Pearl of the Day: Hypomagnesemia

Hypomagnesemia Pathophysiology - second most abundant intracellular cation - acid-base imbalance affects levels of ionized magnesium - may coexist with hypokalemia - essential to many enzymes, including membrane-bound ATPase; metabolism; regulation of PTH secretion - magnesium blocks release of acetylcholine, interferes with release of catecholamines from adrenal medulla - magnesium is absorbed principally in small intestine - associated with hypokalemia due to similar underlying etiologies

Causes - redistribution: IV glucose, IV hyperalimentation, refeeding syndrome, acute pancreatitis, hypoalbuminemia, postparathyroidectomy, osteoblastic metasis - extrarenal losses: lactation, profuse sweating/burns, sepsis, intestinal or biliary fistula, diarrhea - decreased intake: alcoholism, malnutrition, small bowel resection, malabsorption - renal loss: saline or osmotic diuresis, potassium depletion, phosphorus depletion, familial hypophosphatemia, tubulointerstitial renal disease - drugs: loop diuretics, aminoglycosides, amphotericin B, vitamin D intoxication, alcohol, cisplatin, theophylline, PPIs, calcineurin inhibitors - endocrine disorders: SIADH, hyperthyroidism, hyperparathyroidism, hypercalcemic states, hyperaldosteronism

Signs/Symptoms - neuromsucular: tetany, muscle weakness, cerebellar (ataxia, nystagmus, vertigo), confusion, coma, seizures, depression, paresthesias - GI: dysphagia, anorexia - CV: heart failure, dysrhythmias, hypotension, coronary artery vasospasm - hypokalemia, hypocalcemia, anemia - Chvostek and Trousseau signs (traditionally associated with hypocalcemia)

Diagnosis - likely underdiagnosed as levels are rarely drawn - BMP, LFTs, phosphorus, calcium, magnesium, EKG - EKG changes similar to hypokalemia (tachyarrhythmias, afib, torsades de pointes, ventricular tachycardia, ventricular fibrillation) and hypocalcemia  (prolonged QT interval, T wave inversions) due to alteration of intracellular potassium content - enhances digitalis toxicity -> may also contribute to EKG changes - correction for hypoalbuminemia corrected Mg (mmol/L) = measured total Mg + [0.005 x (40 - serum albumin in g/L)] corrected Mg (mEq/L) = measured total Mg x 0.42 + 0.05 x (4 - serum albumin in g/dL)

Treatment - monitor for hypokalemia, hypocalcemia, hypophosphatemia - if asymptomatic, oral magnesium in multiple low doses - for severe and symptomatic, urgent MgSO4 IV replacement - torsades de pointes or eclampsia -> 1 - 4 g or diluted in 100 mL D5 or NS over 10 - 60 min under continuous cardiac monitoring - chronic deficiency -> 6 g MgSO4 per day - chronic alcoholics with delirium tremens -> 8 - 12 g MgSO4 IV on first day (1.5 - 2 g Iv MgSO4 over 1 to 2 hours) - spironolactone maintains magnesium homeostasis and reduces arrhythmias in CHF patients

Resources Tintinalli's Emergency Medicine, 8th Edition

Pearl of the Day: Non-freezing Cold Injuries

Non-freezing Cold Injuries Trench Foot - direct injury to soft tissue sustained from prolonged cooling, accelerated by wet conditions - symptoms: tingling, numbness at affected extremity - signs: pale, mottled, anesthetic, pulseless, immobile foot w/o immediate change after rewarming - 2 - 3 days: perfusion can return to foot; formation of bullae, edema, increased hyperemia - weeks: anesthesia can persist, may be permanent - months - years: hyperhidrosis, cold sensitivity - severe forms: gangrene, tissue sloughing - management: supportive and keep foot clean and dryly bandaged; can consider vasodilator drugs, oral prostaglandins (can increase skin temperatures) - prophylaxis: good boot fit, keeping warm, changing out of wet socks

