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IV Fluids - Miller's Anesthesia (10e)

1. Classification of IV Fluids

Crystalloids

Colloids

• Albumin (4%): Reasonable choice for volume expansion; 4% solution is hypo-osmolar (274 mOsm/L). In the SAFE trial subset of severe TBI patients, albumin was associated with increased mortality, though this finding has been questioned due to randomization imbalances. Potentially beneficial in subarachnoid hemorrhage (SAH).
• Hydroxyethyl Starches (HES): Interfere with platelets and the factor VIII complex in addition to causing dilutional reduction of coagulation factors. Effects proportional to molecular weight and hydroxyethyl substitution ratio. Should be used cautiously; respect manufacturer dosage limits. Concerns about adverse renal effects in critical care settings have made many clinicians reluctant to use these.
• Dextrans: Generally avoided due to effects on platelet function.

Hypertonic Saline (HS)

• Draws fluid into the vascular space from the interstitium, enhancing volume restoration relative to an equivalent volume of isotonic solution.
• Studied extensively in hemorrhagic shock resuscitation - results in trauma patients are inconclusive overall.
• Greatest apparent benefit in polytrauma with concurrent TBI - improved neurologic status demonstrated in some studies.
• Commonly used as an osmotic agent to manage raised ICP. In one systematic review of 13 studies (593 patients), HS was associated with decreased all-cause mortality vs. mannitol.
• Neurocritical Care Society guidelines support hyperosmolar therapy for ICP reduction in TBI, SAH, ischemic stroke, and ICH - though neurologic outcomes are not clearly affected.

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2. Principles of Fluid Selection

For Neurosurgery

1. Maintain normovolemia - to support normal MAP
2. Avoid reduction of serum osmolarity - free water lowers serum osmolarity and causes cerebral edema in both normal and abnormal brain

• Normal saline and balanced salt solutions (LR, Plasma-Lyte) are most commonly used intraoperatively.
• In large-volume administration (e.g., massive trauma, aneurysm rupture), the authors recommend alternating LR and normal saline liter-by-liter to balance the risks of both.
• For crystalloid vs. colloid: reducing colloid oncotic pressure (COP) produces only very small transcapillary gradients compared to osmolarity changes. For most elective craniotomies, colloid is not needed. In massive resuscitation, a combination of isotonic crystalloid and colloid may be appropriate.

For Trauma / Hemorrhagic Shock

• Isotonic crystalloids (NS, LR, Plasma-Lyte) are the initial resuscitative fluids.
• Damage Control Resuscitation (DCR): The modern paradigm - limit crystalloids, favor blood component therapy (RBCs + plasma + platelets in balanced ratios). DCR has been associated with improved outcomes for over two decades.
• Early administration of plasma reduces risk of dilutional coagulopathy.
• RBCs remain the mainstay of treatment for hemorrhagic shock (hematocrit ~50-60% per unit; restores O2-carrying capacity as effectively as colloids).

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3. Perioperative Fluid Quantity

Traditional (Weight-Based) Approach

• Based on the 4-2-1 rule (Holliday-Segar) for calculating maintenance fluid needs.
• Crystalloid used to replace blood loss in a 3:1 ratio to account for redistribution to extravascular compartment.
• Much of the physiologic basis has been questioned.

Liberal vs. Restrictive Fluids

• Giving >3,500-5,000 mL of crystalloid intraoperatively (when not targeting physiologic endpoints) is associated with: weight gain, cardiopulmonary dysfunction, impaired wound healing, delayed GI recovery, and longer hospital stay.
• The RELIEF trial (3,000 patients, major abdominal surgery) compared restrictive (median 3.7 L) vs. liberal (median 6.1 L) fluid regimens - no difference in disability-free survival at 1 year, but restrictive group had higher rates of surgical site infection (16.5% vs. 13.6%) and renal replacement therapy (0.9% vs. 0.3%). This warns against excessive restriction.
• A post-operative weight gain of approximately +1.5 kg is a useful benchmark.

Goal-Directed Therapy (GDT)

• Measures key hemodynamic variables (cardiac output, O2 delivery) and uses fluids +/- inotropes/vasopressors to optimize tissue perfusion.
• Targets physiologic endpoints (cardiac index >4.5 L/min/m², DO2I >600 mL/min/m²) rather than giving preset volumes.
• Evidence supports GDT reducing postoperative morbidity in high-risk major surgery.
• Stroke volume variation (SVV) - variation in stroke volume with the respiratory cycle during positive-pressure ventilation - is a reliable predictor of decreased intravascular volume and is used to guide fluid therapy.

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4. Key Clinical Pearls

• Hyperchloremic metabolic acidosis is a known consequence of large-volume NS; clinical significance is debated, but may adversely affect renal blood flow and GFR.
• Glucose-containing fluids are generally avoided intraoperatively in neuro patients - hyperglycemia aggravates cerebral ischemia. The threshold for treatment is ~250 mg/dL, targeting <200 mg/dL.
• Temperature: RBCs are stored at 4°C and can cause hypothermia if not warmed before infusion.
• Hyperbaric environment: In hyperbaric chambers, IV fluid administration requires special pumps capable of handling pressure differentials up to 3 ATA; glass bottles should be excluded due to risk of explosive rupture during decompression.

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IV Fluids - Classification, Contents, and Indications

(Miller's Anesthesia, 10e - Theory & Viva)

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PART 1: CLASSIFICATION BY TONICITY

Viva point: Lactated Ringer's (LR) is technically slightly hypotonic (273 mOsm/L) but is used as an isotonic replacement fluid. Normal saline at 308 mOsm/L is slightly hypertonic. Plasma-Lyte at 294 mOsm/L is the most physiologically matched to plasma.

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PART 2: DETAILED CLASSIFICATION WITH CONTENTS

A. CRYSTALLOIDS

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1. Normal Saline (0.9% NaCl) - ISOTONIC

• Initial resuscitation in trauma/hemorrhagic shock
• Hypovolemia (any cause)
• Hypochloremic metabolic alkalosis (e.g., from vomiting/nasogastric losses)
• Hypercalcemia treatment (volume expansion + loop diuretics)
• Diluent for blood products (LR causes RBC clumping due to calcium content)
• Hyponatremia correction
• Replacing upper GI losses (high Cl⁻ content matches gastric secretions)

• Large volumes cause hyperchloremic metabolic acidosis (due to excess Cl⁻ lowering the strong ion difference/SID)
• Excess NaCl and water load is excreted more slowly than balanced crystalloids
• May adversely affect renal blood flow and GFR (hyperchloremia)
• Contains no potassium, no bicarbonate, no calcium

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2. Lactated Ringer's (LR) / Hartmann's Solution - MILDLY HYPOTONIC

• Most intraoperative fluid replacement (blood/third-space losses)
• Burns resuscitation (Parkland formula uses LR)
• Acute blood loss replacement
• Replacing lower GI losses (high K⁺ and HCO₃⁻ match small/large bowel secretions)
• General fluid resuscitation where large volumes needed

• Hypotonic (273 mOsm/L) - can lower serum osmolarity with very large volumes, potentially worsening cerebral edema in TBI/neurosurgery
• Contains calcium - cannot be used to dilute blood products (calcium chelates citrate anticoagulant, may cause clotting)
• Lactate metabolism may be impaired in severe liver failure
• In animal models, LR increases hepatic and intestinal apoptosis after hemorrhagic resuscitation (via reperfusion injury) - unlike whole blood or hypertonic saline

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3. Plasma-Lyte / NormosolR - ISOTONIC (BALANCED)

• Preferred balanced crystalloid in patients at risk of acidosis (hemorrhagic shock)
• When normal saline-related hyperchloremic acidosis is a concern
• General perioperative maintenance and replacement
• Suitable for patients needing large-volume crystalloid resuscitation

• pH of 7.4 - closest to plasma
• No calcium - safe to use with blood products
• Acetate and gluconate (not lactate) - metabolized peripherally, not just in the liver; safer in hepatic dysfunction
• Favorable strong ion difference (SID) - does not cause metabolic acidosis

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4. 5% Dextrose (D5W) - HYPOTONIC (effectively free water)

• Pure maintenance fluid to replace insensible losses (free water losses)
• Hypernatremia correction
• Hypoglycemia (though 10-50% dextrose preferred for frank hypoglycemia)
• Postoperative maintenance component (in combination fluids)
• Vehicle for IV drug infusions

