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41 Notes on paediatric medicine

The term paediatric refers to animals under 6 months of age that can be further subdivided into neonates, infants, weanlings and juvenile animals. Changes in physiology and haemodynamics occur as animals progress through these stages. In particular, there are important pharmacological considerations with respect to neonates (up to 2 weeks old) and infants (2–6 weeks old).

Neonatal and infant medicine is one area with which veterinary surgeons and nurses are often least familiar. In the author’s experience, many owners are unwilling to commit substantial resources for veterinary care of the sickest neonates and infants and this lack of familiarity and experience is therefore not surprising.

The Healthy Neonate

• Spends almost all its time nursing or sleeping until 2–3 weeks old.
• Inadequate milk intake usually results in constant crying, failure to gain weight, and reluctance to nurse; supplemental feeding or a healthy vaccinated foster dam may be required.

Physical examination

Approximate normal physiological parameters are shown in Table 41.1. Healthy neonates are lively and plump. An estimation of general health and physical condition can be made by assessing the following:

• Suckling reflex
• Rooting reflex (opening and closing of the lips, moving the head in search for milk)
• Righting reflex when placed in dorsal recumbency: present at birth and strengthens over the first 4 weeks
• Adequate weight gain (see below)
• Coat condition: should be shiny
• Bowel sounds: usually auscultable.

Table 41.1 Approximate guidelines for physiological parameters in neonatal puppies and kittens

Physiological parameter Normal values or findings
Heart rate Puppies: 180–200 beats per minute; kittens: 250 beats per minute; decreases from 4 weeks old
Respiratory rate 20–30 breaths per minute
Rectal temperature Average 36.0°C at birth; adult values by 4 weeks old
Mean arterial blood pressure Considerably lower than adults; may not normalize until several months of age
Opening of eyes Usually by 14 days old (5–14 days)
Vision Usually normal by 3–4 weeks old
Menace response May take 2–3 months to develop but can be sooner
Pupillary light reflexes Present when eyes first open; normal by 3 weeks old
Opening of ear canals Usually 6–14 days old
Hearing Mature by 3–4 weeks old
Olfaction Well developed at birth
Pain sensation Present at birth
Withdrawal reflex Usually develops by 1 week old
Ambulation Usually develops by 2–3 weeks old
Gag reflex Usually not present until after 10 days old

Specific problems to examine neonates for include:

• Cleft palate
• Umbilical hernia
• Umbilical infection: the umbilical cord usually falls off by 3 days of age and the umbilicus should be dry. A soft erythematous umbilicus, possibly with a discharge, is suggestive of bacterial omphalitis
• Open fontanelle: may be associated with fading or future neurological signs. Many toy canine breeds have open fontanelles and small open fontanelles may be normal in kittens
• Cardiac murmur: may be innocent or pathological
• Protruding eyelids: ophthalmia neonatorum may cause protrusion of the eyelids before they are fully open, with or without a purulent discharge; due to infection with Staphylococcus sp or other normal flora
• Nonpatent urogenital or anal opening.

Body weight

Birth weight

Canine

• 100–200 g for toy breeds
• 400–500 g for large breeds
• More than 700 g for giant breeds

Feline

Average birth weight 90–110 g.

Weight gain

Approximate guidelines for daily weight gain:

• Puppies should gain 2.2–2.7 g for every kg of anticipated adult weight each day, or have a daily weight gain of 5–10% of their birth weight. Healthy puppies usually will have doubled their birth weight by 10 days of age.
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• Kittens should gain a minimum of 7–10 g per day (can be as much as 15–30 g) and healthy kittens usually will have doubled their birth weight by 14 days of age.

Clinical Tip

• Weight is a very useful parameter to assess in neonates and failure to gain weight is a consistent early sign of illness.
• Neonates should ideally be weighed daily, and in order to maximize the reliability of these data, weighing should be done at the same time of the day and at the same time with respect to feeding.

