OVERVIEW

What is pulmonary encephalopathy?

Pulmonary encephalopathy, also known as CO₂ narcosis or cardiopulmonary cerebral syndrome, is a syndrome characterized by mental disorders and neurological symptoms caused by hypoxia and carbon dioxide retention due to respiratory failure.

Pulmonary encephalopathy is not a disease itself but rather a secondary brain manifestation resulting from respiratory, cardiovascular, or other systemic conditions. It is the leading cause of death in patients with chronic cor pulmonale and requires active prevention and treatment.

Is pulmonary encephalopathy common?

Yes, it is common, particularly among patients with chronic thoracic or pulmonary diseases.

SYMPTOMS

What are the manifestations of pulmonary encephalopathy?

The brain is highly sensitive to hypoxia, which can easily lead to brain dysfunction: early mild to moderate hypoxia may present as increased excitability, impaired judgment, restlessness, and confusion; severe hypoxia or late-stage hypoxia may shift from excitation to inhibition, manifesting as apathy, drowsiness, or even coma, convulsions, and ultimately death due to respiratory and circulatory center suppression.

The clinical manifestations of pulmonary encephalopathy are related to both the speed and severity of hypoxia and carbon dioxide retention. It is primarily caused by carbon dioxide narcosis due to hypoxia and hypercapnia:

• Early symptoms may include insomnia, agitation, difficulty concentrating, head discomfort, memory decline, poor mental state, reduced intelligence, and mild visual impairment.

• Subsequently, varying degrees of neuropsychiatric symptoms may appear, such as headache, dizziness, irritability, confusion, hallucinations, delusions, asterixis, myoclonus, increased intracranial pressure, conjunctival edema, and cyanosis.

• Further progression may lead to drowsiness, stupor, seizures, and in severe cases, loss of consciousness, coma, and respiratory depression.

• Extreme hypoxia can cause irreversible damage to brain neurons within minutes.

CAUSES

What causes pulmonary encephalopathy?

The pathogenesis of pulmonary encephalopathy is not yet fully understood, but it is primarily attributed to the combined effects of hypoxia, carbon dioxide retention, and acidosis damaging cerebral blood vessels and brain cells.

The brain has a high oxygen demand, accounting for about 1/5 to 1/4 of the body's total oxygen consumption. Therefore, brain tissue, especially the neurons in the cerebral cortex, is highly sensitive to hypoxia. Any disease that severely impairs pulmonary ventilation and/or gas exchange, leading to respiratory failure, can result in pulmonary encephalopathy.

Common causes include:

• Airway obstruction: Inflammation, spasms, edema, tumors, foreign bodies, or scar contractures in the trachea or bronchi—such as acute exacerbations of chronic obstructive pulmonary disease (COPD) or bronchial asthma—can cause airway spasms, edema, or mucus blockage, impairing pulmonary ventilation.

• Pulmonary parenchymal diseases: Conditions affecting alveoli and/or lung interstitium, such as pneumonia, emphysema, or silicosis, can reduce gas exchange efficiency.

• Pulmonary vascular diseases: Pulmonary embolism or vasculitis can impair alveolar blood circulation, affecting gas exchange.

• Cardiac diseases: Severe valvular heart disease, pericardial diseases, arrhythmias, or cardiomyopathy can disrupt blood circulation, leading to impaired gas exchange.

• Chest wall and pleural disorders: Chest trauma, severe pneumothorax, massive hemothorax or pleural effusion, or pleural thickening/adhesions can restrict chest movement and lung expansion, causing ventilation dysfunction.

• Neuromuscular diseases: Central nervous system disorders (e.g., brain injury, encephalitis) may suppress the respiratory center. Conditions like myasthenia gravis, poliomyelitis, tetanus, or electrolyte imbalances can weaken respiratory muscles, impairing ventilation.

DIAGNOSIS

How to diagnose pulmonary encephalopathy?

Generally, doctors diagnose it based on the presence of underlying respiratory, cardiac, or neuromuscular diseases, varying degrees of neuropsychiatric abnormalities, and blood gas analysis confirming respiratory failure. A diagnosis is made after excluding other causes of neurological or psychiatric disorders.

