Delirium in the postanesthesia care unit

Published on 07/02/2015 by admin

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Last modified 22/04/2025

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CHAPTER 114

Delirium in the postanesthesia care unit

Carla L. Dormer, MD

Postoperative delirium is an acute onset of altered or fluctuating mental status combined with significant inattention that can present in multiple ways. Although often thought to include one or more of the following manifestations—hyperarousal, agitation, hyperactivity, and even frank psychosis—postoperative delirium more often exhibits as hypoactivity, which may include flat affect, withdrawal, and lethargy.

Postoperative delirium occurs more frequently at the extremes of age, as well as following certain operations. In children, delirium is relatively common (with a reported incidence of approximately 30%), manifesting as emergence excitement or agitation (e.g., inconsolable crying or disorientation) occurring within the first 10 min of arrival in the postanesthesia care unit (PACU) and resolving within an hour. If children are still asleep when brought to the PACU, they can nonetheless experience agitation, but it will occur later in their PACU stay.

Predisposing and perioperative risk factors

Risk factors for postoperative delirium are summarized in Box 114-1. Patients with no risk factors have a 9% chance of developing postoperative delirium. For those with one or two risk factors, the chance increases to 23%, and for those with three or four risk factors, it’s up to 83%. Multiple hypotheses have been proposed as to why certain individuals are at risk for developing delirium. In elderly patients, contributing factors include smaller brain mass (atrophy) and a decreased number of neurons, as well as decreased neurotransmitter (acetylcholine, serotonin, and dopamine) production and receptor density. Accordingly, the elderly appear to have limited “cognitive reserve.” Therefore, even minor disturbances can lead to postoperative delirium. Specifically, severe illness, cognitive impairment with and without dementia, dehydration, and substance abuse have been shown to be predisposing risk factors. Preexisting diminished executive function and depression are independent predictors of postoperative delirium.

Box 114-1 Predisposing and Perioperative Factors Associated with Increased Risk for Delirium in Postanesthesia Care Unit

Predisposing Factors	Perioperative Factors
Abnormal glycemic control Age >65 y ASA score ≥3 BUN/Cr >18 Cognitive dysfunction or dementia ^† Depression Excessive alcohol use Illicit drug use or use of ≥3 prescription drugs Immobility Intracranial injury Male sex Neurologic disease ^‡ Sensory impairment, particularly visual Sepsis Use of β-adrenergic receptor blocking agents Metabolic derangements

Airway obstruction

Bladder distention

Duration of operation >1 h

Duration of preoperative fluid fasting *

Electrolyte imbalance

Emergent versus elective procedure

High-risk operation

Hypoxia or hypercapnia

Orthopedic operation

Pain

Prolonged mechanical ventilation

Sensory overload

Use of specific drugs for anesthesia and analgesia ^§

ASA, American Society of Anesthesiologists; BUN/Cr, blood urea nitrogen/creatinine ratio.

^*Duration of preoperative fluid fasting ≥6 h, as compared with 2-6 h, increases the risk for development of postoperative delirium.

^†Particularly impairment in executive function.

^‡Alzheimer disease and Parkinson disease.

^§Drugs administered perioperatively that have been associated with an increased risk for development of postoperative delirium include anticonvulsants, atropine, benzodiazepines, corticosteroids, droperidol, fentanyl (larger doses), H2 receptor antagonists, ketamine, meperidine, metoclopramide, and scopolamine.

Perioperative risk factors also include high-risk surgical procedures (cardiac, thoracic aortic, noncardiac thoracic, orthopedic), breast and abdominal procedures, as well as prolonged operations. Many of these high-risk operations are associated with embolic phenomenon (e.g., air, thrombus, cement), large fluid shifts, and substantial rates of blood transfusion. Inflammation may also be involved; cytokines are released in response to surgical stress and have been associated with neuronal death. Given this information, one could conclude that regional anesthesia might be associated with less postoperative delirium than is general anesthesia because fewer sedatives and opioids are used with the former. However, this conclusion has yet to be substantiated.

Acetylcholine is important for maintenance of arousal, attention, and memory, whereas dopamine has an opposing effect. Thus, perioperatively administered medications that decrease levels of acetylcholine or increase levels of dopamine can lead to delirium (Figure 114-1). Central anticholinergic syndrome, caused by blockade of muscarinic cholinergic receptors in the central nervous system, manifests as decreased heart rate and contractility, bronchial constriction, decreased salivary secretions, intestinal and bladder contraction, relaxation of sphincters, and delirium. Sedatives, such as benzodiazepines, as well as opioids (especially meperidine because it is structurally similar to the anticholinergic, atropine) are prime contenders. Corticosteroids, H₂-receptor antagonists, and anticonvulsants have also been implicated. Renal and hepatic dysfunction compromise clearance of these medications, resulting in further exacerbation of delirium.

Figure 114-1 Decreased levels of acetylcholine (ACh) and increased levels of dopamine (DA) or cortisol (ACTH) can lead to postoperative delirium.

In children, the highest incidence of postoperative delirium occurs in those too young (i.e., aged 2-4 years) to communicate in words when awakening from anesthesia, thereby making the differentiation between delirium and pain more difficult. Treating preoperative anxiety has some beneficial effect. When compared with the use of other inhaled anesthetics, sevoflurane and desflurane use is associated with a higher incidence of postoperative delirium in children. Using desflurane for maintenance of anesthesia after a sevoflurane induction reduces the severity of emergence delirium, when compared with sevoflurane induction and maintenance.

Diagnosis

Screening tools have been developed and adapted for use in the PACU to assess patients for the presence of delirium (Table 114-1). The Nursing Delirium Screening Scale appears to be the most sensitive in detecting postoperative delirium, which is largely a diagnosis of exclusion. Common metabolic derangements that are associated with delirium include hyponatremia, hypoglycemia or hyperglycemia, hypokalemia or hyperkalemia, hypercalcemia, hypermagnesemia, lactic acidemia, hypothermia, hypothyroidism, and adrenal insufficiency. Arterial hypoxemia and alveolar hypoventilation are potential respiratory-associated causes of delirium. Postoperative nausea and vomiting and infection (e.g., urinary tract infection, pneumonia, or septicemia) should also be considered in patients who exhibit signs of postoperative delirium.

Table 114-1

Tools Used to Score Delirium in Postanesthesia Care Unit

Feature	CAM	DDS	Nu-DESC
Number of questions	4	5	5
Responses	Yes/No	0-2 scale	Weighted score for each of 4 possible responses
Domains measured	Acute onset or fluctuating course, inattention, disorganized thinking, altered level of consciousness	Disorientation, inappropriate behavior, inappropriate communication, illusions or hallucinations, psychomotor retardation	Orientation, hallucinations, agitation, anxiety, paroxysmal sweating