13.2 Chemical Injuries: Acids (Coagulation Necrosis), Alkalis (Liquefactive Necrosis), Hydrofluoric Acid (Calcium Gluconate), and Decontamination
Key Takeaways
- Primary decontamination mandates immediate removal of all saturated clothing, footwear, and jewelry, followed by copious, continuous, low-pressure water irrigation; dry chemical powders (e.g., dry lime, dry lye) MUST be thoroughly brushed off before water application to avoid generating severe exothermic heat.
- Chemical neutralization—attempting to treat acid burns with bases or alkali burns with acids—is strictly contraindicated in clinical burn practice because the resultant exothermic chemical reaction generates extreme heat that compounds chemical damage with severe thermal burns.
- Acids (pH < 7.0) produce coagulation necrosis by denaturing and precipitating cellular proteins, forming a thick, leathery protective eschar that physically limits deeper penetration, whereas alkalis (pH > 7.0) produce liquefactive necrosis via saponification of fats and protein hydrolysis, causing progressive, deep, penetrating tissue liquefaction that requires prolonged irrigation (1–2 hours).
- Hydrofluoric acid (HF) is a unique, lethal inorganic acid that penetrates deeply as unionized molecules; free fluoride ions (F⁻) avidly scavenge systemic calcium (Ca²⁺) and magnesium (Mg²⁺) while poisoning Na⁺/K⁺ ATPase pumps, precipitating refractory hypocalcemia, profound hypomagnesemia, fatal hyperkalemia, and lethal ventricular arrhythmias (Torsades de Pointes, VF).
- The pathognomonic hallmark of hydrofluoric acid toxicity is excruciating, deep, intractable pain out of proportion to visible cutaneous findings; definitive management requires immediate topical massage of 2.5% calcium gluconate gel until complete pain cessation, escalating to subcutaneous infiltration, intra-arterial infusion, or systemic IV calcium/magnesium replacement as indicated.
13.2 Chemical Injuries: Acids (Coagulation Necrosis), Alkalis (Liquefactive Necrosis), Hydrofluoric Acid (Calcium Gluconate), and Decontamination
Core Knowledge: Chemical burns account for approximately $5%\text{ to }10%$ of all burn center admissions but contribute disproportionately to morbidity, prolonged hospitalization, and permanent disability. Unlike thermal injuries where tissue destruction ceases once the heat source is removed, chemical agents continue to react with, denature, and destroy cellular components until they are mechanically eliminated, fully diluted, or bound by specific antidotes. Immediate, systematic decontamination takes precedence over all other interventions except primary airway stabilization.
1. Fundamental Principles of Chemical Burn Decontamination
The severity of a chemical burn is determined by chemical concentration, contact duration, quantity, physical state, lipid solubility, and mechanism of action. Immediate pre-hospital and emergency department interventions follow rigid safety protocols:
CARDINAL RULES OF CHEMICAL DECONTAMINATION
┌────────────────────────────────────────────────────────────────────────┐
│ 1. Rescuer Protection (PPE): Don full chemical-resistant personal │
│ protective equipment (nitrile/butyl rubber gloves, face shields, │
│ fluid-impervious gowns) before touching the contaminated patient. │
├────────────────────────────────────────────────────────────────────────┤
│ 2. Immediate Garment Removal: Strip all contaminated clothing, shoes, │
│ belts, and jewelry immediately; clothing traps chemicals against │
│ skin, converting superficial contact into deep full-thickness burns.│
├────────────────────────────────────────────────────────────────────────┤
│ 3. Dry Chemical Powders: BRUSH FIRST, THEN LAVAGE! │
│ Powders such as dry lime (calcium oxide) or dry lye must be │
│ mechanically brushed off completely prior to initiating water flow. │
├────────────────────────────────────────────────────────────────────────┤
│ 4. Copious, Low-Pressure Water Irrigation: Continuous tap water or │
│ saline lavage (minimum 20–30 min for acids; 1–2 hours for alkalis) │
│ until tissue surface pH is restored to neutrality (pH 7.0–7.5). │
├────────────────────────────────────────────────────────────────────────┤
│ 5. ABSOLUTE PROHIBITION OF CHEMICAL NEUTRALIZATION: │
│ Never apply neutralizing acids to alkali burns or bases to acid │
│ burns. The exothermic heat of neutralization causes severe thermal │
│ coagulation overlay on top of existing chemical tissue damage. │
└────────────────────────────────────────────────────────────────────────┘
Special Chemical Handling Exceptions:
- Dry Lime (Calcium Oxide, $\text{CaO}$): Contact with water converts calcium oxide to calcium hydroxide [$\text{Ca(OH)}_2$] via an intense exothermic reaction that releases extreme heat. It must be brushed off thoroughly with dry towels or brushes before any water irrigation begins.
