175

X

Chapter 25

Postoperative Thrombocytopenia

Elizabeth Kaplan

BACKGROUND Common hematologic abnormality after major surgery, ■

although actual incidence not reported in literature [ 1 ] . De fi ned as platelet count <150,000. Generally, platelets >50,000 ■

are not associated with signi fi cant bleeding. Spontaneous bleeding usually does not occur with platelets >20,000.

EVALUATION ■ History : Review medications (e.g., heparin), transfusion his-tory, symptoms of infection, symptoms/history of liver disease. ■ Exam : Assess for infection, splenomegaly, signs of liver disease, evidence of thrombosis. ■ Differential diagnosis : Degree of thrombocytopenia is useful in helping to determine etiology, as shown in Table 25.1 . Other etiologies not speci fi c to the postoperative setting should also always be considered including ITP, sequestration, and malig-nancy-associated. ■ Labs : Consider the following studies; however send only those that are appropriate to the clinical situation: CBC, reticulocyte, haptoglobin, PT/PTT/INR, fi brinogen and peripheral smear, and heparin-induced thrombocytopenia (HIT) panel. ■ Consultation : Consider hematology consult if no obvious etiol-ogy is found or if levels are low enough that platelet transfusion is considered. ■ Treatment : Platelet transfusions are usually indicated only for platelets <10,000 or <50,000 with active bleeding—important to discuss with the surgical team. Intramuscular injections

C.J. Wong and N.P. Hamlin (eds.), The Perioperative Medicine Consult Handbook, DOI 10.1007/978-1-4614-3220-3_25, © Springer Science+Business Media New York 2013

176 THE PERIOPERATIVE MEDICINE CONSULT HANDBOOK

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177CHAPTER 25: POSTOPERATIVE THROMBOCYTOPENIA

X

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178 THE PERIOPERATIVE MEDICINE CONSULT HANDBOOK

should be avoided in patients who are thrombocytopenic. Other drugs that interfere with platelet function (NSAIDs, aspirin, beta-lactam antibiotics) should generally be avoided depending on the indication.

HEPARIN-INDUCED THROMBOCYTOPENIA HIT is an increasingly recognized cause of perioperative complica-tions, including skin necrosis, DVT, pulmonary embolism, venous sinus thrombosis, and stroke [ 2, 3 ] . HIT must be recognized in order to treat and prevent potentially catastrophic complications.

WHEN TO SUSPECT [ 2, 3 ] 1. Unexplained thrombocytopenia 2. Thrombosis associated with thrombocytopenia 3. Platelet count that has fallen 50% or more from a baseline value

(note that it may still be in the normal range) 4. Necrotic skin lesions at heparin injection sites

AND Prior exposure to heparin

Platelet counts do not usually fall below 20,000 as a consequence of ■

HIT, and other causes (drug-induced thrombocytopenia, DIC, ITP, etc.) should be suspected if the platelet count is in this range. Postoperative patients (particularly those with long spine surgeries) ■

often have depressed platelet counts for days postoperatively, but if the platelet count fails to rebound or falls 50% or more from a baseline value, a diagnosis of HIT should be entertained. Nonimmune-mediated decrease in platelet count is seen in many ■

patients within 2 days of starting heparin, but causes a lesser drop and will usually rebound despite continued heparin treatment.

TIME COURSE Development of HIT varies depending on patients’ prior exposure to heparin (and whether they already have antibodies). It is important to realize that a patient may present with HIT after stopping heparin (Table 25.2 ).

179CHAPTER 25: POSTOPERATIVE THROMBOCYTOPENIA

X

DIAGNOSIS HIT is a clinical diagnosis, but certain lab tests are useful in support-ing the diagnosis. HIT is caused by antibodies against the heparin/platelet factor 4 complex, and multiple tests are available to assess for the presence of these antibodies. The ELISA immunoassay that is the most common test used is extremely sensitive but not speci fi c. A nega-tive test can be useful in ruling out the diagnosis, but a positive test does not con fi rm it without further supporting features. We recom-mend fi rst checking heparin antibody ELISA assay [ 4 ] . If the ELISA test is positive and there is a high clinical suspicion, then treat as HIT positive. If there is high clinical suspicion of false positive, a serotonin release assay (SRA) can be checked [ 4 ] .

TREATMENT Stop all heparin products (this includes heparin fl ushes). ■

Start a non-heparinoid anticoagulant (direct thrombin inhibi- ■

tors argatroban and lepirudin are approved for use in the USA).Pharmacy protocols exist for this treatment and will vary from hospital to hospital. Start warfarin (only AFTER non-heparinoid anticoagulant has ■

been started) with a plan to anticoagulate for at least 6 weeks, but NOT until the patient’s platelet count is greater than 100–150 K due to the risk of transient hypercoagulability. Therapy should be overlapped for at least 5 days prior to dis- ■

continuation of the direct thrombin inhibitor. Hematology consultation is indicated when treating hospital- ■

ized patients with HIT.

TABLE 25.2 TIMING OF PRESENTATIONS OF HIT

Early Within the fi rst 1–2 days of starting heparin

Seen in patients with prior exposure to heparin (usually in the preceding 3 months), and hence prior antibodies

Usual Within 5–10 days of starting heparin therapy

Presumed to be due to the formation of new antibodies

Late After discontinuation of heparin therapy. May be >2 weeks or more from last exposure to heparin

Can occur after the patient’s dis-charge from the hospital. Suspect in a patient returning to the hospital with a new thrombotic complication, particularly after an orthopedic or other surgery where heparin prophy-laxis was used

180 THE PERIOPERATIVE MEDICINE CONSULT HANDBOOK

PREVENTION Low-molecular-weight heparins (enoxaparin, dalteparin, etc.) ■

appear to have a lower risk of HIT, and should be used when appropriate. Avoid unnecessary use of heparin. ■

CAN PATIENTS WITH A HISTORY OF HIT EVER BE RECHALLENGED WITH HEPARIN? While not recommended if other forms of anticoagulation are available, most patients with immune-mediated HIT lose their HIT antibodies within 3 months of ceasing therapy, and short-term hepa-rin use (such as for cardiac bypass surgery) has been shown to be safe [ 5 ] .

REFERENCES 1. Chang JC. Review: postoperative thrombocytopenia: with etiologic, diagnostic and therapeu-

tic consideration. Am J Med Sci. 1996;311(2):96–105. 2. Arepally G, Ortel T. Heparin-induced thrombocytopenia. N Engl J Med. 2006;355(8):809–17. 3. Coutre S. Heparin-induced thrombocytopenia. Topic update 10/17/2011. In: Basow DS, editor.

UpToDate. Waltham, MA; Wolters Kluwer 2012. http://www.uptodateonline.com . Accessed Jan 2012.

4. University of Washington Medical Center Anticoagulation Services suggestions for clinical management of suspected heparin-induced thrombocytopenia (HIT). http://uwmcacc.org/pdf/VTE_HIT.pdf . Accessed 1 Dec 2011.

5. Follis F, Schmidt CA. Cardiopulmonary bypass in patients with heparin-induced thrombocy-topenia and thrombosis. Ann Thorac Surg. 2000;70:2173–81.