Management of post-partum hemorrhage and the role of the obstetric anesthesiologist

Detection of Postpartum Hemorrhage Using Compensatory Reserve Index in Patients Undergoing Cesarean Delivery

BACKGROUND

Postpartum hemorrhage (PPH) is the leading cause of maternal death worldwide. Early recognition and management are imperative for improved outcomes. The compensatory reserve index (CRI) is a novel physiological parameter that trends changes in intravascular volume, by continuously comparing extracted photoplethysmogram waveforms to a reference model that was derived from a human model of acute blood loss. This study sought to determine whether the CRI pattern was differential between those who do and do not experience PPH during cesarean delivery and compare these results to the American Society of Anesthesiologists (ASA) standards for noninvasive monitoring.

METHODS

Parturients undergoing cesarean delivery were enrolled between February 2020 and May 2021. A noninvasive CRI monitor was applied to collect continuous CRI values throughout the intraoperative and immediate postpartum periods. Patients were stratified based on blood loss into PPH versus non-PPH groups. PPH was defined as a quantitative blood loss >1000 mL. Function-on-scalar (FoS) regression was used to compare trends in CRI between groups (PPH versus non-PPH) during the 10 to 60-minute window after delivery. Two subanalyses excluding patients who received general anesthesia and preeclamptics were performed.

RESULTS

Fifty-one patients were enrolled in the study. Thirteen (25.5%) patients experienced PPH. Pregnant patients who experienced PPH had, on average, lower postdelivery CRI values (-0.13; 95% CI, -0.13 to -0.12; P < .001) than those who did not experience PPH. This persisted even when adjusting for preeclampsia and administration of uterotonics. The average mean arterial pressure (MAP) measurements were not statistically significant (-1.67; 95% CI, -3.57 to 0.22; P = .09). Similar trends were seen when excluding patients who underwent general anesthesia. When excluding preeclamptics, CRI values remained lower in those who hemorrhaged (-0.18; 95% CI, -0.19 to -0.17; P < .001).

CONCLUSIONS

CRI detects changes in central volume status not distinguished by MAP. It has the potential to serve as a continuous, informative metric, notifying providers of acute changes in central volume status due to PPH during cesarean delivery.

Patient Blood Management programs for post-partum hemorrhage

Patient blood management (PBM) strategies aim to maintain hemoglobin concentration, optimize hemostasis, and minimize blood loss to improve patient outcomes. Because postpartum hemorrhage (PPH) is a leading cause of maternal mortality and blood product utilization, PBM principles can be applied in its therapeutic approach. First, pre-operative identification of risk factors for PPH and identification of peri-delivery anemia should be conducted. Iron supplementation should be used to optimize hemoglobin concentration before delivery; it can also be used to treat anemia in the postpartum period after severe PPH. Both acute normovolemic hemodilution and intraoperative cell salvage can be effective techniques to reduce allogeneic blood transfusion during or after surgical procedures. Furthermore, these strategies appear to be safe when used in the pregnant population.

The relationship between INTEM/HEPTEM coagulation time ratio and heparin plasma concentration in obstetric patients: an exploratory in vitro investigation

PURPOSE

Unfractionated heparin continues to be one of the main agents used for thromboprophylaxis in obstetrics, which can complicate the placement of neuraxial anesthetics. In this study, we explored the relationship between a point-of-care coagulation test (thromboelastometry) and plasma heparin concentrations in vitro.

METHODS

We obtained blood from consenting obstetric patients with uncomplicated pregnancies in their third trimester who were not in labour and had a specific hematocrit range. Blood was processed and analyzed. We added increasing amounts of unfractionated heparin to samples from 0 to 0.3 U·mL^-1 in 0.05 U·mL^-1 increments to simulate increasing doses of unfractionated heparin. We performed INTEM and HEPTEM testing in parallel with activated partial thromboplastin time (aPTT) testing. We created a model of the relationship between heparin concentration and the INTEM/HEPTEM coagulation time (IH CT) ratio using nonlinear regression. A similar model for aPTT was also created.

