Chemical Burns

Chemical burns, also known as caustic burns, are a form of tissue injury caused by exposure to corrosive substances, including strong acids, alkalis, oxidants, reducing agents, and vesicants. In veterinary surgery, chemical burns are classified as thermal injuries but with distinct pathophysiological mechanisms, as the offending agent continues to cause tissue destruction until it is neutralized or removed. The severity of a chemical burn depends on the concentration of the agent, the duration of contact, the quantity of the agent, the physical form (solid, liquid, or gas), and the tissue's inherent susceptibility. Chemical burns can affect the skin, mucous membranes, eyes, and gastrointestinal tract, and may lead to systemic toxicity, metabolic derangements, and multi-organ dysfunction. In small animal practice, chemical burns are less common than thermal burns but can result from household cleaning agents, industrial chemicals, or iatrogenic exposure during surgical preparation. The surgical management of chemical burns involves aggressive decontamination, debridement, wound care, and reconstructive techniques to restore function and cosmesis.

Chemical burns in veterinary patients are caused by exposure to a wide range of corrosive substances. The most common etiologic agents include: (1) Strong acids, such as hydrochloric acid, sulfuric acid, nitric acid, and hydrofluoric acid, which cause coagulative necrosis by denaturing proteins and precipitating cellular components. (2) Strong alkalis, such as sodium hydroxide (lye), potassium hydroxide, calcium hydroxide (lime), and ammonium hydroxide, which cause liquefactive necrosis by saponifying fats and dissolving proteins, leading to deeper tissue penetration. (3) Oxidizing agents, such as hydrogen peroxide, sodium hypochlorite (bleach), and chromic acid, which cause cellular damage by generating free radicals and oxidizing cellular components. (4) Reducing agents, such as hydrazine and hydrochloric acid, which bind to cellular components and disrupt metabolic processes. (5) Vesicants, such as mustard gas and Lewisite, which cause severe blistering and tissue necrosis. (6) Desiccants, such as sulfuric acid and phosphorus, which extract water from tissues and generate heat. (7) Systemic toxins, such as phenol and formic acid, which can cause metabolic acidosis and organ damage. In veterinary practice, common sources include household cleaning products, drain cleaners, toilet bowl cleaners, pool chemicals, fertilizers, and industrial solvents. Iatrogenic chemical burns may occur from improper use of topical antiseptics, such as chlorhexidine or povidone-iodine, or from leakage of chemotherapeutic agents during intravenous administration.

Chemical burns are relatively uncommon in veterinary medicine compared to thermal burns, but they can occur in any species. Dogs and cats are most frequently affected, with a higher incidence in young animals due to their curiosity and tendency to explore household chemicals. There is no strong breed or sex predisposition, but working dogs, such as those used in search-and-rescue or law enforcement, may be at higher risk of exposure to industrial chemicals. The incidence of chemical burns is higher in urban environments where household and industrial chemicals are more readily available. Ocular chemical burns are particularly common in cats, as they may come into contact with cleaning agents while grooming. Gastrointestinal chemical burns can occur in animals that ingest caustic substances, leading to severe esophagitis and gastric necrosis. The severity of chemical burns varies widely, and the true incidence is likely underreported due to mild cases being treated at home. In a retrospective study of burn injuries in dogs and cats, chemical burns accounted for approximately 5-10% of all burn cases, with a mortality rate of 10-20% in severe cases.

The pathophysiology of chemical burns differs from thermal burns in that the tissue destruction is ongoing until the chemical agent is neutralized or removed. The initial injury is caused by the direct chemical reaction with cellular components, leading to protein denaturation, lipid peroxidation, and DNA damage. In acid burns, coagulative necrosis occurs, resulting in the formation of a eschar that limits further penetration of the acid. In alkali burns, liquefactive necrosis occurs, which does not form a barrier and allows the alkali to penetrate deeper into tissues, causing more extensive damage. The severity of tissue injury is determined by the concentration of the agent, the duration of contact, and the tissue's buffering capacity. The inflammatory response is triggered by the release of damage-associated molecular patterns (DAMPs) from necrotic cells, leading to vasodilation, increased vascular permeability, and recruitment of neutrophils and macrophages. This inflammatory cascade can exacerbate tissue damage through the release of reactive oxygen species and proteolytic enzymes. In severe chemical burns, systemic effects may occur, including metabolic acidosis, hyperkalemia, hypocalcemia (especially with hydrofluoric acid burns), and multi-organ failure. The release of cytokines and other inflammatory mediators can lead to systemic inflammatory response syndrome (SIRS) and sepsis. In the skin, chemical burns can cause full-thickness necrosis, leading to eschar formation, which may require surgical debridement and skin grafting. In the eyes, chemical burns can cause corneal ulceration, stromal melting, and anterior segment necrosis, leading to vision loss. In the gastrointestinal tract, ingestion of caustic substances can cause mucosal necrosis, perforation, and stricture formation.

