Guedel's classification

Guedel's classification is a means of assessing of depth of general anesthesia introduced by Arthur Ernest Guedel (1883-1956) in 1937.

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 (1813-1858) 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 (commonly referred to as simply "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 (such as succinylcholine and tubocurarine) changed the concept of general anesthesia as it could produce temporary paralysis (a desired feature for surgery) without deep anesthesia. Most of the signs of Guedel's classification depend upon the muscular movements (including respiratory muscles), and paralyzed patients' traditional clinical signs were no longer detectable when such drugs were used. Since 1982, ether is not used in United States. Now, because of the use of intravenous induction agents with muscle relaxants and discontinuation of ether, Guedel’s classification is regarded as obsolete. Depth of general anesthesia can now be estimated using devices such as the BIS monitor, however, the use of BIS monitoring remains controversial.

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