Postoperative thrombocytopenia

Prevalence

• 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.

Timing

• 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:
  • Drugs:
    • Heparin-induced thrombocytopenia (HIT)
    • Drug induced immune thrombocytopenia (DITP) from perioperative medication, such as:
      • Vancomycin
      • Cephalosporins
      • 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)

Pathophysiology

• Causes:
  • Pseudothrombocytopenia – EDTA-related platelet clumping
  • Hemodilution:
    • 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.

Reference