ANESTHETICS-Contd...
INTRAVENOUS ANESTHETICS:-
The followings are the general anesthetics that are unlike inhalers that can be given through the intravenous route to produce anesthesia.
Classes of I.V. Anesthetics:-
1.Barbiturates
2.Benzodiazepines
3.Opioids
4.Other Hallucinogens and Dissociative agents
1.BARBITURATES:-
As we have already known barbiturates are derivatives of barbituric acid either as salts or esters(a product with any alcohol). But salts are mostly used in practice.
Thiopental
An ultra short-acting barbiturates widely used as an adjunct with inhalation anesthetics or with any other.
It rapidly induces anesthesia in combination with other anesthetics. It has a fast onset of induction, and anesthesia occurs within 10 to 30 seconds after the injection.
Mechanism:-
As a barbiturates thiopental acting by binding at GABA-A receptor and thereby opening the chloride ion influx to produce hyperpolarization of the neuron beyond the threshold so that an action potential is nullified and the neurons are inhibited to relax.
The ultrashort duration of activity is accounted for by the high lipid solubility of thiopental which leads to the quick entry of the blood-brain barrier into the CNS and produces the anesthetic effect.
The effect lasts so rapidly because of the lipid solubility which results in rapid elimination from the CNS and the drug gets redistributed into the highly vascularised other muscles and fat and the effect lasts.
Metabolism:
Thiopental is metabolized in the liver more slowly than its redistribution and hence after a prolonged infusion the recovery may be slow.
100% drug is metabolized in the liver.
Thiopental is a teratogenic drug and hence it can cross into the placenta.
Thiopental, after metabolized, is excreted in the urine.
Side Effects:-
1.On Cardio Vascular System:-
Thiopental lowers B.P. and cardiac output. Peripheral vascular resistance is not affected.
2.On Respiratory System:-
Thiopental depresses the respiratory center in the brain.
It decreases carbon dioxide response to the center and causes hypoxia. It reduces cerebral blood flow and thereby decreases the oxygen demand by the brain. This effect is useful in treating patients who has cerebral edema.
3.Laryngospasm
4.Bronchospasm
5.Acute porphyric crisis by inducing the synthesis of delta-aminolevulinic acid in the liver.
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