JAGS 49:1327–1334, 2001© 2001 by the American Geriatrics Society 0002-8614/01/$15.00

Environmental Risk Factors for Delirium in Hospitalized Older People

Jane McCusker, MD, DrPH,*

§

Martin Cole, MD,

†

�

Michal Abrahamowicz, PhD,

§¶

Ling Han, MD,

§

John E. Podoba,

§

and Leila Ramman-Haddad

‡

OBJECTIVES:

To evaluate the relationship of environ-mental risk factors in hospitals to changes over time in de-lirium symptom severity scores.

DESIGN:

Observational prospective clinical study withrepeated measurements, several times during the first weekof hospitalization and then weekly during hospitalization.

SETTING:

University-affiliated general community hos-pital.

PARTICIPANTS:

Four hundred forty-four patients age65 and older admitted to the medical wards: 326 with de-lirium and 118 without delirium. Patients with prior cog-nitive impairment were oversampled.

MEASUREMENTS:

The severity of delirium symptomswas measured with the Delirium Index, a scale developedand validated by our group, based on the Confusion As-sessment Method. Potential environmental risk factors as-sessed included isolation, hospital unit, room changes, lev-els of sensory stimulation, aids to orientation, and presenceof medical (e.g., intravenous) or physical restraints.

RESULTS:

Controlling for initial severity of delirium andpatient characteristics, variables significantly related to anincrease in delirium severity scores included hospital unit(intensive care or long-term care unit), number of roomchanges, absence of a clock or watch, absence of readingglasses, presence of a family member, and presence ofmedical or physical restraints.

CONCLUSION:

The associations of intensive care andmedical and physical restraints with severity of deliriumsymptoms may be due to uncontrolled confounding by in-dication. However, the other factors identified suggest po-

tentially modifiable risk factors for symptoms of deliriumin hospitalized older people.

J Am Geriatr Soc 49:1327–1334, 2001.

Key words: older; delirium; hospital; risk factor

D

elirium is a cognitive disorder characterized by acuteonset and impairment in perception, cognition, and

behavior. It occurs frequently in older hospital inpatientsand is associated with adverse outcomes, including longerhospital stay, increased mortality, and higher rates of insti-tutionalization.

1

Risk factors for delirium in the hospital setting includeimmobility, medications, iatrogenic events, intercurrent ill-ness,

2–4

sensory deprivation and social isolation.

5

How-ever, many of these factors have not been systematicallystudied. The association of delirium with visual and hear-ing impairment suggests that reduction of environmentalstimuli has a role in this disorder.

2

There is some evidenceto suggest that sensory deprivation experienced by pa-tients placed in windowless hospital rooms is associatedwith higher rates of delirium. In one study, 20 patients(40%) placed in an intensive care unit (ICU) without win-dows developed delirium compared with nine patients(18%) in an ICU with windows.

6

Similarly, the incidenceof hallucinations and delusions was 48% in patients in awindowless ICU compared with only 26% in an ICU withtranslucent windows.

7

In a third study, patients were ran-domly assigned to single-care or two-bed rooms; 64% ofthose assigned to single-care rooms experienced one ormore disturbances (visual, auditory, body-touch, smell,taste, cognitive disturbances, and noncompliant behavior)compared with 34% of patients in two-bed rooms.

8

In astudy of inpatients with hip fracture, being in a room byoneself, presence of a visible timepiece, and use of a televi-sion were associated with lower confusion scores.

9

Alter-natively, sensory overload (too much noise and activity)may have a negative effect.

5

Environmental factors associ-ated with confusion in older surgical patients includedfewer interactions with significant others and, contrary toexpectations, the presence of more orienting objects.

10

A

From the *Department of Clinical Epidemiology and Community Studies,

†

Department of Psychiatry, and

‡

Infection Control Department, St. Mary’s Hospital;

§

Department of Epidemiology and Biostatistics and

�

Department of Psychiatry, McGill University;

¶

Division of Clinical Epidemiology, Mont-real General Hospital, Montreal, Canada and Scientist, Canadian Institutes for Health Research.

Funded by the Medical Research Council of Canada and the Fonds de la Re-cherche en Santé du Québec.

Address correspondence to Jane McCusker, Department of Clinical Epidemiology and Community Studies, 3830, avenue Lacombe, Room 2508, Montreal, Quebec H3T 1M5 Canada.

