Statewide, Population-Based, Time-Series Analysis of the Frequency and Outcome of Pulmonary Embolus in 318,554 Trauma Patients

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Abstract
The low occurrence, nonspecific signs and symptoms, and high rate of associated morbidity and mortality of pulmonary embolus (PE) create major problems in the prevention, diagnosis, and treatment of PE. The purpose of this study was to analyze the frequency and outcome of PE in an entire state's trauma population using a large, population-based, hospital discharge data base. With the inclusion of an entire population, the reported incidence, high risk groups of patients, and specific risk factors regarding PE were assessed. A multivariate, logistic regression model was created from the data to determine predictive power of selected risk factors in patients at risk. The data source was a statewide, hospital discharge data base that includes data on all hospitalized patients for all of the hospitals in North Carolina. Data were available from 1988 to 1993. Using primary discharge diagnosis and nine additional ICD-9 coded diagnoses from the discharge abstract, patients were selected by presence of diagnostic codes for traumatic injury (800-959.9) and PE (415.1). Statistical analysis was performed using univariate and multivariate analysis to determine significant risk factors and to create a candidate model for the prediction of risk in the study population. Of 318,554 patients, 952 (0.30%) had a recorded diagnosis of PE. The mortality rate for patients with PE (26%) was 10 times higher than the mortality rate in patients without PE (2.6%). In evaluating specific risk factors, age was a significant predictor of the risk of PE: 0.05% for patients under age 55 and 0.7% in those 55 years and over. The rate of PE, 0.3%, was low for the entire study population, but was highest in patients with injuries of the extremities, 0.53%. Increasing Injury Severity Score and Abbreviated Injury Scale score for determined body systems were also found to correlate with an increasing risk of PE. Over the course of the study, the incidence of PE among patients discharged from non-trauma centers showed a significant decrease. There was also a decrease in the mortality in non-trauma centers for PE. This finding cannot be due to coding changes coincident with the advent of diagnosis related groups because it would be associated with more vigorous combing of charts for diagnoses? It may well be that the use of prophylactic measures in injured patients initially used at trauma centers was adopted by the physicians at non-trauma centers over this time with the resultant decline in PE and associated mortality. From the univariate linear regression models, a logistic regression model was created that confirmed age as the most significant risk factor, followed by Injury Severity Score and Abbreviated Injury Scale score for soft tissue, extremity, and chest. The calculated area under the receiver operator characteristic curve was 0.72. Using a large, population-based data base, we were able to determine the reported incidence of PE among trauma patients and establish specific risk factors. The reported incidence of PE in this population is low, 0.30%. The mortality among those with PE, however, is significant at 26%. In this study, age, Injury Severity Score, and injury to specific body regions (soft tissue, extremity, chest) were associated with an increased risk of PE. The investigation of prophylaxis of PE and the general management of injured patients may be influenced by the overall low reported frequency of PE and the specific high risk populations described in this study. In light of the low incidence of PE in patients without specific risk factors, prophylactic interventions cannot be routinely recommended unless their benefits clearly outweigh their risks.