BOOKS OF RtfiDIfGS - PAHO/WHO

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Controlling ¡he system
The shortage deliveries and the rotational returns for cach Iospital arc nionitored in
order to dltect chainges iii hospilal requircilecils. Evcy Iwo wccks thc "discrepaincy"
hctween tIhe hospilal's cstinialtdt and expected usagc during these two wceks is computed.
This discrcpancy is added to the cuniulative discrepancy frorn prior weeks to form
an updated cumulative discrepancy. which, togctiher with thic nutiiber ol wccks included
in it. ald ihe vyaluc ol thic lhospitall's expected usage. are used to compute the "normalized
cumulative discrepancy" of this week. This last value is compared with a statistically
establishcd "limit;" if it excecds the lirnit, it is concluded that a shift in usagc level has
occurred. New usage cstimaUes arc conmputcd. and new distribution schedules are prepared.
Otlherwise, no action is takcn.
Since the mix of the eight blood types is a function of the ethnic mix of the
population, which is in a state of transition for some of the hospitais tested, the above
control procedure was established for cach of the blood types as wcll as for all types of
whole hlood and all types of red blood cells. Adjustmenis were made either by blood type
or for all blood types. It was found that this had the unfortunatc characteristic that if
overall usage was increasing or decrcaising, individual blood types tended to go out of
control in consecutive evaluaítioni cycles belore the total usage chart went out of control.
liis causcd an excessive number of distribution changes. For this reason, the concept of
"waming limits" and "action limits' was set up. A changc is only milde il onc of the
blood types exceeded Ihe action limnits. However, at that time if any other blood type also
excecded tlhe warning limits, then that distribution would also be changed at the same
time.
Daily inve'ntory ailjustment
The resulting regional blood flow is illustrated in Figure 5. In this figure the
aging of the RBC inventory is indicated down the center of the figure with the
scheduled movement of blood to HBB's indicated to the left of the figure and the
nonscheduled movenment to the right. The long-dated, stock-dated, and short-dated
RBC inventories refer to blood units that are suitable respectively for rotation shipments,
for retention shipments, and solely for supplemental shipments - which are
filled by the oldest available units. The arrows indicate the blood flow that is normalized
to 1,000 units collected.
On the basis of this anticipated regional blood flow, the RBC's inventory is
evaluated and adjusted daily. Stock-dated inventory balancing is performed late each
afternoon after all rotational returns have been received. It involves the part of the
flow circled towards the bottom of Figure 5. The available stock-dated inventory is
compared to the retention shipments that are scheduled, the anticipated supplemental
shipments plus a small reserve for unusual circumstances which is shown as becoming
short-dated inventory. When the inventory for any product exceeds these requirements,
the excess units are designated as surplus, and transshipped to the New
York Blood Services (NYBS) division of GNYBP. When stock-dated inventory is
tThe usage is determined by combining the known weekly scheduled distributions with the recorded
supplemental deliveries and rolational relums to form an estimate of actual usage.
INTERFACES Noveniber 1979