Hypermagnesemia and hypomagnesemia Notes

NOTES NOTES HYPERMAGNESEMIA & HYPOMAGNESEMIA GENERALLY, WHAT ARE THEY? PATHOLOGY & CAUSES ▪ Abnormal levels of magnesium in the blood ▪ Hypomagnesemia: < 1.7mg/dL ▪ Hypermagnesemia: > 2.4mg/dL SIGNS & SYMPTOMS ▪ Mild variations are usually asymptomatic, severe imbalances may result in potentially fatal arrhythmias and neurological complications DIAGNOSIS LAB RESULTS ▪ Assessment of blood magnesium levels ▪ Further tests are useful to establish underlying cause TREATMENT MEDICATIONS ▪ Identify and treat any underlying causes ▪ Hypermagnesemia ▫ Administer calcium gluconate → competes for magnesium binding sites ▪ Hypomagnesemia ▫ Supplemental magnesium HYPERMAGNESEMIA osms.it/hypermagnesemia PATHOLOGY & CAUSES ▪ Blood magnesium levels above 2.4mg/dL CAUSES ▪ Renal failure ▫ Kidneys unable to efficiently excrete magnesium (most common cause) ▪ Excessive intake ▫ Ingesting larger amounts of magnesium than the kidneys are able to excrete (supplements or medication e.g. magnesium hydroxide, often used for heartburn or constipation) 804 OSMOSIS.ORG ▫ Excessive IV administration (e.g. treatment of preeclampsia) ▪ Cellular breakdown (excessive release) ▫ Tumour lysis syndrome, rhabdomyolysis COMPLICATIONS ▪ Impaired signal transmission across neuromuscular junction → muscle weakness (magnesium inhibits calcium influx at neuromuscular junction), inhibition of parathyroid hormone release, hypocalcemia, cardiac bradyarrhythmias

Chapter 113 Hypermagnesemia & Hypomagnesemia SIGNS & SYMPTOMS ▪ Nausea ▪ Drowsiness ▪ Tingling sensation in the face (facial paresthesia) ▪ Progressive loss of deep tendon reflexes (earliest sign) ▪ Coma ▪ Muscular paralysis ▪ Respiratory failure ▪ Cardiac arrest DIAGNOSIS ▪ ECG changes similar to those of hyperkalemia, increased PR interval, widened QRS complex, bradyarrhythmias LAB RESULTS TREATMENT MEDICATIONS ▪ Calcium gluconate injection ▫ Calcium and magnesium compete for binding sites ▫ Reserved for severe, symptomatic hypermagnesemia ▪ Loop diuretics increases the urinary excretion of magnesium OTHER INTERVENTIONS ▪ Identify and stop the source of excessive intake ▫ If normal renal function, with relevant history or possible iatrogenic cause, cessation of excessive intake sufficient treatment ▪ Hemodialysis ▫ In severe cases magnesium can be externally filtered from the blood ▪ Blood free magnesium level > 2.4mg/dL ▪ Renal function testing ▫ Urea, creatinine clearance test (levels increase with renal failure) OTHER DIAGNOSTICS ▪ Thorough examination of individual’s history often reveals cause Figure 113.1 Illustration depicting calcium channel inhibition due to hypermagnesemia, causing delayed muscle contraction. OSMOSIS.ORG 805

HYPOMAGNESEMIA osms.it/hypomagnesemia PATHOLOGY & CAUSES ▪ Low levels of magnesium in the blood, <1.7mg/dL CAUSES ▪ Insufficient renal reabsorption ▫ Loop and thiazide diuretics ▫ Nephrotoxic drugs (amphotericin B, calcineurin inhibitors, cisplatin) ▫ Hypercalcemia ▫ Channelopathies (genetic mutations that affect the ion channels through which electrolytes like magnesium are reabsorbed) ▫ Diabetes (osmotic diuresis carries electrolytes along with water) ▪ Insufficient gastrointestinal absorption ▫ Malnutrition: dietary insufficiency ▫ Malabsorption: sufficient quantities are consumed, but insufficient amounts are absorbed because of rapid gastrointestinal transit time (e.g., chronic diarrhea) or medications (e.g., proton pump inhibitors) ▪ Hungry bone syndrome ▫ Surgical removal of the thyroid or parathyroid RISK FACTORS ▪ Alcohol use disorder (causes a mixed hypomagnesemia, poor diet and alcohol increases excretion) COMPLICATIONS ▪ Hypokalemia: magnesium interferes with excretion of potassium ▪ Hypocalcemia: parathyroid gland is dependent on magnesium to function 806 OSMOSIS.ORG SIGNS & SYMPTOMS ▪ Neuromuscular ▫ Without magnesium, calcium more readily enters neuron, exits sarcoplasmic reticulum → more excitable nerves, muscles ▪ Cardiac arrhythmias ▫ Premature atrial contractions ▫ Premature ventricular contractions ▫ Increased risk of torsades de pointes (particularly with concurrent class III antiarrhythmics) ▫ Increased risk of arrhythmias associated with digoxin toxicity ▪ ECG changes ▫ PR prolongation ▫ QT prolongation ▫ T wave flattening ▪ Hypocalcemia often occurs alongside hypomagnesemia. Either/both conditions may cause ▫ Tetany (intermittent muscle spasms throughout the body) ▫ Hyperreflexia ▫ Chvostek’s sign (facial muscles twitch after facial nerve lightly finger tapped 1cm/0.39in below zygomatic process) ▫ Trousseau’s sign (blood pressure cuff occludes brachial artery → pressure makes nerve fire → muscle spasm makes wrist and metacarpophalangeal joints flex) ▫ Seizures DIAGNOSIS LAB RESULTS ▪ Measure free unbound magnesium in the serum, <1.7mg/dl

Chapter 113 Hypermagnesemia & Hypomagnesemia TREATMENT MEDICATIONS ▪ Treat underlying cause ▪ Mild asymptomatic: oral supplementation usually sufficient ▪ Severe and/or symptomatic: magnesium sulphate may be administered intravenously OSMOSIS.ORG 807