Background: Recently, opioid-containing periarticular multimodal drug injection (PMDI) has become a common practice for pain management after artificial joint replacement surgery. The aim of this retrospective study was to investigate the incidence of postoperative respiratory depression (RD) by examining respiratory rate (RR) and arterial oxygen saturation (SpO2) in the patients who received opioid-containing PMDI. 

Methods: We examined the digital records of patients who met all of the following conditions: 1) underwent total knee or hip arthroplasty at our institution; 2) received a PMDI (containing morphine 5–10 mg) during surgery; 3) had their postoperative RR and SpO2 continuously recorded; and 4) received no opioid either for spinal/epidural anesthesia during surgery or for postoperative analgesia continuously intra and postoperatively. The incidence of postoperative RD, defined as RR < 10 breaths/min for 5 minutes or longer and/or SpO2 < 90% for 1 minute, between the end of surgery and the morning of the first postoperative day. 

Results: We included 23 patients who met the conditions. Of these, five patients (22%) had RD, only RR < 10 breaths/min, 23 times in total (median 3, range 1–10) after surgery. The median time from PMDI to RD occurrence was 180 minutes (range 70–505), and the median RD event duration was 400 seconds (309–1449). There were no cases of patients with SpO2 < 90%. 

Conclusion: Although no hypoxic episode occurred in the current study, PMDI containing opioids can cause postoperative RD. Careful postoperative respiratory monitoring is essential for early detection and treatment.

04 / Respiratory Depression After Intraoperative Opioid-Containing Periarticular Multimodal Drug Injection