Low CVP = fluid challenge? No.
Take home message: CVP is a measure of preload, but not of preload responsiveness.
The graph below explains why a low CVP should not determine whether fluid boluses should be given or not.
*EEO – end-expiratory occlusion; PLR = passive leg raise
This graph shows that the slope of the curves (Frank-Starling curves) differ for patients with normal and poor ventricular systolic function. A low CVP (i.e. cardiac preload) does not predict fluid responsiveness. As seen in the graph, a heart with normal systolic function and low CVP will respond to a fluid bolus, whereas one with a poor ventricular systolic function will not.
Other static indicators of cardiac preload:
- global EDV
- flow time of aortic flow (esophageal Doppler)
- LV EDD (echo).
The use of CVP – a good marker of preload (not preload responsiveness) and a key determinant of cardiac function. Determines pressure gradient for organ perfusion (which is MAP-CVP). High CVP values impair renal perfusion.
Dynamic testsshould be used to predict fluid responsiveness. A preload challenge (spontaneous [mechanical ventilation] or provoked [PLR or EEO or fluids]) should be given and the effects on stroke volume should be observed to detect preload responsiveness.
Fluids are drugs whose dose must be carefully titrated to the needs of the patient.
Graph below shows 112 paired measurements of blood volume and CVP in postoperative patients. Scatter plot analysis shows no correlation between the two values. (Marino, 2014)
Monnet, et al. Prediction of fluid responsiveness: an update. Ann Intensive Care. 2016 Dec;6(1):111. Epub 2016 Nov 17.