TIME OF DAY, WEEKDAY, AND SEASON ARE ASSOCIATED WITH BLOOD PRESSURE MEASURED IN THE EMERGENCY DEPARTMENT

Abstract

Objective: Elevated blood pressure is often observed in the emergency department. Although it sometimes is explained by factors such as pain, anxiety, or white coat syndrome, it is nevertheless associated with incident atherosclerotic CVD and should not be disregarded. However, the impact of other factors on blood pressure in this setting is largely unknown. Therefore, we aimed to investigate whether season, weekday, or time of day is associated with patients’ systolic blood pressure in the emergency department. Design and method: In this electronic health record study, we selected all visits by adult patients with at least one measured blood pressure from a university hospital emergency department between 2010 to 2016. Systolic and diastolic blood pressure, age, sex, time of day, weekday, and month of the visit were derived from the hospital's electronic health records. Linear regression was used to estimate the relationship between time factors and blood pressure. Sex, age with restricted cubic splines, inclusion year, and emergency desk were included as covariates in the analysis. Results: A total of 604,091 ED-visits were included in the study. The systolic blood pressure was higher in visits during winter; 2.3 mm Hg (95% CI: 2.1-2.4), spring; 1.6 mmHg (95% CI: 1.4–1.7) and autumn; 1.7 mmHg (95% CI 1.5–1.9) compared to visits in the summer. When accounting for confounders, the systolic blood pressure was higher in visits during evening; 2.8 mm Hg (95% CI: 2.7–3.0) and night; 2.2 mmHg (95% CI: 2.0–2.5) compared to visits in the morning. Minor differences were observed in the afternoon (+0.3 mm Hg, 95% CI 0.1-0.4) and on the weekend (+0.3 mmHg, 95% CI 0.2–0.5). Conclusions: The time and season of the visit are associated with blood pressure measured in the emergency department. The systolic blood pressure on a winter evening was 5 mm Hg higher on average compared to a summertime morning visit. Our findings suggest that these factors should be considered while assessing the patient's future risk associated with a high blood pressure reading in the emergency department.