Review of: Svenson JE, Abernathy MK: "Ketamine for prehospital use: new look at an old drug." American Journal of Emergency Medicine. 25(8), 977-980, 2007.
This article describes the experience an air medical program has had with the use of ketamine as an analgesic. The researchers administered ketamine to 40 patients and tracked the occurrence of adverse outcomes. Ketamine was administered to wide range of patients -- from two months to 70 years of age -- suffering from an assortment of conditions such as acute coronary syndrome to multiple trauma and burns. The dose was 1 mg/kg administered intravenously or 5 mg/kg administered intramuscularly. Twelve patients required repeat dosing to sustain analgesia.
Although the authors don't provide any objective evidence to support their claims that the patients attained sufficient analgesia, they do tell us that none suffered any adverse reactions. However, again, they don't define what they would consider to be adverse reactions.
The researchers spend the majority of the paper explaining ketamine's suspected mechanism of action through its dissociative effects at low dose and analgesic effects at high doses. The authors contend that the drug is safe and should, therefore, be considered as a possible alternative to traditional narcotics.
I'm encouraged to see more programs expanding the horizon of pre-hospital analgesia. Unfortunately, this paper isn't a scientific comparison of ketamine with any other type of treatment. However, it is an excellent review of how ketamine works and why it may be superior to narcotics.
For instance, it's believed that the dissociative "out of body" state that has made this drug a popular one of abuse can also relieve the patient from pain. It does this by essentially disconnecting their consciousness from the pain. While doing this, ketamine induces a trance-like state. This trance-like state also has some hemodynamic consequences that could be useful in trauma, including an increase sympathetic tone leading to a rise in blood pressure. This very same effect could be deleterious to the cardiac patient, but morphine may share this negative cardiac effect through the release of histamine.
I'm not sure I'm ready to embrace the use of ketamine as a pre-hospital analgesic because it fails one or more of the Dr. Wesley EMS pharmacology rules. A pre-hospital medication should be rapid in onset (this one is), effect titratable (this one isn't), short half-life (depends on the ketamine dose) and have a reversal agent (no antidote but time for ketamine).Still, a very interesting paper from my colleagues here in Wisconsin.