Fluid therapy: Recognize and respond to fluid overload

Fluid therapy is an essential, sometimes lifesaving, treatment for veterinary patients.  But just like any other drug or treatment, fluid therapy has its own risks and potential side effects. One of the biggest concerns veterinary teams should be aware of is fluid overload, which can become life threatening if not properly treated.

Why fluid overload occurs 

Fluid overload can occur for many reasons, but most cases are iatrogenic, when fluids are administered to a patient in excess. Individual patient comorbidities can also increase the risk of fluid overload, particularly in patients with concurrent renal, hepatic, and cardiac disease.  

Because of the role individual patient factors play in fluid overload, the 2024 AAHA Fluid Therapy Guidelines for Dogs and Cats suggest using the term “fluid intolerance” to emphasize each animal’s unique response to fluid administration. However, given that fluid overload is currently the most widely recognized terminology in the profession, it is the primary term used in the guidelines and this article. 

The pathophysiology of fluid overload is outlined in Section 6 of the guidelines. It begins with hypervolemia (excess fluid in the intravascular space) and progresses to overhydration of the interstitial space, which leads to tissue edema, organ dysfunction, and cavitary effusions.  

The importance of patient monitoring 

All patients receiving fluid therapy should be closely monitored for signs of fluid overload. Patients should be weighed every 6 to 12 hours when receiving fluids, and an increase of 10% body weight over baseline is a marker of overhydration. Additional physical examination findings in patients with hypervolemia may include bounding pulses, serous nasal discharge, development of a new heart murmur or gallop rhythm, increased respiratory rate and/or effort, wet lung sounds, jugular vein distention, and peripheral edema. 

It is important to remember that hypertension is a poor marker of hypervolemia, especially in patients with normal renal function. In patients with acute kidney injury or chronic kidney disease, however, hypertension may be a sign of hypervolemia.  

Additional monitoring parameters can include decreases in PCV, total protein, BUN, and urine specific gravity. Radiographic and ultrasonographic changes will also occur with fluid overload and are summarized in Table 15 below. 

Preventing fluid overload 

Treatment of fluid overload is difficult and not always successful in its advanced stages, so the best approach is to prevent fluid overload from occurring in the first place. Prevention strategies include: 

• Use low volume resuscitation instead of administering the full “shock volume” as many veterinarians have been taught in the past. Fluid boluses should be given in small aliquots, and patient perfusion parameters should be reassessed following each bolus to determine if additional boluses are needed. If hypotension is nonresponsive to fluid boluses, additional treatment such as vasopressors and correction of electrolyte and glucose disturbances may be needed. 

• Avoid the blanket use of “twice maintenance” fluids and create tailored fluid rates for each patient.  

• Consider all fluid intake for each patient when determining the total fluids received in a 24-hour period. This includes the total volume of IV fluids, IV drugs, flushes, and enteral intake. 

• Utilize enteral routes for fluid intake, especially for patients at high risk of hypervolemia such as those with heart disease, renal disease, and hepatic disease. 

• Closely monitor the amount of fluids received during anesthetic procedures, especially lengthy procedures. 

Treatment of fluid overload 

There is no single treatment that is effective for fluid overload. When signs of hypervolemia are detected, fluid therapy should be discontinued, and patient movement should be increased. When detected early, this treatment may be sufficient to resolve the problem.  

For patients with signs of fluid overload, including respiratory distress, significant peripheral edema, cavitary effusions, or organ dysfunction, treatment is more intensive. Fluids should be discontinued in favor of oxygen therapy. Diuretics may be helpful, but they also may not be sufficient to resolve fluid overload. In some cases, referral for hemodialysis is required, but successful treatment is not guaranteed.  

Key takeaways 

Fluid overload is a serious, life-threatening complication of fluid therapy. Treatment is difficult, so prevention of this condition through the judicious use of fluids is essential. Patients should be monitored closely for signs of fluid overload as the earlier this is recognized, the better the prognosis. There is no one-size-fits-all recommendation for fluid therapy, but the 2024 AAHA Fluid Therapy Guidelines for Dogs and Cats provide comprehensive guidance for the safe use of fluid therapy based on the needs of each patient. 

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Disclaimer: The views expressed, and topics discussed, in any NEWStat column or article are intended to inform, educate, or entertain, and do not represent an official position by the American Animal Hospital Association (AAHA) or its Board of Directors.