Propofol and hyperventilation for the treatment of increased intracranial pressure in rabbits

Using a rabbit model of intracranial hypertension, we studied (a) the additive effect of propofol and hyperventilation (HV) on increased intracranial pressure (ICP), (b) the ICP-lowering effect of additive therapy (i.e., propofol plus HV versus HV plus propofol), and (c) whether combined therapy induced cerebral ischemia. Twenty-three New Zealand White rabbits were studied, of which seven were control animals. The animals were anesthetized with midazolam and fentanyl. An extradural balloon was used to increase ICP to 26+/-2 mm Hg. Elevation of ICP resulted in a >50% reduction in ipsilateral somatosensory evoked potential (SEP) amplitude. The rabbits were then randomized to be treated with propofol followed by HV (Group 1, n = 8) or HV then propofol (Group 2, n = 8). With HV, PaCO2 was reduced from 41+/-2 mm Hg to 27+/-3 mm Hg. In Group 1 rabbits, the ICP decreased with treatment (from 26+/-2 to 12+/-2 mm Hg). The reduction in ICP was significantly greater (P = 0.008) than that in Group 2 rabbits (from 26+/-2 to 16+/-5 mm Hg). In both groups, propofol and HV had an additive effect in reducing ICP. Further, when propofol was used as the initial treatment, there was a significant increase in SEP amplitude that was not apparent in Group 2 rabbits. In conclusion, we found propofol and HV to be additive in the treatment of increased ICP. In animals treated with propofol followed by HV, there was a greater decrease in ICP than in rabbits treated initially with HV and then propofol.

We have demonstrated that propofol has a greater effect on increased intracranial pressure than hyperventilation when used as the initial treatment and that the two treatments are additive. Should control of intracranial pressure be required after the administration of propofol, then hyperventilation may be added to the treatment.