When APAP may not be suitable

Hypoventilation resulting in inadequate removal of carbon dioxide (CO2) from the body is often detected on overnight sleep studies. When hypoventilation occurs in the context of using APAP (Auto-Positive Airway Pressure) therapy, it can have potentially dangerous consequences. Here's why:

1. Increased carbon dioxide levels: Hypoventilation leads to an accumulation of CO2 in the bloodstream. In individuals undergoing APAP therapy, this can be particularly problematic because APAP is primarily used to treat sleep-related breathing disorders such as obstructive sleep apnea (OSA), which are characterized by periods of reduced or blocked airflow. In OSA, the airway becomes partially or completely blocked, resulting in decreased oxygen intake and increased CO2 levels. If hypoventilation occurs in combination with APAP therapy, it further impairs CO2 removal and can lead to dangerously high levels of carbon dioxide in the blood, a condition known as hypercapnia.

2. Respiratory acidosis: Hypercapnia resulting from hypoventilation causes a condition called respiratory acidosis. Excessive CO2 leads to increased acidity in the blood, disrupting the pH balance. Acidosis can have various effects on the body, including impaired organ function, altered mental status, and cardiac arrhythmias.

3. Reduced oxygen supply: In addition to the impaired removal of CO2, hypoventilation can decrease the amount of oxygen taken in during breathing. When combined with APAP therapy, which is designed to improve airflow and oxygenation, hypoventilation compromises the effectiveness of the treatment. Insufficient oxygen supply can lead to hypoxemia, a condition characterized by low oxygen levels in the blood, which can have severe consequences for the organs and tissues.

4. Increased cardiovascular strain: Hypoventilation, hypercapnia, and hypoxemia put additional strain on the cardiovascular system. The body attempts to compensate for the imbalance by increasing heart rate and blood pressure. Prolonged strain on the cardiovascular system can contribute to the development or exacerbation of heart disease, particularly in individuals with pre-existing cardiovascular conditions.

Therefore, hypoventilation in the context of APAP therapy is dangerous because it disrupts the removal of CO2, impairs oxygenation, leads to respiratory acidosis, and increases cardiovascular strain. It is crucial for individuals using APAP therapy to ensure proper ventilation and promptly address any signs or symptoms of hypoventilation or breathing difficulties by seeking medical attention.

In summary: With severe oxygen desaturation <80%SpO2, evidence of hypoventilation and predominantly central sleep apnoea would be reasons to not utilise APAP. A sleep physician review and a laboratory based sleep study with CPAP titration is recommended.