Chapter 14

1. Chapter 14 Assessment and Care of Patients with Acid-Base Imbalances

2. Normal Blood pH • Keeping pH within the normal range involves balancing acids and bases in body fluids. • Normal pH for arterial blood—7.35 to 7.45. • Normal pH for venous blood—7.31 to 7.41.

3. Normal Blood pH(Cont’d) • Changes from normal blood pH interfere with many normal functions by: • Changing the shape of hormones and enzymes. • Changing the distribution of other electrolytes, causing fluid and electrolyte imbalances. • Changing of excitable membranes. • Decreasing the effectiveness of many hormones and drugs.

4. Introduction to Acid-Base Chemistry • Acids • Bases • Buffers • Body fluid chemistry: • Bicarbonate ions • Relationship between carbon dioxide and hydrogen ions • Calculation of free hydrogen ion level

5. Sources of Acids • Incomplete breakdown of glucose • Destruction of cells • Bicarbonate

6. Respiratory Acid-Base Control Mechanisms • When chemical buffers alone cannot prevent changes in blood pH, the respiratory system is the second line of defense against changes: • Hyperventilation • Hypoventilation

7. Respiratory Acid-Base Control Mechanisms (Cont’d)

8. Renal Acid-Base Control Mechanisms • The kidneys are the third line of defense against wide changes in body fluid pH. • Stronger for regulating acid-base balance but take longer than chemical and respiratory mechanisms to completely respond. • Kidney movement of bicarbonate. • Formation of acids. • Formation of ammonium.

9. Compensation • The body attempts to correct changes in blood pH. • pH below 6.9 or higher than 7.8 is usually fatal. • Respiratory system is more sensitive to acid-base changes; can begin compensation efforts within seconds to minutes. • Renal compensatory mechanisms are much more powerful and result in rapid changes in ECF composition not fully triggered unless imbalance continues for several hours to days.

10. Respiratory Compensation • Lungs compensate for acid-base imbalances of a metabolic origin. • Example: Prolonged running causes buildup of lactic acid, hydrogen ion levels in the ECF increase, pH drops; breathing is triggered in response to the increased carbon dioxide levels to bring the pH level back to normal.

11. Renal Compensation • A healthy kidney can correct or compensate for changes in blood pH when the respiratory system either is overwhelmed or is not healthy. • Example: Person has chronic obstructive pulmonary disease, retains carbon dioxide in the blood, blood pH level falls (becomes more acidic); kidney excretes more hydrogen ions and increases the reabsorption of bicarbonate back into the blood.

12. Acid-Base Imbalances • Metabolic acidosis • Respiratory acidosis • Combined metabolic and respiratory acidosis • Metabolic alkalosis • Respiratory alkalosis

13. Metabolic Acidosis • Overproduction of hydrogen ions • Under-elimination of hydrogen ions • Underproduction of bicarbonate ions • Over-elimination of bicarbonate ions

14. Respiratory Acidosis • Retention of CO: • Respiratory depression • Inadequate chest expansion • Airway obstruction • Reduced alveolar-capillary diffusion

15. Combined Metabolic and Respiratory Acidosis • Uncorrected respiratory acidosis always leads to poor oxygenation and lactic acidosis. • Combined acidosis is more severe than metabolic or respiratory acidosis alone. • Cardiac arrest is an example of a problem leading to combined metabolic and respiratory acidosis.

16. Collaborative Care • History • CNS changes • Neuromuscular changes • Cardiovascular changes • Respiratory changes: • Kussmaul respiration • Skin changes • Psychosocial assessment

17. Laboratory Assessment • Metabolic acidosis: • pH <7.35 • Bicarbonate <21 mEq/L • PaO2 normal • PaCO2 normal or slightly decreased • Serum potassium high

18. Laboratory Assessment (Cont’d) • Respiratory acidosis: • pH <7.35 • PaO2 low • PaCO2 high • Serum bicarbonate variable • Serum potassium levels elevated if acidosis is acute • Serum potassium levels normal or low if renal compensation is present

19. Interventions—Metabolic Acidosis • Hydration • Drugs: • Insulin to treat DKA • Antidiarrheal drugs • Bicarbonate only if serum bicarbonate levels are low

20. Interventions—Respiratory Acidosis • Maintain a patent airway, and enhance gas exchange • Drug therapy • Oxygen therapy • Pulmonary hygiene • Ventilation support • Prevent complications

21. Alkalosis • Metabolic alkalosis: • Base excesses—excessive intake bicarbonates, carbonates, acetates, and citrates • Acid deficit—prolonged vomiting, excess cortisol, hyperaldosteronism, thiazide diuretics, prolonged NG suction

22. Alkalosis (Cont’d) • Respiratory alkalosis: • Hyperventilation—anxiety, fear, improper vent settings, stimulation of central respiratory center due to fever, DNS lesion, and salicylates

23. Collaborative Care • Assessment • CNS changes—positive Chvostek’s and Trousseau’s signs • Neuromuscular changes—tetany • Cardiovascular changes • Respiratory changes

24. Interventions • Prevent further losses of hydrogen, potassium, calcium, and chloride ions. • Restore fluid balance. • Monitor changes.