Paramedic Response Time: Does It Affect Patient Survival?

Abstract

One marker of quality emergency medical services care is measured by meeting an 8-minute response time guideline. This guideline was based on results of paramedic response times for nontraumatic cardiac arrest patients and has not been studied in unselected patients. The objective of this study was to evaluate the effect of paramedic response time on survival to hospital discharge in unselected patients in a large urban setting while controlling for a number of potentially important confounders, including level of illness severity. This was a retrospective cohort study performed in an urban 911-based ambulance service system. Patients transported by paramedics to a single urban county teaching hospital from January 1, 1998, to December 31, 1998, were included. Data collected included patient demographics; paramedic response, scene, and transport times; the nature of the medical complaint; and whether the patient survived to hospital discharge. Multivariable logistic regression models were developed using response time as the primary independent variable and survival to hospital discharge as the dependent variable. Covariates included scene time, transport time, age, gender, and level of illness severity. Of 34,111 calls involving emergency response, 11,078 patients (32%) were transported to the study institution and 10,382 (94%) had response time data available. Of these, 9,559 patients (92%) had data available to categorize them into groups based on their level of illness severity and were thus included in the study. A survival benefit was identified for response times <or=4 minutes (odds ratio [OR], 0.70; 95% confidence interval [CI] = 0.52 to 0.95). No survival benefit was identified when response time was modeled as a continuous variable (OR, 1.01; 95% CI = 0.98 to 1.04) or when dichotomized at 8 minutes (OR, 1.06; 95% CI = 0.80 to 1.42). A paramedic response time within 8 minutes was not associated with improved survival to hospital discharge after controlling for several important confounders, including level of illness severity. However, a survival benefit was identified when the response time was within 4 minutes for patients with intermediate or high risk of mortality. Adherence to the 8-minute response time guideline in most patients who access out-of-hospital emergency services is not supported by these results.