Tox in The Land: Carbon Monoxide
Carbon Monoxide Poisioning
It is a silent killer due to its colorless, odorless and tasteless properties
Formed by an incomplete combustion of anything containing carbon
Why do we need to know about this?
Per the CDC:
~50,000 ED visits yearly are contributed to CO exposures
430 deaths in the US each year from accidental exposures
Pathophysiology
-Tissue Hypoxia-
Rapidly absorbed via inhalation
Primarily in blood bound to hemoglobin
200-250x greater affinity
Up to 15% of total body CO content is taken up by tissue bound to myoglobin
Left shift on oxyhemoglobin dissociation curve
-Inflammatory Cascade-
Carbon monoxide does two things:
Releases nitrous oxide —> endothialial damage
At the same time: Impaired cardiac function due to hypoxia —> altered cerebral blood flow
WBCs interact with damaged endothelium -> brain lipid perioxidation —> inflammation
CLINICAL PRESENTATION
-Exposure-
Where?
Motor vehicle exhaust
Truck beds/boats
Propane powered equipment indoors
Burning charcoal, wood, or natural gas for heating/cooking
Gas kitchen stoves
Gasoline powered generators
Methylene chloride
When?
Seasonal
>1/3 cases occurring in winter
Clustered around natural disasters or power failures
Everyone in the family got sick… on the same day (even the dog!)
-Signs & Symptoms-
Early symptoms: flu like illness
Most common symptom: dull, frontal headache
Can be misdiagnosed as a viral syndrome
Physical exam:
Cherry red skin?
Really only postmortem
Retinal hemorrhages
Bullous lesions
Secondary to prolonged immobility
Neuro: focal neurologic deficits, ataxia, confusion
-Cardiotoxicity-
Oxygen deficiency in the heart —> chest pain, dyspnea, syncope
Acute mortality typically due to ventricular dysrhythmia
Severe cases can lead to myocardial stunning àdecreased LVEF
Troponin elevations with or without EKG changes or CAD
-Neurotoxicity-
Acute Neurotoxicity:
Varied headache, confusion to seizures, focal deficits, and coma
Delayed Neurologic Sequelae:
Cognitive impairment, affective disorders
Can occur 4-5 weeks after exposure
Risk factors:
Prolonged exposure
GCS <9
Seizures at time of presentation
Leukocytosis
DIAGNOSIS & TESTING
-Diagnostic Criteria-
History of exposure
Symptoms consistent with exposure
Elevated COHb
Level does not always correlate with severity depending on timing of presentation
-Testing-
Carboxyhemoglobin
1-2% in non-smoker
4-10% in active smoker
>10% concerning for exposure
Other labs: ABG/VBG, lactate, CK, troponin, POC glucose
EKG
Imaging: CXR, CT head
TREATMENT
Initial resuscitation with ABCs
100% Oxygen
Hyperbaric oxygen
Remainder is supportive
IVF
Treat traumatic injuries
Avoid hyperthermia due to increased O2 demand
-100% Oxygen-
Half life of COHb
Room air 4-6 hours
100% O2 on non-rebreather 1 hour
Hyperbaric O2 ~20 minutes
Continue until resolution of symptoms and/or COHb <5%
-Hyperbaric oxygen-
Benefits:
Decreased half life
Increases amount of dissolved oxygen 10x
Prevents brain lipid peroxidation and ischemic reperfusion injury
Risks:
Barotrauma
Heart failure
Lack of availability
Human data on benefits is not strong
Per ACEP Clinical Policy: Emergency physicians should use HBO2 therapy or high flow normobaric therapy for acute CO poisoned patients. It remains unclear whether HBO2 therapy is superior to normobaric oxygen therapy for improving long term neurocognitive outcomes. (Level B recommendation)
A Cochrane review from 2011 examined six clinical trials; two were positive trials showing decreased neurologic sequelae, and the remaining four trials failed to demonstrate a benefit. However, all of the studies suffered from various degrees of methodologic flaws, and it was unclear whether hyperbaric oxygen improves long-term neurocognitive outcomes. Two additional trials published since the Cochrane review were negative
Indications (for the boards, real life-use your clinical judgement)
Level > 25%
Level > 15% if pregnant or evidence of fetal distress
CO has a higher affinity for fetal hemoglobin
Focal neurologic deficits
GCS <15 or altered mental status
LOC, seizure, or coma
Cardiac manifestations: MI/arrhythmia
Outcome of patients experiencing cardiac arrest with carbon monoxide poisoning
Per a study in 2001 by Hampton et al, out-of-hospital cardiac arrest associated with carbon monoxide poisoning was uniformly fatal despite hyperbaric treatment
Medical directors of hyperbaric treatment facilities estimated 74% likelihood of survival for hypothetical patient with this presentation
DISPOSITION: Who can we discharge?
No high risk features
Observation period
Symptom resolution
Psych evaluation if needed
Safe discharge plan
SUMMARY
Silent killer
Diagnosis is made on history
Get the carboxyhemoglobin level
100% O2 for everyone
Indications for HBO2:
>25% or >15% if pregnant
FNDs/AMS/Seizures/LOC
Cardiac manifestations
POST BY: DR. DANIELLA RAO (PGY2)
FACULTY EDITING BY: DR. LAUREN PORTER (MEDICAL TOXICOLOGIST)
REFERENCES
Tomaszewski C. Carbon Monoxide. In: Nelson LS, Howland M, Lewin NA, Smith SW, Goldfrank LR, Hoffman RS. eds. Goldfrank's Toxicologic Emergencies, 11e. McGraw Hill; 2019. Accessed October 13, 2021. https://accessemergencymedicine.mhmedical.com/content.aspx?bookid=2569§ionid=210264419
Maloney GE. Carbon Monoxide. In: Tintinalli JE, Ma O, Yealy DM, Meckler GD, Stapczynski J, Cline DM, Thomas SH. eds. Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 9e. McGraw Hill; 2020. Accessed October 15, 2021. https://accessemergencymedicine.mhmedical.com/content.aspx?bookid=2353§ionid=220747690
https://www.emrap.org/episode/emrap2019/toxicology
https://www.aliem.com/carbon-monoxide-poisoning-time-year/
Hampson NB, Zmaeff JL. Outcome of patients experiencing cardiac arrest with carbon monoxide poisoning treated with hyperbaric oxygen. Ann EmergMed. 2001;38(1):36-41. doi:10.1067/mem.2001.115532
Allred EN, Bleecker ER, Chaitman BR, et al. Short-term effects of carbon monoxide exposure on the exercise performance of subjects with coronary artery disease [published correction appears in N Engl J Med 1990 Apr 5;322(14):1019]. N Engl J Med. 1989;321(21):1426-1432. doi:10.1056/NEJM198911233212102\
https://www.acep.org/patient-care/clinical-policies/carbon-monoxide-poisoning/
https://emcrit.org/ibcc/co/#symptoms_&_presentation