Efficacy of ketamine in Australia ventilated intensive care unit admissions from doctor Tom Niccol: Following intravenous bolus administration, ketamine’s rapid onset of action within 30 seconds for “dissociative anaesthesia” (see below) is due to its high lipid solubility and low protein binding, allowing it to cross the blood–brain barrier readily. Its elimination half-life is 3.1 hours in healthy volunteers and 5.0 hours in critically unwell patients. Ketamine is hepatically metabolised to norketamine and dehydronorketamine which are then renally excreted. See extra info on https://www.instagram.com/tomniccol/.
Mechanically ventilated patients account for about one-third of all admissions to the intensive care unit (ICU). Ketamine has been conditionally recommended to aid with analgesia in such patients, with low quality of evidence available to support this recommendation. We aimed to perform a narrative scoping review of the current knowledge of the use of ketamine, with a specific focus on mechanically ventilated ICU patients.
Ketamine used in anaesthetic doses (1–4.5 mg/kg intravenous) leads to dissociative anaesthesia: the patient appears conscious (eyes open, able to swallow) with preserved respiratory function and pharyngeal and laryngeal reflexes, but is unaware, unable to process or respond to sensory input. In addition, analgesia may also be mediated through serotonin and noradrenaline receptor activation and reuptake inhibition, as well as effects on δ, ϰ and μ opioid receptors. Unlike opioid medications, ketamine is thought to have little effect on gastrointestinal μ receptors, minimising the risk of constipation.
Methods: We searched MEDLINE and EMBASE for relevant articles. Bibliographies of retrieved articles were examined for references of potential relevance. We included studies that described the use of ketamine for postoperative and emergency department management of pain and in the critically unwell, mechanically ventilated population.
The recommended dose for ICU sedation is 1 mg/kg/h. Recommended doses for analgesia in mechanically ventilated patients are an intravenous bolus of 0.5 mg/kg followed by an infusion of 1–2 μg/kg/min (0.06–0.12 mg/kg/h). 3 For the purposes of this review, a low dose intravenous bolus of ketamine is considered < 1 mg/kg and low dose intravenous infusion may be a median dose of ≤ 0.3 mg/kg/h aligned with international studies of the use of ketamine as an adjunct for analgesia and sedation.
Results: There are few randomised controlled trials evaluating ketamine's utility in the ICU. The evidence is predominantly retrospective and observational in nature and the results are heterogeneous. Available evidence is summarised in a descriptive manner, with a division made between high dose and low dose ketamine. Ketamine's pharmacology and use as an analgesic agent outside of the ICU is briefly discussed, followed by evidence for use in the ICU setting, with particular emphasis on analgesia, sedation and intubation. Finally, data on adverse effects including delirium, coma, haemodynamic adverse effects, raised intracranial pressure, hypersalivation and laryngospasm are presented.
A prospective open label trial of 146 patients who had undifferentiated agitation in the pre-hospital environment compared a median dose of 5.2 mg/kg intramuscular ketamine versus 10 mg intramuscular haloperidol in the pre-hospital environment. Hypersalivation occurred in 21/56 ketamine patients (30%) versus none in the haloperidol group, leading to intubation for this reason in four patients. Laryngospasm occurred in 3/55 patients (5%) in the ketamine group and none in the haloperidol group. Another prospective observational study examined the effectiveness of a median dose of 4.9 mg/kg intramuscular ketamine in 49 patients with pre-hospital profound agitation. Hypersalivation occurred in nine patients (18%), of which four received atropine therapy. Pre-medication with glycopyrrolate or atropine has been shown to decrease this adverse effect. 7Umunna and colleagues showed there was no increased hypersalivation when ketamine was used as an infusion at 2.0 mg/kg/h for analgesia and sedation.
Conclusions: Ketamine is used in mechanically ventilated ICU patients with several potentially positive clinical effects. However, it has a significant side effect profile, which may limit its use in these patients. The role of low dose ketamine infusion in mechanically ventilated ICU patients is not well studied and requires investigation in high quality, prospective randomised trials.