Disease Description (Causes and Symptoms)
- Definition and pathophysiology: Carbon monoxide (CO) is a colorless, odorless gas that binds to hemoglobin in the blood to form carboxyhemoglobin (COHb). CO has an affinity for hemoglobin that is dozens of times higher than that of oxygen, rapidly reducing oxygen-carrying capacity. It also makes it difficult for hemoglobin to release oxygen, causing tissue hypoxia. In addition, it may have direct toxic effects on the cellular respiratory system (e.g., cytochrome oxidase).
- Main causes: Incomplete combustion (briquettes, gas, propane, heating appliances, vehicle exhaust, fire scenes), using heating appliances or running engines in enclosed spaces, etc.
- Symptoms (acute/chronic): Headache, dizziness, nausea and vomiting, shortness of breath, chest pain, rapid pulse, loss of consciousness, and motor or cognitive impairment. Mild chronic exposure may cause fatigue, dizziness, memory impairment, and insomnia.
- Severity indicators: Concentration in the air and exposure duration, and blood COHb concentration (diagnostic significance). Pregnant individuals and people with cardiovascular disease may be severely affected by lower levels of exposure.
Treatment Methods
- Immediate treatment
- Stop the exposure and move the patient to an area with fresh air.
- Administer 100% oxygen (non-rebreather mask) — oxygen administration rapidly shortens the COHb half-life.
- In cases of loss of consciousness or apnea, perform basic life support (airway management, artificial ventilation, chest compressions).
- Hospital treatment
- Oxygen therapy: Continue administering high-concentration (100%) oxygen to lower COHb. Treatment is determined based on symptom resolution and the COHb target (e.g., usually <5–10%).
- Hyperbaric oxygen therapy (HBO): Considered/recommended in the following cases
- Loss of consciousness, neurological abnormalities (confusion, seizures, convulsions, etc.), or syncope
- Markedly elevated COHb (generally about 25% or higher in adults; a lower threshold for pregnant individuals—15–20% or higher in some recommendations)
- Myocardial ischemia or arrhythmia, or persistent shortness of breath
- When the risk of delayed neurological injury is considered high
- Cardiac and neurological monitoring: ECG, troponin testing, and neurological observation.
- Supportive treatment: Hemodynamic stabilization, mechanical ventilation if needed, and treatment of complications.
- Criteria for continuing treatment: Determined based on improvement in symptoms, COHb level, and clinical status. In pregnancy, treatment is more proactive because of the risk to the fetus.
- Precautions (self-care and emergencies)
- Administer 100% oxygen as soon as possible, including during transport to a medical facility.
- A pulse oximeter overestimates oxygen saturation because of CO and is therefore unreliable in cases of CO exposure.
- Eliminate the source of exposure and inspect equipment (boilers, fuel-burning appliances).
Outpatient Visit Checklist (Including Example Questions)
- Items/materials to prepare or bring
- A list of medications currently being taken (including prescription, over-the-counter, and herbal medicines)
- Past medical conditions (cardiovascular disease, cerebrovascular disease, and whether pregnant)
- Exposure-related information: time and place of exposure, estimated exposure duration, equipment used (boiler, stove, tent, etc.), and whether others were in the same space
- Test results received from the emergency department (or another hospital) (arterial blood gas/COHb test, ECG, chest imaging, etc.)
- Course of symptoms (time symptoms began and pattern of changes)
- Materials to show the doctor during the outpatient visit: Previous COHb levels (if possible), emergency department report, and copies of imaging/test results
- Example questions (phrasing patients can use directly)
- “What is my current COHb level, and what does this level mean?”
- “Do I need hyperbaric oxygen therapy? What are the benefits and risks of the treatment?”
General Example Questions to Ask the Doctor
- What are the main side effects of this medication (or treatment)? (e.g., HBO side effects, oxygen toxicity)
- What is the expected course and prognosis based on my condition (test results)?
- What symptoms should I watch for after discharge, and when should I return to the hospital?
- If I am pregnant, are additional tests needed for the fetus?
Disease-Specific Example Questions
- Pregnancy-related: “I was exposed during pregnancy. What are the criteria for recommending fetal assessment (ultrasound, fetal monitoring) or hyperbaric oxygen therapy?”
- Treatment indication/timing: “Based on my COHb level (or symptoms), is hyperbaric oxygen therapy recommended? If so, how many sessions are needed and at what pressure will it be performed?”
(Reference/additional information summary) Diagnosis uses arterial blood COHb measurement (including co-oximetry), and caution is needed because standard pulse oximetry misinterprets CO as oxygen saturation. Complications include acute myocardial ischemia and arrhythmia, as well as delayed neurological symptoms (cognitive impairment, behavioral changes, parkinsonism, etc.); the risk of fetal injury is high during pregnancy. For prevention, regular inspection of heating appliances and boilers, indoor ventilation, and installation of carbon monoxide detectors are important.