• After glucose is metabolized, this is effectively free water - distributes throughout total body water (2/3 intracellular, 1/3 extracellular)
• Never use for resuscitation - no electrolytes, no intravascular volume expansion
• Can worsen cerebral edema (lowers serum osmolarity)
• Intraoperative hyperglycemia aggravates cerebral ischemia - avoided routinely in neuroanesthesia
• Can cause dilutional hyponatremia postoperatively

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5. 0.18% NaCl + 4% Dextrose ("Dextrose-Saline") - HYPOTONIC

• Pediatric maintenance fluid (traditionally)
• Part of adult postoperative maintenance (alongside isotonic fluids)
• Provides free water + minimal electrolytes for daily maintenance needs

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6. Hypertonic Saline (3%, 7.5% NaCl) - HYPERTONIC

• Severe symptomatic hyponatremia (3% NaCl, controlled infusion)
• Raised intracranial pressure (ICP) - draws free water from brain via osmotic gradient (superior to or equivalent to mannitol)
• Polytrauma with concurrent TBI - improved neurologic outcomes in some studies
• Hemorrhagic shock resuscitation under austere/military conditions (small volume, enhanced effect)

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B. COLLOIDS

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1. Albumin - ISOTONIC (4%) or HYPERTONIC (20-25%)

• Intravascular volume expansion when crystalloids alone are inadequate
• Spontaneous bacterial peritonitis (SBP) in cirrhosis (prevents hepatorenal syndrome)
• Large-volume paracentesis replacement
• Hypoalbuminemia with symptomatic edema
• Subarachnoid hemorrhage (SAH) - potential neuroprotective benefit
• Burns (delayed phase, after 24h)

• The SAFE trial: in patients with severe TBI (GCS 3-8), 4% albumin was associated with increased mortality - but the finding is questioned due to randomization imbalances and the hypo-osmolarity of the 4% preparation
• Albumin has no albumin-specific hazard from a physiologic standpoint - if edema formation is a concern, it applies equally to all colloids (FFP, starches)
• ALIAS trial (acute stroke): albumin did not improve neurologic outcome; associated with increased CHF rates
• Most expensive of the colloid options

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2. Hydroxyethyl Starch (HES) - ISOTONIC or HYPERTONIC

• Derived from amylopectin (plant starch); available in different molecular weights (MW) and molar substitution ratios (MS)
• The higher the MW and MS, the greater the coagulopathy

• Perioperative intravascular volume expansion
• Should be avoided in sepsis/critical illness (proven AKI and mortality increase in VISEP, 6S, CHEST trials)

• Interferes with platelets and factor VIII complex (von Willebrand factor) - dilutional + direct effect
• Coagulopathy proportional to MW and degree of hydroxyethyl substitution
• Reports of neurosurgical bleeding when dosage limits exceeded or used on successive days (accumulation effect)
• Multiple RCTs (VISEP, 6S, CHEST) show increased AKI and need for renal replacement therapy in critical illness/sepsis
• Miller's: use with caution; respect manufacturer dosage limits; use additional restraint when there are other causes of coagulopathy

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3. Dextrans - HYPERTONIC

• Polysaccharide glucose polymers (Dextran 40, Dextran 70)

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4. Gelatins - ISOTONIC

• Derived from bovine collagen (Gelofusine, Haemaccel)
• Less data available compared to starches

• Shorter intravascular half-life than starches
• Less data on renal safety than starches
• Some risk of anaphylaxis (bovine origin)
• Miller's notes: limited comparative data with crystalloids; no consistent clinical benefit over crystalloids

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PART 3: INDICATIONS BY CLINICAL SCENARIO (Viva-Ready)

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PART 4: KEY VIVA CONCEPTS

• Normal saline / LR: ~75-80% goes to interstitium, ~20-25% stays intravascular
• Colloids (albumin, HES): ~80% stays intravascular
• D5W (free water): distributes across total body water - only ~8% stays intravascular

• 4 mL/kg/h for first 10 kg
• 2 mL/kg/h for next 10 kg (10-20 kg)
• 1 mL/kg/h for each kg above 20 kg

Blood Transfusion, Reactions, Massive Transfusion & Blood Conservation

Miller's Anesthesia, 10e + Recent Evidence

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PART 1: TRANSFUSION REACTIONS

Classification of Transfusion Reactions

TRANSFUSION REACTIONS
├── IMMUNE-MEDIATED
│   ├── Hemolytic (Acute / Delayed)
│   ├── TRALI
│   ├── Febrile Non-Hemolytic (FNHTR)
│   ├── Allergic (Urticarial / Anaphylactic)
│   └── TA-GvHD
└── NON-IMMUNE
    ├── TACO
    ├── Septic (Bacterial Contamination)
    ├── Citrate Toxicity
    ├── Hyperkalemia
    ├── Hypothermia
    ├── Metabolic Alkalosis
    └── Iron Overload (chronic)

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1. ACUTE HEMOLYTIC TRANSFUSION REACTION (AHTR)

• Hemoglobinuria (pink/red urine) - most common first sign
• Unexplained hypotension
• Bleeding diathesis (DIC)

• As little as 50 mL incompatible blood can exceed haptoglobin binding capacity (~100 mg Hb/100 mL plasma)
• Free Hb >100 mg/dL = red plasma
• Free Hb >150 mg/dL = hemoglobinuria
• Complement activation releases histamine and vasoactive amines

1. Acute Renal Failure - precipitation of Hb as acid hematin in distal tubule causing mechanical tubular blockage
2. DIC - complement activation triggers coagulation cascade

1. Stop the transfusion immediately
2. Maintain urine output >75-100 mL/h by:
   • IV fluids (crystalloid/mannitol)
   • Furosemide if above ineffective
3. Alkalinize the urine (sodium bicarbonate - makes Hb more soluble, prevents acid hematin precipitation)
4. Assay urine and plasma Hb concentrations
5. Check platelet count, PT, PTT, fibrinogen (screen for DIC)
6. Return unused blood to blood bank for repeat crossmatch
7. Send patient's blood and urine to blood bank
8. Prevent hypotension to maintain renal blood flow

• Direct antiglobulin test (DAT/Coombs) - shows antibody attached to transfused donor RBCs
• Serum haptoglobin (decreased), plasma Hb, urine Hb, bilirubin (increased)

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2. DELAYED HEMOLYTIC TRANSFUSION REACTION (DHTR)

• Unexplained drop in Hb post-transfusion
• Mild jaundice
• Hemoglobinuria (rarely)
• Rarely fatal

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3. TRANSFUSION-RELATED ACUTE LUNG INJURY (TRALI)

• Hit 1: Patient factors (surgery, sepsis, shock, mechanical ventilation)
• Hit 2: Donor antibodies (anti-HLA or anti-neutrophil antibodies) activating recipient neutrophils

• Plasma/whole blood from multiparous female donors (most common - reduced by male-predominant plasma donation)
• High IL-8 levels
• Liver surgery, chronic alcohol abuse, smoking
• High peak airway pressures, positive fluid balance

• Stop the transfusion
• Supportive care (oxygen, ventilatory support as for ARDS)
• Notify blood bank - quarantine all units from implicated donor
• HLA testing of patient if possible
• Recovery within 96 hours in most patients
• No specific pharmacologic therapy

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4. TRANSFUSION-ASSOCIATED CIRCULATORY OVERLOAD (TACO)

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5. FEBRILE NON-HEMOLYTIC TRANSFUSION REACTION (FNHTR)

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6. ALLERGIC REACTIONS

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7. TRANSFUSION-ASSOCIATED GRAFT-VERSUS-HOST DISEASE (TA-GvHD)

• Severely immunocompromised patients
• Recipients of directed donations from first/second-degree relatives (shared HLA haplotypes - lymphocytes not recognized/eliminated)

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8. TRANSFUSION-RELATED IMMUNOMODULATION (TRIM)

• Cancer recurrence after tumor resection
• Postoperative infections
• Virus reactivation

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9. OTHER NON-INFECTIOUS RISKS (Table 45.18)

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PART 2: MASSIVE TRANSFUSION - DEFINITION, COMPLICATIONS & MANAGEMENT

Definition

• ≥3 units RBCs in 1 hour with ongoing need
• Loss of >50% blood volume in 3 hours

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The Lethal Triad of Massive Hemorrhage

        HYPOTHERMIA
           /   \
          /     \
COAGULOPATHY --- ACIDOSIS

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Complications of Massive Transfusion

