Effect of intrathecal morphine plus patient-controlled analgesia with morphine versus patient-controlled analgesia with morphine alone on total morphine dose 24hours post-surgery: a systematic review

Objective:The objective of this review was to evaluate the effects of preoperative intrathecal morphine (ITM) in addition to patient-controlled analgesia with morphine (PCAM) versus PCAM without preoperative ITM on total morphine dose in the first 24hours postoperatively in adult patients undergoing abdominal or thoracic surgery.Introduction:Postoperative pain is a significant problem for patients undergoing major abdominal and thoracic surgery. Intrathecal morphine can reduce postoperative pain and reduce intravenous (IV) morphine requirements during the first 24hours after surgery; however, the amount of IV morphine dose reduction achieved has not been well established. This knowledge could help anesthesia providers determine if ITM is an appropriate analgesic option for patients.Inclusion criteria:This review included studies with participants 18 years of age or older receiving general anesthesia for abdominal or thoracic surgery. Studies were included that used the intervention of preoperative ITM in addition to PCAM versus PCAM without preoperative ITM. Total morphine dose in milligrams during the first 24hours after surgery was the outcome of interest.Methods:A search of PubMed and CINAHL was conducted for studies published between January 1984 and October 2018 using the key terms intrathecal, morphine, postoperative, pain, patient-controlled analgesia and general anesthesia. Index terms and keywords from identified articles were used to search CINAHL, Cochrane Central Register of Controlled Trials (CENTRAL), Embase, ClinicalTrials.gov, Ovid MEDLINE, ProQuest Dissertations and Theses/Nursing and Allied Health Databases, and Scopus. The reference lists of articles that underwent critical appraisal were searched for additional studies. Methodological quality was assessed using the JBI Critical Appraisal Checklist for Randomized Controlled Trials. Two independent reviewers assessed each selected article. Study results were pooled in statistical meta-analysis using the JBI System for the Unified Management, Assessment and Review of Information, and two studies were described in narrative form. Differences in IV morphine dose between the ITM plus PCAM and PCAM alone groups were calculated to produce the weighted mean difference (WMD) utilizing a 95% confidence interval (CI). Heterogeneity was assessed using chi (2) and I-2 values. Subgroup analysis was conducted on two studies that included IV non-opioid analgesia in addition to ITM and PCAM for postoperative analgesia.Results:Seven RCTs with a total sample size of 352 patients were included in this review. Five studies that evaluated postoperative total morphine dose in milligrams with and without preoperative ITM were included for statistical meta-analysis, with 277 participants from four countries. Total morphine dose was significantly reduced in patients who received ITM (WMD = -24.44mg, 95% CI -28.70 to -20.18mg) compared to PCAM without ITM. Subgroup analysis of two studies involving 112 participants using IV acetaminophen in addition to ITM and PCAM indicated no additional benefit after ITM was already administered (WMD = -25.93, 95% CI -32.05 to -19.80mg). Two studies with 75 participants were described narratively because total morphine dose was reported as median rather than mean values.Conclusions:In this review, ITM provided a significant decrease in overall total morphine dose during the first 24hours after surgery in abdominal surgery patients. The addition of IV non-opioids to the postoperative analgesia protocol showed no additional reduction in postoperative IV morphine dose between groups.Systematic review registration number:PROSPERO CRD42018100613