Ch. 10

Kidney Function and Acid-Base Balance in Older Adults

  • Impaired acid-base balance can occur in older adults, particularly those with major illnesses or trauma.

  • Decreased kidney function associated with aging leads to slightly elevated serum creatinine levels.

  • Decreased muscle mass in aging results in reduced daily breakdown of muscle, which in turn reduces serum creatinine levels.

  • Therefore, normal or minimally elevated serum creatinine values may mask substantially reduced kidney function in older adults.

Fluid Volume Depletion and Assessment

  • A patient experiencing volume depletion can show elevated serum creatinine levels out of proportion to actual kidney function.

  • A ratio greater than 21 can indicate concentrated urine due to fluid volume depletion (FVD).

  • Key causes of fluid volume deficit include:

    • Loss of water and electrolytes through vomiting, diarrhea, and fistulas.

    • Increased fluid loss due to fever, excessive sweating, and burns.

    • Blood loss, gastrointestinal suction, and third space fluid shifts.

  • Early detection and management of fluid volume disturbances are crucial.

Assessment Techniques for Older Adults

  • In most adult patients, monitoring skin turgor is a useful method to detect subtle changes in fluid balance.

  • However, skin turgor assessment is less reliable in older adults due to reduced skin elasticity.

  • Alternative assessments include:

    • Examination of sinus filling and vein filling in the hands and feet, which is more useful for detecting fluid volume deficit in older adults.

Interventions for Incontinence and Hydration in Older Adults

  • For patients with incontinence, nursing interventions may include:

    • Encouraging the use of protective clothing or devices.

    • Carrying a urinal in vehicles for convenience.

    • Regulating fluid intake to facilitate access to toilet facilities during the day.

  • It is recommended for older adults without cardiovascular or kidney dysfunction to maintain adequate fluid intake, especially in hot or humid conditions.

Medical Management of Fluid Volume Disturbances

  • The fluid challenge test is utilized to evaluate a patient's hemodynamic response to fluid administration.

  • During this test, specific volumes of fluid are given at designated rates while monitoring vital signs, breath sounds, level of orientation, central venous pressure, and urine output.

Selection of Water and Electrolyte Solutions

  • Different isotonic solutions and their considerations:

    • 0.9% NaCl (Normal Saline):

      • Concentration: 154 mEq/L sodium and chloride.

      • Isotonic and similar in composition to plasma.

      • Caution: Should not be administered in cases of kidney injury due to potassium content, which can lead to hyperkalemia.

    • 5% Dextrose in Water (D5W):

      • Provides 50 g of dextrose and supplies 170 calories of free water.

      • Used for treatment of hyponatremia and dehydration.

      • Should not be used in excessive volumes during early postoperative periods due to stress reactions.

    • Dextrins (D5W):

      • Available in low molecular weight (40) and high molecular weight (70) forms.

      • Acts as a colloid solution and serves as a plasma volume expander.

      • Can affect clotting by coating platelets, decreasing the ability to clot, and can remain in circulation up to 24 hours.

Sodium Intake and Dietary Recommendations

  • Patients are advised to reduce sodium intake by:

    • Avoiding foods high in sodium and reading food labels to determine salt content.

    • Understanding that sodium chloride (table salt) contributes significantly to edema.

    • Utilizing seasoning substitutes like lemon juice, onions, and garlic, while being cautious with potassium-based substitutes for those on potassium-sparing diuretics.

Fluid and Electrolyte Imbalances in Clinical Practice

  • Disturbances in electrolyte levels are common and require corrective action based on clinical history, physical examinations, and laboratory findings.

Sodium Imbalances

  • Hyponatremia (Sodium Deficit):

    • Definition: Serum sodium level below 135 mEq/L.

    • Causes include:

      • Diuretic use, loss of gastrointestinal fluids, kidney disease, adrenal insufficiency.

    • Symptoms include:

      • Thirst, elevated body temperature, swollen dry tongue, sticky mucous membranes, hallucinations, lethargy, irritability, seizures, and pulmonary edema.

    • Laboratory findings include decreased serum sodium, high urine sodium, altered urine specific gravity and osmolality, and changes in central venous pressure.

Potassium Imbalances

  • Hypokalemia (Potassium Deficit):

    • Definition: Serum potassium level below 3.5 mEq/L.

    • Causes include:

      • Diarrhea, vomiting, gastric suction, corticosteroid use, and potassium-wasting medications such as ACE inhibitors.

    • Symptoms include muscle weakness, arrhythmias, abdominal distension, and ECG changes like prolonged PR intervals.

    • IV potassium administration requires caution and should utilize an infusion pump only.

Calcium Imbalances

  • Hypocalcemia (Calcium Deficit):

    • Definition: Serum calcium level below 8.5 mg/dL.

    • Causes include:

      • Hypoparathyroidism due to thyroid surgery, malabsorption syndromes, chronic diarrhea, and vitamin D deficiency.

    • Symptoms include numbness, seizures, irritability, bronchospasm, and prolonged QT intervals on ECG readings.

Conclusion

  • Continuous assessment and management of fluid and electrolyte imbalances are crucial in older adults, particularly those with decreased kidney function or other underlying medical conditions.

  • Regular evaluation of risk factors, early intervention, and patient education on dietary management can mitigate complications related to fluid and electrolyte disturbances.