Which patients are at highest risk for iatrogenic fluid overload and how do I monitor for it?

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The highest-risk patients for iatrogenic fluid overload are those with cardiovascular disease, renal dysfunction (acute kidney injury, chronic kidney disease, or protein-losing nephropathy), liver disease, hypoalbuminemia, and those receiving large fluid volumes. Dogs with oligo-anuric renal failure are particularly susceptible because they cannot excrete excess fluid, yet frequently receive aggressive fluid therapy.14 Cardiovascular disease and renal dysfunction are the two most consistently identified risk categories in dogs. Dogs that developed fluid overload during hospitalization were significantly more likely to have cardiovascular disease and were more likely to fall into one of three renal dysfunction categories: protein-losing nephropathy, chronic kidney disease (CKD), or acute kidney injury (AKI).4 Dogs and cats with CKD can have marked derangements in their ability to regulate fluid homeostasis, and animals with AKI are frequently oliguric, compounding the risk when large fluid volumes are administered to optimize renal blood flow and glomerular filtration rate.4 Fluid overload is clinically defined by a body weight increase of at least 5–10% or a positive fluid balance of the same magnitude when intake and output are measured. In clinical practice it is suspected when a patient shows evidence of pulmonary edema, peripheral edema, or body cavity effusion.2 Monitoring centers on serial body weight, clinical signs of volume excess, and vigilant fluid balance tracking. Clinical signs of volume overload include serous nasal discharge, chemosis, tachypnea, altered breathing pattern, restlessness, cough, tachycardia, ascites, pulmonary crackles on auscultation, and polyuria.5 Body weight should be monitored carefully and frequently — in neonates and pediatric patients this means several times per day — and is the most reliable early indicator across all patient populations.5 Patients with AKI or CKD receiving aggressive fluid therapy require particularly close