Capnography for assessing nocturnal hypoventilation and predicting compliance with subsequent noninvasive ventilation in patients with ALS

Abstract

Background: Patients with amyotrophic lateral sclerosis (ALS) suffer from hypoventilation, which can easily worsen during sleep. This study evaluated the efficacy of capnography monitoring in patients with ALS for assessing nocturnal hypoventilation and predicting good compliance with subsequent noninvasive ventilation (NIV) treatment.

Methods: Nocturnal monitoring and brief wake screening by capnography/pulse oximetry, functional scores, and other respiratory signs were assessed in 26 patients with ALS. Twenty-one of these patients were treated with NIV and had their treatment compliance evaluated.

Results: Nocturnal capnography values were reliable and strongly correlated with the patients' respiratory symptoms (R(2) = 0.211-0.305, p = 0.004-0.021). The duration of nocturnal hypercapnea obtained by capnography exhibited a significant predictive power for good compliance with subsequent NIV treatment, with an area-under-the-curve value of 0.846 (p = 0.018). In contrast, no significant predictive values for nocturnal pulse oximetry or functional scores for nocturnal hypoventilation were found. Brief waking supine capnography was also useful as a screening tool before routine nocturnal capnography monitoring.

Conclusion: Capnography is an efficient tool for assessing nocturnal hypoventilation and predicting good compliance with subsequent NIV treatment of ALS patients, and may prove useful as an adjunctive tool for assessing the need for NIV treatment in these patients.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1. The average level of end-tidal carbon dioxide (ETCO2) measured by waking supine capnography correlated significantly with arterial partial pressure of carbon dioxide (PaCO2) level, as measured by arterial blood gas analysis (p<0.001).

Figure 2. Correlations between nocturnal respiratory symptoms (orthopnea) with respiratory monitoring results.

Scores from orthopnea questionnaire were strongly correlated with the average level of ETCO2 (R2 = 0.305, p = 0.004) (A) and the duration of hypercapnea measured by nocturnal capnography (R2 = 0.211, p = 0.021) (B).

Figure 3. Receiver operating characteristic (ROC) curve for the duration of nocturnal hypercapnea relative to the total sleep time (ETCO2>47%) and the average nocturnal ETCO2 level (avr ETCO2) as predictors of good compliance with subsequent noninvasive ventilation (NIV) treatment.

The areas under the curve (AUCs) were 0.846 (95% confidence interval, CI: 0.628–1.000) and 0.856 (95% CI: 0.00–1.000), respectively.

Figure 4. The average ETCO2 level obtained with brief wake capnography screening (wake avr ETCO2) correlated significantly with symptoms of patients for nocturnal hypoventilation (orthopnea; p = 0.021) (A) and duration of nocturnal hypercapnea relative to the total sleep time (nocturnal ETCO2>47%; p<0.001) (B).

Figure 5. ROC curves for average ETCO2 measured by wake capnography screening and average SaO2 measured by wake pulse oximetry screening as predictors of good compliance with subsequent NIV treatment.

The AUC values were 0.840 (95% CI: 0.628–1.000) and 0.192 (95% CI: 0.000–0.389), respectively.