1. DILUTIONAL COAGULOPATHY

• Platelet count falls to <100 × 10⁹/L after 10-15 units of blood
• Miller's threshold: Platelet count <75 × 10⁹/L = reliable predictor of hemorrhagic diathesis from dilutional thrombocytopenia
• However: platelet counts rarely fall as low as predicted from pure dilution (splenic/bone marrow release partially compensates)
• Acute dilutional thrombocytopenia causes bleeding at a much higher platelet count than chronic thrombocytopenia (e.g., ITP)

• Fibrinogen levels fall significantly when blood is replaced with PRBCs + crystalloid (unlike whole blood replacement where fibrinogen remains stable unless DIC develops)
• Fibrinogen is critical for effective clot formation - must be monitored and supplemented early
• If PTT ≥1.5x normal with other tests normal: suggests low factors V and VIII → treat with FFP or cryoprecipitate

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2. HYPOTHERMIA

• Blood stored at 4°C - infusion of large volumes causes core temperature to fall
• Temperature <30°C: ventricular irritability and cardiac arrest
• Even small decreases in temperature significantly impair both coagulation factors and platelet function
• Shivering increases metabolic demands, worsening tissue ischemia

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3. CITRATE TOXICITY AND HYPOCALCEMIA

• Citrate (anticoagulant in stored blood) chelates ionized calcium → hypocalcemia
• Consequences: dysrhythmia, hypotension, myocardial depression
• Risk increased with: infusion rate >1 unit/10 minutes, pediatric patients, liver disease (impaired citrate metabolism), hyperventilation
• Even at these rates, ionized calcium may not fall enough to cause bleeding alone
• Note: Blood transfusions provide citrate which generates bicarbonate → may cause metabolic alkalosis post-transfusion

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4. HYPERKALEMIA

• Stored blood K⁺: 19-50 mEq/L at 21 days; 45-60 mEq/L at 42 days
• Despite high K⁺ in storage, net K⁺ gain is only ~10 mEq/L when blood loss is considered
• For clinically significant hyperkalemia: must infuse blood at ≥120 mL/min
• More common in: neonates, patients with renal failure
• Irradiated RBC units have even higher K⁺ levels

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5. ACID-BASE DISTURBANCES

• Initial state during massive hemorrhage: metabolic acidosis (lactic acidosis from hypoperfusion, citric acid in stored blood)
• Post-resuscitation: metabolic alkalosis (from citrate conversion to bicarbonate, volume replacement)
• Empirical bicarbonate is NOT indicated - should be guided by serial ABGs

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6. DISSEMINATED INTRAVASCULAR COAGULATION (DIC)

• Fibrinolytic system is simultaneously activated (tPA from damaged tissue)
• Tumor necrosis factor and endotoxins further activate coagulation

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Damage Control Resuscitation (DCR)

1. Limit crystalloids - aggressive crystalloid causes dilutional coagulopathy, hypothermia, abdominal compartment syndrome, and worsened outcomes
2. Balanced blood component therapy - RBC : FFP : Platelets in ratios approaching 1:1:1 (whole blood equivalent)
3. Permissive hypotension - until surgical hemorrhage control is achieved (avoid over-resuscitation before bleeding is controlled)
4. Hemorrhage control first - damage control surgery before full resuscitation

• Military and major trauma centers use ratio-based transfusion (RBC:FFP ~1:1 to 2:1) rather than strict laboratory thresholds
• Fresh whole blood: 1 unit equivalent to 8-10 platelet units for treating transfusion-induced coagulopathy

• Fibrinogen is the first coagulation factor to reach critically low levels during major hemorrhage
• Supplement early via cryoprecipitate or lyophilized fibrinogen concentrate

• RCT: 324 trauma patients at risk of MT
• 4-Factor Prothrombin Complex Concentrate (4F-PCC, 25 IU/kg) vs placebo, all receiving ratio-based transfusion (RBC:FFP 1:1 to 2:1)
• Result: No reduction in 24-hour blood product consumption
• Safety concern: Thromboembolic events 35% (4F-PCC) vs 24% (placebo) - relative risk 1.48, P=0.03
• Conclusion: Does NOT support systematic use of 4F-PCC in massive transfusion patients

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PART 3: BLOOD CONSERVATION STRATEGIES

A. PREOPERATIVE

• Identify and treat iron deficiency, B12/folate deficiency, or anemia of chronic disease before elective surgery
• IV iron supplementation in iron-deficient patients
• Erythropoiesis-stimulating agents (ESAs/erythropoietin) in selected patients

• Patient donates their own blood 4-6 weeks before surgery
• Largely fallen out of favor: wastage rates, cost, and not useful in emergency settings
• Still useful in complex elective cases where crossmatching is difficult (rare antibodies)

• Stop antiplatelet agents (aspirin 7-10 days, clopidogrel 5-7 days prior) when safe
• Stop anticoagulants appropriately (bridge where indicated)

• If bowel prep required: give 1-2L balanced crystalloid + K⁺ to prevent hypovolemia at induction

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B. INTRAOPERATIVE

• Blood suctioned from surgical field is processed (washed, filtered, concentrated) and reinfused
• The most effective intraoperative blood conservation technique

• Major cardiac, vascular, orthopedic, hepatic surgery
• Obstetric hemorrhage (with leukocyte depletion filter)

• Bacterial contamination of surgical field
• Malignancy (relative) - though leukocyte filters may reduce tumor cell reinfusion risk
• Amniotic fluid contamination (relative - filtered ICS now used in obstetrics)

• [PMID 40465098 - Spine Deform 2025]: Systematic review - ICS is effective for blood conservation in both pediatric and adult spinal surgery, reducing allogeneic transfusion requirements
• [PMID 35023053 - Reprod Sci 2022]: Meta-analysis - ICS in high-risk cesarean section reduces allogeneic transfusion without adverse neonatal or maternal outcomes

• Blood drawn from patient immediately before surgery
• Volume replaced with crystalloid/colloid (normovolemia maintained)
• Diluted blood remains in circulation during surgery (less Hb lost per mL bled)
• Drawn blood (with preserved platelets and clotting factors) re-infused at end of surgery
• Most effective when large blood loss is expected and preoperative Hb is high

• Controlled reduction of MAP to 50-65 mmHg to reduce surgical field bleeding
• Used in major orthopedic (hip/spine), ENT, maxillofacial surgery
• Agents: volatile anesthetics, beta-blockers, nitroprusside, nitroglycerin, remifentanil
• Contraindications: IHD, cerebrovascular disease, renal insufficiency, uncontrolled hypertension

• [PMID 40751727 - Ann Emerg Med 2026]: RCT - TXA timing critically affects mortality impact after trauma; earlier administration provides greater benefit
• [PMID 37043652 - NEJM 2023]: RCT (NEJM) - TXA to prevent obstetrical hemorrhage after cesarean delivery: reduced postpartum hemorrhage without significant safety concerns
• [PMID 35977357 - Anesth Analg 2022]: Review - TXA applications and limitations: supports use across surgical settings, with evolving evidence in non-trauma hemorrhage contexts

• Minimally invasive surgery (laparoscopic, robotic) - less blood loss
• Meticulous surgical hemostasis
• Positioning to reduce venous congestion in operative field
• Topical hemostatic agents (thrombin, fibrin glue, oxidized cellulose)
• Bone wax, electrocautery, argon beam coagulation
• Tourniquets in limb surgery

• Desmopressin (DDAVP): Releases vWF from endothelial stores; useful in platelet dysfunction (uremia, aspirin effect, type 1 vWD)
• Recombinant Factor VIIa (rFVIIa): Reserved for life-threatening uncontrolled hemorrhage unresponsive to conventional therapy (off-label in most non-hemophilia settings); high thromboembolism risk

• Use TEG/ROTEM to guide targeted blood product administration rather than empiric ratios
• Identifies specific deficiencies (fibrinogen, platelets, clotting factors, fibrinolysis) and treats them precisely
• Reduces unnecessary FFP and platelet transfusion

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C. POSTOPERATIVE

• Evidence-based threshold: Hb <7 g/dL in most patients (including critically ill)
• Higher threshold (Hb <8 g/dL) for: cardiac surgery, active cardiac disease, hemodynamically unstable patients
• [PMID 42115060 - Br J Anaesth 2026]: Systematic review of 40 national PBM guidelines - most guidelines define restrictive transfusion as Hb threshold of 7 g/dL (22 guidelines) or lower (9 guidelines). However, national guidelines remain fragmented; comprehensive multidisciplinary coordination is lacking globally.
• [PMID 38936555 - J Clin Epidemiol 2024]: Meta-analysis - important methodological warning: transfusion strategy trials excluding patients transfused outside the study period are more likely to show a trend favoring restrictive strategies - potential selection bias in the existing literature.

