General anesthesia is the conventional anesthesia or general anesthesia (Greek nàrkosi: to put to sleep). This form of anesthesia first enabled the development of today’s surgical standards. It is used for operations that are not reasonable for the awake patient. General anesthesia forms a very large subfield of anesthesia. In Germany, anesthesia may only be performed by a specialist, the so-called anesthesiologist. General anesthesia is defined by some basic goals or conditions of the patient:
- Hypnosis – extinction of consciousness.
- Amnesia – extinction of the ability to remember.
- Analgesia – painlessness
- Muscle relaxation – drug-induced relaxation of the muscles.
- Attenuation of vegetative reflexes – blocking any reactions of the organism to the potentially harmful stimuli (stress shielding).
Indications (areas of application)
The indications for the subtypes of general anesthesia vary by procedure and are highlighted in the subsections.
Before surgery
Before any surgery, the anesthesiologist (anesthesiologist) must conduct an educational interview with the patient to clarify questions, obtain a medical history, and inform the patient of risks and complications.The patient often receives premedication. This is administered about 45 minutes before the procedure and serves primarily to anxiolysis (anxiety resolution).Immediately before the induction of anesthesia, the anesthesiologist makes sure of the identity of the patient so that there is no confusion. It is obligatory to ask about the last food intake and to check the oral and dental status (also for forensic traceability in case of damage during intubation). Before any planned anesthesia, the patient must be fasting, otherwise the risk of aspiration (carryover of food residues into the airway) is increased. For emergency procedures performed on non-fasted individuals, a special form of anesthesia induction, Rapid Sequence Induction, is used to address the increased risk of aspiration.Medical monitoring is now begun, this includes: Electrocardiogram (ECG), pulse oximetry (measurement of pulse and oxygen content of the blood), venous access (for the anesthetic drugs and other medications), blood pressure measurement (if necessary, invasive arterial blood pressure measurement in high-risk patients).
The procedure
In addition to preparation and thorough anamnestic exploration of the patient to rule out risks, medications are of central importance. Hypnotics are drugs that induce unconsciousness (“sleep”). For general anesthesia, inhalation narcotics e.g. nitrous oxide (laughing gas), injection anesthetics, analgesics e.g. opioids, and muscle relaxants are used. The different variants of general anesthesia are derived, among other things, from the different compositions of these components. To achieve the above-mentioned goals of general anesthesia, the following groups of drugs are mainly used:
- Analgesics (painkillers) or opioid analgesics (e.g., morphine).
- Anesthetics or hypnotics, e.g., inhalation narcotics (anesthetics).
- Muscle relaxants
- Antiemetics (medications against vomiting)
A very important pillar of general anesthesia is securing the airway. Since the drugs administered for anesthesia often also have a respiratory depressant effect (slowing breathing), the patient’s breathing must be secured and supported. The following options are available:
- Intubation – securing the airway with an endotracheal tube (called a tube for short; it is the breathing tube, a hollow plastic probe inserted into the trachea (windpipe)). This form of ventilation should not be performed, for example, singers, because it can affect the vocal cords.
- Face mask – ventilation via a mask that is placed over the mouth and nose.
- Laryngeal mask – The so-called laryngeal mask is placed over the larynx in the throat.
- Laryngeal tube – The laryngeal tube secures the airway by closing the esophagus with a balloon and the supplied air flows into the trachea. For this, a tube with two openings in the esophagus, which it closes, comes to lie.
- Combitube – Double tube that lies in the trachea and esophagus and is blocked (occluded) depending on its position in the esophagus. This tube is used in patients who are difficult to intubate, because here finding the trachea often causes problems.
General anesthesia proceeds in various stages as follows:
- Initiation – Flooding of the drugs to achieve hypnosis, amnesia, analgesia and muscle relaxation. In this phase, the drugs reach the concentrations of action that are required.
- Maintenance – Only when anesthesia is stable can surgery be performed. The drugs must be given so that the level of action is constant. In addition, the drug supply is adjusted to the need regulated, so that any changing situation can be responded to flexibly.
- Discharge – Following the operation, the drugs are eliminated and the anesthesia is discharged, although the pain medication persists.
Forms of general anesthesia:
- Balanced anesthesia – This form of anesthesia is one of the most common and is used primarily for long and medium length adult procedures. It should not be used in the presence of increased intracranial pressure (“intracranial pressure increase) and a tendency to malignant hyperthermia (uncontrolled increase in body temperature) (contraindications).The following medications are used: oxygen, volatile inhalation anesthetic, opioid, nitrous oxide and relaxant if necessary.
- Intravenous anesthesia (IVA) – This form of anesthesia is used for short and medium length procedures.The following drugs are used: oxygen, intravenous hypnotic, nitrous oxide, opioid, relaxant if necessary.
- Total intravenous anesthesia (TIVA) – TIVA is performed if the use of nitrous oxide is to be avoided.The following drugs are used: oxygen, intravenous hypnotic, opioid, relaxant if necessary, but not nitrous oxide.
- Pure inhalation anesthesia – Pure inhalation anesthesia is used primarily in children. The contraindications are the same as those for balanced anesthesia, but the unstable circulatory situation is added.The following drugs are used: oxygen, volatile inhalation anesthetic, nitrous oxide or relaxant if necessary, but no opioid.
