Fluid therapy in the sick patient

First, determine the initial rate and volume based on whether the patient needs whole body rehydration or vascular space volume expansion. Next, determine the fluid type based on replacement and maintenance needs as described in the following sections. Fluid therapy for disease falls into one or more of the following three categories: the need to treat changes in volume, content, and/or distribution.

Typically, the goal is to restore normal fluid and electrolyte status as soon as possible (within 24 hr) considering the limitations of comoribund conditions. Once those issues are addressed, the rate, composition, and volume of fluid therapy can be based on ongoing losses and maintenance needs. Replace the deficit as well as normal and abnormal ongoing losses simultaneously (e.g., continued vomiting/diarrhea as described in the “Changes in Fluid Volume” section). Accurate dosing is essential, particularly in small patients, to prevent volume overload.

Monitor response to fluid therapy

Individual patients’ fluid therapy needs change often. Monitor for a resolution of the signs that indicated the patient was in need of fluids (Table 1). Monitor for under-administration (e.g., persistent increased heart rate, poor pulse quality, hypotension, urine output), and overadministration (e.g., increased respiratory rate and effort, peripheral and/or pulmonary edema, weight gain, pulmonary crackles [a late indicator]) as described in Table 1. Patients with a high risk of fluid overload include those with heart disease, renal disease, and patients receiving fluids via gravity flow.16

Cats require very close monitoring. Their smaller blood volume, lower metabolic rate, and higher incidence of occult cardiac disease make them less tolerant of high fluid rates.7,18