- Thrombocytopenia (defined as a platelet count of <150 × 109/L) occurs after major surgery in 30% to 60% of patients:
- 56% of cardiac surgery patients
- 28% of hip surgery patients
- Almost all patients undergoing major surgery have a significant decline in platelet count (e.g., 20% or 30%) compared with their preoperative baseline platelet count.
- A platelet count decrease is normal and expected within 4 days of surgery – the majority of cardiac surgery patients have a nadir platelet count on postoperative days 2 to 3, with the platelet count returning to baseline by day 5.
- Later onset thrombocytopenia (after 4 days of surgery) raises concerns for other causes such as:
- Heparin-induced thrombocytopenia (HIT)
- Drug induced immune thrombocytopenia (DITP) from perioperative medication, such as:
- Glycoprotein IIb/IIIa inhibitors
- Post-transfusion purpura (PTP)
- Disseminated intravascular coagulation
- Artificial surface exposure:
- Ventricular assist devices
- Intra-aortic balloon pumps
- Indwelling catheters (e.g., extracorporeal membrane oxygenation)
- Pseudothrombocytopenia – EDTA-related platelet clumping
- Proportional to the amount of crystalloid, colloid, and non–platelet-containing blood products administered.
- Dilutional thrombocytopenia manifests within minutes to a few hours following surgery.
- Proportional reductions in hemoglobin, hematocrit, and the white blood cell count are typically seen along with the platelet decrease.
- Accelerated platelet consumption related to surgical hemostasis.
- Immune mediated:
- New antibody production usually take at least 5 days to manifest.
- Therefore DITP, HIT, or PTP usually become manifest during the second postoperative week.
- Thrombopoietin response:
- Takes 3 to 4 days to increase platelet production by the bone marrow megakaryocytes.
- Results in a physiological “overshoot” in the platelet count. Postoperative platelet counts peak at two- to threefold the patient’s preoperative platelet count at approximately postoperative day 14.
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