Toxic alcohols Flashcards
Discuss risk assessment for ETOH intoxication
ETOH ingestion causes rapid dose dependent CNS depression with a high degree of inter-individual variability
Dose may be estimated if the number os standard drinks is known (10g ethanol in a standard drink)
Co-ingestion of other CNS depressants increases the risk of respiratory depression
Discuss Toxicokinetics of ETOH
Rapidly absorbed following oral administration - distributes readily to total body water (VD 0.6Lkg)
ETOH is oxidised by cytosolic and microsomal alcohol dehydrogenases to form acetaldehyde which in turn is metablised by aldehyde dehydrogenase to acetate. Both steps incolve the reduction of NAD to NADH
It is metabolised by zero order kinetics – in most cases decrease by approximatly 4mmol/l/hour
The production of NADH decreases conversion of lactate to pyruvate and inhibits gluconeogenesis and fatty acid oxidation
Discuss sources of ethylene glycol and risk assessment of same
Used for two main purposes as a raw material in the manufacture of polyester fibers and for antifreeze formulations.
Ingestion of >1ml/kg is potentially lethal
-all deliberate self poisoning are assumed to be potentially lethal
-Unintenional infegestion of less than a mouthful is benign and dose not require hosptial evaluation
-Coingestion can complicate risk assessment
Demral and inhalation exposures does not lead to EG intoxication
Discuss toxic mechanisms of ethylene glycol
Causes CNS effects similar to those seen with ETOH – the more important toxic effects are due to metabolites rather that the parent compound
Severe HAGMA develops secondary to accumulation of glycolic acid and lactate
Calcium oxalate crystals form in tissues including the renal tubules, myocardium, muscles and brain. Hypoglycaemai follows due to increase in NADH
ACute oliguric renal failure occurs secodnary to the nephrotoxic effects of both glycolic acid and clacium oxalate
Discuss toxicokinetics of EG
Rapidly absorbed following ingestions - peak concentrations occur within 1-2 hours
VD across the total body water with rapid CNS penetration
It is metabolised subsequently by alcohol dehydrogenase and aldehyde dehydrogenase into glycoaldehyde and glycoclic acid which in turn is converted into glyoxylic acid and oxalic acid
In the absence of ethanol or fomepizole the elimination half life is 3-9 hours. In the present of ethanol which competitively inhibits ADH elimination half life is extended to 14-17 hours
EG is eliminated exclusively by the kidney
Discuss clinical features of EG intoxications
Clinical course is often described in three stages (CNS, cardiopulmonary and renal) but these are artificial descriptions of a rapid clinical course
-Initial clinical features develop within the first 1-2 hours and are similar to those of ETOH intoxication
Progressively severe features develop over the subsequent 4-12 hours
-dysponoea , tachypnoea, tachycardia, hypternsion and decreased LOC progressing to shock coma, seizure and death
Flank pain and oliguira indicate acute renal failure
Late cranial neuropathies involving CN 2,5,7,8,9,10 and 12 are described up to 5-20 days later
Discuss invesitgations in EG
ECG, BGL and paracetamol level
EUC, serum lactate, serum osmolalatiy, arterial blood gases and CMP are all needed
- Elevated osmolar gap , HAGMA and hyperlactaemia are all indicators of intoxication
- HAGAM with lactaemia, +- osmolar gap and hypocalcaemia is pathognomic of EG intoxication
- Elevated serum lactate must be interpreted with care as some lab assays do not differentiate between glycol ate and lactae
Urine microscopy - presence of oxalate crystals in the urine is pathognomonic of ethylene glycol intoxication
Discuss Resus of EG intoxications
ABCD
- If patient requiring intubation attention needs to be taken to ensure adequate respiratory rate is maintained as these patient are often significantly acidotic and require ventilatory compensation
- Can consider bicarb bolus if concerned acidosis is worsening n
Detect and correct hypoglycaemia, hyperkalaemia and hypomagnesaemia - only correct hypocalcaemia if there is refractory seizures or prolonged QT
Discuss DEAD of EG intoxications
D - GIT decontamination is not idnicated
E: - HD is the definitive magnement of EG intoxication - during HD elimination halflife is reduced to 2.4-3.5 hours
-lactate free dialysates with added bicarb may assist correction of acidaemia
-Indications for HD
—History of large EG infestion with osmlolar gap >10
—Acidaemai with pH<7.3
—Ethylene glycol level >8 mmol/L
End points
- correction of acidosis
-osmolar gap <10
-ethylene glycol level <3.2mmol/l
A- ETOH and fomepizole are used in the treatment of supspected or confirmed EG as a temporising measure while awaiting HD
Discuss Disposition and follow-up
Children who remain well after suspected unintentional ignestion and have a normal venous bicarb level at 4 or more hours post ingestion may be discharged
Adutls who remain clinically well after accidental ingfestion and have a normal venous bicarb level at 4 hours are fit for discharge
All symptomatic patients and those with deliberate ingestion are assumed ot have potentially lethal intoxication and are admitted to hospital for further evaluation
Normal osmolar gap dose not exlcude intoxication, absence of symptoms dose not exclude signifiacnt ingestion
-Care if ADH is blocked by ETOH symptoms may be delayed in onset
Discuss sources of and risk assessment of isopropanol (isopropyl alcohol)
Sources: hand sanitisers, disinfectants, solvents window cleaners and perfumes.
