INS AND OUTS OF FOAL FLUID THERAPY
PAMELA WILKINS, DVM, MS, PHD, DACVIM-LA, DACVECC University of Illinois, Champaign-Urbana IL USA
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3 ADJUSTMENT OF FLUIDS FOR ONGOING LOSSES One should adjust the fluid and sodium requirements for ongoing losses exceeding the maintenance requirements. These losses can take the form of diarrheal losses and excessive urine output, such as those with glucose diuresis and renal damage resulting in an increased fractional excretion of sodium. The normal fractional excretion of sodium in neonatal foals is less than that of adult horses, usually less than 1% (J.E. Palmer, unpublished data). In the critically ill foal the sodium requirement can be met with as little as 140 mEq of sodium per day, less than administered in a single liter of normal equine plasma. One can address sodium deficits by separate infusion of sodium- containing fluids, although this may not be necessary if one considers the sodium being administered in other forms, including drugs administered as sodium salts and any constant rate infusions (pressors, inotropes, etc.) that are being provided as solutions made with 0.9% sodium chloride. 4 MONITORING DURING FLUID THERAPY The author has used this approach to fluid therapy for the last few years and believes that the percentage of foals suffering from generalized edema - and related problems - has decreased. If one takes this approach to fluid therapy, one should take the weight of the patient once daily, or even twice daily, and monitor the fluid intake and output as closely as practical. One should evaluate any larger than anticipated weight gains or losses.
2 APPROPRIATE FLUID MANAGEMENT The problem of appropriate fluid management in critically ill neonates has been recognized by medical physicians for years and has resulted in changes in fluid management of these patients. The approach taken has been one of fluid restriction, in particular sodium restriction but also free water restriction, and has resulted in improved outcome and fewer complications, such as patent ductus arteriosus and necrotizing enterocolitis. The calculations used for maintenance intravenous fluid support in these patients takes into consideration the ratio of surface area to volume and partially compensates for insensible water losses. Maintenance fluids are provided as 5% dextrose to limit sodium overload and provide sufficient free water to restore intracellular and interstitial requirements. The calculation for maintenance fluid administration is as follows: First 10 kg body mass 100 ml/kg/day Second 10 kg body mass 50 ml/kg/day All additional kilograms of body mass 25 ml/kg/day As an example, the average 50-kg foal would receive 1000 ml/day for the first 10 kg of body mass, 500 ml/day for the next 10 kg of body mass, and 750 ml/day for the remaining 30 kg of body mass for a total of 2250 ml/day. This translates to an hourly fluid rate of about 94 ml/hr.
One should not expect urine output to approach the reported normal of 300 ml/hr for a 50-kg foal because the free water administered is limited, unless the patient is experiencing diuresis (glucosuria, resolution of the syndrome of inappropriate antidiuretic hormone secretion, resolution of previous edematous state, renal disease). One should obtain the urine specific gravity several times daily and should determine fractional excretion of sodium at regular intervals. If the volume of urine produced by the patient is measured accurately, one can determine sodium losses accurately and can obtain creatinine clearance values. (continued)
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