Emergence Delirium: Anesthetic Agents
Basic, Clinical Sciences: Anesthesia Procedures, Methods, and Techniques
According to Miller’s Anesthesia, approximately 10% of adult patients over the age of 50 will experience some degree of post-op delirium 1-5 days of after surgery. Preoperative risk factors for the development of emergence delirium include age greater than 70 years, pre-existing cognitive impairment, decreased functional status, alcohol abuse, prior history of delirium, psychiatric disease, and sleep deprivation. Intraoperative risk factors include high surgical blood loss, hematocrit of less than 30% and an increased number of transfusions. Intraoperative hemodynamic derangements, use of N2O, or the use of general anesthesia versus regional techniques have not been shown to increase risk of delirium or long term postoperative cognitive dysfunction (POCD).
Central cholinergic insufficiency is a potential underlying cause of emergence delirium exacerbated by opioids (methadone, meperidine), sedatives (antipsychotics), and anticholinergics (atropine). Ketamine is associated with undesirable psychotomimetic side effects (e.g. disturbing dreams and delirium) during emergence and recovery, which is less common in children, in those pre-medicated with benzodiazepines, and patients in whom propofol was used as part of a total intravenous anesthetic. Lidocaine can reduce the incidence of emergence delirium when given as an infusion during the case. Addition of opioid may reduce incidence of delirium, though as stated above, not those that are capable of producing central cholinergic insufficiency.
Separate from emergence delirium, Miller distinguishes emergence excitement as a transient, confused state associated with emergence from general anesthesia. It is more common in children with >30% experiencing some sort of agitation or delirium. The peak incidence is from ages 2-4 years with an incidence in adults of only 3-5%. This excitement is associated with rapid “wake up” from insoluble volatile anesthetics such as desflurane and sevoflurane and has a lower incidence with isoflurane and halothane. It may be a reflection of the agent used rather than rapidity of wake-up. Some studies have suggested that the use of propofol leads to a smoother wake up than the inhalational agents. Additionally, a slow wake up from volatiles does not reduce the overall incidence.
Risk factors for emergence delirium include intrinsic characteristics of the volatile anesthetic, severity of postoperative pain, the type of surgery, age, existence of preoperative anxiety, the patient’s underlying temperament, and adjunct medications the patient received. Specifically in adults, the administration of preoperative midazolam, breast surgery, abdominal surgery, and length of surgery are all correlated with an increased incidence of emergence delirium. Prophylactic measures include the reduction of preoperative anxiety, the effective treatment of postoperative pain, and the cultivation of a stress-free recovery environment. Medications useful in the prophylaxis and treatment of emergence excitation include midazolam, clonidine, dexmedetomidine, fentanyl, ketorolac, and physostigmine.