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. OCTOBER 2001–VOL. 49, NO. 10 JAGS

recent study of inpatients age 65 and older admitted tomedical or surgical units found that a high number ofmedications administered during hospitalization, surgery,a high number of procedures, and intensive care treatmentwere associated with the development of delirium.

11

Otherenvironmental variables presumed to perpetuate deliriumin the hospital setting are targeted by proposed guidelinesand protocols for nursing care.

5,12

These include the pres-ence of familiar possessions and aids to orientation such aclock and calendar, eyeglasses and hearing aids if needed.

To our knowledge, the relationships of these environ-mental factors to the severity of symptoms of deliriumhave received little research attention. Thus, the goal ofthis study was to investigate the relation of environmentalfactors in an acute care hospital to changes in severity ofsymptoms of delirium in older medical inpatients. Wewere particularly interested in the effect of isolation (re-lated to control of infections due to antibiotic-resistantbacteria),

13–15

but other environmental factors of interestincluded room type, room changes, levels of sensory stim-ulation, hospital unit, and presence of orienting objectsand family members. The study is a secondary analysis ofdata collected in two related, concurrent studies on delir-ium, a randomized controlled trial of management of de-lirium and a nonexperimental prospective study of theprognosis of delirium that included nondelirious controls.To meet the study objectives, we collected supplementaryinformation on patient isolation to link with study data.

METHODS

The study was conducted at a 400-bed primary acute caregeneral hospital in Montreal. A study nurse was responsi-ble for patient screening and enrollment in the two studies.Only patients age 65 and older admitted from the emer-gency department to the medical services were included inthe studies. We excluded patients with a primary diagnosisof stroke, those admitted to the oncology unit, those ad-mitted to the intensive care unit (ICU) or cardiac monitor-ing unit (CMU) unless they were transferred to a medicalward within 48 hours of admission, and those who did notspeak English or French. For the trial only, patients wereexcluded if they were admitted to the geriatric service or iftheir initial cognitive status score using the Short PortableMental Status Questionnaire (SPMSQ)

16

was 10, indicat-ing maximal impairment.

The study nurse administered the Confusion Assess-ment Method (CAM)

17

to those who made three or moreerrors on the initial SPMSQ or whose nursing notes indi-cated symptoms of delirium; delirium was diagnosed if thepatient met criteria for delirium. Those whose initialSPMSQ score was

�

3 and those whose initial SPMSQ was

�

3 but who scored negative on the CAM were rescreenedwith the SPMSQ daily for the next week. The CAM wasadministered (or readministered) if the SPMSQ error scoreincreased or there was evidence from the nursing notes ofsymptoms of delirium. Controls were selected from pa-tients screened for delirium but free of this condition. Tobalance the distributions of age and prior cognitive im-pairment among cases and controls, the sampling methodtook into account the patient’s age and initial SPMSQscore. Thus, controls were selected from patients age 70

and older, and only a subsample of patients with SPMSQscores

�

3 was included.

Hypotheses

We hypothesized that the following environmental factorswould increase the severity of symptoms of delirium: isola-tion, single-bed room, room changes, location in a roomfurther from a nursing station, excessively high or lownoise level, inadequate lighting, absence of aids to orienta-tion (clock, calendar, personal possessions), absence of afamily member, and presence of medical (e.g., intravenousor oxygen tubing) or physical restraints.

Outcome Measure

The Delirium Index (DI) is an instrument developed byour group for the measurement of the severity of symp-toms of delirium.

18

It is based solely upon observation ofindividual patients, without additional information fromfamily members, nursing staff, or patients’ medical charts.Seven of nine symptom domains assessed on the CAM (in-cluding disorders of attention, thought, consciousness, ori-entation, memory, perception, and psychomotor activitybut excluding acute onset and sleep-wake disturbance) arerated on the following impairment scale: 0

�

absent, 1

�

mild, 2

�

moderate, 3

�

severe. The total score rangesfrom 0 (no symptoms) to 21 (maximum severity). This in-strument was designed to be used in conjunction with theMini-Mental State Examination (MMSE)

19

: the first fivequestions of the MMSE constitute the basis of observa-tion. We established the interrater reliability, concurrentcriterion validity, and sensitivity to change of the DI in 30patients with delirium who were rated simultaneously andindependently by one or two research assistants and a ge-riatric psychiatrist on up to four occasions.

