The Influence of Seasonal Variation on Patients with Pulmonary Embolism: A Four-Year Retrospective Analysis

Rationale

The seasonal impact on pulmonary embolism (PE) remains an unexplored topic in prior literature in the United States. In this study, we explore the national inpatient sample (NIS) to determine how seasonal variation may impact such patients. We evaluated clinical outcomes such as all-cause mortality, length of stay, total charges, acute kidney injury, and myocardial infarction to enhance our understanding of its collective impact.

Methods

We analyzed data from the 2016-2019 NIS to identify patients admitted with a principal diagnosis of PE. Patients were stratified based on season. Categorical variables were compared using chi-square tests and continuous variables with independent samples t-testing. To adjust for potential confounding variables, we employed logistic and linear regression models. Confounders were selected through a univariate screen with a p value cutoff of less than 0.1. Additionally, the Charlson comorbidity index was utilized to account for the presence of comorbid conditions to gauge disease severity.

Results

In our analysis, we identified a total of 750,030 hospitalizations (weighted) with a principal diagnosis of PE as shown in Figure 1. The seasonal and monthly admission rates are outlined in Figure 2. There was a statistically significant difference in all-cause mortality (odds ratio [OR]: 1.09, p-value=0.046) during winter compared to summer. There was a statistically significant increase in acute myocardial infarction injury (odds ratio [OR]: 1.06, p-value=0.034), acute kidney injury (odds ratio [OR]: 1.05, p-value=0.044), and total charges prior to deduction (adjusted coefficient: $2,186, p-value<0.001) during fall compared to spring. There was a statistically significant increase in length of stay (adjusted coefficient: 0.11 Days, p-value=0.002) and sepsis (odds ratio [OR]: 1.15, p-value=0.032) during winter compared to spring.

Conclusions

Compared to patients admitted during spring or summer, patients with PE admitted during the winter or fall were associated with a longer length of stay and higher total charges in addition to increased risk of all-cause mortality, acute myocardial infarction, acute kidney injury, and sepsis. These findings could be explained by several reasons including increased incidence of infections in winter leading to critical illness, colder temperatures increasing blood viscosity, abnormal coagulation due to platelet and coagulation factor dysfunction, and reduced mobility during winter increasing risk of venous thromboembolism. Literature reflects correlations between winter and increased cardiovascular complications which increases risk for pulmonary embolisms.

No relevant conflicts of interest to declare.