What tests are needed for patients with pulmonary encephalopathy? Why are these tests performed?

The diagnosis of pulmonary encephalopathy requires a detailed medical history, observation of neuropsychiatric symptoms, and relevant tests to confirm the diagnosis, assess severity, identify causes, and rule out other conditions.

• Arterial blood gas analysis: Uses a blood gas analyzer to measure H⁺ concentration and dissolved gases (mainly CO₂ and O₂) in arterial blood, determining respiratory failure, acid-base imbalance, severity, and treatment efficacy. Under standard conditions (sea level, resting state, breathing air), PaO₂ < 60 mmHg (normal: 80–100 mmHg), with or without PaCO₂ > 50 mmHg (normal: 35–45 mmHg), indicates respiratory failure. A pH < 7.35 (normal: 7.35–7.45) suggests acidosis. Avoid mistakenly testing venous blood.

• Chest imaging: Includes X-rays, CT, or ventilation/perfusion scans to identify causes of respiratory failure.

• Lumbar puncture and cerebrospinal fluid analysis: Performed if brain/spinal cord infection is suspected to rule out related conditions.

• Brain imaging: Head CT or MRI to exclude neurological/psychiatric disorders caused by brain diseases.

• Venous blood tests: Such as CBC, electrolytes, thyroid function, and biochemistry to assess comorbidities and identify causes.

What conditions should pulmonary encephalopathy be differentiated from?

It should be distinguished from central nervous system diseases (e.g., stroke, hemorrhage, infection, trauma, tumors) and systemic conditions with neurological manifestations (e.g., hepatic encephalopathy, uremic encephalopathy, lupus encephalopathy, toxic encephalopathies, or electrolyte imbalances like diabetic ketoacidosis and hyperosmolar coma).

TREATMENT

Which department should I visit for pulmonary encephalopathy?

Respiratory Medicine.

Does pulmonary encephalopathy require hospitalization?

Yes.

How should pulmonary encephalopathy be treated?

• The treatment of pulmonary encephalopathy primarily focuses on improving hypoxia, excessive CO₂, and acidosis. Therefore, airway patency should be maintained. Under the premise of oxygen therapy (nasal cannula or mask) and mechanical ventilation if necessary to improve lung function, the underlying primary disease should be actively treated (e.g., bronchodilators for asthma, closed thoracic drainage or surgery for pneumothorax).

• Combine with rational use of antibiotics for anti-infection therapy, correct acid-base imbalance and electrolyte disturbances, and strengthen supportive treatment.

• For patients with significant mental abnormalities who cannot cooperate with treatment, sedatives with minimal impact on respiratory function, such as haloperidol, can be used.

DIET & LIFESTYLE

What should patients with pulmonary encephalopathy pay attention to in their diet?

Provide high-protein, high-vitamin, light, and easily digestible foods. Avoid eating too quickly to prevent aspiration and choking.

What should patients with pulmonary encephalopathy pay attention to in daily life?

Keep warm and avoid exposure to cold or drafts. Assist patients with expectoration, turning over, and preventing suffocation, bedsores, falls, and self-harm or harm to others during episodes of mental disturbance.

Do patients with pulmonary encephalopathy need follow-up examinations? How?

This depends on the underlying cause. If it is an acute condition (e.g., suffocation due to a foreign object) and has been cured, follow-up may not be necessary. However, most cases involve chronic diseases, so regular outpatient follow-ups and relevant examinations (e.g., pulmonary function tests) should be conducted.

PREVENTION

Can pulmonary encephalopathy be prevented?

For patients with chronic respiratory or cardiovascular diseases, it is recommended to maintain oxygen therapy, protect against cold to avoid catching chills, avoid crowded places to prevent infections, ensure adequate rest, maintain a regular lifestyle, eat a balanced diet, enhance immune resistance, strengthen respiratory function exercises, and attend regular hospital follow-ups. These measures can help reduce the occurrence of pulmonary encephalopathy.