9. HEMATOLOGIC CONCERNS
HEMATOLOGIC PARAMETERS FOR SURGERY
A platelet count of 50,000 or more does not pose a significant bleeding risk, even for major surgery. (The exceptions are with CNS and cardiac surgeries, for which the recommended platelet count is closer to 80,000.) Spontaneous bleeding usually does not occur until the platelet count is in the 10,000 to 20,000 range or less. Transfusion of 10 units of platelets can be expected to raise the patient's platelet count by 30,000 to 60,000. (One superpack of platelets is the equivalent of 6 to 10 units in one bag, which is about 250ml total volume.) Transfused platelets survive approximately 4 days unless there is increased platelet destruction.
WHITE BLOOD CELLS:
The total WBC count is not as important as the absolute neutrophil count (the ANC) with regard to infection risk. The ANC is calculated from the CBC by multiplying the total WBC count by the percentage of functional neutrophils (segs + bands). An ANC of 1000 or more is not associated with any increased infection risk postoperatively. The risk of infection increases somewhat as the ANC falls below 1000, but rises markedly as the ANC drops below 500. GCSF is recommended for any surgical patient with an ANC under 500. Between 500 and 1000, GCSF should certainly be considered for procedures involving nonsterile sites, such as the bowel or any area of potential infection. (GCSF dose is 300mcg SQ daily for a normal size person.) Prophylactic antibiotics should also be administered in such cases.
There are no clear-cut guidelines for acceptable preoperative Hgb levels and the need for transfusion. Hgb of 10 grams or more is ideal for oxygen-carrying capacity and coronary blood flow, but this level may not be necessary for surgical patients without underlying cardiovascular disease. Furthermore, many patients have chronic anemia with Hgb levels well under 10 grams, and it is unclear for these patients what exactly is an acceptable level to take them to surgery and what level to maintain them postoperatively.
Surgical mortality has been shown to increase with lessening levels of preoperative Hgb, but a clear critical level has been noted at 8 grams, at which point a surgical patient is 16 times more likely to die if below that level preoperatively than above it. Anticipated blood loss from surgery must also be considered in determining the need for transfusion preoperatively. (One unit of PRBCs is about 250ml total volume.)
Patients with SICKLE CELL ANEMIA undergoing major surgery should be transfused preoperatively to Hgb level of 10 grams or more, as this has been shown to minimize the risk of postoperative sickle cell crisis. After surgery, the optimal Hgb level for sickle cell patients is unclear, but generally I recommend maintaining Hgb at or above 9 grams in the immediate postoperative period (in addition to aggressive IVF hydration and oxygenation).
For major surgery, bleeding risk is not significantly increased if INR < 1.5 ; for superficial procedures, it is reasonably safe to perform surgery with INR < 2.0. (For intraocular and CNS procedures, however, complete normalization of the protime is recommended.)
4 units of FFP generally is enough to reverse a major coagulopathy; 2 units can be given if coagulopathy is less pronounced. The effect of FFP lasts only about 6 hours, and one unit is approximately 200ml total volume.
Intrinsic abnormalities of prolonged PTT but normal protime are not common. These include hemophilia, certain factor deficiencies, and the lupus anticoagulant (which does not increase bleeding risk at all and may actually cause a hypercoagulable state). Von Willebrand's disease is a relatively common condition and may also be associated with a prolonged PTT, although the central defect is related to platelet adhesion and not factor deficiency. Furthermore, an unexpectedly prolonged PTT result must always be repeated, since lab error with this test is not unusual. *History is the key to determining if a patient with an isolated, prolonged PTT truly has a significant bleeding tendency.
VON WILLEBRAND'S DISEASE
*The most common congenital coagulopathy. It is due primarily to a deficiency in von Willebrand factor, which is necessary for normal platelet adhesion; it is also associated with a deficiency of factor VIII. Multiple types recognized (Type I is most common; IIa, IIb; III is rare). Furthermore, the degree of bleeding varies from patient to patient.
1) DDAVP is effective in the majority of patients, but type IIb and III do not respond. (Type IIb patients may actually develop thrombocytopenia with DDAVP.) Dose is 0.3 mcg/kg-maximum 20 mcg-IV in 50cc NS over 30 minutes as a single dose with almost immediate effect. Repeat dose can be given in 12 to 24 hours, but only for 2 to 3 doses total, then the effect is lost. Repeated dosing may also cause hyponatremia.
2) Plasma products may be required for major surgery, even if DDAVP is given. Cryoprecipitate is a pooled plasma product that is enriched in factor VIII and von Willebrand factor. A standard dose is 10 units (bags) every 12 hours, which should be continued until post-surgical bleeding is no longer a concern. (This is a small amount of fluid and can be run over 30 minutes.) Cryoprecipitate is frequently in short supply but, if needed, it can be acquired by the blood bank from elsewhere within a matter of hours. Although generally not ideal, FFP can be given instead of cryoprecipitate. I recommend an initial dose of 4 units followed by 2 to 4 units every 6 hours if cryoprecipitate is unavailable.
3) Humate-P is a purified, virus-inactivated concentrate of factor VIII and von Willebrand factor, an ideal therapy for patients with moderate to severe von Willebrand's disease who require major surgery. Unfortunately, Humate-P is not stocked in our pharmacy, is very costly, and needs to be special ordered more than a day in advance. Dose is 20-40 IU/kg every 12 to 24 hours for 3 days, then once a day for up to 7 days if needed.