Luis H. Tello, MV, MS, DVM
Burns in small animals involve trauma patients with extensive lesions in the skin and eventually also in the subcutaneous and muscular layers, leading to many metabolic and organic complications. Thermal injuries represent severe mechanical damage to the cells of each layer of the integument.
In general, the majority of the burn cases in veterinary medicine are local burn injuries with less than 20% and more commonly around 5% of the body surface affected. They are caused by domestic, in-hospital, or in-grooming accidents.
Domestic conditions such as boiling liquids, direct heat from fireplace, hot metals (such as irons), but also devices used at veterinary hospitals or grooming facilities, such as hair dryers or heating pads, are common sources of burns for dogs and cats. However, it is important to clarify that the severity and the extent of the local burn injury depends not only on the temperature but also on the duration of thermal contact.
Severe burn cases are extremely complex, with compromise of respiratory, cardiovascular, electrolyte, metabolic, immune and energy pathway systems, and require a proper understanding and management of physiology, endocrinology, and nutrition and immunology status of the patients, to provide them appropriate treatment.
Hypoproteinemia due to the protein loss is a serious issue, because, combined with the fluid shifts and hypovolemia, it sets the stage for severe shock and hypotension. Hypovolemia leads to a decrease in cardiac output and this leads to tissue and organ hypoperfusion and cellular hypoxia. Many organs and tissues are affected simultaneously, while the kidneys, in particular, are extremely sensitive to decreases in blood pressure. Acute renal failure is a common complication in severe patients, and its prevention and assessment should be included as part of the diagnosis and treatment protocol of burn patients. In addition, persistent hypovolemia and hypotension can lead to acute ischemic failure of other organs such as the lungs, liver, and gastrointestinal tract.
Calculating the affected surface is part of the regular approach in human patients. While there are many standards to calculate affected surface in people, doing so in small animals is more complex due to the high variability in sizes and weights. One accepted proposal is to calculate the total surface by burned body segments: Each forelimb means 9%, each rear limb means 18%, head and neck 9%, trunk and abdomen each represent 18% of the body surface.
Burn depth classification has been changed in veterinary medicine from the classic human-medicine degrees system to another according the layers affected.
Affect only the outermost layer of the skin, the epidermis (the human equivalent is a first-degree burn). Sunburns in white coated dogs and cats are good examples. Commonly the skin exhibits desquamation and looks dry. With no complications, heals in 2–5 days via almost no scar.
Partial thickness burns
This is the veterinary equivalent to the human second-degree burn. The burns involve the epidermis and the superficial layer of the dermis, you can see blisters and sometimes the skin is denuded. The hair is well attached and usually mixed with yellow exudates. These lesions are very painful and edematous. Commonly scarring occurs. May heal in 10–14 days via new epithelialization.
Full thickness burns
Is the equivalent to third-degree burn; affects the epidermis, dermis, and subcutaneous tissue. Generally patients are presented in shock status, the skin looks dry and bloodless, the hair coat can be easily epilated just pulling, and there is no pain sensation. Large scar remains after a prolonged and slow healing process. Mortality is common.
Some protocols also use the term "burns with bone involvement" to refer to the human 4th-degree burns, but there is no consensus about that term.
Burns as Emergency: General Approach
I Stage Care: From Arriving to 36 Hours
The initial assessment should start with the general physical condition, systemic compromise, amount of body and surface affected, plus degree of local injury. If the loss of skin is large enough, euthanasia can be recommended.
Animals affected by smoke inhalation should be placed on 100% oxygen early after they arrive to ICU. Inhalation of hot air and heat may lead to upper airway obstruction due to the development of airway edema. Early endotracheal intubation is crucial and must be performed if physical exam shows signs of airway burn damage or if patient shows respiratory distress. It is important to consider that pulse oximetry cannot evaluate the severity of hypoxia because of the lack of capability to differentiate between oxygenated hemoglobin and carboxyhemoglobin.
The initial therapy is oriented to relieve the pain with cold direct application in the burn area: chilly water, soak towels, cold tap water are good alternatives.
