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Does the Choice of Fluid Matter in Major Surgery?
INTRODUCTION
Intravenous (IV) fluid therapy is known to have a major impact on surgical outcomes and, as a result, has been the focus of many clinical studies. The overall aim is to maintain normal intravascular volume, tissue fluid, and electrolytes but avoid fluid and sodium overload. The first use of IV fluid therapy dates back to the 1831 European cholera epidemic when attempts were made by physicians to develop the optimal mixture of constituents added to water to infuse into patients with life-threatening dehydration caused by cholera. Even then the goal of creating a solution as close as possible to plasma was the primary goal. So why almost 200 years later is there still so much controversy over which type of fluid to use for major surgery? The reasons are multifactorial and due to the ongoing changes in surgical and perioperative practice. Surgical techniques and perioperative management of patients has seen a radical change in the last 20 years with the introduction of minimally invasive surgery using laparoscopic and robotic-assisted approaches and the adaption of enhanced recovery after surgery (ERAS) pathways. This means that fluid studies in non-ERAS pathways are not always relevant to modern-day perioperative surgical practice.
Optimal minimally invasive surgery has led to a reduction in blood loss and tissue damage, leading to reduced perioperative fluid shifts compared with traditional open surgery through large abdominal incisions so administered fluid volumes are lower. ERAS pathways have reduced the quantity and amount of time a patient receives IV fluids during the perioperative period. ERAS pathways mean patients are no longer starved and dehydrated before surgery and are given carbohydrate drinks up to 2 hours before surgery. Diligent perioperative administration of fluid and maintenance of mean arterial pressure (MAP) greater than 65 mm Hg by the anesthesiologist maintain organ and gut perfusion and reduce extracellular fluid shifts in the operating room. Patients are no longer kept nil by mouth after surgery; instead there is resumption of oral intake within a few hours of surgery and commencement of protein drinks or normal diet within 24 hours of surgery, allowing the early cessation of IV fluids, which reduces the risk for salt and water overload from ongoing IV fluid administration.
This chapter will focus on the current controversies of the type of IV fluid used in the perioperative patient for elective major surgery. Resuscitation, trauma surgery, massive blood loss, and septic emergency patients are not in scope. The chapter explores what solutions offer advantages or disadvantages for clinical use and the importance of timing of administration and quantity of fluid used.
OPTIONS AND EVIDENCE
Types of Intravenous Fluids
Crystalloids
Crystalloids are solutions of sterile water with the addition of different amounts and types of electrolytes. Depending on the additional constituents, they may result in solutions that are hypotonic, isotonic, or hypertonic with respect to plasma. There has been increased focus on creating crystalloids that have a similar electrolyte composition to plasma and have a buffer, with the term “balanced” being used. Examples of balanced crystalloids include traditional Hartmann’s solution and Ringer’s lactate where lactate is the buffer. More modern solutions use acetate and gluconate such as Plasmalyte A (Baxter Healthcare Corp, USA) and Normosol (Hospira Inc, USA). This has been in response to the increasing recognition that 0.9% normal saline can lead to hyperchloremic acidosis if used as the main resuscitation and maintenance IV fluid.
Dextrose-containing solutions.
Routine perioperative use of 5% dextrose solutions can lead to significant plasma hyponatremia. Children in particular are more likely to develop clinically significant symptoms of hyponatremia at higher plasma sodium levels than adults, so dextrose solutions should be combined with NaCl to avoid this with appropriate dextrose and potassium supplementation. Winata et al. showed that adults are also at risk for hyponatremia when dextrose solutions are used. In 659 patients, 161 patients (24%) developed postsurgical hyponatremia with dextrose administration being a key factor. Subgroup analysis by surgical sites showed that association of dextrose administration with hyponatremia was most evident in upper gastrointestinal (GI) and hepatobiliary surgery. Dextrose-only solutions should therefore be restricted perioperatively to supplementing when maintenance of blood glucose is warranted and postoperatively when increased free water is required. Administering too much glucose intravenously may also cause hyperglycemia, which is associated with increased perioperative complications, particularly at a time of stress, and reduced insulin sensitivity perioperatively. A dextrose 5%/normal saline 0.45% solution can be a useful postoperative IV fluid where there are no ongoing fluid shifts or losses and the patient cannot take fluid by mouth. Dextrose solutions can also be used as a diluent for drug infusions rather than 0.9% saline to reduce Na and Cl administration.
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