Urination and defecation

• Unable to urinate voluntarily for the first 2–3 weeks of life; urination stimulated by maternal licking of the genital region.
• Can only defecate when stimulated by maternal licking of anal region:
– Meconium (soft, yellow-brown, relatively odour-free) passed for the first 2 days of life
– Faeces then become light to medium brown in colour and pasty in consistency; typically they do not become solid until after weaning
– Overfeeding by owners is a common cause of diarrhoea.

Clinical Tip

• Neonates require maternal licking of the genital and anal regions in order to urinate and defecate, and this is potentially readily overlooked if neonates are hospitalized away from the dam. In such cases the genital and anal regions can be stimulated by gentle stroking for example with a warm moist cotton wool ball.
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Clinical Pathology

Clinical Tip

• Venepuncture in neonates is usually performed using a jugular vein and the author would strongly encourage the prior application of EMLA® cream 5% (AstraZeneca) (see Ch. 5). Both the difficulties in obtaining samples and especially the small blood volume of these animals mean that it is absolutely crucial to plan tests carefully so as to coordinate interventions, to take the minimum volume of blood required, and to run only tests that are essential. Maximum use should be made of any blood taken and chemistry analysers that only require low volume samples should be used as much as possible. In addition, peripheral blood smear examination is usually more than adequate and uses much less blood than performing a full haematology profile.
• At least in the context of clinical pathology that requires blood sampling, it is an unavoidable reality that neonates are unlikely to receive as intensive investigation or monitoring as an older animal. This needs to be accepted and embraced from the outset and does not preclude these patients from nevertheless receiving excellent care. Common sense is very much needed so that for example empirical glucose supplementation may be provided to sick neonates as they are prone to hypoglycaemia rather than performing frequent venepuncture for blood glucose measurement.

See Table 41.2. Reference ranges used for adult animals are not always appropriate for neonates and this is essential to remember in order to avoid misdiagnosis. In addition, there is limited information available in the veterinary literature and what is available is regrettably typically based on studies performed on laboratory or experimental animals.

Table 41.2 Guidelines for interpretation of clinicopathological findings in puppies and kittens

Parameter Puppies Kittens
Haematocrit, packed cell volume (PCV)
Within adult range at birth
Decreases thereafter
Nadir usually at about 4 weeks old (coincides with weaning)
Normalizes by 3–6 months old
Within adult range at birth
Decreases thereafter (usually decreases proportionally less than in puppies)
Nadir usually at about 4–6 weeks old (coincides with weaning)
Normalizes by 3–6 months old
Leucogram, platelet count
Typically as for adult dogs
Possible mild lymphocytosis based on adult range by 3 weeks old
Typically as for adult cats
Possible leucocytosis based on adult range by 8–9 weeks old
Glucose Similar to adult range Similar to adult range
Albumin
Lower than adult range at birth
Increases thereafter and usually normalizes by 2–4 months old
Lower than adult range at birth
Increases thereafter and usually normalizes by 2–4 months old
Globulin
Lower than adult range at birth
Increases thereafter and usually normalizes by 6 months old
Lower than adult range at birth
Increases thereafter and usually normalizes by 6 months old
Bilirubin
May be greater than adult range (perhaps 2–3 times maximum)
Usually normalizes by 6 weeks old
May be greater than adult range (perhaps 5 times maximum)
Usually normalizes by 6 weeks old
Alkaline phosphatase (ALP) Greater than adult range (perhaps 40–80 times maximum) Greater than adult range (perhaps 3–6 times maximum)
Gamma glutamyl transferase (GGT) Greater than adult range (perhaps 150–500 times maximum) Similar to adult range
Blood urea nitrogen (BUN) May be lower than adult range May be lower than adult range
Creatinine May be lower than adult range May be lower than adult range
Calcium, phosphorus Increased due to bone growth Increased due to bone growth
Urine specific gravity
Isosthenuric (1.007–1.015) for a few days after birth
Increases with age to reach normal concentrating ability by 8–10 weeks old (can take up to 6 months)
Isosthenuric (1.007–1.015) for a few days after birth
Increases with age to reach normal concentrating ability by 8–10 weeks old (can be delayed but less so than puppies)
Glucosuria, proteinuria May be normal in puppies (usually less than 8 weeks old) May be normal in kittens (usually less than 8 weeks old)

General Treatment Concepts

Nursing Aspect

Very young animals are much less able to cope with illness than older animals and require much more attentive nursing and monitoring. The role of the nurse is never more important than in the care of neonates and infants. Although most of the treatment measures implemented are nonspecific and supportive in nature, these animals are almost entirely dependent on their caretakers in the absence of their dams.

