Methanol toxicity: Difference between revisions
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****Only parent alcohol is osmotically active | ****Only parent alcohol is osmotically active | ||
****Delayed presentation may mean that much of it is already metabolized | ****Delayed presentation may mean that much of it is already metabolized | ||
*Toxic alcohol levels | *Toxic alcohol levels - Methanol | ||
**<20 mg/dL - asymptomatic | **<20 mg/dL - asymptomatic | ||
**>20 mg/dL - CNS symptoms may appear | **>20 mg/dL - CNS symptoms may appear |
Revision as of 02:39, 22 April 2015
Background
- Found in antifreeze, windshield washer fluid, solvents
- Colorless, volatile liquid with distinctive “alcohol” odor
- Parent compound causes only mild inebriation; metabolite (formic acid) causes toxicity
- Binds to cytochrome oxidase > blockade of oxidative phosphorylation > lactic acidosis
- Most exposures from ingestion; may be systemically absorbed after inhalation or dermal exposure but rarely causes significant clinical toxicity
Clinical Features
- Symptoms begin 12-24hr after ingestion (may occur even later if ETOH is co-ingested as EtOH competes with alcohol dehydrogenase and has greater affinity for the enzyme than methanol)
- CNS depression
- Confusion, ataxia, depressed mental status, seizure
- Less inebriating than ethanol or ethylene glycol
- Visual disturbances (50% of pts)
- Development may precede or parallel that of other clinical symptoms
- Cloudy or blurry vision ("stepping out into a snowstorm")
- Anion-gap acidosis
- May be severe (bicarb < 5, pH < 7)
- Compensatory tachypnea
- CVS
- Tachycardia
- Hypotension --> can progress to shock
- RESP
- Tachypnea
- SOB (compensating for metabolic acidosis) --> may progress to respiratory depression and/or failure
- GI
- Abdo pain
- N/V
- Anorexia
- Pancreatitis and gastritis
- Transaminitis (transient)
- CNS depression
Work-Up
- Chemistry
- Anion gap acidosis
- Serum Osm
- Osm gap (measured - calculated)
- Calculated serum osm = 2Na + BUN/2.8 + glucose/18 + ethanol/4.6
- Normal is < 10
- Note: Cannot rule out toxic ingestion with a "normal" osmol gap
- Only parent alcohol is osmotically active
- Delayed presentation may mean that much of it is already metabolized
- Osm gap (measured - calculated)
- Toxic alcohol levels - Methanol
- <20 mg/dL - asymptomatic
- >20 mg/dL - CNS symptoms may appear
- >50 mg/dL - ocular problems
- >150-200 mg/dL - risk of fatality
- Ethanol level
- VBG
Treatment
- ADH enzyme blockade
- Fomepizole
- Indications:
- Ethylene glycol level >20mg/dL
- Suspected significant ethylene glycol ingestion w/ ETOH level <100mg/dL
- Coma or AMS in pt w/ unclear history and osm gap >10
- Coma or AMS in pt w/ unclear history and unexplained met acidosis and ETOH level <100
- Dosing
- 15mg/kg IV over 30min; follow by 10mg/kg q12hr until level <20 or acidosis resolves
- Indications:
- Ethanol
- BAL of 100-150 completely saturates alcohol dehydrogenase
- IV: load 800mg/kg; then give 100mg/kg/hr
- Oral: 3-4 1-oz "shots" of 80-proof liquor); then give 1-2 "shots" per hour
- Fomepizole
- Correction of metabolic acidosis with bicarbonate
- Bicarbonate 1-2mEq/kg IV bolus to attain pH = 7.45-7.50
- Follow by infusion of 150mEq/L in D5 @ 1.5-2x maintenance fluid rate
- Monitor for worsening hypocalcemia
- Bicarbonate 1-2mEq/kg IV bolus to attain pH = 7.45-7.50
- Dialysis
- Indications:
- Refractory metabolic acidosis (pH <7.25) w/ AG >30
- Renal insufficiency
- Visual symptoms
- Deteriorating vital signs despite aggressive supportive care
- Electrolyte abnormalities refractory to conventional therapy
- Methanol level >50mg/dL (controversial)
- Indications:
- Enchanced formic acid metabolism
- Folinic acid 50mg IV q4hr
See Also
Source
- Rosen's
- Tintinalli