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FACP. Colegio de médicos de Tarragona Nº 4305520 / fgcapriles@gmail.com




Sunday, January 24, 2016

Volume status vs volume responsiveness

Resultado de imagen de PulmCCM
PulmCC - January 21, 2016
...Another recent publication has analyzed the diagnostic accuracy of using IVC assessment for detecting fluid responsiveness in the ‘spontaneously breathing’ patient. Importantly, in this study, it is clear that no patients are receiving any form of invasive or non-invasive ventilation. This is notable, as a patient may breathe ‘spontaneously’ while triggering invasive [e.g. pressure support] or non-invasive [e.g. BiPAP] forms of respiratory support. What was ultimately found was that an IVC collapsing index more than 42% revealed an excellent specificity, but a fairly poor sensitivity for the prediction of fluid responsiveness. These findings are important and somewhat similar to another, previous study which considered a similar patient population, although it is unclear if this earlier study excluded spontaneously breathing patients receiving assisted ventilation...
Consider the diagram below which depicts the determinants of the pressure within the IVC, prior to an inspiration.
Volume status versus volume responsiveness
On this final point, it should be apparent that a patient’s ‘volume status’ [i.e. the degree of plasma volume] is physiologically distinct from a patient's ‘volume responsiveness’ [i.e. whether or not an increase in plasma volume will result in an increase in cardiac output]. As in the diagram above, volume status is but one determinant of venous return to the heart; however it is how the heart handles its venous return that defines volume responsiveness. It follows that a patient can be hypervolemic and volume responsive or hypovolemic and volume unresponsive. For further information please watch these physiology lectures [Chapters 6D, 8A & 8F]
Bedside ultrasound is a great power; it therefore demands great responsibility