CARBON MONOXIDE POISONING

Transcription

1 CARBON MONOXIDE POISONING Matthew Valento, MD Assistant Professor, UW Department of Emergency Medicine Washington Poison Center Carbon monoxide (CO) Incomplete combustion of carbon-containing compounds Odorless, colorless, tasteless Leading cause of poisoning morbidity and mortality Faulty furnaces Burning of charcoal, wood, natural gas Hanukkah Eve windstorm of

2 Carbon monoxide: pathophysiology Binds to hemoglobin CO binds to hemoglobin with much greater affinity than oxygen Incapable of transporting oxygen Decreased offloading of oxygen to tissue Acute sequelae: tissue hypoxia Oxidative stress Lipid peroxidation, free radical formation, microvascular inflammation, endothelial disruption Delayed neurocognitive effects Thom SR, et al. Neuronal nitric oxide synthase and N-methyl-D-aspartate neurons in experimental carbon monoxide poisoning. Toxicol Appl Pharmacol Feb 1;194(3):

3 Carbon monoxide: clinical presentation Headache, nausea, vomiting, weakness Can be misdiagnosed as flu or viral illness Syncope, chest pain, ataxia, confusion Ventricular dysrhythmia (common cause of death) Delayed neurocognitive effects Memory loss, impaired concentration, depression, parkinsonism Can appear days to weeks post-exposure Can resolve spontaneously or be lifelong Carbon monoxide: diagnosis At the hospital: carboxyhemoglobin (COHgb) measurement Normal : 0-5% Caveat: wide variation in symptoms at various levels Caveat: this number goes down as soon as the patient is removed from the environment! In the field: Portable cooximetry (useful screening tool) Pulse oximetry not reliable (COHgb misinterpreted as oxyhemogloblin) 3

4 Carbon monoxide: management Or: Do all of these patients have to go to Virginia Mason?? Carbon monoxide: management High flow oxygen (NRB mask or ETT) Most cases of CO poisoning can be managed with supportive care and supplemental oxygen!! Displaces CO from hemoglobin Half-life of COHgb from ~5 hours to 1 hour Carbon monoxide: management I repeat: mainstay of therapy is immediate administration of oxygen Any hospital can do this Can be started in the field Treat until COHgb is < 5% 4

5 Hyperbaric oxygen therapy Hyperbaric oxygen: why? HBO is NOT for clearance of COHgb HBO is NOT to save lives or reverse toxicity in severely poisoned patients We use HBO to prevent delayed neurologic effects hopefully 5

6 Hyperbaric oxygen In animals: Accelerates regeneration of cytochrome oxidase Restores mitochondrial function Prevents some elements of microvascular inflammatory cascade In clinical trials: Ehh depends on which study you read!! Hyperbaric oxygen: studies Raphael et al (1989): No benefit detected in HBO group, BUT! Seriously ill patients not randomized to oxygen alone Significant delay to treatment (mean, 7.1 hours) Suboptimal pressures (2.0 ATA) Thom et al (1995): HBO decreased delayed neurologic sequelae from 23% to 0%, BUT! Patients with syncope were excluded Hyperbaric oxygen: studies Scheinkestel et al (1999): No significant difference in outcome between HBO and 100% oxygen groups, BUT! Over 50% lost to follow-up at one month! Disproportionate number of suicide cases (69%) Delayed time to treatment (mean 7.1 hours) Weaver et al (2002): Significant decrease in neurologic sequelae for HBO group (NNT of 5), BUT! Differences only detected in very specific neuropsychiatric testingno difference in ability to perform ADLs Fast time to treatment (< 2 hours!!) 6

7 Hyperbaric oxygen: studies This is an area of some controversy! If you want a paper to support HBO for CO poisoning, you can find several If you want a paper to refute HBO for CO poisoning, you can find several!! Strong animal evidence, relatively safe, but limited supply! Hyperbaric oxygen Underwater and Hyperbaric Medical Society: Recommends HBO for all patients with signs of serious toxicity American College of Emergency Physicians: It remains unclear whether HBO is superior to oxygen alone for prevention of long-term neurologic sequelae Indications for HBO therapy* Syncope / loss of consciousness Coma Seizure Altered mental status Abnormal cerebellar function Prolonged exposure (> 24 hours) Age > 36 years Fetal distress COHgb > 25% * Goldfrank s Toxicologic Emergencies 7

8 My recommendations Immediate removal from environment Immediate administration of high-flow oxygen (NRB) Treat until COHgb < 5% Burn patients should go to a burn center, trauma patients should go to a trauma center, etc. Critically ill patients should go to the nearest hospital My recommendations Not all these patients need to be transported directly to Virginia Mason Patients can be transported to the nearest hospital and triaged from there This includes mass casualty incidents Ideal HBO patient: > 36 y/o with syncope or other neurologic symptoms Medics can discuss this with Medic One doc at Harborview My recommendations Patients with indication for HBO should prompt consideration of this therapy Discuss this with the on-call hyperbaricist at VM Families can go together Neurologic symptoms warrant HBO no matter what the level is! Ideally, patients should be treated within 6 hours of exposure Do not send the patient back into a dangerous environment!! 8