Hydrofluoric (HF) acid is an extremely powerful inorganic acid and a vigorous dehydrating agent. Anhydrous hydrofluoric acid and hydrofluoric acid in aqueous solutions range in appearance from colorless to slightly tinted. Hydrofluoric acid has a pungent odor and is extremely corrosive. This acid can be found in a number of workplaces including glass etching, oil refineries, steel mills, cleaning HVAC systems and within the home as rust removers and detergents. Hydrofluoric acid burns present with a unique concern for systemic fluoride toxicity which can lead to cardiac arrhythmias and death.
Hydrofluoric acid exposure requires immediate specific and specialized medical treatment. Not only can this strong acid cause burns, but the fluoride ion can be quickly absorbed through the skin. With the dilute solutions, there will have delayed injury because ions will penetrate through the skin before dissociating and causing complications. A dermal injury is reported as the most common observed injury with burns to the fingers being one of the most concerning injuries for workers.
Hydrofluoric acid exposure is a rare occurrence throughout the globe compared to other industrial injuries. A 10-year study in China reported 690 patients with burns and a little over half being involved with hydrofluoric acid and sulfuric acid. Most of the chemical burns occurred in the summer and autumn seasons. A 20-year survey from Taiwan only had 324 identified calls of hydrofluoric acid with the majority of those incidents being dermal in nature. Even with these few studies, the exposure is still estimated to be more than 1000 cases per year. Because of the nature of the occupations with the greatest potential injury from and exposure to hydrofluoric acid exposure, the majority of patients are adult males.
Hydrofluoric acid has three separate mechanisms of injury: (1) the corrosive nature of the acid with free hydrogen ions, (2) the fluoride ion penetration of the dermal layer and destruction of the underlying tissues, and (3) the fluoride ion absorption into the bloodstream and formation of insoluble salts via hydrofluoric fixation with calcium and magnesium. Additionally, the fluoride ions will form soluble salts with other cations that will then allow for transport and diffusion to other areas of the body, causing further tissue destruction when those salts dissociate and the fluoride ion is released. With the destruction of underlying tissues, there will be a release of potassium into the bloodstream causing the cardiac arrhythmias.
Depending on the location of the hydrofluoric acid exposure and the percentage of the acid, patients can present immediately with severe caustic burns to the body and pain. Solutions greater than 14.5% will produce immediate symptoms, 12% solutions can take up to an hour, and solutions less than 7% can take hours before symptoms occur. The concern exists for ocular injury and respiratory injury when any chemical is splashed/sprayed in the face. Patients will indicate an increasing pain in the area of the burn.
History should include any exposure to hydrofluoric acid, rust removers, or cleaning agents within the past 24 hours. One should ascertain the concentration of the solution and the use of protective agents or any other chemical that was contained in the solution.
Assessment should include immediate evaluation for life-threatening emergencies including airway compromise, respiratory distress, and cardiac arrhythmias. Additionally, one can assess for pulmonary edema, ocular injuries, and symptoms of hypocalcemia including Chvostek and Trousseau signs and tetany.
Electrolyte imbalance is one of the hallmark concerns for hydrofluoric acid exposure. Immediate electrolyte assessment includes calcium, potassium, and magnesium. Patients will develop hypocalcemia, hypomagnesia, and hyperkalemia. Cardiac monitoring and electrocardiography are important to assess significant burns for QT prolongation with hypocalcemia, peaked T waves/arrhythmias for hyperkalemia, and Torsades de Pointes for hypomagnesia. Chest x-rays should be performed on all patients with respiratory exposure.
Initial treatment for HF acid includes quick assessment, removal of soiled clothing, decontamination with copious amounts of water, and assessment and management life-threating conditions.
Treatment modalities of dermal exposure include calcium gluconate soaking, intravenous calcium gluconate (10%), and topical use of calcium gluconate gel (2.5%). After 30 minutes, reassess the patient, and if pain persists, subcutaneous infiltration of calcium gluconate is recommended at a dose of 0.5 mL of a 5% solution per square centimeter of surface burn extending 0.5 cm beyond the margin of involved tissue. Additional topical therapy includes benzalkonium chloride (Zephiran Chloride) concentration of (0.13%). Side effects of use include stinging pain or allergic reaction (urticaria, pruritus, dyspnea, chest tightness, swelling of the face, lips or tongue).
If the eyes are exposed to HF, it may penetrate to internal structures. Initial treatment for eye exposure includes irrigation for 5 minutes with water followed by topical ophthalmic anesthetic solution and intermittent irrigation using a sterile 1% calcium gluconate solution via a Morgan lens for 20 minutes. Other treatment modalities include irrigation with Hexafluoride.
HF acid inhaled in high concentrations may cause glossitis (obstruction of the airway) and acute pulmonary edema. Management would include artificial respiration for the patient with severe exposure. Individuals who are breathing require 100 % oxygen with a 2.5% to 3% calcium gluconate nebulized solution. Noninvasive positive pressure ventilation may be necessary for individuals who develop pulmonary edema. Treatment of severe cases includes endotracheal intubation for airway protection and a surgical airway if necessary.
Burns with concentrated HF are usually very serious, with the potential for significant complications due to fluoride toxicity. Concentrated HF liquid or vapor may cause severe burns, metabolic imbalances, pulmonary edema, and life-threatening cardiac arrhythmias. Even moderate exposures to concentrated HF may rapidly progress to fatality if left untreated. Burns larger than 25 square inches (160 square cm) may result in serious systemic toxicity. Relief of pain is the only indication of the effectiveness of treatment. Therefore, the use of any analgesic agents is not advisable.
A person who has HF burns greater than four square inches should be admitted immediately to an intensive care unit and carefully monitored for 24 to 48 hours. Anyone who has been exposed to gaseous HF and experiences respiratory irritation also should be admitted to and monitored in an intensive care unit. Blood sampling should be taken to monitor fluoride, potassium, and calcium levels. In some cases, hemodialysis is necessary for fluoride removal and correction of hyperkalemia and recurrent hypocalcemia.