Volatile liquid anesthetics: fluorinated compounds
These drugs are liquids that are converted into a vapor state using specialized vaporizers in the anesthesia machine before being delivered to the patient. Classic representatives include halothane, enflurane, and isoflurane, as well as the more modern sevoflurane and desflurane.
Isoflurane is an isomer of enflurane and favorably differs from its predecessors in its safety profile. This drug does not provoke cardiac rhythm disturbances (arrhythmias) and is completely devoid of hepatotoxic and nephrotoxic properties, meaning it does not damage the liver and kidneys.
Sevoflurane is one of the most popular modern drugs in this group. It possesses a number of outstanding pharmacokinetic characteristics:
- Very rapid onset of the surgical stage of anesthesia.
- Exceptionally easy control over the depth of anesthesia during surgery.
- Rapid emergence and recovery of the patient from anesthesia.
In addition, sevoflurane has a minimal negative impact on internal organs, weakly affects hemodynamic parameters (cardiovascular system function) and respiration. Due to this safety profile, it has found widespread use not only in large inpatient facilities, but also in ambulatory surgery.
Volatile liquid anesthetics: ethers
The classic representative of this group is diethyl ether (anaesthetic ether). Today in modern practice it is used extremely rarely due to its pronounced disadvantages, although it possesses undeniable pharmacodynamic advantages.
Advantages of ether:
- Very high anesthetic potency.
- A wide margin of safety, providing a safe dosage range (difficult to overdose to a fatal outcome).
- Powerful analgesia and excellent myorelaxation (skeletal muscle relaxation).
Disadvantages and side effects:
- Extremely slow induction of anesthesia and a prolonged, prominent excitation stage.
- Slow emergence from anesthesia (recovery takes about 30 minutes, and complete restoration of central nervous system functions takes several hours).
- Local irritant effect. Ether vapors stimulate the secretion of salivary and bronchial glands. This can lead to reflex respiratory depression, a sharp decrease in heart rate (bradycardia), and vomiting.
It is also important to remember the physicochemical risks: ether vapors are extremely flammable and become explosive when mixed with air (or nitrous oxide).
Gaseous anesthetic agents
Dinitrogen oxide, better known as nitrous oxide ($N_2O$), is a colorless, odorless gas. It does not burn on its own, but actively supports combustion.
The main feature of nitrous oxide is its low anesthetic potency. Achieving a deep surgical stage of anesthesia using only this gas is possible solely under hyperbaric conditions (under elevated pressure). Under normal conditions, the effect strictly depends on the concentration of the substance in the inspiratory mixture:
- 20% $N_2O$ provides pronounced analgesia.
- 80% $N_2O$ produces only superficial anesthesia without myorelaxation.
Rules of administration: To avoid tissue oxygen starvation (hypoxia), nitrous oxide is strictly contraindicated to administer in pure form. It is always used in a mixture with oxygen. At the same time, the proportion of nitrous oxide must not exceed 80%, and the proportion of oxygen must be at least 20% (which roughly corresponds to the oxygen content in atmospheric air).
Anesthesia with such a gas mixture occurs rapidly, the excitation stage is absent, and the drug is easy to control. The patient's emergence occurs in the very first minutes after stopping the gas flow.
Nitrous oxide is actively used for anesthesia in short surgical interventions (e.g., in dentistry and gynecology), for pain relief during childbirth, and in emergency medicine for relieving severe pain in myocardial infarction and acute coronary syndrome.
Briefly: answers to topical questions
What stages of anesthesia and changes occur during the administration of diethyl ether?
The classic picture of anesthesia upon administration of diethyl ether includes 4 stages. The drug is characterized by slow induction and prolonged emergence.
Changes and specific features of action:
- Excitation stage — proceeds protractedly and prominently.
- Secretion — stimulation of salivary and bronchial glands occurs.
- Complications — the risk of reflex respiratory depression, bradycardia (decreased heart rate), and vomiting arises.
- Emergence from anesthesia — slow (about 30 min), full restoration of CNS functions takes several hours.
To avoid forgetting the proportions for gas anesthesia, recall the composition of ordinary air: we breathe a mixture where about 20% is oxygen. Similarly, in the anesthetic mixture with nitrous oxide, oxygen must be at least 20% to prevent the patient from suffocating.
Class and exam questions
Is it possible to perform complex major abdominal surgery using nitrous oxide alone?
No, under normal (normobaric) conditions, nitrous oxide provides only superficial anesthesia and does not ensure the myorelaxation required for surgical work. It is used either for minor interventions or combined with other, more potent anesthetics.
Why did diethyl ether almost disappear from modern operating rooms?
Due to high explosion hazard, irritating effect on the respiratory tract, risk of reflex respiratory arrest, and very slow, difficult emergence from anesthesia with a prolonged excitation stage.
What is the main advantage of inhalation administration over intravenous?
In controllability. An intravenous drug cannot be "extracted" from the blood after administration, whereas an inhalation anesthetic is continuously eliminated through the lungs with each expiration, allowing instant adjustment of the depth of sleep.
What else to study on this topic
- The working principle of vaporizers in modern anesthesia and respiratory machines
- Mechanisms of hepatotoxicity of older halogenated anesthetics (halothane)
- Detailed analysis of the stages of ether anesthesia (analgesia, excitation, surgical, emergence)
- Effect of sevoflurane and isoflurane on cerebral blood flow and intracranial pressure
- Combined endotracheal anesthesia: how inhalation agents are combined with muscle relaxants
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