ASSESSMENT OF BUSHFIRE-AFFECTED WILDLIFE

3.1 Classifying burns

Classification of a burn injury helps determine the sever­ity of the injury and consequently the impact on the patient, both locally at the site of the burn and systemi­cally (Vaughn and Beckel 2012).

Burns are classified according to burn depth and per­centage of total body surface area (TBSA) involved (Vaughn and Beckel 2012). In human medicine, various schematics have been developed to determine the per­centage of TBSA burnt and to account for changes in body proportion that occur with growth. Accurate sche­matics are not available for the wide range of animal spe­cies seen in veterinary practice; therefore, percentage TBSA involved should be estimated based on clinical judgement. Additionally, the location of burns must be considered in the assessment of the patient. Burns to eye­lids, nose, lips, genitals, feet, tail and pouch have a poor prognosis due to scarring and loss of function and may impact survival. In many species, footpad burns may cause catastrophic loss of function (Baek et al. 2023). These animals are unlikely to meet criteria for release (see section 3.3.2 for euthanasia criteria).

3.1.1 Burn depth

• Superficial: epidermis only.

• Partial thickness: epidermis, upper one-third of dermis to full dermis. Heal over 1-2 wk with little or no scarring.

• Full thickness: epidermis, dermis and subcutis. Require surgical intervention.

It is important to be aware that clinical assessment of burn depth may underestimate the true depth (Baek et al. 2023).

3.1.2 Percent total body surface area

• In adult humans >20% TBSA is considered a severe burn injury (SBI), but in a child >10% is considered SBI. Similarly, the smaller an animal patient the higher the surface area to volume ratio and therefore TBSA ≤5-10% is likely to have greater systemic effects than in larger animals.

• Local burns covering a small percentage of TBSA do not result in metabolic derangements and therefore aggressive systemic therapy is generally not required.

• SBI >10-30% TBSA (dependant on size of animal) results in severe metabolic, cardiovascular and pulmo­nary derangements requiring intensive management or euthanasia.

It is important to be aware that the true severity of burns may only become apparent a few days after the original burn injury.

3.2 Smoke inhalation and thermal respiratory injury Wildlife with external burn injuries will often have asso­ciated smoke inhalation and thermal respiratory injury. If severe, it is often rapidly fatal. Morbidity and mortal­ity are exaggerated in patients with severe dermal burns plus smoke inhalation and thermal respiratory injury. The clinical effect, or death, due to smoke inhalation may be acute or seen several days to weeks after expo­sure, may occur in unburnt animals remote from a fire but exposed to smoke and may go undiagnosed (Peters et al. 2021).

Injury to the respiratory tract results from thermal burns to the upper respiratory tract and inhalation of particulate matter and gases containing toxins such as sulfur dioxide, acrolein and other aldehydes. Effects of the gases are short-lived, but deposition of particles in the lung leads to both acute and chronic injury.

worst prognostic indicators for burn patients (Baek et al. 2023; L Wicker pers. comm.).

Another significant and sinister sequela to burns of the distal limb and feet is progressive digital necrosis. Secondary and progressive necrosis of tissue deep to these burns has been documented in burn patients and only becomes apparent some time after the initial burn injury. Claws or nails are often lost by rehabilitating wildlife in the weeks and months following footpad burns (Baek et al. 2023). The pathobiology of burn injury progression remains unclear. Burns are complex and dynamic injuries involving endothelial damage, vessel occlusion, thrombo­sis, cytokine release, white blood cell infiltration, apopto­sis and progressive necrosis. Given the minimal soft tissue between the skin (and keratin of nails) and bone in the feet, these processes not only affect the skin but the deeper tissues, including bone.

Paronychia and progressive digital necrosis must be considered possible outcomes for all burns to the feet and must be factored into prognostic decision making (Fig. 27.5).

Changes in the bone may be radiographically apparent before being clinically apparent. Baek et al. (2023) noted lytic and sclerotic changes to the distal phalanges in a koala with abnormal digits at necropsy, supporting the presence of heat radiation damage to the underlying ungual process and more proximal bone. Radiography should be included in the clinical re-evaluation of feet during treatment and rehabilitation. Loss of nails and digits are likely to render an animal unsuitable for release, therefore necessitating euthanasia.

3.3.2 Euthanasia

Euthanasia must be seen as a positive welfare outcome for patients with SBI and/or comorbidities, for those where prognosis for successful treatment, rehabilitation and release are poor and in circumstances where there are no options for appropriate treatment and care (Australian Veterinary Association 2019).

Criteria for euthanasia (adapted from DELWP 2018)

• SBI: where burns cover a significant percentage TBSA (see burn classification)

• severe respiratory compromise or pneumonia due to smoke inhalation

• full-thickness burns involving eyelids, lips, and feet (particularly if bone or tendons involved) (Fig. 27.6)

• deep burns to the scrotum, penis, cloaca or pouch

Fig. 27.5. a) Digital necrosis and paronychia in an eastern grey kangaroo (Macropusgiganteus). Credit: Jasmine Hunter. b) Digital necrosis and paronychia in a sugar glider (Petaurus breviceps). Credit: Chantal Whitten.

Fig. 27.6. Common brush-tailed possum (Trichosurus vulpecula) with severe burns to the feet, eyelids and ears, necessitating euthanasia.

• loss of digits and nails/claws that are likely to impair normal function

• severe ocular damage resulting in blindness

• severe burns to the feet or tail that would necessitate amputation

• advanced age as assessed by tooth wear

• any burn injury or comorbidity that results in perma­nent disability or is likely to impair the animal’s capacity to survive and thrive in the wild

• presence of untreatable comorbidities (disease, severe injury, emaciation)

• the animal is a species for which attempts at treatment are likely to result in poor welfare outcomes (e.g. some adult macropods)

• immature joeys (eyes closed, furless)

• the animal cannot be safely or humanly captured or transported

• resources are not available to adequately treat and care for an animal

• the animal is an introduced pest species.

The objective of euthanasia is to produce immediate or rapid loss of consciousness, followed by death, with a minimum of pain, discomfort or distress. Acceptable methods of euthanasia for Australian native wildlife are the following.

• Intravenous injection of concentrated pentobarbitone (euthanasia solution). This is the preferred method if the animal can be readily and humanely captured, transported and restrained. It must be performed by a veterinarian or veterinary nurse. The animal must be heavily sedated or anaesthetised before administration of the euthanasia solution. If IV access is difficult, intracardiac injection can be used. Carcasses of animals that have been euthanased using pentobarbi­tone must be disposed of by deep burial or incinera­tion as they can pose a risk to scavengers.

• Gunshot or captive bolt to the brain. The use of firearms must only be performed by licensed, author­ised and accredited personnel. Permission must be sought form the IC to carry and use a firearm on fire­grounds. This method is generally only used on the fireground for large macropods and adult wombats that cannot be captured by physical or chemical (darting) means. Even if physical or chemical capture options are available, a single gunshot to the brain is usually more rapid and humane. Use of a captive bolt may be an alternative option to using firearms or drugs but requires training and close access to the animal.

• Blunt trauma. This can be used if neither of the above options is available. A forceful and sharp blow to the back of the skull using a blunt metal or heavy wooden tool or bar is acceptable for larger species that are immobile due to severe injury or debility and smaller mammal, bird or reptile species.

Other methods such as exsanguination, decapitation, drowning, inhalation of motor vehicle exhaust fumes or freezing are not considered humane and are not acceptable.

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