o Plane 1: "light" anaesthesia - the animal still has blink and swallowing reflexes,
and regular respiration. - https://www.uwindsor.ca/animal-care-committee/sites/uwindsor...

Anesthesia Monitoring: What the Values Really Mean
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Surgical anesthesia is the state/plane of GA ... Variations in the response to anesthetics results from ... The most common causes: light anesthetic.

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https://en.wikipedia.org/wiki/Guedel's_classification

Stages of Anesthesia

Stage I (stage of analgesia or disorientation): from beginning of induction of general anesthesia to loss of consciousness.

Stage II (stage of excitement or delirium): from loss of consciousness to onset of automatic breathing. Eyelash reflex disappear but other reflexes remain intact and coughing, vomiting and struggling may occur; respiration can be irregular with breath-holding.

Stage III (stage of surgical anesthesia): from onset of automatic respiration to respiratory paralysis. It is divided into four planes:

Plane I - from onset of automatic respiration to cessation of eyeball movements. Eyelid reflex is lost, swallowing reflex disappears, marked eyeball movement may occur but conjunctival reflex is lost at the bottom of the plane
Plane II - from cessation of eyeball movements to beginning of paralysis of intercostal muscles. Laryngeal reflex is lost although inflammation of the upper respiratory tract increases reflex irritability, corneal reflex disappears, secretion of tears increases (a useful sign of light anesthesia), respiration is automatic and regular, movement and deep breathing as a response to skin stimulation disappears.
Plane III - from beginning to completion of intercostal muscle paralysis. Diaphragmatic respiration persists but there is progressive intercostal paralysis, pupils dilated and light reflex is abolished. The laryngeal reflex lost in plane II can still be initiated by painful stimuli arising from the dilatation of anus or cervix. This was the desired plane for surgery when muscle relaxants were not used.
Plane IV - from complete intercostal paralysis to diaphragmatic paralysis (apnea).

Stage IV: from stoppage of respiration till death. Anesthetic overdose-caused medullary paralysis with respiratory arrest and vasomotor collapse. Pupils are widely dilated and muscles are relaxed.

In 1954, Joseph F. Artusio further divided the first stage in Guedel's classification into three planes.[9]

1st plane The patient does not experience amnesia or analgesia
2nd plane The patient is completely amnesic but experiences only partial analgesia
3rd plane The patient has complete analgesia and amnesia

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plane =+

level
stage
degree
standard
stratum
position
rung
echelon
footing