A narcotic is a drug that can cause deep unconsciousness and painlessness in the central nervous system for diagnostic or surgical purposes. The different narcotics have different effects on the receptors and signal molecules in the brain, which explains the different effects of the substances. A distinction is made between inhalation narcotics and injection narcotics. The former are absorbed via the respiratory system, i.e. they are administered to the patient in gaseous form via a mask during an operation and then inhaled. Injection narcotics are injected into a vein.
The current mainly clinically used inhalation narcotics are isoflurane, sevoflurane, desflurane and enflurane. Laughing gas and halothane are becoming less important. The individual narcotics in this substance class each have different properties, such as their solubility in blood, their potency and their fat solubility.
Fat solubility in particular plays a major role in the effect of inhalation narcotics, as they have to migrate via the respiratory tract into the blood. The more fat-soluble the substances are, the easier it is to do so. This means that inhalation anaesthetics with high fat solubility achieve a higher potency and, above all, lead to a faster onset of action.
In addition, a smaller quantity of the narcotic is needed to achieve the desired depth of anaesthesia. This is in contrast to the blood solubility of inhalation narcotics. Substances with high blood solubility dissolve less easily in fat and therefore require more time to achieve the desired depth of anaesthesia.
In addition, it then takes longer for the narcotic to be washed out and for the patient to wake up again. In order to ensure that the anaesthetic is nevertheless introduced quickly enough, the dose in the gas mixture that the patient inhales is increased in the case of highly blood-soluble inhalation anaesthetics. The inhalation narcotics are excreted mainly via the lungs. The narcotic is then breathed out again.
Effects and side effects
Inhalation narcotics cause the vessels in the brain to dilate. This can lead to an increase in intracranial pressure, which can reduce the blood flow to the brain. Especially for patients who already have increased intracranial pressure or brain tumors, an injection narcotic is therefore preferable.
Furthermore, inhalation anaesthetics can affect the cardiovascular system to varying degrees. The contractile force of the heart muscle may decrease, cardiac arrhythmia may occur and blood pressure may rise or fall. The inhalation anaesthetics sevoflurane and isoflurane are recommended for persons with heart disease, as they relieve the heart most by dilating vessels.
An advantage of inhalation anaesthetics is that they can achieve relaxation of the respiratory tract. This is particularly important in patients with asthma, as the muscles of the airways tend to contract. In principle, inhalation anaesthetics can cause liver and kidney damage. Sevoflurane is particularly popular for the induction of anaesthesia in children, as it has a pleasantly sweet odor.