Anesthetic Techniques: Fluid Management

Abstract

BACKGROUND:

Acute normovolemic hemodilution (ANH) is used in major surgery expected to be accompanied by excessive blood loss. Reducing the hemoglobin content may disturb cerebral oxygen balance. The aim of this study was to assess the effect of ANH on cerebral oxygen balance in patients subjected to brain tumor resection.

METHODS:

Attendees at the 2005 SABM Symposium were fascinated with Dr. Amy Tsai’s presentation, “Microcirculation and Tissue Oxygenation Beyond Hemoglobin.” This present study by Tsai and colleagues, further exploring the role of blood viscosity in maintaining microcirculatory function, provides further laboratory evidence that the present limits with hemodilution may relate more to viscosity than oxygen carrying capacity and that methods to preserve blood viscosity may influence the blood transfusion trigger.

Summary This study provides further evidence that Hb measurement alone is an inadequate transfusion trigger as it does not accurately measure changes in red cell volume (RCV), plasma volume (PV) and blood volume (BV). Slight and colleagues designed this study to record changes in the above at various time points in 30 adult patients scheduled for elective cardiac surgery. Procedures included coronary artery bypass and/or valve replacement surgery.

This article presents a mathematical model to calculate how the constituents of sequentially drawn autologous whole blood units change during the practice of acute normovolemic hemodilution (ANH). ANH is one modality available in the armamentarium for patient blood management. Although its efficacy is still controversial in the literature, many authors have suggested that when combined with other techniques it can be an effective tool to reduce or avoid allogeneic transfusion. It is also purported to contribute to improved microvascular blood flow and tissue perfusion.

Abstract

The authors refer to this study as “one of the most comprehensive head-to-head ex vivo comparisons of commonly used IV fluids in clinical practice.” Using thromboelastography they examine the coagulation effects of different crystalloid and colloid fluid preparations. The fluids were saline, Lactated Ringer’s solution, hetastarch, pentastarch, tetrastarch and human albumin solution.

Summary The authors of this study state that the crystalloid-colloid debate has been widened to a colloid-colloid debate with, in addition to human albumin, many synthetic colloids now available to choose from. In this randomized controlled trial they compare 5% human albumin with a third generation hydroxyethyl start preparation (6% HES 130/0.4) as part of volume replacement in elderly patients (>70 years of age) undergoing major abdominal cancer surgery.

Summary This randomized controlled trial assessed the safety of hypertonic-hyperoncotic solution (HHS) and its hemodynamic effect in children following cardiac surgery with cardiopulmonary bypass for repair of congenital heart defects. 50 consecutive children meeting study criteria were enrolled and randomized to receive either HHS (7.2% sodium chloride with 6% hydroxyethyl starch 200) or isotonic saline solution (0.9% sodium chloride) in the pediatric intensive care unit immediately following surgery to repair atrial or ventricular septal defects. 25 patients made up each group.

Summary This randomized controlled trial was designed to evaluate the effect of heparin-coated oxygenators and substitution of cardiotomy suction with autologous cell salvage on platelet function in patients undergoing coronary artery bypass graft (CABG) surgery on cardiopulmonary bypass (CPB). Earlier animal studies by this group demonstrated that the oxygenator and cardiotomy suction were the parts of the CPB circuit that impacted most on platelet function.

Summary Boodhwani and colleagues conducted this meta-analysis to examine the evidence for ultrafiltration (used to reduce the hemodilution that occurs during cardiopulmonary bypass) as a blood conservation strategy in adult cardiac surgery.