Seasonal variation in the incidence of delirium among the patients of a geriatric hospital

doi:10.1016/S0167-4943(01)00192-3

Archives of Gerontology and Geriatrics

Volume 33, Issue 3, November 2001, Pages 287-293

https://doi.org/10.1016/S0167-4943(01)00192-3 Get rights and content

Abstract

Delirium syndrome is common in the hospitalized elderly population. However, data on its numerous etiological factors are scarce. Clinical observations suggest that delirium incidence could be related to seasonality. In order to evaluate the seasonal influence on the incidence of delirium syndrome among the patients of a geriatric hospital, we performed a retrospective study reviewing the medical records of 5218 patients aged 65 years and older, who were hospitalized in three medical wards between the years 1991 and 1997. The diagnoses of delirium were made according to ICD-9-CM. Of the 4929 subjects enrolled, 3548 (72%) were refered for assessment to the psychiatric or neurologic specialist, because of acute changes in their mental or behavioral status. Of those patients, 312 (6.3%) were diagnosed with delirium at admission, and 234 (4.7%) developed delirium during their hospitalization. Statistical analysis of incidence revealed a seasonal variation, with higher rates in the winter than in the summer months (P<0.001). This study suggests a seasonal influence on delirium syndrome incidence and a possible etiological relation with seasonal factors like the light –dark cycle.

Introduction

The syndrome of delirium is characterized by an acute onset of disturbances of consciousness, attention and global changes in cognition. All these symptoms fluctuate during the day (Kaplan and Sadock, 1994). The syndrome of delirium could be generated by various causes: central nervous diseases, systemic diseases, intoxication or withdrawal from any pharmacological or toxic agent (Inouye et al., 1993, Marcantonio et al., 1994). The evidence that so many causes may generate delirium and also the fact that the general morbidity of elderly people varies according to seasonal factors (Alderson, 1985, McKee, 1989) suggests the existence of possible seasonal differences regarding the incidence of delirium syndrome. In order to evaluate the influence of the seasonal factors on delirium incidence, we compared the monthly incidence of delirium in a group of hospitalized elderly patients during a period of seven years.

Section snippets

Subjects

This was a retrospective study performed during the years 1991–1997 at the Shmuel Harofe Geriatric Hospital, in Israel. The institute is a university hospital, and during the study, the number of beds of each of the three medical wards (35) remained stable as well as the number of the inhabitants in the surrounding area. Data regarding the patients, their clinical presentation, diagnoses and treatment were retrieved from the medical records. The patients' diagnoses were made according to the

Results

Between the years 1991 and 1997, 5218 patients were admitted to the hospital medical wards. Of these patients, 1289 were ineligible: 1041 because they were cognitively impaired and could not communicate; 157 were discharged within 24 h after their admission, 65 had language difficulties, and 26 were unavailable because of protective isolation. Of the 4929 subjects enrolled, 3548 (72%) were refered for assessment to the psychiatric or neurologic specialist, as a result of acute changes in their

Discussion

The main finding of this study is a higher incidence of delirium in winter than in summer (P<0.001). The increase in delirium incidence during winter is higher than expected from the seasonal increase in the general morbidity. Etiological factors of delirium are numerous and various: almost any change in the homeostasis of the body could generate the delirium syndrome (Joseph and Kapoor, 1990); old age in itself represents a risk factor (Kaplan and Sadock, 1994). The incidence of

Acknowledgements

The authors wish to thank to the nurses Meydad Bracha and Wechsler Chana for their contribution in the assessment of the patients.

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Furthermore, alteration in cognition was robustly associated with seasonal changes.11-13 Two previous studies showed a seasonal effect on delirium incidence, with higher incidence in autumn-winter compared to summer months.14,15 However, these findings are limited to general medical patients, and the seasonal effect on delirium remains poorly understood in critically ill surgical patients.
Postoperative delirium is common in critically ill patients and is known to have several predisposing and precipitating factors. Seasonality affects cognitive function which has a more dysfunctional pattern during winter. We, therefore, aimed to test whether seasonal variation is associated with the occurrence of delirium and hospital Length Of Stay (LOS) in critically ill non-cardiac surgical populations.
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Delirium is associated with circadian rhythm disruption. In this study we have explored whether circadian variation of melatonin is an indicator for delirium. Melatonin levels were determined from the first day of hospitalization and up to three days after the onset of delirium. Patients who did not developed delirium exhibited a daily melatonin rhythm, while in patients that developed delirium, the melatonin rhythm was lost and mean melatonin levels were found decreased as early as three days before the diagnosis of delirium, indicating that on arrival to the hospital circadian melatonin disruption can be used as an indicator of delirium.
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Less sunlight exposure was found to be associated with cognitive impairment in a large cohort of healthy volunteers [15]. In a broader extent concerning cognitive impairment in patients, 1 study showed a higher delirium incidence during winter in a geriatric population, suggesting a relation with reduced daylight exposure during that season [6]. In ICU patients, up to now, no studies investigated effects of preadmission daylight exposure on delirium during ICU stay.
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Data of 3198 patients, aged (mean ± SD) 61.9 ± 15.3 years with Acute Physiology and Chronic Health Evaluation II score 16.4 ± 6.6 were analyzed. Delirium incidence was 31.2% and did not vary significantly throughout the year. Twenty-eight-day preadmission photoperiod was highest in spring and lowest in winter; however, no association between light exposure and delirium incidence was found (odds ratio, 1.00; 95% confidence interval, 0.99-1.00; P = 0.72). Furthermore, delirium was significantly associated with age, infection, use of sedatives, Acute Physiology and Chronic Health Evaluation II score, and diagnosis of neurological disease or trauma.
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Interventions as simple as music therapy during the postoperative period reduce the rates of delirium.92 One study reported higher incidence of delirium in the winter,93 suggesting that access to sunlight may be important. Improving ward conditions with spacious rooms, community dining, and unrestricted visiting hours, and encouraging family members to visit and bring familiar items from home are beneficial.94
Evaluation and Management of the Elderly Patient at Risk for Postoperative Delirium
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Interventions as simple as music therapy during the postoperative period reduce the rates of delirium.92 One study reported higher incidence of delirium in the winter,93 suggesting that access to sunlight may be important. Improving ward conditions with spacious rooms, community dining, and unrestricted visiting hours, and encouraging family members to visit and bring familiar items from home are beneficial.94

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View full text

Seasonal variation in the incidence of delirium among the patients of a geriatric hospital

Abstract

Introduction

Section snippets

Subjects

Results

Discussion

Acknowledgements

Biol. Psychiatry

Season and mortality

Health Trends

Apparent seasonal variation in sundowning behavior in a skilled nursing facility

Sleep Res.

Sundown syndrome: etiology and management

J. Psychosoc. Nurs.

Delirium: a test of the Diagnostic and Statistical Manual III criteria on medical inpatients

J. Am. Geriatr. Soc.

Acute brain syndromes

J. Clin. Psychiatr.

A multicomponent intervention to prevent delirium in hospitalized older patients

N. Engl. J. Med.

A predictive model for delirium in hospitalized elderly medical patients based on admission characteristics

Ann. Intern. Med.