Acid-Base Imbalances

1. Acid-Base Imbalances

2. Acid-Base Imbalances • pH< 7.35 acidosis • pH > 7.45 alkalosis • The body response to acid-base imbalance is called compensation • May be complete if brought back within normal limits • Partial compensation if range is still outside norms.

3. Compensation • If underlying problem is metabolic, hyperventilation or hypoventilation can help : respiratory compensation. • If problem is respiratory, renal mechanisms can bring about metabolic compensation.

4. Acid-Base Disturbances • When compensation is appropriate Metabolic acidosis (↓ HCO3, ↓ pCO2) Metabolic alkalosis (↑ HCO3, ↑ pCO2) Respiratory acidosis (↑ pCO2, ↑ HCO3) Respiratory alkalosis (↓ pCO2, ↓ HCO3)

5. Stepwise Approaches • History & physical examination • Arterial blood gas for pH, pCO2, (HCO3) • Use the HCO3 from ABG to determine compensation • Serum Na, K, Cl, CO2 content • Use CO2 content to calculate anion gap • Calculate anion gap • Anion gap = {Na + K - (Cl + HCO3-)} • Determine appropriate compensation • Determine the primary cause

6. 1. Respiratory Acidosis • Carbonic acid excess caused by blood levels of CO2 above 45 mm Hg. • Hypercapnia – high levels of CO2 in blood • Causes: • Chronic conditions: • Depression of respiratory center – drugs or head trauma • Paralysis of respiratory or chest muscles • Emphysema

7. Respiratory Acidosis cont. • Acute conditions: • Adult Respiratory Distress Syndrome • Pulmonary edema • Pneumothorax • Compensation for Respiratory Acidosis: the kidneys eliminate hydrogen ion and retain bicarbonate ion (metabolic alkalosis)

8. Signs and Symptoms of Respiratory Acidosis • Breathlessness • Restlessness • Lethargy and disorientation • Tremors, convulsions, coma • Respiratory rate rapid, then gradually depressed • Skin warm and flushed due to vasodilation caused by excess CO2

9. Treatment of Respiratory Acidosis • Treat underlying dysfunction or disease • Caution should be exercised in the correction of chronic hypercapnia: too-rapid correction of the hypercapnia can result in metabolic alkalosis. Alkalization of the cerebrospinal fluid (CSF) can result in seizures. • Admit to intensive care unit (ICU) if pH (< 7.25) • Oxygen therapy should be used with caution because it may worsen hypercapnia

10. Restore ventilation: invasive or non invasive ventilation • Bicarbonate: Infusion of sodium bicarbonate is rarely indicated. This measure may be considered after cardiopulmonary arrest with an extremely low pH (< 7.0-7.1). In most other situations, sodium bicarbonate has no role in the treatment of respiratory acidosis.

11. 2. Respiratory Alkalosis • Carbonic acid deficit • pCO2 less than 35 mm Hg (hypocapnea) • Most common acid-base imbalance • Primary cause is hyperventilation

12. Respiratory Alkalosis • Conditions that stimulate respiratory center: • Oxygen deficiency at high altitudes • Pulmonary embolism • Acute anxiety • Fever, anemia • Early salicylate intoxication • Cirrhosis • Gram-negative sepsis • Compensation of Respiratory Alkalosis • Kidneys conserve hydrogen ion • Excrete bicarbonate ion (metabolic acidosis)

13. Treatment of Respiratory Alkalosis • The treatment of respiratory alkalosis is primarily directed at correcting the underlying disorder. • Respiratory alkalosis itself is rarely life threatening. Therefore, emergent treatment is usually not indicated unless the pH level is greater than 7.5. • Breathe into a paper bag, beta blocker or sedatives can be helpful in anxiety attacks

14. 3. Metabolic Acidosis • Bicarbonate deficit - blood concentrations of bicarbonate drop below 22mEq/L • Causes: • Loss of bicarbonate through diarrhea or renal dysfunction • Accumulation of acids (lactic acid or ketones) • Failure of kidneys to excrete H+

15. Symptoms of Metabolic Acidosis • Headache, lethargy • Nausea, vomiting, Diarrhea • Coma • Death • Compensation for Metabolic Acidosis • Increased ventilation (respiratory alkalosis) • Renal excretion of hydrogen ions if possible • K+ exchanges with excess H+ in ECF ( H+ into cells, K+ out of cells)

16. Treatment of Metabolic Acidosis • Treating the underlying conditions in high AG states usually is sufficient in reversing the acidosis. • Treatment with bicarbonate is unnecessary, except in extreme cases of acidosis when the pH is less than 7.1-7.2. • HCO3- can be administered intravenously to raise the serum HCO3- level adequately to increase the pH to greater than 7.20.

17. 4. Metabolic Alkalosis • Bicarbonate excess - concentration in blood is greater than 26 mEq/L • Causes: • Excess vomiting = loss of stomach acid • Excessive use of alkaline drugs • Certain diuretics • Endocrine disorders • Heavy ingestion of antacids • Severe dehydration

18. Symptoms of Metabolic Alkalosis • Respiration slow and shallow • Hyperactive reflexes ; tetany often related to depletion of electrolytes • Dysrhythmias • Compensation for Metabolic Alkalosis • Alkalosis most commonly occurs with renal dysfunction, so can’t count on kidneys • Respiratory compensation difficult – hypoventilation limited by hypoxia

19. Treatment of Metabolic Alkalosis • Treat underlying disorder • Replace electrolytes loss • IV sodium chloride in volume depleted patients often need to add potassium • Hydrochloric acid: Intravenous HCl is indicated in severe metabolic alkalosis (pH >7.55) or when sodium or potassium chloride cannot be administered because of volume overload or advanced renal failure. • Dialysis: Both peritoneal dialysis and hemodialysis can be used with certain modifications of the dialysate to correct metabolic alkalosis