Platelet Concentrates
Platelet concentrates are prepared by differential centrifugation
from freshly drawn units of blood or from donors
TABLE 47-16 -- Compatibility of blood with intravenous solutions
|
Hemolysis at 30 Minutes |
|
Blood to Intravenous Solution (1:1 Ratio) |
Room Temperature |
37°C |
|
5% Dextrose in water |
1+ |
4+ |
|
Plasmanate
*
|
1+ |
3+ |
|
5% Dextrose in 0.2% saline |
0 |
3+ |
|
5% Dextrose in 0.4% saline |
0 |
0 |
|
5% Dextrose in 0.9% saline |
0 |
0 |
|
0.9% Saline |
0 |
0 |
|
Normosol-R, pH 7.4
†
|
0 |
0 |
|
Lactated Ringer's solution |
0 (clotted) |
0 (clotted) |
*Cutter
Laboratories, Berkeley, CA.
†Abbott
Laboratories, Chicago, IL.
who specifically donate large amounts of platelets by plateletpheresis techniques.
If platelets are stored at room temperature, they are satisfactory to use 5 days
after collection with constant and gentle agitation. However, in the report of 10
septic platelet transfusions between 1982 and 1985, one half were platelets stored
for 5 days or more. A prospective analysis from 1987 to 1990 resulted in seven cases
of sepsis in patients receiving platelets for thrombocytopenia secondary to bone
marrow failure.[136]
Because use of multidonor
platelet products stored for 5 days results in an incidence of sepsis five times
higher than use of those stored for 4 days, shorter storage times are being emphasized.
The incidence of platelet-related sepsis is about 1 case in 12,000 people.[137]
The estimated incidence of bacterial contamination of platelets is about 1 case
in 2000.[138]
[139]
As indicated in Table 47-7
,
bacterial contamination of blood products is the leading cause of death from blood
transfusions of which contaminated platelets is the most frequent. One death reported
in 2002 was from Salmonella sepsis caused by platelet
transfusion from a donor with a pet snake, which was the source of the bacteria.
[140]
The increased risk of bacterial overgrowth is related to the storage
temperature of 20°C to 24°C. Because there is no test to identify bacterially
contaminated blood products, for any patient who develops a fever within 6 hours
after receiving platelets, sepsis from platelets should be considered. The risk
of platelet-induced sepsis is such a serious problem that many blood banks, including
my own institution, routinely culture all platelet concentrates before giving them
to patients. It is not known how effective routine culture is. If blood products
are stored at 4°C, they should not be used longer than 24 to 48 hours after collection.
The allowable storage time is based on in vivo survival. The longer allowable storage
time at room temperature adds flexibility to the blood bank.
Based on the previous discussion, if platelets were stored at
4°C, the incidence of bacterial growth and subsequent sepsis would decrease.
However, refrigerated platelets are
not as effective in vitro. When platelets are chilled, membrane lipid-phase separation
results in clustering of glycoprotein within the membrane. Blocking this clustering
would prolong the in vivo circulation time of chilled platelets. The method being
developed to make this happen is described by Snyder and Rinder.[141]
Indications for the use of platelets are somewhat difficult to
define. The July 1989 FDA Drug Bulletin stated that platelets should not be given
to patients with immune thrombocytopenia purpura (unless there is life-threatening
bleeding), prophylactically with massive blood transfusion, or prophylactically after
cardiopulmonary bypass. However, the use of fresh blood rather than platelet concentrates
as a source of platelets is still emphasized by some cardiac groups.[140]
The American Society of Anesthesiologists (ASA) Task Force 2 provided the following
recommendations:
- Prophylactic platelet transfusion is ineffective and rarely indicated when
thrombocytopenia is due to increased platelet destruction (e.g., idiopathic thrombocytic
purpura).
- Prophylactic platelet transfusion is rarely indicated in surgical patients
with thrombocytopenia due to decreased platelet production when the platelet count
is greater than 100 × 109
/L and is usually indicated when the platelet
count is below 50 × 109
/L. The determination of whether patients
with intermediate platelet counts (50 to 100 × 109
/L) require therapy
should be based on the patient's risk of bleeding.
- Surgical and obstetric patients with microvascular bleeding usually require
platelet transfusion if the platelet count is less than 50 × 109
/L
and rarely require therapy if it is greater than 100 × 109
/L. With
intermediate platelet counts (50 to 100 × 109
/L), the determination
should be based on the patient's risk for more significant bleeding.
- Vaginal deliveries or operative procedures ordinarily associated with insignificant
blood loss may be undertaken in patients with platelet counts less than 50 ×
109
/L.
- Platelet transfusion may be indicated despite an apparently adequate platelet
count if there is known platelet dysfunction and microvascular bleeding.
Patients with severe thrombocytopenia (<20,000 cells/mm3
)
and clinical signs of bleeding usually require platelet transfusion. However, patients
may have very low platelet counts (much less than 20,000 cells/mm3
) and
not have any clinical bleeding. Patients such as these probably do not need platelet
transfusions. Individuals who have undergone trauma or require surgery need higher
platelet counts, probably 100,000 cells/mm3
, to maintain adequate hemostasis
(see Table 47-5
). Laboratory
determinations and clinical evaluations must be taken into account before a decision
to transfuse platelets is made.
When possible, ABO-compatible platelets should be used. The need
to use them, however, is not well documented. Specific testing is difficult. Aggregation,
the end point of RBC crossmatch, cannot be used because platelets cause clumping.
The platelet membrane has immunoglobulins. Any additional deposit of recipient
antibodies is difficult to detect. Despite the fact that platelets can be destroyed
by antibodies directed against class I human leukocyte antigen proteins on their
membranes and to a lesser extent by antibodies against ABO, platelets chosen for
transfusion probably will continue to be chosen without regard to antigen systems.
[139]
ABO-incompatible platelets produce very adequate
hemostasis.
Platelets may be pooled into a single transfer bag or a syringe
for administration or they may be administered as individual units. Several platelet
administration sets are available for use. These all have filters with a pore size
of about 170 mm. Filters with smaller pore size (i.e., micro-aggregate filters)
should not be used, because they tend to remove a significant number of platelets.
Conversely, small filters are increasingly being used to decrease infectivity.
Standard blood administration sets with 170-m filters are also acceptable. To decrease
the loss of platelets, a 19-gauge needle or larger should be used. To ensure complete
delivery of all the platelets available, the containers should be rinsed with saline.
The effectiveness of platelet transfusions is difficult to monitor.
Under ideal circumstances, one platelet concentrate usually produces an increase
of about 7000 to 10,000 platelets/mm3
1 hour after transfusion to the
70-kg adult. Ten units of platelet concentrates are required to increase the platelet
count by 100,000 cells/mm3
. However, many factors, including splenomegaly,
previous sensitization, fever, sepsis, and active bleeding, may lead to decreased
survivals and decreased recovery of transfused platelets.
Various different types of platelet concentrates have been proposed,
including apheresis (i.e., collecting more platelets from one donor to avoid pooling
of platelets from multiple donors), leukocyte-depleted platelets, and ultraviolet
B-irradiated platelets. The use of these products is reviewed by Kruskall.[139]