- Elemental Metals (Sodium, Potassium, Magnesium, Lithium, White Phosphorus): Elemental sodium and potassium react violently with water to release explosive hydrogen gas and hydroxide ions. They must be smothered with mineral oil, sand, or excised surgically under mineral oil coverage. White phosphorus ignites spontaneously upon air contact and must be kept continuously submerged or covered with water/wet saline gauze.
2. Comparative Pathophysiology: Acids vs. Alkalis
Acids and alkalis destroy biological tissues through fundamentally different biochemical pathways, resulting in distinct clinical trajectories and irrigation requirements.
ACID VS. ALKALI PATHOPHYSIOLOGY
┌────────────────────────────────────┬───────────────────────────────────┐
│ ACIDS (pH < 7.0) │ ALKALIS (pH > 7.0) │
├────────────────────────────────────┼───────────────────────────────────┤
│ • Primary Mechanism: │ • Primary Mechanism: │
│ COAGULATION NECROSIS │ LIQUEFACTIVE NECROSIS │
│ • Protein denaturation & cross-link│ • Saponification of cellular fats │
│ • Forms thick, insoluble, leathery │ • Hydrolysis of protein matrices │
│ ESCHAR (protective coagulum) │ • Progressive, deep PENETRATION │
│ • Self-limiting depth of injury │ • Non-limiting; continues hours │
│ • Irrigation Duration: 20–30 min │ • Irrigation Duration: 1–2 hours │
│ • Common: Hydrochloric, Sulfuric, │ • Common: Sodium hydroxide (lye), │
│ Nitric, Phosphoric acids │ Cement, Ammonia, Drain cleaners │
└────────────────────────────────────┴───────────────────────────────────┘
Acids and Coagulation Necrosis:
Strong acids (e.g., sulfuric acid, battery acid, muriatic acid) donate hydrogen ions ($H^+$), causing rapid cellular dehydration and protein precipitation. The denatured structural proteins cross-link to form a tough, leathery, dark coagulum (eschar). This eschar acts as a physical barrier that restricts deeper penetration of the acid into subcutaneous tissue. Consequently, acid burns typically declare their true depth rapidly and require a minimum of 20 to 30 minutes of continuous irrigation.
Alkalis and Liquefactive Necrosis:
Alkalis (e.g., sodium hydroxide/lye, potassium hydroxide, wet concrete/cement, anhydrous ammonia) donate hydroxyl ions ($OH^-$), creating an aggressive saponification reaction with cellular membrane fatty acids. Alkalis dissolve cellular lipids, hydrolyze structural collagen, and denature protein matrices into soluble gelatinous complexes. Because no protective coagulum forms, the alkali penetrates relentlessly through the dermis, subcutaneous fat, fascial envelopes, and deep muscle beds. Alkalis feel "slippery" or "soapy" to touch and continue destroying tissue for hours or days unless treated with extended, continuous irrigation for 1 to 2 hours (or until serial litmus paper confirms physiological wound bed pH of $7.0\text{--}7.5$).
SPECIAL CHEMICAL: WET CEMENT
┌────────────────────────────────────────────────────────────────────────┐
│ Calcium oxide in dry cement reacts with sweat/water to form CALCIUM │
│ HYDROXIDE (pH 12–13). Construction workers kneeling in wet cement or │
│ wearing saturated boots develop progressive, painless, deep 3rd-degree │
│ alkali burns over several hours due to prolonged insidious contact. │
└────────────────────────────────────────────────────────────────────────┘
3. Hydrofluoric Acid (HF) Burns: High-Yield Medical Emergency
Hydrofluoric acid (HF) is an inorganic acid widely utilized in semiconductor manufacturing, glass etching, rust removers, and petroleum refining. Although classified as a weak acid chemically due to its low dissociation constant ($pK_a = 3.17$), it is biologically one of the most destructive and lethal chemical compounds known to medicine.
HYDROFLUORIC ACID (HF) TOXICITY TRIAD
┌────────────────────────────────────────────────────────────────────────┐
│ 1. Transcellular Diffusion: Non-ionized HF molecules easily diffuse │
│ across lipid-rich cell membranes into deep subfascial and bone beds.│
├────────────────────────────────────────────────────────────────────────┤
│ 2. Scavenging of Divalent Cations (Ca²⁺ & Mg²⁺): Free fluoride ions │
│ avidly bind Calcium and Magnesium, precipitating insoluble │
│ insoluble salts: F⁻ + Ca²⁺ ──► CaF₂ | F⁻ + Mg²⁺ ──► MgF₂ │
├────────────────────────────────────────────────────────────────────────┤
│ 3. Fatal Systemic Electrolyte Derangements: │
│ • PROFOUND HYPOCALCEMIA (Insoluble CaF₂ precipitation) │
│ • PROFOUND HYPOMAGNESEMIA (Insoluble MgF₂ precipitation) │
│ • REFRACTORY HYPERKALEMIA (Inhibition of Na⁺/K⁺ ATPase pumps) │
│ ──► Triggers QTc prolongation, Torsades de Pointes, VF, and Death. │
└────────────────────────────────────────────────────────────────────────┘
Clinical Presentation and the Pathognomonic Clue:
- Pain Out of Proportion to Exam: Free fluoride ions trigger intense neuronal depolarization and peripheral nerve irritation. Patients experience excruciating, unrelenting, deep throbbing bone pain despite minimal visible erythema or blister formation. Any patient presenting with agonizing chemical pain out of proportion to physical skin findings must be treated for hydrofluoric acid exposure until proven otherwise.
