Changes in mental function after anesthesia and surgery were described more than 50 years ago. Because these phenomena have been elucidated in subsequent years, they have been categorized into the distinct syndromes of delirium and postoperative cognitive dysfunction (POCD). This chapter describes the epidemiology of, risk factors for, clinical significance, and, when applicable, management of these syndromes.

I. EPIDEMIOLOGY

Patient populations at increased risk of emergence delirium include those with preexisting structural brain disease (e.g., patients with a history of stroke or Alzheimer dementia), those with existing psychiatric disorders or intellectual impairment, intoxicated patients, children and young adults, those with high levels of preoperative anxiety regarding their procedures, those given psychoactive medications pre- or intraoperatively, and those with preexisting communication difficulties or communication difficulties related to their procedures (nonnative speakers, hearing impaired patients, or those with jaw immobilization as part of their procedure). Anesthetic and surgical factors that increase the risk of postoperative delirium include surgical blood loss, number of intraoperative blood transfusions, intraoperative hemodynamic derangements such as hypotension, intraoperative physiologic derangements such as hypoxia, high intraoperative narcotic use, and general (as opposed to regional) anesthesia.

II. CLINICAL SIGNIFICANCE

Altered mental status postoperatively places patients at risk of significant medical complications such as accidental trauma, dislodgement of equipment needed for treatment (lines, tubes, dressings), and interference with care. In addition, altered mental status in the postanesthetic care unit (PACU) is disturbing to nursing staff and other patients. Significantly altered mental status postoperatively can delay discharge from PACU and increase the care burdens on PACU staff. Emergence delirium can run the gamut from lethargy and confusion to physical combativeness and extreme agitation. In an Australian study, 8% of recovery room incidents reported related primarily to central nervous system dysfunction.

It is important in classifying a patient with altered mental status postoperatively to distinguish between emergence delirium and POCD. Emergence delirium occurs acutely after surgery and involves altered levels of consciousness and level of attention. POCD may be short or long term, appearing in the days to weeks to months following surgery. POCD involves normal level of consciousness but involves a subtle cognitive decline in attention, memory, and ability to learn from the preoperative state. POCD may be temporary or may be permanent.

III. DIFFERENTIAL DIAGNOSIS

It is important to consider the differential diagnosis of altered sensorium postoperatively in order to assess for an underlying pathology. The
differential diagnosis of emergence delirium includes residual medication effect (inhaled anesthetics, narcotics, sedatives including premedications, and anticholinergics), hypoxia, residual neuromuscular blockade mimicking depressed consciousness, hypothermia, hypoglycemia, hyperglycemia with resultant hyperglycemic hyperosmolar coma, hyponatremia, and carbon dioxide narcosis. Rare causes of altered sensorium include local anesthetic toxicity either from overdose or inadvertent subarachnoid injection, nonconvulsive seizures, anoxic brain injury, acute cerebrovascular accident, or, in the correct setting, unrecognized intracranial process such as cerebral hemorrhage, tension pneumocephalus, or other causes of elevated intracranial pressure following neurosurgery. It is also important to evaluate the patient for underlying encephalopathy related to renal or hepatic dysfunction, which may have been exacerbated by surgery.

Postoperative pain or discomfort is an important consideration in the differential diagnosis of postoperative agitation. Less commonly recognized sources of discomfort should be considered such as bladder distention, gastric distention, tight dressings, corneal abrasion, intravenous line infiltration, small objects forgotten underneath the patient, and patient body part malpositioning.