Impact of intrathecal morphine analgesia on the incidence of pulmonary complications after cardiac surgery: a single center propensity-matched cohort study

Background: Acute pain and systemic opioids may both negatively impact respiratory function after cardiac surgery. This study analyzes the local practice of using intrathecal morphine analgesia (ITMA) with minimal parenteral opioid administration in cardiac surgery, specifically the impact on postoperative pulmonary complications (PPCs). Methods: Data from adult patients who underwent elective cardiac surgery between January 2002, and December 2013 in a single center were analyzed. Propensity scores estimating the likelihood of receiving ITMA were used to match (1: 1) patients with ITMA and patients with intravenous analgesia (IVA). Primary outcome was PPCs, a composite endpoint including pneumonia, adult respiratory distress syndrome, and any type of acute respiratory failure. Secondary outcomes were in-hospital mortality, cardiovascular complications, and length of stay in the intensive care unit (ICU) and hospital. Results: From a total of 1'543 patients, 920 were treated with ITMA and 623 with IVA. No adverse event consequent to the spinal puncture was reported. Propensity score matching created 557 balanced pairs. The occurrence of PPCs in patients with ITMA was 8.1% vs. 12.8% in patients with IVA (odds ratio, 0.6; 95% CI, 0.40-0.89; p = 0.012). Fewer patients with ITMA had a prolonged stay in the ICU (> 4 days; 16.5% vs. 21.2%, p = 0.047) or in the hospital (> 15 days; 25.5% vs. 31.8%. p = 0.024). In-hospital mortality and cardiovascular complications did not differ significantly between the two groups. Conclusion: In this study involving cardiac surgical patients, ITMA was safely applied and was associated with fewer PPCs.