Here we study about the physical effects of barbiturates . In normovolemic subjects, thiopental, 4-5 mg/kg IV, produces a transient mild to moderate decrease in blood pressure with a compensatory increase in heart rate. However, bradycardia and junctional rhythm may occur with thiopentone.
This dose of thiopental produces minimal to no evidence of myocardial depression. The most likely explanation for compensatory tachycardia and unchanged myocardial contractility associated with IV administration of thiopental is a carotid sinus baroreceptor-mediated increase in peripheral sympathetic nervous system activity. Well some physical effects of barbiturates are also listed here.
The decrease in systemic blood pressure that accompanies induction of anesthesia with thiopentone is principally due to peripheral vasodilatation, reflecting depression of the medullary vasomotor center and decreased sympathetic nervous system outflow from the CNS.
The resulting dilatation of peripheral capacitance vessels leads to pooling of blood, decreased venous return, and the potential for decreases in cardiac output and blood pressure. Vasodilation of cutaneous and skeletal muscle blood vessels may also contribute to heat loss and decreases in body temperature.
Some physical effects of barbiturates includes direct myocardial depression may also accompany overdoses of barbiturates or the large doses of barbiturates administered to lower ICP. Cardiac dysrhythmias after induction of anesthesia with barbiturates are unlikely in the presence of adequate ventilation and oxygenation.
For the physical effects of barbiturates the effect of thiopental on cardiovascular responses to moderate hemorrhage is minimal. However, hypovolemic patients, who are less able to compensate for peripheral vasodilating effects of barbiturates, are highly vulnerable to marked decreases in systemic blood pressure when these drugs are administered rapidly for the IV induction of anesthesia.
Conceptually, the slow IV administration of thiopental should be more likely to permit compensatory reflex responses and thus minimize systemic blood pressure decreases compared with rapid IV injection.
Thiopentone does not prevent the cardiovascular response due to direct laryngoscopy and intubation. These were some physical effects of barbiturates explained.