Laboratory and Viscoelastic Targets in Major Haemorrhage

During major haemorrhage, laboratory results guide product choice but lag behind the patient. Routine coagulation tests take 45 to 60 minutes, whereas viscoelastic testing gives clot information within 10 to 15 minutes at the bedside. The aim is early, targeted replacement of the deficit that is present, not a fixed ratio alone, and not correction of every abnormal number.

Viscoelastic testing. A whole blood clotting assay that records the time to clot formation, the strength of the clot at fixed times (usually 5 and 10 minutes), the maximum clot strength and clot breakdown. Some assays allow a fibrin-only measurement that blocks platelet contribution and so isolates fibrinogen. Devices differ, so cut-off values are device specific and must come from local validation.

Risk context. Treating by results alone delays resuscitation. Treating without results may over-transfuse. Samples drawn from a line contaminated with heparin or fluid give false results.

Special groups. Pregnancy (fibrinogen is high at term and a value of 2 g/L is already low), liver disease (abnormal tests may overestimate bleeding risk), neonates (reference ranges differ), and patients on anticoagulants. In East Africa, viscoelastic testing is often unavailable, so repeated routine coagulation tests, fibrinogen (Clauss), platelet count, a bedside clot observation test and clinical judgement guide treatment.

Laboratory targets in active bleeding.

Viscoelastic interpretation (principles).

• Prolonged clotting time: factor deficiency. Give plasma or prothrombin complex concentrate.

• Low fibrin-based clot amplitude at 5 to 10 minutes (device specific, often under about 10 mm at 5 minutes): low fibrinogen. Give cryoprecipitate or fibrinogen concentrate.

• Low clot amplitude with normal fibrin-based amplitude: platelet deficit or function loss. Give platelets.

• Clot breakdown early (increased lysis): hyperfibrinolysis. Give tranexamic acid.

• Combined abnormalities: treat fibrinogen first, then platelets and factors, and repeat the test.

Timing. Send samples at baseline, then after each pack or every 30 to 60 minutes, and after each replacement.

Pitfalls. Haemodilution of samples, heparin contamination, hypothermia and acidosis (which worsen results), delay in sample handling, and results that no longer reflect the patient after rapid transfusion.

Red flags. Fibrinogen falling quickly, clot amplitude falling despite replacement, ionised calcium persistently low, and lactate rising.

Plan.

1. Send samples and start resuscitation at once.

2. Give tranexamic acid early and calcium after the first units.

3. If fibrinogen is under 1.5 g/L (under 2 g/L postpartum), give two pools of cryoprecipitate or 3 to 4 g of fibrinogen concentrate, and repeat the level.

4. If platelets are under 50 x 10⁹/L, give one adult dose.

5. If prothrombin time or activated partial thromboplastin time is over 1.5 times normal after fibrinogen is replaced, give plasma 10 to 15 mL/kg, or prothrombin complex concentrate when concentrate is available and appropriate.

6. Repeat tests and adjust.

Where results are not available. Continue balanced resuscitation by the pack plan, give early fibrinogen replacement in obstetric and trauma bleeding, and reassess clinical oozing.

Stopping replacement. When bleeding is controlled and targets are reached, stop. Do not give plasma or platelets to correct values that are not clinically important.

Special groups.

• Pregnancy: act on fibrinogen under 2 g/L early.

• Liver disease: use viscoelastic results to avoid unnecessary plasma.

• Children: weight based doses and neonatal reference ranges.

Monitoring. Repeat the full panel every 30 to 60 minutes while bleeding, with viscoelastic results if available. Record all results with times and products given.

Complications. Over-transfusion with overload and lung injury, thrombosis with excess fibrinogen or prothrombin complex concentrate, and delayed haemorrhage control if results are misread.

Referral and escalation. Haematologist and laboratory consultant early for complex coagulopathy, and to validate local cut-offs.

Disposition. After control, check the panel at 4 to 6 hours and again on the next day. Review thromboprophylaxis once bleeding stops and laboratory targets are met.