TNCC Shock and Fluid Resuscitation 2 — Questions and Answers
Question 1: Which type of shock is characterized by decreased cardiac output due to impaired myocardial contractility following blunt chest trauma?
- Hypovolemic shock
- Distributive shock
- Cardiogenic shock (Correct answer)
- Obstructive shock
Correct answer: Cardiogenic shock
Cardiogenic shock from blunt cardiac injury (myocardial contusion) results in decreased contractility and reduced cardiac output despite adequate intravascular volume.
Cardiogenic shock in trauma most commonly results from blunt cardiac injury (BCI), formerly called myocardial contusion, typically from steering wheel impact or high-speed deceleration. The bruised myocardium has impaired contractility, reducing stroke volume and cardiac output. Unlike hypovolemic shock (volume loss), distributive shock (vasodilation), or obstructive shock (mechanical obstruction to flow), cardiogenic shock involves primary pump failure. Diagnosis: ECG abnormalities (new arrhythmias, ST changes), elevated troponin, echocardiographic wall motion abnormalities. Treatment differs from hemorrhagic shock — excessive fluids worsen pulmonary edema. Management includes inotropic support (dobutamine), careful fluid titration, and treatment of dysrhythmias. Cardiogenic shock can also result from cardiac tamponade (though this is more accurately classified as obstructive) or valvular disruption from blunt trauma.
Question 2: During massive transfusion protocol, which electrolyte abnormality is most likely to cause cardiac arrest?
- Hyponatremia
- Hypocalcemia
- Hyperkalemia (Correct answer)
- Hypomagnesemia
Correct answer: Hyperkalemia
Hyperkalemia from stored blood products (potassium leaks from aged RBCs) can cause fatal cardiac dysrhythmias including ventricular fibrillation and asystole during massive transfusion.
During massive transfusion, multiple electrolyte derangements occur. Hyperkalemia is the most immediately life-threatening because potassium directly affects myocardial conduction. Stored packed RBCs leak intracellular potassium progressively — older units may have extracellular K+ levels of 30-50 mEq/L. Rapid transfusion of multiple units delivers a significant potassium load, especially dangerous when combined with hypothermia (which impairs cellular potassium uptake), acidosis (shifts K+ extracellularly), and renal hypoperfusion (reduced excretion). Hyperkalemia causes peaked T waves, widened QRS, sine wave patterns, and ultimately ventricular fibrillation or asystole. Treatment: calcium gluconate or chloride (cardiac membrane stabilization), insulin with dextrose, sodium bicarbonate, and kayexalate. Hypocalcemia from citrate preservative binding ionized calcium is also significant and can compound the cardiac effects. Monitoring ionized calcium and potassium during MTP is essential.
Question 3: A trauma patient receiving crystalloid resuscitation develops worsening metabolic acidosis. Which crystalloid is LEAST likely to cause hyperchloremic acidosis?
- Normal saline (0.9% NaCl)
- Lactated Ringer's solution (Correct answer)
- Hypertonic saline (3%)
- Half-normal saline (0.45% NaCl)
Correct answer: Lactated Ringer's solution
Lactated Ringer's solution has a chloride concentration (109 mEq/L) closer to plasma (98-106 mEq/L) and contains lactate buffer, making it less likely to cause hyperchloremic metabolic acidosis compared to normal saline (154 mEq/L chloride).
Normal saline contains 154 mEq/L each of sodium and chloride — the chloride concentration is significantly higher than plasma (98-106 mEq/L). Large-volume resuscitation with NS causes hyperchloremic non-anion gap metabolic acidosis by diluting bicarbonate and providing excess chloride, which shifts the strong ion difference and lowers pH. This iatrogenic acidosis complicates the interpretation of lactate and base deficit as resuscitation endpoints. Lactated Ringer's (Na 130, Cl 109, K 4, Ca 3, lactate 28 mEq/L) has a more physiological electrolyte composition. The lactate is rapidly metabolized to bicarbonate by the liver, providing buffering capacity. Multiple studies (including SMART trial) demonstrate that balanced crystalloids like LR are associated with less AKI and lower mortality compared to NS in critically ill patients. LR is the preferred crystalloid for trauma resuscitation per TNCC guidelines. The one exception: LR should not be infused through the same line as blood products due to calcium-citrate interaction causing clotting.
Question 4: Tranexamic acid (TXA) administration in trauma hemorrhage is most effective when given within what time frame from injury?
