Hemodynamic and Fluid Management
What the exam tests
This domain tests integration of preload, contractility, afterload, fluid choice, transfusion, and goal-directed therapy.
Core rules
- Fluid responsiveness is not the same as hypovolemia. Dynamic tests: passive leg raise, stroke volume variation, pulse pressure variation.
- PPV and SVV are unreliable in spontaneous breathing, arrhythmia, low tidal volume, open chest, and high PEEP.
- Balanced crystalloids are preferred for most resuscitation; normal saline causes hyperchloremic metabolic acidosis.
- Transfusion: a restrictive strategy is acceptable in most stable patients; give one unit at a time and reassess. Use thresholds, not a single number for every patient.
- Vasopressors are not a substitute for inadequate perfusion but should not be delayed in septic shock.
- Postoperative fluid overload causes edema, ileus, and respiratory failure.
Worked example
A 70-kg patient after major surgery is hypotensive, MAP 58 mmHg, HR 105, lactate 2.5. Passive leg raise increases stroke volume by 14%. Reasoning: this is a fluid responder; give 250-500 mL balanced crystalloid and reassess. If SV does not rise, consider vasopressor or inotrope and look for bleeding, sepsis, or myocardial dysfunction. Do not give 2 L empirically.
Traps
Using CVP or the "wet or dry" exam alone; giving saline to everyone; ignoring arrhythmia when using PPV; transfusing to a Hb of 10 in a stable patient; missing ongoing hemorrhage.