Comparing Ketamine and Morphine in the Treatment of Acute Fracture Pain

Opioid analgesia is the standard of care for treating moderate to severe pain in the emergency department. It is an effective medication that most practitioners are familiar using. Opioid use is not without risk, however. In managing acute pain, patients may experience hypotension, respiratory depression, hypoxia, nausea and vomiting, dysphoria, and itching. Patients at risk for respiratory depression include those with advanced age, renal failure, or treated with multiple other sedatives.

The current recommended dose for opioid administration for acute pain management is approximately 0.1 mg/kg as a loading dose, although some sources recommend up to 10 mg for patients weighing more than 50 kg. (Ducharme 2011; Yak 2011) A single center study demonstrated that patients received an average of 0.08 mg/kg of morphine, which did not adequately control their pain; no patient received an initial dose of 10 mg.(Bijur 2012) A post-operative pain study demonstrated that patients needed on average 12 mg or a mean weight-based dose of 0.17 mg/kg of morphine to achieve an acceptable level of pain reduction as determined by a 30 mm change on a visual analog scale.(Aubrun 2003) As such even if patients received 1 mg of hydromorphone, their pain would still not be adequately controlled.

Ketamine is a dissociative anesthetic that is a noncompetitive antagonist of N-methyl-D-aspartate (NMDA) receptors. Low dose ketamine (LDK) (0.03-0.05 mg/kg) has analgesic properties by modulating opioid tolerance and hyperalgesia.(Uprety 2013) Currently, ketamine is used in the emergency department for moderate sedations and "awake" intubations. In the pre-hospital setting, it is used in the management of patients with excited delirium and pain control.(Keseg 2014)(Wiel 2014)(Jennings 2013) Benefits include fewer serious adverse effects, especially involving respiratory depression and hypotension which occurs with high-dose or repeat doses of opioids.(Jennings 2013) In addition to not causing hypotension, ketamine can elevate a patient's blood pressure, which may be useful in some circumstances.(Johansson 2009) Emergence delirium is associated with ketamine; this is a rare adverse event and is usually alleviated with benzodiazepines. Additionally, LDK is unlikely to cause the emergence delirium or the dissociation usually associated with larger doses. Another potential complication is laryngospasm. Fortunately, this too is rare and in most cases, patients are easily bagged through the event.

LDK is efficacious in reducing multiple types of pain in a variety of settings. Ketamine infusions can reduce pain from vaso-occlusive pain crises seen in patients with sickle cell anemia.(Uprety 2013)(Neri 2013)(Jennings 2013) In the postoperative setting and intensive care unit, ketamine reduced the amount of morphine required to control pain.(Galinski 2007)(Bell 2006)(Herring 2013) In out-of-hospital trauma patients, ketamine combined with morphine produced superior analgesia to morphine alone. All patients received morphine and were then randomized to receive either morphine or ketamine if further analgesia was required. Ketamine had a change in the visual analog scale (VAS) of -5.6 (CI -6.2 to -5.0) while morphine had had a change of -3.2 (CI -3.7 to -2.7).(Jennings 2012) In another pre-hospital study, ketamine was administered to 1030 patients for pain or anesthesia. No patients incurred ketamine-induced respiratory adverse events.(Bredmose 2009) Preliminary studies have also investigated LDK in the emergency department (ED). Available research mainly consists of retrospective or observational data. In an observational study performed in an urban ED in California, LDK significantly improved patient's pain without adversely effecting blood pressure, heart rate, or respiratory drive. Twenty-four patients over age 18 who received ketamine for any reason were included. Three received ketamine for sedation while the rest received it for analgesia. Most patients received opioids prior to receiving ketamine, although the opioids did not result in improved pain scores. On a scale of 0 to 10, ketamine reduced pain from 8.9 ± 2.1 to 3.9 ± 3.4 (p\<0.0001).(Richards 2013) In another observational, ED based study, ketamine used as an analgesic was investigated. Thirty patients with a variety of painful complaints (abdominal pain, back pain, nephrolithiasis, biliary pain, fractures, sickle cell pain) were enrolled. Patients were initially administered a combination of hydromorphone 0.5 mg and ketamine 15 mg with rescue doses of hydromorphone 1 mg available 15 minutes and 30 minutes after the initial dose of analgesia. In 28 patients (93%), there was a clinically significant decrease of 2 or more points on a numerical rating score measured after the initial administration; 14 patients reported pain scores of 0. Fourteen patients refused any additional hydromorphone and 24 patients (80%) either refused additional hydromorphone at 15 minutes or received a dose at 15 minutes but declined a dose at 30 minutes. Dizziness, nausea, headache, and some dissociative effects were reported.(Ahern 2013) Ketamine administered for analgesia in an urban trauma center was retrospectively reviewed in 35 patients. The most common chief complaint was abscess (46%). The median dose of ketamine received was 10 mg (range 5-35 mg); opioids were co-administered in almost all cases (91%). LDK improved pain scores by at least 3 points in 19/35 patients (54%). Eight patients did not receive a post-drug administration pain score.(Lester 2010) A convenience sample of patients was enrolled in an ED based study in British Columbia. Any patients older than 6 years of age presenting with a painful condition were eligible for enrollment. Patients had to have a score of at least 50 on a 100-mm visual analog score (VAS). All patients received 0.5 mg/kg of intranasal (IN) ketamine and could receive a rescue dose of 0.25 mg/kg IN after 10 minutes for VAS \> 50. Within 30 minutes, 35 patients (88%) had a decrease in VAS of at least 13 mm. Patient reported satisfaction was a mean of 7 (5-9) on a patient satisfaction scale of 1-10. Dizziness, nausea, and fatigue were all reported.(Andolfatto 2013) IN ketamine was also demonstrated as an effective analgesic in other pediatric and adult ED based studies.(Yeaman 2013)(Yeaman 2014) While ketamine has been studied in the ED, the available research has multiple limitations. Most of it consists of observational or retrospective studies. As such, there could be multiple explanations for their results due to multiple, uncontrolled confounders. In addition, most studies included patients with any painful complaint and did not have a comparison or control group. We plan to conduct a prospective, randomized study of ketamine compared to opioids in long bone fractures.