Treatment of neonates typically consists of:

• Temperature control
• Fluid therapy and glucose supplementation
• Nutritional support
• Stimulation of urination and defecation
• Infection control.

Hypothermia

• Neonates are highly susceptible, e.g.
– Relatively large body surface area
– Reduced subcutaneous fat
– Immature thermoregulatory system (e.g. poor peripheral vasoconstriction, inability to shiver until after 1 week of age).
• Causes significant additional energy demand.
• May manifest as unresponsiveness, bradycardia and respiratory depression; may also promote ileus and cause gastro-oesophageal reflux.
• Common sign of sepsis.

Clinical Tip

• Hypothermic neonates should only be warmed once hypovolaemia, if present, has been addressed. They should not, however, be fed until warmed.
• Warming should be performed slowly and the animal must be able to move away from the heat source to avoid thermal injury. In addition, it must be remembered that neonates have a lower normal rectal temperature than older animals and are also unable to pant; they are therefore readily at risk of being overheated.

Warming

• Ambient temperature of 29–32°C recommended.
• Guidelines for target rectal temperatures at which the intensity of warming can be reduced:
– 1–3 days old: 36.5–37°C
– 4–7 days old: 37–37.5°C
– >7 days old: 37.5–38.0°C.
• Warmed (but not hot!) fluids should be administered: warm the fluid line in relatively close proximity to the patient so that the fluid is still warm when it enters the body. This is best achieved using an in-line fluid warmer (e.g. Tempcare® Veterinary Fluid Warmer) but wrapping the line around several hot hands or a hot water bottle may be satisfactory. You must ensure that the patient is not at risk of thermal injury.
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• Warming of fluid bags is far less effective, as cooling occurs within a matter of minutes. Even if the fluid bag can be kept warm, cooling is likely en route to the patient.

Hypoglycaemia

• Neonates are highly susceptible, e.g.
– Immature glucose feedback mechanisms
– Inefficient hepatic gluconeogenesis
– Decreased glycogen stores
– Brain (and heart) are highly dependent on glucose as the energy substrate
– Increased loss of glucose in urine.
• Causes of hypoglycaemia include:
– Vomiting and diarrhoea due to primary gastrointestinal disease or another cause
– Inadequate food and fluid intake
– Infection.
• Hypoglycaemia may manifest as lethargy, depression, poor feeding, crying, and a limp body.

Treatment

• Enteral supplementation
• Parenteral supplementation:
– Intravenous or intraosseous but not subcutaneous or intraperitoneal route
– Glucose solutions (1.25–5%) made up in 0.9% sodium chloride (normal, physiological saline) or Hartmann’s solution (buffered lactated Ringer’s solution) should be used
– A 4% glucose solution in 0.18% sodium chloride is commercially available but should not be used. This solution is markedly hypotonic compared to plasma and can cause potentially very serious electrolyte derangements (see Ch. 4).

Clinical Tip

• It can be both difficult and potentially undesirable to check blood glucose regularly in neonates. The author tends to take an empirical approach to hypoglycaemic neonates, providing a conservative basal level of supplementation with additional treatments being guided by deterioration in the clinical status more than blood glucose measurements.
• The route of administration depends on whether parenteral access is available. Intravenous administration is generally preferred, but the author has used oral glucose solutions (e.g. Glucogel©, BBI Healthcare, Swansea, UK) applied topically to the oral mucosa with good success in a number of cases. As always the level and route of supplementation must be guided by the individual requirements of the patient.
• It is also noteworthy that while hypoglycaemia is clearly undesirable, excessive glucose supplementation may be more problematic in neonates than it is in older animals.

