What are the clinical signs of CO2 (carbon dioxide) narcosis?

Clinical Signs of CO2 Narcosis

The clinical signs of CO2 narcosis include headache, dizziness, confusion, lethargy, nausea/vomiting, progressive alteration in mental status ranging from confusion to coma, and ultimately respiratory depression leading to respiratory arrest if untreated. 1, 2

Primary Clinical Manifestations

Neurological Signs

• Early signs:
  • Headache
  • Dizziness
  • Confusion
  • Lethargy
  • Impaired cognition
  • Irritability

Progressive Manifestations

• Moderate to severe signs:
  • Altered mental status progressing to coma (Glasgow Coma Scale score may decrease significantly) 2
  • Decreased level of consciousness
  • Respiratory depression
  • Respiratory arrest in severe cases 3

Cardiovascular Signs

• Tachycardia (increased heart rate) 2
• Hypertension may be present initially 2

Respiratory Signs

• Increased respiratory effort initially 2
• Increased respiratory rate (tachypnea) 2
• Progressive decrease in respiratory drive
• Shallow breathing patterns

Laboratory Findings

• Arterial blood gas analysis typically shows:
  • Respiratory acidosis (pH < 7.35)
  • Elevated PaCO2 (often > 60 mmHg, can exceed 100 mmHg in severe cases) 3, 2
  • Variable PaO2 depending on supplemental oxygen

Special Considerations

Pupillary Changes

Recent evidence suggests pupillary responses may correlate with CO2 narcosis:

• Changes in pupil size and constriction velocity correlate with respiratory rate and PaCO2 levels 2
• Portable automated pupillometry may help monitor autonomic nervous system function in these patients

Risk Factors

• Chronic obstructive pulmonary disease (COPD) 2, 4
• Neuromuscular disorders (e.g., amyotrophic lateral sclerosis) 3
• Inappropriate oxygen delivery in COPD patients (e.g., high flow without adequate ventilation) 4

Diagnostic Pitfalls

• CO2 narcosis must be distinguished from carbon monoxide (CO) poisoning, which presents differently with:

  • Cherry red skin discoloration (though this is rare) 1
  • Normal or low PaCO2 levels
  • Elevated carboxyhemoglobin (COHb) levels 5

• CO2 narcosis can be precipitated by inappropriate oxygen administration in patients with COPD who rely on hypoxic respiratory drive 4

Clinical Course

Without intervention, CO2 narcosis can rapidly progress from confusion and lethargy to coma and respiratory arrest 3. Prompt recognition and appropriate management with ventilatory support are essential to prevent morbidity and mortality.

In patients with underlying respiratory disorders, CO2 narcosis may develop gradually or suddenly during acute exacerbations, particularly when supplemental oxygen is administered without adequate ventilatory support 4.

Early recognition of the signs of CO2 narcosis is crucial for timely intervention and prevention of respiratory arrest and associated complications.