A 22-year-old woman presented to the labor and delivery suite at 40 weeks’ gestation with mild uterine contractions. The obstetricians decided to augment labor with oxytocin and requested an epidural anesthetic for labor analgesia. The patient’s past medical history was significant for miscarriage during a previous pregnancy. Until 2 weeks ago, she had been receiving enoxaparin (Lovenox) injections, 30 mg twice a day. Her laboratory data were within normal limits except for a platelet count of 76,000 mm −3 .
Who is at risk for developing an epidural hematoma?
Anyone who receives a spinal or epidural anesthetic is at risk for developing an epidural hematoma. Epidural hematoma is an extremely rare event and is generally associated with patients who have disorders of hemostasis. A patient with a clinically active coagulopathy is considered to have an absolute contraindication to regional anesthesia. However, many gray areas exist, and this is especially true in patients with thrombocytopenia.
What is considered a low platelet count from the perspective of epidural catheter placement, and why is there controversy regarding choosing a lowest “safe” platelet count?
An epidural hematoma is a potentially catastrophic complication, which can lead to permanent paralysis. It is prudent to practice in a conservative manner and refrain from epidural anesthesia if the patient is at increased risk of developing this complication. In 1988, and Bromage recommended against epidural anesthesia if the platelet count is <100,000 mm −3 . However, this recommendation has been widely disputed. Thrombocytopenia is the most common hematologic disorder during pregnancy. Choosing an absolute platelet count below which it is considered too dangerous to place a neuraxial anesthetic may dictate the use of general anesthesia, which carries its own risks in a parturient. A review of pregnancy-related deaths found that fatality rates for parturients administered general anesthesia for cesarean delivery were much greater than fatality rates of parturients who received neuraxial anesthesia. Refraining from neuraxial anesthesia during labor and delivery commits the patient, at a minimum, to a painful labor. It is possible that later in the course of labor the woman may require a cesarean delivery, and then general anesthesia would likely be needed.
What is the expected platelet count during pregnancy?
Platelet count decreases by approximately 20% during normal pregnancy; most platelet counts remain >150,000 mm −3 . However, approximately 7% of all parturients present with a platelet count <150,000 mm −3 , and 0.5%–1% present with a platelet count <100,000 mm −3 .
Describe coagulation and the role that platelets play in the process.
Clotting can be thought of as occurring in two phases: primary and secondary hemostasis. Primary hemostasis is the creation of the initial platelet plug, and secondary hemostasis is the creation of the stable fibrin clot. Platelets play an important role in both processes. Generally, blood vessels prevent platelet adhesion by releasing a potent vasodilator, prostacyclin. After vessel wall injury, prostacyclin levels decrease, and platelets adhere to the vessel wall. Adhesion leads to activation and degranulation with release of adenosine diphosphate (ADP), serotonin, and thromboxane, which leads to platelet aggregation. Further aggregation leads to formation of a platelet plug. This plug is unstable and requires fibrin formation (secondary hemostasis), which occurs by activation of the intrinsic or extrinsic coagulation system. Platelets provide the phospholipid membrane on which the coagulation cascade occurs. Platelet abnormalities can be qualitative or quantitative and are the most common hematologic disorders during pregnancy.
What are the causes of thrombocytopenia during pregnancy?
Most cases (99%) of thrombocytopenia during pregnancy are related to one of three causes: hypertensive disorders such as preeclampsia, gestational thrombocytopenia, or idiopathic thrombocytopenic purpura (ITP). When evaluating a parturient with thrombocytopenia, there are two specific issues to consider. The first concern is whether the disorder is static or dynamic ( Table 58-1 ). If the disorder is static, as occurs during gestational thrombocytopenia or ITP, the platelet count is usually stable. If the disorder is dynamic, as occurs during preeclampsia, the platelet count may change rapidly, and it is important to obtain serial platelet counts. The second issue is whether platelet function is normal or abnormal. Platelet function is typically normal in gestational thrombocytopenia and ITP and may be abnormal in preeclampsia.
What tests are available to evaluate platelet function?
A patient who presents with a platelet disorder is difficult to evaluate with standard laboratory tests because both platelet quantity and quality must be assessed. Tests of platelet function have been criticized for being difficult to perform, lacking reproducibility, and being of questionable clinical relevance. The ideal test would be easy to perform, would be inexpensive, and would not require specialized equipment, with results that could be reproduced and correlate with outcome. Bedside tests of coagulation include the thromboelastogram (Thrombelastograph; Haemoscope Corporation, Skokie, IL) and the platelet function analyzer (PFA-100; Dade Behring, Newark, DE).