2017 Volume 82 Issue 739 Pages 2249-2255
1. Background and purpose
Medical aid measures for injuries caused by earthquakes, have been supported by two plans implemented by municipalities. One, the “regional disaster prevention plan”, addresses risks in a region and human casualties. The other, the “regional health care plan”, designates disaster hospitals to receive the injured.
However, these two plans do not define the areas within which hospitals should accept those severely injured in a disaster (called the "disaster medical sphere"). Therefore, the number of severely injured coming to a hospital is difficult to ascertain, despite being an important factor in a hospital's disaster activity plan.
The purpose of this study was to construct a method for setting the disaster medical sphere of a hospital and for estimating the number of incoming severely injured using published data.
2. Method to estimate the number of severely injured coming to a hospital
Based on the fact that survival rate increases with speed of arrival at a hospital, disaster medical spheres are drawn as a Voronoi division using a geographic information system (GIS). The number of injured generated within the disaster medical sphere equals the number of injured coming to the hospital.
Three areas were chosen as cases to test the estimation method, the Tokyo wards western secondary medical zone, the Tokyo wards southern secondary medical zone and Kumamoto Prefecture. The Voronoi diagram resulted in distances between the hospitals being shorter near the center of cities and longer in the suburbs. Also, disaster medical spheres were smaller in the center of cities and larger in the suburbs.
In all cases, the estimated number of severely injured coming to the hospital greatly exceeded the number of emergency patients normally accepted. For the Kumamoto earthquake, when comparing the estimated number with the actual number of severely injured that went to a hospital, differences resulted from variations in model condition settings such as the rate of severe injuries. To describe the division of roles between hospitals, the percentage of the total number of injured accepted by each hospital is designated as “acceptance rate”.
3. Method for evaluating hospital placement based on declining survival rate
Normally, injured are transported from the scene of accident to a hospital by ambulance. However, according to a survey of the Great Hanshin-Awaji Earthquake, the rate of rescue by public services (such as the fire department) was only 20 percent. Most casualties were rescued by bystanders. For medical aid measures, it is necessary to consider the declining survival rate of the wounded over time. Thus the range from within witch injured can reach a hospital within one hour (such as “Golden Hour”) from the scene, is designated as a "self-rescue/community-rescue area". When self-rescue areas were included in the disaster medical spheres for the two secondary medical zone of Tokyo and the coverage rate for the number of severely injured was calculated, the coverage rate was almost 100% in the center of cities and declined in the peripheral areas of wards.
4. Conclusions
Determination of a “disaster medical sphere” using Voronoi division is useful in order to estimate the number of injured coming to a hospital. The inclusion of "self-rescue/community-rescue areas" is a way to consider and evaluate the placement of disaster hospitals.“Acceptance rate” is an indicator showing the importance of each hospital during an earthquake.
