Breath of Fresh Air – Capnography Trends in OHCA

September 5, 2024

Written by Sam Parnell

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Dynamic increases in continuous end-tidal CO₂ (EtCO₂) were associated with increased odds of return of spontaneous circulation (ROSC) for patients with out-of-hospital cardiac arrest (OHCA), but EtCO₂ trended down in patients who did not achieve ROSC.

EtCO₂ is both trendy and timely!
Many guidelines recommend EtCO₂ to confirm advanced airway placement and guide resuscitation during cardiac arrest. However, there is limited data on the association between continuous EtCO₂ levels and patient outcomes during OHCA.

This study was a secondary analysis of EtCO₂ recordings from the Pragmatic Airway Resuscitation Trial evaluating adult patients with nontraumatic OHCA. Continuous EtCO₂ waveform levels over the course of resuscitation were measured, and temporal changes in EtCO₂ were evaluated in relation to ROSC. The authors adjusted for other factors such as age, sex, bystander CPR, initial ECG rhythm, etc.

Overall, 1113 patients with an advanced airway and EtCO₂ capnography were included. Most patients had an unwitnessed arrest (52.0%) and non-shockable rhythm (84.6%). Furthermore, only 17.8% of patients achieved ROSC, and 10.4% survived 72 hours after cardiac arrest. Average duration of resuscitation was 19 minutes for patients without ROSC compared to 24 minutes for patients with ROSC.

Initial EtCO₂ values were similar and did not differentiate ROSC vs non-ROSC. Curiously, 20 minutes prior to the end of resuscitation, median EtCO₂ values were relatively high and did not differentiate ROSC (30.8 mmHg) vs non-ROSC groups (30.5 mmHg). However, temporal trends for median EtCO₂ levels were significantly different between patients with ROSC and those without ROSC. At 10 minutes, the median EtCO₂ for ROSC cases was 39.8 compared to 26.1 mmHg (P < .001) for non-ROSC cases. In cases that achieved ROSC, the median EtCO₂ level increased from 30.5 to 43.0 mmHg (P for trend < .001). In contrast, for non-ROSC cases, median EtCO₂ decreased from 30.8 to 22.5 mmHg (P for trend < .001). A similar trend was noted for patients who survived greater than 72 hours post cardiac arrest. Using a multivariable logistic regression model, the authors found that changes in EtCO₂ over time were linked to the likelihood of achieving ROSC, with an odds ratio of 1.45 (95%CI 1.31-1.61).

How will this change my practice?
Continuous end-tidal CO₂ monitoring is an extremely useful tool during cardiac arrest. This study highlights the importance of using temporal changes in EtCO₂ to guide resuscitation. After reviewing this article, I plan to utilize the change in EtCO₂ levels over time instead of discrete EtCO₂ cutoffs to guide cardiac arrest management and help determine when to terminate resuscitation in the ED.

Source
Temporal Trends in End-Tidal Capnography and Outcomes in Out-of-Hospital Cardiac Arrest: A Secondary Analysis of a Randomized Clinical Trial. JAMA Netw Open. 2024;7(7):e2419274. doi:10.1001/jamanetworkopen.2024.19274. PMID: 38967927.