Intrathecal Morphine for Analgesia in Minimally Invasive Cardiac Surgery: A Randomized, Placebo-controlled, Double-blinded Clinical Trial

Abstract

Background Intrathecal morphine decreases postoperative pain in standard cardiac surgery. Its safety and effectiveness have not been adequately evaluated in minimally invasive cardiac surgery. The authors hypothesized that intrathecal morphine would decrease postoperative morphine consumption after minimally invasive cardiac surgery. Methods In this randomized, placebo-controlled, double-blinded clinical trial, patients undergoing robotic totally endoscopic coronary artery bypass received either intrathecal morphine (5 mcg/kg) or intrathecal saline before surgery. The primary outcome was postoperative morphine equivalent consumption in the first 24 h after surgery; secondary outcomes included pain scores, side effects, and patient satisfaction. Pain was assessed via visual analog scale at 1, 2, 6, 12, 24, and 48 h after intensive care unit arrival. Opioid-related side effects (nausea/vomiting, pruritus, urinary retention, respiratory depression) were assessed daily. Patient satisfaction was evaluated with the Revised American Pain Society Outcome Questionnaire. Results Seventy-nine patients were randomized to receive intrathecal morphine (n = 37) or intrathecal placebo (n = 42), with 70 analyzed (morphine 33, placebo 37). Intrathecal morphine patients required significantly less median (25th to 75th percentile) morphine equivalents compared to placebo during first postoperative 24 h (28 [16 to 46] mg vs. 59 [41 to 79] mg; difference, –28 [95% CI, –40 to –18]; P < 0.001) and second postoperative 24 h (0 [0 to 2] mg vs. 5 [0 to 6] mg; difference, –3.3 [95% CI, –5 to 0]; P < 0.001), exhibited significantly lower visual analog scale pain scores at rest and cough at all postoperative timepoints (overall treatment effect, –4.1 [95% CI, –4.9 to –3.3] and –4.7 [95% CI, –5.5 to –3.9], respectively; P < 0.001), and percent time in severe pain (10 [0 to 40] vs. 40 [20 to 70]; P = 0.003) during the postoperative period. Mild nausea was more common in the intrathecal morphine group (36% vs. 8%; P = 0.004). Conclusions When given before induction of anesthesia for totally endoscopic coronary artery bypass, intrathecal morphine decreases use of postoperative opioids and produces significant postoperative analgesia for 48 h. Editor’s Perspective What We Already Know about This Topic What This Article Tells Us That Is New

Pain Management Strategies for Minimally Invasive Cardiothoracic Surgery

“…Dhawan et al 57 randomly assigned patients undergoing totally endoscopic CABG surgery to either intrathecal morphine (5 μg/kg) or placebo injection. Morphine injection decreased opiate consumption approximately 50% during the first 24 h postoperatively, although there were higher rates of mild nausea.…”

Analgesic efficacy and risk of low-to-medium dose intrathecal morphine in patients undergoing cardiac surgery: An updated meta-analysis

“…Patients in the control groups received local anesthesia of the back, no treatment, or placebo (e.g., intrathecal normal saline). Analysis of the occurrence of respiratory depression including postoperative reintubation or the use of non-invasive ventilation in the five trials with available information ( 3 , 30 – 33 ) showed no such incidence in a total of 234 patients, suggesting the safety of its clinical use. Nevertheless, because of the absence of events indicating respiratory depression in all of the five studies, statistical analysis could not be performed.…”

“…The mean or median age ranged from 25.9 to 67.3 years with a male predominance (>70%, 11 trials). CABG and mixed CABG/valve surgery were performed in eight ( 3 , 31 , 34 – 36 , 39 – 41 ) and four ( 28 , 29 , 33 , 37 ) trials, respectively, while the other three trials were focused on minimally invasive cardiac surgery ( n = 2) ( 30 , 38 ) and valve surgery ( n = 1) ( 32 ). ITM was administered preoperatively in all studies with a maximum dose of 0.5 mg or 7 μg/kg and a minimum dose of 0.25 mg or 0.4 μg/kg.…”

“…ITM was administered preoperatively in all studies with a maximum dose of 0.5 mg or 7 μg/kg and a minimum dose of 0.25 mg or 0.4 μg/kg. Intrathecal morphine was used as a single agent in 12 trials ( 3 , 28 , 30 – 34 , 36 , 38 – 41 ) and as a component of a combined regimen in three studies ( 29 , 35 , 37 ). Patients in the control groups received local anesthesia of the back, no treatment, or placebo (e.g., intrathecal normal saline).…”

Year in Review 2021: Noteworthy Literature in Cardiothoracic Anesthesia

“…While previous studies have demonstrated lower systemic opioid requirements with use of intrathecal morphine for open cardiac surgery, 25 Dhawan et al sought to determine the benefits in minimally invasive cardiac surgery. 26 Pain after mini-thoracotomy and robotic thoracic ports is consistently more significant than that of median sternotomy, 27 warranting additional therapy to achieve analgesia. In this placebo-controlled, double blinded trial, 79 patients were randomized to either intrathecal morphine (5 mcg/kg, 37 patients) or intrathecal saline (42 patients) prior to induction of general anesthesia.…”