Definition
The American anaesthetist Arthur Guedel established in 1920 in studies that anaesthesia consists of different stages. These can be distinguished by reflexes, pupil width, movements, pulse, respiratory drive and consciousness of the patient. Guedel observed these stages during ether anaesthesia and they can only be transferred to a pure gas anaesthesia and not to the venous anaesthesia often used today. The addition of opioids, for example, leads to completely different pupil widths.
How many stages of anesthesia are there?
In the classification according to Arthur Guedel there are four stages of anaesthesia. The first stage is the analgesia and amnesia stage. After that the excitation stage begins.
The third stage is called tolerance stage and the fourth stage is poisoning. These stages can only be clearly observed under pure gas anesthesia. Since pediatric anesthesia is often induced with gas, the stage classification is still recognizable here.
Stage 1
Stage one refers to the analgesia and amnesia phase. This begins with the anaesthetist turning on the gas. First, the sensory areas of the cerebral cortex are paralyzed.
The sensations of temperature and pressure decrease. Initially, the patient is not yet completely free of pain, but the sensation of pain is reduced. In addition, the patient is still conscious and can describe himself that he is tired and dawns away.
Muscle tone, i.e. the ability to tense muscles themselves, is still present. The reflexes can also still be triggered normally. This can be tested by simply tapping with the reflex hammer on the patellar tendon.
Circulation and respiration still function without restriction. The pupil motor function is also not yet restricted. The pupils become smaller when exposed to light and then larger again. If the anesthesia is discontinued at this stage, the patient may have slight memory gaps. Stage one ends with the complete loss of consciousness.
Stage 2
Guedel called the second stage excitation stage. This stage begins with the complete loss of consciousness. The anaesthetic gas leads to a central attenuation, during which no controlled impulses can be emitted from the cerebrum.
Instead of the controlled impulses from the cerebrum, uncontrolled impulses are triggered by the midbrain. These lead to sudden muscle twitches. Therefore, children must lie safely and be strapped in so that they cannot fall off the operating table when gas is introduced.
The affected persons are unconscious and show a strong salivation. The sensation of pain is further reduced. The circulation, i.e. the blood pressure and pulse, and the muscle tone initially increase and the reflexes also become stronger.
This is due to the fact that the cerebrum normally dampens reflexes and this damping now fails. Those affected also have a strong urge to urinate and may lose urine. Breathing is still almost normal, but can be somewhat irregular.
The pupils are dilated. A danger at this stage is vomiting and subsequent inhalation of the vomit, which can lead to pneumonia. The excitation stage does not last long and ends when the tolerance phase begins.