Fluid Therapy in Critical Care

Fluid Therapy in Critical Care

Fluid Therapy in Critical Care Leonel Londoño DVM, DACVECC
Leo Londoño, DVM, DACVECC, is a clinical assistant professor of emergency and critical care and director of the hemodialysis unit at University of Florida. He received his DVM from UF and completed his residency in emergency and critical care at UF after completing a rotating internship at Hollywood animal hospital in south Florida. His research interests include renal and non-renal applications of extracorporeal purification techniques, endothelial and glycocalyx pathophysiology in the critically ill, and hospital-acquired acute kidney injury. PRIMUM NON NOCERE. When used appropriately, IV fluids can improve outcomes in the most critically ill animals. However, inappropriate IV fluid therapy can have harmful effects. Photo Courtesy shutterstock.com/sommart sombutwanitkul.
Intravenous (IV) fluid administration is probably the most frequently used therapy in veterinary hospitals. Aggressive IV fluid resuscitation in emergent patients and continuous IV fluid administration in hospitalized patients have long been considered fundamental in the management of critically ill animals. However, research into whether the type and volume of fluids infused can contribute to comorbidities and decrease the chances of a favorable outcome continues. This article reviews new trends in fluid therapy in human and veterinary critical care medicine and provides some clinical guidelines for fluid administration based on these trends ( FIGURE 1 ). TRENDS IN CRITICAL CARE MEDICINE Avoidance of Synthetic Colloid Solutions
Colloid fluids include natural colloids (e.g., plasma products, purified albumin solutions) and synthetic colloids (e.g., hydroxyethyl starch [HES], dextrans, gelatins). Colloid solutions contain large molecules (molecular weight 10% increase in basal body weight during hospitalization. In several studies of critically ill people, a positive fluid balance has been associated with increased mortality, longer hospitalization periods, and requirement of renal replacement therapies. 19,20 Critically ill dogs have also been identified to have a greater risk of fluid overload with subsequent increased risk of mortality. In one study, dogs that developed fluid overload had a 50% mortality rate. 21 FIGURE 3. Chemosis in a dog with fluid overload.
One of the major pitfalls in veterinary medicine is the lack of close monitoring of body weight in the most critically ill. In the author’s experience, many cases of oligo-anuric AKI that are referred for hemodialysis have a positive fluid balance from overzealous fluid therapy and lack of close monitoring for body weight increase or other clinical signs of edema ( FIGURE 3 ). The physiologic consequences of aggressive fluid therapy, even in patients with renal dysfunction, range from disruption of important cellular processes to severe multiorgan dysfunction ( BOX 1 ). 22 BOX 1 Major Physiologic Consequences of Fluid Overload Disruption of phosphorylation and membrane polarization Increased production of tumor necrosis factor-α and interleukins Altered glucose metabolism and insulin release Decreased cardiac output Increased renal edema and decreased GFR Increased gut permeability and ileus Decreased soft tissue healing Dilution of coagulation factors and increased risk of hemorrhage Use of Early Enteral Nutrition
The systemic benefits associated with early enteral nutrition in critically ill animals are incalculable. It cannot be emphasized enough that early nutrition plays a key role in the management of animals with acute illness. Delaying enteral nutrition is recommended only in critically ill people with uncorrected shock, persistent hypoxia and acidosis, ongoing upper GI bleeding, GI obstruction, severe gastric fluid retention, or abdominal compartment syndrome. 23
The use of nasogastric/nasoesophageal tubes in small animals has been increasing in clinical practice and is improving the management of the most critically ill. These tubes do not require general anesthesia or heavy sedation for placement and for the most part do not cause major discomfort to the animal. When calculating fluid balance, enteral nutrition should be included in the sum of all the intakes. In patients without fluid losses and a zero or positive fluid balance, enteral nutrition can replace IV fluid supplementation and provide a more physiologic delivery of daily water requirements. FLUID ADMINISTRATION IN SPECIFIC DISEASE CONDITIONS
BOX 2 lists some of the most common reasons for IV fluid resuscitation in veterinary medicine. Despite the recognized benefits of fluid therapy in these situations, evidence-based medicine is rarely applied, and the fluid choice and volume administered are often inappropriate. In many cases, inappropriate fluid regimens do not lead to overt harmful effects because the kidneys and cardiovascular system compensate for the excessive volume or supraphysiologic load of electrolytes delivered, but in some cases, inadequate fluid therapy leads to exacerbation of cardiovascular, respiratory, and renal dysfunction in the critically ill. BOX 2 Common Reasons for Intravenous Fluid Resuscitation Hypovolemia (traumatic or nontraumatic hemorrhage or GI/renal fluid loss) Distributive shock from sepsis or other noninfectious causes of systemic inflammation such as pancreatitis or endocrine emergencies (e.g., diabetic ketoacidosis, addisonian crisis) Perioperative hemodynamic optimization Acute or chronic renal disease Severe GI disorders
A major mistake in veterinary medicine is the inappropriate replacement of fluid deficits by delivering fluid to the patient in terms of maintenance rates and not calculated volume over a target of time. For example, giving an animal 2 times the maintenance rate of fluids for replacement of a 6% volume deficit may take over 24 hours. Instead, the desired volume to be replaced should be divided in a short period of time (6 to 12 hours), in addition to maintenance rate of fluids and calculated ongoing losses.
