In patients undergoing total joint arthroplasty who are already receiving multimodal analgesia, there may be added benefit to incorporating intrathecal morphine. According to a recent retrospective study, the addition of intrathecal morphine to a multimodal analgesic regimen improved analgesia after surgery and reduced postoperative opioid consumption and postoperative nausea and vomiting (PONV).
“These data suggest that patients who receive intrathecal morphine have lower rates of PONV and lower opioid consumption,” said Jeremy Pearl, MD, a clinical instructor in the Department of Anesthesia and Perioperative Care at the University of California, San Francisco (UCSF). “However, because this study was retrospective, baseline characteristics were not completely balanced. There may be confounders, and we need a prospective study before definitive conclusions can be drawn.”
As Dr. Pearl reported, although prior studies have shown that intrathecal morphine after total joint arthroplasty leads to reduced postoperative opioid consumption (Br J Anaesth 2000;85:233-237), intrathecal morphine is also associated with increased PONV, pruritus and respiratory depression (Anesth Analg 1988;67:1082-1088). A multimodal analgesic approach for total joint arthroplasty, on the other hand, has shown a significant reduction in postoperative pain compared with a mostly opioid-based approach while minimizing side effects (JAMA 2003;290:2411-2418).
“Until two years ago, the majority of arthroplasty patients at UCSF received multimodal analgesia with intrathecal morphine. Because of concerns regarding the development of itching, nausea, vomiting and respiratory depression, however, we changed our standard, and it’s now up to the provider to determine whether there is a compelling reason why intrathecal morphine should be incorporated,” said Dr. Pearl, who noted that this change in practice provided a “great opportunity” for a retrospective study.
Two Intrathecal Dosing Groups
Dr. Pearl, Pedram Aleshi, MD, and their colleagues retrospectively analyzed 849 patients who had undergone primary total joint arthroplasty at UCSF and received bupivacaine spinal anesthesia alone (control) or with intrathecal morphine. Because of the wide range of intrathecal dosing, the researchers then stratified patients into low-dose (≤100 mcg) or high-dose (>100 mcg) groups. Patients in all three groups received multimodal analgesia, which consisted of an adductor canal perineural catheter, pre- and postoperative acetaminophen, gabapentin and nonsteroidal anti-inflammatory drugs. Perioperative outcome measures included visual analog scale (VAS) pain scores obtained through chart review; incidence of PONV identified by administration of antiemetics (ondansetron); total opioid consumption; distance walked on postoperative day 1; and time to hospital discharge. Multivariate regression predicting PONV was performed to control for confounders, the authors noted.
As Dr. Pearl reported at the 2017 annual meeting of the American Society of Regional Anesthesia and Pain Medicine (abstract 3570), patients who received intrathecal morphine (both high and low dose) had significantly lower mean pain scores on postoperative day 0 compared with patients who did not.
Including intrathecal morphine also resulted in reduced incidence of PONV. Patients who received low- and high-dose intrathecal morphine had a 42.6% and 38.2% rate of PONV, respectively, compared with 50.0% of patients in the control group. Moreover, patients receiving a low dose of intrathecal morphine consumed significantly fewer morphine equivalents (50.9±68.4) than those in the control (81±163.6) and high-dose intrathecal morphine (76.4±156.1) groups.
“We anticipated that increasing the dose of intrathecal morphine would decrease morphine equivalent consumption postoperatively, but this was not observed,” said Dr. Pearl, who noted that differences in baseline characteristics may account for these results.
A significantly greater percentage of patients who received high-dose intrathecal morphine were taking opioids before surgery and likely needed to continue their baseline opioid requirements in the postoperative period, he reported. In addition, the chronic pain patients in the high-dose group also were more likely to be opioid tolerant and thus require opioid dose escalation to achieve equivalent analgesic effect.
Finally, patients receiving intrathecal morphine were able to ambulate significantly farther and in a dose-dependent manner, said Dr. Pearl, who noted that lower average VAS pain scores on postoperative day 0 likely facilitated the increase in mobilization observed on postoperative day 1.
According to the researchers, the study was limited by its design, specifically the lack of randomization, leading to more patients taking preoperative opioids in the high-dose intrathecal morphine group. In addition, inability to control the amount of morphine administered led to significant variations. Finally, VAS pain scores and consumption of morphine equivalents were calculated per calendar day instead of increments of 24 hours postoperatively.
“In theory, early and later case starts should be evenly distributed among groups, but because this study is retrospective, we really couldn’t account for that,” Dr. Pearl acknowledged.
David Birnbach, MD, MPH, vice provost and professor of anesthesiology, obstetrics and gynecology, and public health at the University of Miami, asked whether intrathecal morphine should continue to play a role in this setting.
“It’s difficult to draw a conclusion from a retrospective study, but in my personal practice, low-dose intrathecal morphine (≤100 mcg) makes sense,” Dr. Pearl said. “Also, if a patient is on preoperative opioids, they likely will benefit more than somebody who is opioid naive for their postoperative pain control.”
“Can you explain why patients who received intrathecal morphine experienced less PONV?” Dr. Birnbach asked.
“We think it’s related to decreased opioid consumption in those groups,” Dr. Pearl said. “Although people get PONV from both intrathecal and oral opioid administration, people who did not receive intrathecal morphine required more oral opioids, which probably led to more opioid-induced PONV.”