Normal Coagulation / haemostatic function
Depends on
- Normal vascular endothelium
- Normal number and function of platelets
- Derived from megakaryocytes in BM
- Release vasoconstrictive 5HT, serotonin, TXA2, ADP
- Bind via phospholipid / vWF to form haemostatic plug
- Normal amount of coagulation factors
- Forms stable meshwork of cross-linked fibrin around primary platelet plug (stable haemostatic plug)
- Forms stable meshwork of cross-linked fibrin around primary platelet plug (stable haemostatic plug)
- Essential co-factors - Vit K, calcium
- VitK: Fat soluble leads to carboxylation of factors II, VII, IX, X binding to surface of platelets
- Balanced by fibrinolytic pathway
Coagulation pathway
A series of enzyme-controlled steps resulting in the conversion of soluble plasma proteins (fibrinogen) into insoluble polymerise deposit.
Ie. the formation of a clot!
- Intrinsic cascade (APTT): components intrinsic to blood itself - clots in tube (12,11,9,10,2,1)
- Extrinsic cascade (PT): components activated by extrinsic factors from damaged tissue (7, 10,2,1)
- Factor VII decays fastest in blood + particularly calcium dependent
Surgical Coagulopathy
- Hypothermia - cold results in dysfunctional platelets
- Massive transfusion
- Aspirin
- Heparin (can lead to thrombocytopenia through immunological mechanism "HITS" - heparin induced thrombocytopenia
- DIC / sepsis
Tests of coagulation
| Bleeding Time | Time taken for earlobe to stop bleeding after it's been punctured 3-5 min. Reflects platelet function |
| Clotting Time | Time taken for blood to clot in glass tube (intrinsic pathway) 4-6 min. |
| Activated Clotting Time | Whole blood clotting time 107seconds + /- 13 seconds |
| Prothrombin Time | Measure of extrinsic + common pathways 9-15 seconds |
| Activated Partial Thromboplastin Time | Measure of intrinsic and common pathways 30-40seconds |
| Thrombin Time | Measure of common pathway 14-16s |
| TEG |
Dynamic function of everything |
TEG (Thromboelastography):
| Parameter | Description | Indications/ Implications |
| R-value | Time from initiation of test to initial fibrin formation and movement of pin | Coagulation factor activation |
| K-value | Time from beginning of clot formation until amplitude of TEG reaches 20mm | Coagulation factor amplification |
| Alpha-angle | Coagulation factor amplification | |
| Max-Amplitude | Greatest amplitude of TEG | Platelet aggregation |
| Amplitude at 60mins | Amplitude of TEG 60 minutes after maximal TEG is recorded | Fibrinolysis |
| Clot lysis index |