18

The concor-dance coefficient between DI ratings by a psychiatrist anda research assistant was 0.81 and between two research assis-tants was 0.71. Pearson correlation coefficients were 0.84 be-tween the DI and the Trepacz Delirium Rating Scale (DRS)and 0.71 between change in the DI and change in the DRS.

18

Repeated Measures

Most measures for this study were collected as part of theoriginal study design. These include assessments by a re-search assistant, blind to study group, who visited eachpatient soon after study enrollment, every 2 to 3 days dur-ing the first week, and then at weekly intervals while thepatient remained in hospital. At each assessment, patientswere assessed for severity of delirium symptoms and achecklist of environmental information was completed, in-cluding the patient’s hospital unit, room number, androom type (private, semi-private, and ward). The distanceof the room from the nursing station was categorized us-ing floor maps and inspections as close (high stimulation),intermediate, and distant (low stimulation). The researchassistant noted whether the patient’s surroundings weretoo noisy or too quiet, whether the room was well lit,whether various orientation aids (calendar, clock orwatch, and personal possessions at the bedside) werepresent, whether a family member was present during theassessment, and whether physical restraints or other re-straints from medical interventions (e.g., intravenous oroxygen tubing) were present. The interrater reliability of

JAGS OCTOBER 2001–VOL. 49, NO. 10

ENVIRONMENTAL RISK FACTORS FOR DELIRIUM

1329

these environmental observations was assessed in 29 pa-tients, and indicated 75% to 100% agreement.

Other Measures

Isolation

The current hospital policy requires that all patients ad-mitted to an acute care hospital within the last 6 monthsor transferred from a rehabilitation hospital or any long-term facility are isolated and screened for methicillin-resis-tant

Staphylococcus aureus

(MRSA), and vancomycin-resistant

Enterococcus

(VRE). Results of screening for MRSAtake 48 hours, and VRE screening results are available after72 hours. Consequently, patients who screened negative forMRSA would be isolated for only 48 hours. Patients whoscreened negative for VRE only or for VRE and MRSAwould be isolated for 72 to 96 hours. A patient identified asMRSA- or VRE-positive was maintained in isolation un-til testing negative for three consecutive cultures, taken at72- to 96-hour intervals. Patients who tested positive werekept in long-term isolation until free of the bacterium.

These studies were not initially designed to collect dataon patient isolation. Therefore, the isolation status of all thepatients that were enrolled in the randomized trial and prog-nosis studies were identified through records of MRSA andVRE screening tests in the hospital’s microbiology database.Relevant data were identified using study patient names, hos-pital identification numbers, and the dates of study enroll-ment and assessments. Patients that screened negative forMRSA only were considered to have entered isolation on thedate of the screen and to have been released 2 days later. Pa-tients who screened negative for VRE only or for VRE andMRSA were considered to have entered isolation on the dateof the screen and to have been released 3 to 4 days later. Pa-tients identified as MRSA- or VRE-positive were consideredto have entered isolation on the date of the screen and tohave left after three consecutive negative cultures.

Demographic Variables

The variables age, sex, marital status, and residence wererecorded in study baseline forms.

Dementia

The presence of dementia was assessed from a 16-item In-formant Questionnaire on Cognitive Decline in the Elderly(IQCODE).

20

The IQCODE, (either the original 32-itemor the 16-item short form) has high internal consistencyand test-retest reliability.

20–22

In validation studies againstclinical diagnosis, using a cutoff point of

�

3.38 to definedementia, the sensitivity varied between 75% and 91%and the specificity between 65% and 82%.

20,21

A Frenchversion tested in Quebec had a sensitivity of 75% andspecificity of 95% using a cutoff of

�

3.6 to define demen-tia.

23

We used a cutoff of

�

3.5 to define dementia.

Comorbidity

A nurse abstracter, blind to study group, abstracted data forthe Charlson Comorbidity Index

24

from medical records.

Statistical Methods

Descriptive statistics used to characterize the study popula-tion included proportions for categorical variables and means

and standard deviations for continuous variables. To sum-marize the distributions of DI scores corresponding to dif-ferent subgroups of patients and different categories of envi-ronmental factors, we estimated the overall mean of allrelevant repeated measurements, pooled from all patients.

To test the main study hypotheses we relied on unbal-anced repeated-measures multivariable analyses of vari-ance.

