6.3 Point-of-Care Testing, TEG, Intra-Aortic Balloon Pump & Autologous Blood Salvage

6.3 Point-of-Care Testing, TEG & Autologous Blood Salvage

Major surgery and trauma present severe challenges to hemostatic equilibrium. The Certified Anesthesia Technologist (Cer.A.T.T.) operates sophisticated point-of-care diagnostic instrumentation and intraoperative autotransfusion devices. Mastery of Activated Clotting Time (ACT), viscoelastic whole blood analysis (TEG/ROTEM), and autologous red cell salvage mechanics is essential for optimizing blood conservation and guiding goal-directed resuscitation.

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Point-of-Care Testing (POCT) & Anticoagulation Surveillance

Point-of-Care Testing refers to analytical diagnostic testing conducted at or near the site of patient care. In the operating room, POCT eliminates central laboratory turnaround delays, providing rapid physiological results (within 60 to 120 seconds) that guide immediate clinical interventions.

Activated Clotting Time (ACT)

Activated Clotting Time is the intraoperative standard for monitoring unfractionated heparin anticoagulation during cardiac and vascular surgery:

• Biophysical Principle: Fresh whole blood (typically 1.0 to 2.0 mL) is drawn into a dedicated cartridge or test tube pre-warmed to 37°C containing a contact activator—either kaolin (hydrated aluminum silicate) or celite (diatomaceous earth). The activator triggers the intrinsic and common coagulation pathways via Factor XII (Hageman factor) activation. An automated mechanical plunger, oscillating wire, or magnetic flag detects the moment of fibrin clot formation, recording elapsed time in seconds.
• Clinical ACT Reference Ranges & Target Thresholds:
  • Baseline Normal (Un-anticoagulated): 80 to 120 seconds.
  • Vascular Surgery Target: 200 to 250 seconds (standard systemic heparin bolus of 50 to 100 units/kg prior to arterial cross-clamping for carotid endarterectomy, abdominal aortic aneurysm repair, or peripheral vascular bypass).
  • Cardiopulmonary Bypass (CPB) Target: >400 to 480 seconds (high-dose systemic heparin bolus of 300 to 400 units/kg prior to aortic and right atrial cannulation). Bypass is not started until the institutional ACT target is reached, because inadequate anticoagulation on the circuit's synthetic surfaces risks circuit thrombosis and consumptive coagulopathy.

Heparin Resistance Protocol & Antithrombin III Deficiency

• Mechanism of Heparin: Unfractionated heparin is an indirect anticoagulant. It does not inhibit coagulation factors directly; rather, it binds to Antithrombin III (AT-III), inducing a conformational change that amplifies AT-III's intrinsic inhibitory activity against thrombin (Factor IIa) and Factor Xa by 1,000-fold.
• Definition of Heparin Resistance: A clinical failure to achieve the target ACT (>400 to 480 seconds) despite administering an adequate initial heparin dose (300 to 400 units/kg), followed by a supplemental heparin bolus (100 to 200 units/kg).
• Etiology: The most common etiology is Antithrombin III (AT-III) deficiency. This can be congenital, but is overwhelmingly acquired in surgical patients due to prolonged preoperative intravenous heparin infusions (which downregulate circulating AT-III levels), liver disease (decreased synthesis), nephrotic syndrome (urinary loss), or sepsis.
• Definitive Treatment: When heparin resistance is diagnosed, administering additional heparin is futile because there is insufficient circulating AT-III for heparin to bind. The patient requires exogenous replenishment of Antithrombin III:
  1. Purified Human Antithrombin III Concentrate (Thrombate III): First-line therapy; delivers concentrated antithrombin (dosed by the provider) with little added volume.
  2. Fresh Frozen Plasma (FFP): Second-line therapy; 2 to 4 units of FFP provides endogenous AT-III when purified concentrate is unavailable.

