OVERVIEW

What is acute carbon monoxide poisoning?

Acute carbon monoxide poisoning, commonly known as "gas poisoning," refers to an acute hypoxic disease caused by inhaling high concentrations of carbon monoxide. Its prominent symptoms are those of cerebral hypoxia, such as dizziness and headaches. In severe cases, it may lead to coma or death. Patients with severe poisoning may also experience delayed encephalopathy. Some patients may also exhibit hypoxic changes in other organs, such as the heart, digestive tract, blood, or muscles. Active oxygen therapy or hyperbaric oxygen therapy is key to treatment. There is a false recovery period, and close monitoring is still required after cure.

What harm does carbon monoxide cause to the human body?

Simply put, the body needs to transport oxygen throughout the body, but carbon monoxide competes more aggressively for transport space than oxygen. Therefore, inhaling carbon monoxide leads to poisoning and hypoxia.

The primary function of blood is to bind oxygen to hemoglobin and then transport it throughout the body to meet metabolic needs.

Carbon monoxide has an affinity for hemoglobin that is 200–300 times higher than oxygen. Once it enters the bloodstream, it forms a more stable bond with hemoglobin, hindering oxygen's ability to bind. This greatly reduces the efficiency of oxygen transport in the blood, leading to hypoxia and dysfunction in tissues and organs. In severe cases, it can result in death.

SYMPTOMS

What are the manifestations of acute carbon monoxide poisoning?

The product of carbon monoxide binding with hemoglobin forms carboxyhemoglobin, causing the patient's lips, nail beds, and mucous membranes to exhibit a characteristic cherry-red color. As the concentration of carboxyhemoglobin in the patient's blood increases, the symptoms of poisoning worsen. It is generally classified into mild, moderate, and severe cases:

• Mild: The carboxyhemoglobin concentration in the blood may exceed 10%. Patients mainly experience dizziness, headache, palpitations, nausea, vomiting, general fatigue, and drowsiness. Patients with pre-existing coronary heart disease may develop angina.
  
  
• Moderate: The carboxyhemoglobin concentration in the blood may exceed 30%. The above symptoms worsen, leading to coma. Some physiological reflexes, such as the pupillary response to light, gradually weaken. However, if treated promptly, there are usually no sequelae.
  
  
• Severe: The patient becomes unresponsive to all stimuli, experiencing incontinence, convulsions, severe damage to multiple tissues and organs, or even death. At this stage, the carboxyhemoglobin concentration in the blood may exceed 50%. Even with effective treatment, complications and sequelae may still occur.

Which patients are more likely to experience complications and sequelae from acute carbon monoxide poisoning?

Generally, patients with moderate to severe poisoning or prolonged coma.

What complications can arise from acute carbon monoxide poisoning?

Patients with severe poisoning have a higher risk of complications:

• Hypoxic encephalopathy is the most common complication. Patients may exhibit memory loss, convulsions, dementia, or paralysis. Hypoxia can also cause brain cell swelling, leading to cerebral edema and exacerbating the above symptoms.
• Cardiac complications primarily involve myocardial damage, resulting in arrhythmias, angina, myocardial infarction, or heart failure.
• Respiratory complications may occur due to aspiration of vomit, causing suffocation or aspiration pneumonia, or due to severe hypoxia, leading to acute pulmonary edema or respiratory depression.
• In the blood system, hypoxia increases blood viscosity, raising the risk of thrombotic diseases such as cerebral infarction, pulmonary embolism, or deep vein thrombosis.
• In the digestive system, hypoxia damages the gastrointestinal mucosa, causing stress ulcers or gastrointestinal bleeding.
• Pressure sores may develop in comatose patients, leading to large blisters, redness, and muscle necrosis. The released myoglobin can cause acute tubular necrosis and acute kidney failure.

What is delayed encephalopathy after acute carbon monoxide poisoning?

It refers to a condition where, after effective treatment and apparent recovery (a "pseudo-recovery" period of 2–60 days), patients may develop symptoms such as dementia, hallucinations, tremors, hemiplegia, incontinence, aphasia, blindness, epilepsy, or even catatonia (a state resembling a wooden, unresponsive condition).

How to detect delayed encephalopathy early?

If a patient exhibits persistent sluggishness, memory loss, reduced speech and movement, or catatonia after apparent recovery, delayed encephalopathy should be suspected.

Are there sequelae from acute carbon monoxide poisoning?

Mild poisoning can fully recover. Severe poisoning patients with prolonged coma face a significantly higher risk of complications and delayed encephalopathy. Patients with delayed encephalopathy may suffer permanent symptoms.