25

This approach allowed us to account for possibledependence of subsequent DI measurements for the samepatient and for the unbalanced design (for the fact that thenumber of measurements, and their timing, varied frompatient to patient). In all models, the most recent DI scorewas used as an updated value of the dependent variable.Because the main focus of our analyses was on estimatingthe within-patient effects of changes in environmental fac-tors on delirium severity, rather than on cross-sectionalcomparisons of different subgroups of patients, we had tocontrol for individual patients’ severity of delirium at base-line. Therefore, in all models we adjusted for the baselineDI score. This implied that we estimated effects of variousbetween- and within-patient factors in patients who hadthe same initial DI score. For example, the adjusted effectof isolation represents the estimated difference betweenupdated (most recent) DI scores for two hypothetical pa-tients, one currently isolated and the other not isolated,who have identical baseline DI scores and identical valuesfor all other independent variables included in the model.Thus, a positive value of the estimate would indicate thatisolation is associated with an increase in DI score, inde-pendent of baseline DI and all other variables, and thevalue of the estimated regression coefficient would reflectthe magnitude of this impact. Using this approach, we esti-mated the series of multivariable models, including varioussubsets of independent variables of interest. Variables in-cluded in all models were potential predictors of deliriumseverity, selected a priori: age, dementia, comorbidity,study group, incident versus prevalent delirium, and visualor hearing impairment, represented by their baseline val-ues. Cumulative number of room changes and variablesrepresenting environmental factors were considered time-dependent variables; that is, their values were updated atthe time of each DI measurement. Of the time-dependentvariables, those related to isolation, hospital unit, and cu-mulative number of room changes were also included inall the models. The remaining time-dependent variables,representing specific checklist items, were first included inthe “full model” and then selected into the “final model”using backward elimination of statistically nonsignificantvariables, with the cutoff at P

�

.01. We hypothesized apriori that the effects of particular environmental factorsmight depend on the presence of dementia. To test this hy-pothesis, we used forward selection with the entry crite-rion of

P

�

.10 to identify statistically significant interac-tion(s) with dementia, after adjusting for all variablesincluded in the full model. In additional exploratory anal-yses, we attempted to assess interactions between pairs ofenvironmental factors. Given the large number of poten-tial interactions, we employed a two-step procedure. Thefirst step involved a series of separate regression models,each of which included all independent variables and asimple or group of interaction term(s) related to interac-tions between two specific environmental factors (e.g., in-

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teractions between each of the dummy variables related todifferent hospital units and cumulative number of roomchanges). In the second step, only those groups of pair-wise interactions that resulted in a statistically significantimprovement in the first step of the fit of a model to studydata were considered as candidates for entry into the mul-tivariable model. Forward selection with the entry crite-rion of

P

�

.05 was used to identify those “candidate in-teractions” that were independently associated with the DIscore, after having adjusted for all interaction(s) entered atearlier stages of the selection process. However, because ofthe large number of potential interactions considered andthe absence of a priori grounds to expect specific interac-tion(s), these additional analyses are likely affected by aninflation of type I error and should be considered as hy-pothesis generating. Given the longitudinal nature of ourDI measurements, we selected a priori the first order au-toregressive AR(1) structure of covariance matrix of er-rors, that is, discrepancies between observed and predictedDI scores for subsequent measurements on the same pa-tient. The AR(1) structure, which is classical for longitudi-nal data without temporal cycles, implies that the strengthof correlation decreases proportionally to the distance intime between the corresponding measurements.

25

To assess the robustness of our conclusions with re-spect to the assumptions regarding the multiplicative ver-sus the additive effects of independent variables on the DIscore, we conducted sensitivity analyses, in which the orig-inal DI scores were replaced by their logarithms, after add-ing one to all scores to avoid numerical problems with tak-ing the logarithm of zero. These analyses allowed us toevaluate the effects of the independent variables on a rela-tive rather than an absolute change in the DI score.

All unbalanced repeated measures analyses were car-ried out using SAS procedure MIXED. All models were es-timated using restricted maximum likelihood estimationcriteria. The significance level of 0.05 was used for all hy-pothesis testing.

RESULTS

The study population comprised 444 patients, 227 pa-tients with delirium enrolled in the randomized trial, 99other patients with delirium who were not eligible for therandomized trial, and 118 controls without delirium (Ta-ble 1). These 444 patients contributed more than 2,200 DIassessments, with a mean of five assessments per patient.The study population was predominantly female, cur-rently unmarried, living at home, and demented. Alto-gether 52 patients (11.7%) were in isolation at the time ofat least one study assessment: 34 at their first assessmentand 18 at a later assessment.

