Complex Sleep Apnea Syndrome

In recent years, many studies have found that in the process of using CPAP to treat OSA, when the optimal therapeutic pressure point is reached or close to, central apnea will appear after obstructive respiratory events are basically eliminated. The phenomenon was first called complex sleep apnea syndrome(CompSAS) in 2005.

There are also many scholars questioning this, thinking that CompSAS is not an independent disease, but the emergence of CompSAS inevitably affects the effectiveness of CPAP in the treatment of OSA.

According to the current definition, CompSAS refers to CSA-based sleep-disordered breathing after OSA titration treatment with CPAP, so the short-term treatment effect of CPAP is not good. However, some studies have shown that after several months to one year of long-term CPAP treatment, most of the CSA can disappear, so the CSA that appears in the CPAP treatment of OSA may be temporary. The emergence of CSA may be related to sleep fragmentation and sleep stage migration caused by the initial titration of CPAP.


  • The age of onset of CompSAS mostly occurs between the ages of 50 and 60, and it is more common in men, accounting for about 81% to 83%.
  • The main symptoms are snoring, fatigue, daytime sleepiness, and poor sleep quality.
  • CompSAS is similar to OSA, but may have a higher apnea index and occurs mainly during NREM in the supine position.

There appears to be a turning point during CPAP titration therapy, at which pressure levels are increased to completely clear obstructive events to induce CSA/CSR, and to reduce pressure residual obstructive respiratory events lead to respiratory airflow limitation correlations Arousal, therefore the optimal pressure for positive airway pressure therapy cannot be determined. Although clinical symptoms improved after positive airway pressure therapy, poor sleep quality and daytime fatigue remained.

Causes of CompSAS

The pathogenesis of CompSAS is unclear, and research on it is still at the theoretical stage.
Possible reasons are:

  • CompSAS apnea may be caused by an imbalance of arterial CO2.
  • Excessive use of CPAP may lead to central apnea.
  • Severe upper airway obstruction in patients with OSA impairs the ventilatory control system, which together leads to hypercapnia. However, after the application of CPAP to relieve upper airway obstruction, the CO2 tension may be lower than any ventilation conditions set by CPAP. Central apnea may occur if PaCO2 falls below the CO2 apnea threshold. With the extension of CPAP treatment time, the CO2 threshold that causes apnea gradually decreases, and central apnea will gradually disappear.

Diagnosis of complex sleep apnea syndrome

The diagnostic criteria of CompSAS are that after titration by CPAP, obstructive respiratory events are cleared and the residual central apnea index (CAI) is ≥ 5 times/h, or a predominantly CSR.

Early recognition of CompSAS is important as it appears in the midst of CPAP therapy and responds poorly to CPAP. compSAS needs to be differentiated primarily from OSA.

Treatment of complex sleep apnea syndrome

The goal of treating CompSAS is primarily to reduce AHI to normal, restore normal sleep architecture and reduce daytime sleepiness, thereby reducing associated complications and improving the patient's quality of life.

Although there is no systematic treatment for CompSAS, noninvasive ventilation remains the most effective and promising treatment for CompSAS. Other treatments include lateral sleep, oxygen therapy, inhaled CO2, increased dead space ventilation, and avoidance of excessive CPAP titration therapy.

There is no accepted and proven treatment for those patients with CompSAS who have had poor results with long-term CPAP therapy. In recent years, there has been increasing research into the use of adaptive servo-ventilation (ASV) in the treatment of CompSAS.