Thromboelastogram (TEG) - Comprehensive Answer for AIIMS MD Anaesthesia

Definition and Introduction

"The advantage of VET over traditional coagulation tests is that VET is a real-time, detailed functional assay that provides information about clot formation, propagation, strength, and lysis." - Sabiston Textbook of Surgery, 10e, p. 946

Principle / Mechanism

• A small blood sample (0.36 mL citrated whole blood) is placed in a cylindrical cup that oscillates at a fixed angle (4°45') and frequency (0.1 Hz) around a suspended pin (torsion wire)
• As clot forms, fibrin strands link the cup wall to the pin
• The torque transmitted to the pin is measured by a transducer and recorded as the thromboelastogram
• The amplitude of the trace correlates with clot strength/viscosity

• The blood sample itself vibrates
• A light detector measures meniscus motion as clot forms (resonance technology - no mechanical pin/cup)

"Traditional TEG involves a pin suspended in a sample of patient blood, oscillating at a fixed frequency. As a clot forms and slows the movement of the pin, the torque is measured by a transducer and traced into the thromboelastogram." - Sabiston Textbook of Surgery, 10e, p. 945

The Thromboelastogram - Key Diagram

TEG Parameters - Normal Values and Clinical Significance

Second Classic TEG Diagram (Morgan & Mikhail's)

Flowchart: TEG-Guided Transfusion Algorithm

                    BLEEDING PATIENT
                          |
                    Obtain TEG sample
                          |
            ┌─────────────┴──────────────┐
            |                            |
       Rapid TEG                    Standard TEG
     (+ Tissue Factor)            (citrated whole blood)
     Result in 15 min             Result in 30-45 min
            |                            |
            └────────────┬───────────────┘
                         |
               Analyze TEG parameters
                         |
    ┌────────────────────┼─────────────────────┐
    |                    |                      |
  R time prolonged    K↑ / α angle↓         MA decreased
  (>10 min)          Fibrinogen deficiency   (<50 mm)
    |                    |                      |
Give FFP (or PCC)   Cryoprecipitate        Platelet transfusion
10-15 mL/kg         or Fibrinogen           or DDAVP
    |                concentrate             |
    |                    |                      |
    └────────────────────┼─────────────────────┘
                         |
                   LY30 > 7.5% ?
                         |
                   YES ──┴── NO
                    |          |
               Give TXA    No antifibrinolytic
           (Tranexamic acid  therapy needed
            15 mg/kg IV)
                    |
           Reassess TEG after treatment

Abnormal TEG Patterns

TEG vs. ROTEM - Comparison

Clinical Applications of TEG in Anaesthesia

1. Cardiac Surgery

• Guides anticoagulation monitoring during cardiopulmonary bypass (CPB)
• Detects residual heparin effect after protamine reversal
• Reduces blood product transfusion by targeted therapy
• Differentiates surgical bleeding from coagulopathic bleeding

2. Liver Transplantation

• Major historical application (1985 onward)
• Liver disease = complex coagulopathy (combined deficiency + hyperfibrinolysis)
• TEG guides correction without over-transfusing
• Identifies reperfusion-induced fibrinolysis

3. Trauma / Massive Hemorrhage

• TEG-guided goal-directed resuscitation reduces blood product use
• Identifies trauma-induced coagulopathy (TIC)
• Detects hyperfibrinolysis - guides TXA use
• 2020 EAST guidelines: conditional recommendation for use in bleeding trauma/surgical/ICU patients with suspected coagulopathy
• Replaces empirical 1:1:1 FFP:PLT:PRBC ratio with targeted therapy

4. Obstetric Anaesthesia

• At term, TEG reflects physiological hypercoagulable state (↓R, ↓K, ↑α, ↑MA)
• Guides management of postpartum hemorrhage
• Used in amniotic fluid embolism

5. Neurosurgery / Neurocritical Care

• Guides anticoagulation reversal before emergency procedures

Advantages of TEG Over Conventional Tests

• Does not assess primary hemostasis (platelet plug formation / vessel wall interaction)
• Not reliable for patients on anticoagulants or antiplatelet agents
• Requires specialized equipment and training
• Results may vary based on sample handling, temperature, activators used
• Not standardized across laboratories

Summary Flowchart: Phases of Coagulation on TEG

Time (min) ──────────────────────────────────────────────────►
               |←R→|← K →|
Amplitude       ╱▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔╲____
(mm)          ╱  ↑α angle            ↑MA   ↘ LY30
            ─/                              \────
           ↑                                ↑
    Enzymatic phase                 Fibrinolysis phase
  (thrombin generation)         (plasmin activity)
  Factor activity → R time

