Circadian variation in the time of request for helicopter transport of cardiac patients.

Abstract

The literature has demonstrated circadian rhythms in the occurrence of nonfatal myocardial infarction, ischemia, and sudden death. We hypothesized that requests for helicopter transport of acutely ill cardiac patients followed a similar circadian pattern and differed significantly from requests for helicopter transport of other categories of patients. Prospective study of requests for helicopter transport of 1,128 consecutive air medically transported patients over a 24-month period. One tertiary-care teaching hospital. The periodic structure of the time distribution of cardiac requests for helicopter transport was examined with a two-harmonic regression analysis using a 24-hour period of oscillation. Seven hundred eighty-seven cardiac and 315 noncardiac patients could be evaluated. The times of requests for helicopter transport were tabulated into hourly intervals. Cardiac-related requests for helicopter transport were significantly different from noncardiac-related requests for helicopter transports (P less than .009 by Wilcoxon rank sum test, P less than .032 by Kolmogorov-Smirnov test). The regression model for cardiac requests for helicopter transport was also significant (P less than .0001, R2 = .81) with increasing requests for helicopter transport from 6:00 AM until 12:00 noon. The time distribution of requests for helicopter transport for cardiac patients demonstrates a striking circadian variation not observed in noncardiac patients. This observation strengthens mechanistic inferences from studies of circadian variation and suggests a "morning-loaded" staffing pattern for air medical services predominantly transporting cardiac patients.