Page 424 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

414 FLUID THERAPY

given in a small volume. Thus it may be useful in animals 3. Surgical and obstetric patients with microvascular
in which volume overload may be a concern (e.g., bleeding usually require platelet transfusion if the
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Doberman pinschers with von Willebrand’s disease and platelet count is less than 50 10 /L and rarely
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cardiomyopathy). I have used cryoprecipitate but also require therapy if it is greater than 100 10 /L. With
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have successfully managed dogs with von Willebrand’s intermediate platelet counts (50 to 100 10 /L), the
disease using fresh frozen plasma in mildly affected dogs determination should be based on the patient’s risk for
or by treating both the plasma donor and recipient with more significant bleeding.
DDAVP (1 mg/kg subcutaneously) in more severely 4. Operative procedures ordinarily associated with insig-
affected dogs. Recommendations for the dosage of fresh nificant blood loss may be undertaken in patients with
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frozen plasma range from 6 to 30 mL/kg and for platelet counts less than 50 10 /L.
cryoprecipitate from 1 U/5 to 15 kg. 175 DDAVP also 5. Platelet transfusion may be indicated despite an appar-
may be useful in restoring platelet function in some cases ently adequate platelet count if a known platelet dys-
of iatrogenic platelet dysfunction. It has been used to function and microvascular bleeding are present.
treat increased bleeding times associated with aspirin More recent guidelines also suggest that platelet num-
administration and also platelet defects associated with bers should not be allowed to decrease to less than 50
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cardiopulmonary bypass. 138,156,193 10 /L during massive transfusion and should be greater
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Animals with thrombocytopenia or dysfunctional than 100 10 /L in patients with multiple trauma or cen-
platelets may require platelet infusion before surgery. tral nervous system injury. 77 A platelet count as low as 5 x
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Platelet life span in immune-mediated thrombocytopenia 10 /L is an effective transfusion trigger in human
is considerably shortened, and platelet infusions may be patients with thrombocytopenia who are not undergoing
effective for only a matter of hours. Although it is com- invasive procedures. 168
monplace for platelet-rich plasma to be prepared for Patients with disseminated intravascular coagulation
affected people, this is relatively rare in veterinary medi- (DIC) may need surgical intervention to correct the
cine. Platelet preparations have a short half-life (<5 days) initiating cause of the DIC. Restoration of circulating vol-
and must be maintained on a rocker in a very narrow ume with fresh whole blood or fresh frozen plasma is the
range of temperatures so it is hard to maintain adequate mainstay of preoperative therapy for patients with DIC.
supplies in veterinary medicine. Consequently, most If heparin is used, it should be given at a dosage that does
patients that are thrombocytopenic or have platelet dys- not cause significant prolongation of bleeding time (e.g.,
function are treated with fresh whole blood. The amount 75 U/kg every 8 hours subcutaneously). If heparin is
of blood needed (TV) depends on the platelet count of added to the blood or plasma (same dosage), the
the patient (P E ), the platelet count of the donor blood activated partial thromboplastin time (APTT) should
(P D ), the target platelet count (P T ), and the blood vol- be determined before surgery to ensure that it is not
ume (BV) of the patient: excessively prolonged (i.e., not more than twice normal).
RENAL DISEASE
BV P E þ TV P D ¼ðBV þ TVÞ P T
Patients with chronic renal insufficiency are at risk for
Note: Volumes must be expressed in the same units having their disease exacerbated by the hemodynamic
(i.e., blood volume in microliters if platelet count is per changes during anesthesia and surgery. Affected animals
microliter or platelet count per liter if blood volume is should be managed carefully during the perioperative
in liters). The dosage of a platelet-rich plasma could be period. They should be allowed access to water until
determined using a similar approach but there is uncer- the time of premedication. Any dehydration present
tainty about the actual dosage required. 168 should be corrected before anesthesia.
The ASA guidelines for infusion of platelets are as Patients with severe oliguric renal insufficiency are of
follows: 143 concern because they have severely limited ability to
1. Prophylactic platelet transfusion is rarely indicated excrete an extra fluid load and may already be
when thrombocytopenia is caused by increased plate- hypervolemic and hypertensive. If possible, it is advanta-
let destruction (e.g., idiopathic thrombocytopenic geous to monitor CVP as a guide to fluid therapy in these
purpura). animals. Monitoring CVP provides information on how
2. Prophylactic platelet transfusion is rarely indicated well the heart is able to pump the existing circulating vol-
when thrombocytopenia is caused by decreased plate- ume and allows the anesthetist to watch the response to
let production when the platelet count is greater than fluid therapy in the perioperative period.
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100 10 /L and is usually indicated when the plate-
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let count is less than 50 10 /L. The determination HEPATIC DISEASE
of whether patients with intermediate platelet counts Mild hepatic insufficiency rarely causes clinically relevant
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(50 to 100 10 /L) require therapy should be based disturbances in fluid balance, but substantial alterations
on the risk of bleeding. occur as the severity of hepatic injury progresses. The liver