Can Ketamine Relieve Injury Pain?

Managing severe levels of acute pain while a patient is en route to a nearby hospital is a key part of the duties performed by paramedics. Still, prehospital acute pain is often inadequately managed – one study of ambulance visits to a Parisian suburb found that only around half of patients received adequate prehospital pain relief.

To address this, two British ambulance services are now participating in a new trial to investigate whether ketamine injections may be a more effective pain relief treatment for severe injury pain than the current treatment options available to Britain’s first responders.

Two UK ambulance services to trial ketamine for injury

In the United Kingdom, the strongest painkiller that paramedics are permitted to administer is morphine. But this opioid painkiller presents its own distinct set of challenges – intravenous morphine can be slow to make its effects felt and leave the patient with undesirable side effects including vomiting, drowsiness, or low blood pressure.

Research has suggested that ketamine might be a promising alternative to morphine in dealing with acute prehospital pain, with ketamine formulations already being used by some paramedic services in Australia and Canada. However, despite some scientific study, the current body of research is not considered strong enough or large enough to definitively support the use of ketamine injections by paramedic crews.

The Paramedic Analgesia Comparing Ketamine and MorphiNe in trauma, or “PACKMaN” study is a new trial supported by the University of Warwick, involving the West Midlands Ambulance Service NHS Foundation Trust and the Yorkshire Ambulance Service NHS Trust. The trial, which began this May, will run until early 2022 and test the effectiveness of ketamine pain relief in eligible patients who are transported by these ambulance services.

Eligible patients – those over the age of 16 who have suffered an injury causing severe acute pain and are able to receive injectable painkillers – are enrolled into the trial by the attending paramedics and randomly allocated treatment with either morphine or ketamine. The trial will also look to assess subsequent patient recovery by contacting patients over the phone at 3 and 6 months post-injury to ask about their experiences, and combine this with data recorded by the hospital during their stay. In total, the trial is aiming to enroll over 400 eligible patients over the course of the study time period.

Attending paramedics will be trained to follow strict guidelines in administering morphine and ketamine, with additional naloxone and midazolam medications being made available to treat any adverse side effects arising from the use of either painkiller. The primary outcome for the trial will be measured using the numerical Sum of Pain Intensity Difference (SPID) scores reported by patients. Results are expected to be published later in 2022.

Analytical Cannabis contacted the University of Warwick researchers for comment, but the team declined to respond prior to the trial’s completion.

Ketamine for prehospital pain relief

While the current body of research on ketamine for acute injury pain is small, it does generally appear to support the use of ketamine as a treatment for prehospital pain relief.

A Canadian study published in the Annals of Emergency Medicine journal evaluated the use of intranasal ketamine in addition to the local standard paramedic pain relief procedure using nitrous oxide. The study was randomized and double-blinded, with all patients suffering from acute pain that was scored at a 5 or greater on a verbal numeric rating scale (VNRS) pain assessment. The paramedics found that intranasal ketamine given with nitrous oxide resulted in a clinically significant reduction in pain compared to nitrous oxide with a placebo, with only a small increase in minor adverse events.

In a 12 month retrospective analysis on the use of prehospital ketamine by ambulance services in the Australian Capital Territory, just over two-thirds of all recorded episodes of prehospital ketamine use were for analgesic purposes. They found that around 17% patients receiving prehospital ketamine went on to be intubated – but noted that agitated or combative patients receiving ketamine as a sedative were nearly 3.5 times more likely to be intubated than patients receiving ketamine for pain relief.

One randomized controlled trial published in the Emergency Medicine Journal examined the long-term effects of ketamine treatment for pain relief. Here, the researchers concluded that although ketamine did decrease pain scores on arrival at the hospital compared to morphine in the short-term, this difference did not appear to significantly affect the prevalence of persistent pain or health-related quality of life 6 months after the initial injury.

A review of prehospital ketamine use published in the American Journal of Biomedical Science & Research found that ketamine showed an increased efficacy at reducing pain with fewer adverse events as compared to opioids such as fentanyl. Ketamine for pain relief was also determined to have a better effect on improving systolic blood pressure in patients with severe trauma injuries.