What are the signs and symptoms of carbon monoxide (CO) poisoning?

Signs and Symptoms of Carbon Monoxide Poisoning

Carbon monoxide poisoning presents with a spectrum of nonspecific symptoms ranging from headache, dizziness, nausea, and vomiting in mild cases to loss of consciousness, cardiovascular collapse, and death in severe exposures. 1

Common Clinical Manifestations

Neurological Symptoms

• Headache is the most common symptom, though no characteristic pattern exists that is specific to CO poisoning 1
• Dizziness and confusion are frequent neurological complaints 1
• Loss of consciousness indicates severe poisoning and correlates with worse outcomes 1
• Altered mental status is a common presenting feature 2

Gastrointestinal Symptoms

• Nausea and vomiting occur frequently 1
• General malaise and fatigue are common presentations 1, 2

Cardiopulmonary Manifestations

• Chest pain and shortness of breath may occur, particularly in patients with underlying cardiac disease 1
• Myocardial ischemia can develop even without pre-existing heart disease 2
• Initial tachycardia and hypertension may be present 3
• Arrhythmias including atrial fibrillation can occur 3

Severe Poisoning Features

• Unconsciousness, hypotension, and severe acidemia indicate life-threatening toxicity 4
• Acute respiratory failure requiring mechanical ventilation may develop 2
• Metabolic acidosis, especially in fire-related exposures 1

Critical Diagnostic Challenges

No combination of symptoms either confirms or excludes CO poisoning, making clinical diagnosis particularly challenging 1. Several important caveats exist:

• Symptoms do not correlate with carboxyhemoglobin (COHb) levels, so normal or low COHb should not exclude the diagnosis if exposure history and symptoms are consistent 1, 5
• The classic "cherry red" skin coloration is rare and typically only appears with lethal CO levels 1
• COHb levels may be falsely low in delayed presentations, particularly in smokers 6
• Negative COHb levels should not rule out CO poisoning if history and symptoms are consistent 5

High-Risk Scenarios Requiring Heightened Suspicion

• Cold weather presentations with acute coronary syndrome or arrhythmias warrant high suspicion 1
• Patients with flu-like symptoms during heating season 6
• Multiple family members or cohabitants with similar symptoms 4
• Exposure to fire smoke, indoor heating sources, or enclosed spaces with combustion engines 5

Systemic Complications Beyond Initial Presentation

• Cardiac dysfunction including left ventricular systolic dysfunction and myocardial infarction occurs in approximately one-third of moderate to severely poisoned patients 7
• Acute kidney failure and elevated liver enzymes may develop 6
• Muscle necrosis (rhabdomyolysis) can occur 3
• Pneumonia and pulmonary edema are potential complications 3
• Visual and auditory system changes may be present 3

Delayed Neurological Sequelae

• Delayed neurological sequelae occur in 15-40% of patients, typically days to weeks after acute exposure 7
• The classic triad includes mental deterioration, urinary incontinence, and gait disturbance 3
• Movement disorders, particularly parkinsonism, may develop 3
• Peripheral neuropathy can occur, usually in young adults 3
• Brain imaging may reveal bilateral globus pallidus lesions, the most frequently affected structure 6

Critical Management Pitfalls to Avoid

• Never wait for laboratory confirmation before initiating 100% oxygen therapy 1, 5
• Do not discharge patients without ensuring the CO source has been identified and eliminated 1
• Always schedule follow-up to assess for delayed neurological sequelae 1
• Do not rely solely on COHb monitoring for treatment decisions, as clinical symptoms do not correlate with COHb elimination 5