Are changes in intracranial pressure during intermittent machine haemofiltration dependent upon membrane biocompatibility?

We measured the intracranial pressure, using a subdural catheter in three patients admitted with grade 4 hepatic encephalopathy following paracetamol (aminocetaphen) self poisoning. Acute oliguric renal failure was present in all cases and was treated with daily intermittent machine haemofiltration. Hypovolaemia prior to treatment was corrected and a total of 14 isovolaemic 17 litre exchanges carried out using either a Gambro FH77 (8) or Hospal 3600 (6) haemofilter. Intracranial pressure (ICP) increased during treatment with both types of filter, but the increase was greater in the Gambro FH77 treated group, mean ICP increased from 7.6 +/- 2 mmHg to 12 +/- 3 mmHg at 3 hours (p less than 0.05), this was associated with a greater fall in the percentage change from the pretreatment value of both arterial oxygen tension and total peripheral white blood cell count during the first hour of treatment compared to the Hospal 3600 treated group, 8 +/- 2% vs 1 +/- 2% (p less than 0.05) and 5 +/- 2% vs 3 +/- 2% (p less than 0.05). This suggests that membrane biocompatibility may also play a role in the development of increased intracranial pressure during intermittent machine haemofiltration.