients. A Xenon133 cerebral blood flow (CBF) and a CO2-reactivity (CO2R) test were performed prior to induction of metabolic suppression. The following parameters were continuously monitored: EEG, etCO2, SjvO2, ICP, MAP and bilateral MCA flow velocity (VMCA). PCO2 was obtained before and during propofol-induced EEG burst-suppression in arterial and jugular-venous blood. CMRO2, CMRGlc and Metabolic Ratio (MR = CMRO2/CMRGlc) were calculated. MR < 0.6 was defined as relative hyperglycolysis. ICP decreased by 24.1 +/- 29.0% during burst-suppression. Arterial, jugular-venous and etCO2 also decreased. Multiple regression analysis revealed that CO2 was the strongest predictor for ICP. Lower baseline ICP and normal CO2 reactivity were predictors for normal metabolic suppression reactivity. In studies with normal metabolic ratio, ICP reduction was associated with a reduction in CMRO2. In studies with hyperglycolysis, ICP reduction was poor but CMRGlc decreased significantly. In conclusion, intact CO2R, normal or only moderately elevated ICP and normal MR are predictive of ICP reduction with high dose propofol after head injury.