Measures of overnight oxygen saturation to characterize sleep apnea severity and predict postoperative respiratory depression

Abstract

Background: Sleep apnea syndrome, characterized by recurrent cessation (apnea) or reduction (hypopnea) of breathing during sleep, is a major risk factor for postoperative respiratory depression. Challenges in sleep apnea assessment have led to the proposal of alternative metrics derived from oxyhemoglobin saturation (SpO₂), such as oxygen desaturation index (ODI) and percentage of cumulative sleep time spent with SpO₂ below 90% (CT90), as predictors of postoperative respiratory depression. However, their performance has been limited with area under the curve of 0.60 for ODI and 0.59 for CT90. Our objective was to propose novel features from preoperative overnight SpO₂ which are correlated with sleep apnea severity and predictive of postoperative respiratory depression.

Methods: Preoperative SpO₂ signals from 235 surgical patients were retrospectively analyzed to derive seven features to characterize the sleep apnea severity. The features included entropy and standard deviation of SpO₂ signal; below average burden characterizing the area under the average SpO₂; average, standard deviation, and entropy of desaturation burdens; and overall nocturnal desaturation burden. The association between the extracted features and sleep apnea severity was assessed using Pearson correlation analysis. Logistic regression was employed to evaluate the predictive performance of the features in identifying postoperative respiratory depression.

Results: Our findings indicated a similar performance of the proposed features to the conventional apnea-hypopnea index (AHI) for assessing sleep apnea severity, with average area under the curve ranging from 0.77 to 0.81. Notably, entropy and standard deviation of overnight SpO₂ signal and below average burden showed comparable predictive capability to AHI but with minimal computational requirements and individuals' burden, making them promising for screening purposes. Our sex-based analysis revealed that compared to entropy and standard deviation, below average burden exhibited higher sensitivity in detecting respiratory depression in women than men.

Conclusion: This study underscores the potential of preoperative SpO₂ features as alternative metrics to AHI in predicting postoperative respiratory.

Keywords: Logistic regression; Oxyhemoglobin saturation (SpO2); Postoperative respiratory depression; Prediction; Signal processing; Sleep apnea.

Fig. 1

Sex-differences of sleep apnea and SpO₂ measures in patients with and without postoperative respiratory depression. a apnea–hypopnea index (AHI), b total arousal index, c respiratory-related arousal index, d standard deviation of overnight SpO2 signal (SpO₂ STD), e entropy of overnight SpO₂ signal (SpO₂ ENT), f below average burden (BAB), g average of normalized desaturation burdens of overnight desaturation episodes with ≥ 3% drops (ODB AVG), h standard deviation of normalized desaturation burdens of overnight desaturation episodes with ≥ 3% drops (ODB STD), i entropy of normalized desaturation burdens of overnight desaturation episodes with ≥ 3% drops (ODB ENT), j Overall nocturnal desaturation burden (NDB). RD: respiratory depression. Values show p-values

Fig. 2

Performance of the sleep apnea and SpO₂ measures in predicting postoperative respiratory depression. AHI: apnea–hypopnea index, SpO₂ STD: standard deviation of overnight SpO₂ signal, SpO₂ ENT: entropy of overnight SpO₂ signal, BAB: below average burden, ODB AVG: average of normalized desaturation burdens of overnight desaturation episodes with ≥ 3% drops, ODB STD: standard deviation of normalized desaturation burdens of overnight desaturation episodes with ≥ 3% drops, ODB ENT: entropy of normalized desaturation burdens of overnight desaturation episodes with ≥ 3% drops, NDB: Overall nocturnal desaturation burden. All models included sex, BMI, and pre-existing cardiorespiratory disorders (arterial hypertension, coronary artery disease, stroke, angina, myocardial infarction, heart failure, coronary revascularization, asthma, chronic obstructive pulmonary disease) to adjust for patients’ demographics. The error bars show the 95% confidence interval

Fig. 3

Correlation between apnea–hypopnea index (AHI) and SpO₂ Measures. a standard deviation of overnight SpO2 signal (SpO₂ STD), b entropy of overnight SpO₂ signal (SpO₂ ENT), c below average burden (BAB), d average of normalized desaturation burdens of overnight desaturation episodes with ≥ 3% drops (ODB AVG), e standard deviation of normalized desaturation burdens of overnight desaturation episodes with ≥ 3% drops (ODB STD), f entropy of normalized desaturation burdens of overnight desaturation episodes with ≥ 3% drops (ODB ENT), g Overall nocturnal desaturation burden (NDB). h correlation values

Fig. 4

Correlation between total arousal index and SpO₂ Measures. a standard deviation of overnight SpO₂ signal (SpO₂ STD), b entropy of overnight SpO₂ signal (SpO₂ ENT), c below average burden (BAB), d average of normalized desaturation burdens of overnight desaturation episodes with ≥ 3% drops (ODB AVG), e standard deviation of normalized desaturation burdens of overnight desaturation episodes with ≥ 3% drops (ODB STD), f entropy of normalized desaturation burdens of overnight desaturation episodes with ≥ 3% drops (ODB ENT), g Overall nocturnal desaturation burden (NDB).) correlation values

Fig. 5

Correlation between respiratory-related arousal index and SpO₂ Measures. a standard deviation of overnight SpO₂ signal (SpO₂ STD), b entropy of overnight SpO₂ signal (SpO₂ ENT), c below average burden (BAB), d average of normalized desaturation burdens of overnight desaturation episodes with ≥ 3% drops (ODB AVG), e standard deviation of normalized desaturation burdens of overnight desaturation episodes with ≥ 3% drops (ODB STD), f entropy of normalized desaturation burdens of overnight desaturation episodes with ≥ 3% drops (ODB ENT), g Overall nocturnal desaturation burden (NDB). h correlation values