Introduction
While fluid therapy is a standard procedure during surgery, anesthesiologists disagree over the kind, quantity, and timing of fluids given to patients undergoing major abdominal surgery. It has been noted that a significant contributing factor to morbidity and death after surgery is the perioperative fluid balance. Several solutions for fluid management have been developed and put into clinical practice.
What Is Pre-operative Fluid Management?
The goal of preoperative fluid management measures is to prevent hypovolemia or dehydration in the patient before they enter the operating room. Up to two hours before elective surgery, clear fluid intake can be freely consumed according to several worldwide guidelines, including those issued by the American Society of Anesthesiologists. The recommendations are based on a meta-analysis of randomized trials that shows that giving clear liquids two to four hours before a procedure reduces the risk of aspiration compared to fasting overnight. Since the human body constantly produces saliva in addition to endogenous gastric secretions, the stomach naturally absorbs 500 to 1,250 milliliters of fluid following an eight-hour fast. Consuming clear fluids up to two hours before surgery may promote patient comfort and safety since it lessens appetite and thirst, does not increase stomach volumes, and lowers the acidity of the stomach contents.
How Is Fluid Responsiveness Assessed?
Due to increased fluid losses and usually longer fasting periods, preoperative IV fluids are required for the majority of emergency surgeries as well as occasionally for elective surgeries. Although determining a patient's fluid status accurately can be challenging, most of the time a thorough history and physical examination, along with a few basic tests, should be enough to determine the patient's fluid responsiveness. Patients who have a positive fluid response should be the only ones receiving additional intravenous fluids. The most effective way to assess this is to use the steep part of the Frank-Starling curve, which shows that minor changes in preload will increase Stroke Volume (SV). (Frank-Starling curve is a curve that represents the relationship between stroke volume and end-diastolic volume. Stroke volume is the blood pumped from the left ventricle in a heartbeat. End diastolic volume is the amount of blood in the ventricle at the end of a diastole).
An increase in SV of at least ten percent is commonly used to characterize fluid responsiveness. A decrease in venous return is the primary mechanism by which positive pressure mechanical ventilation causes a cyclic reduction in left ventricular preload; this effect is amplified in hypovolemia. Therefore, differences in SV and pulse pressure during the respiratory cycle will be caused by changes in preload.
How Is Fluid Managed During a Surgical Procedure?
Adequate intraoperative IV fluid management is crucial since both excessive and insufficient resuscitation are linked to adverse outcomes. The most effective manner of administering IV fluids has changed over the last twenty years due to changes in surgical methods and patient routes like Enhanced Recovery After surgery (a special protocol that is patient-centered and evidence-based to reduce a patient’s stress after a surgery), changing research, and prevailing norms. Using robotics and minimally invasive techniques has decreased gross anatomic manipulation and evaporative fluid loss in several operations. Historically, due to apparent third space (an outdated term used to describe the movement of body fluids from the blood into the interstitial spaces) and insensible losses, substantial volumes of IV fluids were administered both during and after surgery, especially during abdominal surgery.
A study conducted around 15 years ago by Brandstrup et al. demonstrated that a restrictive strategy was associated with a much lower rate of problems during abdominal surgery when IV fluid was used liberally. Patients in the liberal group gained over eight pounds of weight after surgery, which was indicative of tissue edema, despite receiving no more than 1.6 gallons of fluid on the day of the procedure. On the other hand, patients in the restriction group gained a maximum of about two pounds of weight and received slightly less than one gallon of liquids on the day of surgery. With the increasing acceptance of Enhanced Recovery After Surgery pathways and the current recommendations supporting a restrictive strategy, the phrase ‘restrictive fluid management’ has gained favor over time. However, the volume of fluid administered under restrictive fluid management has increasingly decreased, and a restrictive regimen intended to prevent postoperative fluid retention indicated by weight gain was referred to as ‘zero balance when it was first established.
Two types of intraoperative fluid requirements are maintenance treatment and volume therapy. More maintenance therapy is required for major procedures involving significant changes in the fluid to cover insensible losses and urine output (starting with the preoperative fast). To evaluate volume responsiveness and treat objective evidence of hypovolemia, volume treatment involves giving intravenous fluid boluses (usually 250 ml) to increase intravascular volume and oxygen delivery.
What Is Post-operative Fluid Management?
Patients are advised to resume oral intake as soon as possible following surgery. This enables discontinuing IV fluid administration in many Enhanced Recovery After Surgery options, frequently before the patient's discharge from the post-anesthesia care unit. The Enhanced Recovery After Surgery pathways stress how important it is to minimize the use of intravascular lines (IV and arterial), nasogastric tubes, urine catheters, and drain tubes after surgery because these devices further limit a patient's freedom of movement.
The findings of the RELIEF (Reflux assessment and quality of life improvement with micronized flavonoids) study, however, advise caution in patients recovering from major abdominal surgery who cannot consume enough food orally. In the restrictive group, there was nearly a twofold increase in the incidence of postoperative acute renal damage, along with a decrease in urine production and an increase in oliguria during and after surgery. Consequently, it would appear reasonable to maintain adjusted IV fluid therapy in patients with impaired oral intake, even though the overall contribution of the postoperative portion of the procedure in RELIEF is unknown.
Conclusion
Perioperative IV fluid management is one of the most popular procedures and areas of responsibility for anesthesiologists. Uncertainty in clinical practice and variations have plagued this issue, which at first glance appears simple. Understanding them and carefully incorporating the most important discoveries into current practice should enhance the care given to patients having major surgery. Before starting vasopressor medication, perioperative patients with hypotension or signs of insufficient tissue perfusion should have their fluid levels optimized.
