A physiology-based approach to ROTEM interpretation for bleeding management in cardiac surgery: A narrative review

ABSTRACT

Perioperative bleeding after cardiac surgery is common, multifactorial, and resource intensive. Conventional coagulation tests are often delayed and do not describe clot development in whole blood, whereas rotational thromboelastometry (ROTEM) provides point-of-care information about clot initiation, clot firmness, residual heparin effect, and fibrinolysis. This narrative review summarizes guideline statements, randomized trials, systematic reviews, and clinically relevant mechanistic literature on viscoelastic testing in cardiac surgery. Literature was identified through targeted searches of PubMed-indexed and major cardiothoracic anesthesia sources, prioritizing patient blood management guidelines, studies of ROTEM- or thromboelastometry-guided transfusion algorithms, and evidence relevant to FIBTEM, HEPTEM, protamine, fibrinogen replacement, platelet contribution, and antifibrinolytic therapy. The review proposes a stepwise approach that begins with clinical context, evaluates EXTEM clotting time, integrates early EXTEM and FIBTEM clot amplitude, uses INTEM and HEPTEM to distinguish residual heparin from non-heparin causes of delayed clot initiation, screens for hyperfibrinolysis, and requires repeat testing after targeted intervention. The framework is intended to complement local transfusion protocols and patient blood management programs, support interdisciplinary communication, and reduce empiric transfusion.

Introduction

Bleeding after cardiac surgery remains a major cause of allogeneic blood product exposure, surgical re-exploration, acute kidney injury, prolonged intensive care, and cost.[1,2,3,4] The problem is rarely explained by a single laboratory abnormality. Cardiopulmonary bypass, hypothermia, hemodilution, residual heparin, platelet dysfunction, fibrinogen depletion, antiplatelet drugs, inflammation, and surgical bleeding can coexist in the same patient.[1,5,6,7,8] As a result, empiric transfusion based on fixed ratios or delayed conventional laboratory tests may fail to address the dominant mechanism of bleeding.[4,9,10,11]

Patient blood management guidelines increasingly support goal-directed hemostatic therapy and point-of-care coagulation testing in cardiac surgery.[1,2,3,12] ROTEM can shorten the interval between blood sampling and actionable hemostatic information, but its value depends on how results are interpreted and embedded in an institutional algorithm.[4,9,10,13] Treating a prolonged clotting time, low clot amplitude, or elevated lysis value without asking why the abnormality occurred may lead to unnecessary plasma, platelet, fibrinogen, or procoagulant therapy.[8,13,14]

This review reframes ROTEM interpretation as a practical diagnostic pathway for anesthesiologists managing bleeding after cardiac surgery. The aim is not to replace local algorithms, manufacturer reference ranges, or surgical judgment, but to provide a reproducible reasoning process that can be adapted to institutional protocols.[1,2,13]

Methods for Literature Selection

This is a narrative review. We conducted targeted literature searches focused on ROTEM, thromboelastometry, viscoelastic hemostatic testing, patient blood management, cardiac surgery, cardiopulmonary bypass, fibrinogen, platelet contribution, heparin reversal, protamine, tranexamic acid, and transfusion algorithms. Priority was given to society guidelines, randomized clinical trials, systematic reviews, meta-analyses, and high-impact perioperative studies relevant to adult cardiac anesthesia.

Articles were selected when they addressed one of four practical questions: how ROTEM should be incorporated into cardiac surgical bleeding algorithms; how EXTEM and FIBTEM should be interpreted together; how INTEM and HEPTEM can help identify residual heparin effect; and how ROTEM findings should guide targeted intervention and reassessment. Because the objective was to create a clinically usable framework rather than a quantitative evidence synthesis, no pooled analysis was performed.

Clinical Context Comes First

ROTEM should be ordered and interpreted for a clinical question, not as a detached screening test.[1,13] The first question is whether there is clinically important bleeding after separation from cardiopulmonary bypass, in the operating room, or in the early intensive care period. A normal or near-normal ROTEM in the presence of heavy surgical field bleeding should prompt renewed attention to surgical hemostasis, graft and cannulation sites, blood pressure, and temperature.[1,8] Conversely, an abnormal ROTEM without active bleeding should not automatically trigger transfusion.[1,13,15]

Before attributing abnormal tracings to coagulopathy, reversible physiologic conditions should be corrected or at least recognized. Hypothermia, acidosis, low ionized calcium, severe anemia, hemodilution, and ongoing anticoagulant or antiplatelet effect can all shape ROTEM results and the response to therapy.[8,12,16] The anesthesiologist should therefore interpret the tracing beside the patient rather than beside the analyzer alone.

