Acids are defined as proton donors (H+), and bases are defined as proton acceptors (OH-). Bases also are known as alkalies. Both acids and bases can be defined as caustics, which cause significant tissue damage on contact. The strength of an acid is defined by how easily it gives up the proton; the strength of a base is determined by how avidly it binds the proton. The strength of acids and bases is defined by using the pH scale, which ranges from 1-14 and is logarithmic. A strong acid has a pH of 1, and a strong base has a pH of 14. A pH of 7 is neutral.
Pathophysiology Most acids produce a coagulation necrosis by denaturing proteins, forming a coagulum (eg, eschar) that limits the penetration of the acid. Bases typically produce a more severe injury known as liquefaction necrosis. This involves denaturing of proteins as well as saponification of fats, which does not limit tissue penetration. Hydrofluoric acid is somewhat different from other acids in that it produces a liquefaction necrosis. The severity of the burn is related to a number of factors, including the pH of the agent, the concentration of the agent, the length of the contact time, the volume of the offending agent, and the physical form of the agent. The ingestion of solid pellets of alkaline substances results in prolonged contact time in the stomach, thus, more severe burns. In addition, concentrated forms of some acids and bases generate significant heat when diluted, resulting in thermal and caustic injury. The long-term effect of caustic dermal burns is scarring, and, depending on the site of the burn, scarring can be significant. Ocular burns can result in opacification of the cornea and complete loss of vision. Esophageal and gastric burns can result in stricture formation. Frequency United States In 2005, the American Association of Poison Control Centers (AAPCC) reported 26,300 cases of exposures to acidic substances, 40,800 cases of exposures to alkaline substances, 23,300 cases of peroxide exposures, and 59,500 cases of bleach exposures. During that time, 1,532 cases of exposure to phenols or phenol products were reported.1 Chemical injuries account for 2-6% of burn center admissions.2 International Worldwide, corrosive substances are commonly used for chemical assault. The most common substances used are lye and sulfuric acid.3 Mortality/Morbidity In the 2005 report of the American Association of Poison Control Centers, exposures to acids and acid-containing products and chemicals resulted in 9 deaths, 129 cases of major toxicity, and 2380 cases of moderate toxicity. Exposures to alkali products and chemicals resulted in 8 deaths, 226 cases of major toxicity, and 3615 cases of moderate toxicity. Exposures to peroxides resulted in 1 death, 5 cases of major toxicity, and 108 cases of moderate toxicity. Exposures to bleaches and chlorite-containing products resulted in 8 deaths, 82 cases of major toxicity, and 2862 cases of moderate toxicity. Exposures to phenol-containing products resulted in 1 death, 5 cases of major toxicity, and 108 cases of moderate toxicity.1 Sex Assaults with caustic chemicals worldwide are more likely to occur against women.3 Age Adults and children are nearly equally exposed to chemical burns. Clinical History Clinical signs and symptoms vary depending on the route of exposure and the particular substances involved. Because of the variety of presentations, the emergency clinicians must be prepared to handle all possibilities. Some exposures, such as hydrofluoric acid, may present without immediate pain and should be considered in patients with complaints of slow-onset deep pain occurring after exposure to an appropriate product. Patient history should include the following: Offending agent, concentration, physical form, pH Route of exposure Time of exposure Volume of exposure Possibility of coexisting injury The timing and extent of irrigation Physical If the exposure was by ingestion, the immediate concern is to protect the patient’s airway. If there is evidence of airway compromise (eg, oropharyngeal edema, stridor, use of accessory muscles), consider establishing a definitive airway. Dermal exposures Size Depth Location Circumferential burns Ocular exposures Visual acuity Presence of periorbital dermal lesions Scleral and corneal lesions (eg, ulcerations, fluorescein uptake) Leakage of vitreous humor Ingestions Presence of oral burns or edema, drooling Dysphagia, stridor, wheezing, dyspnea, tachypnea Abdominal tenderness, guarding, crepitus, subcutaneous air (Hamman crunch) Causes A large number of industrial and commercial products contain potentially toxic concentrations of acids, bases, or other chemicals that can cause burns. Some of the more common products are listed as follows: Acids Sulfuric acid is commonly used in toilet bowl cleaners, drain cleaners, metal cleaners, automobile battery fluid, munitions, and fertilizer manufacturing. Concentrations range from 8% acid to almost pure acid. The concentrated acid is very viscous and denser than water. It also generates significant heat when diluted. These attributes make sulfuric acid an effective drain cleaner. Concentrated sulfuric acid is hygroscopic. Thus, it produces dermal injuries by dehydration, thermal injury, and chemical injury. Nitric acid is commonly used in engraving, metal refining, electroplating, and fertilizer manufacturing. Hydrofluoric acid is commonly used in rust removers, tire cleaners, tile cleaners, glass etching, dental work, tanning, semiconductors, refrigerant and fertilizer manufacturing, and petroleum refining. This is actually a weak acid, and, in dilute form, it will not cause immediate burning and pain on contact. Hydrochloric acid is commonly used in toilet bowl cleaners, metal cleaners, soldering fluxes, dye manufacturing, metal refining, plumbing applications, swimming pool