Septic or stressed neonatal foal physiology is also not conducive to accurate blood
glucose interpretation. Normoglycaemia or even hyperglycaemia are not indicative of
adequate blood glucose stores. During late gestation, the placenta provides 4-8
mg/kg/min glucose to the foetus. Any distress prior to birth (e.g. placentitis), may
stimulate glucogenesis in the foetus, leading to higher than normal resting blood
glucose after birth. Even though these foals have a high blood glucose, they actually
need more exogenous glucose support because they are already using up their
limited glucose stores at birth. In a normal foal, glucogenesis has not started at birth,
leading to low blood glucose at birth (1.4 – 2 mmol/L or 25-35 mg/dL), which
decreases further until glucogenesis or enteral nutrition starts (typically 2 hours after
birth). Perinatal disease may result in failure of either glucogenesis or enteral
nutrition and lead to severe hypoglycaemia.
While the foetus has the luxury of relying on maternal blood glucose regulation, the
neonate has to regulate its own blood glucose. Insulin responses to high blood
glucose can be sluggish (or absent) in the stressed neonate, further complicating
exogenous glucose administration.
Fluid and electrolyte requirements
Neonatal foals are generally not volume depleted directly after birth, except in cases
with active haemorrhage, and may actually be hypervolaemic. Due to their inability to
excrete excess fluid and sodium, excessive fluid therapy should be avoided.
For treating hypovolaemia or septic shock, an initial bolus of 20ml/kg (1L per 50kg
foal) of a balanced electrolyte solution is given over 10-20 min, followed by reevaluation. Indications for this ‘shock bolus’ therapy include poor mentation, poorly
palpable peripheral pulses, and the development of cold distal extremities. This can
be repeated 3-4 times only if necessary. Although higher volumes of fluid may be
required in certain foals, positive inotropes should be considered and blood pressure,
ECG’s and lactate monitored carefully prior to administering additional boluses.
Maintenance fluid requirements are highly variable between foals and there is
therefore no universally correct maintenance fluid rate. Patient monitoring is
imperative to ensure appropriate ongoing therapy. Except for foals with excessive
ongoing fluid losses (e.g. diarrhea), most foals tolerate fluid restriction much better
than fluid overload. The ‘dry maintenance rate’ for fluid therapy, as calculated using
the Holliday-Segar philosophy is significantly restrictive, but typically maintains fluid
balance in critically ill neonates.
Holliday-Segar formula:
• For the first 10kg body weight – 100ml/kg/day
• For the second 10kg body weight – 50ml/kg/day
• For weight in excess of 20 kg – 25ml/kg/day
While fluid overload is to be avoided, glucose containing solutions should not be too
concentrated, and therefore the maintenance rate calculated above may need to be
exceeded until enteral or parenteral nutrition can be initiated.
The author’s maintenance fluid of choice is 5% dextrose in water with added
electrolytes based on the patient’s individual needs, or half strength saline with 5%
dextrose. Sodium, potassium, phosphorus, magnesium and calcium are all
necessary for optimal growth in patients that are not consuming milk and should be
carefully monitored and replaced.
Proceedings
of
the
South
African
Equine
Veterinary
Association
Congress
2016
211