The Tenets of Fluid Therapy
TENET: a principle, belief, or doctrine generally held to be true; especially: one held in common by members of an organization, movement, or profession
Perioperative intravascular volume infusion (fluid therapy) has the purpose of maintaining and restoring, when needed, an effective circulating blood volume and adequate organ perfusion Fluids should be administered to prevent untoward intraoperative or post-operative hypoperfusion and thereby optimize clinical outcomes. Excess fluids and the associated harms of peripheral and pulmonary edema associated should be avoided. Fluid therapy is a fundamental perioperative aspect of resuscitation and stabilization, but should be, like any other treatment, titrated to a predefined effect and with knowledge of its potential side effects. Recently acquired ability to accurately predict fluid responsiveness and clear benefits of attained predefined total blood flow targets to improve patient-centered outcome makes prior approaches, especially those that treated all patients in a similar fashion, inferior. This document refocuses fluid therapy within the context of fluid responsiveness and individualized therapeutic targets.
We have organized this summary into 3 background tenets, 7 perioperative recommendations and 1 post-op recommendation.
- Fluid Therapy impacts clinical outcomes. This is especially true in a subset of patients that often can be identified prior to surgery.
- A patient's hemodynamic physiologic status and hemodynamic stability defines the need for cardiovascular support with the goal to sustain organ perfusion pressure and blood flow. Fluid therapy is one aspect for support. Fluid therapy is often the first line of hemodynamic support. However, fluids requirements vary greatly among patients and not all patients benefit from fluids.
- Hemodynamics are best optimized by systematic consideration of five measures: vascular pressures, intravascular volumes, cardiac function, blood flow and their impact on tissue oxygenation. Hemodynamic optimization may require appropriate fluid therapy, transfusion of blood components and pharmacologic support.
Guidelines and Recommendations
- There should be an individualized perioperative fluid optimization plan and fluid management algorithm for each patient based on these factors:
- patient status (health, age, physiology and co-morbidities)
- surgical risk, based on the type of surgery, the surgical approach and style specific to the individual surgeon.
- the level of hemodynamic monitoring, which is determined by the above considerations.
- Local fluid standard practice, guidelines and algorithms for fluid therapy should be based on physiological principles, evidence-based medicine and local expertise. This requires discussion and consensus of the anesthesiologists in an organization. Setting local standard practice and consensus requires significant group effort.
- Algorithms should not be fixed, but rather should be 'dynamic' and allow for individualizing fluid therapy based on a patients changing physiologic state and responses to fluid and drug therapy. Monitoring needs may change during surgery due to increased patient and surgery risks.
- Key to effective algorithms is to incorporate goal directed therapy (GDT). Algorithms should incorporate strategies for patients who do not respond to fluid therapy (“non-responders”) and important co-morbidities.
- Delivery of fluid therapy: Bolus Therapy is recommended over a continuous infusion as it provides two functions.
- a prompt increase in intravascular volume and usually a needed improvement in perfusion (cardiac output).
- a means to assess the patient’s response to fluid with changes in static and dynamic indices of volume, flow and oxygenation. Such assessment is used to help determine the requirements for additional fluid therapy.
- Fluid Responsiveness is a quantitative assessment of the patient’s ability to respond to a fluid bolus with improved cardiac output or its surrogates. It is most effectively assessed using Dynamic Indices of Fluid Responsiveness, (e.g., respiratory variations in stroke volume or its surrogates) and should be assessed in a uniform manner before and promptly after each fluid intervention bolus). However, static variables of pressure, volume, flow, cardiac function and oxygenation should not be discarded and are used for optimizing the balance between fluid and drug therapy. Intraoperative motion and physiologic artifact (noise) from surgery can interfere with the accurate interpretation of correct dynamic indices.
- Composition (type) of fluid therapy: There are 3 fluid types - crystalloid, colloids and blood. Each has its unique characteristics and role in fluid therapy.
- Crystalloids are best used to replace extracellular volume losses from insensible perspiration and urine output, and have a lesser impact on increasing vascular volume and hemodynamics.
- Colloids selectively increase vascular volume, preload and flow in volume responsive patients. Hemodynamic instability is most promptly and effectively treated with colloids.
- Blood Components are used after significant blood loss or when a patient’s hemoglobin and coagulation drop to a level where there is a concern for inadequate tissue oxygenation or hemostasis, respectively.
- Cases of low complication, short duration, and uneventful surgery are appropriately managed with crystalloids (Day Surgery Patient). Cases of high complexity, long duration and perioperative blood losses are best managed with background crystalloids and colloid boluses to optimize hemodynamics, and blood products per assessments of oxygen adequacy and hemostasis.
- Continuous infusions of crystalloids for insensible losses, which are not significant, are unnecessary. Preoperative volume status is not typically known, but should not be presumed to be inadequate or adequate. Preoperative dehydration due to NPO should be avoided and if necessary a fluid therapy protocol preceding surgery is a special consideration and its correction should be individualized. Insensible losses are most often not significant.
Guidelines are general, similar to this document, while algorithms are highly specific as to variable, ranges and endpoints. The difference is important.
Boluses are best delivered at a rapid rate (5-10 min). Use of an a priori list of specific volumes and infusion at the same rate provides a standardized test for volume responsiveness in order to assess any changes in a patient’s volume status.
- Appropriate Monitoring and Fluid Therapy should continue after surgery - the anesthesiologist and the post-operative intensivist are a team and should confer at handoffs of major cases. Anesthesiologists should monitor the postoperative outcomes of their patients.
Tenets of Fluid Therapy Original Contributors.
Lais HC Navarro, George Kramer, R. Benjamin Voigt, Michael Pinsky, Vijaykumar Tarnal, Giorgio Della Rocca, Joshua A. Bloomstone, Tong-Joo Gan, Sheldon Magder, Timothy E Miller, José Otávio Auler, Azriel Perel, Maxime Cannesson, Michael P Grocott,and Rodrigo M Lima
Signatories to date: Clayton Hines, Nicole Ribeiro Marques,