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Introduction to Acid-Base Balance

Introduction to Acid-Base Balance. N132. Acid_Base Chemistry. Acids E.g carbonic acid (H 2 CO 3 ) *Most Common Bases E.g bicarbonate (HCO3-) * Most Common Buffers. Body Fluid Chemistry. Arterial Blood pH = 7.35-7.45 ECF

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Introduction to Acid-Base Balance

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  1. Introduction to Acid-Base Balance N132

  2. Acid_Base Chemistry • Acids E.g carbonic acid (H2CO3) *Most Common • Bases E.g bicarbonate (HCO3-) *Most Common • Buffers

  3. Body Fluid Chemistry • Arterial Blood pH = 7.35-7.45 • ECF 1 molecule of carbonic acid to 20 free bicarbonate ions (1:20) • Carbonic Anhydrase Equation CO2 + H20  H2CO3  H+ + HCO3-

  4. Body Fluid Chemistry CO2 + H20  H2CO3  H+ + HCO3- • CO2 =  H+ , therefore pH (more acidic) • CO2 =  H+, therefore pH (more basic) • HCO3- =  H+, therefore pH (more basic)

  5. Body Fluid Chemistry • Sources of Acids • Glucose Metabolism • Fat & Protein Metabolism • Anaerobic Metabolism of Glucose & Fat

  6. Body Fluid Chemistry • Sources of Bicarbonate Ions • Breakdown of carbonic acid • Intestinal absorption of ingested HCO3- • Pancreatic production • Movement of intracellular HCO3- into ECF • Kidney reabsorption

  7. Homeostasis

  8. Regulatory Mechanisms • Buffers (1st line of defense) • Chemical (HCO3-) • Proteins (Hemoglobin) • Respiratory (2nd) • Hyperventilation • Hypoventilation • Renal (3rd)

  9. Age-Related Changes • Older Adults • Reduced effective gas exchange • Decreased kidney function • Medications • Diuretics & Digoxin (Often taken by older adults) • Both drugs increase kidney excretion of H+ ions, which can result in an increased blood pH.

  10. Assessment • Kidney function • Hydration Status • I/O • Laboratory data • Renal function blood studies • Blood Urea Nitrogen (8-20mg/dL) • Creatinine (0.5-1.5mg/dL) • Arterial Blood Gases (ABG’s}

  11. Allen’s Test

  12. Assessment CO2 + H20  H2CO3  H+ + HCO3- • pH = 7.35-7.45 (arterial) • PCO2 = 35-45 mmHg • HCO3- = 22-26 mEq/L • PO2 = 80-100mmHg

  13. Acid-Base Imbalances • Acidosis (pH<7.35) • Respiratory Acidosis • Increase CO2 causes an increase in H+ • I.e., Respiratory depression, Inadequate chest expansion, Airway obstruction. • Metabolic Acidosis • Overproduction of H+ • Breakdown of fatty acids • Lactic acid build up • Under elimination of H+ (Renal failure) • Underproduction of HCO3- (Renal Failure) • Over elimination of HCO3- (Diarrhea)

  14. Assessment • Key Features • Neuromuscular: • Lethargy, confusion, skeletal muscle weakness • Cardiovascular: • Early acidosis: Increased HR & CO • Late acidosis: Hypotension, thready pulse • Respiratory: • Nonvoluntary deep, and rapid respirations (Kussmaul)

  15. Acid-Base Imbalances • Alkalosis (pH>7.45) • Respiratory Alkalosis • Decrease CO2 • Hyperventilation • Metabolic Alkalosis • Increases in Bases • Antacids, TPN • Decreases in Acids • Caused by disease or medical treatments • Also prolonged vomiting

  16. Assessment • Key Features • Neuromuscular: • Dizziness, agitation, confusion, hyperreflexia, skeletal muscle weakness • Cardiovascular: • Increases myocardial irritability, HR, thready pulse • Respiratory: • Hyperventilation • Will cause respiratory alkalosis

  17. Putting It All Together • Step one: • Label the pH • Step two: • Find the cause of the acid base imbalance. • Determine respiratory component. • Determine metabolic component. • Step Three: • Assess for compensation. • Step Four: • Check the PaO2 (oxygenation) • If low < 80 indicates an interference with ventilation process (evaluate the patient), supply supplemental oxygen if needed. • If normal 80 – 100 indicates patient is getting enough oxygen. • If PaO2 is > 100, is possible getting too much supplemental oxygen.

  18. Case Studies • Mary, 54 years old suffered an acute anterior wall myocardial infarction and is now in cardiogenic shock. ABG shows a pH of 7.27, PaCO2 38 and HCO3 14. What is her acid – base status?

  19. Case Studies • 85 year old Arthur has chronic obstructive pulmonary disease (COPD). He is currently hospitalized with an upper respiratory infection. His ABGs show a pH of 7.30, PaCO2 - 60 and HCO3 - 26. Describe his acid-base status.

  20. Case Studies • Joan a 45-year-old female sustained major trauma in an automobile accident. She has a NG tube in place that has drained 1,500 ml in the last 24 hours. ABGs show a pH of 7.53, PaCO2 42 and HCO3 34. Describe her acid-base status.

  21. Case Studies • 28-year-old woman has been admitted to your unit for a breast biopsy. While you’re explaining the procedure to her, she becomes noticeably anxious and says she feels dizzy. You note that her respirations have increased to 45 / minute. The doctor orders ABGs. After reviewing the results, pH 7.51, PaCO2 29, PO2 80, HCO3 24. What is her acid-base status?

  22. Introduction to Compensation • If compensation has occurred, the value will move in the same direction as the other components. For example, if the problem is too much base (HCO3 > 26) holding on to acid (PaCO2 > 45) will help bring the pH closer to normal.

  23. Now Try These • pH 7.46, PaCO2 47mmHg, HCO3- 34mEq/L • Determine Acid-Base Imbalance • Compensated or Uncompensated? • pH 7.21, PaCO2 98mmHg, HCO3- 40mEq/L • Determine Acid-Base Imbalance • Compensated or Uncompensated?

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