Table 2 shows the numbers of patients classified byeach of the environmental factors over time (these num-bers are not mutually exclusive because individual patientscould be assessed in multiple environments over the courseof the study), the total number of assessments made withineach category (pooling across patients), and descriptivestatistics for the distribution of DI score for all assessmentswithin each category.

We first examined the relationship of isolation to DIscores (Figure 1). Of the 34 patients who were isolated at

enrollment, 28 had one or more DI assessments after re-lease from isolation. In these patients, the mean DI scoreincreased slightly after release from isolation. Of 18 pa-tients who were isolated after enrollment, nine had one ormore DI assessments before, during, and after isolation.An additional nine patients had DI assessments only be-fore and during isolation. In all three groups of patients,the mean DI scores tended to increase with each transitioninto or out of isolation.

The full and final regression models are shown in Ta-ble 3. All baseline variables were included in the full

Table 1. Selected Characteristics of Study Population (N

�

444)

Categorical Variables n %

Female gender 279 62.8Currently married 138 31.1Living arrangement

Own home 314 70.7Foster home/senior residence 79 17.8Nursing home 50 11.3

Visual/hearing impairment 89 20.0Study group

Delirium: Intervention group 113 25.5Delirium: Control group 114 25.7Delirium: Other* 99 22.3Nondelirium 118 26.6

Dementia presentYes 264 59.5No 122 27.5Unavailable 58 13.1

IsolationAt enrollment 34 7.7After enrolment 18 4.1Neither 392 88.3

Continuous variables Mean SD

Age 83.3 7.0Charlson Comorbidity Index 2.7 2.0

*

Patients who did not meet eligibility criteria for the randomized trial.SD

�

standard deviation.

Figure 1. Mean Delirium Index (DI) scores before, during, andafter isolation.

JAGS OCTOBER 2001–VOL. 49, NO. 10

ENVIRONMENTAL RISK FACTORS FOR DELIRIUM

1331

model, regardless of their statistical significance, whereasthe final model was selected through backward elimina-tion of statistically nonsignificant environmental factorsassessed by checklist items. Both models yield similar re-sults with respect to factors that affect the DI severity. Asexpected, both initial DI scores and presence of dementiawere significantly associated with higher DI scores overtime. Unavailable information on dementia status was alsoassociated with higher DI scores, with a coefficient similarto that for dementia. Several of the environmental vari-

ables were significantly associated with higher DI scores,after adjusting for baseline variables. Individual roomchanges were associated with a small, nonsignificant in-crease in the DI score at the first assessment after the roomchange. However, a higher cumulative number of roomchanges was associated with a significant increase in theDI score. With each additional room change, the DI scoreis estimated to increase by 0.40 (Table 3, Final Model).Thus, among two patients with the same baseline severityand the same values of other relevant variables, the patient

Table 2. Environmental Factors and Associated Delirium Index Scores over Time

Delirium Index Scores*

Environmental Factor Number of Patients n Mean

�

SD Range

Isolation In isolation 52 96 8.0 4.5 0-18Not in isolation 438 2,127 6.9 4.3 0-21

Unit General medical 281 1,139 6.5 4.1 0-21Oncology 20 51 6.4 4.3 0-14Surgery 81 312 6.6 4.9 0-21Long-term care 34 122 8.7 2.3 1-13Mixed (long-term care/medical) 151 583 7.5 4.4 0-21Intensive care 20 41 12.3 5.7 0-18

Recent room change

†

Yes 173 273 8.2 4.9 0-21No 444 1,975 6.8 4.3 0-21

Room type Private 84 265 7.1 4.7 0-21Semi-private 365 1,611 6.7 4.3 0-21Ward 116 372 7.9 4.3 0-20

Stimulation

‡

Low 225 881 7.2 4.3 0-21Moderate 243 948 6.8 4.3 0-21High 105 378 6.3 4.1 0-18

In the same room Yes 403 1,470 6.5 4.3 0-21No 187 346 8.4 4.6 0-21

In a single room Yes 124 418 6.9 4.8 0-21No 385 1,830 7.0 4.3 0-21

Physical restraint Yes 303 969 8.9 4.6 0-21No 383 1,279 5.5 3.5 0-18

Medical restraint Yes 320 1,021 7.5 4.8 0-21No 338 1,223 6.6 3.9 0-18

Surroundings: lighting Well lit 443 2,162 7.0 4.3 0-21Not well lit 61 83 7.3 4.9 0-20

