Background Delirium and pain are common and serious postoperative complications. Subanaesthetic ketamine is often administered intraoperatively for postoperative analgesia and to spare postoperative opioids. Some evidence also suggests that ketamine prevents delirium. The primary purpose of this trial was to evaluate the effectiveness of ketamine in preventing postoperative delirium in older adults after major surgery. Secondary outcomes, viewed as strongly related to delirium, were postoperative pain and opioid consumption. Methods This was a multicentre, international, randomised trial that enrolled adults older than 60 undergoing major cardiac and noncardiac surgery under general anaesthesia. Participants were enrolled prior to surgery and gave written informed consent. We used a computer-generated randomisation sequence. Patients at study sites were randomised to one of three study groups in blocks of 15 to receive intraoperative administration of (i) placebo (intravenous normal saline), (ii) low dose ketamine (0.5 mg/kg) or (iii) high dose ketamine (1 mg/kg). Study drug was administered following induction of anaesthesia, prior to surgical incision. Participants, clinicians, and investigators were all masked to group assignment. Delirium and pain were assessed twice daily in the first three postoperative days using the Confusion Assessment Method and Visual Analog Scale, respectively. Postoperative opioid use was recorded, and hallucinations and nightmares were assessed. Analyses were performed by intention-to-treat and adverse events were evaluated. The Prevention of Delirium and Complications Associated with Surgical Treatments [PODCAST] trial is registered in clinicaltrials.gov; NCT01690988 Findings Between February 6, 2014 and June 26, 2016, 1360 patients assessed and 672 were randomised, with 222 in the placebo group, 227 in the low dose ketamine group, and 223 in the high dose ketamine group. There was no difference in postoperative delirium incidence between those in the combined ketamine groups and those who received placebo (19.45% vs. 19.82%, respectively; absolute difference, 0.36%; 95% CI, −6.07% to 7.38%; p=0.92). There were no significant differences among the three groups in maximum pain scores (p=0.88) or median opioid consumption (p=0.47) over time. There were more postoperative hallucinations (p=0.01) and nightmares (p=0.03) with escalating doses of ketamine. Adverse events (cardiovascular, renal, infectious, gastrointestinal, bleeding), whether viewed individually (P value for each >0.40) or collectively (82/222 [36.9%] in placebo group, 90/227 [39.6%] in low dose ketamine group, 91/223 in high dose ketamine group [40.8%]; P=0.69), did not differ significantly across the three groups. Interpretation The administration of a single subanaesthetic dose of ketamine to older adults during major surgery did not show evidence of reducing postoperative delirium, pain, or opioid consumption, and might cause harm by inducing negative experiences. Given current evidence and guidelines related to ketamine and postoperative analgesia, the unexpected secondary findings regarding pain and opioid consumption warrant replication or refutation in subsequent research. Funding The funders of the study had no role in study design, data collection, data analysis, data interpretation, or writing of the report. The principal investigators (MSA and GAM) had full access to all the data in the study and had final responsibility for the decision to submit for publication.
