STABILISING THE PAEDIATRIC PATIENT
3.1 Hypothermia
Hypothermia is common and life-threatening in neonatal and juvenile animals, particularly orphans. Susceptibility to hypothermia is because of a high surface area to bodyweight ratio, immature thermoregulatory controls and a relative lack of pelage and body fat (Sisak 2007).
Additionally, marsupials are ectothermic at birth, relying on the stable temperature of the pouch for thermoregulation.The high surface area to bodyweight ratio and the relative lack of pelage enables rapid warming by an external heat source. Warming devices and insulating materials, such as heating pads, forced heat blankets, hot water bottles, plastic or bubble wrap and heat lamps, can all be used to maintain normothermia. However, care must be taken to avoid overheating. Human infant humidicribs and thermostatically-controlled brooders are ideal because the temperature and humidity are easier to control and monitor.
Rectal/cloacal or tympanic temperature is generally used to measure body temperature. Small size can be a limiting factor and the lower limit of some thermometers precludes accurate measurement in hypothermic patients. If the patient feels cold and has been exposed to low ambient temperatures, hypothermia can be assumed. Hypothermia must be corrected by slowly warming over a 2-3 hr period (to 35.5°C for marsupial young) before feeding.
The development of endothermy in marsupial young occurs as a continuum of events, with the transition beginning at least halfway through pouch life concurrent with the initiation of thyroid function. In the tammar wallaby, this transition occurs between 55 and 200 d of age at a mass of 70-300 g (Frappell 2008). A myriad of morphological, physiological and behavioural changes that allow for endothermy and the maintenance of body temperature occur across this time period (Andrewartha et al.
2014).Brown adipose tissue is the major site of non-shivering thermogenesis (NST) in newborn placental mammals and plays an important role in the maintenance of body temperature during ambient temperature fluctuations. The presence of brown adipose tissue in marsupials and its role in NST is controversial (Polymeropoulos et al. 2012). There is evidence that skeletal muscle may be the primary NST site in some marsupials and ectothermic red kangaroo PY are capable of mounting a limited thermogenic response, most likely through NST (Andrew- artha et al. 2014).
3.2 Hypoglycaemia
Neonates and juveniles have increased demand, increased urinary loss (a normal lower renal threshold for glucose) and decreased ability to synthesise glucose compared with adults. They have reduced hepatic glycogen stores, small muscle mass, lack significant adipose tissue and have reduced ability to use fatty acids. Additionally, stressed neonates and young juveniles lack the feedback mechanism of hepatic gluconeogenesis to increase blood glucose. This poor glycaemic regulation is important, because alterations from the euglycaemic state profoundly affect neurological status. Although glucose regulation improves with age, anorexic or inappetent young animals, or those that have not had access to food, are likely to be hypoglycaemic (McMichael 2014).
Offering glucose-containing fluids orally or via gavage as soon as the animal is warmed is important to treat and prevent worsening hypoglycaemia.
Where immediate treatment is necessary, infusions of 1 mL/kg of 12.5% dextrose (i.e. dilute 50% dextrose 1:4 with an isotonic crystalloid) followed by a CRI of isotonic fluids supplemented with 1.25-5.0% dextrose are suggested, with regular monitoring of blood glucose where practical. It is important to follow any bolus of dextrose with a dextrose CRI to prevent rebound hypoglycaemia (McMichael 2014). If IV access is not possible and the patient is too unstable for oral therapy, the IO or IP routes can be considered.
3.3 Dehydration, hypovolaemia and fluid therapy
As a general rule, fluid requirements in paediatric patients are higher because of higher losses (decreased renal concentrating ability, higher respiratory rate and, depending on the species and stage of development, a higher metabolic rate). Dehydration can rapidly progress to hypovolaemia and shock if not adequately treated. Common causes in young animals are diarrhoea and inadequate feed intake.
Hypovolaemia results in decreased perfusion and subsequent decrease in oxygen delivery to tissues. In adults, hypovolaemia is compensated for by increasing heart rate, concentrating urine and decreasing urine output. In young animals these compensatory mechanisms may be inadequate or absent. Therefore, restoration of fluid volume is critical.
Adequate assessment of hypovolaemia in small patients can be challenging and some assumptions may need to be made. All paediatric patients with diarrhoea and/or inadequate feed intake should be assumed to be dehydrated and hypovolaemic and treated immediately. This includes fluid therapy and nutritional support. During treatment, electrolyte and glucose status should be monitored if practical.
Regular weighing of the patient (q 12-24 hr), monitoring the dryness of mucous membranes, skin turgor and peripheral circulation in the initial stabilisation period is recommended. Urine specific gravity, BUN and
Fig. 15.4. A critically ill, anorexic eastern grey kangaroo (Macropus giganteus) PY with a nasogastric tube placed for administration of fluid and nutritional support. The tube is secured with a combination of tape and suture. Photo: Taronga Western Plains Zoo
creatinine may be helpful indicators of rehydration, depending on the species and stage of development.
Mild dehydration can be treated by administering warmed SC isotonic crystalloid fluids and supplemental oral fluids.