Fluid therapy

Fluid requirements of very young animals are much higher than for adults, for example due to:

• Higher percentage of total body water
• Greater surface area to body weight ratio
• Higher metabolic rate.

Maintenance rates as high as 10 ml/kg/hr may be required for replacement isotonic crystalloid solutions. However, it is noteworthy that excessive fluid administration may have more serious consequences than in older animals as immature animals have a reduced ability to dilute their urine and thereby excrete the surplus fluid. Close monitoring is therefore indicated, although in practical terms this may be difficult to achieve (e.g. monitoring of packed cell volume and total solids is very difficult). Monitoring weight may be helpful, especially if weight loss occurs as these animals should be gaining weight daily and weight loss may be due to dehydration. Monitoring for an increase in respiratory rate and effort may be the most practical evidence of fluid overload.

Route and rate of fluid therapy depend on the individual patient’s requirements but may also be affected by patient size and compliance, and the expertise of the personnel.

• Enteral feeding if the patient is normothermic and still nursing; warmed subcutaneous or intraperitoneal isotonic crystalloid fluid therapy may also be appropriate for these cases depending on the suspected degree of dehydration and the success of enteral feeding; glucose should not be included in fluids given by these parenteral routes.
• Intravenous or intraosseous fluid therapy for moderate to severe dehydration or hypovolaemia.

Hypovolaemia can be very difficult to detect as changes in perfusion parameters may be due to immature compensatory mechanisms; a conservative approach to fluid resuscitation is recommended. Severe dehydration is the most common cause of hypovolaemia in the very young.

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Drug therapy

• Altered drug absorption, distribution, metabolism, efficacy and elimination are likely when compared to adults, for example due to:
– Greater surface area to body weight ratio
– Reduced body fat and greater water composition (may affect distribution)
– Lower serum concentration of total protein and especially albumin (to which most drugs preferentially bind)
– Reduced renal clearance
– Immature hepatic enzyme systems for oxidation and glucuronidation
– Greater permeability of the neonatal blood–brain barrier
– Immature autonomic nervous system.
• Factors change as animal gets older.
• Neonates are dependent on a high respiratory rate to prevent hypoxia and on a relatively fast heart rate to maintain cardiac output; use drugs causing cardiorespiratory depression very judiciously.
• Try opioids first for sedation; additional drugs should only be added if still required.

Clinical Tip

• Although perhaps not applicable to all drugs, in general dose reduction is appropriate for animals up to 12 weeks of age, and older in some cases. The reader is encouraged to consult datasheets and authoritative drug formularies for more information about specific drugs prior to their use.
• Dose reduction often involves reducing the recommended adult dose by up to 50% and/or increasing the recommended adult dosing interval by up to 50%.

Antimicrobial therapy

• The intestinal flora is more susceptible to disruption by antimicrobial therapy and will cope less well with any subsequent diarrhoea.
• Only use antimicrobial treatment if there is a good clinical indication.
• Beta-lactam antibiotics (e.g. amoxicillin/clavulanic acid, cephalosporins) are usually the first choice and require an increased dosing interval due to the prolonged half-life.
• Metronidazole is recommended for giardiasis and anaerobic infections; dose reduction is required.

Analgesia

Analgesia is highly important in young animals and many of the same principles apply as for adults (see Ch. 5).

Opioids

• Can be used very safely.
• Full (pure) opioids are preferred as they can be readily titrated.
• Avoid preconceptions about the required dose, i.e. whether you should use more or less compared to adults; start at bottom end of the adult dose range and titrate upwards according to the response.
• Naloxone can be used to reverse the effects.

Nonsteroidal anti-inflammatory agents

Avoid at least until the animal is more than 12 weeks of age due to the immaturity of hepatic and renal systems, and inherent difficulties in assessing volume and hydration status.

Local anaesthesia

Use lidocaine at reduced doses (due to immaturity of the peripheral nerves).

Clinical Tip

• EMLA® cream 5% (AstraZeneca) (see Ch. 5) is safe in young animals and the author would strongly encourage its use as extensively as possible.