2.1. Study Population
This cross-sectional study was conducted in two major hospitals in Northern Italy with the voluntary participation of 100 registered female nurses, 50 from each hospital corresponding to approximately 80% of the total eligible workforce. As shown in Figure 1
, the group of 50 nurses in Hospital 1 had been working on a continuous, rapid CW rotation schedule with the following sequence: Morning (6 a.m.–2 p.m.), Afternoon (2 p.m.–10 p.m.), Night (10 p.m.–6 a.m.) followed by 2 rest days (48 h). The other group of 50 nurses, in Hospital 2, had been working on a continuous, rapid CCW rotation schedule with the following sequence. Afternoon (2 p.m.–10 p.m.), Morning (6 a.m.–2 p.m.), Morning (6 a.m.–2 p.m.)/Night (10 p.m.–6 a.m.) followed by 3 rest days (80 h). Both groups worked on an 8-h shift system.
In order to minimize heterogeneity between the two groups, all nurses participating in the study were normotensive and normal-weight (body mass index (BMI) 18–23 kg/m2) and they were deemed eligible for shift work by their respective employing hospitals. In addition, the two groups of nurses were homogeneously enrolled from the same following wards of the two hospitals: Internal Medicine (13/50), Nephrology 12/50), Surgery 13/50, and Cardiology (12/50). Thus, it was assumed that nurses’ job tasks were characterized by comparable physical and cognitive requirements. The local organization of nursing staff decided on the CW shift rotation for the nurses working in Hospital 1 and CCW shift rotation for nurses working in Hospital 2.
Ethical approval was granted by the Local Ethics Committees of the target hospitals. All subjects participating in the study provided an informed consent (ethical approval code: SWNURS-633/CE).
2.2. Data Collection
An ad hoc questionnaire and a daily diary were specially designed for the study with the purpose to assess several aspects that would help determine the nurses’ psychological and physical well-being. Specifically, the quantity and quality of sleep, work performance, and attitude, their level of satisfaction with their social/family life and lifestyle habits were evaluated.
A self-administered questionnaire in a closed question format was answered anonymously by each nurse at the onset of the study. The questionnaire was used to obtain general information about number of years in shift work, whether they had children, sleep quantity and quality, work performance, perception of well-being, lifestyle habits, and overall satisfaction with family and social relationships.
Sleep quantity was calculated as the mean hours during the entire shift cycle. Sleep duration after the night shift was determined by asking about the hours (h) slept on average. (Responses grouped as <6 h, 6–9 h, >9 h).
Sleep quality was evaluated by inquiring about sleep disturbances and by how rested the participant felt. The following questions were asked: ‘Do you have frequent awakening episodes during sleep?’: ‘Do you have difficulty falling asleep?’: ‘Do you feel rested at the start of the shift?’ (yes/no response).
Effects on lifestyle, family, and social life were assessed from questions such as: ‘Do you feel that work interferes with your family life?’: ‘Do you feel that work interferes with your social life?’: ‘Do you find it difficult to manage domestic responsibilities?’ (yes/no response).
Effects on alertness and performance during shifts were evaluated through questions such as: ‘Do you have frequent episodes of inattention at work?’: ‘Do you find it difficult at times to keep up with the work load?’ (yes/no response): ‘During which shift do you have more problems concentrating?’ (morning/afternoon/night response).
In addition, the nurses had to fill out a daily diary at a prefixed time (between 12 noon–3 p.m.) on each work day and on rest days, during one rotation cycle which was 6 days long. Therefore, a total of six daily diaries have been filled out by each nurse during the experimental protocol. The diary, which was kept anonymous, contained questions about the participant’s principle activities in the preceding 24 h. Specifically, they were requested to report the number of hours they had slept in the preceding 24 h and to report the number of hours they slept before and after a night shift, when appropriate. Information about sleep quality was obtained by reporting whether they felt rested at the start of the shift (yes/no). In addition, they were asked about the number of coffee cups consumed in the preceding 24 h and, when relevant, during the night shift.
Each participant returned the completed questionnaire and diaries in a sealed envelope. Once collected, the data was registered and statistically analyzed with the aim of specifically investigating the effect of the direction of rapid shift rotation.
2.3. Statistical Analysis
Statistical analyses were performed on SPSS 20.0 (SPSS, Inc., Chicago, IL, USA) and GraphPad Prism 7.0 (GraphPad Software, San Diego, CA, USA). Data normality was verified by Kolmogorov–Smirnov test. The data obtained from the questionnaire and diary were analyzed using the Chi-square test for categorical variable. A t-student test was applied for between group comparison regarding continuous variables. In order to check whether “age”, “having children”, and “work experience” were associated with the main outcomes in the present study, Phi (for two dichotomous variables) and point-biserial (for one dichotomic and one continuous variable) coefficients were performed. Significance level was set at 5%.