Complexity of blood volume control system and its implications in perioperative fluid management

Abstract

The use of fluid therapy attempts to optimize blood circulation by manipulating the circulating blood volume (BV). BV may be a key intermediate parameter between fluid therapy and the blood circulation, and it has been assumed that BV can be controlled by fluid therapy. In order to construct a fluid therapy protocol, firstly, we have to confirm whether BV can actually be controlled by fluid therapy. Volume kinetics studies and dilution techniques for BV measurements have enabled the actual effects of fluid management on BV to be analyzed in the presence of various pathological conditions. Various studies have shown that the effect of fluid, especially crystalloid, on BV varies considerably among individuals, and even BV values measured at a single time point vary from 40 ml kg(-1) to 110 ml kg(-1). It has become apparent that such wide variations in interindividual BV preclude the establishment of universal optimal fluid management protocols. Thus, secondly, it should be clarified how BV is controlled, and whether or not we can control it. Perioperative BV reportedly changes in a manner that is independent of the in-out fluid balance, but is related to hormonal factors. Because inflammation and some hormones control vascular permeability and the renal adjustment of solutes and fluids, such factors may readjust the BV even after interventional fluid therapy. Perioperative BV may be predominantly controlled by an internal regulatory system, regardless of whether "restrictive" or "liberal" fluid management strategies are employed. Recognizing this physiological control of BV may help us to develop individualized fluid management strategies.

Morbid Obesity and Optimization of Preoperative Fluid Therapy

“…In our opinion, conventional Doppler indices are better and more robust for this purpose than TDI. Thus, in MO, monitoring ΔSV together with conventional dynamic transmitral indices provides sufficient information about volumeresponsiveness, limitations in global stressed volume, and pressure-volume relationship in LV (22,27). In addition, we confirmed that where there are physical limitations for signal acquisition related to body habitus as in MO, detailed comprehensive assessment of filling pressures can be difficult and time-consuming.…”

Fluid therapy in neurotrauma: basic and clinical concepts

“…Where Qf is the total fluid flux out of capillaries (not represent the quantity, but just the speed of water movement [16]) and Kf is the filtration coefficient (the product of the membrane conductance and the membrane surface area), Pc is intravascular hydrostatic pressure, Pi is interstitial hydrostatic pressure, πc is colloid osmotic pressure within the vasculature, πi is interstitial colloid osmotic pressure gradient across the vessel wall, and R is the oncotic reflection coefficient, the tendency of a membrane to impede the passage of oncotically active particles [16,41]. A R of 0 indicates a membrane that is totally permeable to protein while a R of 1 indicates a membrane that completely prevents protein diffusion.…”

“…Distribution terminates when the balance of the hydrostatic pressure and the osmotic pressure cancel each other out. Because the interstitium consists not only of free space but also of absorbent gel, captured water in the gel does not contribute to lowering the osmotic pressure in the interstitium [16]. Therefore, the osmotic pressure does not easily change until the gel is saturated by water movement.…”

“…This is a mechanism of edema formation. Thus, Starling's law does not determine the distribution ratio between plasma and interstitium, it just explains the movement of water through the capillary wall [16]. The original interpretation of an equilibrium including fluid re-absorption at the venous end of the microcirculation is now known to be incorrect through actual measurement of the pressures involved.…”

“…Fluid therapy (FT), as the name implies is a treatment with fluids, thus, is a drug [15]. The final goal of fluid management is to optimize the circulatory system to ensure the sufficient delivery of oxygen to organs [16]. FT is needed for the following requirements: 1.…”