From the Guidelines
Pre-hospital ETCO2 monitoring is crucial for assessing ventilation status and confirming proper endotracheal tube placement, with a target range of 35-45 mmHg, as suggested by the most recent evidence 1.
Importance of ETCO2 Monitoring
ETCO2 monitoring is essential in pre-hospital care for several reasons:
- It helps confirm proper endotracheal tube placement, reducing the risk of esophageal intubation 2.
- It provides valuable information on ventilation status, allowing for adjustments to be made to improve patient outcomes 3.
- It can be used to guide CPR quality, with increasing ETCO2 values during resuscitation correlating with improved cardiac output and potential return of spontaneous circulation 2.
Implementation and Interpretation
For implementation, the ETCO2 detector should be attached to the ventilation circuit between the endotracheal tube and the bag-valve mask or ventilator.
- Colorimetric detectors change color based on CO2 levels, with yellow indicating the presence of CO2 and confirming tracheal placement.
- Quantitative capnography provides continuous numerical readings and waveforms, allowing for more accurate monitoring.
- Low ETCO2 values (<30 mmHg) may indicate hyperventilation, decreased cardiac output, or pulmonary embolism, while high values (>45 mmHg) suggest hypoventilation or increased metabolic activity 1.
- Absent or minimal ETCO2 after intubation strongly suggests esophageal intubation, requiring immediate tube repositioning.
Limitations and Considerations
It is essential to consider the limitations and potential pitfalls of ETCO2 monitoring, including:
- False-positive results can occur after ingestion of carbonated liquids 2.
- False-negative results can occur in the setting of pulmonary embolism, significant hypotension, contamination of the detector with gastric contents, and severe airflow obstruction 2.
- The accuracy of ETCO2 monitoring may be affected by the patient's clinical status, the cause of arrest, and the quality of CPR 3.
Recommendation
Based on the most recent evidence, targeting normocapnia (a partial pressure of carbon dioxide of 35–45 mm Hg) is suggested for adults with return of spontaneous circulation (ROSC) after cardiac arrest 1. This recommendation is based on the latest consensus on cardiopulmonary resuscitation and emergency cardiovascular care science, which suggests that targeting normocapnia is reasonable, despite the lack of evidence for benefit or harm from targeting CO2 values above or below the normal range 1.
From the Research
Pre-hospital ETCO2 Monitoring
- Pre-hospital ETCO2 monitoring is a non-invasive measurement of exhaled CO2, widely established in the pre-hospital environment for verification of endotracheal tube placement 4.
- The American Heart Association recommends ETCO2 measurement for confirmation of all intubations 4.
- ETCO2 monitors are compact, rugged, and have extended battery operating times, making them suitable for pre-hospital use 4.
Clinical Indications and Limitations
- ETCO2 monitoring has been used to guide ventilation in the pre-hospital setting, but its role is expanding 5.
- However, the sole use of ETCO2 to monitor ventilation may lead to avoidable respiratory acidosis, particularly in severely traumatized and burn patients 5.
- ETCO2 did not correlate with measured PaCO2 in a study of 160 patients, with mean ETCO2 significantly lower than mean PaCO2 5.
- Patients arriving acidotic were more likely to die, and mortality, acidosis, and higher base deficits were predictors of a worse correlation between ETCO2 and PaCO2 5.
Diagnostic and Prognostic Value
- Pre-hospital ETCO2 levels can differentiate between cardiac and obstructive causes of dyspnoea, with lower ETCO2 levels predicting congestive heart failure 6.
- ETCO2 has been associated with survival following out-of-hospital cardiac arrest, with both high and low ETCO2 values linked to increased mortality 7.
- A systematic review found that ETCO2 values during cardiac arrest correlate with the likelihood of return of spontaneous circulation and survival, but cannot be used as a mortality predictor in isolation 8.
ETCO2 Values and Outcomes
- Maximum pre-hospital ETCO2 values of <20 mmHg, 20-29 mmHg, and >50 mmHg were associated with increased mortality compared to values of 30-40 mmHg 7.
- An ETCO2 value of <10 mmHg after 20 minutes of monitoring was 96.7% specific and 6.9% sensitive for mortality 7.
- Initial ETCO2 values of more than 1.33 kPa may be 100% sensitive for predicting survival, but this finding is not consistent across all studies 8.