Delirium is a neurocognitive syndrome caused by reversible neuronal disruption due to an underlying systemic perturbation. It is a form of acute end-organ dysfunction which can be used as a marker of brain dysfunction. The fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) published by the American Psychiatric Association establishes diagnostic criteria and descriptions to guide the classification and diagnosis of mental disorders. According to DSM-5, diagnostic criteria for delirium include a disturbance in attention, cognition and/or awareness that develops over a short period and has a fluctuating course. The alterations in brain function should differ from the patient's baseline brain function. Experts have identified three types of delirium namely, hyperactive, hypoactive, and mixed varieties.
Post-operative delirium (POD) can occur from 10 minutes after anesthesia to up to 7 days in the hospital or until discharge. It is commonly recognized in the post-anesthesia care unit (PACU) as sudden, fluctuating, and usually reversible disturbance of mental status with some degree of inattention. Severely reduced arousal or deep sedation should not be confused with alterations in brain function. Hypoactive delirium is the most common form of POD.
Delirium may be due to exacerbation of a primary injury or insult, or a potential new secondary insult or injury. Several studies have tried to identify risk factors predisposing to the development of delirium postoperatively.
DSM-5 categorizes delirium as:
POD should be considered a separate category. The post-operative period is the time period right after surgery until the patient is discharged from the hospital. POD should not be diagnosed separately from emergence delirium although any lucid interval after emergence delirium should be noted.
Factors that can predispose or precipitate post-operative delirium can be broadly divided into preoperative, intraoperative and postoperative causes.
Alcohol and benzodiazepine withdrawal have also been known to cause POD.
POD is common, and the prevalence increases with the severity of the surgical insult. According to DSM-5, the incidence of POD in non-cardiac surgery is anywhere between 15% and 54% depending on the screening test used. The incidence in the intensive care population is up to 70% to 80% during their entire stay. In cardiac surgery patients, the incidence is similarly high, between 26% and 52%.
While the incidence of POD is common and similar to other settings, there is a wide discrepancy in the literature regarding the incidence, partly due to the lack of clearly defined distinction between emergence delirium and POD. Prior studies have focused on hyperactive delirium, typically recognized as the patient in the PACU pulling at lines and tubes and being agitated, likely under-diagnosing hypoactive delirium, the most common, which is characterized by lethargy, decreased responsiveness and decreased activity level. This type will often go undiagnosed if routine delirium monitoring is not used.
Despite these limitations, the incidence and risk factors of POD reported in the literature is strongly influenced by the severity of the surgical insult, comorbidities, and sedative and/or analgesic drug exposure.
Although the International Study of Post-Operative Cognitive Dysfunction 1 (ISPOCD1) concluded that general anesthesia is responsible for postoperative cognitive dysfunction (POCD), later studies showed a similar incidence in sedation and regional anesthesia cases. Both surgery and anesthesia present patients with unique physiological conditions. Surgery causes the release of psychoactive inflammatory markers including interleukin 6 (IL-6), tumor necrosis factor-alpha (TNF-alpha) and IL-1 beta that may contribute to the development of delirium through dopamine, GABA, or cholinergic-mediated pathways. On the other hand, general anesthesia exposes the brain to a myriad of cognitively active drugs that alter the chemical balance in the sleep/arousal pathway. The incidence of delirium is lower in patients exposed to light sedation compared to deep sedation.
The patient can present with hyperactive psychomotor activity and frank psychosis in a hyperactive variety or as withdrawal and lethargy which can easily be mistaken for residual anesthetic effects, in hypoactive variety. Other common features include a fluctuating level of consciousness, disorientation, and impaired executive function.
The first step in the evaluation of POD is to determine if the person is arousable to voice. If the person is not arousable to voice, then that person is considered to be in a coma. After the level of arousal has been determined, the delirium instruments can assess the content of the arousal by examining for fluctuating change in mental status highlighted by inattention and altered level of consciousness. See figure 1.
The Richmond Agitation Sedation Scale (RASS) is the most commonly used assessment tool for the level of arousal. Patients in a state of deep sedation or patients who are unarousable cannot be further assessed for delirium.
Using the DSM-5 criteria, delirium is characterized by:
There are many assessment tools for delirium that have been validated for a variety of patient populations and hospital locations, including postoperatively on the ward or in the intensive care unit.
CAM and variations of CAM are most commonly used. The CAM-ICU and 3D-CAM are brief versions of CAM that perform moment in time assessments for delirium. The CAM-ICU is validated for intubated patients on mechanical ventilation. See figure 1.
The Delirium Detection Scale (DDS) and the Memorial Delirium Assessment Scale (MDAS) can assess the severity of delirium.