Increasing evidence in the human and veterinary literature demonstrates that specific disease conditions require appropriate prescription fluid therapy and an understanding of the possible adverse effects of fluid therapy. Following is some information regarding the approach to IV fluid therapy in common disease states observed in critically ill small animal patients. Anemia
Correction of intravascular volume deficits is essential in stabilizing anemic animals. Normally, oxygen delivery to cells exceeds oxygen consumption by a factor of 3 or 4 under resting conditions. If lower hemoglobin concentrations lead to decreased oxygen delivery, oxygen consumption can remain constant because the cells can increase the amount of oxygen extracted from each hemoglobin molecule.
However, in anemic animals with fluid deficits, oxygen delivery is compromised by not only low concentrations of hemoglobin but also the decreased ability of red blood cells to reach hypovolemic tissues. Although many veterinarians consider dilution of the circulating cell mass an indication for delaying fluid therapy in anemic animals, volume deficits should be corrected to allow the remaining red cells to deliver oxygen. Fluid therapy must be used as described above with goal-directed resuscitative efforts and rapid de-escalation until blood products become available.
The approach to fluid therapy in patients with anemia from hemorrhagic shock ( TABLE 1 ) takes into account the cause of hemorrhage and the cause and timing of blood loss. For example, in animals with acute hemorrhage and risk of exsanguination from trauma, rupture of an intracavitary neoplasm (e.g., splenic hemangiosarcoma), or coagulopathy, permissive hypotension and volume-restricted resuscitation strategies are advocated to prevent blood clot dislodgment and exacerbation of hypovolemic shock. 13 These strategies are implemented after a surgical plan has been established to stop the source of bleeding or blood products become available to replace the components lost.
In animals with ongoing causes of anemia (e.g., immune-mediated hemolysis, chronic inflammation, chronic kidney disease, GI or external parasitism), initial fluid therapy should be guided to rapidly correct fluid deficits or percent dehydration over several hours. If the patient requires a blood transfusion, the use of separate IV access lines (2 IV catheters) is encouraged to rapidly correct both anemia and intravascular volume deficits, with rapid optimization of macrovascular parameters and correction of decreased oxygen delivery to tissues. If the patient is hypotensive or has severe signs of hypovolemic shock due to the combination of anemia and decreased intravascular fluid volume, a bolus of crystalloids (LRS, Plasma-Lyte 148, or Normosol-R 10-20 mL/kg IV over 10 minutes) can be given to more rapidly correct clinical signs of hypovolemia. Cardiomyopathy
Although patients with underlying cardiomyopathies may require fluid therapy because another systemic process is causing volume loss, the use of fluid therapy in animals with cardiomyopathies and evidence of pulmonary edema or concern for congestive heart failure is absolutely contraindicated.
