Extracorporeal techniques in the treatment of poisoned patients.

The role of haemodialysis, haemoperfusion and haemofiltration in the management of poisoned patients is reviewed in light of 15 years' clinical experience. During haemodialysis, blood is pumped across a semipermeable membrane (dialysis) through which the compound diffuses and, during haemoperfusion, through a cartridge that contains activated charcoal to which the compound is adsorbed. During haemofiltration, the constituents of blood that have a relative molecular mass which is below the cut-off point of the hollow fibre membrane (usually less than 40,000) are extracted. Haemofiltration is indicated particularly for aminoglycoside toxicity. The clearance by these three procedures depends on the physicochemical characteristics and kinetics of the toxic compound. In general, if a compound is adsorbed by charcoal, the clearance by haemoperfusion will be higher than that achieved by haemodialysis. Similarly, if a compound is amenable to removal by haemodialysis, its clearance will be greater than that achieved by haemofiltration. The indications for extracorporeal elimination depend on the clinical severity and complications of the overdose, the characteristics of the individual patient and the nature, dose and plasma concentrations of the toxic substance. It is generally accepted that extracorporeal elimination is worthwhile if it increases total body clearance by 30% or more. It has little or no value for intoxication caused by chloroquine, flecainide, methotrexate, paraquat, quinine, and tricyclic antidepressants. The complications of extracorporeal elimination which are encountered most frequently are: hypotension; blood loss; haematomas; metabolic disequilibria; mechanical problems such as air embolism; and, in the case of haemoperfusion, hypocalcaemia, thrombocytopenia and leukopenia. In practice, the compounds for which extracorporeal elimination is used most frequently are the alcohols, lithium and salicylate (haemodialysis) and theophylline (haemofiltration).