Fluid responsiveness assessment in ventilated shock — FFICM MCQ

Correct answer: E — Passive leg raise with real-time stroke volume measurement

The correct answer is E, passive leg raise with real-time stroke volume measurement. This patient has clinical equipoise on fluids: borderline MAP and lactate suggesting possible hypoperfusion, but bilateral B-lines and 6 litres positive balance raising concern for interstitial oedema, so empirical fluid boluses risk harm if he is not preload responsive. Passive leg raise produces a reversible, self-limiting autotransfusion of roughly 300 ml from the legs and splanchnic bed, and a rise in stroke volume (typically greater than 10 percent on a real-time monitor) predicts response to a fluid bolus without actually committing to giving fluid. Pooled data show this manoeuvre has high sensitivity (86 percent) and specificity (92 percent) for predicting fluid responsiveness, making it the appropriate dynamic test in a mechanically ventilated, sedated patient where volume status is genuinely uncertain. Why the other options are wrong: B. Static central venous pressure measurement alone: CVP reflects right atrial pressure and vascular compliance, not volume status, and correlates poorly with fluid responsiveness in ventilated patients regardless of the absolute value. D. Urine sodium concentration: this assesses renal handling of sodium and volume depletion in the context of acute kidney injury, not cardiac preload reserve or stroke volume response. A. Chest radiograph to estimate preload: a CXR shows static pulmonary vascular congestion or oedema pattern but cannot distinguish a fluid responsive from a fluid unresponsive ventricle, and offers no real time haemodynamic information. C. Serum albumin concentration: albumin reflects oncotic pressure, nutritional and inflammatory state, not intravascular volume or fluid responsiveness, and is confounded by capillary leak in pancreatitis. Key point: dynamic preload tests such as passive leg raise with stroke volume monitoring predict fluid responsiveness, whereas static measures (CVP, CXR, albumin, urine sodium) do not.

Reference: NIHR Evidence, 'Simple leg raise test may help in assessing patients' fluid needs in intensive care', evidence.nihr.ac.uk