Opioids are the analgesic drugs for these types of patients using the so-called strong opioids. Morphine fentanyl, buprenorphine, and oxymorphone are the most commonly used. A large-bore peripheral catheter (14–18 G) as soon as possible and a central catheter into the jugular vein should be considered. Give fluid replacement at 4 ml/kg per hour in dogs and 2 ml/kg per hour in cats. Isotonic balanced electrolyte solution like Plasmalyte, Normosol, or Lactated Ringer's is the first choice. Blood glucose should be monitored because of the hyperglycemia and glucosuria that will occur after deep burns.
Potassium levels should be monitored during the first 24 hours to assess hyperkalemia associated to cells' destruction into the burned tissues. Solutions with contents of 4–5 mEq/L of potassium are recommended during this phase.
Check out serum protein levels, urine production, hematocrit level, hemoglobin, electrolytes, and blood gases. If total protein drops below 3 gm/dl, fresh plasma or colloids should be added. Acidosis can be corrected with sodium bicarbonate; 5 mEq/kg of body weight may be given every hour or 30 minutes. If hematocrit falls below 20% or hemoglobin falls below 7 gm/dl, whole blood or washed red blood cells must be added to the treatment. Hct above 30% is the goal.
After starting analgesia and sedation, the hair must be clipped; burn wound can be washed with antiseptic solutions as povidone iodine or chlorhexidine. Necrotic tissues, foreign material and debris must be removed. Burn wounds of first or second degree should be topically treated with antibiotic medication (Silver ointment is the first choice) and bandaged. With third-degree burns, eschar must be removed soon and in a daily frequency. That is a very painful procedure, so anesthesia or proper analgesia should be considered. The scar must be removed to show healthy underlying granulation tissue.
Systemic antibiotics do not penetrate scar, so topical therapy is always indicated with antibiotic ointments and creams. Gentamycin, polymyxin, neomycin, and bacitracin are very effective against the contaminant flora in burn wounds, as well as fluoroquinolones. Some reports state aloe vera shows certain anti-prostaglandin effects that can help to maintain normal dermal vasculature.
II Stage Care: 36 Hours After Arriving to 5 Days
This period of time is transition from flow phase of shock to the hypermetabolic phase. The main problems in this stage are pulmonary problems, hemodynamic stability, renal function, burn wounds care, pain and anxiety control.
The main pulmonary problems come from airway obstruction due to thermal or chemical burn of the airway mucosa. Adequate laryngoscopy is very helpful to assess the real damage. Long-term intubation should be considered if mechanical ventilation is available.
Cough and increased mucous production are very common in this period, related to mucosal irritation. However, the damage and impairment in the ciliary function lead to infections such as bacterial tracheobronchitis, pneumonia or bronchopneumonia. Proper antibiotic selection through culture of secretions is the first choice for these complications.
Evaporation is a major source of water loss within the burn wound areas. Fluid therapy is a keystone during this period of time. Fluids with 5% glucose with small amount of sodium are indicated, because no major losses of sodium occur during this stage. Non-aggressive fluid therapy is currently indicated with end goals of 60–70 mm Hg as MAP, urine production around 1–2 ml/kg/hour. Albumin level around 2,5 g/dL is the goal, and hematocrit should be kept over 30%, considering whole blood transfusion.
It is important to remember that burns have major effects over the immune system, associated with impaired cell mediated immunity, decrease in neutrophil function, and compromise of the humoral immune response. With all these effects, infection should be a major complication in the wound's care. Culture, biopsy analysis, and antibiotic studies must be performed in order to have specific control over infection. Wound cleaning, excision, and escharectomy are regular procedures and can be used to obtain proper samples for culture.
Careful handling of stress, anxiety, and pain are extremely important in the small animal burn patient; narcotics such as morphine, oxymorphone, butorphanol and low doses of benzodiazepines could be used. Phenothiazines must be avoided because of their extrapyramidal side effects in burn patients.
III Stage Care: Inflammation-Infection Period
After 1 week. Sepsis, SIRS and septic shock are common during this period. Adequate nutritional support is very important to clinical outcome. Feeding tubes are first choices in starving animals.
Pulmonary infections and RADS (Respiratory Acute Distress Syndrome) remain as major causes of mortality during this period. Partial ventilatory support could be useful if necessary.
References are available upon request.