1. Optimization of erythropoiesis (preoperative anemia treatment)
2. Minimization of blood loss (intraoperative conservation)
3. Rational use of blood products with appropriate thresholds

• Recombinant erythropoietin with IV iron in surgical patients expected to need transfusion
• Mainly used preoperatively (4-6 weeks before surgery)
• Risks: hypertension, thromboembolism

• Use pediatric sampling tubes where possible
• Batch lab tests to reduce frequency
• Point-of-care testing reduces volume drawn
• (Noted as the area of greatest variability between national guidelines in the 2026 PBM systematic review)

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PART 4: KEY VIVA POINTS

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Blood Conservation Strategies

Miller's Anesthesia, 10e + Recent Evidence (2022-2026)

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OVERVIEW: THE THREE PILLARS OF PATIENT BLOOD MANAGEMENT (PBM)

PATIENT BLOOD MANAGEMENT
         │
    ┌────┴──────┐
    │           │
PILLAR 1    PILLAR 2      PILLAR 3
Optimize    Minimize      Rational use of
Erythro-    Blood         Transfusion &
poiesis     Loss          Tolerance of Anemia

[PMID 42115060 - Br J Anaesth 2026]: Systematic review of 40 national/international PBM guidelines found most agree on a restrictive Hb threshold of 7 g/dL (22/40 guidelines) or lower (9/40 guidelines). Greatest variability: strategies to reduce diagnostic blood loss. National standardisation remains fragmented globally - comprehensive multidisciplinary coordination is lacking. (Dreher et al., Br J Anaesth 2026)

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PART 1: AUTOLOGOUS BLOOD TRANSFUSION (Miller's Ch 45)

1. Preoperative Autologous Donation (PAD)
2. Acute Normovolemic Hemodilution (ANH)
3. Intraoperative / Postoperative Blood Salvage (Cell Salvage)

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1. PREOPERATIVE AUTOLOGOUS DONATION (PAD)

• Hb must be ≥11 g/dL before each donation
• Repeated donations separated by ≥1 week
• Last donation ≥72 hours before surgery (to restore intravascular volume before anaesthesia)
• Note: Red cell mass is NOT restored in 72 hours; full 80% RBC mass recovery takes 25 to >168 days (HEIRS study)

1. Evidence of infection / risk of bacteremia
2. Aortic stenosis (scheduled surgical correction)
3. Unstable angina
4. Active seizure disorder
5. MI or CVA within 6 months of donation
6. High-grade congenital or acquired cardiac lesions

• Blood safety has improved dramatically (HIV/hepatitis C risk from allogeneic blood now very low), so the safety advantage of PAD over allogeneic blood has narrowed considerably
• A meta-analysis showed PAD decreased absolute risk of receiving allogeneic blood by 44%, but the risk of receiving transfusion from any source (autologous or allogeneic) increased by 24% - questioning its use as a true transfusion-sparing practice
• PAD associated with ~12x the post-donation hospitalization rate compared with allogeneic donors (American Red Cross study)
• The proportion of autologous blood collected has significantly decreased since the mid-1990s peak
• Patients undergoing PAD have Hb that is on average 1.1 g/dL lower than non-donors at time of surgery

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2. ACUTE NORMOVOLEMIC HEMODILUTION (ANH)

• The blood that is shed during surgery has a lower Hct (diluted blood), so fewer RBCs are lost per mL of surgical blood loss
• The sequestered whole blood (with intact platelets, clotting factors) is reinfused later - at the end of surgery or when hemostasis is needed

• Blood collected in standard bags with citrate anticoagulant
• Stored at room temperature up to 8 hours or 4°C up to 24 hours
• Reinfused in reverse order of collection (last bag first) - except for the first bag which has the highest Hb, platelets, and clotting factors, and is reinfused when hemostasis is most critical
• Agitation of stored blood to preserve platelets: no formal recommendation required; TEG shows no difference between agitated and stationary storage

• Minimal ANH (removing <15% blood volume): only ~100 mL RBCs saved (~0.5 units PRBCs) - marginal benefit
• ANH targeting post-dilutional Hct of 28% with 2600 mL blood loss: saves ~215 mL RBCs compared to no prior hemodilution
• Larger volumes of hemodilution provide the largest RBC-mass savings

• Meta-analysis of 29 RCTs (1252 ANH patients, 1187 controls) in cardiac surgery: ANH patients received ¾ fewer allogeneic blood units than controls; less postoperative blood cell mass loss (mean loss 388 mL ANH vs 450 mL controls)
• ANH also reduces platelet and plasma requirements because whole blood removal preserves these components
• In cardiac surgery: ANH may protect sequestered blood from cardiopulmonary bypass-induced platelet dysfunction
• Evidence in: hip replacement, hepatic resections, vascular surgery, cardiac surgery, orthognathic surgery

• 30 RCTs, 4,473 patients (cardiac surgery)
• ANH: 27% relative reduction in incidence of allogeneic blood transfusion (RR 0.73, 95% CI 0.60-0.88, p=0.0008)
• Reduced allogeneic RBC volume transfused by 0.75 units (p=0.020)
• Reduced FFP requirements (MD -0.21 units, p=0.025)
• Reduced total blood loss by 64 mL (p=0.012)
• No significant differences in chest tube drainage, surgical revision, or stroke
• Conclusion: ANH is an effective blood conservation strategy in cardiac surgery - reduces allogeneic RBC and FFP requirements

• Severe anemia (pre-existing low Hb)
• Significant cardiovascular disease limiting tolerance of diluted Hb
• Severe pulmonary disease
• Renal insufficiency limiting fluid management

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3. INTRAOPERATIVE CELL SALVAGE (ICS) / AUTOTRANSFUSION

1. Anticoagulant (heparin or citrate) added to the tip of suction catheter
2. Blood collected in reservoir until enough accumulates (500-700 mL needed for processing)
3. Centrifugation separates lower-density plasma from higher-density RBCs
4. Produces 225-250 mL of saline-suspended PRBCs with Hct 50-60%
5. Microaggregate filters (40 µm) used during reinfusion
6. High-capacity systems can provide the equivalent of 12 units/hour in a massively bleeding patient

• 2,3-DPG levels: near-normal in salvaged blood vs up to 90% reduction in stored allogeneic blood
• P50 similar to fresh venous blood; higher than 2-week-old banked blood - better oxygen offloading
• RBC deformability improved compared with PRBCs

• Room temperature: up to 4 hours
• 1°C-6°C: up to 24 hours (if refrigeration begun within 4 hours of collection)
• Must be labeled: patient name, ID, date/time, "For Autologous Use Only"

• Meta-analysis of 75 studies: Cell salvage reduced need for allogeneic transfusion in adult elective surgeries by 38%, saving on average 0.68 units of banked blood. Greatest benefit in orthopedic and cardiac surgery.

• Hypervolemia
• Bacterial contamination (rare clinically; positive cultures sometimes seen)
• Hypotension
• Air embolism (serious risk - mitigated with modern systems preventing direct connection to IV tubing)
• Non-immune and immune hemolysis (from high suction pressure, turbulence, roller pumps)
• Free hemoglobin: nephrotoxic and causes arteriolar vasoconstriction via NO scavenging
• DIC (with large volumes of unwashed shed blood)
• Coagulopathies (shed blood has undergone varying degrees of fibrinolysis)

• Vacuum should not exceed 150 mmHg to minimize hemolysis (higher may occasionally be needed in rapid bleeding)
• Washed salvage preferred over unwashed
• Use leukocyte depletion filters to reduce bacterial and particulate contamination

• Traditionally controversial (amniotic fluid contamination concerns); now widely accepted with leukocyte depletion filters
• [PMID 39704317 - Cochrane 2024]: Cell salvage for PPH - 6 RCTs, 3,476 women (all cesarean) - low-certainty evidence suggests ICS may reduce allogeneic transfusion risk at cesarean (RR 0.45, 95% CI 0.15-1.33); absolute transfusion risk was low (4% without vs 2% with ICS). Evidence remains uncertain for transfusion-related adverse reactions. (Dey et al., Cochrane 2024)
• [PMID 38109996 - AJOG MFM 2024]: Meta-analysis of RCTs - ICS at cesarean delivery reduces allogeneic transfusion without adverse neonatal or maternal outcomes

• [PMID 40465098 - Spine Deform 2025]: Systematic review - ICS effectively reduces allogeneic transfusion requirements in both pediatric and adult spinal surgery. Supports routine use in high blood loss spine procedures.

