Oxygen deprivation state as a marker for the severity of obstructive sleep apnea

Abstract

Introduction Sleep apnea is classified as a sleep disorder characterized by a complete cessation, known as apneas, or impairment (partial cessation) of breathing, known as hypopneas. During obstructive sleep apnea (OSA), the airways become blocked, mostly due to the collapsing of the throat muscles or increased adipose tissue surrounding the airway. Apneas/hypopneas indirectly lead to the over-activity of the sympathetic nervous system. These events lead to a very interrupted sleep pattern and architecture. The most common symptoms of OSA are excessive daytime sleepiness, morning headaches and concentration problems. OSA may lead to various other disorders such as hypertension, diabetes mellitus, depression and heart failure when not treated. Limited research on OSA has been done in developing countries such as South Africa due to limited resources, funding and/or facilities. It is therefore critical that this disorder be studied in specific populations to establish more accurate parameters and normative values for clinicians to diagnose as well as treat the disorder.

Methods A total of 160 patients that had suspected OSA, were referred to a private practice of clinical neurophysiology (B. Tjallinks) by their respective physicians. They were subsequently admitted at a sleep laboratory, based in Pretoria, for a single night to test for the disorder. Full polysomnography (PSG) was used to monitor the patients’ sleep. Various information such as the desaturation index, amount of obstructive sleep apneas/hypopneas, sleep architecture and baseline oxygen-haemoglobin saturation were interpreted from the test. This information was then used to assess the severity of the disorder in the patients. The PSG data were then compared with other aspects of the patient such as BMI, medical history and questionnaires.

Results The oxygen deprivation state (ODS) and the apnea-hyponea index (AHI) were compared with many variables tested during the polysomnogram and it was found that ODS correlated stronger with the majority. The most important independent variables to test for hypoxia in this study was baseline SpO2, minimum SpO2, average desaturation and average duration of events. AHI was correlated (Pearson correlation coefficients) with the baseline SpO2 (-0.4463, weak), minimum SpO2 (-0.4716, weak), average desaturation (0.6701, moderate) and average duration of events (0.3262, weak). ODS was correlated (Pearson correlation coefficients) with the baseline SpO2 (-0.4524, weak), minimum SpO2 (-0.4820, weak), average desaturation (0.7524, strong) and average duration of events (0.5740, moderate). The ODS correlated stronger, even though mildly in some parameters, with all critical variables tested for the severity of hypoxic crisis in OSA.

Conclusion Based on all the study objectives and results, the ODS was able to correlate stronger with the critical polysomnography variables for hypoxia and thus has proven to be a better estimate of hypoxic crisis in the severity of obstructive sleep apnea. A raw grading scale was developed based on the results of this study and are as follows: Normal (ODS ≤ 2.0%), mild (2.0% < ODS ≤ 7.7%), moderate (7.7% < ODS ≤ 17.9%) and severe (ODS > 17.9%).