CO2 narcosis

Background

Normal gas exchange showing compositions of the ambient air, the alveolar air (light blue) with which the alveolar capillary blood equilibrates, and the blood gas tensions in the pulmonary arterial (blue blood entering the lung on the left) and venous blood (red blood leaving the lung on the right). All the gas tensions are in kPa (to convert to mm Hg, multiply by 7.5).

Increased CO2 in the blood leading to depressed mental status
Most commonly seen in acute exacerbations of obstructive pulmonary diseases (e.g. COPD, asthma)
Can also be seen in SCUBA divers

Clinical Features

Differential Diagnosis

Altered mental status

Diffuse brain dysfunction

Hypoxic encephalopathy
Acute toxic-metabolic encephalopathy (Delirium)
- Hypoglycemia
- Hyperosmolar state (e.g., hyperglycemia)
- Electrolyte Abnormalities (hypernatremia or hyponatremia, hypercalcemia)
- Organ system failure
- Hepatic Encephalopathy
- Uremia/Renal Failure
- Endocrine (Addison's disease, Cushing syndrome, hypothyroidism, myxedema coma, thyroid storm)
- Hypoxia
- CO2 narcosis
Hypertensive Encephalopathy
Toxins
TTP / Thrombotic thrombocytopenic purpura
Alcohol withdrawal
Drug reactions (NMS, Serotonin Syndrome)
Environmental causes
- Hypothermia
- Hyperthermia
Deficiency state
- Wernicke encephalopathy
- Subacute Combined Degeneration of Spinal Cord (B12 deficiency)
- Vitamin D Deficiency
- Zinc Deficiency
Sepsis
Osmotic demyelination syndrome (central pontine myelinolysis)
Limbic encephalitis

Primary CNS disease or trauma

Direct CNS trauma
- Diffuse axonal injury
- Subdural/epidural hematoma
Vascular disease
- Intraparenchymal hemorrhage
SAH
Stroke
- Hemispheric, brainstem
CNS infections
Neoplasms
- Paraneoplastic Limbic encephalitis
- Malignant Meningitis
- Pancreatic Insulinoma
Seizures
- Nonconvulsive status epilepticus
- Postictal state
Dementia

Psychiatric

Evaluation

VBG (ABG not required to make this diagnosis^[1])

Management

Hyperventilation with either NIPPV or intubation/mechanical ventilation depending on severity and patient's mental status

Disposition

Admission to a monitored setting

External Links

References

↑ McCanny P, Bennett K, Staunton P, McMahon G. Venous vs arterial blood gases in the assessment of patients presenting with an exacerbation of chronic obstructive pulmonary disease. Am J Emerg Med. 2012; 30(6):896-900.

Authors:

[1] McCanny P, Bennett K, Staunton P, McMahon G. Venous vs arterial blood gases in the assessment of patients presenting with an exacerbation of chronic obstructive pulmonary disease. Am J Emerg Med. 2012; 30(6):896-900.

[1]