Assessment of the depth of anaesthesia
Anaesthesia has been described as a series of four Stages.
The period between administration of an anaesthetic and loss of consciousness.
The period after loss of consciousness, which may include actions such as uncontrolled movement, delirium, vocalization.
The level at which surgery can be performed. Stage 3 anaesthesia is divided into four planes.
- Plane 1: "light" anaesthesia - the animal still has blink and swallowing reflexes, and regular respiration.
- Plane 2: "surgical" anaesthesia - the animal has lost blink reflexes, pupils become fixed and respiration is regular.
- Plane 3: "deep" anaesthesia - the animal starts losing the ability to use the respiratory muscles and breathing becomes shallow; may require assisted ventilation. The surgeries are performed in this plane.
- Plane 4: the animal loses all respiratory effort, and breathing may stop entirely.
Anaesthetic crisis! Respiratory arrest and death from circulatory collapse imminent.