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Acid-Base Imbalance

Acid-Base Imbalance. NRS 440 2010. What is pH?. pH is the concentration of hydrogen (H+) ions The pH of blood indicates the net result of normal acid-base regulation, any acid-base imbalance, and the body’s compensatory mechanisms The human body must maintain a very narrow pH range

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Acid-Base Imbalance

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  1. Acid-Base Imbalance NRS 440 2010

  2. What is pH? • pH is the concentration of hydrogen (H+) ions • The pH of blood indicates the net result of normal acid-base regulation, any acid-base imbalance, and the body’s compensatory mechanisms • The human body must maintain a very narrow pH range • 7.35-7.45

  3. What is pH? • In terms of the human body: • acidosis<------7.4------>alkalosis • Carbon dioxide is the “acid” (CO2) • Normal: 35-45 mmHg • Bicarbonate is the “base” (HCO3) • Normal: 22-26 mEq/L

  4. How does the body maintain pH? • Buffer systems • Prevent major changes in pH by removing or releasing a hydrogen (H+) ion • Act chemically to change strong acids into weaker acids or to bind acids to neutralize their effects • Carbonic acid (H2C03) buffer system neutralized hydrochloric acid 2. Phosphate buffer system neutralizes strong acids

  5. How does the body maintain pH? • Buffer systems • Intracellular and extracellular proteins act as buffer systems • The cell can act as a buffer by shifting hydrogen in and out of the cell

  6. How does the body maintain pH? • Kidneys • Regulate bicarbonate in the ECF • The kidneys will retain or excrete H+ ions or HCO3 ions as needed • Normally acidic urine • Lungs • Control CO2 • Adjust rate and depth of ventilation in response to amount of CO2 in the blood • A rise in arterial blood CO2 stimulates respiration • Oxygen content of arterial blood will also stimulate respiration

  7. Acidosis and Alkalosis • Metabolic acidosis • Decreased HCO3 or increase in other acids • Metabolic alkalosis • Increased HCO3 and excess loss of acids • Respiratory acidosis • Increased PaCO2 due to hypoventilation • Respiratory alkalosis • Decreased PaC02 due to hyperventilation

  8. Imbalances • Imbalances in PaCO2 are influenced by respiratory causes • Imbalances in HCO3 are influenced by metabolic processes

  9. Metabolic Acidosis • Low pH (<7.35) • Low HCO3 (<22 mEq/L) • Body may attempt to compensate by increasing respirations to decrease CO2 High anion gap acidosis • Results from excessive accumulation of fixed acid Normal anion gap acidosis • Results from direct loss of bicarbonate

  10. Metabolic acidosis • Primary feature is decrease in serum HCO3 • Hyperkalemia may also occur due to shift of potassium out of the cells • Hypokalemia may occur once the acidosis is corrected • Treatment is aimed at correcting the metabolic defect • IV bicarbonate • Potassium management • Dialysis

  11. Metabolic Alkalosis • High pH (>7.45) • High serum HCO3 (>26) • Body may attempt to compensate by decreasing respirations to increase CO2 • Treatment is aimed at treating the underlying disorder • Chloride supplementation • Restore normal fluid volume • Maintain potassium • Carbonic anhydrase inhibitor if unable to tolerate volume resuscitation

  12. Respiratory Acidosis • Low pH (<7.35) • High serum CO2 (>42) • Body may attempt to compensate through renal retention of HCO3 (does not happen quickly - hours to days) • Chronic respiratory acidosis occurs with chronic pulmonary disease (eg, emphysema, OSA) • Pt. will often be asymptomatic, as the body has time to compensate • Acute respiratory acidosis may be severe and will produce symptoms

  13. Respiratory Acidosis • Treatment is directed at improving ventilation --> treat the underlying cause • Pulmonary hygiene to clear respiratory tract • Adequate hydration to help clear secretions • Supplemental oxygen • Adjustment of mechanical ventilation as appropriate

  14. Respiratory Alkalosis • High pH (>7.45) • Low PaCO2 (<35) • Always due to hyperventilation • Body may compensate through increased kidney excretion of bicarbonate (does not happen quickly - hours to days) • Treatment is aimed at correcting the cause of hyperventilation • If anxiety-related, may breathe into a closed system (rebreathe CO2)

  15. Interpreting Arterial Blood Gases • pH (7.35-7.45) • PaO2 (80-100 mmHg on room air) • O2 saturation (95-100%) • PaCO2 (35-45 mmHg) • HCO3 (22-26 mEq/L) • Base excess (or deficit) (+2 to -2 mEq/L) • Sum of bases (alkalis)

  16. Interpreting Arterial Blood Gases • 1. Determine if acidosis or alkalosis • *use 7.40 as normal in this step • 2. Determine the component that caused the abnormality in step 1 • 3. Determine if the gas is compensated • If the pH is 7.35-7.45, it is compensated • If the pH is <7.35 or >7.45, it is uncompensated

  17. Case Study • Alan • 17 years old • History of: • Feeling “bad” • Fatigue • Constant thirst • Frequent urination

  18. Case Study • Alan • Blood glucose is 484 mg/dL • Respirations are 28, lungs are clear to auscultation • Breath has a fruity odor

  19. Case Study • Alan • What acid-base disorder would you expect? • What is the treatment for the disorder?

  20. Practice Low <---- Neutral ----> High pH 7.46 CO2 30 HCO3 22

  21. Practice Low <---- Neutral ----> High pH 7.38 CO2 51 HCO3 29

  22. Practice Low <---- Neutral ----> High pH 7.28 CO2 35 HCO3 18

  23. Case Study • Susan’s ABG results are: • pH 7.20 • PaCO2 58 mm Hg • PaO2 59 mm Hg • HCO3- 24 mEq/L • Describe a patient who would have these ABGs, including history and assessment. • What is the treatment?

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