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Intravenous Anesthetics

Q: How does biotransformation and elimination of thiopental sodium occur in the body?

Biotransformation of thiopental sodium (Thiopental sodium) occurs in the liver; however, this process is significantly slower than tissue redistribution. Only 12–16% of the substance is metabolized in the liver per hour. Due to its high lipophilicity, the drug redistributes from the brain and accumulates in adipose tissue. The decline in brain drug concentration via redistribution into fat stores leads to awakening. Subsequent slow release from fat depots back into the bloodstream causes prolonged drowsiness after emergence from anesthesia.

For medical students2 min readUpdated 2026-10-10

Intravenous anesthetics are a pharmacological group of agents with diverse chemical structures used for the induction and maintenance of general anesthesia. Most commonly administered intravenously, they ensure a minimal latency period and allow patients to quickly enter drug-induced sleep without a pronounced excitation phase.

PharmacokineticsHigh lipophilicity allows them to easily cross the blood-brain barrier.

Latency periodExtremely short: the effect occurs almost immediately after administration.

Main disadvantageLow controllability over the depth of anesthesia compared to inhalational agents.

Environmental safetyOperating room air is not polluted by exhaled anesthetic vapors.

Historical Background and Development

Historically, the development of non-inhalational anesthesia is closely tied to major breakthroughs in medical history that established global standards in surgical practice.

N.I. Pirogov (1847): The prominent surgeon first proposed and successfully applied rectal administration of ether. This marked the first step away from exclusively inhalational administration routes.
N.P. Kravkov (1909): A distinguished pharmacologist who proposed using hedonal for intravenous anesthesia. This was the first non-volatile agent used for this purpose.
S.P. Fedorov: A prominent surgeon who adopted Kravkov's formula and conducted large-scale clinical trials of hedonal, firmly establishing intravenous anesthesia in broad surgical practice.

Advantages Over Inhalational Anesthesia

Intravenous anesthetic agents possess several significant advantages that make them drugs of choice for anesthesia induction and short surgical procedures.

Shorter latency period. Drugs act very rapidly, allowing for immediate induction of anesthesia.
Technical simplicity. Administration does not require complex, bulky, and expensive anesthesia delivery systems equipped with vaporizers.
Environmental safety for staff. When using intravenous agents, there is no issue of volatile anesthetics releasing into expired air. This eliminates the need for complex operating room air-scavenging systems and protects the surgical team's health.

Pharmacodynamic and Pharmacokinetic Features

The primary pharmacokinetic feature of these drugs is their high lipophilicity. Due to their ability to dissolve well in fats, anesthetic molecules readily and rapidly cross the blood-brain barrier directly into brain tissue.

Clinical Picture Differences: Unlike inhalational anesthesia, the use of intravenous agents is characterized by an almost complete absence of the excitation phase. The patient falls asleep calmly and rapidly.

Main Disadvantage: The trade-off for speed and simplicity is low controllability over the depth of anesthesia. While inhalational anesthesia allows for rapid changes in the gas concentration within the inspired mixture to terminate its effect, altering the blood concentration of an intravenous agent immediately after injection is impossible. The clinician must wait for redistribution within tissues or metabolism.

Classification by Duration of Action

Modern intravenous anesthetics are classified according to the duration of the effect they produce. There are three main groups:

1. Ultra-short-acting agents (duration of effect up to 15 minutes) This group includes agents for rapid procedures or anesthesia induction: propanidid, propofol, etomidate, ketamine.

2. Intermediate-acting agents (duration of effect from 20 to 30 minutes) These include barbituric acid derivatives: thiopental sodium and hexobarbital.

3. Long-acting agents (duration of effect 60 minutes or more) A typical representative of this group is sodium oxybate.

Mnemonic

To remember ultra-short-acting anesthetics (up to 15 min), use the mnemonic: "PROfessor PROped in the ETOMed clinic" — PROpofol, PROpanidid, ETOMidate, KETamine.

Frequently asked questions

What is the mechanism of action of ketamine on CNS receptors?

Ketamine acts by blocking NMDA receptors in the central nervous system. The drug is a non-competitive antagonist of these receptors, eliminating the excitatory influence of glutamate on CNS structures. Ketamine (Ketamine) is a phencyclidine derivative. By blocking these receptors, it causes functional dissociation within the CNS, leading to dissociative anesthesia accompanied by pronounced analgesia, a mild hypnotic effect, and partial loss of consciousness.

What side effects and complications are associated with propofol?

Propofol is associated with cardiovascular side effects and local administration site reactions.

Hemodynamic disturbances — causes bradycardia, lowers blood pressure, and may exert a negative inotropic effect (decreased myocardial contractility).
Local reactions — pain at the injection site along the vein, as well as a rare risk of phlebitis and thrombosis.
Immune reactions — allergic reactions are possible.

At the same time, the drug is characterized by good tolerability, absence of postoperative vomiting, and lack of hepatotoxicity or nephrotoxicity.

What is dissociative anesthesia, and which intravenous anesthetic induces it?

Dissociative anesthesia is a state of functional dissociation in the central nervous system induced by the intravenous anesthetic ketamine (Ketamine). This type of analgesia is characterized by the following clinical effects:

Analgesia — profound pain relief.
Effects on consciousness — a mild hypnotic effect, amnesia, and only partial loss of consciousness (surgical anesthesia stage is not reached).
Preservation of vital functions — the patient retains spontaneous respiration, muscle tone, and protective reflexes (laryngeal, pharyngeal, cough).

How does biotransformation and elimination of thiopental sodium occur in the body?

Biotransformation of thiopental sodium (Thiopental sodium) occurs in the liver; however, this process is significantly slower than tissue redistribution. Only 12–16% of the substance is metabolized in the liver per hour. Due to its high lipophilicity, the drug redistributes from the brain and accumulates in adipose tissue. The decline in brain drug concentration via redistribution into fat stores leads to awakening. Subsequent slow release from fat depots back into the bloodstream causes prolonged drowsiness after emergence from anesthesia.

Which classic stages of anesthesia are absent or poorly expressed when using intravenous anesthetics?

When using intravenous (non-inhalational) anesthetics, the excitation phase is practically absent. This is one of the key differences and advantages of intravenous anesthesia over inhalational methods. Administration of agents such as thiopental sodium ensures rapid onset of anesthetic sleep and pleasant induction, bypassing the excitation phase. Non-inhalational agents are primarily used for anesthesia induction.

Why do intravenous anesthetics act faster than inhalational ones?

This is due to their high lipophilicity. An agent injected into a vein rapidly reaches the brain and easily crosses the blood-brain barrier, bypassing the lengthy process of accumulation in pulmonary alveoli.

What is the main danger of intravenous anesthesia?

The main drawback is low controllability. An administered dose cannot be quickly removed from the bloodstream if the anesthesia becomes too deep, unlike inhalational gases, the delivery of which can simply be turned off.

Who first proposed using non-volatile substances for anesthesia?

The idea of rectal ether administration was proposed by N.I. Pirogov in 1847, while the first non-volatile agent for intravenous anesthesia (hedonal) was introduced by pharmacologist N.P. Kravkov in 1909.

Go deeper

Mechanisms of action of individual agents: propofol, ketamine, and etomidate.
Pharmacokinetic features of thiopental sodium (redistribution into adipose tissue).
Specific side effects of sodium oxybate during prolonged anesthesia.
The concept of the blood-brain barrier and the physicochemical properties of lipophilic molecules.
Differences between induction and maintenance of anesthesia using non-inhalational agents.