Painful thumb: potential life-threatening poisoning 23rd February,2005 Cynthia Shum

A 52-yr old lady presented with redness and mild pain over right thumb, IF and MF at 10pm History of using rust remover at 11:30am. Pain developed 30mins later. Seen GP, given analgesics. Persistent pain, decided to see AED.

PE:

Vitals: BP 160/93, P 73, afebrile ECG: SR, regular, QRS normal, QTc normal. Na/K normal, Ca 1.19

Management: Topical KY-jelly with Ca gluconate mixed, put in latex glove and fitted on patient. Topical jelly changed Q4H IV analgesics given Plan: IA Ca gluconate if persistent pain Trace the rust remover for confirmation of HF poisoning.

The culprit:

Progress: Pain decreased, D/C after overnight treatment.

Follow up clinic: Day 2

Follow up clinic: Day 14

Follow up clinic: Day 28

Hydrofluoric acid Used for glass etching, electroplating, chips etching in semiconductor industry, rust removal, brick cleaning, porcelain cleaning and leather tanning. Trivial exposure can cause life-threatening complications. Aqueous form contains 3-40% HF Anhydrous form >70% HF

Properties of HF Highly permeable allows deep penetration into tissues prior to dissociating into H+ and F- ions. F- ions avidly bind to intracellular Ca and Mg causing cellular dysfunction and cell death.

Pathophysiology: Systemic toxicity resulted in hypoCa, hypoMg and HyperK is a preterminal event. Myocardial toxicity manifested as conduction failure and ventricular fibrillation. Pain with short onset suggests a very high concentration of exposure

Ca level may drop suddenly that patient may have a precipitous demise without clinical signs of hypocalcemia. Signs of hypocalcemia: carpal spasm, Chvostek sign ECG changes of prolonged QT (hypocalcemia), peaked T (hyperK) are reliable indicators of toxicity.

Local toxicity The higher the concentration, the sooner the onset of pain Severe pain with relatively benign appearance is the rule: hyperemic, subsequent blanching, whitish discoloration and coagulative necrosis as Ca is ppt.

Fatal exposure: Fatal dermal exposure reported in >2.5% BSA with anhydrous HF. All oral or inhalational exposures as well as burns of face, neck are potentially fatal regardless the concentration.

Management: Decontamination Assess systemic toxicity Skin: remove soaking clothes, adequate rinsing affected area, prevent absorption by deliver Ca or Mg salt over the affected area. Eyes: irrigation with NS Ingestion: universally fatal if not treated. NG tube gastric emptying with MgSO4, Ca gluconate/Cl solutions p.o. administration. Assess systemic toxicity ECG, cardiac monitoring, check electrolytes, clotting, T/S, IV lines.

Correct electrolyte imbalances Ca gluconate 0.45 mmol/ml 10-ml vials (1 gm) can be safely given in a peripheral line over 5mins. CaCl2 is available in 1.36mmol/ml in 10ml vials. It is more irritating to the tissues, better use central line MgSO4 is available as 49.3% solution, give 4.72gm (10 ml) slow iv over 20mins. Serial Ca, Mg and K monitoring along with cardiac monitoring and physical examination is needing along the process. Liberal use of analgesic

Local Therapies: Ca/Mg salt delivery to tissue Topical Intradermal IV IA

Topical gel 25ml of 10% Ca gluconate + 75ml KY jelly = 100ml CaCl2 or CaCO3 can be used as alternative MgSO4 4gm can be used if no Ca salts available.

Intradermal Ca If topical gel fails to relief pain in first few minutes, consider 0.5ml/cm2 of 5% Ca gluconate intradermal injection (immediate pain relief)

IA Ca gluconate 10ml 10% Ca gluconate + 40ml NS over 4hrs infusion When large section of the finger pad or area is not amenable to intradermal injection, IA Ca gluconate via radial/ brachial artery: 10ml 10% Ca gluconate + 40ml NS over 4hrs infusion

IV Bier block technique 25ml 2.5% Ca gluconate lasted 5 hrs. Need further studies for effectiveness.