As posted on BIJC before, Asad et al. had performed a systematic review on the usage of ketamine as a continuous infusion (>24h) in intensive care patients. The same authors have now published a narrative review providing a more depth discussion about the pharmacological and pharmacokinetic properties of ketamine. Also they present recommendations for dosing and monitoring in an ICU setting.
The Goodies of Ket
Current evidence shows that Ketamine...
- Has no adverse effects on the gastrointestinal tract (bleeding) and does not cause acute kidney injury (compared to nonsteroidal anti-inflammatory drungs, NSAID's)
- Does not negatively influence bowel motility (in contrast to opioids)
- Preserves laryngeal protective reflexes
- Lowers airway resistance
- Increases lung compliance
- Is less likely to cause respiratory depression
- Is sympathomimetic, facilitates adrenergic transmission and inhibits synaptic catecholamine reuptake, therefore increasing heart rate and blood pressure
The Concerns of Ket
- Might increase pulmonary airway pressure and therefore aggravate pulmonary hypertension
- Might cause well known psychotomimetic effects which are of concern in the critically ill patient as this might predispose to delirium
- Interacts with benzodiazepines via the P450 pathway which could result in drug accumulation and prolonged recovery
Concerns Proven Wrong
- Ketamine need not to be avoided in patients at risk for seizures, particularly when used for analgosedation for short periods in the ICU setting
- Current evidence shows no increased intracranial pressure or associated adverse neurologic outcomes associated with ketamine administration in critically ill patients
The use of ketamine for analgosedation in the ICU continues to lack high-level evidence.However, it is effectively used around the globe and remains an attractive alternative agent for appropriately selected patients. Taking current knowledge and evidence into account this is especially true for patients with severe pain unresponsive to conventional therapies.
Taking precautions and contraindications into account ketamine is considerably safe and even avoids potentially adverse side effects of other agents used.
Erstad BL, J Crit Care, Oct 2016, Vol 35, p 145-149
Continuous Etomidate Suppresses the Adrenal Gland in a Dose-Dependent Manner - A Potentially Life-Saving Intervention
An endogenous Cushing's syndrome, mostly caused by an adenoma of the pituitary gland, is associated with significant morbidity and mortality when left untreated. The condition is closely associated to life-threatening infections, diabetes mellitus, hypertension and increased risk associated with surgery.
For Cushing's disease the first line therapy is surgical removal of the pituitary tumor. Sometimes though urgent medical therapy is needed first. It has been shown, that surgical risk may be significantly reduced if cortisol concentrations are normalised preoperatively. Conditions requiring urgent cortisol-lowering measures are severe biochemical disturbances (e.g. hypokalaemia), immunosuppression or mental instability.
Medical Treatment Options
Ketokonazole (yes, the antifungal agent) and metyrapone are used to suppress adrenal steroidogenesis at enzymatic sites. Both agents carry the risk of postential side effects. Mifepristone, a glucocorticoid receptor antagonist, and pasireotide, a new targeted pituitary therapy, are alternative agents. However, they also have their limits and side effects.
Now that's where etomidate joins the game. Interestingly, etomidate and ketokonazole are chemically closely related... they are both members of the imidazole family. Etomidate is used as an anaesthetic agent since 1972 and became popular for hemodynamic stability and the lack if histamine release. In 1983 a Lancet article noted an increased mortality when etomidate was used in critically unwell patients. In 1984 an article in Anaesthesia first showed a link to low serum cortisol levels caused by etomidate. Until now the discussion continues, whether a single induction dose actually negatively influences patient outcome. A meta-analysis in 2010 was unable confirm this apprehension and the debate continues.
Etomidate suppresses the production of cortisol by inhibiting the mitochondrial cytochrome p450-dependent adrenal enzyme 11-beta-hydroxylase and therefore lower serum cortisol levels within 12 hours. In higher doses it also blocks side chain cleavage enzymes and also aldosterone synthase. It might even have anti-proliferative effects on adrenal cortical cells.
On this basis the idea arose, that etomidate might be a useful therapy for severe hypercortisolaemia.
Continuous Etomidate - What's the Evidence
A review article by Preda et al. in 2012 identified 18 publications about the primary therapeutic usage of etomidate in Cushing's syndrome, most of which were case reports. Review of current literature reveals that etomidate indeed suppresses hypercortisolaemia safely and efficiently in patients requiring parenteral therapy. Moreover, etomidate shows a dose-dependent suppression and allows adjustment of the medication to target cortisol levels. At recommended dosages etomidate is considered safe with almost no serious side effects.
The authors conclude, that etomidate is a useful therapeutic option in a hospital setting when oral therapy is not tolerated or inappropriate.
- Continuous etomidate (in non-hypnotic doses) reduces cortisol concentrations in a dose-dependent manner in both hyper- and eucortisolaemic subjects
- The application of continuous etomidate in Cushing's disease is safe and efficient
- After termination of infusion adrenocortical suppression persists for about 3 hours
- The suspicion, that a single dose of etomidate for rapid sequence inductions might negatively influence patient outcome in the critically ill remains a matter of debate
J Clin Endocrinol Metab. 1990 May;70(5):1426-30.
Preda et al. European Journal of Endocrinology (2012) 167 137-143 OPEN ACCESS
Soh et al. Letter to the Editor, European Journal of Endocrinology (2012) 167 727–728
Ge et al. Critical Care201317:R20 OPEN ACCESS