Question 17

Discuss the advantages and disadvantages of the following three techniques for assessing fluid responsiveness:

a) Pulse pressure variation. (40% marks)

b) Passive leg raising. (30% marks)

c) Fluid bolus. (30% marks)

(Note to candidates: details of how the techniques are performed are not required.)

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College answer

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Discussion

	Advantages	Disadvantages
Pulse pressure variation	Readily available in critical care, where arterial lines are common Some monitoring systems even display PPV as standard Highly sensitive - a threshold of 12% predicts fluid responsiveness with an AUROC curve of 0.94. Fewer errors in calculation than SVV (easier to calculate)	Limited validity in spontaneously breathing patient (in fact , validated only for mandatory ventilation, with tidal volumes of 8ml/kg) Impossible to use during a cardiac arrhythmia Unreliable with valvular heart disease, especially aortic Not going to work with cardiogenic shock (with poor LV function), as stroke volume may not increase in response to increased preload Intracardiac shunts, AV fistulae and severe peripheral vascular disease can all affect the pulse pressure
Passive leg raise	A reversible fluid challenge This method of testing fluid responsiveness is well validated; sensitivity and specificity is 89% and 91%, respectively (Cavallaro et al, 2010) Easy to do at the bedside, and gives rapid results with high sensitivity and specificity to identify fluid responders When measuring cardiac output during this test, the AUC is about 0.95	Validated only for the use of cardiac output monitoring devices (AUC for using pulse pressure variation was only 0.76) You need a patient with both legs intact You rely on an intact pelvis, so this excludes a lot of messy trauma patients (in whom it would be very useful) It can't be done if you have a balloon pump in situ, or post angiography (because you need to lie flat) - and thus a lot of low-cardiac-output cardiogenic shock patients are excluded, which is a pity It can't be done if you are even slightly concerned about your intracranial pressure.
Fluid bolus	Gold standard for fluid responsiveness testing Does not have to be very large, and it can be ceased abruptly if it is clearly not improving the cardiac output Statistically speaking, a number of patients being assessed for fluid responsiveness will actually require fluid resuscitation, which this technically is.	The whole point of assessing fluid responsiveness is that you do it before you give the fluid This is an irreversible fluid challenge There is little agreement on what the volume for such a challenge should be (JL Vincent suggests 200ml over 10min) The response to one challenge does not predict the response to the next challenge Repeated multiple challenges can lead to an undesirably positive fluid balance

References

Cavallaro, Fabio, et al. "Diagnostic accuracy of passive leg raising for prediction of fluid responsiveness in adults: systematic review and meta-analysis of clinical studies." Intensive care medicine 36.9 (2010): 1475-1483.

Teboul, Jean-Louis, et al. "Arterial pulse pressure variation with mechanical ventilation." American journal of respiratory and critical care medicine 199.1 (2019): 22-31.

Vincent, Jean-Louis, and Max Harry Weil. "Fluid challenge revisited." Critical care medicine 34.5 (2006): 1333-1337.

Vincent, Jean-Louis, Maurizio Cecconi, and Daniel De Backer. "The fluid challenge." (2020): 1-3.

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