Maintenance of anaesthesia | Anaesthetics

Maintenance of anaesthesia

Anaesthesia is usually maintained according to a balanced model. This means that anaesthetic gas and intravenously administered medication are used in combination. Under certain circumstances, purely intravenous maintenance may be necessary, in which the medication is administered in exact doses via syringe pumps.

A purely inhaled maintenance of anaesthesia is possible by adding nitrous oxide to a volatile anaesthetic gas, but is no longer common nowadays. After each operation under anaesthesia, the so-called drainage is performed. The drugs are discontinued and it is waited until the active substances have been exhaled or broken down by the body. In some cases, it may be useful to give antidotes to speed up waking up. In most cases, however, analgesic medication should still be given, as strong pain is usually the main symptom after surgery under general anesthesia.

Effect of anaesthetics

Through various mechanisms, all of which intervene in the central nervous system, the sleeping pills induce a deep sleep.The sleeping pill is usually administered at the beginning of the anaesthesia, sleep is then maintained by the anaesthetic gases. Alternatively, the sleeping pill can be administered continuously (TIVA). Since greater pain is to be expected during surgery, opiates are usually used.

They block the pain receptors in the central nervous system and thus the transmission of pain to the brain. However, lighter painkillers such as novalmine sulfone (Novalgin) or paracetamol are also usually administered intravenously. Drugs from the group of muscle relaxants prevent the transmission of the excitation from the nerve cell to the muscle cell.

Since no signal reaches the muscle, it relaxes. Inhalation anesthetics are supplied as gases or vaporized liquids via the trachea. They cause unconsciousness, muscle relaxation and pain inhibition. Inhalation anaesthetics (anaesthetic gas) are used to maintain anaesthesia, and especially in children also to induce anaesthesia. The exact mechanism is not certain, probably many different structures are affected.

What influence do anaesthetics have on liver values?

Whether or not anesthetics have an influence on liver values cannot be said in general terms, but must be discussed separately for each individual drug. Although Propofol is broken down by the liver, it does not usually lead to an increase in liver values. One complication of the administration of propofol is propofol infusion syndrome.

In addition to severe acid-base imbalances, this syndrome also leads to a massive increase in liver values. Ketamine is also broken down via the liver. If ketamine is used properly, only for anesthesia, no changes in liver values should occur.

However, if ketamine is taken over several days, it has a toxic effect on the liver and leads to an increase in liver values. Like most drugs, anaesthetics also have side effects. The most unfortunate side effect of narcotics is the death of the patient.

Nowadays, this side effect is less frequent than it was several decades ago. On average, the mortality rate for patients without relevant concomitant diseases is about 0.4 cases per 100,000 narcoses. A known side effect of anaesthetics is the inhibition of the regulation of the vascular system.

Normally, the muscles of the vascular system are regulated by the autonomic nervous system. This regulation is eliminated by the administration of the anaesthetics, which explains the drop in blood pressure. At the same time, there is a reduced beating power of the heart.

This drop in blood pressure can be compensated for by the administration of fluids or blood concentrates, but in patients with corresponding pre-existing conditions it can lead to cardiac arrhythmia, and even cardiac arrest. Another side effect, which is mainly associated with muscle relaxants, is the occurrence of allergic reactions. In most cases, these are only slightly pronounced, but can sometimes lead to allergic shock, a life-threatening condition that must be monitored by intensive care medicine.

A dreaded side effect of anaesthetics, especially in the group of anaesthetic gases, is the disease pattern of malignant hyperthermia, which is associated with an increased body temperature. The symptoms of malignant hyperthermia are highly variable and usually highly life-threatening. However, the introduction of a new drug (dantrolene) has greatly reduced the mortality rate.

After the operation, the affected person may also feel the effects of the anesthetics. Many patients treated experience moderate to severe nausea and vomiting after the operation. The reason for this is usually the anaesthetic gases used.

In order to prevent this postoperative nausea, inhalation anesthesia can be dispensed with and a purely intravenous anesthesia can be performed. If many anaesthetics are overdosed, undesirable effects can also occur, endangering the patient’s life. The effect and active substance concentration of the anaesthetics must be monitored by an anaesthetist during the entire procedure in order to prevent both over- and underdosing of the drugs.

An overdose would have drastic consequences that endanger the patient’s life. In the worst case, an underdose could no longer ensure that the patient is free of pain during the procedure.It is due to the modern possibilities of monitoring the patient in real time that undesirable side effects of the anaesthetics used can be detected and treated as quickly as possible.