Portable Blood Gas & Electrolyte Analyzers (i-STAT, ABL90)

Handheld and benchtop analyzers utilize electrochemical biosensors to measure whole blood pH, PaCO2, PaO2, Na+, K+, ionized calcium (iCa2+), glucose, lactate, and hematocrit:

• Pre-Analytical Error Prevention:
  • Anticoagulant: Blood must be drawn into a calcium-titrated balanced lithium heparin syringe. Using standard sodium heparin liquid syringes dilutes the sample and artifactually lowers ionized calcium and potassium.
  • Air Bubbles: All microscopic air bubbles must be expelled from the syringe within 5 seconds of collection. Room air contains a PO2 of approximately 150 mmHg and PCO2 near 0 mmHg; residual bubbles cause gas diffusion that falsely elevates measured PaO2 and falsely depresses PaCO2.
  • Sample Mixing: The syringe must be gently rolled between palms and inverted 10 times to resuspend erythrocytes; vigorous shaking causes mechanical shear hemolysis that falsely spikes potassium (K+).

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Glucometers & Hemoglobin Photometers

The ASATT content outline lists glucometers and hemoglobin/hematocrit analyzers among point-of-care equipment, and the ASATT Scope of Practice names glucometry and HemoCue testing as functions preferably performed by Certified Anesthesia Technologists.

• Glucometers: Test strips use glucose oxidase or glucose dehydrogenase chemistry. Accuracy falls with extreme hematocrit values, poor peripheral perfusion, and some interfering substances; the FDA has warned that certain glucose dehydrogenase (GDH-PQQ) strips read falsely high in patients receiving maltose- or icodextrin-containing products. Confirm unexpected values with a laboratory or blood gas analyzer.
• Hemoglobin photometers (e.g., HemoCue): A small microcuvette draws a precise blood volume and the analyzer reads hemoglobin photometrically within about a minute. Fill the cuvette in one continuous motion without air bubbles, wipe excess blood from the outside, and avoid squeezing a fingertip, which dilutes the sample with tissue fluid.
• Quality control: Even CLIA-waived tests require following the manufacturer's instructions, including scheduled control testing, operator training, and documentation; results feed directly into transfusion and insulin decisions.

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Viscoelastic Whole Blood Analysis: TEG and ROTEM

Standard laboratory coagulation tests (PT, INR, aPTT, fibrinogen) are executed on centrifuged, platelet-poor plasma at a static 37°C. They measure only the initial seconds of fibrin formation, offering zero data regarding platelet function, dynamic clot strength, or fibrinolysis. Viscoelastic testing evaluates the complete mechanical lifecycle of a whole blood clot.

Instrumentation Mechanics: TEG vs. ROTEM

• Thromboelastography (TEG 5000): A heated cylindrical cup (37°C) containing 360 μL of whole blood oscillates through an arc of 4°45' every 10 seconds. A stationary pin is suspended inside the cup by a delicate torsion wire. As blood coagulates, fibrin-platelet strands link the rotating cup to the stationary pin, transmitting torque to the pin. An electromechanical transducer converts pin displacement into a continuous graphic amplitude tracing.
• Rotational Thromboelastometry (ROTEM): In ROTEM, the cup is stationary, and the pin oscillates back and forth. Clot development impedes pin rotation, which is measured by an optical sensor.

THROMBOELASTOGRAPHY (TEG) WAVEFORM & PARAMETERS:

  Amplitude (mm)
       ^
   +35 |               /-------------------------\   <- Maximum Amplitude (MA)
       |              /       :                   \     (Platelets 80% + Fibrinogen 20%)
       |             /        :                    \
       |            /         :                     \
     0 +------+----+----------+----------------------+-------> Time (min)
       |<-R-->|<-K->|                                |
       |      |     |                                +-- LY30 (% clot lysis
       |      |     +-- Alpha (α) Angle                  at 30 min post-MA)
       |      |         (Clot Growth Rate)
       |      +-- K-time (Fibrinogen Kinetics)
       +-- R-time (Clot Initiation - Clotting Factors)

TEG Parameters & Goal-Directed Transfusion Algorithms

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Intra-Aortic Balloon Pump (IABP)

The ASATT content outline lists the intra-aortic balloon pump (IABP) as adjunct equipment, and the ASATT Scope of Practice names it among the devices ASATT prefers a Certified Anesthesia Technologist to assist with.

