Background
Respiratory depression (RD) is a significant cause of morbidity and mortality in the postoperative period. Previous studies have shown RD complications to be as high as 3%1,2 and have implicated various contributing factors, including use of neuromuscular blocking agents (NMBAs), opioids, obstructive sleep apnea, unmonitored settings, etc.3-6 Past studies have also identified the potential use of continuous monitoring to mitigate the risk of RD and called for additional investigation.4-6 Given this context, we investigated the potential use of universal continuous monitoring via capnography in the PACU as a means of detecting adverse respiratory events in the postoperative period.
Methods
Using an IRB-approved protocol, 125 patients were enrolled at our institution over a 9-month period as part of a multi-center prospective observational trial. Inclusion criteria consisted of the following: age ≥18 years, ASA score II-IV, procedures necessitating general anesthesia with a duration ≥1.5 hours, use of intraoperative opioids, ≥45 minutes of recovery in the PACU, and discharge to an inpatient setting. Exclusion criteria included pregnancy. The FDA-approved Capnostream20p (CS20p) bedside monitor provided real-time measurements of ventilation parameters (end-tidal CO2, respiration rate, and raw CO2 waveform as a function of time) and oxygenation parameters (heart rate and SpO2). The CS20p was blinded and its alarms silenced to staff and study personnel during standard of care in the PACU. Subsequently, inpatient charts from the first 24 hours post-discharge from the PACU were reviewed for evidence of clinical intervention indicating possible RD (reintubation, ICU admission, administration of naloxone, etc.). Data pertaining to ventilation and oxygenation parameters was collected and is currently undergoing further analysis by Medtronic.
Results
125 patients were enrolled. 61.7% were female; mean age was 54.7±15.1 years (range, 20-82 years); mean BMI was 29.7±7.7 (range, 18-66); and ASA scores were II (47.9%), III (50.0%), and IV (1.1%). Of 125 enrolled patients, 2 were omitted due to the need for unblinded continuous CO2 monitoring per standard of care. Of the remaining 123 patients, 0 patients were documented to necessitate clinical interventions for suspected RD in the first 24 hours post-discharge from the PACU. Both omitted patients had uncomplicated recoveries.
Conclusions
This study did not demonstrate the utility of universal continuous CO2 monitoring in our PACU as none of the enrolled patients required clinical intervention for suspected RD in the first 24 hours after PACU discharge. Therefore, it may be beneficial to continue studying the role of CO2 monitoring in settings with higher rates of RD. While continuous CO2 monitoring may not be necessary for all patients, further investigation into a potential reduction of relative risk in select high-risk patients may be warranted. For example, one patient was removed from our study for unblinded continuous CO2 monitoring due to obesity. Apart from calls for potential universal continuous CO2 monitoring, other risk factors contributing to RD have been addressed and altered (i.e. more judicious administration of opioids, fewer NMBAs). Ultimately, more research is needed to determine what patient populations will most benefit from expanded continuous CO2 monitoring protocols.
