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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

NRS 440

2010


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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


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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


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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


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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


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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


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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


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Imbalances

  • Imbalances in PaCO2 are influenced by respiratory causes

  • Imbalances in HCO3 are influenced by metabolic processes


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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


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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


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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


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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


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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


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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)


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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)


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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


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Case Study

  • Alan

    • 17 years old

    • History of:

      • Feeling “bad”

      • Fatigue

      • Constant thirst

      • Frequent urination


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Case Study

  • Alan

    • Blood glucose is 484 mg/dL

    • Respirations are 28, lungs are clear to auscultation

    • Breath has a fruity odor


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Case Study

  • Alan

    • What acid-base disorder would you expect?

    • What is the treatment for the disorder?


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Practice

Low <---- Neutral ----> High

pH 7.46

CO2 30

HCO3 22


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Practice

Low <---- Neutral ----> High

pH 7.38

CO2 51

HCO3 29


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Practice

Low <---- Neutral ----> High

pH 7.28

CO2 35

HCO3 18


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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?