• [PMID 37777212 - Bone Joint J 2023]: Meta-analysis in revision hip arthroplasty - ICS reduces allogeneic transfusion requirements

• Absolute: Bacterial contamination of surgical field
• Relative: Active malignancy (risk of tumor cell reinfusion - leukocyte filters may reduce but not eliminate), bowel perforation, certain amniotic fluid exposures without filtering

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PART 2: PHARMACOLOGIC BLOOD CONSERVATION

1. ANTIFIBRINOLYTIC AGENTS

A. Tranexamic Acid (TXA)

• Trauma: 1g IV over 10 min (loading), then 1g over 8 hours - must be given within 3 hours of injury (CRASH-2 protocol)
• Surgery: variable; typically 10-15 mg/kg IV pre-incision ± infusion; topical use in joint arthroplasty

• CRASH-2 (2010): TXA reduces all-cause mortality and death from hemorrhage in trauma patients when given within 3 hours of injury. Trend toward harm if given >3 hours.
• [PMID 40751727 - Ann Emerg Med 2026]: RCT - TXA timing critically determines mortality impact after trauma. Earlier administration provides greater benefit; the window of benefit is time-sensitive.
• [PMID 37043652 - NEJM 2023]: RCT - TXA to prevent obstetrical hemorrhage after cesarean delivery: reduced PPH without significant safety concerns (Pacheco et al. for NEJM/C-STAT study)
• [PMID 36800489 - Cochrane 2023]: Network meta-analysis in major vascular surgery - TXA may have no effect on thromboembolic risk (RR 1.10, 95% CI 0.88-1.36) though evidence is low-certainty; topical hemostatic agents (fibrin/thrombin sealants) also evaluated

B. Epsilon-Aminocaproic Acid (EACA)

• Same mechanism as TXA (lysine analogue)
• Less potent, less studied; less commonly used than TXA
• IV infusion; mainly used in cardiac surgery

C. Aprotinin

• Serine protease inhibitor with broad antifibrinolytic effects PLUS direct platelet protection
• Withdrawn from markets after the BART trial showed increased mortality/renal failure
• Available in some countries for cardiac surgery under restricted use
• Higher antifibrinolytic potency than TXA/EACA

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2. DESMOPRESSIN (DDAVP)

• Uremia-related platelet dysfunction
• Mild platelet dysfunction from aspirin/NSAIDs
• Type 1 von Willebrand disease
• Hemophilia A (mild-moderate)
• Liver disease-associated platelet dysfunction

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3. RECOMBINANT FACTOR VIIa (rFVIIa / NovoSeven)

• Hemophilia A or B with inhibitors
• Congenital Factor VII deficiency
• Off-label: Life-threatening, uncontrolled surgical/traumatic hemorrhage unresponsive to all other measures

• High cost
• Significant thromboembolic risk (arterial and venous)
• Off-label use in non-hemophilia patients remains controversial
• Miller's: reserved for situations where transfusion is not an option or as a bridge

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4. HEMOGLOBIN-BASED OXYGEN CARRIERS (HBOCs)

• Severe arteriolar vasoconstriction from NO scavenging by free Hb
• Nephrotoxicity, cardiac toxicity, hypertension
• Meta-analysis of 16 trials (5 products, 3,711 patients): significantly increased risk of MI and death with HBOCs vs controls; 30% increased death risk; 3x MI risk

• Clinical trials have largely failed due to adverse events
• HBOC-201 (Hemopure): Available under FDA Expanded Access (compassionate use)
• Reserved for: Jehovah's Witnesses refusing transfusion, unavailable compatible blood, bridge to hemostatic intervention
• NOT approved for routine clinical use

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PART 3: PREOPERATIVE OPTIMIZATION (Pillar 1)

Anemia Detection and Treatment

1. Screen: CBC + iron studies (ferritin, transferrin saturation) ≥4-6 weeks before elective major surgery
2. Diagnose the cause: iron deficiency, B12/folate deficiency, anemia of chronic disease, chronic kidney disease
3. Treat:
   • Oral iron: First line for iron deficiency without urgency; cheap but slow (4-8 weeks to optimize)
   • IV iron: Faster response; preferred when surgery <4 weeks away or oral iron not tolerated
   • Erythropoiesis-stimulating agents (ESAs/EPO): Combined with IV iron for patients with anemia of chronic disease, renal anemia, or anticipated major blood loss
   • B12/folate: Replace if deficient

• [PMID 36631901 - J Cardiothorac Surg 2023]: Meta-analysis - IV iron for preoperative anemia in cardiac surgery: significantly increases Hb and reduces transfusion requirements
• [PMID 38241670 - Anesth Analg 2024]: Systematic review - even non-anemic iron deficiency is associated with worse outcomes in cardiac surgery; supports treating iron deficiency even before frank anemia develops
• [PMID 41255283 - Int J Surg 2026]: Bayesian network meta-analysis for preoperative anemia in cardiac surgery: evaluates comparative effectiveness of IV iron, EPO, IV iron + EPO, and PAD - IV iron + EPO combination most effective

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PART 4: INTRAOPERATIVE BLOOD CONSERVATION - SURGICAL & ANESTHETIC TECHNIQUES

1. GOAL-DIRECTED HEMOSTATIC THERAPY

• Use TEG (thromboelastography) or ROTEM (rotational thromboelastometry) rather than conventional lab tests (PT/PTT/platelets) to guide transfusion
• Identifies specific hemostatic deficits: clot initiation, clot strength, platelet contribution, fibrinolysis
• Enables targeted component therapy vs. empirical ratios
• Miller's: growing use of point-of-care viscoelastic tests is becoming "more pragmatic" for guiding hemostatic therapy

2. DELIBERATE HYPOTENSIVE ANESTHESIA

• Controlled reduction of MAP to 50-65 mmHg to reduce surgical bleeding
• Used in: major spine surgery, hip arthroplasty, ENT/maxillofacial surgery, neurovascular procedures

3. SURGICAL TECHNIQUE OPTIMIZATION

• Minimally invasive surgery (laparoscopic, robotic, arthroscopic) - substantially reduces blood loss vs open
• Positioning: Anti-Trendelenburg, prone with abdomen free - reduces venous engorgement and bleeding at surgical site
• Tourniquets in limb surgery - near-eliminates intraoperative blood loss
• Meticulous hemostasis: Bipolar/monopolar diathermy, argon beam coagulation, harmonic scalpel
• Bone wax for cancellous bone bleeding (sternum)
• Topical hemostatic agents:
  • Fibrin sealants (Tisseel, Evicel)
  • Thrombin + gelatin matrix (Floseal)
  • Oxidized cellulose (Surgicel)
  • Collagen/thrombin combinations

4. MINIMIZE DIAGNOSTIC BLOOD LOSS

• Use pediatric sampling tubes for adult patients
• Batch laboratory tests - avoid repeated unnecessary draws
• Point-of-care testing (iSTAT, Hemochron) reduces volume drawn
• Inline/non-invasive monitoring where feasible (pulse oximetry Co-oximetry for continuous Hb monitoring - Masimo)

Miller's note + 2026 PBM guidelines review: Strategies to reduce diagnostic blood loss are the area of GREATEST variability between national guidelines - it is the least standardised PBM domain globally.

