Luis H. Tello, DVM, MSc
Burn small animals, are indeed 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. There are many different sources of burn lesions: electrical, chemicals, direct heat, fire, fireworks, etc. Common causes of burn in small animals are domestic accidents but also there is many reports about the use of electrical heating pads during surgery or in cage veterinary hospitals.
Severe burn patients are extremely complex medical cases, with compromise of respiratory, cardiovascular, electrolyte, metabolic, immune and energy pathways systems, and require a proper understanding and management of physiology, endocrinology, nutrition and immunology status of the patients, to give them appropriate treatment.
Burns affect primarily the skin, and the degrees of injury are related to the depth and extension surface affected. The skin have many different roles in the normal physiology of the body: is the primary barrier against invasive infection, the skin help to maintain the body temperature controlling the evaporation of fluids, the skin adapts to aggressions or changes in the environment like pain, cold and heat. All these functions are impaired in burned animals and have been related as secondary cause of death.
Hypoproteinemia due to the protein loss is a serious issue because combined with the fluid shifts and hypovolemia set 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 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.
Burns are evaluated in general according the severity of the damage in the body system, while the severity of insult is address according the length of tissues exposure, the surface affected, the type of heat source, and the previous condition of the patient: healthy, sick, old, young, etc.
Affected surface is part of the regular approach in human patients. While there is many standards to calculate affected surface in people, 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 18% each one 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, is the human equivalent is a first-degree, burns such as a sun burns are common in white coat dogs and cats, skin redness is present, the skin is hyperesthetic. There are no blisters and normally these burns heal on their own with no scars.
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 denude. The hair is well attached and usually mixed with yellow exudates. These lesions are very painful. Commonly scarring occurs.
Full Thickness Burns
Is the human equivalent is third-degree burn, affects the epidermis, dermis, and subcutaneous tissue. Generally patient are presented in shock status, the skin looks dry and not perfused and as matter of fact do not bleed if you cut it, the hair coat can be easily epilated just pulling, there is no pain sensation. Large scar remains after a prolonged and slow healing process.
Burns as Emergency
The care of burn patient will therefore divided into 3 stages:
From arriving to 36 hours
Early period: 36 hours after arrive to 5 days
Inflammation-Infection period, after the first week
Stage I Care: From Arriving to 36 Hours
The initial assessment should start with de general physical condition, systemic compromise, amount of body and surface affected, plus degree of local injury. If the lost of skin are larger enough, euthanasia can be recommended.
People involved in fires have respiratory injury due to the inhalation of air heated to a temperature higher than 150C°, results in burns into the mouth, oropharynx, and upper airway. Pulmonary damage due to smoke inhalation is the major cause of mortality in human beings. Deaths are associated to the fall of oxygen concentration in the environment, inhalation of carbon monoxide and dioxide during combustion and cyanide toxicity. This mechanism is rare in small animals, apparently because they walk almost at the floor's level.
Animals affected by smoke inhalation should be placed on 100% oxygen early after arrive to ICU. Inhalated heat, produce upper airway obstruction due to airway edema. Early endotracheal intubation is crucial, and must to be performed if physical exam shows signs of airway burn damage or if patient show respiratory distress. It is important consider that pulse oximetry cannot evaluate the severity of hypoxia because his lack of capability to differentiate between oxygenated hemoglobin and carboxyhemoglobin.
The initial therapy is oriented to relief the pain with cold direct application in the burn area: chilly water, soak towels, cold tap water are good alternatives. Oxymorphine alone or combined with Acetylpromazine in neuro-leptoanalgesia is indicated to pain control in dogs. Cats can be treated with Diazepam plus Ketamine.
Oxygen 100-150 ml/Kg/ per minute should be initiated, as soon as possible and a central catheter into jugular vein should be placed. Give fluid replacement at 4 ml/Kg per hour in dogs and 2 ml/Kg per hour in cats. Isotonic balanced electrolyte solution like Lactated Ringer´s or normal Saline is the first choice. Free glucose fluids must be avoided because hyperglycemia and glucosuria will occur after deep burns.
Potassium levels should be monitored because during the first 24 hours it will be a rise with severe 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 start analgesia treatment, the hair must to 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. Eschar remove must to show healthy underlying granulation tissue.
Systemic antibiotics do not penetrate eschar, 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 with Aloe Vera shows certain antiprostaglandin effect that can help to maintain normal dermal vasculature.
Stage II Care: 36 Hours After Arrive, 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:
Proper care of burn wounds
Pain and anxiety control
The main pulmonary problems came up 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 damaged and impairment in the ciliary function, leads to infections as: bacterial tracheobronchitis, pneumonia or bronchopneumonia. Proper antibiotic selection trough culture of secretions is the first choice for these complications.
Evaporation is a major source of water loss within the burn wounded areas. An estimation of the loss must be obtained to perform proper fluid therapy. Anemia is another complication cause by red cells destruction plus bone marrow impairs production.
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 during this stage. No aggressive fluid therapy is currently indicated: 60-70 mmHg as mean arterial pressure, checking urine production around 1-2 ml/Kg/ hour. Albumin level around 2,5 g/dL is the goal, with hematocrit should be kept over 30%, considering whole blood transfusion.
It is important to remember that burn animals has major effects over the immune system, associated to impaired cell mediated immunity, decrease in the neutrophils function, and compromise of the humoral immune response. With all these effects, infection should be a major complication in the wounds care. Culture, biopsy analysis and antibiotic studies must be performed in order to specific control over infection. As wound cleaning, excision and escharotomy are regular procedures, can be used to obtain proper samples for culture.
Careful handling of stress, anxiety and pain are extreme important in the small animal burn patient: narcotics as morphine, oxymorphine, butorphanol and low doses of benzodiazepines are indicated. Phenothiazines must be avoided because their extrapyramidal side effects in burn patients.
Stage III Care: Inflammation-Infection Period, After the First Week
Sepsis, SIRS and septic shock are common during this period. Adequate nutritional support are very important for clinical outcome. Feeding tubes are first choices in starving animals. Pulmonary infections and RADS (Respiratory Acute Distress Syndrome) remain as major cause of mortality during this period. Partial ventilatory support could be useful if necessary.
Treatment in human patients commonly includes anabolic agents, in order to attenuate catabolism during this phase. There is no information available in small animals patients to support this management.
Pain control in the burn patient is a very important issue due to ethic, and physiological impacts that the pain can have. Technicians and pet nurses should be aware of the importance of decrease a patient's discomfort. Nurse care small details should not be overlooked. Allowing the patient room to move comfortably despite bandages, elevating wounded areas, and maintaining a clean, dry environment in which to sleep will contribute significantly to a patient's comfort level.