Assess Clot Initiation with EXTEM Clotting Time

EXTEM clotting time reflects activation of coagulation through a tissue factor-dependent pathway.[8,13,17] In a bleeding cardiac surgical patient, a prolonged EXTEM clotting time suggests delayed clot initiation. Common explanations include coagulation factor deficiency, dilutional coagulopathy, residual anticoagulant effect, severe hypofibrinogenemia, or profound physiologic derangement.[8,12,13] A normal EXTEM clotting time makes major failure of clot initiation less likely and shifts attention toward clot strength and stability.

The key teaching point is that EXTEM clotting time is a starting point, not a diagnosis. Plasma or prothrombin complex concentrate should not be given reflexively without integrating surgical bleeding, antithrombotic history, recent protamine administration, laboratory data when available, and local protocol thresholds.[1,8,12,13]

Interpret Early Clot Firmness Using EXTEM A5 and FIBTEM A5

Early clot amplitude at 5 minutes is useful because clinical bleeding decisions often cannot wait for maximum clot firmness.[13,18] EXTEM A5 reflects the combined contribution of fibrinogen, platelets, and other cellular elements to early clot strength. FIBTEM A5 suppresses the platelet contribution and highlights the fibrin-based component of the clot.[8,13,14] Reading these channels together is the practical core of ROTEM-guided therapy after cardiopulmonary bypass.[4,9,10]

A low EXTEM A5 with a low FIBTEM A5 points toward inadequate fibrin-based clot strength and should raise concern for hypofibrinogenemia or impaired fibrin polymerization.[8,14,17,18,19] A low EXTEM A5 with a relatively preserved FIBTEM A5 suggests reduced platelet contribution, although ROTEM does not directly measure platelet receptor function.[13,20] In that situation, platelet count, preoperative antiplatelet exposure, bypass duration, temperature, and clinical bleeding severity matter.[1,21,22]

Separate Residual Heparin from Other Causes with INTEM and HEPTEM

After cardiac surgery, residual heparin or protamine imbalance is a frequent concern.[5,23,24,25] INTEM is more sensitive to heparin effect than EXTEM, while HEPTEM contains heparinase and helps determine whether prolonged intrinsic pathway clotting time is heparin-mediated.[8,13,23] If a prolonged INTEM clotting time corrects in HEPTEM, residual heparin effect is likely. If HEPTEM remains prolonged, the problem is less likely to be heparin alone and may reflect factor deficiency, hemodilution, or another anticoagulant effect.[8,13]

This distinction matters because additional protamine is not benign. Excess protamine can impair coagulation and platelet function and has been associated with increased bleeding after cardiopulmonary bypass.[24,25] The ROTEM pattern should therefore be interpreted with the activated clotting time trend, heparin and protamine doses, bypass duration, and the surgical field.[5,23]

Look for Hyperfibrinolysis When Clot Formation is Adequate but Bleeding Persists

Maximum lysis provides information about clot breakdown over time.[8,13,26] Hyperfibrinolysis is less common than fibrinogen depletion or platelet-related clot weakness in many cardiac surgical settings, but when present it requires a different response.[8,26] If clot initiation and early clot firmness appear adequate but lysis is excessive, antifibrinolytic therapy and reassessment of ongoing bleeding are more rational than repeated empiric component transfusion.[26,27]

Many cardiac surgery patients receive prophylactic tranexamic acid, and large randomized data support its ability to reduce bleeding and transfusion in coronary-artery surgery.[27] Marked fibrinolysis despite prophylaxis should trigger careful review of dosing, timing, renal function, and other causes of persistent bleeding. ROTEM should be used to support treatment decisions but not to delay urgent surgical control when bleeding is mechanical.[1,8]

Reassess After Each Targeted Intervention

ROTEM-guided management is iterative.[4,9,10,13] After fibrinogen concentrate, cryoprecipitate, platelets, plasma, prothrombin complex concentrate, protamine, or antifibrinolytic therapy, repeat testing should confirm whether the intended abnormality improved. This prevents escalation based on stale data and helps the team recognize when the dominant problem has changed.[1,13]

Repeat testing also supports team communication. A shared sequence such as ‘EXTEM CT acceptable, FIBTEM A5 low, fibrinogen replaced, repeat A5 improved, bleeding persists from surgical source’ is more useful than listing values without interpretation. In institutions building ROTEM pathways, this communication format may be as important as the numeric threshold table.[13] A practical summary of this approach is shown in Table 1.

