BOOKS OF RtfiDIfGS - PAHO/WHO

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analytical approximalions were derived for Poisson usage, relating the number of
retention units in each shipment to the resultant utilization rates with the desired
inventory level as a parameter.
This rclationship is illustrated for a fixed utilization rate of 98% by the family of
broken lines in Figure 2 where the scheduling factor P is the fraction of mean daily
usage that is replaced by retention shipments. As an example, if a HBB's mean daily
usage for a given blood product is 1.5, thecn the HBB can achicve a utilization rate of
98% by any of the lollowing combinations: desired inventory 1= 1 and P =0.89, or
1=3 and P =0.82, or 1=5 and P =0.70.
0.9
a: 0 7
FIGURE 2. Utilization Rale Model.
/
- / CALCULATED
L0. / I ¡ 3 /OPTIMAL
I 0.ó r I / ,--- I=S
FEASIBLE
.(/) Y I / SOLUTIONS
: 1INVENTORY
LEVEL
0.5 I I I
0.5 1.0 1.5 2.0 2.5
MEAN DAILY USAGE, U
It was shown thatthis stocking procedure maintains the mean inveqtory close to
this desired inventory level most of the time. It was also shown that adding additional
stages of returns and redistribution would make only slight improvements in the
availability rate and utilization rate achieved. Since multiple redistributions introduce
severe logistical problems and significant transportation costs, distribution
strategies involving more than two stages of distribution were not investigated.
Properties of desirable regional allocation strategies
Having derived models enabling us to predict the availability and utilization
rates of a HBB fc- any rotation/retention policy implemented by the RBC, the
regional allocation problem was examined. It was assumed that some fixed penalty
costs were associated with every nonavailable unit and every nonutilized unit, and
the objective was to determine the distribution policy parameters so as to minimize
the total expected regional cost.
INTERFACES November 1979