Air Ambulance Transport Times and Advanced Cardiac Life Support Interventions during the Interfacility Transfer of Patients with Acute ST-segment Elevation Myocardial Infarction

Abstract

Objectives. To characterize transport times for the interfacility air ambulance transport of patients with acute ST-segment elevation myocardial infarction (STEMI), to estimate the proportion of patients at risk of in-transport clinical decompensation, and to explore associated risk factors for such. Methods. The electronic medical records of 35 air ambulance programs in the United States from December 2003 through December 2008 were reviewed. We defined clinical decompensation during transport as the combined outcome of either cardiopulmonary arrest or the receipt of any of a prespecified set of advanced life support (ALS) interventions. Multiple logistic regression employing generalized estimating equations to model autocorrelation of measures within air ambulance programs was used to explore the relationship between time from dispatch to transport and the outcome of interest. Results. Three thousand seven hundred sixty-seven transports of STEMI patients were identified during the period of interest. Eighty-five percent of rotor wing transports (median 80 minutes, interquartile range [IQR] 66–104) and 7% of fixed-wing transports (median 162 minutes, IQR 142–210) attained a total transfer time of ≤2 hours. Clinical decompensation in transport occurred in 182 of 3,767 (4.8%, 95% confidence interval [CI] 4.2–5.6%) transports. The most frequent critical ALS interventions were the administration of antiarrhythmics and the initiation of vasopressors. The odds ratios (ORs) for clinical decompensation comparing higher pretransport time quartiles with the lowest quartile (i.e., Q1: 6–50 minutes) were as follows: Q4: 82–1,500 minutes, OR 2.5 (95% CI 1.3–4.8, p = 0.007); Q3: 64–81 minutes, OR 1.9 (95% CI 1.0–3.6, p = 0.0499); and Q2: 51–63 minutes, OR 1.45 (95% CI 0.7–3.1, p = 0.34). Cardiac arrest or need for an ALS intervention prior to transport and a history of diabetes were also predictive of the outcome of interest. Conclusions. The majority of interfacility rotor-wing air ambulance transfers of patients with STEMI achieved a total transfer time of ≤2 hours. Clinical decompensation requiring ALS treatment occurred in a small percentage of patients. Diabetes, prior arrest or decompensation, and delays to transport were associated with clinical decompensation in the air. Efforts to reduce delays to transport may reduce this risk in transported patients.

Key words: :

• myocardial infarction
• patient transfer
• cardiac arrest