5. NORMOVOLEMIC MANAGEMENT

• Maintain normovolemia to support cardiac output and O2 delivery
• Avoid unnecessary fluid overload (dilutes Hb below transfusion threshold)
• Balanced crystalloids preferred over normal saline (less hyperchloremic acidosis)

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PART 5: POSTOPERATIVE BLOOD CONSERVATION

1. RESTRICTIVE TRANSFUSION STRATEGY (Pillar 3)

• [PMID 42115060 - Br J Anaesth 2026]: 40 national guidelines - most agree on Hb 7 g/dL or lower as the restrictive threshold. Prehospital and acute care guidance remains scarce.
• [PMID 38936555 - J Clin Epidemiol 2024]: Important methodological warning - RCTs on restrictive vs. liberal transfusion that exclude patients transfused outside the study period artificially favor restrictive strategies. The current evidence base for restrictive transfusion may overestimate its benefit.
• [PMID 40152861 - JAMA Netw Open 2025]: RCT - Practical anemia bundle in critical illness (batching labs, smaller tubes, EPO, IV iron) accelerated hemoglobin recovery vs. usual care - supports multimodal PBM in ICU

2. POSTOPERATIVE CELL SALVAGE

• Drain blood from surgical drain systems, reprocess, and reinfuse
• Useful in total joint arthroplasty (knee, hip), cardiac surgery
• Quality of postoperative shed blood is lower than intraoperative salvage (more activated/fibrinolysed)
• Limited to 6 hours of collection initiation before reinfusion

3. EARLY ORAL INTAKE

• Miller's: Encourage early return to oral fluids/nutrition - reduces reliance on IV therapy
• Early oral nutrition reduces postoperative complications and decreases length of stay

4. TREATMENT OF POSTOPERATIVE ANEMIA

• IV iron supplementation in iron-deficient patients with postoperative anemia
• ESA/EPO where appropriate (renal patients, major surgery)
• Avoid unnecessary re-operation bleeding

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PART 6: BLOOD CONSERVATION IN SPECIAL SITUATIONS

Jehovah's Witnesses and "Bloodless Surgery"

• Decline allogeneic (and often autologous) blood transfusions on religious grounds
• Management integrates all blood conservation strategies simultaneously:
  • Preoperative: IV iron + EPO for 4-6 weeks, optimize Hb to maximum achievable
  • Intraoperative: ANH, cell salvage (closed circuit continuous), deliberate hypotension, meticulous surgical hemostasis, TXA, minimize blood sampling
  • Postoperative: Strict restrictive threshold (Hb 4-5 g/dL tolerated in some), EPO, iron, HBOCs under compassionate use if life-threatening
• [PMID 37172869 - Curr Probl Cardiol 2023]: Meta-analysis - cardiac surgery in Jehovah's Witnesses: outcomes are similar to those of non-Witnesses when comprehensive bloodless strategies are employed

Damage Control Resuscitation (Trauma)

• Limit crystalloids; use balanced ratio transfusion (RBC:FFP:platelets approaching 1:1:1)
• TXA within 3 hours of injury
• Permissive hypotension until surgical hemorrhage control
• Goal-directed hemostatic therapy with TEG/ROTEM
• Early FFP - prehospital administration shown to improve 30-day mortality (Sperry et al.)

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VIVA SUMMARY TABLE

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BLOOD CONSERVATION STRATEGIES

MD Anaesthesia - Theory & Viva (Miller's 10e + Recent Evidence)

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CLASSIFICATION

BLOOD CONSERVATION STRATEGIES
│
├── A. PREOPERATIVE
│   ├── 1. Preoperative anemia optimization
│   │   ├── Oral iron
│   │   ├── IV iron
│   │   └── Erythropoiesis-stimulating agents (ESAs)
│   ├── 2. Preoperative Autologous Donation (PAD)
│   └── 3. Drug management (stop antiplatelets/anticoagulants)
│
├── B. INTRAOPERATIVE
│   ├── Autologous Techniques
│   │   ├── 4. Acute Normovolemic Hemodilution (ANH)
│   │   └── 5. Intraoperative Cell Salvage (ICS)
│   ├── Pharmacologic
│   │   ├── 6. Antifibrinolytics (TXA, EACA, Aprotinin)
│   │   ├── 7. Desmopressin (DDAVP)
│   │   └── 8. Topical hemostatics
│   └── Anesthetic/Surgical
│       ├── 9. Deliberate hypotensive anesthesia
│       ├── 10. Surgical technique optimization
│       └── 11. Goal-directed hemostatic therapy (TEG/ROTEM)
│
└── C. POSTOPERATIVE
    ├── 12. Restrictive transfusion strategy
    ├── 13. Postoperative cell salvage
    ├── 14. Minimize diagnostic blood loss
    └── 15. IV iron / EPO postoperatively

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PATIENT BLOOD MANAGEMENT (PBM) - THE OVERARCHING FRAMEWORK

Exam pearl: The 2026 systematic review of 40 national guidelines (Dreher et al., Br J Anaesth 2026, [PMID 42115060]) confirms international consensus on Hb 7 g/dL as the restrictive transfusion threshold. The single most variable domain globally: strategies to reduce diagnostic blood loss.

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A. PREOPERATIVE STRATEGIES

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1. PREOPERATIVE ANEMIA OPTIMIZATION

• Faster Hb response (2-3 weeks vs 6-8 weeks)
• Not affected by GI absorption issues
• Single dose infusions available (ferric carboxymaltose, iron sucrose)

• Anemia of chronic disease not responding to iron alone
• Anticipated major blood loss surgery
• Patients refusing transfusion (Jehovah's Witnesses)
• Give with IV iron to maximize erythropoietic response
• Start 4-6 weeks preoperatively

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2. PREOPERATIVE AUTOLOGOUS DONATION (PAD)

• Hb ≥11 g/dL before each donation
• Donations separated by ≥1 week
• Last donation ≥72 hours before surgery (allows intravascular volume restoration - but NOT red cell mass recovery)

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3. ANTICOAGULANT AND ANTIPLATELET MANAGEMENT

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B. INTRAOPERATIVE STRATEGIES

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4. ACUTE NORMOVOLEMIC HEMODILUTION (ANH)

• Blood shed during surgery has a lower Hct (hemodiluted blood) → fewer RBCs lost per mL of blood loss
• Sequestered whole blood retains viable platelets and clotting factors (unlike stored blood)
• Reinfusing whole blood provides comprehensive hemostatic support

• Minimal ANH (<15% blood volume): saves only ~100 mL RBCs = ~0.5 units PRBCs (marginal)
• ANH to Hct 28% + 2600 mL blood loss: saves ~215 mL RBC mass vs no prior hemodilution
• Benefit is proportional to amount of hemodilution AND volume of blood lost

• ANH protects the sequestered blood from cardiopulmonary bypass-induced platelet dysfunction
• The removed platelets and factors are reinfused after bypass - better functional quality

• Pre-existing anemia (Hb <10 g/dL)
• Severe cardiac disease (unable to tolerate reduced Hb)
• Severe pulmonary disease
• Severe renal dysfunction
• Hemoglobinopathies

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5. INTRAOPERATIVE CELL SALVAGE (ICS) / AUTOTRANSFUSION

Blood suctioned from surgical field
         ↓
Anticoagulant (heparin/citrate) added at suction tip
         ↓
Collected in reservoir (500-700 mL needed for processing)
         ↓
Centrifugation - separates plasma (low density) from RBCs (high density)
         ↓
Washed with normal saline
         ↓
Produces 225-250 mL PRBCs at Hct 50-60%
         ↓
Reinfused through 40 µm microaggregate filter

• Major cardiac, vascular, orthopedic (spine, hip, arthroplasty) surgery
• Hepatic resections, liver transplant
• Obstetric surgery (with leukocyte depletion filter)
• Expected blood loss >500-1000 mL
• Patients refusing allogeneic blood

• Air embolism (most serious; mitigated by modern systems)
• DIC (large volumes of unwashed shed blood)
• Non-immune hemolysis (suction trauma)
• Free hemoglobin: nephrotoxic; causes vasoconstriction via NO scavenging
• Bacterial contamination (rare clinically)
• Hypervolemia, coagulopathies

• Suction vacuum ≤150 mmHg (minimizes hemolysis)
• Washed > unwashed salvage
• Leukocyte depletion filters especially for oncology and obstetrics

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6. ANTIFIBRINOLYTIC AGENTS

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7. DESMOPRESSIN (DDAVP)

• Type 2B vWD: releases abnormal vWF that binds platelets spontaneously → thrombocytopenia (worsens condition)
• Type 3 vWD: no vWF stores to release - ineffective
• Cardiovascular disease: can cause vasodilation and hypotension (via V2 effect)
• Hyponatremia risk with repeated doses (antidiuretic effect)
• Tachyphylaxis develops with repeated doses (stores deplete in 24-48 hours)

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8. TOPICAL HEMOSTATIC AGENTS

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9. DELIBERATE HYPOTENSIVE ANESTHESIA

• Major spine surgery (especially scoliosis correction)
• Total hip/knee arthroplasty
• Radical neck dissection, maxillofacial surgery
• Middle ear surgery (operating field optimization)
• Hepatic resections
• Neurovascular procedures

