see also: [[Methemoglobinemia]] [bear carbon monoxide poisoning weaver criteria](bear://x-callback-url/open-note?id=586EF3E3-401A-4B3E-AC4B-A60C9C1F110A-1261-00000065AFCA009D&header=carbon%20monoxide%20poisoning%20weaver%20criteria) > [!important] Key Points > - **risk_dose**:: >25% carboxyhb > - **Antidote**:: 100% O2 8h (24 if preg), +/- hyperbaric O2 if risk factors > - **key_points**:: higher affinity of Hb than O2, prevents O2 offloading, **colourless and odorless** deaths usually pre-hospitally can be ==accidental exposure== eg furnace, etc # Risk assessment - Age >55 * COHb >25% ; half-life 74 min on 100% O2; 320 min on air * outcome is poorly correlated with carboxyhaemoglobin level * LOC or coma * cerebellar signs * Persistent neuro dysfunction * metabolic acidosis * Myocardial ischema * Pregnant * foetal hb binds CO more avidly, rendering foetus more susceptible to CO poisioning ![[Pasted image 20230712005308.png]] # Toxic Mechanism - Carbon monoxide has 210 times the affinity for haemoglobin than oxygen. Binding therefore renders haemoglobin oxygen transport less effective. Hypoxia results. - CO binds to intracellular cytochromes. - CO initiates endothelial oxidative injury, lipid peroxidation and an inflammatory cascade. This process is probably responsible for the delayed neurological sequelae. ## toxicokinetics The *elimination half-life* of carboxyhaemoglobin (COHb) is determined by the dissolved oxygen tension of the blood and varies as follows: • Room air: 240 min • 100% oxygen: 90 min • 100% oxygen at three atmospheres: 23 min. # Clinical features ==most patients present with headache, nausea, and varying degrees of altered mentation, which rapidly resolves with oxygen therapy == history of transient LOC is common CNS - headache, nausea, dizziness - confusion, poor concentration - ataxia - seizures/coma Cardio - tachy and HTN - ischaemic ECG changes - hypotension - dysrhythmias - AMI Resp - non-cardiogenic pulm oedema Metabolic - [[lactic acidosis]] - rhabdo - hyperglycemia Other - DIC - bullae, aloppecia, sweat gland necrosis - # Treatment - 100% oxygen or high flow until all symptoms have resolved and for at least 8 hours - pregnant patients receive 100% oxygen for 24 hours while fetal well being is assessed - hyperbaric oxygen may be indicated in higher risk patients **NRB vs hyperbaric** *NRB* - effectively reduces T1/2.  easy to apply immediately.  but only delivers 60% FiO2 really, and relies on patient's ventilation and patent airway. *hyperbaric O2* - maximal reduction in T1/2 of CO Hb.  possible improvement in long-term neurologically outcome; large retrospective cohorts show small survival benefit. # Disposition - ALOC or cardiovascular instability → HDU / ICU - normal conscious state AND COHb <5% after 6 hours of O2 → discharge if otherwise mentally well