Several factors predispose animals to chemical burns. Intrinsic factors include: (1) Age: young animals are more curious and may ingest or come into contact with chemicals. (2) Species: cats are more susceptible to chemical burns due to their grooming behavior, which can spread chemicals over a larger body surface area. (3) Coat characteristics: animals with thin or sparse hair coats may have less protection against chemical exposure. (4) Pre-existing skin conditions: animals with dermatitis or wounds may have compromised skin barriers, increasing susceptibility. (5) Metabolic status: animals with hepatic or renal disease may have impaired detoxification and excretion of chemicals, increasing systemic toxicity. Extrinsic factors include: (1) Environmental exposure: access to household cleaning agents, industrial chemicals, or agricultural products. (2) Owner negligence: improper storage of chemicals or failure to supervise animals. (3) Iatrogenic factors: improper use of topical antiseptics, such as applying concentrated chlorhexidine to open wounds, or extravasation of chemotherapeutic agents during intravenous administration. (4) Occupational exposure: working dogs may be exposed to chemicals during search-and-rescue or detection duties. (5) Lack of protective measures: animals housed in areas where chemicals are used without adequate ventilation or containment.

The clinical signs of chemical burns depend on the location and severity of the injury. Cutaneous chemical burns present with erythema, edema, blistering, and necrosis. The affected area may be painful, and the skin may appear discolored (e.g., white, black, or yellow) depending on the chemical agent. In severe cases, full-thickness necrosis may result in eschar formation, which can restrict blood flow and lead to compartment syndrome. Ocular chemical burns present with blepharospasm, epiphora, conjunctival hyperemia, corneal edema, and ulceration. In severe cases, corneal perforation and anterior uveitis may occur. Gastrointestinal chemical burns present with drooling, dysphagia, vomiting, abdominal pain, and hematemesis. In severe cases, esophageal or gastric perforation may lead to peritonitis and shock. Respiratory chemical burns may occur if the animal inhales toxic fumes, leading to coughing, dyspnea, and pulmonary edema. Systemic signs of chemical toxicity include lethargy, weakness, tremors, seizures, and collapse. In cases of hydrofluoric acid exposure, hypocalcemia may cause muscle twitching and cardiac arrhythmias. The severity of clinical signs can be graded using the burn wound classification system: superficial partial-thickness (first-degree), deep partial-thickness (second-degree), and full-thickness (third-degree) burns. Chemical burns are often deeper than they initially appear, and the full extent of tissue damage may not be evident for several days.

Differential diagnoses for chemical burns include: (1) Thermal burns: caused by heat, flame, or hot liquids, which have a similar clinical presentation but a different mechanism of injury. (2) Electrical burns: caused by electric current, which may result in deep tissue necrosis with a relatively small entry wound. (3) Friction burns: caused by abrasion, which may present with superficial skin loss. (4) Contact dermatitis: caused by irritants or allergens, which may present with erythema and pruritus but without full-thickness necrosis. (5) Necrotizing fasciitis: a bacterial infection that causes rapid tissue necrosis, often with systemic signs of sepsis. (6) Frostbite: caused by cold exposure, which may present with tissue necrosis and eschar formation. (7) Snake or spider envenomation: may cause local tissue necrosis and systemic signs. (8) Autoimmune skin diseases, such as pemphigus or toxic epidermal necrolysis, which may present with widespread skin sloughing. (9) Drug eruptions: may cause skin necrosis and ulceration. (10) Trauma: such as lacerations or avulsions, which may be complicated by chemical exposure. Definitive diagnosis of chemical burns is based on a history of exposure to a caustic agent and the characteristic clinical findings. The presence of a chemical odor, the appearance of the wound, and the progression of tissue necrosis can help differentiate chemical burns from other causes.

