Goal-Directed Fluid Therapy: What the Mind Does Not Know, the Eye Cannot See

Abstract

Dear Editor, Y our recent first (1, 2) and second (3, 4) round fluid debates were enjoyable and interesting. The editor and authors are to be congratulated for an excellent distillation of the key elements of this important discussion. We have a few comments relative to key points that were made.First, Drs. Della Rocca and Vetrugno state that dynamic indices cannot be used as indicators of fluid responsiveness (FR) during open chest conditions. Respectfully, we disagree. The authors provide us with two "supporting" references, one by Wyffels (5), and the other by Lansdorp (6). The first of these two papers included 15 patients, 10 of whom exhibited dynamic indices (DynI) that were less than 10% or were within the gray zone (7,8). DynI within these ranges are unlikely to be associated with FR. Of note, all patients demonstrated physiologic concordance with the passive leg raising (PLR) maneuver: Stroke volume variation (SVV) and pulse pressure variation (PPV) decreased and the cardiac index (CI) rose, even during open chest conditions, though the rise in CI was not statistically significant in this small sample. The second paper by Lansdorp investigated FR in post-cardiac surgical patients within the Intensive Care Unit (ICU) and does not address the use of dynamic indices during open chest conditions. The idea that DynI lose their predictive ability during open chest surgery is also supported by de Waal who demonstrated that DynI were no more useful than static indicators for predicting FR during open chest conditions (9). Contrary to these findings, Reuter (10), Suehiro (11), Lee (12), Kang (13), and Rex (14) have all demonstrated that DynI can be used to predict FR during cardiothoracic surgery. How is the practicing anesthesiologist to reconcile these contradictory conclusions? This question was best answered by Jean Louis Teboul, who not only described a plausible physiologic mechanism based on transpulmonary pressure changes generating meaningful DynI during open chest conditions, but also provides us with a solid understanding of how DynI should be interpreted during open chest conditions. Assuming that appropriate clinical conditions are met for using DynI (15), Teboul states "the presence of high PPV (or SVV) is indicative of fluid responsiveness under both closed and open chest conditions. However, under open conditions, other tools are still required to diagnose the origin of hemodynamic instability because the presence of low PPV and SVV cannot preclude a positive hemodynamic response to fluid." (16). As with any hemodynamic parameter, the clinician must be aware of its underlying physiologic mechanism, its clinical meaning, and the pitfalls that may derail its interpretation.