Acid-base balance and electrolytes: case studies (Proceedings)

Water balance

     a. clinical measures of water balance

     b. laboratory measures of water balance

     c. water intake

     d. water loss

1. Dehydration- terms describe resulting state of hydration, not what is lost

     a. isotonic dehydration

     b. hypertonic dehydration

     c. hypotonic dehydration

2. Compensatory mechanisms abnormal water balance

     a. Renal blood flow (eg dehydration)

          • Decreased renal blood flow

          • Decreased GFR

          • Decreased urine production

          • (increased urine specific gravity)

     b. Hormonal changes

          • ADH

          • Renin

          • Angiotensin

          • Aldosterone

          • Atrial natiuretic factor

Sodium balance

1. Hyponatremia (see table 22.4, page 334)

     a. pseudohyponatremia

     b. dilution of total body sodium

     c. loss of sodium

2. Hypernatremia (see table 22.4, page 334)

     a. excessive sodium retention

     b. water loss in excess of sodium (hypertonic dehydration)

Chloride balance

1. Hypochloremia and hyperchloremia

     a. often the same mechanisms as hyponatremia/hypernatremia (table 22.4)

     b. may be a primary: eg secretory diarrhea

Potassium balance

1. Hypokalemia (see table 22.5, page 336)

     a. redistributional

          • insulin

          • catecholamines

          • metabolic alkalosis

     b. absolute

          • secretory diarrhea (Na is reabsorbed instead of K)

          • Renal loss

               √ Increased urine flow

               √ Nonreabsorbable anions

               √ sulfates, phosphates, ketoacids, lactate

               √ metabolic alkalosis

               √ third space syndromes

               √ feline kaliopenic nephropathy-polymyopathy syndrome

2. Hyperkalemia (see table 22.5, page 336)

     a. pseudokyperkalemia

     b. redistributional hyperkalemia

     c. absolute hyperkalemia

Acid-base disorders

1. Definitions

     a. pH

     b. Henderson-Hasselbach equation

          • General

          • Specific for biological systems

     c. metabolic disturbances

     d. respiratory disturbances

     e. acidosis

     f. alkalosis

     g. base excess

     h. base deficit

     i. anion gap

     j. strong ion difference

2. Simple acid-base disorders

3. Compensation

4. Combined or "mixed" acid-base disorders

5. Characterization of an acid-base disorder

     a. Requires measurement of pH, HCO3- and pCO2

     b. Arterial versus venous samples

Acid base disorders

• Simple metabolic acidosis

• Simple metabolic alkalosis

• Compensated metabolic acidosis

• Compensated metabolic alkalosis

• Simple respiratory acidosis

• Simple respiratory alkalosis

• Compensated respiratory acidosis

• Compensated respiratory alkalosis

• Combined or "mixed" acid-base disorders

Evaluation of the anion gap

Estimates changes in "unmeasured" ions without actually analyzing them

Unmeasured anions

     o Sulfates

     o Phosphates

     o Lactate

     o Pyruvate

     o Ketoacids

     o Ethylene glycol metabolites

     o Salicylic acid metabolites

     o Plasma proteins (deprotonated)

Unmeasured cations

     o Calcium

     o Magnesium

     o Immunoglobulins (protonated)

Using the strong ion difference in acid base evaluation

     o Dissects more factors that may be at play in causing acid-base/electrolyte disorders.

     o Equations are complex.

     o Based on assumptions about normal values for each species