• Purpose: Counterpulsation support for a failing left ventricle, for example in cardiogenic shock, refractory myocardial ischemia, or difficult separation from cardiopulmonary bypass.
• Placement: A catheter-mounted balloon is usually inserted through a femoral artery and positioned in the descending thoracic aorta, with the tip just distal to the left subclavian artery and the balloon above the renal arteries. Balloon volume (commonly 30 to 50 mL) is chosen by patient height.
• Driving gas: Helium, because its low density allows rapid inflation and deflation and it dissolves in blood if the balloon ruptures.
• Timing:
  • Inflation at the start of diastole, timed to the dicrotic notch of the arterial waveform, produces diastolic augmentation and raises coronary perfusion pressure.
  • Deflation just before systole, before the aortic valve opens, lowers aortic end-diastolic pressure, which reduces afterload and myocardial oxygen demand.
  • The console triggers from the ECG R wave or the arterial pressure waveform. Support ratios of 1:1, 1:2, or 1:3 are used as the patient is weaned.

Early inflation and late deflation are the most harmful timing errors.

• Contraindications: Significant aortic regurgitation, aortic dissection, and severe aortoiliac disease.
• Complications and troubleshooting: Limb ischemia distal to the insertion site, balloon malposition that blocks the left subclavian or renal arteries, thrombocytopenia, and balloon rupture. Blood or brown flecks in the helium tubing signal rupture: stop pumping and notify the provider immediately, because the catheter must be removed promptly.

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Autologous Blood Salvage (Cell Saver) Technology

Autologous cell salvage is an operative blood conservation strategy that recovers shed blood from the surgical field, cleanses and concentrates the erythrocytes, and reinfuses them into the patient.

Clinical Indications

• Anticipated surgical blood loss >1,000 mL or >20% of estimated blood volume.
• Complex cardiac, aortic, major vascular, orthopedic revision, and spine fusion surgeries.
• Patients with rare red blood cell antibodies or religious objections to allogeneic transfusion (e.g., Jehovah's Witnesses who accept closed-circuit continuous autotransfusion).

AUTOLOGOUS CELL SALVAGE PROCESSING CYCLE:

[Surgical Field] --(Suction Wand + Anticoagulant: Heparin/ACD-A 1:5-1:7)-->
       │
       ▼
[Cardiotomy Reservoir] (40-120 µm Gross Filter traps bone/clots)
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[Latham Centrifuge Bowl] (Spins @ 5,600 rpm: RBCs pack at perimeter; waste floats)
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[0.9% Normal Saline Wash] (500-1,000 mL washes free Hb, heparin, debris into Waste Bag)
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[Reinfusion Bag] (Packed Washed RBCs: Hct ~50-65%; few platelets or factors)

Mechanical Components & Operational Cycle

1. Dual-Lumen Suction Wand & Anticoagulant Delivery:
   • A specialized dual-lumen aspiration line delivers anticoagulant directly to the tip of the surgical suction wand, mixing with shed blood at the moment of collection.
   • Anticoagulant Solutions:
     • Heparinized Saline: 30,000 units of unfractionated heparin per 1,000 mL of 0.9% normal saline.
     • Acid Citrate Dextrose Formula A (ACD-A): Alternative anticoagulant, particularly for patients with Heparin-Induced Thrombocytopenia (HIT).
   • Mixing Ratio: Standard delivery is about 1 part anticoagulant to 5 to 7 parts blood (roughly 15 mL anticoagulant per 100 mL of blood collected), with the drip rate increased during brisk hemorrhage.
   • Aspiration Vacuum Level: Vacuum pressure must be regulated between -100 and -150 mmHg. Higher suction produces shear stress that damages red cells (hemolysis).
2. Cardiotomy Collection Reservoir: Blood passes through a 40 to 120 μm depth filter that traps bone chips, surgical cement, tissue fragments, and gross fibrin clots.
3. Centrifuge Bowl (Latham Bowl): Blood is pumped into a rotating conical centrifuge bowl spinning at 4,800 to 5,600 rpm. Centrifugal force separates blood elements by specific gravity:
   • Dense red blood cells (specific gravity 1.090) are thrown outward, packing tightly against the outer bowl wall.
   • Buffy coat (white blood cells and platelets, 1.070) and supernatant plasma (1.025) migrate to the inner radius.
4. Washing Phase: Once the bowl is filled with packed red cells, countercurrent washing begins. A minimum of 500 to 1,000 mL of 0.9% normal saline (or Plasma-Lyte) is pumped through the bottom of the spinning bowl. The saline cascades through the packed erythrocytes, washing anticoagulant, plasma-free hemoglobin, cellular stroma, and activated inflammatory mediators out through the top effluent port into a waste collection bag.
5. Emptying Phase: The centrifuge stops, and the packed, washed erythrocytes are pumped into a sterile reinfusion bag for administration.