Patients that are being treated for congestive heart failure, especially geriatric animals, tend to have an increase in kidney values during hospitalization, most likely due to unmasked chronic renal disease and ongoing cardiorenal syndrome. It is imperative to recognize that increases in renal functional markers such as creatinine are not an indication for IV fluid therapy in animals currently undergoing treatment for congestive heart disease. In these situations, worsening of the pulmonary function leads to decreased oxygen delivery to tissues, especially the kidneys and heart. Sepsis and Septic Shock
No specific guidelines are available for IV fluid therapy in animals with signs of systemic inflammatory response syndrome or sepsis; therefore, fluid therapy recommendations ( TABLE 1 ) are extrapolated from the international guidelines for management of sepsis and septic shock in people. 6 Some of the recommendations from the Surviving Sepsis Campaign are based on animal studies of sepsis. 6 Acute Kidney Injury and Renal Dysfunction
Fluid therapy in hypovolemic patients with AKI is aimed at optimizing cardiac preload and stroke volume to restore systemic blood pressure, cardiac output, and, as a result, renal perfusion pressure ( TABLE 1 ). Unfortunately, overzealous fluid therapy without close monitoring of body weight and daily fluid intake is common, with deleterious effects on GFR 11,22 and other organ systems. The choice of fluid also appears to have a pivotal role in renal function and mortality, especially in critically ill and septic human patients, where chloride restriction and avoidance of synthetic colloids may improve outcome and reduce the requirement for extracorporeal blood purification. 2,3,5,9,12-15
Another major pitfall in the management of animals with AKI or ureteral/urethral obstructions is the lack of identification of polyuric (high-output) phases associated with diuresis. During the recovery phase of AKI, animals can quickly go from an oligo-anuric urine output state to a polyuric phase with sometimes excessive fluid loss. The polyuric phase can be easily missed if urine output and body weight are not monitored in the hospital, or when animals are sent home after functional renal markers such as creatinine and urea start improving.
Similarly, cats commonly develop postobstructive diuresis after alleviation of urethral obstruction. 24 In cases of urinary obstruction, especially in the acute resuscitation phase, the fluid choice should be one that rapidly corrects electrolyte and acid-base imbalances. Two studies have demonstrated that the use of balanced crystalloids (e.g., LRS, Plasma-Lyte) instead of 0.9% saline solution leads to a more rapid correction of electrolyte and pH abnormalities in obstructed cats. 25,26 Pulmonary Disease
No specific guidelines exist in veterinary medicine to help guide fluid therapy in animals with lung disease, so fluid therapy should be judicious and tailored to each patient. Pulmonary conditions such as infectious or aspiration pneumonia and noncardiogenic pulmonary edema can worsen without judicious use of fluids. In these cases, fluid therapy should be titrated on an individual basis.
Fluid therapy can exacerbate pulmonary dysfunction by increasing hydrostatic pressure and endothelial dysfunction caused by inflammation at the level of the pulmonary capillaries, ultimately leading to fluid extravasation and impaired gas exchange. 22 Based on human studies showing better outcomes and decreased need for mechanical ventilation, fluid therapy in an animal with suspected or diagnosed pulmonary disease should be restricted, with the aim of having a zero or negative fluid balance. 27 If a cardiogenic cause of pulmonary edema is suspected, fluid therapy should not be initiated until underlying heart conditions are ruled out. Hypoalbuminemia
Albumin is responsible for up to 80% of the oncotic pull within the intravascular compartment. The use of crystalloids in severely hypoalbuminemic animals can lead to further extravasation of water into the interstitial space and worsening of edema in vital organs. As mentioned above, the use of colloids to increase oncotic support and reverse edema is now in question. Crystalloid therapy should be considered as a resuscitation strategy in a hypoalbuminemic animal with severe cardiovascular collapse only when plasma products or albumin are not available.
