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Coagulation Cascade + Periop Bleeding Management
TEXTPhysiology IV · 10 min read
Intrinsic, extrinsic, and common pathways tell you which test is broken. TEG/ROTEM tells you what to actually transfuse.
After this lesson you can
2 min read7 sections- Map intrinsic + extrinsic + common pathways.
- Interpret PT/INR + PTT in context.
- Apply TEG/ROTEM to bleeding patient.
- Recall coagulation factor half-lives + replacement.
Classic cascade — three pathways
PT/INR measures this.
PTT measures this.
Mnemonic for vitamin-K-dependent factors: 1972 (II, VII, IX, X) + protein C, protein S.
Warfarin inhibits gamma-carboxylation of these.
Heparin potentiates antithrombin inhibits IIa + Xa.
Cell-based model (modern view)
Three overlapping phases on cell surfaces: initiation (TF-bearing cell, small thrombin burst), amplification (platelet activation, cofactor activation V/VIII/XI on platelet surface), propagation (large thrombin burst on platelet surface, fibrin polymerization).
Why it matters: explains why factor concentrates work when single-factor models predict failure, and why platelets are essential even when factor levels are nominally adequate.
Reading abnormal labs
Isolated prolonged PTT — VIII/IX/XI (hemophilia), heparin, lupus anticoagulant.
Both prolonged — common pathway (X, V, II, fibrinogen), DIC, severe liver disease, dilutional.
Thrombocytopenia — quantitative platelet problem.
Normal coags + bleeding — qualitative platelet (uremia, antiplatelet drugs), vWD, factor XIII deficiency.
TEG/ROTEM viscoelastic testing
R-time / CT (clot initiation) — prolonged = factor deficiency FFP.
K-time / CFT + alpha angle (clot kinetics) — flat = fibrinogen cryo.
MA / MCF (clot strength) — low = platelet/fibrinogen platelets + cryo.
LY30 / ML (lysis) — high = fibrinolysis TXA.
Goal-directed transfusion cuts blood-product use 30-50% vs empiric ratios.
Massive transfusion protocol
Ratio 1:1:1 (PRBC:FFP:platelets) per PROPPR trial — slightly better mortality vs 2:1:1.
TXA within 3 hr of trauma (CRASH-2, MATTERs) — load 1 g over 10 min, infuse 1 g over 8 hr.
Calcium replacement (citrate chelation from blood products) — ionized Ca <1.0 1 g CaCl₂ per 4 units PRBC.
Hypothermia + acidosis + coagulopathy = lethal triad — warm everything.
Reversal agents
25-50 U/kg + vitamin K 10 mg IV.FFP if PCC unavailable.
Dabigatran: idarucizumab (Praxbind) 5 g IV.
Apixaban/rivaroxaban: andexanet alfa (Andexxa) or PCC 50 U/kg if unavailable.
Heparin: protamine 1 mg per 100 U heparin given in last 2-3 hr (max 50 mg dose, slow push — hypotension).
Aspirin/P2Y12: platelets if surgical bleeding (rarely indicated for elective).
Periop antiplatelet/anticoagulant holds
Bridge with LMWH only if high-risk (mechanical mitral, AF with CHADS₂ ≥5, recent VTE).
DOACs: 24-48 hr for low-risk procedure, 48-72 hr for high-risk (apixaban/rivaroxaban).
Dabigatran: longer with renal impairment.
Aspirin: continue for most surgeries (cardiac, vascular); hold 7 days for closed-space (intracranial, posterior eye).
P2Y12 inhibitors: clopidogrel 5d, ticagrelor 3-5d, prasugrel 7d.
DAPT after DES: defer elective ≥6 mo (ideally 12 mo).
⚠ Common pitfalls
- Treating elevated INR in cirrhosis as bleeding diathesis — patients often have balanced hemostasis.
- Reversing with FFP alone — PCC much faster + less volume.
- Forgetting that fibrinogen <1.5-2 is the bleeding-relevant threshold — replace with cryo or concentrate.
- Confusing PT and PTT — extrinsic vs intrinsic; ddx narrows by which is prolonged.
💎 Clinical pearls
- TEG: R = factor activity (FFP), MA = platelet/fibrinogen (platelets + cryo), LY30 = fibrinolysis (TXA).
- Factor VII half-life ~5 hr (shortest) — prolonged PT seen earliest.
- Fibrinogen consumed first in massive bleeding — early cryo replacement in MTP.
- PT/INR measures extrinsic (factor VII); PTT measures intrinsic (VIII, IX, XI, XII).
Recap
- TEG: R = factor activity (FFP), MA = platelet/fibrinogen (platelets + cryo), LY30 = fibrinolysis (TXA).
- Factor VII half-life ~5 hr (shortest) — prolonged PT seen earliest.
- Fibrinogen consumed first in massive bleeding — early cryo replacement in MTP.
- PT/INR measures extrinsic (factor VII); PTT measures intrinsic (VIII, IX, XI, XII).
Mark each section done to complete the module.