From the Guidelines
Hypercapnia with normal or near-normal oxygen levels on venous blood gas analysis is typically caused by hypoventilation, which can result from various factors including respiratory center depression, neuromuscular disorders, severe COPD or asthma, obesity hypoventilation syndrome, and chest wall restrictions. The most recent and highest quality study on this topic is from 2019, which focuses on the evaluation and management of obesity hypoventilation syndrome 1. According to this study, hypoventilation can lead to elevated serum bicarbonate levels and hypoxemia, which can serve as surrogate markers for hypercapnia. Some of the key causes of hypercapnia with normal or near-normal oxygen levels include:
- Respiratory center depression from opioids, sedatives, or neurological disorders
- Neuromuscular disorders such as myasthenia gravis, Guillain-Barré syndrome, and ALS
- Severe COPD or asthma with air trapping
- Obesity hypoventilation syndrome
- Chest wall restrictions such as kyphoscoliosis and severe obesity
- Mechanical ventilation issues like inappropriate settings or dead space ventilation The underlying pathophysiology involves inadequate minute ventilation relative to CO2 production, while oxygen supplementation or adequate diffusion capacity maintains normal oxygen levels, as noted in a previous guideline on oxygen use in adults 1. Management should focus on identifying and treating the underlying cause while supporting ventilation as needed, which may include the use of bronchodilators, reversal agents, non-invasive ventilation, or mechanical ventilation in severe cases.
From the Research
Causes of Hypercapnia
- Hypercapnia, or elevated partial pressure of carbon dioxide (CO2), can be caused by various factors, including chronic obstructive pulmonary disease (COPD) and obesity hypoventilation syndrome (OHS) 2
- Neuromuscular disorders, such as amyotrophic lateral sclerosis (ALS), and restrictive thoracic disorders can also lead to hypercapnia 3
- Sepsis, a life-threatening condition that occurs when the body's response to an infection becomes uncontrolled, can also cause hypercapnia 4
- Respiratory failure, which can be caused by a variety of factors, including COPD, OHS, and pneumonia, can also lead to hypercapnia 5
Pathophysiology of Hypercapnia
- Hypercapnia can occur when the body's ability to remove CO2 from the blood is impaired, such as in respiratory failure 2
- The partial pressure of arterial carbon dioxide (PaCO2) can increase when the lungs are not able to remove enough CO2 from the blood, leading to hypercapnia 4
- Hypercapnia can also occur when the body's production of CO2 increases, such as during sepsis or other conditions that cause increased metabolism 5
Effects of Hypercapnia on the Body
- Hypercapnia can cause respiratory acidosis, a condition in which the blood becomes too acidic due to the increased levels of CO2 2
- Hypercapnia can also cause decreased peripheral tissue and visceral organ perfusion, which can lead to organ dysfunction and failure 5
- Elevated CO2 levels can also affect cognitive function and respiratory function, particularly during exercise or in individuals with pre-existing respiratory conditions 6