       ←─────────────────────────────────────────→
                CLOT FORMATION PHASE
     R = factors    K/α = fibrinogen    MA = platelets

Key Points for AIIMS Exam

1. TEG was first described by Hartert (1948) - became clinically practical in 1980s
2. R time = coagulation factors (prolonged → give FFP)
3. K time and α angle = fibrinogen (abnormal → give cryoprecipitate)
4. MA = platelet function (80% platelet contribution, 20% fibrin) (decreased → platelets/DDAVP)
5. LY30 = fibrinolysis (elevated → TXA)
6. Rapid TEG adds tissue factor to give results in 15 minutes
7. TEG and ROTEM values are NOT interchangeable
8. The characteristic "cigar/sausage-shaped" tracing = normal clot formation and lysis
9. Primary fibrinolysis on TEG = "closed loop" or "clot lysis" pattern (MA reached then rapid return to baseline)
10. In pregnancy: TEG shows hypercoagulable state (↓R, ↓K, ↑α, ↑MA) - begins in first trimester

• Sabiston Textbook of Surgery, 10e, Section: Viscoelastic Testing, p. 945-946 and Section: Rotational Thromboelastometry, p. 2232-2233
• Morgan & Mikhail's Clinical Anaesthesiology, 7e, Chapter 39, Fig. 39-5, p. 1542-1543
• Miller's Anesthesia, 10e, Chapter 58, Table 58.4
• Rockwood & Green's Fractures, 10e, Chapter 14, p. 3051-3058

Thromboelastogram (TEG) - 10 Marks Answer for AIIMS MD Anaesthesia

1. Introduction and Historical Background

"The early thromboelastograph (TEG) developed by Hartert in 1948 has evolved into two independent viscoelastic monitors: the modern TEG (TEG 5000 Hemostasis Analyzer System, Haemnetics) and rotational thromboelastometry (ROTEM, TEM Systems)." - Miller's Anesthesia 10e, Ch. 46

"These tests measure the rate of clot initiation, maximum clot strength, and time to lysis using citrated whole blood samples with the potential for point-of-care testing. As opposed to standard coagulation assays such as PT, aPTT, and INR studies, viscoelasticography provides a more complete assessment of coagulation in vivo, as it assesses the primary and secondary hemostatic pathways in a cell-based format." - Barash's Clinical Anesthesia 9e, Ch. 17

2. Principle and Mechanism

• A small 0.35 mL sample of whole blood is placed into a disposable cuvette maintained at 37°C
• The cuvette continuously rotates around an axis of approximately 5 degrees
• A sensor "piston" attached by a torsion wire to an electronic recorder is lowered into the blood
• An activator (most often kaolin or celite) initiates clot formation
• As the fibrin-platelet plug evolves, the piston becomes enmeshed within the clot, transferring rotation of the cuvette to the piston, torsion wire, and electronic recorder
• The mechanical resistance is translated into an electronic waveform subject to quantitative analysis

• Measures movement of a meniscus formed by whole blood in a microfluidics chamber
• Using frequencies from 20-500 Hz, the meniscus is vibrated; as a clot forms, clot-strength-specific resonance frequencies are detected by a photodetector and converted into TEG-equivalent units

3. The TEG Tracing and Parameters

Diagram 1: Standard TEG Parameters (from Sabiston/Barash framework)

Diagram 2: TEG vs ROTEM Parameters Side-by-Side (Barash Fig. 17-5)

TEG Parameters - Normal Values and Meaning

"R value (reaction time) measures time to initial clot formation. Maximum amplitude provides a measure of clot strength and may be decreased by either qualitative or quantitative platelet dysfunction or decreased fibrinogen concentration. The α angle and K values measure rate of clot formation..." - Miller's Anesthesia 10e, Ch. 46

"VHA tracings typically represent four phases of clot kinetics: initiation, propagation, clot strength, and fibrinolysis. Platelets account for 70-80% of the peak resistance curve." - Barash's Clinical Anesthesia 9e, Ch. 53

4. Actual TEG Tracings from Miller's (Fig. 46.5)

5. Typical TEG Patterns in Common Conditions (Morgan & Mikhail Fig. 33-7)

6. TEG vs ROTEM - Key Differences

"TEG provides results in terms of R = reaction time and K = clot formation kinetics, α-angle = tangential angle to midline, MA = maximum amplitude indicating clot strength, and LY30 = percent lysis at 30 minutes. ROTEM measures similar metrics with different labels including CT = clot time, CFT = clot formation time, MCF = maximum clot formation, and CLI30 = clot lysis index at 30 minutes." - Barash's Clinical Anesthesia 9e, Ch. 17, Fig. 17-5

