Use of the osmolal gap to guide the start and duration of dialysis in methanol poisoning

Abstract

Rapid diagnosis and treatment of methanol poisoning is mandatory. Dependence on serum methanol analysis in this situation may delay diagnosis and treatment. The anion and osmolal gaps have been recommended for use as diagnostic tools, but the use of these gaps to evaluate the length of hemodialysis treatment has only been emphasized in a few reports. We evaluated the usefulness of the osmolal gap in estimating the need for dialysis and the duration of this treatment in 17 methanol-poisoned subjects. Patients were part of a recent outbreak of methanol poisoning, in which the diagnosis upon admission was mainly based on use of the anion and osmolal gaps. The duration of dialysis generally followed the standard recommendation of 8h. During dialysis, blood samples were frequently collected and analyzed to determine acid-base status and serum methanol and to calculate the osmolal gap. In nine patients, the duration of dialysis was compared with the duration necessary to normalize serum methanol and the osmolal gap. There was a good correlation between serum methanol and the osmolal gap during hemodialysis (y=1.09x+3.82; R(2)=0.92). The osmolal gap therefore gives a good estimate of the serum methanol level during hemodialysis, and could have saved a total of 23 h of dialysis treatment (34%) in nine patients had it been applied. In the absence of serum methanol analyses, the osmolal gap is useful to assess the indication for and duration of hemodialysis in methanol-poisoned patients. In mass poisoning situations, use of the osmolal gap makes it possible to reduce the duration of dialysis in a safe manner.