Chilblains or Pernio - mild inflammatory lesions of skin from long-term intermittent exposure to damp, nonfreezing ambient temperatures - most common areas: feet (toes), hands, ears, lower legs - risk factors: countries with cold or temperate, damp climate; young females with Raynaud's phenomenon, immunologic abnormalities - signs/symptoms: pruritus, tingling, numbness; localized edema, erythema, cyanosis; ulcerations, bullae - rewarming can result in tender blue nodules that persist for several days - management: supportive, rewarm skin, elevate extremity - some studies support use of nifedipine 20 mg PO q8h, pentoxifylline 400 mg PO q8h, limaprost 20 mcg PO q8h as prophylaxis and treatment - topical corticosteroids may be effective

Panniculitis - mild degrees of necrosis of subcutaneous fat tissue during prolonged exposure to temperatures above freezing - in children, may be on cheeks; on thighs and buttocks of females involved in equestrian activities - upon resolution, may result in cosmetic defects (e.g., uneven skin) - no effective treatment

Cold Urticaria - hypersensitivity to cold air or water that may lead to anaphylaxis (rare) - associated with increased affinity of IgE to mast cells and viral infections - diagnosis confirmed with cold water test - treatment: similar to urticarial lesions from other causes (e.g., antihistamines); can consider leukotriene receptor antagonists, topical capsaicin

Resources Tintinalli's Emergency Medicine, 8th Edition

Pearl of the Day: Anticholinergic Toxicity

Anticholinergic Toxicity Background - sources: antihistamines, belladonna, mydriatic agents (e.g., tropicamide, cyclopentolate), TCAs, benztropine, phenothiazines, clozapine, olanzapine, Amanita muscaria - can be absorbed through ingestion, smoking, or ocular use - muscarinic blockade delays gastric emptying -> absorption and peak clinical effects are delayed - cholinergic receptors: muscarinic, nicotinic - central anticholinergic syndrome: fever, agitation, delirium, coma - peripheral anticholinergic syndrome: tachycardia, flushed dry skin, dry mouth, ileus, urinary retention - risk of toxicity is dose related

Signs/Symptoms - dry as a bone, red as a beet, hot as a hare, blind as a bat, mad as a hatter, stiff as a pipe - usually sinus tachycardia (wide-complex tachydsyrhythmias with diphenhydramine occur from sodium-channel blockade, not anticholinergic effect) - delirium described as restlessness, irritability, disorientation, auditory and visual hallucinations (e.g., Lilliputian hallucinations) - dysarthria described as staccato speech, high-pitched cries - myoclonus

Diagnosis/Work-up - BMP, CPK, urine toxicology - positive drug screen only indicates exposure, does not imply overdose - differential diagnosis: viral encephalitis, Reye's syndrome, head trauma, post-ictal state, neuroleptic malignant syndrome

Treatment - activated charcoal if ingestion within 1 hour, though may be beneficial beyond 1 hour of ingestion - multidose activated charcoal not recommended with impaired GI motility - supportive care, IVF, temperature monitoring and treatment - agitation -> benzodiazepines IV; avoid physical restraints - wide-complex tachydysrhythmias -> sodium bicarbonate IV

Physostigmine - 0.5 - 2 mg (pediatrics 0.02 mg/kg) by slow IV over 5 min - reversible acetylcholinesterase inhibitor that crosses blood-brain barrier - adverse effects of bradycardia and seizures more likely in patients without anticholinergic effects -> should not be used as diagnostic challenge - mixed evidence - may be better at controlling agitation and reversing delirium than benzodiazepines - indications: seizure, delirium, narrow QRS supraventricular tachydysrhythmias, hemodynamic deterioration - effects may occur within 15 - 20 min, requires continuous cardiac monitoring for bradycardia - may repeat dosing - asymptomatic for 6 hours -> no repeat dosing required - contraindications: asthma, intestinal/bladder obstruction, cardiac conduction disturbances, sodium-channel antagonist poisoning

Disposition - symptomatic patients (including those receiving physostigmine) require hospital obervation for at least 24 hours - patients with mild symptoms that resolve within 6 hours may be discharged

Resources Tintinalli's Emergency Medicine, 8th Edition https://lifeinthefastlane.com/ccc/anticholinergic-syndrome/