Surroundings: sound Too noisy/quiet 159 262 7.4 4.2 0-20Normal 438 1,984 6.9 4.2 0-21

Radio/TV on On 72 120 5.3 3.7 0-16Not on 441 2,128 7.1 4.4 0-21

Clock/watch Present 291 1,201 6.0 4.1 0-21Absent 294 1,013 8.1 4.4 0-21

Calendar Present 68 179 6.7 4.0 0-18Absent 430 2,029 7.0 4.4 0-21

Personal possessions Yes 117 348 5.9 3.7 0-18No 421 1,900 7.2 4.4 0-21

Wearing glasses Yes 212 1,586 5.7 3.6 0-19No 375 661 7.5 4.5 0-21

Using hearing aid Yes 37 86 6.3 4.2 0-18No 433 2,161 7.0 4.4 0-21

Family present Yes 132 234 7.2 4.9 0-21No 426 2,013 6.9 4.3 0-21

*

Distribution of all relevant Delirium Index scores across all patients.

†

The first observation after room change.

‡

Based on distance of room from nursing station.SD

�

standard deviation; TV

�

television.

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MCCUSKER ET AL

. OCTOBER 2001–VOL. 49, NO. 10 JAGS

who changed rooms five times is expected to have a DIscore 2 points higher than the patient who remained in thesame room.

Hospital unit was also associated with the DI score.When in the ICU, patients were estimated to have DIscores 4.6 points higher than when in the medical units.Long-term care was associated with an increase of almost1 point in the DI compared with medical wards, but thiswas not statistically significant (

P

�

.07). Similarly, thepresence of dementia and physical restraints was indepen-

dently associated with a, approximately 1-point increasein the DI score.

The estimated effects of other statistically significantcorrelates of DI score were weaker, ranging from an in-crease of 0.4 associated with medical intervention and ab-sence of a clock or watch to an increase of 0.8 if the patienthad no reading glasses. Finally, the presence of a familymember during the assessment was associated with an in-crease of about half of a point. The following environmen-tal variables did not significantly affect the average DI

Table 3. Results of Repeated-Measures Analyses with Mixed Regression Models of the Effects

Full Model Final Model

Variable (Reference Category) Beta*

�

SE

P

-value

†

Beta*

�

SE

P

-value

†

Baseline variablesDelirium Index score 0.54 0.03

�

.01 0.54 0.03

�

.01Age 0.03 0.02 .09 0.03 0.02 .08Charlson Comorbidity Index score 0.09 0.06 .7 0.11 0.06 .09Length of follow-up (days)

�

0.01 0.01 .20

�

0.02 0.01 .08Dementia:

Present (absent) 1.13 0.28

�

.01 1.09 0.28

�

.01Missing (absent) 0.98 0.46 .03 1.13 0.45

�

.01Study group:

RCT: Intervention (control)

�

0.32 0.31 .30

�

0.43 0.31 .17Other

‡

(control) 0.28 0.31 .37 0.16 0.31 .594Prevalent delirium (incident delirium) 0.39 0.35 .27 0.44 0.35 .21Visual/hearing impairment: 0.00 0.32 .99 0.12 0.32 .70

Time-dependent variablesNumber of room changes 0.37 0.17 .03 0.40 0.16 .01

(effect of each additional change)Hospital unit

Oncology (medical) 0.50 0.66 .46 0.50 0.66 .45Surgical (medical)

�

0.69 0.38 .07 �0.37 0.35 .30Long-term care (medical) 0.81 0.52 .12 0.93 0.51 .07Mixed (medical) 0.26 0.29 .37 0.30 0.29 .30ICU (medical) 4.37 0.61 �.01 4.62 0.60 �.01

In isolation: 0.27 0.42 .51 0.31 0.41 .44Stimulation level§

Moderate (low) �0.23 0.25 .35 �0.24 0.24 .32High (low) �0.14 0.35 .69 �0.21 0.34 .54

Not in the same room 0.11 0.19 .55 — —In a single room 0.50 0.31 .10 — —Physical restraint 1.24 0.17 �.01 1.21 0.17 �.01Medical restraint 0.41 0.19 .03 0.42 0.19 .02Surroundings not well-lit 0.00 0.34 .99 — —Surroundings too noisy/quiet 0.13 0.21 .52 — —Radio/TV on 0.06 0.29 .85 — —Clock/watch absent 0.41 0.19 .03 0.41 0.19 .03Calendar absent �0.13 0.30 .67 — —Absence of personal possessions 0.44 0.24 .07 — —Not wearing glasses 0.82 0.19 �.01 0.81 0.19 �.01Not using hearing aids 0.19 0.46 .67 — —Family absent �0.48 0.26 .07 �0.55 0.26 .03Akaike’s Information Criteria �4378.56 �4436.94

