Chapter 68: Disorders of Potassium and Magnesium Homeostasis

KEY CONCEPTS

• Potassium regulates many biochemical processes in the body and is a key cation for electrical action potentials across cellular membranes.

• The kidney is the primary route of potassium elimination.

• In patients with concomitant hypokalemia and hypomagnesemia, it is imperative to correct the hypomagnesemia before the hypokalemia.

• Potassium chloride is the preferred potassium supplement for the most common causes of hypokalemia.

• Hyperkalemia is a common occurrence in patients with acute kidney injury or chronic kidney disease.

• Hypomagnesemia is commonly caused by excessive gastrointestinal or renal magnesium wasting.

• Hypermagnesemia is predominantly observed in patients with acute or chronic kidney disease.

• Severe hypermagnesemia may affect the neuromuscular and cardiovascular systems.

Patient Care Process^* for the Management of Potassium and Magnesium Disorders

Collect

• Patient characteristics (eg, age, race, sex)

• Patient history (past medical, family, social—dietary habits)

• Current medications including over-the-counter medications, herbals, dietary supplements

• Subjective data

  • Musculoskeletal and neuromuscular review of systems

  • Intake (food and fluid) and output (urine and stool)

• Objective data

  • BP, heart rate (HR), height, weight

  • Labs (eg, basic metabolic panel, calcium, magnesium, phosphorus)

  • Other diagnostic tests when indicated (eg, ECG, urinalysis, urine electrolytes)

Assess

• Presence of symptoms of an electrolyte disorder

• Presence of ECG changes (see Fig. 68-1)

• Severity of electrolyte disorder (eg, change from baseline value, timing of development of electrolyte disorder)

• Kidney function (eg, eGFR, creatinine clearance, presence of chronic kidney disease)

• Current medications that may contribute to electrolyte disorder (see Tables 68-1, 68-6, and 68-8)

• Current diet that may contribute to electrolyte disorder (see Tables 68-2 and 68-9)

Plan^*

• Identification of the most likely cause of the electrolyte disorder and discontinuation of offending medication or substance (if applicable)

• Dietary modifications (see Tables 68-2 and 68-9)

• Drug therapy regimen including specific medication, dose, route, frequency, and duration; specify the continuation and discontinuation of existing therapies (see Tables 68-4, 68-5, and 68-7)

• Monitoring parameters including efficacy (eg, potassium, magnesium, SCr), safety (medication-specific adverse effects), and need for repeat or additional drug therapy

• Patient education (eg, purpose of treatment, dietary and lifestyle modification, drug therapy)

• Referrals to other providers when appropriate (eg, physician, dietician)

Implement^*

• Provide patient education regarding all elements of treatment plan

• Use motivational interviewing and coaching strategies to maximize adherence

• Schedule follow-up

Follow-up: Monitor and Evaluate

• Resolution of electrolyte disorder and prevention of further episodes

• Presence of adverse effects

• Development/progression of kidney impairment

• Patient adherence to treatment plan using multiple sources of information

Preclass Engaged Learning Activity

Watch the video entitled “Hyperkalemia in Primary Care Practice” by the National Kidney Foundation. This 11-minute video provides a brief overview of the risks associated with hyperkalemia, the various causes of hyperkalemia, and prevention and treatment strategies. The video is useful to enhance student understanding of the ...