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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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Presentation Transcript
what is ph
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
what is ph3
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
how does the body maintain ph
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

how does the body maintain ph5
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
how does the body maintain ph6
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
acidosis and alkalosis
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
imbalances
Imbalances
  • Imbalances in PaCO2 are influenced by respiratory causes
  • Imbalances in HCO3 are influenced by metabolic processes
metabolic acidosis
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
metabolic acidosis14
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
metabolic alkalosis
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
respiratory acidosis
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
respiratory acidosis18
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
respiratory alkalosis
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)
interpreting arterial blood gases
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)
interpreting arterial blood gases23
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
case study
Case Study
  • Alan
    • 17 years old
    • History of:
      • Feeling “bad”
      • Fatigue
      • Constant thirst
      • Frequent urination
case study25
Case Study
  • Alan
    • Blood glucose is 484 mg/dL
    • Respirations are 28, lungs are clear to auscultation
    • Breath has a fruity odor
case study26
Case Study
  • Alan
    • What acid-base disorder would you expect?
    • What is the treatment for the disorder?
practice
Practice

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

pH 7.46

CO2 30

HCO3 22

practice28
Practice

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

pH 7.38

CO2 51

HCO3 29

practice29
Practice

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

pH 7.28

CO2 35

HCO3 18

case study30
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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