High- versus low-dose ketamine for analgesia in older adults in the emergency department

Background and objectives

Ketamine is increasingly being utilized in the management of acute pain in the emergency department (ED), including for older adults, a population at increased risk of adverse effects from medications. We aimed to compare the safety and analgesic effects of high-dose (≥0.3 mg/kg) to low-dose (<0.3 mg/kg) intravenous (IV) ketamine among older ED patients.

Methods

Multi-center, retrospective cohort study of adults ≥60 years who received IV ketamine for pain between 2018 and 2021. The primary outcome was pain improvement as measured by the Numerical Rating Scale (NRS) pain score within 60 min after administration. Secondary outcomes included adverse effects (early discontinuation, nausea, rescue benzodiazepines and intubation) and the need for rescue analgesia. Linear regression was used to assess the association between the change in NRS pain scores and dose after adjusting for baseline pain, requiring an additional dose of ketamine, and receiving an opioid.

Results

A total of 130 older adults received ketamine as an analgesic (37 high-dose, 93 low-dose). Median age was 69.2 years, 52 % were women, 40 % had a history of substance use disorder. Prior to ketamine, 76 % received alternate analgesics and 23 % antiemetics. Baseline mean pain score was lower in the high-dose group (6.7 vs. 8.3, difference −1.7 [95 % CI −2.6 to −0.7], p = 0.013). Change in NRS pain scores were similar between the high-dose and low-dose groups (−2.4 [95 % CI −3.6 to −1.3] vs −1.6 [95 % CI −2.2 to −0.9], p = 0.27). After adjustment for baseline pain score, the high-dose group had a larger reduction in pain scores (−1.3 [95 % CI −2.6 to −0.1], p = 0.042) and percent change of pain (−23.8 % [95 % CI −42.1 % to −5.4 %], p = 0.012). There was no significant difference in rates of rescue analgesia (35.1 % vs. 44.1 %, p = 0.35) or early discontinuation (29.7 % vs. 32.3 %, p = 0.78). Rates of adverse effects were similar.

Conclusion

High-dose and low-dose ketamine reduced pain scores in older adults. High-dose ketamine led to a greater reduction in pain scores, and there was no observed difference in adverse effects or the need for rescue analgesia. One-third needed discontinuation of ketamine in both groups.