Anesthesiologists routinely use capnography for both general anesthesia and sedation. We consider this the standard of care for sedation. This is not the case for nonanesthesiologists (e.g., specialists and nurses) administering deep sedation. Should it be? Does capnography use prevent hypoxemia?
Dr. Kim van Loon, Division of Anesthesiology Intensive Care and Emergency Medicine, University Medical Center Utrecht, Utrecht, the Netherlands, and coauthors randomized over 400 adults undergoing minor gynecologic procedures to receive either capnography or only standard monitoring. The results of their analysis are published in this month’s issue of Anesthesia & Analgesia in the article titled “Capnography During Deep Sedation with Propofol by Nonanesthesiologists: A Randomized Controlled Trial.”
The authors hypothesized that patients undergoing deep sedation with propofol where capnography was used would have a lower incidence of hypoxemia. For the trial, oxygen was not routinely administered. Pulse oximetry was monitored for both the capnography and standard care groups,
The incidence of hypoxemia (Spo2 <91%) was 25.7% in the capnography group and 24.9% in the standard care group. The number of patients who experienced profound hypoxemia (Spo2 <81%) was similar across groups (3.4% vs. 2.9%), and the number of those whose hypoxemic episode was prolonged (≥60 sec) did not differ significantly (3.9% vs. 1.4%). Nonetheless, most hypoxemic episodes were ≤15 sec. The incidence of airway manipulation, e.g., jaw-thrust, was higher for patients who received capnography (49.5% vs. 32.1%). Supplemental oxygen use was similar: it was administered in 12.6% of the capnography group and 8.1% of the standard care group.
This interesting manuscript demonstrates that when patients breathe room air, capnography does not provide a notable “early warning” of impending hypoxemia during deep sedation with propofol. It shows that withholding supplemental oxygen to detect hypoventilation is a bogus concept. Withholding supplemental oxygen in sedation patients results in high levels of hypoxia. Even if patients are monitored with capnography, the incidence of hypoxia is unacceptable.
The significant incidence of hypoxemia (25%) suggests that the combination of supplemental oxygen plus capnography might be a safer option. Indeed, the study that needs to be done is an evaluation of whether capnometry makes a difference in patients receiving supplemental oxygen. This study did not provide evidence that capnography improves patient safety because the study design increased the risk of hypoxia in all patients.