Table 1.

Practical ROTEM interpretation pathway for bleeding after cardiac surgery

Decision point	ROTEM focus	Likely interpretation	Clinical action
Is there clinically important bleeding?	Clinical field, chest tube output, hemodynamics	ROTEM is most useful when linked to active bleeding or high-risk reassessment.	Correct temperature, pH, calcium, anemia, and surgical causes while testing.
Is clot initiation delayed?	EXTEM CT	Delayed initiation may reflect factor deficiency, dilution, anticoagulant effect, or severe physiologic derangement.	Avoid reflex plasma/PCC; integrate with context and local thresholds.
Is early clot strength reduced?	EXTEM A5 with FIBTEM A5	Low EXTEM A5 plus low FIBTEM A5 suggests weak fibrin-based clot strength.	Consider fibrinogen replacement according to local protocol.
Is platelet contribution reduced?	Low EXTEM A5 with preserved FIBTEM A5	Reduced platelet contribution; ROTEM does not directly test platelet receptor function.	Review platelet count, antiplatelet drugs, bypass duration, and bleeding severity before platelet transfusion.
Is residual heparin likely?	INTEM CT and HEPTEM CT	Correction in HEPTEM supports heparin effect; persistent prolongation suggests non-heparin causes.	Consider protamine only when supported by dosing history, ACT trend, and ROTEM pattern.
Is the clot breaking down?	Maximum lysis	Excessive lysis suggests fibrinolysis rather than inadequate clot formation.	Consider antifibrinolytic therapy and reassess.

A5, amplitude at 5 min; ACT, activated clotting time; CT, clotting time; EXTEM, tissue factor-activated assay; FIBTEM, EXTEM-based fibrin clot assay with platelet inhibition; HEPTEM, INTEM assay with heparinase; INTEM, intrinsically activated assay; PCC, prothrombin complex concentrate; ROTEM, rotational thromboelastometry.

Implementation in a Cardiac Anesthesia Service

A practical ROTEM program should combine clinical triggers, analyzer logistics, treatment thresholds, product availability, and education.[1,4,9,13] Protocols should specify when to draw the sample, who runs the test, who interprets it, how results are communicated, and when repeat testing is required. Thresholds should be aligned with local product options and national regulation. For example, a center using fibrinogen concentrate will operationalize low FIBTEM values differently from a center that relies on cryoprecipitate.[1,14]

Education should emphasize pattern recognition rather than memorization of isolated parameters.[28] Simulation cases can ask trainees to decide whether the tracing suggests fibrinogen deficiency, platelet contribution failure, residual heparin, hyperfibrinolysis, surgical bleeding, or a mixed picture. Debriefing should include the potential harms of overtreatment as well as the harms of delayed treatment, because transfusion in cardiac surgery is consistently associated with important morbidity, resource use, and outcome concerns.[1,29,30,31]

Limitations

ROTEM does not directly measure platelet receptor function, endothelial contribution to hemostasis, vascular integrity, or the surgical source of bleeding.[13,20] It is less informative if the clinical team ignores pre-analytical variables, sampling timing, device quality control, or local reference ranges.[12,13,32] Evidence supporting viscoelastic testing is strongest when it is embedded in a complete patient blood management program, not when it is used as an isolated device.[1,4,6,7]

The framework presented here is deliberately conservative. It supports targeted therapy but avoids universal numeric cutoffs because assays, reagents, patient populations, and product availability vary across institutions.[1,13] Each center should validate its algorithm locally and audit transfusion, bleeding, re-exploration, thrombotic events, and cost outcomes.[1,4,9]

Conclusion

ROTEM is most useful in cardiac surgery when interpreted as a physiology-based decision pathway.[1,4,9,13] The anesthesiologist should start with clinical bleeding and correctable physiology, then move sequentially through clot initiation, early clot firmness, fibrinogen contribution, platelet contribution, residual heparin assessment, and clot lysis. Linking each ROTEM pattern to a targeted intervention and repeating the test after treatment can reduce empiric transfusion and improve interdisciplinary bleeding management.[4,9,10,33] The approach should complement, not replace, local patient blood management protocols and surgical judgment.[1,2,8]

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.