7. TEG-Guided Transfusion Algorithm - Flowchart

         BLEEDING PATIENT WITH SUSPECTED COAGULOPATHY
                            │
               Obtain TEG (citrated whole blood)
               Add kaolin activator → run at 37°C
               Actionable results in 5-10 minutes
                            │
            ┌───────────────┼──────────────────┐
            │               │                  │
        R > 10 min    K↑ / α < 53°         MA < 50 mm
        (prolonged)   (fibrinogen           (low platelet
            │          deficiency)           function)
            │               │                  │
          Give FFP    Give Cryoprecipitate   Platelet
          10-15 mL/kg  or Fibrinogen          transfusion
          or PCC        concentrate           or DDAVP
                            │
                   LY30 > 8% OR EPL > 15%?
                            │
                    YES ────┴──── NO
                     │             │
             Tranexamic acid    Observe
             (TXA) 15 mg/kg     Monitor
             Aminocaproic acid
                     │
              Reassess TEG after each intervention

8. CCT vs VHA - Comparison Table (Barash Table 53-3)

9. Clinical Applications in Anaesthesia

Cardiac Surgery

"Many TEG-guided and ROTEM-guided algorithms have been studied and shown to reduce blood product use effectively in cardiac surgery-related hemorrhage." - Miller's Anesthesia 10e, Ch. 46

• Identifies residual heparin effect post-CPB
• Differentiates surgical bleeding from coagulopathic bleeding
• Detects excess fibrinolysis during bypass
• Some centers routinely use TEG to identify causes of bleeding after CPB (Morgan & Mikhail 7e)

Trauma / Massive Hemorrhage

"TEG and ROTEM identify the specific deficiencies, freeing the practitioner from reliance solely on the 1:1:1 transfusion ratio DCR approach. Both TEG and ROTEM assess the rate of clot formation and clot stability, reflecting the interactions between the coagulation cascades, platelets, and the fibrinolytic system." - Morgan & Mikhail 7e, Ch. 39

• Detects trauma-induced coagulopathy (TIC) early
• VHA can identify both hyperfibrinolysis (early TIC) and fibrinolytic shutdown (late TIC)
• CCT cannot reliably identify hyperfibrinolysis; VHA can
• Clot amplitude <35mm at 5 min on ROTEM predicts need for massive transfusion (detection rate 77%)

Liver Disease / Transplantation

"TEG, ROTEM, and Sonoclot are the optimal methods of demonstrating the global state of the coagulation system at a specific moment in time in any patient with liver disease. A patient with an INR of 3, for example, may also have anticoagulant factors so reduced that the patient is in a hypercoagulable state." - Morgan & Mikhail 7e, Ch. 33

• INR only examines the procoagulant side; VHA reveals the full picture
• Detects real-time fibrinolysis during reperfusion
• Prevents over-transfusion in patients with apparent but balanced coagulopathy

Obstetric Anaesthesia

"At term gestation, TEG analysis reflects a hypercoagulable state with decreased time to start of clot formation (R), decreased time to specified clot strength (K), increased rate of clot formation (α), and increased clot strength (MA)." - Miller's Anesthesia 10e, Ch. 58, Table 58.4

• Guides management of PPH
• Physiological pregnancy TEG: ↓R, ↓K, ↑α, ↑MA (changes begin in 1st trimester)

10. Limitations of TEG

• Does not assess primary hemostasis (platelet adhesion, vWF-vessel wall interaction)
• Unreliable for patients on anticoagulants (Warfarin, DOACs) or antiplatelet therapy
• Susceptible to vibration artifacts (addressed in newer cartridge-based devices)
• Requires frequent calibration (1st generation devices)
• Lack of specificity with abnormal findings; qualitative interpretation challenges
• Results not interchangeable between TEG and ROTEM platforms
• ITACTIC trial (cited in Barash 9e): most recent multicenter RCT - no difference in mortality compared to CCT-guided resuscitation (though criticised for low TIC prevalence in study population)

Key Points Summary (Memory Aid: R-K-Alpha-MA-LY)

• Miller's Anesthesia, 10e - Ch. 46 (Viscoelastic Measures of Coagulation, p. 6747-6751), Ch. 58 (Table 58.4), Ch. 66 (Trauma)
• Barash, Cullen & Stoelting's Clinical Anesthesia, 9e - Ch. 17 (Viscoelastic Testing, p. 1278), Ch. 53 (VHA in Trauma, p. 4522-4524, Table 53-3)
• Morgan & Mikhail's Clinical Anaesthesiology, 7e - Ch. 33 (Point-of-Care Viscoelastic Coagulation Monitoring, Fig. 33-7), Ch. 39 (TEG in Trauma, Fig. 39-5)