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10. SURGICAL TECHNIQUE OPTIMIZATION

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11. GOAL-DIRECTED HEMOSTATIC THERAPY (TEG/ROTEM)

• Performed at bedside / in OR in real time
• Reflects whole blood clotting including platelets and fibrinolysis
• Results in 10-20 minutes vs hours for lab tests
• Reduces unnecessary FFP and platelet transfusion
• Identifies hyperfibrinolysis (major component of trauma coagulopathy)
• Miller's: growing use is "becoming more pragmatic" for guiding hemostatic therapy

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C. POSTOPERATIVE STRATEGIES

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12. RESTRICTIVE TRANSFUSION STRATEGY

• 1 unit PRBCs at a time, reassess after each unit
• Each unit raises Hb by approximately 1 g/dL in a 70 kg adult

• Old: "10/30 rule" - transfuse if Hb <10 g/dL or Hct <30%
• Current: Hb 7 g/dL for most patients; 8 for cardiac/orthopedic

• [PMID 42115060 - Br J Anaesth 2026]: 40 national PBM guidelines - 22/40 define threshold as Hb 7 g/dL; 9/40 use lower thresholds. Most variable domain: diagnostic blood loss reduction.
• [PMID 38936555 - J Clin Epidemiol 2024]: Meta-analytic warning: trials excluding patients transfused outside the study window artificially favor restrictive strategies - interpretation of current literature requires caution.

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13. MINIMIZE DIAGNOSTIC (IATROGENIC) BLOOD LOSS

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14. POSTOPERATIVE CELL SALVAGE

• Blood drained from surgical drains (orthopedic cases) is filtered and reinfused within 6 hours of collection initiation
• Quality of shed wound blood is lower than intraoperative salvage (more activated, fibrinolysed, diluted)
• Studies in TKR, THR show modest benefit
• Combined intraoperative + postoperative cell salvage generally more effective than either alone

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15. IV IRON + EPO POSTOPERATIVELY

• Accelerates recovery from postoperative anemia
• [PMID 40152861 - JAMA Netw Open 2025]: RCT - "Practical Anemia Bundle" in ICU (batching labs, smaller tubes, EPO, IV iron) produced faster Hb recovery vs usual care - supports multimodal PBM approach in critical illness

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HEMOGLOBIN-BASED OXYGEN CARRIERS (HBOCs) - SPECIAL TOPIC

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BLOOD CONSERVATION IN SPECIAL SCENARIOS

Jehovah's Witnesses - Comprehensive Bloodless Protocol

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VIVA QUESTION BANK

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Blood Conservation Strategies

Concise MD Exam Answer

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CLASSIFICATION (Write this first — gets immediate marks)

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THREE PILLARS OF PATIENT BLOOD MANAGEMENT (PBM)

1. Optimize erythropoiesis - treat preoperative anemia
2. Minimize blood loss - surgical + pharmacologic techniques
3. Rational transfusion - evidence-based thresholds (Hb 7 g/dL)

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PREOPERATIVE

Anemia Optimization

• Screen ≥4-6 weeks before elective surgery
• Iron deficiency (prevalence 23-33%): oral iron → IV iron if <4 weeks to surgery
• EPO + IV iron for anemia of chronic disease
• Key fact: Even non-anemic iron deficiency worsens cardiac surgical outcomes

Preoperative Autologous Donation (PAD)

• Donate own blood weeks before surgery; Hb must be ≥11 g/dL; last donation ≥72h pre-op
• Why declining: Blood safety improved; paradoxically increases overall transfusion risk by 24%; causes preoperative anemia (↓Hb by 1.1 g/dL); 12× post-donation hospitalization rate
• Current role: Rare blood phenotypes, multiple alloantibodies, religious objections

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INTRAOPERATIVE

Acute Normovolemic Hemodilution (ANH)

• Hemodiluted blood shed intraoperatively = fewer RBCs lost per mL blood loss
• Collected blood retains viable platelets + clotting factors (unlike stored PRBCs)
• Reinfused in reverse order (first bag saved for last — has highest Hb + platelets)
• Target post-dilutional Hct: ~28%
• Storage: room temp ≤8h; 4°C ≤24h

• Meta-analysis 30 RCTs, 4,473 patients (2026): 27% reduction in allogeneic transfusion, ↓0.75 units RBC, ↓0.21 units FFP

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Intraoperative Cell Salvage (ICS)

• Anticoagulant (heparin/citrate) at suction tip
• 500-700 mL field blood needed to process one batch → yields 225-250 mL PRBCs
• Quality advantage: 2,3-DPG near-normal vs 90% reduced in stored blood; better O2 offloading
• Suction vacuum must not exceed 150 mmHg (hemolysis)
• Reinfuse through 40 µm microaggregate filter

• Absolute: bacterial contamination, bowel perforation
• Relative: malignancy, amniotic fluid (use leukocyte filter)

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Antifibrinolytics

• Must give in trauma within 3 hours of injury - beneficial; >3 hours - potentially harmful (CRASH-2)
• 2026 RCT (Ali et al., Ann Emerg Med): timing critically determines mortality impact

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DDAVP (Desmopressin)

• Mechanism: Releases vWF + Factor VIII from endothelial Weibel-Palade bodies
• Dose: 0.3 mcg/kg IV over 20-30 min; tachyphylaxis in 24-48h
• Use: Uremia, aspirin effect, Type 1 vWD, mild Hemophilia A
• Don't use in: Type 3 vWD (no stores to release), Type 2B vWD (releases abnormal vWF → thrombocytopenia)

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TEG/ROTEM-Guided Therapy

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Deliberate Hypotension

• Reduce MAP to 50-65 mmHg to decrease surgical field bleeding
• Contraindications: IHD, CVA, renal failure, uncontrolled HTN, severe anemia
• Agents: volatiles, remifentanil, labetalol, SNP, dexmedetomidine

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Surgical Techniques

• MIS (laparoscopic/robotic), tourniquet (limb), bipolar diathermy, harmonic scalpel, topical hemostatics (fibrin glue, Floseal, Surgicel), correct positioning (reduces venous engorgement)

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POSTOPERATIVE

Restrictive Transfusion Threshold (Most marks in short note)

• Old "10/30 rule" is obsolete
• 2026 systematic review of 40 national guidelines: 22/40 agree on Hb 7 g/dL
• Transfuse 1 unit at a time; each unit raises Hb ~1 g/dL; reassess before next

Minimize Diagnostic Blood Loss

• Pediatric tubes, batch tests, point-of-care testing, inline sampling systems
• Most variable PBM domain globally (good exam fact)

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VIVA QUICK-FIRE ANSWERS

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ONE-LINE DEFINITIONS (For short notes / viva opening)

• PAD: Autologous blood donated weeks before surgery; declining use
• ANH: Blood withdrawn after induction, replaced with fluid; reinfused after bleeding stops
• ICS: Surgical blood suctioned, washed, reinfused as PRBCs intraoperatively
• TXA: Antifibrinolytic lysine analogue; give within 3h of trauma
• DDAVP: Releases endothelial vWF; use in uremia and Type 1 vWD
• PBM: Multidisciplinary strategy to optimize erythropoiesis, minimize loss, and use transfusion rationally
• Restrictive strategy: Transfuse at Hb <7 g/dL (most patients); avoids harm from unnecessary transfusion

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Massive Transfusion - Complications

Concise MD Exam Summary

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DEFINITION

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THE LETHAL TRIAD

        HYPOTHERMIA
           /    \
          /      \
   ACIDOSIS ——— COAGULOPATHY

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COMPLICATIONS OF MASSIVE TRANSFUSION

Mnemonic: "HATCH-DC"

Hypothermia, Acid-base, Thrombocytopenia, Citrate toxicity, Hyperkalemia, DIC, Coagulopathy

---

1. HYPOTHERMIA

• Blood stored at 4°C → core temperature drops with massive infusion
• Even small ↓ temperature impairs both clotting factors AND platelets
• <30°C → ventricular irritability → cardiac arrest
• Prevention: Warm blood through thermostat-controlled water bath (38°C)

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2. ACID-BASE DISTURBANCES

• Empirical bicarbonate is NOT indicated - guide by serial ABGs

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3. DILUTIONAL THROMBOCYTOPENIA

• PRBCs contain no platelets → platelets diluted as blood replaced
• Platelet count falls to <100 × 10⁹/L after 10-15 units
• Miller's threshold: Platelet <75 × 10⁹/L = reliable predictor of hemorrhagic diathesis
• Actual fall less severe than predicted (splenic + bone marrow release compensates)
• Key difference: Acute thrombocytopenia causes bleeding at much higher count than chronic (e.g., ITP) - because platelet function also impaired

