The drug ketamine does not lower levels of pain or reduce the need for pain-killing opioid drugs in the days after an operation, according to US researchers.
They noted that anaesthetists often give patients low doses of the drug during operations, with recent studies even suggesting it might alleviate post-surgical delirium and confusion in older adults.
“We were particularly surprised by the lack of an effect on post-operative pain”
However, in their study, published in The Lancet, indicated that the drug achieved none of these benefits.
Furthermore, they noted that older surgery patients who received ketamine during surgery were more likely to experience hallucinations and nightmares.
The researchers followed 672 surgery patients in four countries – the US, Canada, India and South Korea – who were all at least 60 years old.
During surgery, the patients either received no ketamine, a very low dose of the drug, or a slightly higher dose – matching those routinely given to surgery patients by anaesthetists.
The patients were then evaluated for several days after surgery. Researchers asked about pain, kept track of the amount of opioids needed to control it, and evaluated them twice daily for delirium.
“There’s been a big increase in the amount of ketamine given in the operating room”
Lead author Professor Michael Avidan, from Washington University, said: “In recent years, there’s been a big increase in the amount of ketamine given in the operating room because clinicians are trying to prevent pain after surgery without relying on opioid drugs.
“We found that the current practice of giving low doses of ketamine to patients during surgery is not having the desired effect,” he said. “So we need to determine whether higher doses might be more effective, or we need to find other alternatives to opioids.”
Professor Avidan added that because the study had the same results at different sites in different countries made him confident that the way ketamine was being used during surgery was not having the desired effect on delirium and post-operative pain.
“While not helping with those things, ketamine was causing other problems for patients, such as an increase in hallucinations and nightmares,” he added.
Study co-author Professor George Mashour, from the University of Michigan, said: “Overall, patients who develop delirium have worse outcomes and are at higher risk for long-term cognitive decline. So it’s really important to try to prevent it if we can.
“We were particularly surprised by the lack of an effect on post-operative pain,” he added.