Question

Causes of delirium in the elderly post anesthesia

Answer 1

The risk factors for developing delirium are additive (Marcantonio et al 1994); therefore, recognizing a patient with multiple risk factors for delirium should trigger the surgeon to implement environmental and supportive measures that have been proven to prevent the onset and shorten the duration of delirium (Inouye 2006) (see Figure 1B).

Go to:Diagnosis

Delirium is defined as an acutely altered and fluctuating mental status with features of inattention and an altered level of consciousness. Post-operative cognitive dysfunction should be distinguished from delirium and is defined as a disorder in thought processes which effect cognition in terms of memory, comprehension, and attention (Bryson and Wyand 2006). Over 50% of delirium on inpatient services is unrecognized by the clinical team (Milisen et al 2002). Understanding the three motor types of delirium helps the clinician to recognize the presence of delirium (Meagher and Trzepacz 2000). First, hyperactive delirium occurs when a patient is restless, irritable, combative, or agitated. Second, hypoactive delirium presents with lethargy, decreased alertness/motor activity, and unawareness. And third, the mixed subtype of postoperative delirium has characteristics of both hypoactive and hyperactive delirium. The incidences of the motor subtypes of postoperative delirium are: hypoactive 71%, mixed 29%, and hyperactive is rare (Marcantonio et al 2002).

The diagnosis of delirium is established through using existing delirium assessment methods. The Confusion Assessment Method-Intensive Care Unit (CAM-ICU) is a straight-forward tool with established reliability and validity for assessing delirium (Ely et al 2001). The CAM-ICU combines an assessment of the patient’s sedation or level of consciousness with an evaluation of mental status, inattention, disorganized thinking, and an altered level of consciousness (Ely et al 2001). To assess the level of sedation, the CAM-ICU utilizes the Richmond Agitation and Sedation Score which is a 10 point scale that provides discrete criteria for levels of sedation and agitation (Ely et al 2003). The benefit of the CAM-ICU is that it provides a brief and easy delirium assessment tool that can be administered by both physicians and nurses (McNicoll et al 2005). The CAM-ICU should be performed daily on all patients who have multiple risk factors (older than 65 years, cognitive dysfunction, multiple co-morbidities) for developing postoperative delirium.

The Mini-Mental State Examination (MMSE) is another tool for assessing cognitive status (Folstein et al 1975). The MMSE measures orientation, attention, calculation, recall, and language, which allows both for screening cognitive dysfunction and following fluctuations over time. Other bedside tests to determine the presence of delirium include the executive clock drawing task, the Informant Questionnaire on Cognitive Decline in the Elderly and the Memorial Delirium Assessemnt Scale (Moraga and Rodriguez-Pascual 2007).

Go to:Evaluation

After the diagnosis of delirium has been established, a standardized work-up to exclude organic or identifiable causes of delirium is necessary. The initial step of the evaluation is a complete history and physical exam with cognitive assessment specific for delirium. Further work-up requires the surgeon to tailor their evaluation to an individual patient but can be broken into four main areas:

Laboratory evaluation

Several reversible metabolic causes of delirium are readily diagnosed with standard laboratory tests. Routine blood work includes: electrolytes, glucose, arterial blood gas, calcium, phosphate and magnesium. Correction of the underlying abnormality is completed to reverse the delirium