Most surgical procedures in which ether anesthesia was used were performed at this stage of anesthesia, which is divided into four planes.⁴ Plane 1 is entered when the lid reflex is abolished and respiration becomes regular. During this plane, the vomiting reflex is gradually abolished. The nurse working in the PACU must know that swallowing, retching, and vomiting reflexes tend to disappear in that order during induction and reappear in the same order during emergence from anesthesia.

Plane 2 lasts from the time the eyeballs cease to move and become concentrically fixed to the beginning of a decrease of activity of the intercostal muscles, or thoracic respiration. The reflex of laryngospasm disappears during this plane. Plane 3 is entered when intercostal activity begins to decrease. Complete intercostal paralysis occurs in lower plane 3, and respiration is produced solely by the diaphragm. Plane 4 lasts from the time of paralysis of the intercostal muscles to the cessation of spontaneous respiration.

Tracheal tug often appears in association with deep anesthesia and intercostal paralysis. This effect represents an unopposed action of the diaphragm, which displaces the hilum of the lung and thereby increases traction on the trachea.

Stage IV lasts from the time of cessation of respiration to failure of the circulatory system. This level of anesthesia is called the stage of overdose.

When ether was used as the sole inhalation agent, these signs and stages were seen in reverse order on emergence from the anesthetic. No one clinical sign can be considered a reliable indicator of anesthetic depth by itself. All clinical signs must be viewed in the context of the patient’s status along with the particular characteristics of the individual anesthetic agent used.

Some of the more reliable indicators of depth of anesthesia for the more modern inhalation anesthetics include changes in breathing pattern, eye movement, lacrimation, and muscle tone. Because the ventilation is under autonomic control, it is the most sensitive indicator of depth of anesthesia. In the PACU, a patient who uses diaphragmatic ventilation without the intercostal muscles should be considered to be in surgical anesthesia. As the ventilatory pattern returns to a more normal rate, rhythm, and pattern, the patient can be considered to be in light anesthesia and about to have total emergence. Eye movement as opposed to pupillary size is a good indicator of anesthetic depth. Light anesthesia is present with eye movement. Deeper anesthesia is present when the eyes are close together in a cross-eyed position. Lacrimation does not occur during surgical anesthesia when a patient receives desflurane (Suprane), isoflurane (Forane), or sevoflurane (Ultane). Conversely, if a patient received one of those drugs and has tearing, light anesthesia can be considered to be present. As the depth of anesthesia is increased, the amount of muscle tone decreases. Therefore, if a patient in the PACU lacks muscle tone, especially in the jaw and abdomen, the patient should be considered to be in a surgical depth of anesthesia. With the assessment of the degree of muscle tone, the perianesthesia nurse must critically assess the degree of reversal of skeletal muscle relaxants (see Chapter 23) before determining the depth of anesthesia with the criterion of muscle tone. Finally, because the determinants of anesthesia depth have such a high degree of variability, all possible assessment tools should be incorporated into the care of the patient in the PACU. The bottom line is constant vigilance of the patient’s physiologic parameters during emergence from anesthesia and the institution of appropriate nursing interventions based on an ongoing assessment.