Is There a "Blind Spot" in Point-of-Care Testing for Residual Heparin After Cardiopulmonary Bypass? A Prospective, Observational Cohort Study

Accurate protamine:heparin matching (not just smaller protamine doses) decreases postoperative bleeding in cardiac surgery; results from a high-volume academic medical center

BACKGROUND

A multidisciplinary Quality Assurance/Performance Improvement study to identify the incidence of "heparin rebound" in our adult cardiac surgical population instead detected a thromboelastometry pattern suggestive of initial protamine overdose in 34% despite Hepcon-guided anticoagulation management. Analysis of our practice led to an intervention that made an additional lower-range Hepcon cartridge available to the perfusionists.

METHODS

One year later, an IRB-approved retrospective study was conducted in >500 patients to analyze the effects of the intervention, specifically focusing on the impact of the initial protamine dose accuracy and 18-h mediastinal chest tube drainage (MCTd).

RESULTS

No differences were observed between group demographics, surgical procedures, duration of CPB or perioperative blood product transfusion. Both groups were managed using the same perfusion and anesthesia equipment, strategies, and protocols. The median initial protamine dose decreased by 19% (p < .001) in the intervention group (170 [IQR 140-220] mg; n = 295) versus the control group (210 [180-250] mg; n = 257). Mean 18-h MCTd decreased by 13% (p < .001) in the intervention group (405.15 ± 231.54 mL; n = 295) versus the control group (466.13 ± 286.73 mL; n = 257). Covariate-adjusted mixed effects model showed a significant reduction of MCTd in the intervention group, starting from hour 11 after surgery (group by time interaction p = .002).

CONCLUSION

Though previous investigators have associated lower protamine doses with less MCTd, this study demonstrates that more accurately matching the initial protamine dose to the remaining circulating heparin concentration reduces postoperative bleeding.

Heparin Rebound: An In-Depth Review

The common conception of "heparin rebound" invokes heparin returning to circulation in the postoperative period after apparently adequate intraoperative reversal with protamine. This is believed to portend increased postoperative bleeding and provides the rationale for administering additional empiric doses of protamine in response to prolonged coagulation tests and/or bleeding. However, the relevant literature of the last 60+ years provides only a weak level of evidence that "rebounded" heparin itself is a significant etiology of postoperative bleeding after cardiac surgery with cardiopulmonary bypass. Notably, many of the most frequently cited heparin rebound investigators ultimately concluded that although exceedingly low levels of heparin activity could be detected by anti-Xa assay in some (but not all) patients postoperatively, there was no correlation with actual bleeding. An understanding of the literature requires a careful reading of the details because the investigators lacked standardized definitions for "heparin rebound" and "adequate reversal" while studying the phenomenon with significantly different experimental methodologies and laboratory tests. This review was undertaken to provide a modern understanding of the "heparin rebound" phenomenon to encourage an evidence-based approach to postoperative bleeding. Literature searches were conducted via PubMed using the following MeSH terms: heparin rebound, heparin reversal, protamine, platelet factor 4, and polybrene. Relevant English language articles were reviewed, with subsequent references obtained from the internal citations. Perspective is provided for both those who use HepCon-guided management and those who do not, as are practical recommendations for the modern era based on the published data and conclusions of the various investigators.

Characterization of Acute Traumatic Coagulopathy in Cats and Association with Clinicopathological Parameters at Presentation

OBJECTIVE

 This study aimed to document rotational thromboelastometric (ROTEM) characteristics of traumatized cats and to investigate associations between clinicopathological parameters and acute traumatic coagulopathy (ATC). A secondary goal was to determine the relevance of autoheparinization in injured cats.

STUDY DESIGN

 Cats presenting with acute (<12 hours) trauma were eligible. Cats were allocated to the ATC group (≥2 hypocoagulable parameters) or non-ATC group (≤1 hypocoagulable parameter) based on ROTEM analysis. Clinicopathological parameters were compared between groups and regression was used to find variables associated with ATC. Heparinase-modified ROTEM (HepTEM) was used to assess for heparin effects in a subgroup.

RESULTS

 Fifty-three cats were included, and the incidence of ATC was 15%. Prolongation of both intrinsic and extrinsic clotting times (CT) was the most frequently altered ROTEM variable in the ATC group, but CT_InTEM-prolongation also occurred in 47% of non-ATC cats. The incidence of autoheparinization, defined as concurrent CT_InTEM prolongation and CT_InTEM:HepTEM ratio >1.1, was 41% and was observed in both cats with and without ATC. None of the evaluated clinicopathological parameters were different between groups or associated with ATC.

CONCLUSIONS

 Acute traumatic coagulopathy in cats is mainly characterized by prolonged CT. No relationship between clinicopathological variables and ATC was identified and prediction of ATC based on these variables was not possible. While autoheparinization is important in cats, it is not the sole cause for ATC.