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Objectives <p>In obesity hypoventilation syndrome (OHS), nocturnal hypoventilation can precede daytime respiratory failure. Therefore, the hypercapnic burden index was introduced to quantify sleep-related CO₂ retention.</p> Methods <p>Thirty-one patients who underwent polysomnography with transcutaneous capnography and met OHS criteria were retrospectively included in this single-center cross-sectional study. The area above the predetermined transcutaneous partial pressure of CO<sub>2</sub> thresholds of 45 mmHg (thresh45) and 50 mmHg (thresh50) from the extracted capnography graphs was computed and statistical associations between the calculated areas exceeding the CO<sub>2</sub> limits (OOL Area) and maximum nocturnal CO₂ (maxCO₂), mean nocturnal CO₂ (meanCO₂) and the percentage of predicted forced vital capacity (FVC%) were examined.</p> Results <p>Very strong positive correlations were revealed between maxCO<sub>2</sub> and both thresh45 (Spearman’s rho = 0.906, <i>p</i> &lt; 0.000001) and thresh50 (Spearman’s rho = 0.953, <i>p</i> &lt; 0.000001), as well as between meanCO<sub>2</sub> and both thresh45 (Spearman’s rho = 0.918, <i>p</i> &lt; 0.000001) and thresh50 (Spearman’s rho = 0.937, <i>p</i> &lt; 0.000001), thereby validating hypercapnic burden against classic nocturnal hypercapnia metrics. Significant negative correlations of these metrics with FVC% (Spearman’s rho = −0.49, <i>p</i> = 0.01 and Spearman’s rho = −0.45, <i>p</i> = 0.02, respectively) also supported it as a marker of functional impairment. While not outperforming classic metrics in this regard, it captured clinically relevant variability, as several outliers displayed better alignment of FVC% with threshold-based indices than with meanCO₂.</p> Conclusion <p>This underscores the heterogeneity of nocturnal hypoventilation in OHS and the potential value of more nuanced markers in individual patients, as daytime hypercapnia might not be present yet, and maxCO<sub>2</sub> and meanCO<sub>2</sub> do not account for low or intermittent but cumulative CO<sub>2</sub> elevations. Identifying such outliers is clinically important, as these patients may be at heightened risk of progression or may respond differently to interventions such as non-invasive ventilation.</p>

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Beyond mean and maximum CO₂: introducing hypercapnic burden as a marker of sleep-related hypoventilation

  • 期刊论文

  • 发表日期：

    2026年4月1日

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  • Alexandros Kalkanis,
  • Mavroudis Eleftheriou,
  • Aliki Karkala,
  • Bertien Buyse,
  • Dries Testelmans

摘要

Objectives

In obesity hypoventilation syndrome (OHS), nocturnal hypoventilation can precede daytime respiratory failure. Therefore, the hypercapnic burden index was introduced to quantify sleep-related CO₂ retention.

Methods

Thirty-one patients who underwent polysomnography with transcutaneous capnography and met OHS criteria were retrospectively included in this single-center cross-sectional study. The area above the predetermined transcutaneous partial pressure of CO2 thresholds of 45 mmHg (thresh45) and 50 mmHg (thresh50) from the extracted capnography graphs was computed and statistical associations between the calculated areas exceeding the CO2 limits (OOL Area) and maximum nocturnal CO₂ (maxCO₂), mean nocturnal CO₂ (meanCO₂) and the percentage of predicted forced vital capacity (FVC%) were examined.

Results

Very strong positive correlations were revealed between maxCO2 and both thresh45 (Spearman’s rho = 0.906, p < 0.000001) and thresh50 (Spearman’s rho = 0.953, p < 0.000001), as well as between meanCO2 and both thresh45 (Spearman’s rho = 0.918, p < 0.000001) and thresh50 (Spearman’s rho = 0.937, p < 0.000001), thereby validating hypercapnic burden against classic nocturnal hypercapnia metrics. Significant negative correlations of these metrics with FVC% (Spearman’s rho = −0.49, p = 0.01 and Spearman’s rho = −0.45, p = 0.02, respectively) also supported it as a marker of functional impairment. While not outperforming classic metrics in this regard, it captured clinically relevant variability, as several outliers displayed better alignment of FVC% with threshold-based indices than with meanCO₂.

Conclusion

This underscores the heterogeneity of nocturnal hypoventilation in OHS and the potential value of more nuanced markers in individual patients, as daytime hypercapnia might not be present yet, and maxCO2 and meanCO2 do not account for low or intermittent but cumulative CO2 elevations. Identifying such outliers is clinically important, as these patients may be at heightened risk of progression or may respond differently to interventions such as non-invasive ventilation.