Management of Hypovolaemia and Dehydration in the Neonatal Patient

Philip R Judge BVSc MVS PG Cert Vet Stud MACVSc (Vet Emergency and Critical Care; Medicine of Dogs)

Introduction:

Hypovolaemia refers to a decrease in the amount of fluid circulating in the bloodstream. In the adult animal, short-term blood volume loss may be compensated for by an increase in heart rate, and heart muscle contractility, along with blood vessel constriction in the intestines, skin and kidneys, to raise blood pressure. This is followed, shortly thereafter, by an increase in kidney retention of sodium and water, mediated by release of anti-diuretic hormone and aldosterone – both of which serve to reduce fluid loss from the patient.

In the neonate, these mechanisms are poorly developed – being only fully functional at about 6-8 weeks of age. In fact, in neonates, these responses may be completely absent during the early weeks of life. 

• The neonatal myocardium (heart muscle) has less ability to contract than the adult myocardium, making it harder for the neonate to increase cardiac output in response to decreasing blood volume
• The kidneys are unable to conserve body water
• The muscle in blood vessel walls that enables them to constrict is poorly developed in neonates, resulting in lower blood pressures in neonates, and a decreased ability to respond to hypovolaemia

Because of these things, when a neonate is hypovolaemic following trauma, or some sort of fluid loss caused by diarrhoea, for example, they do not show the same signs of shock as adults. This makes the diagnosis of hypovolaemia and shock more challenging than in the adult patient. 

In addition, the diagnosis of dehydration – utilising skin tenting, sunken eyes, and dry mucous membranes, are more challenging to detect in the neonate. Puppies and kittens have a high daily water requirement, and greater losses than adults through respiratory tract and kidneys. Any disease in fluid intake can lead to dehydration

In summary, the unique problems in puppies and kittens that make them uniquely susceptible to severe dehydration and hypovolaemia. 

• High daily fluid requirement
• Inability to concentrate or dilute urine
• Lower water content of skin – making hydration assessment impossible with skin-tenting
• High metabolic rate
• High respiratory rate

Because of the challenges of making a clinical diagnosis of shock and dehydration in the neonate, the following guideline has been developed:

Assume all neonates with diarrhoea, vomiting and inadequate fluid intake (including poor sucking/feeding) are dehydrated and potentially hypovolaemic

General guidelines on the management of shock in the neonate are presented below:

Guidelines for the Management of Shock and Dehydration in Neonates

1. Route of administration
   1. Fluids may be administered by the following routes
      1. Intravenous
      2. Intraosseous
      3. Intraperitoneal
      4. Subcutaneous
      5. Oral
   2. For volume replacement (shock and severe dehydration), the intravenous and intraosseous routes are preferred. Other routes of administration do not support immediate access to systemic circulation – meaning the benefits of fluid therapy will be delayed.
   3. Intravenous access is usually best achieved in the jugular vein
   4. Intraosseous access is best achieved via the humerus or femur
2. Fluid type and preparation
   1. A balanced, polyionic solution such as lactated Ringer’s solution, Ringer’s acetate, Normosol, or PlasmaLyte is recommended for initial volume resuscitation in most circumstances
   2. Dextrose/glucose solutions and blood products may be recommended in certain circumstances (hypoglycaemia and anaemia, respectively)
   3. Fluids should be warmed to body temperature prior to administration
3. Treatment:
   1. For severe dehydration and shock
      1. Administer 40-45 ml/kg/hr bolus of warm lactated Ringer’s solution over 30-40 minutes.
         1. The fluid rate is equivalent to
            1. 1.35 ml per 30 grams/hr OR
            2. 0.23 ml/30 g IV over 10 minutes OR
            3. 7.5 ml/kg IV over 10 minutes
         2. Continue fluid therapy using small boluses every 10 minutes until Capillary refill time and mucous membrane colour improves
         3. Symptoms of fluid overload indicate fluid restriction is required, and include
            1. Increased respiratory rate and effort
            2. Serious nasal discharge
            3. Chemosis (swelling of surface mucous membranes of the eyes)
            4. Ascites
            5. Excessive weight gain
            6. Development of peripheral oedema
   2. For maintenance
      1. Maintenance fluid rates for neonatal puppies and kittens are reported to be 40-80 ml/kg/day
      2. Following correction of intravenous fluid deficits as outlined above, the fluid rate should be reduced to 2-3.3 ml/kg/hr
   3. For ongoing losses – these are estimated as follows
      1. 1 tablespoons of neonatal diarrhoea is equivalent to 15 ml fluid 
      2. Fluid to replace losses should be replaced over the period in which it has occurred e.g. if diarrhoea occurs every hour – replacement boluses of fluid should be provided every hour
   4. Glucose – many inappetent patients may be unable to maintain normal glucose concentrations in circulation. Administer a 1.25-2.5% solution by continuous infusion at 1-2 ml/kg/hr. Be sure to reduce the rate of replacement fluid by this amount, to avoid fluid overload.
4. Animals that do not improve (lethargy, poor urine output, high blood lactate, cold extremities, failure to nurse etc.), or that have infection (wounds, diarrhoea, and vomiting) may occasionally require the use of drugs like noradrenaline or dobutamine, which increase blood pressure (noradrenaline) and cardiac output (dobutamine), in order to improve perfusion
5. Discontinuation of fluid therapy
   1. Fluid therapy should be weaned
      1. When hydration is normal, and the puppy or kitten can maintain fluid balance by eating and drinking normally
   2. Procedure: decrease fluid rate by 25-50% per 24-hour period until the animal is weaned from fluids

References:

1. Johnson CA, Casal ML. Neonatal resuscitation: canine and feline. Management of Pregnant and Neonatal Dogs, Cats, and Exotic Pets. 2012 Aug 3:77-92.
2. Johnson AK, Johnson JA. Neonatal Resuscitation and Care. In Feline Reproduction 2022 Jul 14 (pp. 98-108). GB: CABI.
3. Davidson AP. Neonatal resuscitation: Improving the outcome. Veterinary Clinics: Small Animal Practice. 2014 Mar 1;44(2):191-204.