Hovda et al used the anion and osmolal gaps to guide management of a patient with methanol poisoning. The authors are from Ullevaal University Hospital and Ostfold Central Hospital in Norway.
Molecular weight of methanol: 32.04 g
Molecular weight of formic acid: 46.03 g
Parameters:
(1) anion gap in mmol/L
(2) osmolal gap in mOsm per kg water
Anion Gap |
Osmolal Gap |
Status |
Management Steps |
---|---|---|---|
<= 20 |
<= 25 |
subtoxic |
A, B |
<= 20 |
> 25 |
early toxic |
B, C, D, F |
> 20 |
<= 25 |
late toxic |
B, C, D, E, F (if visual disturbances present) |
> 20 |
> 25 |
intermediate toxic |
B, C, D, E, F |
A: Observe
B: Monitor blood gases.
C: Administer bicarbonate if in metabolic acidosis
D: Administer antidote (fomepizole)
E: Administer folinic acid.
F: Consider hemodialysis
The authors also correlated serum methanol and folate levels with osmolal and anion gaps, respectively.
osmolal gap in mOsm per kg water =
= (1.03 * (serum methanol in mmol/)) + 12.71
If this is converted to mg/dL
osmolal gap in mOsm per kg water =
= (0.3215 * (serum methanol in mg/dL)) + 12.71
anion gap in mmol/L =
= (1.12 * (serum formate in mmol/L)) + 13.82
If this is converted to mg/dL
anion gap in mmol/L =
= (0.2433 * (serum formate in mg/dL)) + 13.82
Purpose: To evaluate a patient with methanol poisoning using the algorithm of Hovda et al.
Specialty: Toxicology, Emergency Medicine, Critical Care, Ophthalmology
Objective: severity, prognosis, stage, overdose and reversal
ICD-10: T57.1,