The passive leg raising test to guide fluid removal in critically ill patients.

Background: To investigate whether haemodynamic intolerance to fluid removal during intermittent renal replacement therapy (RRT) in critically ill patients can be predicted by a passive leg raising (PLR) test performed before RRT.

Methods: We included 39 patients where intermittent RRT with weight loss was decided. Intradialytic hypotension was defined as hypotension requiring a therapeutic intervention, as decided by the physicians in charge. Before RRT, the maximal increase in cardiac index (CI, pulse contour analysis) induced by a PLR test was recorded. RRT was then started.

Results: Ultrafiltration rate was similar in patients with and without intradialytic hypotension. Thirteen patients presented intradialytic hypotension, while 26 did not. In patients with intradialytic hypotension, it occurred 120 min [interquartile range 60-180 min] after onset of RRT. In the 26 patients without intradialytic hypotension, the PLR test induced no significant change in CI. Conversely, in patients with intradialytic hypotension, PLR significantly increased CI by 15 % [interquartile range 11-36 %]. The PLR-induced increase in CI predicted intradialytic hypotension with an area under the ROC curve of 0.89 (95 % interval confidence 0.75-0.97) (p < 0.05 from 0.50). The best diagnostic threshold was 9 %. The sensitivity was 77 % (95 % confidence interval 46-95 %), the specificity was 96 % (80-100 %), the positive predictive value was 91 % (57-100 %), and the negative predictive value was 89 % (72-98 %). Compared to patients without intolerance to RRT, CI decreased significantly faster in patients with intradialytic hypotension, with a slope difference of -0.17 L/min/m(2)/h.

Conclusion: The presence of preload dependence, as assessed by a positive PLR test before starting RRT with fluid removal, predicts that RRT will induce haemodynamic intolerance.