What does hypercarbia (elevated carbon dioxide (CO2) levels) indicate?

From the Guidelines

Elevated CO2 levels in the blood (hypercarbia) indicate that the body is not effectively removing carbon dioxide, which is a waste product of metabolism, suggesting respiratory dysfunction or other underlying conditions that compromise the body's ability to expel CO2. This condition typically suggests respiratory dysfunction, where the lungs are unable to adequately expel CO2 during breathing. Common causes include chronic obstructive pulmonary disease (COPD), severe asthma attacks, respiratory depression from medications (particularly opioids or sedatives), neuromuscular disorders affecting breathing muscles, or sleep apnea. In some cases, elevated CO2 may result from metabolic conditions like severe vomiting or certain kidney disorders.

Key Points to Consider

• Symptoms of high CO2 include headache, confusion, drowsiness, flushed skin, and in severe cases, loss of consciousness.
• Treatment depends on the underlying cause but often includes oxygen therapy, bronchodilators like albuterol for airway obstruction, non-invasive ventilation such as CPAP or BiPAP, or mechanical ventilation in severe cases.
• The body normally maintains CO2 balance through the respiratory system, with the brain stem automatically adjusting breathing rate and depth based on blood CO2 levels, so persistent elevation suggests this regulatory mechanism is compromised 1.

Clinical Implications

• Hypercarbia can lead to serious complications, including acidosis and coma, especially in vulnerable patients with COPD, chest wall deformities, or muscle weakness 1.
• Studies have shown that between 20% and 50% of patients with AECOPD or with obesity-hypoventilation syndrome (OHS) are at risk of carbon dioxide retention if they are given an excessively high concentration of oxygen 1.
• Oxygen-induced hypercapnia in patients with AECOPD can be avoided by giving targeted lower concentration oxygen therapy to vulnerable patients and aiming for a target range of 88–92% 1.
• AHRF complicates around 20% of acute exacerbations of COPD, signaling advanced disease, a high risk of future hospitalizations, and limited long-term prognosis 1.

From the Research

Hypercarbia Indications

Hypercarbia, or elevated carbon dioxide (CO2) levels, can indicate several conditions, including:

• Acute hypercapnic ventilatory failure, which is becoming more frequent in critically ill patients 2
• Respiratory acidosis, or primary hypercapnia, which results from an increase in arterial partial pressure of carbon dioxide 3, 4
• Alveolar hypoventilation, which can be caused by various factors such as chronic obstructive pulmonary disease (COPD), asthma, or spinal cord injury 3, 4
• Increased carbon dioxide production, which can occur in various conditions such as sepsis or malignant hyperthermia 3
• Abnormalities of the chest wall and respiratory muscles, which can lead to respiratory acidosis 3
• Submissive hypercapnia, a condition where the respiratory controller prioritizes conserving the work of breathing over maintaining normocapnia, often seen in severe COPD patients 5

Pathophysiological Mechanisms

The pathophysiological mechanisms of hypercarbia include:

• Decrease in minute volume 2
• Increase in dead space 2
• Increase in carbon dioxide (CO2) production per sec 2
• Alveolar hypoventilation 3, 4
• Abnormal respiratory drive 3
• Abnormalities of the chest wall and respiratory muscles 3

Clinical Implications

Hypercarbia can have significant clinical implications, including:

• Compromise at the cardiovascular, cerebral, metabolic, and respiratory levels 2
• High burden of morbidity and mortality 2
• Delayed skeletal muscle repair and regeneration 6
• Increased fatty acid oxidation in skeletal muscle cells 6