Toxicological Coma

Introduction

• Coma is a manifestation of many different agents
• Must consider:
  • Direct toxic effects on CNS
  • Secondary effects on CNS e.g. hypoxaemia, hypoglycaemia, hyponatraemia, hypotension, seizures or cerebral oedema
  • Alternative non-toxicological causes e.g. ICH, metabolic encephalopathy, neurotrauma or meningo-encephalitis

Primary neurological agents

• Alcohols – Ethanol, ethylene glycol, methanol, isopropyl alcohol
• Antipsychotics – Amisulpride, chlorpromazine, clozapine, olanzapine, quetiapine
• Anticonvulsants – Carbamazepine, Lamotrigine, valproic acid
• Antidepressants – SSRI’s, TCA’s
• Antihistamines – Diphenhydramine, promethazine
• Antimalarials – Chloroquine, quinine
• Baclofen
• Beta-blockers – Propranolol

Primary neurological agents

• Central alpha-2 agonists – Clonidine
• Cholinergics – Carmabates, acetylcholinesterase inhibitors e.g. donepezil, nicotine, organophosphates
• Hydrocarbons – Essential oils, toluene
• Local anaesthetics
• Mushrooms of Gyromitra species
• NSAID’s
• Opioids
• Sedative-hypnotic agent

Secondary neurological agents

• Cerebral oedema – Salicylates, valproic acid
• Hypoglycaemia – Insulin, beta-blockers, sulfonylureas
• Hypotension – CCB, glycosides, beta-blockers
• Hypoxaemia
  • Methaemoglobinaemia, CO, cyanide, hydrogen sulfide
• Neuroleptic malignant syndrome – Antipsychotics
• Seizures – Bupropion, propranolol, isoniazid, tramadol, venlafaxine, TCA
• Serotonin syndrome – MAOi, SSRI, SNARIs

Risk assessment

• Must diagnose:
  • Non-toxicological causes of coma
    • ABG, Chem20, head CT, LP, blood/urine cultures, EEG
  • Complications of coma
    • Pulmonary aspiration, rhabdomyolysis, AKI, compartment syndromes, pressure areas, hypoxic brain injury
    • Need ABG, Chem20, CK, CXR
  • Specific toxicities that require specific interventions
    • Screening ECG, BSL, paracetamol level
    • ABG, anion gap, lactate, osmolarity and osmolar gap
    • Specific drug levels: Carbamazepine, ethanol, ethylene glycol, methanol, salicylate, valproic acid, phenobarbitone

Agents causing coma that need specific intervention

• Carbamazepine: Multi-dose activated charcoal +- haemodialysis
• Isoniazid: Pyridoxine
• Opioids: Naloxone
• Organophosphate: Atropine and pralidoxime
• Phenobarbitone: MDAC and haemodialysis
• Salicylate: Haemodialysis
• Sulfonylureas: Dextrose and octreotide infusion
• Toxic alcohols: Ethanol/fomepizole +/- haemodialysis
• Valproic acid: Haemodialysis

Last Updated on October 13, 2020 by Andrew Crofton