Nonpharmacological followed by pharmacologic interventions should be employed early in the course of delirium to mitigate the risk of long-term adverse sequelae. Nonpharmacological interventions have been tried and have proven to be effective. Notable examples are the Hospital Elder Life Program (HELP) and modified HELP. These programs use multidisciplinary teams that work on reorienting the patient, socialization, daily visits from the family, feeding and nutrition balance, managing sleep-wake cycles, noise reduction, providing sensory aids and early mobilization. Using 3 protocols administered daily; i.e., orienting communication, oral and nutritional assistance, and early mobilization, Chen et al. demonstrated a significant reduction in the incidence of delirium in the intervention group.
The ABCDEF bundle used in the ICU has also been associated with improved brain function outcomes.
Hayhurst et al. showed that patients receiving a daily goal-directed mobility program had more days alive and free of delirium, had shorter lengths of hospital stay, were more functionally independent at discharge and were more likely to discharge to home.
To institute prevention strategies, early intervention, and treatment, patients should be evaluated for their risk of POD. In the PACU, reorientation should be started immediately, for example, saying the patient name, current location, type of surgery and surgeon's name. Physical factors such as a distended bladder, hypoventilation, uncomfortable patient positioning, and pain should be addressed promptly.
Several pharmacologic agents have been used to prevent and treat delirium in a high-risk population. Continued delirium should be dealt with aggressively by reversing continued effects of anesthetic agents. Flumazenil (0.2-mg increments), naloxone (0.04-mg increments), and physostigmine because it crosses the blood-brain barrier (1- to 2-mg increments), can reverse the effects of benzodiazepines, opioids, and muscle relaxants. Haldol, which is often used for acute management of delirium, shortens the severity of delirium episodes but does not change the incidence and is also not effective for prophylaxis in high-risk elderly populations. Dexmedetomidine has emerged as a useful adjunct to general anesthesia. Intraoperative infusion of dexmedetomidine was shown to reduce the incidence of POD in high-risk elderly population. Its use in children and in ICU patients has been shown to decrease the incidence of emergence agitation, nausea and vomiting, and postoperative pain. However, its optimal intraoperative dose, infusion or boluses, has not been established. Dexmedetomidine was also found to accelerate resolution of delirium, use of fewer antipsychotics and earlier extubation in patients in the ICU in whom agitated delirium prevented extubation. In another study, patients receiving dexmedetomidine had their delirium resolve faster, had less oversedation, less need for noninvasive ventilation and had shorter ICU stay compared to those on haloperidol.
Drugs that increase acetylcholinesterase availability, antipsychotic drugs such as haloperidol have shown no benefit over placebo for the treatment of delirium. Since benzodiazepine sedation has been strongly tied to delirium, propofol and dexmedetomidine have become the mainstay of ICU sedation. Djaiani et al. demonstrated that patients receiving dexmedetomidine had less incidence of and shorter duration of delirium compared to those receiving propofol.
The patient’s vitals should be checked promptly and arterial blood gases with blood glucose levels checked while performing a complete physical exam. This would give an estimate of hemoglobin, electrolytes, and blood glucose values. If signs of new focal neurologic deficits are present, then a computed tomographic scan of the head should be strongly considered.
Perioperative suggestions to reduce delirium and brain dysfunction include:
No drug has gained FDA approval for the prevention and treatment of delirium. There are limited data on effective prophylactic agents as well as limited data on effective initial therapies. Haloperidol and atypical antipsychotics (olanzapine, quetiapine, risperidone) are commonly used despite limited data on efficacy.
Antipsychotics may cause oversedation, respiratory depression, QT prolongation, neuroleptic malignant syndrome, and hypoactive delirium. Dexmedetomidine requires an infusion and ICU stay.
POD is associated with significantly worse patient outcomes. There is emerging evidence that POD can lead to a higher likelihood of postoperative cognitive dysfunction, prolonged brain dysfunction, early dementia, and acceleration in the cognitive decline of Alzheimer's patients. Delirium in the PACU is a sign of further brain dysfunction in the hospital, worse cognition at the time of discharge, and increased likelihood of being admitted at a nursing or rehabilitation facility as opposed to going home. Most studies have shown an association between delirium and increased risk of death.
Patients with postoperative delirium may be at a higher risk of aspiration, especially in emergency surgery where nil per os (NPO) guidelines were not followed. POD is associated with a prolonged hospital stay and increased health care costs, increased risk of institutionalization after discharge and increased risk of disability.
Early mobilization, attention to hydration, supplemental oxygen, excellent pain control, reviewing medication administration, prevention, and management of medical complications and geriatrics consultations in high-risk patients have been successful at decreasing delirium rates.
Sleep enhancement, extra nutrition, vision and hearing protocols, and staff education have also been shown to decrease delirium rates.
Multi-component prevention programs have been shown to reduce the incidence of delirium across medical and surgical patients by approximately 30%. It is important to adopt an interprofessional approach to managing patients at risk of developing POD. Reorienting the patient, calming the patient while looking for obvious and nonobvious precipitating factors in the post-operative period is important. Successful implementation of an interprofessional programs, such as HELP and modified HELP and ABCDEF bundle at various hospitals, has shown encouraging results.
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