CAUSES

What is carbon monoxide?

Carbon monoxide is a colorless, odorless, and toxic gas produced by incomplete combustion of carbon-containing materials (such as charcoal, coal, firewood, and gas) in daily life and industrial production.

What are the causes of acute carbon monoxide poisoning?

Acute carbon monoxide poisoning is most common during the heating season in winter and early spring. In daily life, it often occurs in poorly ventilated environments where coal stoves, charcoal hot pots, or gas water heaters are used. In industrial settings, acute carbon monoxide poisoning typically happens during metallurgy or chemical manufacturing in poorly ventilated conditions.

DIAGNOSIS

What diseases can acute carbon monoxide poisoning be easily confused with?

Acute carbon monoxide poisoning is easily confused with cerebrovascular diseases, encephalitis, meningitis, diabetic ketoacidosis, and other conditions causing unconsciousness due to poisoning. Immediate hospital examination is required.

What emergency tests are needed for patients with acute carbon monoxide poisoning?

• Patients will routinely undergo measurements of body temperature, pulse, respiration, and blood pressure.
• A more specific test is the measurement of carboxyhemoglobin (abnormal hemoglobin bound to carbon monoxide instead of oxygen) in the blood.
• Head CT, electrocardiogram (ECG), complete blood count, myocardial enzymes, renal function, and coagulation tests are crucial for detecting complications.
• Doctors may also select targeted tests based on each patient's specific condition.

What is the significance of carboxyhemoglobin measurement in diagnosing acute carbon monoxide poisoning?

Carboxyhemoglobin measurement is highly significant for confirming acute carbon monoxide poisoning, but blood samples must be taken early, as carboxyhemoglobin levels gradually decline hours after leaving the exposure site.

Does a positive carboxyhemoglobin test always indicate acute carbon monoxide poisoning?

Patients with chronic bronchitis, pulmonary heart disease, or long-term smokers may also test positive for carboxyhemoglobin, though usually at lower levels. For example, smoking one pack of cigarettes daily can raise blood carboxyhemoglobin levels to 5%–6%.

Why is a head CT scan necessary for diagnosing acute carbon monoxide poisoning?

Many patients with acute carbon monoxide poisoning exhibit symptoms like dizziness, headaches, or even unconsciousness, which must be differentiated from cerebrovascular diseases. Additionally, some patients may develop cerebrovascular complications due to poisoning, making a head CT scan essential.

What should patients keep in mind during a head CT scan for acute carbon monoxide poisoning?

• Patients must cooperate fully, remain still, and avoid movement to prevent image artifacts that may hinder diagnosis.
• Patients at risk of vomiting should lie on their side during the scan to prevent aspiration or choking.
• Pregnant patients must inform the doctor for necessary protective measures.

Why is an ECG necessary for acute carbon monoxide poisoning?

Acute carbon monoxide poisoning can cause hypoxic damage to the heart muscle and may trigger myocardial infarction. An ECG helps detect and treat such complications early.

What should patients keep in mind during an ECG for acute carbon monoxide poisoning?

Since the upper body must be exposed for an ECG, patients should stay warm. They should relax and breathe calmly to avoid muscle tremors that could affect ECG readings.

TREATMENT

What are the treatment measures for acute carbon monoxide poisoning?

• Oxygen inhalation can promote the elimination of carbon monoxide;
• Hyperbaric oxygen therapy can quickly relieve hypoxia;
• Brain edema is most severe 24–48 hours after severe poisoning, requiring intravenous mannitol to reduce cerebral edema;
• If the patient experiences convulsions, diazepam or phenytoin sodium can be administered;
• Prevention and treatment of complications such as infection and fever should be addressed;
• Prevention of sequelae such as delayed encephalopathy should be emphasized.

Which department should be consulted for acute carbon monoxide poisoning?

The patient should go to the emergency department of a hospital as soon as possible.

What is the role of hyperbaric oxygen therapy in acute carbon monoxide poisoning?

Hyperbaric oxygen therapy increases the oxygen dissolved in the patient's blood and enhances oxygen diffusion into cells, thereby rapidly correcting tissue hypoxia. Each session typically lasts half an hour, and severe poisoning usually requires continuous treatment for one month, though the duration may vary depending on the condition.

Should hyperbaric oxygen therapy continue after the patient regains consciousness from acute carbon monoxide poisoning?

