case 58 - thrombocytopenia in pregnancy

Question 1

what is the expected PLT count during pregnancy?

Answer 1

• PLT count either is normal or decreases by approx 20% during normal pregnancy
• typially still remains > 150 k

Question 2

briefly describe clotting mechanism, starting from plt adhesion to fibrin clot formation

Answer 2

• primary hemostasis = initial plt plug (unstable)
• secondary hemostasis = stable fibrin clot
• vessel wall injury -> release vWF -> allows PLT to attach to wall injury (adhesion)
• adhesion leads to degranulation of PLT with release of ADP & thrombaxane (activation)
• activation leads to recruitment of more PLT to site of injury to form a platelet plug (aggregation)
• PLT plug is unstable, activation of intrinisic and extrinsic coagulation pathway -> stable fibrin clot formation

Question 3

what are causes of thrombocytopenia in pregnancy?

Answer 3

1) gestational thrombocytopenia
* static process -> PLT count is stable
2) idiopathic thrombocytopenic purpra
* static process -> PLT count is stable
3) Pre-eclampsia

• dynamic process -> Plt count changes rapidly
• can also be assoc with abnormal PLT function

Question 4

what is a good bedside test to measure PLT function, and what exactly are you looking for on this test?

Answer 4

Platelet function -> thromboelastogram (TEG)

Maximum Ampltude

• strength of clot
• correlates best with PLT function

Question 5

is spinal hematoma more common with spinal or epidural neruaxial anesthesia?

Answer 5

overall, risk of epidural/spinal hematoma is low

• 1:150,000 - 1:250,000
• most cases occur with pre-existing coagulopathies
• more likely to occur in an epidural than spinal
• risk still present after epidural catheter removal

Question 6

How do you evaluate a patient with a low platelet count? Would you place an epidural in a patient with a PLT count of 75,000? how exactly will you assess their candidacy for a neuraxial technique?

Answer 6

• no absolute PLT cutoff exists
• base decision to obtain PLT count on h&p and clinical signs

1) history and physical

• pre-eclamptic?
• history of easy brusing, petechiae, ecchymosis?

2) obtain PLT count if necessary

• PLT count stable?
• PLT cound rapidly decreasing?

3) risk of general anesthesia vs risk of epidural hematoma

Overall

• if pt has history of bruising, consider consulting hematologist to assess PLT function
  
  • avoid regional until further assessment
• if pt PLT count is decreasing (pre-eclampsia), consider avoiding reigonal unless risk v benefit
• if plt count stable and > 75,000, do regional

Question 7

what are practical recommendations regarding neuraxial anesthesia in a parturient who presents with a low PLT count?

Answer 7

• use lowest conc of LA necessary to produce analgesia while preserving motor function
• neurochecks q1-2 hours for motor block
• if patient develops motor block out of proportion to LA induced motor blockade -> immediate MRI and neurosurg eval
  
  • decompression surgery must be performed within 6-12 hrs to preserve function

Question 8

what is the difference between unfractioned heparin and LMWH?

Answer 8

Unfractioned heparin (UH)

• anticoagulant by binding to AT III -> potentiates inhibition of factors IIa (thrombin) and Xa
• AT III + heparin complex also binds to thrombin directly to inhibit it (more thrombin inhibition)
• increase PTT
• reversed with protamine

LMWH

• anticoagulant by binding to AT III -> potentiates inhibition of factors IIa (thrombin) and Xa
• AT III + LMWH heparin does not bind to inactivate additional thrombin (unlike UH)
• same anti-Xa activity as UH
• less thrombin inhibition (IIa) than UH
• measure effect by anti-factor Xa assay

Question 9

why do some pregnant patiens take LMWH?

Answer 9

Pregnancy

• hypercoaguable state
• some pts have pre-existing hypercoaguable disorders in addition to pregnancy: AT III deficiency, antiphospholipid syndrome, protein C or S defiency

LMWH vs UH vs Warfarin

• warfarin teratogenic -> therefore do not take
  
  • UH and LMWH are NOT tertaogneic
• UH -> requires blood testing for therapeutic level
• LMWH -> more predictable, does not require freqnest testing
  
  • less risk of HIT (more with heparin)
  • less risk of osteoperosis (more with heparin)

Question 10

what are ASRA guidelines for LMWH and neuraxial procedures?

Answer 10

1) monitoring anti-Xa level is NOT recommended
* not predictive of risk of bleeding
2) concomitant meds, like anti-plt agents or oral anticoagulants -> potentiate risk of spinal hematoma
3) Epidural/spinal placement

• spinal single shot may be safest choice for neuraxial anes
• wait 12 hours after last dose of prophylactic LMWH
• wait 24 hours after last dose of therapeutic LMWH

4) bloody/traumatic placement
* wait 24 hours before restarting LMWH
5) indwelling catheters

• initiate first dose of LMWH 24 hours after, but remove epidural catheter first, and initiate LMWH 2 hours after removal
• if patient has epidural catheter and is recieveing LMWH, then wait 12 hours after last of LMWH before removing catheter.