- Lethal Surface Area Threshold: Exposure to concentrated HF ($49%\text{--}70%$) involving as little as $1%\text{ to }2%$ TBSA (the size of a palm), or $>5%$ TBSA of low-concentration HF, can cause fatal systemic hypocalcemia and refractory cardiac arrest within hours.
CALCIUM GLUCONATE THERAPEUTIC ESCALATION PROTOCOL
┌────────────────────────────────────────────────────────────────────────┐
│ FIRST-LINE: Topical 2.5% Calcium Gluconate Gel │
│ • Formulated by mixing 3.5 g USP calcium gluconate powder in 100 g │
│ water-soluble lubricant (or 10 mL of 10% IV calcium gluconate in │
│ 30 g surgical lubricant like Surgilube/K-Y). │
│ • Massaged continuously into the burn wound. │
│ • CLINICAL ENDPOINT: Continue application until complete PAIN RELIEF. │
├────────────────────────────────────────────────────────────────────────┤
│ SECOND-LINE: Subcutaneous / Intradermal Infiltration │
│ • Indication: Failure of topical gel to resolve pain within 30–45 min. │
│ • Agent: 10% Calcium Gluconate (NEVER use calcium chloride; causes │
│ tissue sloughing/necrosis). Infiltrate 0.5 mL/cm² with 30-gauge needle│
├────────────────────────────────────────────────────────────────────────┤
│ THIRD-LINE: Intra-Arterial Infusion (for Digital / Hand HF Burns) │
│ • Indication: Multiple digital burns where local injection risks │
│ compartment syndrome or digital vascular compromise. │
│ • Protocol: 10 mL 10% calcium gluconate in 40–50 mL D5W infused via │
│ brachial/radial artery catheter over 4 hours. │
├────────────────────────────────────────────────────────────────────────┤
│ SYSTEMIC RESCUE: Intravenous Repletion & Continuous Telemetry │
│ • Continuous IV infusions of Calcium Gluconate and Magnesium Sulfate │
│ titrated to normalize ionized calcium, serum magnesium, and QTc. │
└────────────────────────────────────────────────────────────────────────┘
4. Ocular Chemical Exposures and Morgan Lens Decontamination
Chemical splashes to the eye constitute a true ophthalmic emergency. Alkalis penetrate the anterior chamber of the eye within seconds, destroying corneal endothelial cells and causing permanent blindness (corneal melting and cataractogenesis).
EMERGENCY OCULAR LAVAGE PROTOCOL
┌────────────────────────────────────────────────────────────────────────┐
│ 1. Topical Anesthetic: Instill 1–2 drops of 0.5% Proparacaine or │
│ Tetracaine to alleviate severe blepharospasm and facilitate exam. │
├────────────────────────────────────────────────────────────────────────┤
│ 2. Morgan Lens Insertion: Connect a Morgan lens to an IV infusion set │
│ delivering Normal Saline or Lactated Ringer's. Insert lens beneath │
│ the eyelids and run continuous, copious fluid flow. │
├────────────────────────────────────────────────────────────────────────┤
│ 3. Irrigation Volume: 1 to 2 Liters per eye minimum. │
├────────────────────────────────────────────────────────────────────────┤
│ 4. Endpoint pH Testing: Turn off irrigation, wait 5–10 minutes for eye │
│ fluids to equilibrate, then test the conjunctival fornix with pH │
│ litmus paper. Irrigation must continue until neutral pH (7.0–7.4) │
│ is consistently maintained. │
└────────────────────────────────────────────────────────────────────────┘
A worker in a chemical packaging facility sustains an exposure to dry lime (calcium oxide) powder across both forearms and torso. What is the immediate priority nursing action upon arrival at the decontamination suite?
How does the pathophysiological mechanism of an alkali burn differ from that of an acid burn?
A glass factory worker presents with a 2% TBSA chemical splash from concentrated hydrofluoric acid (HF) to the right hand. The patient is screaming in agonizing pain, but the skin only demonstrates faint, patchy erythema without blisters. What is the primary clinical endpoint when administering topical 2.5% calcium gluconate gel?