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

Carbon Monoxide Poisoning: Clinical Presentation

Carbon monoxide poisoning presents with nonspecific symptoms that most commonly include headache, dizziness, nausea, vomiting, and fatigue, though no combination of symptoms can definitively confirm or exclude the diagnosis. 1

Primary Symptom Categories

Neurological Manifestations

• Headache is the most common symptom, though there is no characteristic pattern specific to CO poisoning 1
• Dizziness, confusion, disorientation, and memory loss occur frequently 1, 2
• Loss of consciousness indicates severe poisoning and is associated with worse outcomes 1
• Impaired manual dexterity may be present even at lower exposure levels 2

Gastrointestinal Symptoms

• Nausea and vomiting are common presenting complaints 1
• These symptoms contribute to the nonspecific nature that leads to frequent misdiagnosis 3

Cardiopulmonary Manifestations

• Chest pain and shortness of breath occur, particularly in patients with pre-existing ischemic heart disease 1
• Individuals with coronary disease may experience angina and decreased exercise tolerance at carboxyhemoglobin levels as low as 1-9% 2
• Severe cases can progress to myocardial stunning, left ventricular dysfunction, arrhythmias, and cardiovascular collapse 4

Constitutional Symptoms

• Fatigue and general malaise are common early presentations 1
• Weakness is frequently reported 2

Severity Correlation with Carboxyhemoglobin Levels

A critical pitfall is assuming symptoms correlate with COHb levels—they do not. 1

• COHb levels of 15-30% typically produce the nonspecific symptoms described above 2
• COHb levels of 30-70% lead to loss of consciousness and potentially death 2
• However, symptoms do not reliably predict COHb levels, making clinical assessment challenging 1

Diagnostic Challenges and Common Misconceptions

The "Cherry Red" Myth

• The classic "cherry red" skin coloration is rare and typically only appears with lethal levels of CO poisoning, making it an unreliable diagnostic sign 1

Diagnostic Confirmation

• No combination of symptoms either confirms or excludes a diagnosis of CO poisoning 1
• A high index of suspicion is warranted, particularly during cold weather and in patients presenting with acute coronary syndrome or arrhythmias 1
• The diagnosis relies on clinical suspicion combined with proven or probable CO exposure, not just laboratory values 5

Severe Poisoning Indicators

Immediate Life-Threatening Presentations

• Unconsciousness, hypotension, and severe acidemia indicate critical poisoning 3
• Acute respiratory failure may develop 3
• Metabolic acidosis may be present, especially if exposure occurred during a house fire 1

Cardiac Complications

• Myocardial ischemia can occur from both hypoxia and increased thrombogenicity 4
• Lethal arrhythmias and electrocardiographic changes may develop 6
• Pulmonary edema can complicate severe cases 6

Delayed Neurological Sequelae

• Following resolution of acute symptoms, there may be a lucid interval of 2-40 days before development of delayed neurological sequelae (DNS) 2
• DNS manifests as diffuse demyelination with lethargy, behavior changes, forgetfulness, memory loss, and parkinsonian features 2
• Approximately 75% of patients with DNS recover within 1 year 2

Critical Management Pitfalls to Avoid

Three common errors can significantly worsen patient outcomes:

• Waiting for laboratory confirmation before initiating 100% oxygen therapy—oxygen should be started immediately based on clinical suspicion 1
• Discharging patients without ensuring the CO source has been identified and eliminated, which risks re-exposure 1
• Not scheduling follow-up to assess for delayed neurological sequelae, which can develop weeks after the initial exposure 1

Special Populations

Pregnancy

• CO poisoning during pregnancy carries high risk for both mother and fetus 6
• Complications include increased maternal complication rates, fetal death, developmental disorders, and chronic cerebral lesions in the fetus 6

Pre-existing Cardiac Disease

• Patients with ischemic heart disease are particularly vulnerable and may experience symptoms at much lower COHb levels than healthy individuals 2