Etomidate

Etomidate is a short-acting, injectable non-barbiturate anesthetic agent. It is particularly valued in veterinary medicine for its **cardiovascular stability**, making it an excellent alternative to thiopental or propofol for anesthetic induction in compromised patients. **Key Clinical Highlights:** * **Hemodynamic Stability:** Causes minimal changes to heart rate, blood pressure, and cardiac output, making it ideal for patients with preexisting cardiac dysfunction or shock. * **Neurological Benefits:** Decreases cerebral blood flow, oxygen consumption, and intracranial pressure, which is beneficial for patients with head trauma. * **Endocrine Effects:** Reversibly inhibits the enzyme 11-beta-hydroxylase, leading to **adrenocortical suppression** (decreased cortisol production). Critically ill patients may require corticosteroid supplementation. * **Lack of Analgesia:** Etomidate provides hypnosis and amnesia but **no analgesia**; appropriate analgesic protocols must be used concurrently.

กลไกการออกฤทธิ์: While the exact mechanism is not definitively proven, etomidate is known to act primarily as a positive allosteric modulator and direct agonist at the **GABA_A receptor** in the central nervous system. * **Mechanism:** Binds to a specific site on the GABA_A receptor → enhances the affinity of the inhibitory neurotransmitter GABA for the receptor → increases transmembrane chloride conductance → hyperpolarizes the postsynaptic neuron → profound CNS depression and hypnosis. * **Endocrine Mechanism:** Directly inhibits **11-β-hydroxylase** (and to a lesser extent 17-α-hydroxylase) in the adrenal cortex → blocks the conversion of 11-deoxycortisol to cortisol → transient adrenal insufficiency.

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