Volume II: Nurse Keith

Gas Exchange

  • Gas exchange occurs when oxygen is transported to cells and carbon dioxide and other wastes are transported away from cells

  • There are three (3) mechanisms needed for gas exchange to occur:

    • Ventilation

      • Refers to movement of air ins and out of the lungs

      • The drive to breathe is regulated in the brainstem

      • Chemoreceptors measure the amount of carbon dioxide in the blood and when the threshold is met, a breath is triggered

      • When a breath is triggered - diaphragm depresses, chest wall expands, negative pressure is created

    • Transport of oxygen and carbon dioxide through RBCs

    • Perfusion

      • Refers to the blood flow through the arteries and capillaries that deliver nutrients and oxygen to cells and remove cellular wastes

Key Terms

  • Anemia

    • Lack of RBCs or hemoglobin causing insufficient oxygenation to the body

  • Hyperventilation

    • Too much air movement

    • Breathing too quickly or too deeply or both

  • Hypoxemia

    • Lack of oxygen in the blood

  • Hypoxia

    • Lack of oxygen in the cells

  • Respiration

    • Movement of oxygen and carbon dioxide across membranes

  • Ventilation

    • Movement of air in and out of the lungs

Laboratory Tests for Gas Exchange

  • Arterial Blood Gas or ABG

    • Direct and invasive measure of dissolved partial pressure of oxygen, carbon dioxide, and bicarbonate

  • Hemoglobin or Hgb

  • Oxygen saturation

    • Percentage of hemoglobin that is bound with oxygen

  • Red blood cells or RBCs

    • Transport oxygen and carbon dioxide

    • Less RBCs = Less Hgb = Decreased oxygenation

Red flags in Gas Exchange

  • Increasing respiratory rate and increased use of accessory muscle

    • This demonstrates increased work of breathing

    • Restlessness is an early sign that hypoxia is developing

  • Changes in breath sounds

    • Assess all lung fields and note any trends in changes in the character of breath sounds

  • Changes in vital signs

    • Increased heart rate will occur when oxygen availability decreases - because the body has to work extra hard to deliver oxygen to vital organs

    • Increased respiratory rate will occur to compensate as well, unless the patient is on CNS depressants that cause decreased respiratory rate

    • Changes in laboratory values

Acid/Base Balance

  • Human body always strives for stability by maintaining a consistent pH of 7.35 - 7.45

  • Acid-base balance is influenced by the concentration of hydrogen ions in body fluids

Anatomy and Physiology Review

  • Buffer System

    • This is the fastest and most efficient way to achieve acid-base balance

  • Respiratory

    • If the body is too basic, the respiratory system will increase acidity by retaining carbon dioxide - making respirations shallow and slow to blow less carbon dioxide

  • Renal

    • If the body is too acidic, the renal system will decrease excretion of bicarbonate, neutralizing the acid

    • If the body is too basic, the renal system will increase excretion of bicarbonate to make pH more acidic

Key Terms in Acid/Base Balance

  • Compensated

    • pH is corrected but both respiratory and metabolic mechanisms are out of the normal ranges

  • Partially Compensated

    • Balancing systems are activated but they have not successfully corrected the imbalance

  • Partial Pressure

    • Measurement of the amount of gas in arterial blood

  • pH

    • Measurement of the amount of acid or base present in the blood

  • Uncompensated

    • None of the mechanisms designed to correct an imbalance has been activated or effective

Laboratory Tests for Acid/Base Balance

  • pH

    • Normal is 7.35 - 7.45

  • pCO2

    • Normal is 35 - 45

  • pO2

    • Normal is 80 - 100

  • HCO3

    • Normal is 22 - 28

  • Creatinine

    • The most important laboratory value to determine renal function

    • If elevated, kidneys are not working efficiently and may not effectively regulate HCO3

  • Potassium

    • Important to normal cardiac electrical conduction

    • Any changes in potassium can predispose the patient to abnormal heart rhythms

    • Potassium will increase when creatinine is rising due to renal function

  • Trend potassium and creatinine laboratory values together

Pathophysiology

  • Metabolic acidosis

    • Decreased bicarbonate or HCO3

    • Uncompensated metabolic acidosis

      • pH is low

      • HCO3 is low

      • CO2 is normal

    • Partially compensated metabolic acidosis

      • pH is low

      • HCO3 is low

      • CO2 decreases

    • Compensated metabolic acidosis

      • pH is normal

      • HCO3 and CO2 are outside normal ranges

  • Respiratory acidosis

    • Increased CO2

    • Uncompensated respiratory acidosis

      • pH is low

      • CO2 is high

      • HCO3 is normal

    • Partially compensated respiratory acidosis

      • pH is low

      • CO2 is high

      • HCO increases

    • Compensated respiratory acidosis

      • pH is normal

      • CO2 and HCO3 are outside normal ranges

  • Metabolic alkalosis

    • Increased HCO3

    • Uncompensated metabolic alkalosis

  • Respiratory alkalosis