For animals too weak to suck effectively, oral fluid replacement can be given via an orogastric or nasogastric tube (Fig. 15.4). Correct placement of indwelling nasogastric tubes should be confirmed radiographically. Tubes can be sutured and/or taped to the head. Bandaging the forefeet can reduce the risk of self-removal of the tube.Severe dehydration necessitates IV fluid therapy. As a general rule, a slow bolus of 20-30 mL/kg of warm isotonic crystalloid fluids is given initially followed by CRI (60-80 mL/kg per day plus ongoing losses). Losses can be estimated (e.g. 2 tablespoons of diarrhoea is equal to 30 mL of fluid). If hypoglycaemic, dextrose is added to the IV fluids at the lowest amount that will maintain nor- moglycaemia (start with 1.25% dextrose) (McMichael 2014). If clinically indicated, synthetic colloids and/or plasma from a healthy donor can be given by slow IV infusion (2-5 mL/kg bolus followed by 1 mL/kg per hr as needed) (Lee and Cohn 2017).
Large volumes of fluid administrated over short periods of time are poorly tolerated. Syringe pumps or Buret- rol sets should be used to help avoid fluid overload in patients requiring systemic fluid replacement.
3.4 Sepsis
Sepsis may develop secondary to wounds or respiratory and GI infections. Clinical signs are non-specific and include reluctance to feed, decreased urine output and cold extremities. Stabilise as described above. Ideally, culture and susceptibility testing of the source of infection should be performed to direct antibiotic choice; however, empirical broad-spectrum antibiotics can be started before receipt of results (McMichael 2014) (see Appendix 4).
3.5 Pain
Studies in human infants and laboratory animal neonates show that when anaesthesia or analgesia is withheld, altered pain sensitivity and increased anxiety occurs with subsequent painful experiences, when compared with subjects receiving analgesia (Mathews et al. 2014). Although care should be taken with dosing (see Appendix 4), pain must be addressed to facilitate normalisation of feeding and physiological function.
For most species the judicious use of opioids and NSAIDs is preferred for painful conditions and procedures. Local anaesthesia is useful in some circumstances and non-pharmacologic analgesic interventions such as warmth, suckling and mother-offspring contact can be used. The capacity to experience pain is not present in all mammalian species at birth (Mellor 2010), with differences related to the neurological maturity of neonates. In marsupials, pain perception may not develop until after one-third to one-half of pouch life. Research on tammar wallaby development, for example, reveals that until around 120 d after birth there is a lack of behavioural or electroencephalographic (EEG) signs of conscious perception, but by 160-180 d of age major developmental changes in the neurological system have occurred that indicate suffering from pain is possible (Diesch et al. 2010).3.6 Nutrition
Information on the nutritional composition of milk from a range of Australian native mammal species, as well as appropriate hand-rearing formulae and target intakes, have been published (Gage 2002; Jackson 2003; McCracken 2008; Vogelnest and Woods 2008). A colostrum supplement (e.g. Impact™ bovine colostrum supplement, Wom- baroo Food Products, Glen Osmond, SA) can be offered to newborn eutherians with suspected failure of passive transfer to provide immunoglobulins and other protective proteins to boost passive immunity before starting on formula. For marsupial PY, in the absence of more targeted products, Impact™ is used by some carers as a nutraceutical throughout the rearing process to emulate the ongoing provision of immunoglobulins during the various phases of lactation, with a short-term increase in dose recommended by the manufacturer just before first pouch emergence. The subclasses and amounts of immunoglobulin present in Impact™ have not been described and although there is the possibility of bovine immunoglobulins providing cross-species protection for various pathogens there is little solid evidence to support this in marsupials.
Consequently, the clinical improvements attributed to this practice by some are derived from anecdotal reports and may be confounded by other factors.For semi-weaned animals, species-appropriate solid foods should be made available (see Chapter 14).
In all cases, stabilisation of the patient is required before attempting to feed full-strength formula. After a period of fasting, illness or dehydration, rehydration solutions are initially offered followed by species-appropriate formula diluted with water or an electrolyte solution. If well tolerated, the formula concentration can be gradually increased.
If faced with an orphan of an unfamiliar taxonomic group, contacting organisations with particular species knowledge and experience can be an informal but valuable source of practical advice. For native rodents and the dingo (Canis familiaris), extrapolation from well- established techniques for their domestic counterparts is appropriate.
If the patient is unable to feed because of weakness or injury, alternative means of delivering adequate nutrition may need to be considered (e.g. by gavage or nasogastric tube) (Fig. 15.4). Selection and correct preparation of an appropriate formula for the species and stage of development are important, as is utilising suitable equipment. For bottle-fed animals consideration needs to be given to the teat shape and size, as well as the diameter of the hole through which formula flows (McCracken 2008). Lapping from spoons, bowls, syringes or the clean palm of a hand may be appropriate for some species at certain
Fig. 15.5. An orphaned short-beaked echidna (Tachyglossus aculeatus) lapping formula from the palm of a carer's hand. Photo: Taronga Wildlife Hospital
stages of development (Fig. 15.5) and can reduce the risk of aspiration of formula. Very small patients, such as microbats, can be fed via a plastic cannula or a foam tip (Olsson and Woods 2008; Lyons and Wimberley 2016).
4.