Manifestations of Carbon Monoxide Poisoning
Carbon monoxide poisoning presents with nonspecific symptoms, most commonly headache, dizziness, nausea/vomiting, confusion, fatigue, chest pain, shortness of breath, and loss of consciousness. 1
Clinical Presentation
Common Symptoms
- Headache (most common symptom)
- Dizziness
- Nausea and vomiting
- Confusion
- Fatigue
- Chest pain
- Shortness of breath
- Loss of consciousness 1
Important Clinical Points
- No single symptom is either sensitive or specific for CO poisoning
- Symptoms correlate poorly with carboxyhemoglobin (COHb) levels 1
- No characteristic headache pattern exists that is typical of CO poisoning 1
- High index of suspicion is warranted, particularly during cold weather, in patients with acute coronary syndrome and arrhythmias 1
Physical Examination Findings
- "Cherry red" skin coloration is a medical myth in most cases
- This finding is rare and typically only present with lethal carboxyhemoglobin levels
- Less than 50% of individuals dying from CO poisoning have "cherry red" skin when measured by reflectance spectrophotometry 1
Cardiovascular Manifestations
CO poisoning can cause significant cardiovascular complications:
- Myocardial stunning
- Left ventricular dysfunction
- Pulmonary edema
- Cardiac arrhythmias
- Acute myocardial ischemia (due to increased thrombogenicity)
- Hypotension
- Lethal arrhythmias
- Electrocardiographic changes 2
Neurological Manifestations
- Disorientation
- Confusion
- Coma
- Seizures
- Delayed neuropsychiatric impairment (occurring 2-28 days after poisoning)
- Parkinsonian features 3, 4
Laboratory Diagnosis
Carboxyhemoglobin Levels
- Confirms clinical diagnosis of CO poisoning
- Normal levels:
- 3-4% or less in nonsmokers
- Less than 10% in smokers 1
- Smokers typically have COHb levels of 3-5%
- Each pack of cigarettes smoked per day increases COHb by approximately 2.5% 1, 5
- COHb levels correlate poorly with symptoms or prognosis 1
Important Diagnostic Considerations
- Laboratory spectrophotometry (CO-oximeter) is required for accurate measurement
- Standard pulse oximetry cannot detect carboxyhemoglobin
- Either arterial or venous blood may be used for measurement 1
Complications and Sequelae
Immediate Complications
- Cardiovascular collapse
- Respiratory failure
- Death 2
Delayed Neurologic Sequelae (DNS)
- Occurs after a lucid interval of 2-40 days
- Characterized by diffuse demyelination in the brain
- Symptoms include lethargy, behavior changes, forgetfulness, memory loss, and parkinsonian features
- 75% of patients with DNS recover within 1 year 3
Long-term Effects
- Neuropsychological abnormalities may persist even with normal imaging
- Increased short-term and long-term mortality, particularly with myocardial toxicity 2
- Peripheral neuropathies (less common) 3
Special Populations
Pregnant women:
- High risk for both mother and fetus
- Increased short-term complication rate for mothers
- Can cause fetal death, developmental disorders, and chronic cerebral lesions in the fetus 4
Common Pitfalls in Diagnosis
- CO poisoning is frequently overlooked or misdiagnosed
- Symptoms may be attributed to viral illness, food poisoning, or other common conditions
- Symptoms may be masked by exacerbation of underlying conditions like congestive heart failure 6
- COHb levels may be falsely low if there has been a delay between exposure and testing
- Approximately one-third of nonfatal cases go undetected and undiagnosed 6
Prevention
- CO alarms should be installed in every residence, particularly in hallways outside sleeping areas
- CO alarms should be replaced every 5-7 years per manufacturer's instructions
- Public education about proper use of generators and risks of indoor fuel combustion 1
Understanding the varied and nonspecific manifestations of carbon monoxide poisoning is crucial for early recognition and appropriate management to prevent morbidity and mortality.