Population Density, Call-response Interval, and Survival of Out-of-hospital Cardiac Arrest

International Journal of Health Geographics, 2011, 10:26

Hideo Yasunaga, Hiroaki Miyata, Hiromasa Horiguchi, Seizan Tanabe, Manabu Akahane, Toshio Ogawa, Soichi Koike, and Tomoaki Imamura

“Background: Little is known about the effects of geographic variation on outcomes of out-of-hospital cardiac arrest (OHCA). The present study investigated the relationship between population density, time between emergency call and ambulance arrival, and survival of OHCA, using the All-Japan Utstein-style registry database, coupled with geographic information system (GIS) data.

A map of emergency medical service centers in the Tokyo metropolitan area and surrounding areas coupled with population information. Dots indicate locations of emergency medical service centers. Green shading indicates population density. White areas are uninhabited. Lines are highways and national roads. Drawn with ArcGIS.

“Methods: We examined data from 101,287 bystander-witnessed OHCA patients who received emergency medical services (EMS) through 4,729 ambulatory centers in Japan between 2005 and 2007. Latitudes and longitudes of each center were determined with address-match geocoding, and linked with the Population Census data using GIS. The endpoints were 1-month survival and neurologically favorable 1-month survival defined as Glasgow-Pittsburgh cerebral performance categories 1 or 2.

“Results: Overall 1-month survival was 7.8%. Neurologically favorable 1-month survival was 3.6%. In very low-density (<250/km2) and very high-density ([greater than or equal to]10,000/km2) areas, the mean call-response intervals were 9.3 and 6.2 minutes, 1-month survival rates were 5.4% and 9.1%, and neurologically favorable 1-month survival rates were 2.7% and 4.3%, respectively. After adjustment for age, sex, cause of arrest, first aid by bystander and the proportion of neighborhood elderly people [greater than or equal to]65 yrs, patients in very high-density areas had a significantly higher survival rate (odds ratio (OR), 1.64; 95% confidence interval (CI), 1.44 – 1.87; p<0.001) and neurologically favorable 1-month survival rate (OR, 1.47; 95%CI, 1.22 – 1.77; p<0.001) compared with those in very low-density areas.

“Conclusion: Living in a low-density area was associated with an independent risk of delay in ambulance response, and a low survival rate in cases of OHCA. Distribution of EMS centers according to population size may lead to inequality in health outcomes between urban and rural areas.”

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