The Efficacy of Peripheral Opioid Antagonists in Opioid-Induced Constipation and Postoperative Ileus: A Systematic Review of the Literature.

Opioid-induced constipation has a negative impact on quality of life for patients with chronic pain and can affect more than a third of patients. A related but separate entity is postoperative ileus, which is an abnormal pattern of gastrointestinal motility after surgery. Nonselective µ-opioid receptor antagonists reverse constipation and opioid-induced ileus but cross the blood-brain barrier and may reverse analgesia. Peripherally acting µ-opioid receptor antagonists target the µ-opioid receptor without reversing analgesia. Three such agents are US Food and Drug Administration approved. We reviewed the literature for randomized controlled trials that studied the efficacy of alvimopan, methylnaltrexone, and naloxegol in treating either opioid-induced constipation or postoperative ileus. Peripherally acting µ-opioid receptor antagonists may be effective in treating both opioid-induced bowel dysfunction and postoperative ileus, but definitive conclusions are not possible because of study inconsistency and the relatively low quality of evidence. Comparisons of agents are difficult because of heterogeneous end points and no head-to-head studies.

Postoperative Analgesia in Patients Undergoing Primary or Revision Knee Arthroplasty with Adductor Canal Block.

BACKGROUND: Multimodal analgesia featuring peripheral nerve blocks decreases postoperative pain for patients undergoing primary total knee arthroplasty (TKA). Many anesthesiologists and surgeons advocate for the use of adductor canal blocks (ACBs) for analgesia, which result in less weakness compared to femoral nerve blocks. Few data exist to guide analgesic management in total knee revision (TKR), considered to be more painful than primary TKA. We hypothesized that TKR patients with a continuous ACB would use more opioids than primary TKA patients who received the same analgesic regimen. METHODS: A retrospective study of 58 TKA and TKR patients who received ACBs in a multimodal protocol was conducted from 1/2014 to 3/2016. Exclusion criteria included patients who took ≥ 20 mg of morphine daily preoperatively. The primary outcome was 48-hour opioid consumption. Secondary outcomes included pain ratings, catheter boluses, and catheter infusion rate changes over 48 hours. RESULTS: For the primary outcome of 48-hour opioid consumption, there was no significant difference between groups. Postoperative pain ratings were not significantly different during the overall 48-hour time period. There were also no significant differences in catheter boluses and infusion rate changes. Least squares regression analysis revealed a positive correlation between number of previous knee surgeries and postoperative pain level. CONCLUSIONS: Patients who underwent TKR with continuous ACB experienced a similar postoperative analgesic course as primary TKA patients. Within the TKR cohort, the number of previous revisions was positively associated with pain level. Larger prospective studies with TKR are needed to confirm these findings.