End-tidal carbon dioxide, a point-of-care biomarker to assess severity in acute asthma: A systematic review

Accurate severity assessment in acute asthma is vital to guide patient management and disposition. End-tidal carbon dioxide (EtCO₂) has been proposed as a real-time measure for this purpose. This study aimed to systematically review literature on EtCO₂ measurement in assessing the severity of acute asthma exacerbations.

Five databases were searched. Studies with patients of any age with acute asthma exacerbations and at least one clinical outcome measure were included. Studies on intubated patients and outpatients were excluded. Two independent reviewers screened abstracts and then full texts for eligibility.

1242 records were identified and 11 studies were included in the review. Three out of five studies found significant differences in capnography measures between patients eventually admitted and those discharged from the emergency department. Patients with lower initial EtCO₂ were more likely to require hospital admission. Other components of the capnography waveform were associated with disposition, including a larger alpha angle and a lower ratio between phase III duration and respiratory rate being associated with hospital admission. Seven studies examined correlations between capnography measures and other markers of airway obstruction and weak or absent correlations were generally found. Three studies reported significant change in capnography measures after treatment.

Lower EtCO₂ may predict poorer outcome in acute asthma exacerbations. Other measures taken from the capnography waveform appear to be useful indicators of severity. Addressing patient selection issues and conducting prognostic accuracy studies of EtCO₂ with clinical endpoints may provide meaningful evidence for clinical practice.