*Beta is the regression coefficient representing the estimated mean difference between Delirium Index (DI) scores in a given category of an independent variable and thecorresponding reference catergory, adjusted for all other variables in the model.†P-value for the two tailed test of the null hypothesis of no association between a given independent variable and DI score.‡Patients who did not meet eligibility criteria for the randomized trial.§Based on distance of room from nursing station.SE � standard error; RCT � randomized control trials; ICU � intensive care unit; TV � television.

JAGS OCTOBER 2001–VOL. 49, NO. 10 ENVIRONMENTAL RISK FACTORS FOR DELIRIUM 1333

score: isolation, a single-bed room, distance from the nurs-ing station, noise and lighting level, presence of a radio orTV, presence of a calendar, and use of a hearing aid.

When the full and final models were re-estimated usingthe log-transformed DI score as the dependent variable, theresults remained quite similar. Most variables that were sig-nificant correlates of higher DI score in the original analysesremained so in the analysis of transformed DI scores andvice versa. The only exceptions were cumulative number ofroom changes (P � .21), use of medical restraints (P � .12),and absence of a family member (P � .98), which becamenonsignificant after logarithmic transformation was em-ployed. In most cases, the estimated magnitudes of the ef-fects of particular variables did not change materially either.For example, the ICU was associated with a 61% increaseof the DI score. Taking into account that the overall meanDI was close to 7.0, this increase corresponds quite well tothe estimated increase of approximately 4.4 associated withICU in the original analyses (Table 3).

Forward selection of interactions between dementia andenvironmental factors identified a statistically significantinteraction with the cumulative number of room changes(P � .01). The impact of room changes on the severity ofdelirium was much stronger in patients without dementia(average increase of 0.94, P � .001, for each additionalchange) than for those with dementia, and the latter effectwas statistically nonsignificant and very close to null. Someother factors, including isolation, showed a similar trendtoward weaker impact among demented patients but the cor-responding interactions were not statistically significant.

Additional exploratory analyses identified three statis-tically significant interactions between pairs of environ-mental factors. First, the effect of the cumulative numberof room changes varied depending on the level of stimula-tion (P � .011). Although room changes had little impacton patients in rooms with lower or moderate stimulationlevels, a higher number of room changes had a strong im-pact on increasing DI scores if the patient was in a roomwith high stimulation. Secondly, the effect of isolation onincreasing DI scores increased significantly (P � .055)with a higher number of room changes. Finally, the impactof moderate stimulation on increasing DI scores washigher (P � .024) in patients in the unit with mixed medi-cal and long-term care patients than in the reference groupon a general medical floor. However, given the large num-ber of interactions being tested, these results should be in-terpreted with caution.

DISCUSSIONThis study has investigated the potentially “deliriogenic”effects of some environmental factors in hospitals, using arepeated measures study design. This design (and corre-sponding statistical methodology), focussing upon within-subject changes over time in the severity of symptoms ofdelirium, is a powerful method for examining the effects oftime-dependent environmental variables. In comparisonwith cross-sectional analyses, it enhances statistical powerand reduces the risk of confounding by unmeasured or un-known differences between patients. Our sensitivity analy-ses, using logarithmic transformation of the DI scores,were conducted to determine whether the environmentalfactors affected the relative rather than the absolute sever-

ity of symptoms. The effects of most variables, includingICU stay, which was associated with very high absolute DIscores, were unchanged. Because the DI was designed byour group as an additive scale of severity of deliriumsymptoms,18 and because of greater simplicity of interpre-tation, we have based our conclusions on the primaryanalyses of untransformed DI scores.

