BOOKS OF RtfiDIfGS - PAHO/WHO

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population center; the use of secondary outer standards could ame. FACILTY
liorate the situation o thiose who represent the 5 percent of demand LOCATION
that is ex mpted Iromn tlie regulation standard.
Still other uses u thie maximal coverirng model are possible: alter
maximizing coverage within a stated time, one may seek tiue solution
tihat minimizes the average service time for tiose outside the stand;trd.
Tite economic and geograpliic options available to planning
regiouis difler cnoughl that each region miglit benefit. both in service
and in cost. from "fine-tuning" its EMS plan by examining many
such secondary solutions withisn the regulation standards.
Sonme work has already beien done oin ;aplying time other two
toutexxit.ee models, tihe p-median andl tihe location set covering models.
to emnergenry ambulance services. The work of ReVelle, Tore.
gas, and Falkson [38) cited carlier extends the location set covering
model t to twn nore detai:ld tspects o! tie EMIS locatiosn problemn.
()nc ol limes, .Isp:Cts concerns travel stieC oli tihe link froni demant d
¡point to care facility alter time patient is pickcd t up whlidi needs to bc
considered in determining ambulance locations. The other aspect is
that demands in the real world tend to occur along continuouis roads
rather tihan at discrete o Berins. erln. l. 'elle. anit Elzinga [43) used
time p.mediant framework to investigate tie riisinimum average time
when the travel from demand to point of care is included. We
have not yet applied the maximal covering nmodel to these more detailed
expressions ol the problem, but it will be usefucl to discuss here
omrne possibilities inherent in sulch an application. These possibili.
ties si: :.d ir,- of interest to EMS policy makers, since they allow the
evalative standarda diseussed in the regulations to be extended to
include the link from demand point to point of care.
When an ambulance arrives at the scene o a call. certain limited
care may be given the patient, depending on time training and equipment
of the arriving personnel. The time standards for response to
calls apparently apply only to the arrival of the ambulance at the
scene. Thle purpose of tire ambulance is twofold. however. and the
second function is transporting the patient to a staffed antd equipped
emergency care center.
Without meaning to suBgest dilterent values lor the time standards.
it would seem useful to apply a time standard to the entire
time between dispatch of the vehicle and the patient's arrival at the
emergency care facility. 11 thie 30.minute response standard were extended
to cover both functions. more vehicles and locations would
be required to achieve the stated coverage. Two standards might be
formulated. one for time time from ambulance dispatch to the emergency
scene, tihe other for the entire time from dispatch to the appropriate
site of care. Time addition of this new standard provides
another yardstick widi whicl lto nmeasure the effectivenes of an emergency
recovery system. Modeling with this added standard does noU
seem to present any insurmountable challenge. UMNER
Still another standard could be applit 1 lor the time from dernand
cene to hospital. Application of such a stalidard, however, is not