Does End Tidal CO₂ Monitoring During Emergency Department Procedural Sedation and Analgesia With Propofol Decrease the Incidence of Hypoxic Events? A Randomized, Controlled Trial

Study objective

We determine whether the use of capnography is associated with a decreased incidence of hypoxic events than standard monitoring alone during emergency department (ED) sedation with propofol.

Methods

Adults underwent ED propofol sedation with standard monitoring (pulse oximetry, cardiac and blood pressure) and capnography and were randomized into a group in which treating physicians had access to the capnography and a blinded group in which they did not. All patients received supplemental oxygen (3 L/minute) and opioids greater than 30 minutes before. Propofol was dosed at 1.0 mg/kg, followed by 0.5 mg/kg as needed. Capnographic and SpO₂ data were recorded electronically every 5 seconds. Hypoxia was defined as SpO₂ less than 93%; respiratory depression, as end tidal CO₂ (etco₂) greater than 50 mm Hg, etco₂ change from baseline of 10%, or loss of the waveform.

Results

One hundred thirty-two subjects were evaluated and included in the final analysis. We observed hypoxia in 17 of 68 (25%) subjects with capnography and 27 of 64 (42%) with blinded capnography (P=.035; difference 17%; 95% confidence interval 1.3% to 33%). Capnography identified all cases of hypoxia before onset (sensitivity 100%; specificity 64%), with the median time from capnographic evidence of respiratory depression to hypoxia 60 seconds (range 5 to 240 seconds).

Conclusion

In adults receiving ED propofol sedation, the addition of capnography to standard monitoring reduced hypoxia and provided advance warning for all hypoxic events.

Introduction

Procedural sedation and analgesia for the management of acute procedural pain and anxiety in the emergency department (ED) is part of core competency in emergency medicine.¹ The American College of Emergency Physicians and the American Society of Anesthesiology recommend continuous monitoring of pulse rate and rhythm, respiratory rate, blood pressure, and pulse oximetry during moderate and deep sedation.2, 3

The use of real-time capnography as an adjunct to current procedural sedation safety and monitoring practice is under increasing scrutiny. Capnography noninvasively measures the partial pressure of carbon dioxide in exhaled breath and is tightly correlated with arterial CO₂ in patients with normal lung function. Capnography is a well-researched technology that has been used in anesthesia practice for patient safety monitoring for more than 35 years.4, 5

Minute ventilation is depressed by sedatives by reducing respiratory rate or tidal volume.⁶ Respiratory depression may produce hypercapnia (respiratory rate is affected proportionally greater than tidal volume) or hypocapnia (tidal volume is affected proportionally greater than respiratory rate).⁶ An absolute change from baseline of greater than 10 mm Hg or loss of the end tidal CO₂ (etco₂) waveform has been suggested to identify patients at risk of developing significant respiratory depression.⁷

There is now compelling evidence that capnography identifies respiratory depression well before the onset of hypoxia.8, 9, 10 This modality should allow physicians to intervene to improve ventilatory status. Whether physicians can use capnography to decrease sedation-associated hypoxia remains unclear.

Although pulse oximetry, pulse rate, and blood pressure monitoring are considered routine practice during ED procedural sedation and analgesia, capnography is not. If the addition of capnography helps physicians reduces hypoxia, then perhaps it should also be routine.

We determine whether physician use of real-time capnography is associated with a 15% decrease in the incidence of hypoxia compared with standard monitoring alone during ED procedural sedation with propofol.