Perioperative fluid administration: another form of "work-life balance".

“K EEPING the balance” is a traditional, yet still modern, intention of human beings—as well as a central target of perioperative fluid administration. While the triumphal procession of balanced solutions appears unstoppable, quantitative perioperative fluid balance, which is the focus of the study by Kiefer et al. in this issue of ANESTHESIOLOGY, remains one of the most difficult challenges in the operating theater. In our clinical routine, only a few forms of fluid losses out of the circulation are measurable. Although imperceptible, perspiration, deficits caused by preoperative fasting and bowel preparation, and fluid shifts below the body surface remain a dark horse. For decades, it has been well-established clinical practice to liberally infuse fluid in the face of hypotension during or after induction of general and/or neuraxial anesthesia—and to replace fluid deficits caused by overnight fasting and bowel preparation. This practice was believed to be not too much of a problem because fluid compartments were grasped as a dynamic equilibrium where the kidneys handle any potential overload. The nevertheless frequently well-recognized accompanying interstitial edema was considered the inevitable price of cardiovascular stability. The new millennium, however, has brought important physiologic insights indicating that this concept might cause patients to pay a heavy price. Fluid overload has been shown to negatively affect vascular barrier competence, increase cardiopulmonary complications, and prolong recovery of bowel function and hospital stay and should, therefore, most probably be avoided in certain patient collectives. Unfortunately, despite several promising recent studies, perioperative fluid management remains a field where evidence-based medicine leaves us out in the rain. The reason is quite simple. To create reliable evidence, prospective randomized trials have to compare the traditional approach to a new therapeutic idea in a sufficiently high number of patients. If the “study” group shows a better outcome than the “control,” the study treatment is what has to be done in the future. If not, everything remains unaffected. Indeed, perioperative fluid therapy followed a transnational common principle during the past decades that is best described as “liberal. ” Unfortunately, there is not only no worldwide standardized approach. In addition, national and regional differences have led to a wild freestyle mix of crystalloids, colloids, and vasoactive drugs. This lack of agreement has punched itself through to the literature and has led to sometimes even irrational debates as well inconsistent terminology in various study groups. The “restrictive” treatment in one study is called the “liberal” control in the next. This reflection of local strategies within the control groups— instead of general practice—produced data of limited significance, causing misinterpretations and preventing data pooling. Despite of the results from individual studies, the generally much less recognized methodology is questionable. Accordingly, it is currently impossible to formulate evidencebased guidelines for optimal procedure-specific perioperative fixed-volume regimes. Lack of evidence, however, should not be misused as a justification for continuing current therapeutic arbitrariness. Rather, as long as evidence is not available, we must “get back to basics” and medical practice should be guided by physiologic principles and scientific facts. In the long history of human life, the body’s ability to maintain intravascular normovolemia is an essential prerequisite and obviously very important for survival. Conclusively, it is not astonishing that the human body is well adapted to overnight sleeping without fluid supply, which normally does not lead to intravascular hypovolemia. Maintaining this fine-tuned, balanced physiologic state perioperatively by causally treating actual problems seems to be the most logical and “rational” approach. This would implicate to treat intravascular deficits caused by acute bleeding with isooncotic preparations and restoring anesthesia-related vasodilation with a vasopressor. Crystalloids, from this physiological standpoint, should be used to replace ongoing extracellular loss that is the result of urinary output and a realistically calculated rate of insensible perspiration which is, at most 1 ml/kg/h, far below common perception. To those who still believe in basic physiology, it is not surprising that the results of the few available studies on outcomes in this field point in the same direction. It has been indicated repeatedly that a too-positive perioperative volume balance causes a significant perioperative body weight gain by interstitial Accepted for publication November 11, 2010. The authors state to have held lectures for Baxter Deutschland GmbH (Unterschleißheim, Germany), Fresenius Kabi Deutschland GmbH (Bad Homburg, Germany), B Braun, Melsungen AG (Melsungen, Germany), Serumwerk Bernburg AG (Bernburg, Germany) and CSL Behring GmbH (Marburg, Germany). In addition, the authors have received unrestricted research grants from Serumwerk Bernburg AG (Bernburg, Germany), CSL Behring GmbH (Marburg, Germany) and Fresenius Kabi Deutschland GmbH (Bad Homburg, Germany).