When used, the effects of IV crystalloid fluids are short lived, as 80% of the fluid volume infused leaves the intravascular space within 20 to 30 minutes of administration. The long-term approach for fluid therapy in hypoalbuminemic patients should include early enteral nutrition, which not only can optimize water balance but also improve oncotic support through increased delivery of nutrients to the GI tract. Gastrointestinal Disease
GI emergencies are among the most common reasons for prescribing fluid therapy in small animals. Outpatient IV or subcutaneous crystalloid supplementation to correct fluid deficits caused by vomiting, diarrhea, and lack of oral water intake is common practice in veterinary medicine. Appropriate fluid therapy for animals with GI conditions should include calculation of total fluid deficit from physical examination findings along with measurement of ongoing losses and calculation of required daily intake to maintain homeostasis. References
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Yunos NM, Bellomo R, Glassford N, et al. Chloride-liberal vs. chloride-restrictive intravenous fluid administration and acute kidney injury: an extended analysis. Intensive Care Med 2015;41:257-264. Raghunathan K, Shaw A, Nathanson BH, et al. Association between the choice of IV crystalloid and in-hospital mortality among critically ill adults with sepsis. Crit Care Med 2014;42:1585-1591. Raghunathan K, Bonavia A, Nathanson BH, et al. Association between initial fluid choice and subsequent in-hospital mortality during the resuscitation of adults with septic shock. Anesthesiology 2015;123:1385-1393. Young JB, Utter GH, Schermer CR, et al. Saline versus Plasma-Lyte A in initial resuscitation of trauma patients: a randomized trial. Ann Surg 2014;259:255-262. Drobatz KJ, Cole SG. The influence of crystalloid type on acid-base and electrolyte status of cats with urethral obstruction. J Vet Emerg Crit Care 2008;18(4):335-361. Cunha M, Freitas CG, Carregaro AB, et al. Renal and cardiorespiratory effects of treatment with lactated Ringer’s solution or physiologic saline (0.9% NaCl) solution in cats with experimentally induced urethral obstruction. Am J Vet Res 2010;71(7):840-846. Hoste EA, Maitland K, Brudney CS, et al. Four phases of intravenous fluid therapy: a conceptual model. Br J Anaesth 2014;113(5):740-747. Hashimoto S, Sanui M, Egi M, et al. The clinical practice guideline for the management of ARDS in Japan. J Intensive Care 2017;5:50. Claesson J, Freundlich M, Gunnarsson I, et al. Scandinavian clinical practice guideline on fluid and drug therapy in adults with acute respiratory distress syndrome. Acta Anaesthesiol Scand 2016;60:697-709. Kelm DJ, Perrin JT, Cartin-Ceba R, et al. Fluid overload in patients with severe sepsis and septic shock treated with early goal-directed therapy is associated with increased acute need for fluid-related medical intervention and hospital death. Shock 2015;43(1):68-73. Vaara ST, Korhonen AM, Kaukonen KM, et al. Fluid overload is associated with an increased risk for 90-day mortality in critically ill patients with renal replacement therapy: data from the prospective FINNAKI study. Crit Care 2012;16:R197. Cavanagh AA, Sullivan LA, Hansen BD. Retrospective evaluation of fluid overload and relationship outcome in critically ill dogs. J Vet Emerg Crit Care 2016;26(4):578-586. Cotton BA, Guy JS, Morris JA, et al. The cellular, metabolic, and systemic consequences of aggressive fluid resuscitation strategies. Shock 2006;26(2):115-121. ATLS Subcommittee, American College of Surgeons’ Committee on Trauma, and International ATLS Working Group. Advanced trauma life support (ATLS): the ninth edition. J Trauma Acute Care Surg 2013;74(5):1363-1366. Francis BJ, Wells RJ, Rao S, et al. Retrospective study to characterize post-obstructive diuresis in cats with urethral obstruction. J Feline Med Surg 2010;12(8):606-608. The National Heart, Lung, and Blood Institute Acute Respiratory Distress Syndrome (ARDS) Clinical Trials Network. Comparison of two fluid-management strategies in acute lung injury. N Engl J Med 2006;354:2564-2575. Fluid Therapy in Critical Care Learning Objectives
Readers will be able to describe new trends in prescription of intravenous (IV) fluid therapy during critical illness and apply these principles to common clinical scenarios identified in small animals. Readers will also able to identify appropriate monitoring techniques to guide prescription of IV fluid therapy. TOPIC OVERVIEW
This article provides an overview of the current trends of fluid therapy in critical care, with emphasis in 4 main categories: avoidance of synthetic colloids and chloride-rich fluids, prevention of fluid overload, early enteral nutrition, and staged fluid therapy prescription.
The article you have read has been submitted for RACE approval for 1 hour of continuing education credit and will be opened for enrollment when approval has been received. To receive credit, take the approved test online for free at vetfolio.com/journal-ce . Free registration on VetFolio.com is required. Questions and answers online may differ from those below. Tests are valid for 2 years from the date of approval. In people with sepsis and septic shock, the use of synthetic colloids has been associated with: a. Increased risk of acute kidney injury (AKI) b. Increased risk of mortality c. Coagulopathies d. All of the above Which of the following isotonic crystalloids contains the highest concentration of chloride? a. LRS c. 0.9% Saline d. Normosol-R In critically ill dogs and cats, veterinarians should titrate IV fluid therapy with the aim of achieving __ fluid balance. a. 0%