Plane 4 of stage 3 anesthesia is characterized by which of the following?

• A. Plane 1 description
• B. Plane 2 description
• C. Plane 4: intercostal paralysis; fully dilated pupils
• D. Plane 3 description

Answer: (C)

In Stage III anesthesia, depth is described by planes that reflect progressively deeper levels of unconsciousness and physiological suppression. The deepest of these planes is characterized by intercostal muscle paralysis, meaning the chest wall can no longer move effectively and ventilation relies on the diaphragm, often leading to marked reduction in tidal volume or apnea. At the same time, autonomic changes progress and the pupils become fully dilated. So the description of plane four as intercostal paralysis with fully dilated pupils matches this deepest level of surgical anesthesia, where the patient is most at risk for respiratory and cardiovascular complications. The shallower planes would show progressively preserved chest wall movement and less pupil dilation, so they don’t fit the deepest state.