Comparison of Intravenous Push Dose of Low Dose Ketamine to Short Infusion of Low Dose Ketamine for Treatment of Moderate to Severe Pain in the Emergency Department: A Prospective, Randomized, Double-Blind Study

Ketamine is a noncompetitive N-methyl D-aspartate (NMDA) receptor antagonist that blocks the release of excitatory neurotransmitter glutamate and provides anesthesia, amnesia and analgesia by virtue of decreasing central sensitization and "wind-up" phenomenon. At low (sub-dissociative, analgesics) doses of 0.1-0.4 mg/kg either as an adjunct to opioid analgesics or as a single agent, ketamine provides good analgesia while preserving airway patency, ventilation, and cardiovascular stability. In addition, the low-dose of ketamine increases the analgesic potency of opioids thus decreasing their requirements. Several recent studies of low-dose ketamine administered together with morphine provided acceptable pain relief to 55-60% of patients with minor side effects of dizziness, nausea and feeling of unreality. More recently the investigators conducted a research comparing Low-Dose Ketamine to Morphine for Moderate to Severe Pain in the Emergency Department with respect its analgesic efficacy and safety. Results demonstrated similar pain relief at 30 min between 2 groups. However, 70% of patients in ketamine group had minor side effects at 5 min and 35% of patients at 30 min, as compared to 51% at 5 min. and 31% at 15 min. in the morphine group. The most common side effects reported by ketamine patients were dizziness, nausea, feeling of unreality, and mood changes.

Based on the above mentioned data from our previous published research study, we hypothesized that low-dose ketamine given as a short infusion over 15 min will provide similar analgesic efficacy as an intravenous push-dose but with much less side effects. There are several research papers that support our hypothesis.

A prospective, randomized trial compared two analgesic regimens, morphine with ketamine (K group) or morphine with placebo (P group) for severe acute pain in 73 trauma patients with a visual analog scale (VAS) score of at least 60/100. Morphine was administered at 0.1mg/kg and patients in the K group received 0.2 mg/kg of intravenous ketamine over 10 minutes, and the patients in the P group received isotonic sodium chloride solution. The results showed comparable change in VAS score at 30 minutes (34 mm (K) vs. 39 mm (P)) but reduced morphine consumption in the ketamine group (0.14 mg/kg (K) vs 0.2 mg/kg (P)).

A double-blind trial of 40 adult patients with acute musculoskeletal trauma compared a low-dose ketamine by subcutaneous infusion (0.1 mg/kg/h) with intermittent morphine (0.1 mg/kg IV every 4 hours ) and demonstrated better pain relief, less sedation and less nausea and vomiting with ketamine infusion than with intermittent morphine. In addition, none of the patients in ketamine group required supplementary analgesia.

A prospective case series of 20 unselected adult ED patients with acute pain that evaluated analgesic feasibility of low-dose ketamine infusion was conducted in an urban public hospital over a course of 5 months. Patients received 15mg of intravenous push dose ketamine that was followed by continuous ketamine infusion at 20mg per hour for one hour. Optional morphine (4 mg) was offered at 20, 40 and 60 minutes. Pain intensity was assessed at regular intervals for 2 hours using a 10-point verbal numerical rating scale (NRS), along with vital signs and levels of sedation. Results showed that fifteen patients reported clinically significant pain relief at 60 minutes and 13 at 120 minutes; and eighteen patients reported mild or modest side effects including dizziness, fatigue and headache.