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Acid Base Imbalances

Acid Base Imbalances. Acid-Base Regulation. Body produces significant amounts of carbon dioxide & nonvolatile acids daily Regulated by: Renal excretion of acid (H+ combines with phosphate or ammonia, which are excreted) Respiratory excretion of CO2

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Acid Base Imbalances

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  1. Acid Base Imbalances

  2. Acid-Base Regulation • Body produces significant amounts of carbon dioxide & nonvolatile acids daily • Regulated by: • Renal excretion of acid (H+ combines with phosphate or ammonia, which are excreted) • Respiratory excretion of CO2 • Buffer systems (hemoglobin, phosphate, bicarbonate, proteins)

  3. Measurement • Arterial: • Normal pH 7.36-7.44; normal HCO3 25; normal pCO2 40 • Peripheral venous: • pH is 0.02-0.04 lower than arterial • HCO3 is 1-2 mEq/L higher than arterial • pCO2 is 3-8 mmHg higher, depending on peripheral extraction and use of O2

  4. Respiratory Acidosis

  5. Definition • Decreased pH due to pulmonary CO2 retention (hypoventilation causes hypercapnea) • CO2 retention causes increased H2CO3 production – causes acidemia • Serum HCO3 is normal acutely, and increases as compensation occurs

  6. Causes • Increase in PaCO2 • Anything which causes a decrease in minute ventilation has the potential to cause respiratory acidosis • Airway • CNS depression • Pulmonary disease • Hypoventilation of neuromuscular conditions

  7. Symptoms • CO2 narcosis: • Headache, blurred vision • Asterixis, tremors, weakness • Confusion, somnolence • If prolonged: • Signs of increased ICP • Papilledema

  8. Compensation • Acutely: • intracellular proteins buffer • HCO3 is formed by the intracellular buffers • Compensation is insignificant • Chronically • Renal retention of HCO3 is the primary buffering system • Onset: 6-12 hrs, takes days to complete

  9. Compensation • Acute: • HCO3 increases 1 mEq/L for every 10 mmHg rise in PCO2 • Insignificant effect on pH • Chronic: • HCO3 increases 3.5-5 mEq/L for every 10mmHg rise in PCO2 • Can almost normalize pH • Usually results in hypochloremia

  10. Management • Must increase minute ventilation • Must also improve ventilation • Bronchodilators, postural drainage, antibiotics (i.e. treat underlying cause) • Role of hypoxic drive???

  11. Respiratory Alkalosis

  12. Causes • Increased minute ventilation • Leads to low pCO2, high pH • If acute, HCO3 is normal • If chronic, HCO3 will drop due to renal comp. • Causes: • CNS diseases, hypoxemia, anxiety, hypermetabolic states, toxic states, hepatic insufficiency, assisted ventilation

  13. Symptoms • Mimic hypocalcemia • Depend on degree, acuity & cause • Due to irritability of CNS & PNS, and increased cerebral vascular resistance • Paresthesias of lips, extremities; lightheadedness, dizziness, muscle cramps, carpopedal spasms

  14. Management • Treat underlying cause • i.e. remove stimulus • Treat symptoms • E.g. benzos, pain medication, rebreathing mask (allows CO2 retention)

  15. Metabolic Alkalosis

  16. Definition • Low pH due to increased HCO3 or decreased H+ • Requires loss of H+ or retention of HCO3 • Must know PCO2… elevation of HCO3 could be due to renal compensation for chronic respiratory acidosis

  17. Causes • Increased HCO3 reabsorption due to volume, K+ or Cl- loss • Loss of H+ and Cl- from vomiting and NG suctioning can lead to HCO3 retention • Renal impairment of HCO3 excretion

  18. Causes • Hypovolemic • Vomiting/suction, diuretics, adenomas • Euvolemic/Hypervolemic • Exogenous mineralocorticoids, ectopic ACTH, Cushing’s, severe hypoK, adenoCA • Unclassified • Milk-alkali syndrome, IV PCN rx, metabolism of organic acid anions, massive transfusion, nonparathyroidhypercalcemia

  19. Treatment • Treat underlying causes • Replace losses • May be saline-responsive or saline resistant

  20. Metabolic Acidosis

  21. Mechanism • Increased production of acids • Decreased renal excretion of acids • Loss of alkali

  22. Alcoholic Ketoacidosis • Normal glucose • High ketones • Drinking binge; starvation

  23. Lactic Acidosis • 2 different forms; l- and d- • Increased production vs. decreased elimination • Systemic • Sepsis, hypovolemia, hypoxia • Localized • E.g. bowel ischemia, metformin, HIV meds

  24. Treatment • Correct underlying cause • Reduce O2 demand • Ensure adequate O2 delivery to tissues • HCO3 • Given to improve hemodynamic consequences of acidosis

  25. Summary • Look at pH • Look at pCO2 and HCO3 • Look at patient!! • Treat the patient, not the numbers

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