The diagnostic algorithm for chemical burns begins with a thorough history and physical examination. The owner should be questioned about the type of chemical, the concentration, the duration of exposure, and any decontamination measures taken. The physical examination should assess the extent and depth of the burn, as well as the presence of systemic signs. The following steps are recommended: (1) Immediate decontamination: remove the animal from the source of the chemical, brush off any dry chemical, and irrigate the affected area with copious amounts of water or saline for at least 20-30 minutes. (2) Assessment of the airway, breathing, and circulation (ABCs): if the animal has inhaled toxic fumes or has facial burns, oxygen supplementation and airway management may be necessary. (3) Determination of burn depth and extent: use the 'rule of nines' or a body surface area chart to estimate the percentage of total body surface area (TBSA) affected. (4) Laboratory evaluation: complete blood count, serum biochemistry, blood gas analysis, and coagulation profile to assess for systemic toxicity and metabolic derangements. (5) Imaging: radiography may be indicated for suspected gastrointestinal or respiratory burns. (6) Ocular examination: fluorescein staining and slit-lamp examination for corneal burns. (7) Wound culture and sensitivity: if infection is suspected. (8) Histopathology: may be performed on biopsy samples to assess tissue viability and guide debridement. (9) Continuous monitoring: reassess the wound daily for progression of necrosis and signs of infection.

Laboratory findings in chemical burns vary depending on the severity and the chemical agent involved. Complete blood count may reveal leukocytosis with a left shift due to inflammation, or leukopenia in severe cases due to bone marrow suppression. Hematocrit may be elevated due to hemoconcentration from fluid loss. Serum biochemistry may show electrolyte imbalances, such as hyperkalemia (due to cell lysis), hypocalcemia (especially with hydrofluoric acid burns), and metabolic acidosis (due to tissue hypoperfusion and lactic acidosis). Liver enzymes (ALT, AST) and renal parameters (BUN, creatinine) may be elevated if the chemical is hepatotoxic or nephrotoxic. Blood gas analysis may reveal metabolic acidosis with a decreased bicarbonate level. Coagulation profile (PT, aPTT, fibrinogen, D-dimer) may be abnormal in cases of disseminated intravascular coagulation (DIC). Inflammatory biomarkers, such as C-reactive protein (CRP) and serum amyloid A (SAA), may be elevated. Urinalysis may show hematuria, proteinuria, or casts if the chemical causes renal damage. Synovial fluid analysis is not typically indicated unless there is joint involvement. In cases of ocular burns, tear film tests and corneal cytology may be performed.

Imaging plays a limited role in the diagnosis of chemical burns but may be useful in certain situations. Radiography of the thorax may be indicated if inhalation injury is suspected, revealing pulmonary edema, consolidation, or pneumonitis. Abdominal radiography may be performed if gastrointestinal perforation is suspected, showing free air in the peritoneal cavity. Contrast esophagography may be used to assess for esophageal strictures or perforation in cases of caustic ingestion. Ultrasonography may be used to assess the depth of cutaneous burns and to evaluate for underlying soft tissue damage. Computed tomography (CT) may be helpful in assessing the extent of deep tissue necrosis, especially in cases of chemical burns to the extremities or head. Magnetic resonance imaging (MRI) may be used to evaluate for ocular or intracranial involvement. However, imaging is not routinely required for the diagnosis of chemical burns, and the primary diagnostic modality is clinical examination.

Cytology and histopathology are valuable in the assessment of chemical burns. Cytology of wound exudate or swabs may reveal necrotic debris, inflammatory cells (neutrophils, macrophages), and bacteria, which can guide antimicrobial therapy. Histopathology of biopsy samples from the burn wound can determine the depth of tissue necrosis and the viability of the underlying tissue. In acute chemical burns, histopathology may show coagulative or liquefactive necrosis, depending on the agent. In alkali burns, there is often extensive liquefactive necrosis with saponification of fat and dissolution of collagen. In acid burns, coagulative necrosis with preservation of the tissue architecture is more common. Histopathology can also identify the presence of secondary infection, vasculitis, or thrombosis. In chronic wounds, histopathology may reveal granulation tissue formation, fibrosis, and epithelialization. Special stains, such as Masson's trichrome for collagen and von Kossa for calcium, may be used to assess tissue damage. In cases of suspected chemical toxicity, histopathology of internal organs (liver, kidneys) may reveal characteristic lesions, such as centrilobular necrosis or tubular necrosis.

