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2.BENZODIAZEPINES

For detailed information regarding benzodiazepines see Post under the heading Anxiolytics in this blog.

In anesthetic practice the most commonly used benzodiazepines are as follows:-

1.Midazolam

2.Diazepam

3.Lorazepam

These agents are used for preoperative sedation, intraoperative sedation for procedure not requiring analgesias such as colonoscopy and cardioversion, and as adjuncts with other agents to produce anesthesia.

Mechanism

As we already know that benzodiazepines bind at their own receptors very adjacent to the GABA-A receptor and thereby enhance the binding of GABA and its effect of chloride ion influx and thereby make neurons to be hyperpolarized which leads to the prevention of the action potential and the result is neuronal relax. Unlike barbiturates that act directly on the GABA, receptors benzodiazepines have slow onset of action.

Midazolam is useful as a preoperative anesthetic as it reduces the post-operative trauma by causing loss of memory of events (Amnesia) to calm the patient. Midazolam has the advantage of faster onset of action, greater potency, and faster elimination when compared with diazepam and other benzodiazepines.

Side Effects

1.Moderate to severe respiratory depression

2.Withdrawal symptoms

3. Contraindicated with opioids as the combination can produce cardiac and respiratory arrest.

Antagonist

Flumazenil is used to reverse benzodiazepine poisoning. As the drug is short-acting and the dose should be repeated every one hour.

3.OPIOIDS

Opioids are opium alkaloids available naturally as morphine and its derivatives.

Most commonly used opioids as anesthetic agents are as follows:-

1.Fentanyl

2.Morphine

Opioids are used as anesthetics in cardiac surgery and other major surgeries in which cardiac reverse is limited.

Fentanyl is more frequently used than morphine because of its greater potency and its lesser impact on the respiratory system than does morphine.

Side Effects

1.I.V.opioids will cause chest block so that expiration is difficult.

2.Respiratory depression

3.Postoperative trauma.

Antagonist

Naloxone is used as an antagonist to reverse opioid poisoning

4.INNOVAR

Innovar is generical droperidol, a butyrophenone, often combined with fentanyl and nitrous oxide to produce neurolept anesthesia, combined analgesia with amnesia.

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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.