Signs and symptoms of CO poisoning are non-specific and can range from flu-like symptoms (headache is most common) to coma. While usually thought of in the winter months due to space heaters, they can occur throughout the year. Therefore, clinical suspicion is paramount in diagnosis, especially with patients presenting from a fire.
CO binds to Hgb with 200x greater affinity than oxygen. Therefore, labs can show a metabolic acidosis and elevated lactate due to a shift to anaerobic metabolism. COHb levels are considered toxic if >3% in nonsmokers, and >10% in smokers. Symptoms and COHb levels do not correlate well and pulse oximetry is unreliable (check a vbg and the pulse CO-oximeter). Also order a pregnancy test, EKG/trop for ischemia/arrhythmias, CK for rhabdo, CXR if concerned for pulmonary edema, and CT/MRI if there are neurologic changes.
For treatment, as you should know, ABCs are first. Intubate if necessary as patients these patients may have smoke inhalation injuries. Then initiate 100% O2 with a NRB (or through the ETT) as it reduces the half-life of CO from 4 hours to 60-90 minutes. If the patient is only mildly symptomatic, they can be discharged after 4 hours of observation, symptom resolution, and return of COHb level to normal. COHb levels of >25% (>15% in pregnant patients) should make you think about hyperbaric oxygen therapy (board world). In the real world, if a patient has severe symptoms (LOC, AMS, coma, cardiac ischemia), you should consider HBO. There is controversy regarding if it actually reduces the risk of neuropsychiatric sequelae (Parkinsonian features, seizure disorders, intellectual impairment). For patients that fall in between these two presentations, consider admission for continued oxygen therapy and normalization of COHb levels.