Viscoelastic Testing in Obstetrics 2023

Your pager goes off for a postpartum hemorrhage (PPH) on the labor floor. While the patient is hemodynamically stable, the estimated blood loss is almost 2 liters, so you place additional large-bore intravenous access while drawing off a “rainbow set” of labs. You also draw a blood gas and an additional citrated tube of blood for viscoelastic testing so you can begin goal-directed therapy while waiting for the results of your other tests. The blood gas shows a hematocrit of 20, so you begin to transfuse packed red blood cells. Your viscoelastic testing suggests factor and fibrinogen deficiencies, so you begin to transfuse FFP and cryoprecipitate. Meanwhile, your traditional blood tests have only just arrived at the laboratory. This all-too-common scenario demonstrating PPH complicated by disseminated intravascular coagulation illustrates the real-time information that viscoelastic testing can provide to aid in the swift diagnosis and treatment of coagulopathy on the labor floor. Hemorrhage remains the number-one cause of maternal mortality worldwide and number-two cause in the United States (Lancet Glob Health 2014;2:e323-33; asamonitor.pub/3KQxXRR). Viscoelastic testing is one tool we may be able to add to our armamentarium to mitigate this risk. In this article, we will further describe viscoelastic testing and its utility in obstetrics with respect to PPH management and neuraxial block placement while providing a short summary of the literature demonstrating its benefit in clinical outcomes.

Viscoelastic testing refers to several types of point-of-care tests that assess whole blood hemostasis from initial clot formation to clot lysis. A graphical representation is created based on these kinetic changes, which can then be interpreted to guide therapy instead of relying on protocolized transfusion guidelines. Furthermore, unlike traditional coagulation studies that test plasma, viscoelastic testing evaluates whole blood. This process provides information that may be more reflective of the true coagulation profile of the patient than static traditional coagulation studies (Front Med 2015;2:62). By providing real-time information, providers can more swiftly diagnose and treat coagulopathy without having to wait for the long processing times of traditional coagulation studies.

The two predominant viscoelastic testing systems are thromboelastography (TEG) and rotational thromboelastometry (ROTEM) (Transfusion 2020;60:S70-4). Both tests provide users with similar graphical representations of hemostasis, but the device mechanisms and variable names are slightly different. While there is no evidence of one system being superior to the other, ROTEM may offer some advantages over TEG (Clin Lab Haematol 2005;27:81-90; Transfus Med Rev 2017;31:11-25). While TEG provides a snapshot of whole blood hemostasis and clot breakdown, ROTEM provides its user with up to five different assays that can specifically assess different arms of the coagulation cascade (INTEM, EXTEM, FIBTEM) while also assessing the effects of antifibrinolytics (APTEM) and heparin (HEPTEM). The HEPTEM assay contains heparinase, which neutralizes the effect of heparin, if present. This assay may be particularly useful for timing of procedures/neuraxial block placement in patients who are on heparin. There is evidence that an INTEM to HEPTEM clotting time ratio around one may suggest little to no heparin activity (Can J Anaesth 2022;69:597-604), which might provide reassurance to anesthesiologists contemplating neuraxial block placement in a patient who has been on heparin and whose care may be time sensitive, although more research is needed in this area.

In addition to guiding blood product resuscitation and procedure timing, the data gleaned from these tests may also reveal or confirm coagulopathy in at-risk patients during pre-anesthetic consultations. This can help with decision-making regarding neuraxial block placement in patients at increased risk of spinal epidural hematoma (J Thromb Haemost 2020;18:1813-38). In fact, Huang et al. found that among patients with platelets less than 100,000 mm³, neuraxial block placement is safe above a platelet count of 56,000 mm³ when the TEG is normal (AANA J 2014;82:127-30). This finding is consistent with the Society for Obstetric Anesthesia and Perinatology consensus statement, which suggests a platelet count cutoff of 70,000 x 10⁶/L for safe neuraxial block placement (Anesth Analg 2021;132:1531-44).

Although the use of viscoelastic testing has been shown to reduce mortality and blood product utilization in cardiac surgery and liver transplantation through large randomized controlled trials, there are fewer studies that demonstrate consistent findings in obstetrics (Transfusion 2020;60:S70-4; Cochrane Database Syst Rev 2016;2016:CD007871). While Snegovskikh et al. demonstrated fewer hysterectomies, ICU admissions, blood products transfused, and lower estimated blood loss when ROTEM was used to guide transfusion management in their retrospective cohort study, Mallaiah et al. did not find such a reduction in hysterectomies or ICU admissions (Anaesthesia 2015;70:166-75; J Clin Anesth 2018;44:50-6). Mallaiah et al. did, however, demonstrate a reduction in blood products transfused and transfusion-associated circulatory overload (TACO) when FIBTEM was used to guide fibrinogen concentrate transfusions (Anaesthesia 2015;70:166-75). Although many studies have shown positive outcomes for viscoelastic testing in obstetrics, more randomized controlled trials are needed to demonstrate consistent clinical outcome benefit.

When available, viscoelastic testing is an invaluable tool in the management of patients on the labor floor. Whether it is used to guide blood product therapy during a postpartum hemorrhage, aid in decision-making regarding neuraxial block placement, or for timing of procedures in a patient on heparin, viscoelastic testing’s potential for clinical benefit is clear. However, there are costs associated with running samples, such as cartridges, reagents, etc., so its use should be limited to when it is clinically indicated or for research purposes.