Fluids, Transfusion and Positioning
Fluids
Understand the physiology of body fluid compartments and the rationale for balanced crystalloids versus saline. Know that large-volume 0.9% saline causes hyperchloremic metabolic acidosis. Understand the concept of goal-directed fluid therapy and the risk of both under- and over-resuscitation. Know the indications for colloids and the concerns about hydroxyethyl starch.
Transfusion
Know the indications for red cell transfusion (usually Hb <7 g/dL in most patients, <8 g/dL in cardiac disease), the risks of transfusion reactions, and the management of acute hemolytic transfusion reaction. Understand massive transfusion protocols and the ratio of plasma to platelets to red cells. Know the presentation and treatment of transfusion-related acute lung injury (TRALI) and transfusion-associated circulatory overload (TACO).
Positioning
Understand the physiologic consequences of the supine, Trendelenburg, reverse Trendelenburg, prone, lateral, and sitting positions. Know the risk of pressure injuries, nerve injuries (ulnar nerve at the elbow, brachial plexus with arm abduction), and the hemodynamic effects of the sitting position (venous air embolism).
Traps
Questions often test the difference between TRALI and TACO, or the appropriate fluid for a patient with a head injury (avoid hypotonic fluids). Another trap is the belief that a hemoglobin threshold of 10 g/dL is routine; modern practice favors restrictive transfusion. Also know that the prone position reduces cardiac output and can worsen ventilation-perfusion matching.
Worked Example
A trauma patient receives 6 units of red cells and becomes hypotensive with bilateral infiltrates on chest X-ray within 6 hours. Consider TRALI; management is supportive with oxygen and ventilation, and diuretics are not the primary treatment (unlike TACO).