Characteristics of Washed Autologous Red Blood Cells

• High Hematocrit: Concentrated to a hematocrit of 50% to 65%.
• Superior Biochemical Quality: Preserves normal intracellular 2,3-diphosphoglycerate (2,3-DPG) and adenosine triphosphate (ATP) levels, offering superior oxygen-carrying capacity compared to stored allogeneic bank blood.
• THE CRITICAL COAGULATION DEFICIT: Centrifugal washing removes most plasma, clotting factors (fibrinogen, factors V and VIII), and platelets. The salvaged product is essentially red cells in saline with little clotting capability. Transfusing large volumes of salvaged blood alone leads to dilutional coagulopathy, requiring concurrent administration of plasma, cryoprecipitate, and platelets guided by TEG.

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Contraindications & Critical Safety Hazards

Absolute Contraindications

1. Aspiration of Topical Hemostatic Agents:
   • Topical hemostatics (microfibrillar collagen [Avitene], oxidized regenerated cellulose [Surgicel], absorbable gelatin sponge [Gelfoam], and topical bovine/human thrombin) applied to the surgical field MUST NEVER be suctioned into the cell salvage reservoir.
   • Mechanism of Harm: These procoagulant materials can pass the reservoir filter and are not reliably removed by washing. If reinfused, they can activate coagulation systemically and have been associated with disseminated intravascular coagulation (DIC).
   • Action: The technologist must instruct the surgical scrub and surgeon to divert suction to regular operating room wall waste suction whenever topical hemostatics are utilized.
2. Pneumatic Pressure Infusion of Unpurged Reinfusion Bags:
   • FATAL AIR EMBOLISM HAZARD: Autologous blood reinfusion bags contain variable quantities of air. The reinfusion bag must NEVER be placed inside a pressurized pneumatic cuff while connected to the patient.
   • If pressure is applied to an unpurged bag, the air is driven into the patient's venous system as soon as the blood empties, which can cause a massive, fatal air embolism.
   • If rapid reinfusion is required, air must be completely aspirated from the bag using a syringe, or gravity flow must be utilized.
3. Toxic Chemical Irrigants:
   • Solutions that lyse cells or cause systemic toxicity if reinfused: sterile water (induces immediate hypotonic cell rupture and massive hemolysis), hydrogen peroxide, povidone-iodine (Betadine), alcohol, or topical antibiotic washes not approved for intravenous use.

Relative Contraindications

1. Bacterial / Fecal Contamination: Entry into the gastrointestinal tract with gross fecal or purulent contamination. In life-threatening hemorrhage where banked blood is unavailable, blood may be salvaged using extra washing combined with a leukocyte reduction filter (LRF) and broad-spectrum intravenous antibiotics, as the provider directs.
2. Malignant Tumor Cells: Surgical fields containing disrupted malignant neoplasms. While historically contraindicated due to fear of hematogenous metastasis, many centers now permit salvage during oncologic surgery when combined with irradiation of the salvaged blood or leukocyte depletion filters, which greatly reduce nucleated tumor cells.
3. Amniotic Fluid: Historically an absolute contraindication during Cesarean delivery due to the theoretical risk of amniotic fluid embolism (AFE). Current guidelines permit cell salvage during Cesarean hysterectomy or postpartum hemorrhage; initial amniotic fluid is scavenged to wall waste, and salvaged blood is reinfused through a leukocyte depletion filter.