Daytime Hypercapnia in Adult Patients with Obstructive Sleep Apnea in China
Obstructive sleep apnea (OSA) is a prevalent sleep-disordered breathing condition that has garnered significant attention due to its association with various comorbidities and its impact on patient health. One of the critical aspects of OSA is the occurrence of daytime hypercapnia, which has been reported in varying incidences across different populations. This article delves into the findings of a retrospective study conducted in China, which aimed to explore the prevalence and clinical characteristics of daytime hypercapnia in adult patients with OSA.
The study was conducted from January 2013 to February 2021 in the sleep unit of a hospital in Beijing, China. The research included adult patients aged 18 years and older who had undergone polysomnography, pulmonary function tests, and arterial blood gas analysis. Patients were excluded if they had an apnea-hypopnea index (AHI) of less than 5 events per hour, if central or mixed apnea/hypopnea was the primary suspicion, or if they had significant pulmonary function impairment, as indicated by a forced expiratory volume in 1 second (FEV1) to forced vital capacity (FVC) ratio of less than 70% or predicted FEV1 and FVC percentages of less than 80%, unless the impairment was due to obesity. A total of 294 participants were included in the study.
Polysomnography was performed using the Embla N7000 system, and respiratory events were scored according to the 2017 American Academy of Sleep Medicine criteria. Nocturnal hypoxemia was assessed using the oxygen desaturation index (ODI), minimum and mean arterial oxygen saturation (SaO2) values, and the percentage of time spent with oxygen saturation below 90% during total sleep time (SIT90%). Pulmonary function tests were conducted using a standard spirometer, and arterial blood gas analysis was performed with the ABL800 analyzer. Hypercapnia was defined as a partial pressure of carbon dioxide in arterial blood (PaCO2) of 45 mmHg or higher.
The prevalence of daytime hypercapnia in the study population was found to be 8.16%, with 24 out of 294 patients meeting the criteria. Among these hypercapnic patients, 58.33% were diagnosed with obesity hypoventilation syndrome (OHS), which is characterized by obesity (BMI ≥30 kg/m2), daytime hypercapnia, and sleep-disordered breathing, excluding other causes of alveolar hypoventilation. The incidence of daytime hypercapnia in patients with OSA alone was 3.57%, or 10 out of 280 patients.
The study compared eucapnic and hypercapnic patients with OSA and found no significant differences in gender, age, BMI, FEV1/FVC ratio, or AHI between the two groups. However, hypercapnic patients had lower percentages of predicted FEV1 and FVC, lower daytime PaO2 and SaO2, higher bicarbonate levels, and more severe nocturnal hypoxia, as indicated by higher ODI and SIT90% values and lower minimum and mean SaO2 values. In a multivariable adjusted model, higher bicarbonate levels and lower percentages of predicted FVC were significantly associated with daytime hypercapnia.
The findings of this study suggest that the prevalence of daytime hypercapnia in Chinese patients with OSA is lower than previously reported in other Asian populations. The study highlights the importance of considering comorbidities such as OHS when assessing daytime hypercapnia in OSA patients. The presence of higher bicarbonate levels was identified as the best predictor of daytime hypercapnia, with an odds ratio of 6.533. The study also noted that non-obese patients with OSA and daytime hypercapnia had an incidence rate of 5.56%, but the prognosis for these patients remains unclear.
The study has several limitations, including its retrospective design, which did not allow for the analysis of other pathophysiological features, complications, and prognosis of OSA. Additionally, the screening for pulmonary function and arterial blood gas analysis was not routine for all OSA patients, leading to a smaller sample size. The authors recommend large-scale, multicenter, prospective studies to confirm these findings and further explore the mechanisms and prognosis of OSA patients with daytime hypercapnia.
In conclusion, this study provides valuable insights into the prevalence and clinical characteristics of daytime hypercapnia in adult patients with OSA in China. The findings underscore the importance of differential diagnosis between OSA and OHS, particularly in obese patients, and highlight the need for further research to better understand the implications of daytime hypercapnia in OSA patients.
doi.org/10.1097/CM9.0000000000001602
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