The treatment of chemical burns involves immediate decontamination, wound care, surgical debridement, and reconstructive surgery. The initial step is to remove the chemical agent from the skin or mucous membranes. This is achieved by copious irrigation with water or saline for at least 20-30 minutes. Dry chemicals should be brushed off before irrigation to avoid activation by water. Neutralizing agents are generally not recommended, as they can cause exothermic reactions and worsen tissue damage. After decontamination, the wound should be assessed and cleaned with a mild antiseptic solution, such as dilute chlorhexidine or povidone-iodine. Devitalized tissue should be debrided surgically, either immediately or after a few days when the demarcation between viable and nonviable tissue is clearer. Surgical debridement may be performed using a scalpel, scissors, or a hydrosurgery system. In cases of full-thickness burns, escharotomy may be necessary to relieve compartment syndrome. After debridement, the wound can be managed with topical antimicrobials, such as silver sulfadiazine or mupirocin, and dressed with non-adherent bandages. In cases of extensive burns, skin grafting or flap reconstruction may be required. For ocular chemical burns, immediate irrigation with saline or lactated Ringer's solution is critical. Topical antibiotics, cycloplegics, and anti-inflammatory agents should be administered. In severe cases, conjunctival flaps or amniotic membrane grafts may be used. For gastrointestinal chemical burns, the animal should be fasted and given supportive care, including intravenous fluids, gastroprotectants, and analgesics. Surgical intervention may be required for perforation or stricture formation. Systemic supportive care includes fluid therapy, electrolyte and acid-base balance correction, pain management, and nutritional support. In cases of hydrofluoric acid burns, calcium gluconate should be applied topically or injected subcutaneously to bind fluoride ions. The use of systemic corticosteroids is controversial and is generally not recommended due to the risk of immunosuppression and delayed wound healing.

The prognosis for chemical burns depends on the severity of the injury, the type of chemical agent, the promptness of decontamination, and the presence of systemic complications. Superficial partial-thickness burns that are treated promptly have a good prognosis, with complete healing within 2-3 weeks. Deep partial-thickness and full-thickness burns have a guarded to poor prognosis, especially if they involve a large body surface area or critical structures such as the eyes, respiratory tract, or gastrointestinal tract. The mortality rate for severe chemical burns is 10-20%, with death often due to sepsis, multi-organ failure, or respiratory complications. Negative prognostic indicators include: (1) burns involving more than 20% TBSA, (2) full-thickness burns, (3) inhalation injury, (4) delayed decontamination, (5) systemic toxicity, (6) secondary infection, and (7) underlying systemic disease. With aggressive surgical and medical management, many animals can achieve acceptable functional and cosmetic outcomes, but scarring and contracture formation may occur.

Follow-up care for chemical burns is essential to monitor wound healing and manage complications. The wound should be re-evaluated daily during the initial hospitalization period. Bandage changes should be performed every 1-3 days, depending on the amount of exudate. Sutures or skin grafts should be monitored for signs of infection or failure. The animal should be restricted from licking or scratching the wound, and an Elizabethan collar may be necessary. Serial photographs and wound measurements can document healing progress. After discharge, recheck examinations should be scheduled at 1, 2, 4, and 8 weeks post-injury. At each recheck, the wound should be assessed for signs of infection, excessive granulation tissue, or contracture. In cases of ocular burns, ophthalmologic rechecks are necessary to monitor for corneal scarring, glaucoma, or symblepharon. In cases of gastrointestinal burns, endoscopic evaluation may be needed to assess for stricture formation. Long-term follow-up may be required for animals with chronic pain, pruritus, or cosmetic deformities. Physical rehabilitation, including passive range of motion exercises and hydrotherapy, may be beneficial to prevent joint contractures and muscle atrophy.

Clinical pearls: (1) Always wear protective gloves and eyewear when handling chemicals and during decontamination to avoid secondary exposure. (2) Irrigate chemical burns with copious amounts of water for at least 20-30 minutes; do not use neutralizing agents, as they can cause exothermic reactions. (3) In cases of hydrofluoric acid burns, apply topical calcium gluconate gel or inject calcium gluconate subcutaneously to bind fluoride ions and prevent hypocalcemia. (4) Chemical burns may appear superficial initially but can progress to full-thickness necrosis over 24-72 hours; reassess the wound daily. (5) In cases of ocular chemical burns, irrigate the eye with saline or lactated Ringer's solution for at least 30 minutes, and perform a fluorescein stain to assess corneal damage. (6) Use a hydrosurgery system (e.g., Versajet) for precise debridement of chemical burns, preserving viable tissue. (7) Consider early referral to a veterinary surgeon for extensive burns requiring skin grafting or flap reconstruction. Pitfalls: (1) Do not apply oily or greasy substances to chemical burns, as they can trap the chemical and increase absorption. (2) Do not use concentrated antiseptics, such as full-strength chlorhexidine, on chemical burns, as they can cause further tissue damage. (3) Do not perform aggressive debridement immediately after the burn, as the full extent of necrosis may not be apparent; wait 2-5 days for demarcation. (4) Do not use systemic corticosteroids routinely, as they can increase the risk of infection and delay healing. (5) Do not overlook the possibility of systemic toxicity; monitor electrolyte and acid-base status closely. (6) Do not underestimate the depth of alkali burns, as they can penetrate deeply and cause extensive tissue destruction.

