| Stage I | Analgesia state: Patient is conscious and rational, with decreased perception of pain. |
| Stage II | Delirium stage: Patient is unconscious; body responds reflexively; irregular breathing pattern with breathholding. |
| Stage III | Surgical anesthesia: Increasing degrees of muscle relaxation; unable to protect airway. |
| Stage IV | Medullary depression: There is depression of cardiovascular and respiratory centers. |
