Today's Veterinary Practice

MAR-APR 2018

Today's Veterinary Practice provides comprehensive information to keep every small animal practitioner up to date on companion animal medicine and surgery as well as practice building and management.

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PEER REVIEWED 56 FLUID THERAPY: PART 2 Polyuria Patients with high urine output (>2 mL/kg per hour) often cannot meet their fluid demands through oral intake and require IV fluid support. Fluid therapy plans can be calculated in the same manner as in patients with a normal urine output, with special consideration for the "ongoing losses" part of the calculation. If a urinary collection system is in place, quantification of urine output is relatively simple. In patients without urinary catheters, use of absorbent pads or nonabsorbable litter to collect and weigh urine can facilitate measurement of urine output (1 mL of urine weighs approximately 1 g). Patients with postobstructive diuresis frequently need high fluid rates that exceed what appears to be appropriate to meet ongoing urinary losses. Clinicians should not be dissuaded from providing these patients with the amount of fluid calculated. Close monitoring for both fluid overload and underload is needed. Once the patient appears to be euhydrated, adjustment of the fluid rate every 2 hours based on the urine output (sometimes called "matching ins and outs") can be used to ensure that the patient's fluid needs are met. MONITORING FLUID THERAPY Monitoring is an essential component of fluid therapy, and patients receiving IV fluids should be reassessed several times a day to determine whether the fluid plan needs to be altered. The patient should be weighed at least once daily and have at least 2 physical examinations per day to assess intravascular volume and hydration status. The examination should include cardiothoracic auscultation, evaluation of interstitial hydration, mucous membrane color and capillary refill time, and pulse quality. In patients that have more dynamic or challenging fluid needs, more frequent assessments of body weight and physical examination (up to every 4 to 6 hours) may be required. Serial monitoring of respiratory rate and effort is required because one of the first signs of pulmonary edema is an increase in both. Clinical signs of fluid overload include those listed in BOX 3 . In dogs, thoracic radiographs can show an interstitial-to-alveolar pattern in the perihilar region or caudodorsal lung fields; this pattern may be more diffuse in cats ( FIGURE 4 ). Left atrial enlargement and enlargement of the pulmonary vasculature can FIGURE 4. Three-view thoracic radiographs of a cat with fluid overload. Note the tall cardiac silhouette, enlarged pulmonary vessels, bilateral pleural effusion, and generalized interstitial pattern with patchy alveolar infiltrates in the perihilar region and right cranial, right middle, left cranial, and left caudal lungs. An esophageal feeding tube and central venous dialysis catheter are also present.

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