Continuing hyperbaric oxygen therapy after the patient regains consciousness can reduce or prevent sequelae such as delayed encephalopathy, so the treatment should be adhered to as prescribed.

How should hypoxic encephalopathy caused by acute carbon monoxide poisoning be treated?

• Persist with hyperbaric oxygen therapy;
• Administer intravenous mannitol to gradually reduce cerebral edema;
• Use brain cell metabolism-promoting drugs such as adenosine triphosphate (ATP), coenzyme A, and cytochrome C.

How should myocardial damage caused by acute carbon monoxide poisoning be treated?

• The key treatment remains correcting hypoxia;
• Consider using drugs like nitroglycerin to improve myocardial blood supply and coenzyme Q10 to enhance myocardial metabolism;
• Measures to reduce cardiac burden, such as treating fever and controlling fluid intake, should be taken.

How to prevent pneumonia after acute carbon monoxide poisoning?

Keep the patient warm; position unconscious patients on their side to prevent aspiration of vomit; administer antibiotics if necessary.

How to treat increased blood viscosity and the risk of thrombotic diseases after acute carbon monoxide poisoning?

Administer oral or intravenous fluids to prevent blood concentration due to dehydration; assess the patient's risk of thrombotic diseases and consider using anticoagulants like heparin to prevent thrombosis.

How to prevent stress ulcers and gastrointestinal bleeding caused by acute carbon monoxide poisoning?

Carbon monoxide poisoning may cause necrosis of the gastrointestinal mucosa due to hypoxia, leading to stress ulcers and gastrointestinal bleeding. To prevent such complications, the following measures can be taken:

• Protect the digestive tract: Adjust the patient's diet (fasting, liquid, semi-liquid, or regular meals) based on digestive function.
• Suppress gastric acid: Administer proton pump inhibitors like omeprazole intravenously to protect the gastrointestinal mucosa if necessary.
• Perform endoscopy and treatment promptly when conditions permit.

DIET & LIFESTYLE

How to Self-Rescue in Case of Acute Carbon Monoxide Poisoning

If still conscious, move quickly to a ventilated window or door to breathe fresh air. If symptoms persist, seek immediate medical attention at the nearest hospital.

Additionally, take self-protection measures. When entering a carbon monoxide-affected area, ensure proper ventilation by opening windows, avoid open flames or electrical devices, and refrain from turning lights on or off.

How to Rescue Others in Case of Acute Carbon Monoxide Poisoning

If the victim is unconscious, immediately move them to an area with fresh air, preferably with access to oxygen.

Place the victim in the recovery position (on their side) to prevent airway obstruction by vomit, and keep them warm.

If breathing has stopped, begin cardiopulmonary resuscitation (CPR) immediately.

Perform CPR following these steps:

• Ensure the environment is safe.
• Shout and tap the victim's shoulders to check for responsiveness.
• Lay the victim flat on a firm surface, loosen tight clothing, and check for breathing (or abnormal breathing) within 10 seconds by observing chest movements.
• If unresponsive and not breathing (or only gasping), instruct someone to call emergency services (120) and fetch an AED if available.
• Begin CPR at a 30:2 compression-to-ventilation ratio.
• Perform 30 chest compressions (5-6 cm depth) at the center of the chest (lower half of the sternum, slightly below the nipple line).
• Open the airway using the head-tilt/chin-lift method and deliver 2 rescue breaths:
  - Place one hand on the forehead and pinch the nose.
  - Lift the chin to tilt the head back, sealing your mouth over the victim's mouth.
  - Deliver two 1-second breaths, observing chest rise (both breaths within 10 seconds).
• For infants: Cover both mouth and nose with your mouth to deliver breaths, ensuring visible chest rise without over-ventilation.
• Continue cycles of 30 compressions and 2 breaths until spontaneous breathing resumes, professional help arrives, or an AED is ready for use.

Call 120 or transport the victim to the nearest hospital immediately.

PREVENTION

In daily life, what are the preventive measures for acute carbon monoxide poisoning?

• Ensure good ventilation in environments where charcoal, coal fires, or gas stoves are used. Install an exhaust fan if necessary.
• Install chimneys for stoves in living spaces, ensuring they are structurally sound and well-ventilated. Some poisoning cases occur due to chimneys facing the wrong wind direction.
• Minimize air circulation between rooms using charcoal, coal fires, or gas stoves and living areas. Avoid shared ceilings, wall openings, or underground pipes. For example, some poisonings happen when boiler room ceilings connect to bedroom ceilings.
• Install a carbon monoxide detector and alarm system.