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Fig. 5. Chemical structure of etomidate.

ductance of chloride channels, resulting in inhibition of postsynaptic neurons.

Of clinical significance, the administration of propofol commonly causes a decrease in both systemic vascular resistance and cardiac contractility, hence resulting in decreased cardiac output. This reduction in systemic vascular resistance (and vasodilation) is considered caused by decreased sympathetic vasoconstrictor activation of vascular smooth muscle (43). The inhibition of sympathetic tone by propofol is reported to be greater than inhibition of parasympathetic activity; this may result in significant bradycardia and even asystole (44-46). The induced decrease in cardiac contractility is likely because of decreases in calcium uptake into the sarcoplasmic reticulum. Decreased reuptake of calcium results in less calcium available for the next activation sequence (47).

Again it should be noted that, in patients with decreased left ventricular function (e.g., the elderly and patients with hypovolemia), the administration of propofol may result in severe hypotension. Therefore, the careful titration of propofol and adequate intravascular hydration are important for these types of patients.

4.6. Etomidate

Etomidate (Fig. 5) is an imidazole compound that is water soluble at lower pH and lipid soluble at physiologic pH. Rapid loss of consciousness is accomplished after intravenous injection of etomidate (0.2-0.4 mg/kg). It is important to recognize that etomidate lacks analgesic properties and does not blunt sympathetic responses to direct laryngoscopy and endotracheal intubation.

Generally, etomidate provides cardiovascular and pulmonary stability; typical induction doses of etomidate result in minimal changes in heart rate and cardiac output. Myocardial contractility is well maintained at doses needed to induce general anesthesia (23) and is considered to produce less myocardial depression compared to thiopental (48). Etomidate does not induce significant histamine release, but it does depress adrenocortical function by inhibiting the conversion of cholesterol to cortisol (49). Specifically, a single induction dose of etomidate can cause adrenal suppression for 5-8 h (50), and a continuous infusion of etomidate will cause further adrenocor-tical suppression.

Table 7

Nondepolarizing Muscle Relaxants

Table 7

Nondepolarizing Muscle Relaxants

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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