RESULTS

Seventy-seven patients were included in the study. Only one concentration of heparin was added to blood samples of each patient. At a concentration of 0.05 U·mL^-1, the IH CT ratio was less than or equal to 1.1 in 9/11 (82%) samples. Activated partial thromboplastin time was not prolonged (> 35 sec) until a concentration of 0.1 U·mL^-1 heparin was added. In all samples, the IH CT ratio was prolonged at a concentration ≥ 0.2 U·mL^-1 as measured by thromboelastometry; however, at no concentration of heparin was aPTT prolonged in all samples.

CONCLUSION

The point-of-care IH CT ratio may be useful in identifying the presence of little to no heparin activity. Further research is needed to determine if this ratio can predict heparin activity in vivo.

The impact of crystalloid versus colloid on coagulation as measured by thromboelastometry in term parturients: an in vitro study

OBJECTIVE

A pilot study to examine the impact of crystalloid versus albumin hemodilution in vitro on coagulation using thromboelastometry in pregnant patients.

METHODS

This prospective, observational pilot study included seventy-six pregnant patients at term (≥37 weeks) without history of bleeding or clotting disorder or on anticoagulation. Blood was collected and diluted with either Plasma-Lyte or albumin at the following levels: 0%, 20%, 25%, 30%, 35%, 40%, 45%, 55%, 60%, 65%, 70%, 75%, 80%. Thromboelastometry was performed to assess for coagulation changes.

RESULTS

There was a small, statistically significant difference in the FIBTEM A5 between the Plasma-Lyte and albumin samples. However, the predicted probability of coagulopathy, using FIBTEM A5 less than 12 mm, was not different between the groups at any dilution. There was no difference in EXTEM clotting time at low-moderate levels of hemodilution. At dilutions above 40%, the albumin group had a significantly greater prolongation in clotting time compared to the Plasma-Lyte group.

CONCLUSION

When albumin is used at low-moderate levels of hemodilution in vitro in parturients there is no additional risk of coagulopathy compared to hemodilution with crystalloid. Given that colloids are frequently used to restore intravascular volume during massive hemorrhage, these results support that during early stages of hemorrhage, albumin may not contribute to additional coagulopathy beyond that of hemodilution, although further in vivo studies are needed.

The effects of hemodilution on coagulation in term parturients: an in vitro study utilizing rotational thromboelastometry

Objective: To examine the impact of hemodilution on components of blood coagulation using rotational thromboelastometry (ROTEM^®) in term parturientsMethods: This is a prospective, observational pilot study including 35 healthy, parturients at term (≥37 weeks) without history of bleeding or clotting disorder or on medication affecting coagulation. Venous blood samples were collected and divided into specimen tubes to generate varying degrees of hemodilution with Plasma-Lyte (0%, 20%, 25%, 30%, 35%, 40%, 45%, 55%, 60%, 65%, 70%, 75%, 80%). ROTEM^® was performed to assess for coagulation changes.Results: EXTEM (extrinsically activated assay) clotting time (CT) became prolonged at 65% hemodilution and above, and the median CT was in the coagulopathic range (>80 s) at a dilution of 80%. FIBTEM (extrinsically activated assay with platelet inhibitor) amplitude at 5 min (A5) began to diminish at 35% hemodilution, with the median A5 in the coagulopathic range (<12 mm) at 55% hemodilution. The area under the curve (AUC) for EXTEM and FIBTEM consistently declined as hemodilution increased. Greater decreases in FIBTEM AUC were seen compared to EXTEM AUC, with the ratio of FIBTEM:EXTEM AUC at each dilution demonstrating a statistically significant difference from baseline.Conclusion: All thromboelastometry values demonstrated a hypocoagulable trend as hemodilution increased. However, the samples analyzed by the FIBTEM assay trended toward a coagulopathy at a lower degree of hemodilution compared to the EXTEM assay. As FIBTEM tests analyze the role of fibrinogen in hemostasis and EXTEM tests analyze the role of platelets, our findings suggest that platelets may be able to withstand higher degrees of hemodilution before impairing hemostasis compared to fibrinogen. These findings support the growing body of literature that in early stages of severe obstetric hemorrhage, the prioritization of fibrinogen replacement may be critical in preventing further coagulopathy.