The results of our primary analyses, using untrans-formed DI scores, suggest that several factors are associ-ated with greater severity of delirium symptoms, evenwhen controlling for initial severity of delirium and otherrelevant patient characteristics, including age, length ofstay, comorbidity, dementia, and visual or hearing impair-ment. These potentially modifiable risk factors includemultiple room changes, care on the intensive care or long-term care unit, use of medical or physical restraints, ab-sence of a clock, watch, or reading glasses, and presence ofa family member. However, care must be taken in inter-preting these associations, some of which may not becausal. It seems likely that the higher delirium severityscores obtained during assessments in the ICU and thoserelated to patient restraints and restraints from other med-ical interventions (such as intravenous catheters and oxy-gen masks) are related, at least in part, to the medical con-ditions for which ICU care and these other interventionswere indicated, because these interventions occur at thesame time as the various medical problems themselves.Nevertheless, the use of physical and certain medical re-straints (bladder catheters) have previously been identifiedas independent precipitating risk factors for delirium.3 Asregards stay on the surgical unit by some patients and pos-sible exposure to surgery and general anesthetics, stay onthe surgical unit was not associated with DI scores thatwere different from those on the medical unit (Table 3).Therefore, it did not appear that surgery or anesthesia hadan important effect on delirium severity scores in thisstudy. Nursing staff calling in family members when thepatient’s condition worsens may explain the associationbetween presence of a family member and more severesymptoms of delirium, the opposite of what had been hy-pothesized. Previous research in postoperative patientssuggests that effective utilization of family members in pa-tient care may reduce symptoms of delirium.26 However,unless family members are instructed in appropriate in-volvement, it is possible that their presence may affect de-lirious patients adversely.

We can be more confident that the higher mean delir-ium severity scores during assessments on the long-termcare unit are caused by environmental rather than patientfactors. Patients are transferred to the long-term care unitafter they have become medically stable, but cannot returnto their previous residence and are waiting for institutionalplacement. Thus, although cognitively impaired patientsare more likely to be transferred to the long-term careunit, their severity of symptoms was significantly greaterduring their long-term care stay than during the rest oftheir hospital stay.

Room changes are unlikely to be due to patient fac-tors; in our hospital, they are usually made for administra-tive reasons. Each individual room change did not contrib-ute significantly to greater severity of delirium symptoms,but the cumulative number of such changes did. An early

1334 MCCUSKER ET AL. OCTOBER 2001–VOL. 49, NO. 10 JAGS

report, based on anecdotal clinical experience, suggestedthat hospital room transfers disrupt the older patient’sability to correctly perceive environmental cues, resultingin misinterpretation of stimuli.27

We found that isolation did not appear to have an ef-fect independent of other environmental changes. In fact,in the small group of patients who were assessed before,during, and after isolation, the average DI scores tended toincrease over time, with each move. However, in explor-atory analyses, the effect of isolation was greater in pa-tients with a greater number of room changes. The findingthat patients who were isolated at enrollment had higherDI scores probably reflects the hospital policy requiringpatients admitted from long-term care facilities or hospi-talized during the previous 6 months to be isolated untilthey screen negative for MRSA and VRE. There has beenlittle previous research on the effects of isolation on themental status of patients,28 although increased anxiety anddepression have been reported.29

We also found that, although the tendency for the in-creasing number of room changes to be associated with anincrease in DI severity was quite marked in patients with-out dementia, these changes had little impact on DI scoresamong demented patients. Together with a trend towardsimilar interactions between dementia and other environ-mental factors, this finding may suggest that demented pa-tients are less sensitive to environmental changes.

Although the environmental risk factors considered inthis study have seldom been studied systematically, manyof them are targeted by interventions designed to reducethe risk of delirium in hospitalized patients.5 However, arisk-factor intervention strategy that included protocolsfor orientation of cognitively impaired patients, visual andhearing aids for patients with these impairments, sleep,immobility, and dehydration was found to reduce the inci-dence but not the severity of delirium.30 Unfortunately, therelative contribution of each component of this multifacet-ted intervention was not assessed.

It is important to note some limitations of this study.First, this was a secondary analysis of data collected forother purposes. Therefore, not all environmental factors ofinterest were measured. For example, we did not prospec-tively measure isolation; this variable was inferred fromlaboratory data, and there may have been some misclassi-fication, which could bias the results toward the null.Also, intervening medical events and changes in severity ofillness over time were not assessed. Nevertheless, manyimportant variables were measured prospectively as partof the evaluation of process of care conducted for the ran-domized trial. Second, the results of our exploratory anal-yses should be interpreted with caution because they arenot based on a priori hypotheses.

Our main findings are that several, potentially modifi-able, factors appear to increase the severity of symptomsof delirium. These symptoms can be upsetting to patientsand family members and can increase the burden of carefor hospital staff and the hospital length of stay.

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