A simple method to estimate the required dialysis time for cases of alcohol poisoning.
Background
Conventional dialysis management of ethylene glycol and methanol poisoning includes frequent intradialytic determinations of serum toxin concentration. Dialysis is continued until a target toxin concentration is reached. Initially, the required dialysis duration is unknown, making planning difficult. We devised a simple method to estimate the duration of dialysis required and avoid quantitation of multiple toxin samples.
Methods
Using the assumption that toxic alcohols would have a dialysis clearance similar to urea, we proposed that required dialysis time (hours) to reach a 5 mmol/L toxin concentration target would be: [-V ln(5/A)]/0.06k, where V (liters) is the Watson estimate of total body water, A is the initial toxin concentration (mmol/L), and k is 80% of the manufacturer-specified dialyzer urea clearance (mL/min) at the initial observed blood flow rate. Directly measured dialysis and renal toxin clearance, and true dialysis requirement by conventional treatment protocol were compared with our estimate in two methanol and three ethylene glycol poisonings treated with Fresenius F8 dialyzers.
Results
There were no clinically or statistically significant differences between predicted dialysis duration (7.6 ± 1.9 hours, ±SD) and that actually provided using hourly toxin concentration sampling (7.4 ± 1.9 hours). Renal toxin clearance was negligible compared to that of dialysis, and predicted dialysis clearance did not differ significantly from that observed.
Conclusions
The simple estimate method is sufficiently valid to guide the prescription of dialysis for toxic alcohol poisoning. Data required at dialysis start include only the initial toxin concentration, dialyzer manufacturer's specified urea clearance at initial observed blood pump speed, and patient demographics to estimate total body water. This approach allows for planned dialysis therapy, without the need for additional toxin concentration measurements until dialysis is completed.
