Fluid can also be replaced by SC, IP, IV, or IO routes.6,8,9 In minimally dehydrated patients that are still nursing, SC and IP warmed fluids are adequate. To help prevent infection, abscess formation, or inappropriate osmotic shifts, fluids given by these routes should not contain dextrose. Only warm isotonic crystalloids such as Normosol-R (hospira.com), lactated Ringer’s solution (LRS), or 0.9% NaCl should be used SC or IP; note that before 6 weeks of age, the lactate in LRS may not be metabolized effectively to bicarbonate.8 PO, SC, or IP fluids should only be given when the neonate is normothermic; they should not be used in hypovolemic, shocky patients because of the very slow absorption. When giving IP fluids, aseptic technique is of utmost importance. Repeated doses of IP fluids are not recommended (ie, because of increased risk for septic peritonitis).
IV access may be difficult to obtain in neonates. Peripheral venous access with a 22- to 24-gauge catheter may be attempted. Often, placement of a small cephalic catheter in the jugular vein is necessary, provided there are no contraindications (eg, coagulopathy, thrombocytopenia). Both IV and IO catheters may be flushed to maintain patency when not in constant use. Catheters should be flushed with 0.9% saline; the use of heparinized flushes is not necessary and can result in accidental excessive heparin administration.10
In the event that central or peripheral venous access is not available, use of an IO catheter may be necessary for fluid therapy. An 18- to 22-gauge spinal or hypodermic needle can be placed in the head of the tibial crest, tibial tuberosity, wing of ileum, trochanteric fossa of the femur, or greater tubercle of the humerus.8,9 Aseptic technique should be used when placing IO catheters. Most drugs, fluids, and even blood products that are typically delivered by the IV route can be delivered through an IO catheter. Although the IO catheter can be lifesaving, it can be difficult to wrap and protect and, rarely, can result in fractures or infection.
In severely dehydrated or hypovolemic patients, initial shock doses of a balanced crystalloid should be used (ie, 30–45 mL/kg for dogs, 20–30 mL/kg for cats). Serial examinations should be done after the bolus to reassess response and evaluate the need for further fluid resuscitation. Maintenance fluid rates of 80 (pediatric) to 180 (neonatal) mL/kg q24h should be implemented depending on the age of the patient, in addition to adjusting for ongoing losses (eg, vomiting, diarrhea).6 Dextrose supplementation should be implemented quickly in hypoglycemic neonates (eg, 0.5–1.5 mL/kg of 50% dextrose, diluted 1:3, followed by a 2.5%–5% CRI in IV fluids).
Although pediatric pups and kittens are more like adults in terms of vital parameters and renal function, they still have increased maintenance water requirements compared with adults.6 These slightly older pups and kittens may require fluid therapy as a result of disease associated with ongoing losses (eg, vomiting, diarrhea). Potassium supplementation typically is required, and careful monitoring of blood glucose and electrolytes is warranted. Although colloids can be used, puppies and kittens normally have a lower colloid osmotic pressure (COP) than adults. If necessary, a colloid (eg, hetastarch, 1 mL/kg/h) or plasma can be used to keep COP above 15 mm Hg.6