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4. COAGULOPATHY OF MASSIVE TRANSFUSION

• First factor to reach critically low levels during major hemorrhage
• Falls significantly when blood replaced with PRBCs + crystalloid (unlike whole blood replacement)
• Monitor and supplement early (cryoprecipitate or fibrinogen concentrate)

• If PTT ≥1.5× normal + other tests normal → low Factors V + VIII → treat with FFP or cryoprecipitate

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5. DIC (DISSEMINATED INTRAVASCULAR COAGULATION)

Hypoxia + Acidosis + Stagnant blood flow
              ↓
Release of Tissue Thromboplastin (+ TNF, endotoxins)
              ↓
Massive coagulation cascade activation
              ↓
Consumption of Factors I, II, V, VIII + Platelets
              ↓
Simultaneous fibrinolytic activation (tPA from damaged tissue)
              ↓
PARADOX: Clotting + Bleeding simultaneously

• Treat the underlying cause (control hemorrhage, treat sepsis)
• FFP for factor replacement
• Cryoprecipitate for fibrinogen (<150 mg/dL)
• Platelets if <50 × 10⁹/L with bleeding
• Avoid heparin (unless thrombotic-predominant DIC)
• TEG/ROTEM-guided component therapy

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6. CITRATE TOXICITY / HYPOCALCEMIA

• Citrate (anticoagulant in stored blood) chelates ionized calcium
• Result: ↓iCa²⁺ → dysrhythmia, hypotension, myocardial depression
• Risk ↑ with: infusion rate >1 unit/10 minutes, liver disease, neonates, hyperventilation
• Even at these rates, ionized Ca²⁺ may not fall enough to cause bleeding alone
• Treat: IV calcium chloride (10 mL of 10%) or calcium gluconate

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7. HYPERKALEMIA

• Stored blood K⁺: 19-50 mEq/L at 21 days; 45-60 mEq/L at 42 days; even higher in irradiated units
• Net K⁺ gain only ~10 mEq/L (because blood loss also removes K⁺)
• Clinically significant only at infusion rate ≥120 mL/min
• High risk: neonates, renal failure patients
• Paradox: metabolic alkalosis post-transfusion drives K⁺ intracellularly → may cause hypokalemia later

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SUMMARY TABLE: ALL COMPLICATIONS AT A GLANCE

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DAMAGE CONTROL RESUSCITATION (DCR) — Prevents the Triad

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VIVA QUICK-FIRE

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Hypokalemia - Correction

Miller's Anesthesia 10e | MD Exam & Viva

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DEFINITION & SEVERITY

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CAUSES (Table 43.7 - Miller's)

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CLINICAL FEATURES

ECG Changes (in order of severity):

Mild hypokalemia:
  → ST depression
  → T-wave flattening / depression
  → Prominent U-wave (hallmark - U > T in same lead)

Progressive:
  → Prolonged QT (T merges with U)
  → Atrial fibrillation
  → Ventricular ectopics → VT → VF

Neuromuscular:

• Muscle weakness, fatigue, cramps
• Severe: ascending paralysis, respiratory failure
• Smooth muscle: ileus, constipation

Metabolic:

• Metabolic alkalosis (K⁺ depletion → H⁺ enters cells; kidneys paradoxically retain H⁺ in K⁺ depletion)
• Nephrogenic diabetes insipidus (impaired urine concentrating ability)

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PERIOPERATIVE SIGNIFICANCE (Miller's)

"All logic dictates that hypokalemia should be associated with increased perioperative morbidity - however, no data support this conclusion." - Miller's 10e

1. Optimize neuromuscular function
2. Reduce cardiac irritability
3. Maintain K⁺ >4.0-4.5 mEq/L when acute arrhythmias exist

• Enhanced sensitivity to non-depolarizing muscle relaxants
• Risk of digitalis toxicity (hypokalemia potentiates digoxin)
• Risk of arrhythmias especially with volatile anaesthetics (sensitize myocardium)
• Metabolic alkalosis → left-shifted O₂ dissociation curve → impaired O₂ offloading

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CORRECTION PRINCIPLES

Key Numbers to Know (Miller's):

• Maximum IV infusion rate: ≤0.5 mEq/kg/hour
• K⁺ concentration >40 mEq/L = irritant to peripheral veins → must use central venous catheter
• Target K⁺ in arrhythmia patients: >4.0-4.5 mEq/L

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CORRECTION PROTOCOL

Step 1: Estimate Deficit

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Step 2: Choose Route

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Step 3: IV Replacement Guide

• 10 mEq/h via peripheral IV is the conventional safe upper limit for peripheral

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Step 4: Correct Co-existing Deficiencies

• Mg²⁺ is required for Na⁺/K⁺-ATPase pump function
• Hypomagnesaemia → renal K⁺ wasting → refractory hypokalemia that will not correct until Mg²⁺ is replaced
• Give Mg²⁺ sulphate 1-2g IV over 15-30 min if Mg²⁺ <0.8 mmol/L

• Correct metabolic alkalosis (alkalosis drives K⁺ intracellularly)
• Replace phosphate if also depleted (e.g., re-feeding syndrome)

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Step 5: Treat the Cause

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MONITORING DURING CORRECTION

• Serum K⁺ every 2-4 hours during IV replacement
• Continuous ECG monitoring if K⁺ <2.5 mEq/L or active arrhythmia
• Urine output (ensure adequate renal function before aggressive replacement)
• Recheck Mg²⁺, phosphate, acid-base
• Stop IV K⁺ and switch to oral when K⁺ >3.0-3.2 mEq/L and patient stable

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VIVA QUICK-FIRE

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Hypokalemia Correction Formulas

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FORMULA 1: ESTIMATE TOTAL BODY K⁺ DEFICIT

The factor 0.4 represents the distribution volume of K⁺ (40% of body weight = ECF + partial ICF equilibration)

• Patient: 70 kg; Serum K⁺ = 2.8 mEq/L; Target = 4.0 mEq/L
• Deficit = (4.0 − 2.8) × 70 × 0.4
• = 1.2 × 70 × 0.4 = 33.6 mEq (minimum estimate)

Caveat: This formula underestimates true deficit because 98% of K⁺ is intracellular. For every 1 mEq/L fall in serum K⁺, actual total body deficit is ~200-400 mEq. Use the formula to calculate the initial replacement dose, then recheck and re-dose.

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FORMULA 2: IV INFUSION RATE CHECK

• Max rate: 0.5 mEq/kg/h (peripheral or central)
• Peripheral max concentration: 40 mEq/L (= 0.04 mEq/mL)
• Central line required if concentration >40 mEq/L

• 20 mEq KCl in 500 mL NS = 40 mEq/L
• At 500 mL/h → delivers 20 mEq/h
• For 70 kg patient: max rate = 0.5 × 70 = 35 mEq/h max (central)

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FORMULA 3: SAFE PERIPHERAL DRIP CALCULATION

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FORMULA 4: EFFECT OF ACID-BASE ON K⁺

• Patient on ventilator: if you correct alkalosis (↓pH by 0.1) → K⁺ rises 0.6 mEq/L
• Correct alkalosis before or alongside K⁺ replacement

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WORKED CLINICAL SCENARIO (Write in exam)

• Deficit = (4.0 − 2.6) × 60 × 0.4 = 1.4 × 60 × 0.4 = 33.6 mEq (minimum)
• True deficit likely 280-560 mEq (1.4 × 200-400)

• Give 40 mEq KCl via central line in 500 mL NS over 2 hours (20 mEq/h)
• Recheck K⁺ after 2 hours

• If Mg²⁺ <0.8 mmol/L → give MgSO₄ 2g IV simultaneously

• pH 7.48 is driving K⁺ intracellularly; correct ventilation/alkalosis to improve K⁺

• Recheck K⁺ every 2 hours; repeat infusions until K⁺ >3.5 (general) or >4.0 (arrhythmia)
• Switch to oral KCl once K⁺ >3.2 and stable

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SUMMARY TABLE (Copy in exam)

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VIVA POINT

Miller's specifically states: infusion rate must be slow enough to allow equilibration throughout the entire ECF — rapid infusion raises serum K⁺ without correcting intracellular deficit, and risks cardiac toxicity from transient hyperkalemia.