Among over 100,000 adults undergoing general anesthesia for non-cardiac, non-neurosurgical, and non-transplant procedures, low-dose ketamine (0.35 mg/kg or less) given during surgery was associated with a 26% lower odds of postoperative delirium within 7 days compared to no ketamine, with an absolute risk reduction of 0.7%. Higher doses of ketamine did not affect delirium risk. The dose-response relationship was U-shaped, with the lowest delirium risk at cumulative doses of 0.25–0.34 mg/kg.
A low-dose ketamine infusion in the intensive care unit (ICU) after surgery reduced fentanyl consumption by 15% (68 µg over 24 hours) compared with placebo, a small but statistically significant opioid-sparing effect. The effect appeared stronger in patients who had intraabdominal surgery. Pain and sedation scores did not differ between groups, and no acute adverse effects were observed. However, a secondary follow-up (average 43 months later) of 45 patients found that those who received ketamine reported a higher incidence of frightening and delusional memories of their ICU stay (65% vs 41%). Low-dose ketamine modestly reduces opioid use but may increase the risk of traumatic memories after critical illness.