Inhalation Anesthetics
Inhalation agents are administered via the respiratory tract. The primary agents 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 This drug possesses high anesthetic potency. From a safety perspective, its undeniable advantage is that it is non-flammable and non-explosive (distinguishing it favorably from ether). However, the drug has significant cardiovascular effects:
- Increases vagal tone, which naturally causes bradycardia.
- Key feature: Halothane sensitizes (i.e., increases the sensitivity of) myocardial adrenergic receptors to the action of endogenous catecholamines—adrenaline and noradrenaline. This creates a high risk of dangerous arrhythmias during procedures.
Nitrous Oxide This gas features highly favorable pharmacokinetics: it has a very short duration of after-effects, ensuring rapid patient recovery. The drug has low toxicity, specifically, it is completely devoid of hepatotoxicity.
The main drawback of nitrous oxide is its low anesthetic potency (narrow anesthetic window). Using it as a sole agent to achieve deep surgical anesthesia is impossible, as this would inevitably lead to hypoxia. For this reason, nitrous oxide is used exclusively in combinations with other drugs or for mild analgesia (e.g., during labor).
Intravenous Anesthetics
Intravenous anesthetics include agents such as propanidid, ketamine, and thiopental sodium.
Ketamine This 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 hemodynamic effect manifests as hypertension (significant blood pressure elevation) and tachycardia (rather than hypotension or bradycardia).
- With slow intravenous administration, ketamine does not cause apnea (respiratory arrest).
- The primary issue with the drug lies in its central nervous system side effects. During recovery, patients frequently experience psychomotor agitation (delirium) and vivid visual hallucinations.
Thiopental Sodium 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 binding to specific barbiturate receptors that are part of the GABA-A receptor complex. Allosteric modulation occurs, which powerfully enhances the natural inhibitory influence of GABA on the nervous system. Thiopental sodium pharmacokinetics deserve special attention. It is highly lipophilic, causing it to easily sequester (accumulate) in adipose tissue. With repeated doses, this leads to a pronounced hangover effect in the form of prolonged drowsiness.