Principles of Circulating Blood Volume Replacement

1. Normal Blood Volume (Reference Values)

2. Goals of Volume Replacement

• Maintain oxygen-carrying capacity (hemoglobin/hematocrit)
• Restore coagulation factor activity
• Correct the metabolic consequences of shock (acidosis, hypothermia)
• Avoid the complications of over-resuscitation (dilutional coagulopathy, tissue oedema, abdominal compartment syndrome)
• Mulholland and Greenfield's Surgery, 7e

3. Classification of Volume Loss (Hemorrhagic Shock)

4. Types of Replacement Fluids

A. Crystalloids

• Distribute across the entire extracellular space (interstitial + intravascular), so only ~25% remains intravascular
• Require 3-4x the volume lost to restore intravascular volume
• Large volumes cause dilutional coagulopathy, acidosis, and tissue oedema
• Preferred for initial resuscitation: 20 mL/kg boluses in children; 1-2 L boluses in adults

B. Colloids

• Larger molecules that remain in the intravascular compartment longer (better plasma volume expansion per mL given)
• Crystalloid requires 8-fold greater volumes than colloid to achieve equivalent plasma expansion
• Examples: albumin, hydroxyethyl starch, gelatin solutions
• Meta-analyses show no clear mortality benefit over crystalloids in most settings; colloids remain more expensive
• Use is context-dependent (perioperative, burns after 24 h)

C. Hypertonic Saline (3% or 7.5%)

• Draws water from intracellular and interstitial compartments into the vascular space
• Achieves volume resuscitation with low infused volumes - particularly useful in austere/military settings and for concurrent traumatic brain injury
• Can cause hyperchloremic acidosis
• Given as a one-time bolus (5% hypertonic saline) in the early phase of resuscitation
• Benefit over isotonic saline not confirmed by large RCTs for general trauma
• Mulholland and Greenfield's Surgery, 7e

D. Blood Products

• Packed Red Blood Cells (pRBCs): Restore oxygen-carrying capacity. Transfused in 10 mL/kg increments in children (~500 mL equivalent in a 70 kg adult). Formula for PRBC volume needed:

(Target Hct - Current Hct) x Weight (kg) x 80 / 65

• Fresh Frozen Plasma (FFP): Replaces coagulation factors. Dosed at 10-20 mL/kg. Used when coagulopathy is present or when >30 mL/kg blood products transfused in children.
• Platelets: Dosed at 1 unit/5 kg in children. Required if >30 mL/kg transfused or platelet count falls below threshold.
• Cryoprecipitate: Rich in fibrinogen and factor VIII; used as an adjunct in trauma-induced coagulopathy.
• Schwartz's Principles of Surgery, 11e

5. Modern Strategies

A. Damage Control Resuscitation (DCR)

• Permissive hypotension: Target systolic BP ~90 mmHg (MAP ~60 mmHg) before definitive hemorrhage control. This prevents "popping the clot" and worsening hemorrhage. Avoid in TBI, blunt trauma, elderly, and patients with cardiac/carotid disease.
• Early blood product administration: Minimize crystalloid, prioritize RBCs, FFP, and platelets
• 1:1:1 ratio (RBC:FFP:Platelets): Reconstitutes "whole blood," reduces dilutional coagulopathy. Derived from military data showing improved survival. Adopted in civilian massive transfusion protocols (MTP).
• Tranexamic acid (TXA): Antifibrinolytic; effective if given within 3 hours of injury. Reduces risk of death from bleeding. Recommended by CRASH-2 trial and military guidelines (15 mg/kg IV bolus over 20 minutes, then 2 mg/kg/h for 8 hours in children).
• Avoid the lethal triad: Hypothermia + acidosis + coagulopathy - mutually self-reinforcing and fatal.
• Mulholland and Greenfield's Surgery, 7e

B. Massive Transfusion Protocol (MTP)

• 40 mL/kg blood products needed in adolescents

• 50 mL/kg in children/infants

• Tietz Textbook of Laboratory Medicine, 7e; Mulholland and Greenfield's Surgery, 7e

C. Goal-Directed Therapy (GDT)

• Titrate fluid to measurable endpoints: stroke volume (SV), stroke volume variation (SVV), cardiac output
• Administer 250 mL boluses of colloid or crystalloid aiming for a 10% rise in SV
• Continue until SV no longer increases (Starling plateau)
• Reduces postoperative complications, renal impairment, respiratory failure, and hospital stay
• Monitors: esophageal Doppler, arterial waveform analysis (FloTrac, LiDCO), echocardiography
• Miller's Anesthesia, 10e

6. Endpoints of Resuscitation

7. Special Considerations

• Pediatrics: Blood volume ~80 mL/kg; start with 20 mL/kg crystalloid boluses x2, then 10 mL/kg pRBC if no improvement
• Ruptured AAA: Permissive hypotension (SBP 70-90 mmHg) to operating room; PRBC:FFP ratio <2:1
• Burns: Parkland formula (4 mL/kg x %TBSA burned); half in first 8 hours, half over next 16 hours; crystalloid is first choice
• TBI + hemorrhage: Avoid permissive hypotension; maintain MAP ≥80 mmHg to preserve cerebral perfusion pressure