Treatment of Methanol and Ethylene Glycol Poisoning: METHODS
Experimental Design
For this retrospective study, patients admitted to The Ottawa Hospital—General Campus, an adult tertiary-care hospital, for methanol or ethylene glycol poisoning between January 1995 and February 2002 were identified by screening the hospital’s medical records for specified codes from the International Classification of Diseases, 9th revision, and their medical records were reviewed. The study was approved by the Research Ethics Board of The Ottawa Hospital.
Patients
Patients were defined as having methanol poisoning if they had an initial serum concentration of methanol of at least 6.2 mmol/L or 2 of the following laboratory findings: arterial pH less than 7.3, serum bicarbonate concentration less than 20 mmol/L, or serum osmolal gap greater than 10 mmol/kg.
Patients were defined as having ethylene glycol poisoning if they had an initial serum concentration of ethylene glycol of at least 3.2 mmol/L or 3 of the following laboratory findings: arterial pH less than 7.3, serum bicarbonate concentration less than 20 mmol/L, serum osmolal gap greater than 10 mmol/kg, or oxaluria.
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All patients had to have received at least 6 h of IV ethanol therapy. At the Ottawa Hospital, the ethanol infusion is administered intravenously as a 10% volume/volume solution in 5% dextrose in water.
Outcome Measurements
The study had 2 main objectives: to determine the effectiveness of IV ethanol therapy in cases of methanol or ethylene glycol poisoning and to evaluate the safety of IV ethanol therapy. To evaluate effectiveness, survival to hospital discharge was determined. In addition, visual impairment in association with methanol poisoning and changes in renal function in association with ethylene glycol poisoning were assessed. Visual disturbances secondary to methanol poisoning were based on any documentation in the medical record of a change in visual acuity at the time of hospital discharge. Renal dysfunction was defined as elevation in serum creatinine concentration above the upper limit of normal (106 pmol/L) at any time during the hospital stay in patients with no known prior renal dysfunction or an absolute increase in serum creatinine concentration of greater than 100 pmol/L in patients with prior renal dysfunction. Serum creatinine concentration and the requirement for dialysis at discharge were noted. As a secondary outcome measure, the appropriateness of dosing relative to current guidelines (Table 1) was assessed. Doses were considered appropriate if within 15% of those recommended by the guidelines. Safety was assessed by determining the occurrence and incidence of hypoglycemia, defined as serum glucose concentration less than 4 mmol/L during infusion of ethanol.
Table 1. Guidelines for Ethanol Dosing in Methanol or Ethylene Glycol Poisoning
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The frequency of rate changes during the ethanol infusion, the total number of determinations of serum ethanol concentration, and the proportion of these that were greater than the target of 22 mmol/L during IV ethanol infusion were assessed. These variables were chosen to evaluate the appropriateness of ethanol dose selection and the intensity of laboratory monitoring.
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