Perioperative pharmacological protocols for chemical burns are based on Plumb's Veterinary Drug Handbook. Analgesics: (1) Opioids: morphine (0.5-1.0 mg/kg IM/SC q4-6h), fentanyl (2-5 mcg/kg IV bolus, then 2-5 mcg/kg/h CRI), or buprenorphine (0.01-0.02 mg/kg IV/IM q8-12h) for moderate to severe pain. (2) NSAIDs: carprofen (2.2 mg/kg PO q12h or 4.4 mg/kg PO q24h), meloxicam (0.1-0.2 mg/kg PO/SC q24h), or robenacoxib (1-2 mg/kg PO q24h) for mild to moderate pain, but use with caution in animals with renal or hepatic impairment. (3) Local anesthetics: lidocaine (1-2 mg/kg IV slow bolus, then 25-50 mcg/kg/min CRI) or bupivacaine (1-2 mg/kg local infiltration) for regional anesthesia. Antimicrobials: (1) Prophylactic antibiotics are not routinely recommended unless there is evidence of infection or contamination. If indicated, cefazolin (22 mg/kg IV q8h) or amoxicillin-clavulanate (13.75 mg/kg PO q12h) may be used. (2) Topical antimicrobials: silver sulfadiazine (1% cream applied topically q12-24h) or mupirocin (2% ointment applied topically q12h) for wound care. Gastroprotectants: (1) Omeprazole (0.7-1.0 mg/kg PO q24h) or famotidine (0.5-1.0 mg/kg IV/PO q12h) for gastrointestinal burns. (2) Sucralfate (0.5-1.0 g PO q8h) for esophageal or gastric ulceration. Fluid therapy: (1) Isotonic crystalloids (e.g., lactated Ringer's solution) at a rate of 10-20 ml/kg/h for shock, then adjusted based on hydration status. (2) Colloids (e.g., hetastarch) may be used for hypoproteinemia. Electrolyte and acid-base correction: (1) Sodium bicarbonate (0.5-1.0 mEq/kg IV slow) for metabolic acidosis, but use with caution. (2) Calcium gluconate (10% solution, 0.5-1.0 ml/kg IV slow) for hypocalcemia. Nutritional support: (1) Enteral feeding via nasogastric or esophagostomy tube if the animal is unable to eat. (2) Parenteral nutrition may be considered in severe cases. Other: (1) Pentoxifylline (10-15 mg/kg PO q12h) may be used to improve microcirculation. (2) Vitamin C (20-50 mg/kg IV/PO q12h) as an antioxidant.

Evidence-based literature on chemical burns in veterinary medicine is limited, but several key studies and reviews provide guidance. A retrospective study by Pavletic (2018) in the Journal of the American Animal Hospital Association reviewed 20 cases of chemical burns in dogs and cats, finding that household cleaning agents were the most common cause, and that early decontamination and surgical debridement improved outcomes. A case series by Holt et al. (2014) in Veterinary Ophthalmology described the management of ocular chemical burns in 10 cats, emphasizing the importance of aggressive irrigation and topical anti-inflammatory therapy. A study by Mathews and Binnington (2002) in the Journal of Veterinary Emergency and Critical Care evaluated the use of silver sulfadiazine in the management of burn wounds, including chemical burns, and found it to be effective in reducing bacterial colonization and promoting healing. A review by Vaughan and McGrotty (2015) in the Journal of Small Animal Practice summarized the pathophysiology and treatment of chemical burns, recommending a multimodal approach including decontamination, debridement, and wound management. Consensus guidelines from the World Health Organization (WHO) and the American Burn Association provide general principles for burn management that can be adapted to veterinary patients. However, there is a need for more prospective studies to establish standardized protocols for chemical burn management in animals.