Fluid, Electrolyte & Acid-Base Disorders

Rationale

Many disease processes can cause serious disturbances in the fluid, electrolyte and acid-base status of patients. The general internist must be prepared to identify and correct these disturbances as efficiently as possible.

Prerequisites

Basic courses in physiology and pathology, and the introductory required preclinical course in physical diagnosis.

Specific Learning Objectives

1. Knowledge: Students should be able to define and describe:
   1. pathophysiology of hypo- and hypervolemia, hypo- and hypernatremia, hypo- and hyperkalemia, hypo- and hypercalcemia, simple and mixed acid-base disorders, hypo- and hyperphosphatemia, hypo- and hyper-magnesemia (respiratory acidosis & alkalosis, and metabolic acidosis & alkalosis)
   2. presenting symptoms and signs of the above disorders
   3. the importance of total body water and its distribution
   4. the differential diagnosis of hypo- and hypernatremia in the setting of volume depletion, euvolemia and hypervolemia
   5. how to distinguish hyponatremia from pseudohyponatremia
   6. how to identify spurious hyperkalemia or acidosis-related hyperkalemia
   7. risks of too rapid or delayed therapy for hyponatremia
   8. the most common causes of respiratory acidosis, respiratory alkalosis, metabolic acidosis and metabolic alkalosis
   9. calculate the anion gap and explain its relevance to determining the cause of a metabolic acidosis
   10. how to differentiate saline responsive from saline resistant metabolic alkalosis
   11. changes in total body water distribution that occur with aging
   12. how altered mental status can contribute to electrolyte disorders
   13. tests to use in the evaluation of fluid, electrolyte and acid-base disorders
   14. indications for obtaining an arterial blood gas
   15. the types of fluid preparations to use in the treatment of fluid and electrolyte disorders
2. Skills: Students should demonstrate specific skills including:
   1. history-taking skills: Students should be able to obtain, document, and present an age-appropriate medical history, that differentiates among etiologies of disease including:
      1. eliciting appropriate information from patients with volume overload, including recent weight gain, edema or ascites, symptoms of heart failure, dietary sodium intake, changes in medications, noncompliance and intravenous fluid regimens.
      2. eliciting appropriate information from patients with volume depletion, including recent weight loss, thirst, gastrointestinal losses, urinary losses, oral intake, insensible losses and intravenous fluid regimens.
      3. eliciting appropriate information from patients with electrolyte problems, including use of diuretics and other medications, gastrointestinal losses, and history of relevant medical conditions (e.g., heart failure, liver disease, renal disease, pulmonary disease, central nervous system disease and malignancy).
   2. physical exam skills: Students should be able to perform a physical exam to establish the diagnosis and severity of disease including:
      1. measurement of orthostatic vital signs
      2. identify signs of volume overload including peripheral edema, pulmonary edema, ascites
      3. identify signs of volume depletion including tachycardia, orthostatic hypotension, dry mucous membranes, poor skin turgor
      4. identify signs of sodium disorders including lethargy, weakness, encephalopathy, delirium, seizures
      5. identify signs of potassium disorders including weakness, fatigue, constipation, ileus, cramping, tetany, hypo- or hyperreflexia
      6. identify signs of calcium disorders including cramping, tetany, Chvostek’s & Trousseau’s sign, seizures, anorexia, constipation, polyuria, hypo- or hyperreflexia, stupor, coma
   3. differential diagnosis: Students should be able to generate a prioritized differential diagnosis recognizing specific history and physical exam findings that distinguish between:
      1. hypo- and hypervolemia
      2. hypo- and hypernatremia
      3. hypo- and hyperkalemia
      4. hypo- and hypercalcemia
      5. hypo- and hyperphosphatemia
      6. hypo- and hypermagnesemia
      7. respiratory acidosis & alkalosis
      8. metabolic acidosis & alkalosis
   4. laboratory interpretation: Students should be able to recommend when to order diagnostic and laboratory tests and be able to interpret them, both prior to and after initiating treatment based on the differential diagnosis, including consideration of test cost and performance characteristics as well as patient preferences
      1. laboratory and diagnostic, when appropriate, tests should include:
         • serum osmolality
         • urinary sodium
         • fractional excretion of sodium
         • anion gaps
         • ECG findings in hyper- and hypokalemia
   5. communication skills: Students should be able to:
      1. explain the results of the evaluation to the patient
   6. basic and advanced procedure skills: Students should be able to:
      1. insert a peripheral intravenous catheter
      2. obtain an arterial blood gas
      3. assist in the insertion of a central venous catheter
   7. management skills: Students should be able to develop an appropriate evaluation and treatment plan for patients including:
      1. write appropriate fluid orders for the treatment of hypo- and hypervolemia, hypo- and hypernatremia, hypo- and hyperkalemia, hypo- and hypercalcemia
      2. write appropriate orders for replacing sodium, potassium, calcium, phosphates, and magnesium
      3. write appropriate orders for correcting hyperkalemia, hypercalcemia, hyperphosphatemia and hypermagnesemia
      4. calculate the water deficit that needs to be corrected to treat hypernatremia
      5. identify indications for administration of bicarbonate
      6. explain to a patient why intravenous fluids are needed
      7. access and utilize appropriate information systems and resources to help delineate issues related to fluid, electrolyte and acid-base disorders
3. Attitudes and Professional Behaviors: None