A 32-year old male with no past medical history is brought to the emergency department after being injured in a bomb blast. On examination he is suspected to have a splenic injury and is supposed to undergo an emergency laparotomy. Which of the following is the ideal anaesthetic agent of choice?
Ans. c. Etomidate (Ref: Morgan 4/e p167, 194, 199)A 32-year -old male with no past medical history is brought to the emergency department after being injured in a bomb blast. On examination he is suspected to have a splenic injury and is supposed to undergo an emergency laparotomy. The ideal anaesthetic agent of choice would be etomidate, as it has minimal effects on the cardiovascular system."Abdominal trauma patient especially with splenic injury are at high risk of hypotension, etomidate is agent of choice as it has minimal effects on the cardiovascular system.""Etomidate has minimal effects on the cardiovascular system. A mild reduction in peripheral vascular resistance is responsible for a slight decline in arterial blood pressure. Myocardial contractility and cardiac output are usually unchanged. Etomidate does not release histamine.""Opioids: In general, opioids do not seriously impair cardiovascular function. Meperidine tends to increase heart rate (it is structurally similar to atropine). Ramifentanyl, and alfentanyl are associated with vagus-mediated bradycardia With the exception of meperidine, the opioids do not depress cardiac contractility. Nonetheless, arterial blood pressure often falls as a result of bradycardia, venodilation, and decreased sympathetic reflexes, sometimes requiring vasopressor (eg., ephedrine) support. Meperidine and morphine evoke histamine release in some individuals that can lead to profound drops in systemic vascular resistance and arterial blood pressure.""Halothane: A dose-dependent reduction of arterial blood pressure is due to direct myocardial depression. 2.0 MAC of halothane results in a 50% decrease in blood pressure and cardiac output."EtomidateEtomidate is a carboxylated imidazole compound that is a selective positive allosteric modulator at GABA-A receptorQUnlike thiopental does not appear to affect other pentameric ion channels.It is structurally unrelated to other agents.Mechanism of Action:Selective positive allosteric modulator at GABA-A receptorQPharmacokinetics:It is rapidly acting general anesthetic agent with a short duration of action (2-3 min), resulting predominantly from redistribution, although it is also eliminated rapidly from bodyQ.Characteristic Features:It is characterized by hemodynamic stability, minimal respiratory depression and cerebroprotective effectQ.It is a sedative hypnotic but lacks analgesic propertiesQAs with thiopental, cerebral blood flow and metabolism, intracranial and intraocular pressure all fall with etomidateQAs with methohexital, excitatory phenomenon (on induction) may be seen which can be prevented by benzodiazepine premedication or concomitant use of opioid.Central sympathetic out flow is stimulated, which maintains hemodynamics. Because of minimal cardiovascular effect, CPP is well maintained.It enhances somatosensory evoked potentials on EEG.Side-Effects:It causes adrenocortical suppressionQ by inhibiting enzymes 11-beta hydroxylase (mainly) and 17-alpha hydroxylase involved in cortisol and aldosterone (mineralocorticoid) productionQ. Vitamin C supplementation restores cortisol level.Excitatory phenomenon causing myoclonus, hiccups and other involuntary movements (40%); emergence phenomenon causing restlessness and delirium during recoveryQHigh incidence of nausea and vomiting (highest among all IV anesthetics i.e. ~40%)Pain on injection; Vitamin C deficiency; ThrombophlebitisQ
Remifentanil
Morphine
Etomidate
Halothane
Anaesthesia For Special Situations