Study design and participants
This was a prospective observational study. This single-center study recruited older patients (>65 years) who underwent surgery, under general or spinal anesthesia, for urological diseases and were postoperatively treated in the general ward of a tertiary care hospital in a metropolitan area of Japan between April and September 2019. Eligible patients were enrolled if they provided consent for study participation. The exclusion criteria were: (1) ICU admission, (2) low consciousness level before the surgery (Japan Coma Scale 100–300), (3) inability to speak Japanese, (4) impaired judgment because of developmental disorders or cognitive decline, and (5) preoperative onset of delirium. Participants with missing data for the dependent variables were excluded from the analysis.
In the primary analysis of this study, we specified the key independent variables from the Comprehensive Geriatric Assessment-short version (CGA7), which comprises seven items. To calculate the sample size, the smaller incidence rates in the outcome holders and non-outcome holders require at least 6 to 10 patients per independent variable for logistic regression analysis . Shim et al.  reported POD and SSD incident rates to be 58.1% among older patients undergoing surgery. Thus, we calculated that a minimum of 100 participants were required for the primary analysis
The ward nurses assessed all patients for POD and SSD for five days—the day before surgery, the day of surgery, and three consecutive days post-surgery—using the Japanese version of the Confusion Assessment Method (CAM), which was developed from the diagnostic criteria specified in the Diagnostic and Statistical Manual of Mental Disorders-Ⅲ , which enabled easy screening for delirium. We defined the assessment periods in this study based on prior studies . On the day before surgery, the CAM was applied once during the day shift (from hospitalization until 17:00). Postoperatively, patient evaluation with the CAM was undertaken three times in a day, once during each shift (9:00 to 17:00, 17:00 to 1:00, and 1:00 to 9:00). The ward nurses received training that imparted basic knowledge on the identification of postoperative delirium and learned how to use CAM to ensure consistency in the assessments by a researcher. The training was designed to minimize the burden on the ward nurses with reference to the Short CAM Training Manual , as well as a previous study , and included: (1) the presentation, (2) a SHORT CAM POST-TEST in accordance with the instructions in the Short CAM Training Manual, and (3) an assessment for delirium in three situations, provided by a case presentation video and discussion.
Measurement of study variables
Outcomes: the incidence of POD and SSD
We specified the incidence of both POD and SSD as outcomes because episodes of SSD are closely related to POD [5, 6]. Patients were evaluated for both POD and SSD by using the CAM, which comprises four criteria: (1) acute onset and fluctuating course, (2) inattention, (3) disorganized thinking, and (4) altered level of consciousness. The CAM algorithm for the diagnosis of delirium requires the presence of both the first and the second criteria, and of either the third or the fourth criterions . In this study, POD was defined by the diagnosis of delirium based on the CAM algorithm. The SSD was defined as a presence of one or more CAM criteria and the absence of a diagnosis of delirium based on the CAM algorithm [6, 11, 13, 24]. The CAM can be completed in less than 5 minutes , and the Japanese version of the CAM has high sensitivity (83.3%) and high specificity (97.6%) when validated for use by nurses compared with psychiatrists . We obtained permission for the use of the Japanese version of CAM from the copyright holder (Hospital Elder Life Program) and the developer (Akira Watanabe).
Demographic characteristics and surgical clinical variables
The demographic characteristics and surgical clinical variables were defined as independent variables, and CGA7 was set as the key independent variable. We obtained age, sex, the Barthel Index, Charlson Comorbidity Index (CCI), history of dementia and cerebrovascular disease, medication use, emergency admission, visual and hearing disabilities, the Independence degree of daily living for the demented elderly, the stage of long-term care need, and the score from the CGA7 at the baseline. The use of physical restraints (belt and mitten), and bed sensors (clip and bed sensors) were examined for the day of surgery and all three days after surgery. We gathered the lesion site, operative method, anesthesia type, operative duration, intraoperative blood loss, preoperative and postoperative results of laboratory blood tests [white blood cell (WBC), red blood cell (RBC), hemoglobin (Hb), hematocrit (Ht), platelet (Plt), total protein (TP), albumin (Alb), blood urea nitrogen (BUN), creatinine (Cr), sodium (Na), potassium (K), chlorine (Cl), calcium (Ca), and C-reactive protein (CRP)], the use of narcotic analgesics, and the number of days that the patient’s regular medication was interrupted postoperatively as surgical clinical variables that were recorded on all five days.
The CCI is a severity classification scoring tool for comorbidities (0 to 37); increasing score indicates worse illness . The Barthel Index is an objective scale to evaluate the ADL with scores ranging from 0 to 100; increasing score indicates greater independence . Both of these tools have good reliability and validity.
Independence degree of daily living for the demented elderly and the stage of long-term care need are the assessments of the appropriate care requirements of older adults and that have been developed by the Ministry of Health, Labour and Welfare of Japan. Independence degree of daily living for the demented elderly has five levels: Ⅰ, Ⅱ, Ⅲ, Ⅳ, and M, with M indicating maximum dependence. The stage of long-term care need has seven levels: support needed (1 and 2) and care needed (1 to 5); care needed 5 indicates maximum dependence.
The CGA7 is a screening tool that extracted seven key items from a total of 40 items in four validated scales: Barthel Index, revised version of Hasegawa’s Dementia Scale, Vitality Index, and Geriatric Depression Scale . The CGA7 assesses functioning for older adults on aspects in the geriatric physical, psychological, and social domains. The CGA7 comprises the following questions: CGA1 (motivation): “Can the subject greet the examiner by himself/herself?”, CGA2 (cognitive function): “Can the subject repeat ‘cherry blossoms, cats, trains’?,” CGA3 (instrumental ADL): “Can the subject go to the hospital by himself/herself?,” CGA4 (cognitive function): “Can the subject recall three words in CGA2 and repeat that?,” CGA5 (ADL): “Can the subject take a bath by himself/herself?,” CGA6 (ADL): Can the subject use the toilet by himself/herself?,” and CGA7 (emotion/mood): “Do the subject feel he/she is powerless?”). The CGA7 is assessed with “can”/“yes” or “cannot”/“no” for each question; negative outcomes on the CGA7 indicate older adults have low functioning. The specific assessment of the reliability and validity of the CGA7 test was deemed unnecessary because all four scales from which the tool was compiled have good reliability and validity.
We conducted logistic regression analysis (Forward Selection: Likelihood Ratio) with POD and SSD as the dependent variables. The primary analysis was carried out with the key independent variables in the CGA7. The secondary analysis incorporated the CGA7 and the related variables of the POD and SSD. Before the logistic regression analysis, data were analyzed by using the Student’s t-test, Mann–Whitney U test, chi-square test, and Fisher's exact test to identify the factors related to POD and SSD. Variables with a p-value <0.2 on the univariate analysis were included in the secondary analysis. All data were analyzed in SPSS statistics version 26 and the significance level was set at p<0.05.