Can expired carbon dioxide (CO2) be used to assess cardiopulmonary resuscitation (CPR) quality?

Can End-Tidal CO2 Be Used to Assess CPR Quality?

Yes, end-tidal CO2 (ETCO2) monitoring can and should be used to assess CPR quality when available, as it provides real-time feedback on the effectiveness of chest compressions and correlates with cardiac output during resuscitation. 1

Guideline-Based Recommendations

The 2015 American Heart Association guidelines recommend using physiologic parameters including quantitative waveform capnography to monitor and optimize CPR quality when feasible (Class IIb, LOE C-EO). 1 The 2010 International Consensus similarly states that continuous capnography or capnometry monitoring, if available, may be beneficial by providing feedback on the effectiveness of chest compressions. 1

How ETCO2 Reflects CPR Quality

Direct Correlation with Compression Parameters

• ETCO2 values directly correlate with chest compression depth during CPR. For every 10mm increase in compression depth, ETCO2 increases by 1.4 mmHg. 2
• Compression rate alone does not predict ETCO2 over the dynamic range of actual compression delivery. 2
• ETCO2 reflects cardiac output and myocardial blood flow generated by chest compressions during the low-flow state of CPR. 1, 3

Ventilation Effects

• Excessive ventilation rate decreases ETCO2 values. For every 10 breaths/min increase in ventilation rate, ETCO2 decreases by 3.0 mmHg. 2
• This relationship allows providers to optimize both compression and ventilation parameters simultaneously. 2

Clinical Thresholds and Actions

During Active CPR

If PETCO2 is <10 mmHg during CPR, immediately attempt to improve chest compression quality by optimizing compression depth, rate, and recoil. 3, 4 Multiple studies demonstrate that ETCO2 values below 10 mmHg after 20 minutes of CPR are associated with only a 0.5% likelihood of return of spontaneous circulation (ROSC). 5

Prognostic Values

• ETCO2 values >10 mmHg are substantially associated with achieving ROSC. 1, 5
• Initial or 20-minute ETCO2 >20 mmHg appears to be a better predictor of ROSC than the 10 mmHg cutoff. 5
• Case-averaged ETCO2 values in patients who achieve ROSC are significantly higher (34.5±4.5 mmHg) compared to those who do not (23.1±12.9 mmHg). 2

Detection of ROSC

An abrupt increase in ETCO2 is a sensitive early indicator of ROSC, often preceding detection by vital signs. 1, 6 This typically manifests as a rapid rise peaking at approximately 2 minutes after ROSC. 6

Implementation Algorithm

Step 1: Establish Monitoring

• Apply continuous waveform capnography immediately upon advanced airway placement. 3
• Ensure proper equipment function and tube placement confirmation. 3

Step 2: Interpret Initial Values

• **If initial ETCO2 <10 mmHg:** Immediately optimize compression depth (target >50mm), ensure full chest recoil, and verify compression rate 100-120/min. 3, 2
• If initial ETCO2 10-20 mmHg: Continue high-quality CPR with attention to compression parameters.
• If initial ETCO2 >20 mmHg: Maintain current CPR quality while addressing reversible causes.

Step 3: Monitor Trends

• Decreasing ETCO2 during CPR indicates deteriorating compression quality or worsening patient physiology. 6
• Adjust compression technique if ETCO2 trends downward. 2
• Reduce ventilation rate if ETCO2 is low despite adequate compressions. 2

Step 4: Recognize ROSC

• Sudden increase in ETCO2 (often to >30-40 mmHg) indicates possible ROSC. 6
• Pause briefly to check for pulse when abrupt ETCO2 rise occurs. 1

Important Caveats and Limitations

Special Populations

In single-ventricle patients following Stage I palliation, PETCO2 may not be a reliable indicator of CPR quality because pulmonary blood flow changes rapidly and does not necessarily reflect cardiac output during CPR. 1 Standard CPR should still be provided, but ETCO2 interpretation requires caution in this population.

Technical Factors Causing Falsely Low Values

• Bronchospasm or mucous plugging of the endotracheal tube 3
• Kinking or obstruction of the endotracheal tube 3
• Circuit leaks or disconnections 4
• Equipment malfunction 4

Prognostic Limitations

While low ETCO2 values are associated with poor prognosis, some patients with ETCO2 values outside typical ranges have survived. 1 Therefore, ETCO2 should guide CPR optimization efforts but not serve as the sole criterion for terminating resuscitation. 1

Evidence Quality Considerations

The recommendation is based primarily on Level 4 evidence from observational studies showing correlations between ETCO2 and outcomes. 1 No clinical studies have directly examined whether titrating resuscitative efforts to ETCO2 values improves survival or neurologic outcomes. 1 However, the physiologic rationale is sound, the monitoring is non-invasive and continuous, and the evidence consistently demonstrates that ETCO2 reflects CPR-generated blood flow. 2, 7, 6