Predicting Fluid Responsiveness

Dr. Trivedi

Monnet X, Dres M, Ferré A, Le Teuff G, Jozwiak M, Bleibtreu A, Le Deley MC, Chemla D, Richard C, Teboul JL. Prediction of fluid responsiveness by a continuous non-invasive assessment of arterial pressure in critically ill patients: comparison with four other dynamic indices. Br J Anaesth. 2012 Sep;109(3):330-8. Epub 2012 Jun 26.

            A debate within the realm of anesthesia continues over the best hemodynamic monitoring tool. Traditional static measures such as central venous pressure and pulmonary artery occlusion pressures are now being replaced by dynamic indices. Monnet and colleagues sought to compare non invasive arterial pulse pressure variation (PPV) to invasive PPV, respiratory variation of pulse contour-derived stroke volume, and changes in cardiac index induced by passive leg raising (PLR) and end-expiratory occlusion (EEO) tests. The PPV, the respiratory variation of arterial pulse pressures induced by mechanical ventilation, estimates stroke volume with relatively good accuracy. PLR acts as a “self volume challenge” and the effects of PLR on the cardiac output can predict fluid responsiveness. The EEO is a newer tool which involves  occluding the respiratory circuit for a few seconds at end-expiration interrupting the venous return that occurs at each mechanical inspiration resulting increase in cardiac preload.  Patient populations which may have the greatest benefit from new dynamic indices, the critically ill with hemodynamic failure, were chosen as the focus for this study. 47 critically ill patients were chosen. Baseline non-invasive and invasive PPVs, stroke volume variation, and changes in cardiac index induced by PLR and EEO were recorded. The patient was then administered 500 ml of saline and the response recorded. CNAP could not record arterial pressures in 8 patients which the authors attribute to severe vasoconstriction from vasopressors and/or micro thrombi. Fluid increased cardiac index by ≥15% in 17 'responders' out of the remaining 39 patients. A limitation is that in patients with low tidal volumes the changes in intrathoracic pressure might be so low that changes in cardiac preload could be too low to challenge the preload-dependent stroke volume. The PLR may be useful in this case since it would allow testing for fluid responsiveness even in ventilated patients with low tidal volumes and lung compliance. The authors found that combing multiple dynamic indices did not prove to have higher accuracy in terms of fluid responsiveness and that non-invasive assessment of PPV appears to be of great utility in this patient population. 

Estimating fluid status in the post surgical ICU can be challenging as patients indices are increasingly challenged by failing organs and influenced by measures such as dialysis. In addition to the influence of ventilation, the PPV can also be invalidated by developed arrhythmias which are frequent in this population. In addition to the use of PPV and other static and dynamic measures, I found the use of transthoracic ultrasound to be of great utility in a situation of uncertainty. A quick look at the heart by the anesthesiologist at bedside can reveal valuable information about the overall function/contractility of the heart as well as fluid status as the heart may appear overfilled/ volume overloaded or under filled/ “kissing.”