Thermal burns are a common presentation for a range of different reptile species. It is unknown exactly why they are so prone to thermal injury, but it has been theorised that reptiles have different pain receptors compared to mammals. This could explain the lack of withdrawal reflex in response to thermal pain, as reptiles will continue to sit upon a heat source that is causing thermal burns (Mader, 2006). Thermal burns could also be an indication of a clinically ill reptile that is weak or unable to move away from a heat source. Burns can be classified from first to fourth degree (Pees and Hellebuyck, 2019) and can have significant systemic consequences if not recognised and treated correctly.
Thermal burns usually occur due to prolonged contact with inappropriate or faulty heating equipment (Figure 1). Hot rocks or heat mats can malfunction and overheat when not properly thermostatically controlled (Scheelings and Hellebuyck, 2019), and many cases of hot rocks or heat mats short-circuiting and causing burns to reptiles have been reported in the literature (Fraser and Girling, 2004; Mader, 2006; Scheelings and Hellebuyck, 2019). Burns can also occur when basking lamps are provided without adequate protective housing or are placed too close to the reptile’s basking spot (Figure 2).
Upon the presentation of a reptile patient for thermal burns, a full physical examination must be performed. The extent of the burns should be identified as well as the cause of the burns. Fully assess the patient – are there any defects that could inhibit the patient’s ability to move away from a heat source? Is there any clinical reason as to why the patient might be seeking more heat than is normal for the species, such as a clinically apparent infection? A full husbandry review should be performed, including asking the client the temperatures of both the hot and cooler end of their vivarium or chosen housing, the way in which heat is provided and if that heat source is thermostatically controlled. If temperatures within the vivarium are below the preferred optimum temperature zone for the patient, they may be seeking out heat in ways they may not if adequate heat was provided, for example snakes wrapping themselves around heat bulbs for warmth.
Diagnosis of thermal burns is made from history and physical examination (Wellehan and Gunkel, 2004). Burn classification is based on the severity and thickness of the wound in a similar way to mammalian burns. First- degree burns (Figure 3) are superficial, involving the epidermis (Fraser and Girling, 2004), and due to exposed nerve endings, these burns are painful (Scheelings and Hellebuyck, 2019). First-degree burns are of least concern, but should be monitored closely as if they are not kept clean they can result in secondary bacterial infection (Pees and Hellebuyck, 2019). Second-degree burns, involving the epidermis and underlying dermis, present as blistering and bruising of the affected area, often with a crusty covering to the burn (Mader, 2006). These burns are also painful and should be treated with adequate analgesia. Third-degree burns result in the destruction of the epidermis, dermis and underlying adnexal structures, including the nerve endings, which may result in a lack of pain with this type of injury (Fraser and Girling, 2004). These can be severe and result in months of treatment with contracture of the skin due to scar formation and, in some cases, skin grafts may be required (Mader, 2006). Fourth-degree burns involve destruction of the entire skin thickness and the underlying tissues including muscle and bone, sometimes resulting in entry into the coelomic cavity (Scheelings and Hellebuyck, 2019).
The extent of a thermal burn may not become apparent until days or weeks after the initial trauma (Scheelings and Hellebuyck, 2019). It is therefore important to continue reassessing the affected areas throughout treatment. Any necrotic skin should be debrided under local or general anaesthesia and it is often at this point that the client becomes aware of the extent of the damage. Some burns will look worse before they look better as the degree of tissue damage becomes clear.
Analgesia should be a priority in treatment, with the type of analgesia depending on the severity of the burn. Opioids such as morphine or hydromorphone can be used in severe cases with non-steroidal anti-inflammatories for less serious burns (Scheelings and Hellebuyck, 2019). The author tends to administer opioids when the patient is under care in hospital and discharge with oral tramadol and non-steroidal anti-inflammatories for home care. It is important to remember that off-licence use of medications should be discussed with the owners prior to dispensing and that a range of drug doses are available in peer-reviewed literature; however, it is each veterinary surgeon’s responsibility to ensure adequate and sensible analgesia in reptile patients.
In acute cases, the patient should be immediately immersed in cold water or have a cold compress applied for 15 to 20 minutes to limit further tissue damage (Fraser and Girling, 2004); however, most cases present a number of days later. Fluid therapy should be considered in reptiles with large surface areas of burnt skin, as fluid loss occurs through burnt skin (Scheelings and Hellebuyck, 2019). This can be provided in the form of warmed lactated Ringer’s solution either subcutaneously, intracoelomically or intravenously.
The risk of secondary bacterial and fungal infection is high, especially as most burns tend to be on the ventral surface of the patient and therefore in contact with the substrate and environment. For this reason, the wound should be cleaned at least once daily with dilute chlorhexidine or iodine (Mader, 2006) and topical silver, such as silver sulfadiazine cream, should be applied (Fraser and Girling, 2004). Ideally the wounds should be covered with a non-adherent, silver- or honey-impregnated dressing daily (Scheelings and Hellebuyck, 2019); however, practically, this can be difficult and in some cases the dressing may need to be sutured to the patient (Fraser and Girling, 2004). Initially bandage changes may need to be performed daily in conjunction with frequent debriding of necrotic tissue. In burns with a large surface area, systemic antibiosis may be considered, especially if concurrent surgical debridement is planned (Pees and Hellebuyck, 2019).
Substrate within the vivarium should be changed to kitchen paper or another clean, non-adherent substance to prevent further trauma. Supplemental nutrition should also be considered, as burn injuries can cause loss of proteins and hypoproteinaemia (Scheelings and Hellebuyck, 2019) and pain from the injury can result in anorexia. Finally, the cause of the burn should be identified and removed. It is important that the heat source is not removed without another supplemental heat source being introduced, as it is imperative that the reptile patient stays warm and within its preferred optimum temperature zone during the healing process, which may take months.
All reptile species require supplemental heat; however, it is essential to ensure that this heat is provided with adequate thermostatic control. A number of different types of thermostats are commercially available depending on the type of heat source used. Heat sources should not be used without thermostatic control and it is important for reptile keepers to constantly monitor the temperatures within the vivarium to ensure the patient is being provided the temperatures required to thrive. As the veterinarian, it is important to be aware of the optimum temperature ranges for different reptile species and to work with clients to ensure these are provided to patients.
Thermal burns can take months to heal; however, reptiles are surprisingly resilient creatures. Analgesia and hygiene are cornerstones of the treatment of thermal burns in reptiles and care must be taken that secondary infections do not occur. Treatment of thermal burns can be rewarding; however, the clients must be adequately informed of the length of treatment and overall costs of treatment, which can span many months.