Hypomagnesemia

• Common Electrolyte Abnormality: Hypomagnesemia frequently occurs in critically ill patients.
• Intracellular Cation: Magnesium is a major intracellular ion.
• Energy Utilization: Plays a key role in energy transfer, storage, and utilization.
• Enzyme Co-factor: Essential for membrane Na+/K+ ATPase activity, contributing to membrane stabilization.
• Physiological Roles:
  • Nerve Transmission: Involved in the transmission of nerve impulses.
  • Cardiac Excitability: Crucial for heart rhythm stability.
  • Neuromuscular Conduction: Facilitates muscle nerve signaling.
  • Muscular Contraction: Important for muscle function.
  • Vasomotor Tone: Regulates blood vessel tone.
• Administration: Intravenous magnesium sulfate (IV MgSO4) is commonly used for treatment.

Causes of Hypomagnesemia (RRID)

• Reduced Intake:
  • Total parenteral nutrition (TPN)
  • Gastrointestinal loss (malabsorption, malnutrition, Crohn’s disease, celiac disease)
  • Chronic alcoholism
  • Poorly controlled type 2 diabetes
• Redistribution:
  • Insulin therapy
  • Hungry bone syndrome
• Increased Loss:
  • Diarrhea
  • Nasogastric (N/G) secretions
  • Renal disorders
  • Renal tubular acidosis (RTA)
• Drugs:
  • Amphotericin B
  • Aminoglycosides
  • Carbenicillin
  • Diuretics
  • PPI
    • Prolonged use of PPIs has been associated with hypomagnesemia.
    • Measure magnesium levels before and periodically during prolonged PPI treatment, especially with concomitant digoxin or other hypomagnesemia-inducing drugs.

Effects of Hypomagnesemia

• Early signs of deficiency include
  • loss of appetite
  • nausea
  • vomiting
  • fatigue
  • weakness.
• Neurological:
  • Confusion
  • Irritability
  • Delirium
  • Tremors
• Cardiac:
  • Tachyarrhythmias: Wide QRS, prolonged PR interval, ventricular arrhythmias, Torsades de Pointes
  • Refractory hypokalemia and hypocalcemia
• Metabolic:
  • hypokalaemia, hypocalcaemia

Therapeutic Indications

• Magnesium Deficiency: Increased mortality and prolonged ICU stay if untreated.
• Arrhythmias: Post-ischemia or cardiac surgery
• Post Myocardial Infarction (MI)
• Asthma/Severe Bronchospasm
• Pre-eclampsia/Eclampsia
• Subarachnoid Hemorrhage (SAH) Management
• Tocolytic Agent: Used in labor management
• Pheochromocytoma Surgery
• Hypokalemia: Hypomagnesemia must be corrected
• Irukandji Syndrome: Unproven efficacy

Eclampsia

• Standard of Care: Magnesium sulfate is the treatment of choice.
• Efficacy: Reduces the rate of progression from pre-eclampsia to eclampsia by half.
• Seizure Management: More effective than phenytoin or benzodiazepines (MAGPIE trial 2002, Cochrane review 2003).
• Dosage: 4g IV over 5 minutes, followed by 1g/hr (target level: 2-4 mmol/L).

Arrhythmias

• Diagnosis Challenges: Total body magnesium deficiency difficult to diagnose.
• Post Cardiac Surgery: IV magnesium shown to reduce post-op atrial fibrillation (AF) and ventricular arrhythmias.
• Guidelines: Not currently endorsed by AHA/European Heart Association.
• Comparison to Amiodarone: May be as effective for treating rapid AF (Critical Care Med, 1995).
• Torsades de Pointes: Recommended treatment but no RCTs.
• Digitalis-induced Arrhythmias: Effective management.

Post Myocardial Infarction

• Controversy: Conflicting evidence.
• Early Trials: LIMIT2 showed mortality benefit.
• Later Trials: ISIS4 and MAGIC unable to replicate findings.

Asthma/Bronchospasm

• Effectiveness: Improves FEV1 and PEFR in severe cases, no mortality improvement.
• Selected Patients: May benefit more, particularly pediatric patients.
• Dosage: 5-10 mmol IV over 20 minutes.
• Cochrane Review: 2000 review suggests more trials needed.

SAH Management

• Animal Studies: IV magnesium effective in reversing induced vasospasm (Stroke, 1991).
• Human Studies: Mixed results; additional benefits when combined with nimodipine (Neurosurgery 2000, Stroke 2005, Journal of Neurosurgery 2002).
• Controversy: Latest trials inconclusive.

Replacement

• IV Therapy: For symptomatic patients.
• Oral Sustained-Release Preparations: For asymptomatic and enterally fed patients.
• Concurrent Issues: Correct hypokalemia and hypocalcemia when present.

Preferred Magnesium Preparations

• First Line:
  • Magnesium-L-aspartate  (MagMin^@; Mag-Sup^@):
    • Preferred choice for treatment and prevention of magnesium deficiency in adults, adolescents, and children from 2 years.
    • 1.55 mmol per tablet/37.4 mg per tablet
• Second Line:
  • Magnesium glycerophosphate (Neomag®): For those unable to tolerate Magnaspartate. Available as 4 mmol chewable tablets, licensed for treatment and prevention in adults, adolescents, and children from 4 years.
  • Magnesium glycerophosphate liquid (MagnaPhos®): Unlicensed but manufactured to GMP standards, most cost-effective liquid for those unable to take licensed preparations.