Abstract

OBJECTIVES: We monitored increases in CO2 levels during sleep by measuring transcutaneous pCO2 (PtcCO2 ) to determine its relationship with polysomnographic data in normocapnic patients with obstructive sleep apnea syndrome (OSAS).

MATERIAL AND METHODS: Between October 2011 and December 2012, 139 patients underwent PtcCO2 monitoring with polysomnography. All patients were evaluated with arterial blood gas (ABG) measurements and pulmonary function tests (PFTs). We excluded 13 patients with COPD and/or daytime hypercapnia and 29 patients whose PtcCO2 records could not be evaluated.

RESULTS: The patients’ mean age was 46.8±10.3 years. Fifty-nine patients (60.8%) were male, and 38 (39.2%) patients were female. The mean overnight PtcCO2 was ≤45 mm Hg in 84 (86.6%) patients and >45 mm Hg in 13 (13.4%) patients. In the group with PtcCO2 >45 mm Hg, 10 patients had an apnea-hypopnea index (AHI) >15, and 3 patients had an AHI<15, without a statistically significant difference (p=0.078). The mean apnea and apnea/interapnea periods were similar. The mean PtcCO2 values correlated with time spent when the SpO2 was <90% (r=0.220, p<0.031). When we grouped the patients by AHI, 60 (61.8%) patients had an AHI>15 (moderate to severe OSAS), and 37 (37.2%) had an AHI<15 (mild OSAS). Of the former group, 16.7% had a mean PtcCO2 >45 mm Hg, whereas this ratio was 8.1% in the latter group. The difference was not statistically significant (p=0.359). In the group with an AHI>15, the highest PtcCO2 levels were significantly higher (p<0.05).

CONCLUSION: We conclude that seemingly eucapnic OSAS patients may experience hypercapnia when sleeping, and PtcCO2 monitoring may be useful in the early diagnosis of hypercapnia.