- 6 hours
- 3 hours (Correct answer)
- 12 hours
- 24 hours
Correct answer: 3 hours
The CRASH-2 trial demonstrated that TXA reduces mortality from hemorrhage when administered within 3 hours of injury. Administration after 3 hours may increase mortality.
Tranexamic acid (TXA) is an antifibrinolytic agent that inhibits plasminogen activation, reducing fibrinolysis and stabilizing blood clots. The CRASH-2 trial (2010) — a landmark RCT of 20,211 trauma patients in 40 countries — demonstrated that TXA given within 3 hours of injury significantly reduced death from hemorrhage (4.9% vs 5.7%) and all-cause mortality. Critically, TXA given AFTER 3 hours actually INCREASED mortality (4.4% vs 3.1%), likely by stabilizing microvascular thrombi and worsening organ dysfunction. The recommended dose is 1g IV over 10 minutes, followed by 1g IV over 8 hours. TXA is now included in many massive transfusion protocols and military tactical combat casualty care guidelines. It is inexpensive, stable at room temperature, and has a favorable safety profile when given within the time window. Pre-hospital TXA administration is increasingly implemented to maximize the benefit of early treatment.
Question 5: Which assessment finding differentiates obstructive shock from hypovolemic shock?
- Tachycardia is present in obstructive but not hypovolemic shock
- Distended neck veins are present in obstructive shock but flat in hypovolemic shock (Correct answer)
- Both present identically and cannot be differentiated clinically
- Hypovolemic shock causes bradycardia while obstructive shock causes tachycardia
Correct answer: Distended neck veins are present in obstructive shock but flat in hypovolemic shock
Obstructive shock (cardiac tamponade, tension pneumothorax) presents with distended neck veins from impaired venous return to the heart, while hypovolemic shock presents with flat neck veins from volume depletion.
Both obstructive and hypovolemic shock present with hypotension, tachycardia, and decreased cardiac output, but the mechanism differs fundamentally. In hypovolemic shock, decreased intravascular volume means decreased venous return — the neck veins are flat and collapsed, and CVP is low. In obstructive shock, a mechanical obstruction prevents adequate ventricular filling or ejection despite adequate volume. Cardiac tamponade: pericardial fluid compresses the heart, impeding filling — blood backs up, distending neck veins (Beck's triad: hypotension, JVD, muffled heart sounds). Tension pneumothorax: increased intrathoracic pressure compresses the heart and great veins — blood backs up, distending neck veins (with tracheal deviation and absent breath sounds). Massive PE: right ventricular outflow obstruction. The presence of JVD in a hypotensive trauma patient should immediately raise suspicion for obstructive causes and trigger specific interventions (pericardiocentesis, needle decompression) rather than just volume resuscitation.
Question 6: A trauma patient in hemorrhagic shock has received 4 units of PRBCs and remains hypotensive with a heart rate of 140. The next priority in the massive transfusion protocol is:
- Switch to crystalloid-only resuscitation
- Continue balanced transfusion with plasma and platelets in a 1:1:1 ratio with PRBCs (Correct answer)
- Administer vasopressors as the primary intervention
- Stop all transfusion and obtain a CT scan
Correct answer: Continue balanced transfusion with plasma and platelets in a 1:1:1 ratio with PRBCs
Current evidence supports a balanced 1:1:1 ratio of PRBCs to plasma to platelets during massive transfusion to address both oxygen-carrying capacity and coagulopathy simultaneously.
The PROPPR trial (2015) established that a 1:1:1 ratio of PRBCs:plasma:platelets during massive transfusion achieves better hemostasis and reduced 24-hour mortality compared to a 1:1:2 ratio. The rationale: hemorrhagic shock involves loss of whole blood — replacing only RBCs creates dilutional coagulopathy (insufficient clotting factors and platelets), worsening the lethal triad. Balanced transfusion replaces all blood components proportionally. Ongoing massive transfusion protocol management includes: (1) Continue 1:1:1 until hemorrhage control is achieved. (2) Monitor with point-of-care testing — TEG/ROTEM (thromboelastography) guides component therapy. (3) Administer calcium (citrate in blood products chelates ionized calcium). (4) Warm all products. (5) Consider cryoprecipitate if fibrinogen <150 mg/dL. (6) Vasopressors are adjuncts to volume replacement, not substitutes — they are used when MAP remains inadequate despite adequate volume resuscitation. Crystalloid-only resuscitation for hemorrhagic shock is associated with worse outcomes.
TNCC Shock and Fluid Resuscitation 2
Which type of shock is characterized by decreased cardiac output due to impaired myocardial contractility following blunt chest trauma?