Inhalational anesthetics
The inhalation group of agents is administered via the respiratory tract. The main representatives requiring detailed analysis are halothane and nitrous oxide. It is important to remember that sevoflurane is also an inhalation anesthetic, whereas lidocaine is a local anesthetic, and morphine is an opioid analgesic.
Halothane (Fluothane) This drug possesses high narcotic potency. From a safety perspective, its undeniable advantage is that it is non-flammable and non-explosive (which favorably distinguishes it from ether). However, the drug exerts a pronounced effect on the cardiovascular system:
- It increases vagus nerve tone, which naturally causes bradycardia.
- Key feature: halothane sensitizes (i.e., increases the sensitivity of) myocardial adrenoceptors to the action of endogenous catecholamines—adrenaline and noradrenaline. This creates a high risk of developing dangerous arrhythmias during the procedure.
Nitrous oxide This gas is characterized by highly favorable pharmacokinetics: it has a very short duration of after-effects, which ensures rapid patient recovery. The drug has low toxicity, in particular, it is completely devoid of hepatotoxicity.
The main drawback of nitrous oxide is its low narcotic potency (narrow therapeutic index). Using it as a sole anesthetic (mononarkoz) to achieve a deep surgical stage is impossible, as this will inevitably lead to hypoxia. For this reason, nitrous oxide is used exclusively in combinations with other drugs or for light analgesia (e.g., during childbirth).
Non-inhalation (intravenous) anesthetics
Non-inhalation anesthetics include such drugs as propanidid, ketamine, and sodium thiopental.
Ketamine The drug induces so-called dissociative anesthesia. Unlike the vast majority of other anesthetics, ketamine does not depress, but rather stimulates the sympathoadrenal system. Consequently, its effect on hemodynamics manifests as hypertension (a significant increase in blood pressure) and tachycardia (rather than hypotension or bradycardia).
- Upon slow intravenous administration, ketamine does not cause apnea (respiratory arrest).
- The main problem with the drug lies in its central nervous system side effects. Upon emergence from anesthesia, patients frequently experience psychomotor agitation (delirium) and vivid visual hallucinations.
Sodium thiopental Belongs to the barbiturate class. The drug is renowned for extremely rapid onset of anesthesia—surgical sleep occurs literally "at the tip of the needle."
Its mechanism of action involves interaction with specific barbiturate receptors that are part of the GABA-A receptor complex. Allosteric modulation occurs, which powerfully enhances the natural inhibitory effect of GABA on the nervous system. The pharmacokinetics of sodium thiopental deserves special attention. It has high lipophilicity, which causes it to easily depot (accumulate) in adipose tissue. With repeated administrations, this leads to a pronounced after-effect in the form of prolonged drowsiness.
Briefly: answers to topical questions
Which drugs belong to non-inhalation anesthetics?
Non-inhalation (intravenous and rectal) anesthetics include the following drugs:
- Hexobarbital (Hexenal) — a barbituric acid derivative.
- Sodium thiopental — a barbiturate.
- Propanidid (Sombrevin, Epontol) — an ultrashort-acting anesthetic.
- Ketamine (Ketalar, Ketajest) — a drug for dissociative anesthesia.
- Sodium hydroxybutyrate (GHB) — an agent with antihypoxic effect.
- Propofol (Diprivan) — an emulsion for intravenous administration.
- Etomidate — a drug used for total intravenous anesthesia.
This group also includes althesin (baytinal) and viadril.
What are the contraindications for ketamine use?
A contraindication for ketamine use is hypertension. Ketamine stimulates the cardiovascular system, increases blood pressure, and accelerates heart rate. It is indicated for shock in patients with arterial hypotension.
What is the duration of action of propanidid?
Propanidid is an ultrashort-acting drug; the duration of anesthesia ranges from 1.5 to 4.5 minutes. Narcotic sleep occurs 17–30 seconds after intravenous administration. The brief duration of action is due to rapid hydrolysis by plasma cholinesterase enzyme. Consciousness returns after 2–3 minutes, psychomotor functions recover within 20–30 minutes. The patient can be discharged from the outpatient clinic 25–30 minutes after awakening.
What stages of anesthesia are characteristic of diethyl ether?
Diethyl ether is characterized by four classical stages of anesthesia according to Guedel.
- Stage I — Analgesia (consciousness preserved, eyelids closed).
- Stage II — Excitement (eyelids tightly clenched, skin color bright red).
- Stage III — Surgical or tolerance stage (divided into 4 planes depending on the depth of CNS depression, state of eyelids, and skin color).
- Stage IV — Recovery (eyelids alternately half-open or closed).
Overdose leads to a pale-cyanotic skin color and wide opening of the eyelids.
Differences of ketamine from other anesthetics: it "excites" rather than depresses (causes tachycardia, hypertension, and hallucinations).
Class and exam questions
Why can halothane be dangerous during stress or administration of adrenaline?
Halothane sensitizes myocardial adrenoceptors to catecholamines (adrenaline and noradrenaline). This sharply increases the risk of cardiac arrhythmias.
Can nitrous oxide be used as the sole agent for deep anesthesia?
No, due to low narcotic potency, nitrous oxide used alone (mononarkoz) does not provide a deep surgical stage without causing severe hypoxia. It is used only in combinations or for obstetric analgesia.
Why might a patient experience prolonged drowsiness after sodium thiopental administration?
Sodium thiopental has high lipophilicity. The drug accumulates (is stored) in adipose tissue, and with repeated administrations, this causes a prolonged after-effect.
What side effects can be encountered upon awakening after ketamine?
Upon emergence from dissociative anesthesia with ketamine, visual hallucinations and delirium (psychomotor agitation) are frequently observed from the CNS side.
What else to study on this topic
- Mechanisms of myocardial sensitization to catecholamines
- Principles and features of dissociative anesthesia
- Structure and function of the GABA-A receptor complex
- Effect of drug lipophilicity on their redistribution in tissues
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