Risk assessment
- Causes dose related CNS depression
- As little as 1ml/kg of a 70% solution causes symptoms of inebriation and more than 4ml/kg may cause coma and respiratory depression
- Children - minor ingestions such as a taste or a lick do not require evaluation unless symptoms develop >3ml are associated with symptoms and should be monitored. Significant toxicity has been reported from dermal absorption following application of rubbing lacohol to small children as an antipyretic measure
Discuss toxic mechanisms of isoprolyl alcohol
Augmentation of the GABAa receptor complex is thoguht to be central to effects. Production of acetone and severe ketonaemia may contribute to CNS depression
Severe HAGMA is not a feature of isopropanol intoxication as acetone is not further metabolised to any great extent
It is a GIT irritant and causes dose-dependant CVS depression
Discuss toxicokinetics of isopropanol
Rapidly and well absorebed following ingestion, dermal contact or inhalation.
VD to total body water 0.6L/Kg
40% of the absorbed dose is excreted unchanged by the kidney and lungs, the remainder is metabolised by hepatic ADH to form acetone. Acetone is excreted mostly unchagned by the lungs and less extent kidneys
Affinity of ADH for isopropyl alcohol is much less compared to ETOH and elimination Half life is correspondingly much slower if coingestion occurs
Discuss clinical features of isoproyl alcohol
Intoxication syndrome indentical to ethanol develops
The duration of inebriation is longer than following ethanol
Ketosis may be indicated by the breath odour of acetone
Discuss invesitgations of isoproyl alcohol
ECG, paracetmaol, BSL
Osmolar gap in the absence of significant HAGMA indicates isopropyl alcohol intoxication
Discuss management
ABCD
DEAD is not indicated
– HD very effective but supportive care adequate
Discuss source and risk assessment of methanol
Source
- Carburettor cleaning lfuid
- Chemical applications in industry
- Solvent in thinners, varnishes paints and enamels
- Model aeorplane and car fuel
- Feul additive
- Dyes and stains
- Wood alcohol and spirits
Ingestion of >0.5ml/kg of 100% methanol is potentially lehal
Dermal or inhalational exposures is unlikley to led to methanol intoxication although it sis reported in the context of inhalational solvent abuse
Discuss toxic mechanisms of methanol
Production and accumulation of formic acid produces a severe anion gap acidosis and direct cellular toxicity due to inhibition of cytochrome oxidase. Retinal injury and edema leads to blindness
In the brain subcortical white matter haemorrhages and putamenal oedema classicaly occur
Late Hyperlactataemia occurs due to inhibitoin of cellular oxidative metabolism
Discuss toxicokinetics of methanol
Rapidly absorbed with peak levels occuring within 30-60minutes.
Rapid distribution across total body water
Metabolised in the liver by alcohol dehydrogenase to formaldehyde which in turn is metbaolsed to formic acid
Elimination hlaf life is 24 hours
ETOH concentration of 22mmool/l competitievily inhibts ADH so that mehtanol cannot be metabolised to formaldehyde
Methanol elimination half life increases to 48 hours as methanol is exclusively eliminated via the kidney and pulmonary routes
Discuss clinical features of methanol intoxication
Mild CNS intoxication is evident within 1 hour of ingestion - nausea vomitng and abdominal pain may ocur
Following a latent period of 12-24 hours symtpoms of headahce, dizziness, vertigo, dyspnoea, blurred vision and photophobia develop
Sever intoxication include tachypnoea, drowsiness and blindness
Progressive obtundation leading to coma and seizures heralds the onset of cerebral oedema - papilloedema is characteristic with progressive demyeliniation and up to 1/3 of patient suffer irreversible visual complicaitons
Discuss investigation for methanol intoxications
HAGMA, hyperlactaemia and elevated osmolar gap are surrogate markers of itnxociation
CT scan demonstrates characteristic ischaemic or haemorrhagic injury ot the basal ganglia in patient with permanent neurogloical sequalae
+ the same as the other toxic alcohols
Discuss resus of severe methanol intoxications
A: - if indicated need to set adeqaute resp rate to maintain compensation for HAGMA
-reduced PH below 7.30 augments formic acid inhibition of cytochrom oxidase – if below 7.3 administer 50mmol aliquots of bicarb to raise the ph
Treat seizures, hypoglycaemia
Folic acid is given at 50mg IV 6 hourly and continued until poisoning is definitively treated
Discuss DEAD of methanol intoxication
D: -not indicated
E- HD is the definitive management of methanol intoxication
-indication same as for ethylene glycol
Antidoes - ETOH and fomepiazole
Discuss risk assessment of hydrocarbons
Hydrocarbons include (petroleum, toluene, essential oils, kerosene)
Whether ingested or inhaled can cause rapid onset of CNS depression, seizures and cardiac dysrhythmias
-Aspiration can lead to chemical pneumonitis
THe major risk following acute ingestion are early CNS depression and seizures. For most petroleum distillates more than 1-2ml/kg is required to cause signicicant systemic toxicity
Ingestion of as little as 10mls of eucalyptus oil or other essential oil may lead to CNS depression and seizures always wihtin 1-2 hours.
High viscosity compounds (motor oil, petroleum jelly) have very low risk of systemic toxicity or chemical pneumonitis
CHildren
-ingestion of 5mls of eucalyptus oil or other essential oils is associated with rapid onset of coma