cleaners, and laboratory chemicals. Concentrations range from 5-44%. Hydrochloric acid is also known as muriatic acid. Phosphoric acid is commonly used in metal cleaners, rustproofing, disinfectants, detergents, and fertilizer manufacturing. Acetic acid is commonly used in printing, dyes, rayon and hat manufacturing, disinfectants and hair wave neutralizers. Vinegar is dilute acetic acid. Formic acid is commonly used in airplane glue, tanning, and cellulose manufacturing. Chloroacetic acids Monochloroacetic acid is used in the production of carboxymethylcellulose, phenoxyacetates, pigments, and some drugs. It has significant systemic toxicity because it enters and blocks the tricarboxylic acid cycle, inhibiting cellular respiration. It is highly corrosive. Dichloroacetic acid is used in manufacturing chemicals. It is a weaker acid than trichloroacetic acid, and it does not inhibit cellular respiration. Trichloroacetic acid is used in laboratories and in chemical manufacturing. It is highly corrosive and “fixes” tissues it contacts. It does not inhibit cellular respiration. Phenol and cresols Phenol, also known as carbolic acid, is a weak organic acid used in the manufacture of resins, plastics, pharmaceuticals, and disinfectants. Cresols are dihydroxybenzenes that are used as wood preservatives, degreasing agents, and chemical intermediates. These substances are very irritating to the skin and can be absorbed through the skin to produce systemic toxicity. Bases Sodium hydroxide and potassium hydroxide are used in drain cleaners, oven cleaners, Clinitest tablets, and denture cleaners. They are extremely corrosive. Clinitest tablets contain 45-50% sodium hydroxide (NaOH) or potassium hydroxide (KOH). Solid or concentrated NaOH or KOH is denser than water and generates significant heat when diluted. Both the heat generated and the alkalinity contribute to burns. Calcium hydroxide also is known as slaked lime. It is used in mortar, plaster, and cement. It is not as caustic as NaOH, KOH, or calcium oxide. Sodium and calcium hypochlorite are common ingredients in household bleach and pool chlorinating solution. Pool chlorinators also contain NaOH and have a pH around 13.5, making them very caustic. Household bleach has a pH around 11 and is much less corrosive. Calcium oxide, also known as lime, is the caustic ingredient in cement. It generates heat when diluted with water and can produce a thermal or caustic burn. Ammonia is used in cleaners and detergents. The dilute form is not highly corrosive. Gaseous anhydrous ammonia is used in a number of industrial applications, particularly in fertilizer manufacturing. It is very hygroscopic (has a high affinity for water). It produces injury by desiccation and heat of dilution in addition to causing a chemical burn. It can cause severe skin burns as well as pulmonary injury. Phosphates commonly are used in many types of household detergents and cleaners. Substances include tribasic potassium phosphate, trisodium phosphate, and sodium tripolyphosphates. Silicates include sodium silicate and sodium metasilicate. They are used to replace phosphates in detergents. Dishwashing detergents are alkaline, primarily to builders such as silicates and carbonates. They are moderately corrosive. Sodium carbonate is used in detergents. It is moderately alkaline, depending on the concentration. Lithium hydride is used to absorb carbon dioxide in space technology applications. It vigorously reacts with water to generate hydrogen and lithium hydroxide. It can produce thermal and alkaline burns. Oxidants Bleaches: Chlorates are the primary chemicals used as bleaches in the United States. Household bleach is alkaline with a pH of 11-12, but it is dilute enough that it is minimally irritating to the skin. More concentrated, industrial strength chlorates may be more damaging to the skin. Peroxides: Household-grade hydrogen peroxide (3%) produces minimal-to-no skin irritation. Concentrations of 10% may cause paresthesias and blanching of the skin. Concentrations of 35% or more will cause immediate blistering. Chromates: Potassium dichromate and chromic acid are common industrial chemicals used in tanning, waterproofing fabrics, corrosion inhibitor, painting, and printing, and they are also used as an oxidizing agent in chemical reactions. Chromates can result in severe skin burns and subsequent systemic toxicity, including renal failure. Manganates: Potassium permanganate is a strong oxidizing agent that is used in dilute solutions as a disinfectant or sanitizing agent. In dilute solutions, it is minimally irritating to the skin. In concentrated form or pure crystals, it can cause severe burns, ulcerations, and systemic toxicity. Other substances White phosphorus: This chemical is used as an incendiary in the manufacture of munitions, fireworks, and fertilizer. White phosphorus is spontaneously oxidized in air to phosphorus pentoxide, giving off a yellow flame and a dense white smoke with a garlic odor. After explosions of munitions or fireworks, small particles of phosphorus can become embedded in the skin and continue to smolder.2 Metals: Elemental lithium, sodium, potassium, and magnesium react violently with water, including water on the skin. Hair coloring agents contain persulfates and concentrated solutions of peroxides. Straightening agents may contain concentrated alkali. Chemical burns can result if these are not diluted properly or have a prolonged contact time with the scalp. Burns with various products have been reported in the literature.4 Vesicants: These agents are primarily chemical warfare agents and are also known as blister agents. They include sulfur and nitrogen mustards, arsenicals, and phosgene oxime. For more information see CBRNE – Vesicants, Mustard: Hd, Hn1-3, H and CBRNE – Vesicants, Organic Arsenicals: L, ED, MD, PD, HL