Prediction of nocturnal hypoventilation by daytime capillary bicarbonate measurements in children

Background: Nocturnal hypoventilation (NH) contributes substantially to morbidity and mortality, especially in children with neuromuscular disorders, yet reliable daytime predictors are lacking. Transcutaneous CO₂ (TcCO₂) monitoring during sleep is the diagnostic gold standard, but sleep laboratory resources are limited. Renal bicarbonate retention reflects sustained hypercapnia and may serve as a daytime surrogate marker. This study examined the association between morning capillary blood bicarbonate levels and nocturnal hypercapnia in a large pediatric cohort. Methods: This monocentric retrospective study analyzed overnight TcCO2 recordings between 2014 and 2025 from all patients aged 0–18 years regardless of underlying disease or respiratory support. Only technically adequate recordings≥ 6 hours were included. NH was defined as mean TcCO₂≥ 50 mmHg. Capillary blood gas analysis was performed within one hour after awakening. TcCO₂ parameters and blood gas values were analyzed using group comparisons, linear regression and ROC analyses. Subgroup analyses excluded patients with diuretic therapy/ renal disease and were stratified by respiratory support. Results: A total of 958 TcCO₂ recordings from 406 patients were analyzed. NH was present in 151 recordings. Morning bicarbonate was significantly higher in patients with NH compared to those without (28.89± 4.29 vs. 25.15± 2.88 mmol/l; p< 0.001). Mean TcCO₂ showed a statistically significant positive linear relationship with morning bicarbonate (R²= 0.252). ROC analysis yielded an AUC of 0.78 with an optimal bicarbonate cut-off of 26.8 mmol/l (sensitivity 72%, specificity 76%). Diagnostic performance remained stable after excluding patients with diuretic use/ renal disease (AUC 0.77–0.78). Elevated morning bicarbonate was associated with higher nocturnal CO₂ burden across all respiratory support modalities, including spontaneous breathing. Morning bicarbonate< 26 mmol/l demonstrated a high negative predictive value (> 90%) for excluding NH. Conclusion: Morning bicarbonate correlates significantly with nocturnal hypercapnia and represents a practical daytime screening marker for pediatric NH. Morning bicarbonate< 26 mmol/l reliably excludes clinically relevant nocturnal CO₂ retention across various clinical conditions and respiratory support modalities. However, elevated bicarbonate alone lacks sufficient specificity and should be followed by confirmatory nocturnal CO₂ monitoring. Publication History Article published online: 26 February 2026 © 2026. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany