What is the role of end-tidal carbon dioxide (ETCO2) monitoring during sedation?

From the Guidelines

End-tidal CO2 (ETCO2) monitoring is strongly recommended during procedural sedation to detect respiratory depression early, as it provides earlier detection of hypoventilation than pulse oximetry alone, allowing for prompt intervention before critical respiratory compromise occurs. ETCO2 monitoring should be used alongside standard monitoring (pulse oximetry, heart rate, blood pressure) for all moderate to deep sedation cases, regardless of the medications used. Normal ETCO2 values range from 35-45 mmHg; values above 50 mmHg indicate hypoventilation, while values below 30 mmHg suggest hyperventilation. A sudden drop in ETCO2 or absence of waveform may indicate apnea or airway obstruction requiring immediate intervention. For implementation, place the sampling line at the nares for spontaneously breathing patients or connect to the breathing circuit for intubated patients. Begin monitoring before sedation administration and continue until the patient fully recovers.

Key Points to Consider

• ETCO2 monitoring is particularly important when using opioids like fentanyl or sedatives like propofol, midazolam, or ketamine, which can all cause respiratory depression 1.
• The use of capnography in procedural sedation has been supported by various studies, which have shown its effectiveness in detecting hypoventilation and respiratory depression earlier than pulse oximetry alone 1.
• The American Society of Anesthesiologists (ASA) has concluded that CO2 monitoring "should be considered for all patients receiving deep sedation and for patients whose ventilation cannot be observed directly during moderate sedation" 1.
• While there is some uncertainty about the clinical relevance of ETCO2 monitoring, the available evidence suggests that it can improve patient safety by allowing for prompt intervention before critical respiratory compromise occurs 1.

Implementation and Monitoring

• Place the sampling line at the nares for spontaneously breathing patients or connect to the breathing circuit for intubated patients.
• Begin monitoring before sedation administration and continue until the patient fully recovers.
• Monitor ETCO2 values and waveforms closely, and be prepared to intervene promptly if signs of hypoventilation or respiratory depression are detected.
• Use ETCO2 monitoring in conjunction with standard monitoring (pulse oximetry, heart rate, blood pressure) to provide a comprehensive picture of the patient's respiratory status.

From the Research

Benefits of End Tidal CO2 Monitoring

• End tidal CO2 (ETCO2) monitoring can decrease the incidence of hypoxic events during sedation with propofol 2
• ETCO2 monitoring can provide advance warning for hypoxic events, with a median time of 60 seconds from capnographic evidence of respiratory depression to hypoxia 2
• Capnography is increasingly favored over pulse oximetry for monitoring respiratory function, as it can detect respiratory depression earlier 3

Accuracy of CO2 Monitoring

• The accuracy of ETCO2 measurements depends on the device used, the amount of supplemental oxygen, the amount of oral breathing, and the patient's minute ventilation 4
• CO2 sampling bite blocks and nasal cannulas can accurately monitor respiratory rate during sedation, but may not provide accurate ETCO2 measurements 4

Monitoring Requirements for Sedated Patients

• Current recommendations for monitoring sedated patients include patient responsiveness, blood pressure, respiratory rate, heart rate, and oxygen saturation 5
• ETCO2 monitoring can be used to monitor adequacy of ventilation, which is critical for patient safety during sedation 5

Improving Patient Safety with ETCO2 Monitoring

• ETCO2 monitoring can improve patient safety during propofol-based sedation by decreasing the incidence of CO2 retention and apnoeic events 6
• The use of ETCO2 monitoring can also shorten recovery time and reduce the need for airway interventions 6