BOOKS OF RtfiDIfGS - PAHO/WHO

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since they substantially overestimate the necessary number of beds in SIMULATION
most cases. OF HOSPITAL
OCCUPANCY
Simulation Model
The Admissions Scheduling and Control System
In order to model and simulate a hospital, specific rules, policies,
and priorities regarding patient admissions must be defined. The
admissions -guidelines of the Admissions Sclieduling and Control System
(ASCS) developed by Hancock et al. [51 are used in this model.
Simulation studies have predicted that hospitals using this system
would operate at occupancies in excess of those found in most hospitals,
and implementation of the ASCS in several hospitals has shown
these predictions to be realistic [6,7]. A facility using the ASCS should
require fewer beds to meet demand and thus should operate at a lower
cost. A model using the ASCS should predict the optimum number
of beds needed to operate a hospital.
In the ASCS, admissions to the hospital are classified in three
categories: emergency, scheduled, and call-in. An emergency patient is
defined as one requiring immediate admission to the hospital. Thus
an emergency admission is uncontrollable and may be considered a
random event. Scheduled and call-in patients are elective and thus do
not require'immediate admission; they may be put on a v.aiting list
or scheduled for admission at some future date. The admission of a
scheduled patient is planned for a specific time-in the future, and a
call-in patient is called in for admission at the hospital's convenience.
Thus, if at some time during the day the hospital has beds available,
patients are called in.
A turnaway is defined as an emergency patient who cannot be
accommodated in the normal manner because all hospital beds are
full. A cancellation is defined as a scheduled admission that must
be cancelled in order to save room for emergency patients who may
arrive before the next day's discharges. Thus a scheduled admission
is cancelled in order to prevent the possibility of an emergency turnaway
later in the day. In practice, cancelled patients are rescheduled
at the next open date or are called in with the highest priority. In
this study, turnaways were constrained to be between 1 and S percent
of all emergency arrivals and cancellations were constrained to be
between 1 and 3 percent of all scheduled admissions. These percentages
were chosen because they appeared to be acceptable to the hospitals
that had become aware of the ASCS.
At some point during the day when all discharges are known, the
hospital must decide if it is necessary to call in patients or to cancel
any scheduled admissions. This decision is based on the census reduction
allowance (CRA) and the cancellation allowance (CA). The CRA
and the CA represent the upper and lower bounds on the number of
beds left empty at the decision point and may be different for each
day ,. e week. The number of filled beds includes those to be occupied
by patients scheduled for admission later in the day. If the number
of empty beds is g_ eter than the CRA, patients are called in until