Luis H. Tello, DVM, MS
Small Animal Teaching Hospital, College of Veterinary Medicine, University of Chile
Burnt small animals are trauma patients with many complications over them. There are many different sources of burn lesions: electrical, chemicals, direct heat, fire, fireworks, etc. A common cause of burn in small animals is the use of electrical heating pads during surgery or in cage hospital management.
The care of burn patient will therefore be divided into 3 stages:
1. From arriving to 36 hours
2. Early period: 36 hours after arrive to 5 days
3. Inflammation-Infection period, after the first week
Burn injuries are extremely complex, with compromise of respiratory, cardiovascular, dermatological 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, help to maintain the body temperature controlling the evaporation of fluids, 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.
Affected surface can be approached by burned body segments: Each forelimb means 9% each rear limb means 18%, head and neck 9%, Trunk and abdomen 18%. Burn depth has been classified according the degrees of injury:
Superficial or first degree involves the epidermis layer, partial-thickness or second degree involves the epidermis and mid to deep amount of dermis, and the full-thickness or third degree there is complete destruction of the skin and compromise structures of the subcutaneous.
Burns as emergency
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 lost area of skin are large enough, euthanasia can be recommended.
People involved in fires have respiratory injury due to the inhalation of air heated to a temperature higher than 150°C that 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 more rare in small animals, apparently because they walk almost at floor level.
Animals affected by smoke inhalation should be placed on 100% oxygen early after arrive to ICU. Inhalated heat produces upper airway obstruction due to 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 consider that pulse oximetry cannot evaluate the severity of hypoxia because its lacking capability to differentiate between oxygenated hemoglobin and carboxyhemoglobin.
The initial therapy is oriented to pain relief 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 neuroleptanalgesia is indicated for 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, every hour or 30 minutes. If hematocrit falls below 20% or, hemoglobin falls below 7 g/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; (Silvadene 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 note 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.
Last reports with Aloe vera shows certain antiprostaglandin effects that can help to maintain normal dermal vasculature.
II Stage Care: 36 hours after arrive to 5 days
This period of time is a 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 come 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 damage and impairment of ciliary function, leads to infections as: bacterial tracheobronchitis, pneumonia or bronchopneumonia. Proper antibiotic selection trough culture of secretions are the first choice for this 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 caused by red cells destruction plus bone marrow impaired production.
Fluid therapy is a keystone during this period of time. Fluids with 5% glucose with small amount of sodium are indicated because there are no major losses of sodium during this stage. No aggressive fluid therapy are 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 neutrophil 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. Wound cleaning, excision and escharotomy are regular that 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.
III Stage 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) remains as major causes of mortality during this period.
Partial ventilatory support could be useful if necessary.
Treatment in human patients commonly include anabolic agents, in order to attenuate catabolism during this phase. There is no information available in small animals patients to support this management.
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