Muhammad K Rafiq.
Value of periodic transcutaneous daytime Carbon dioxide monitoring in screening for Respiratory failure in patients with Amyotrophic lateral sclerosis.
Pak J Neurological Sci Jan ;14(1):22-7.

Background: There is no single test currently available, which can predict respiratory failure in patients with amyotrophic lateral sclerosis (ALS) with high sensitivity and specificity. This study explores the potential use of transcutaneous carbon dioxide (PtcCO2) monitoring in early detection of respiratory failure in ALS. Methods: This is a prospective observational cohort study consisting of 50 consecutive patients with ALS. The participants underwent 3 monthly assessments for symptoms of respiratory failure, forced vital capacity (FVC) and PtcCO2 monitoring. Once respiratory failure was clinically suspected by the treating physician, further follow-up was stopped. The presence of respiratory failure was confirmed with an overnight capnometry. Results: Symptoms of respiratory failure were the most powerful tool, alerting the physician to the possibility of respiratory failure. All the patients where respiratory failure was confirmed on overnight capnometry had symptoms of respiratory failure. 37% of these patients had FVC of > 50% predicted and only 13% had daytime hypercapnia. None of the patients had daytime hypercapnia without any other marker of respiratory failure. There was statistically significant difference between the day time PtcCO2 and median overnight PtcCO2 (p=0.0002). Conclusions: This study has emphasised the importance of symptom history as a screening tool to suspect respiratory failure in ALS. Once again, the limitations of FVC in predicting respiratory failure is demonstrated in this study. A normal daytime PtcCO2 may be falsely reassuring and day time hypercapnia is a late finding which implies established respiratory failure.

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