Since general anesthesia first became widely used in late 1846, assessment of anesthetic depth was a problem. To determine the depth of anesthesia, the anesthetist relies on a series of physical signs of the patient. In 1847, John Snow and Francis Plomley attempted to describe various stages of general anesthesia, but Guedel in 1937 described a detailed system which was generally accepted. This classification was designed for use of a sole inhalational anesthetic agent, diethyl ether, in patients who were usually premedicated with morphine and atropine. At that time, intravenous anesthetic agents were not yet in common use, and neuromuscular-blocking drugs were not used at all during general anesthesia. The introduction of neuromuscular blocking agents changed the concept of general anesthesia as it could produce temporary paralysis without deep anesthesia. Most of the signs of Guedel's classification depend upon the muscular movements, and paralyzed patients' traditional clinical signs were no longer detectable when such drugs were used. Since 1982, ether is not used in the United States. Now, because of the use of intravenous induction agents with muscle relaxants and the discontinuation of ether, elements of Guedel’s classification have been superseded by depth of anaesthesia monitoring devices such as the BIS monitor; however, the use of BIS monitoring remains controversial.
Stages of Anesthesia
Stage I : from beginning of induction of general anesthesia to loss of consciousness. Stage II : 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 : 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 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.
Stage IV: from stoppage of respirationtill 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.
