Understanding Blood Gases and Their Analysis

Jun 1, 2025

Blood Gases and Arterial Blood Gas Analysis

Introduction

  • Focus on gases in the blood: Oxygen and Carbon Dioxide.
  • Concentrations measured as partial pressure.
    • Higher partial pressure = higher amount of gas.

Partial Pressure in the Atmosphere

  • Oxygen: 160 mm Hg
  • Carbon Dioxide: 0.3 mm Hg
  • During inspiration and expiration:
    • Oxygen breathed out: 120 mm Hg
    • Carbon Dioxide breathed out: 27 mm Hg

Role of Plants

  • Plants use CO2 to produce energy and release O2.
  • Cycle: Humans breathe in O2, produce CO2, which plants use.

Gas Exchange in the Lungs

  • Alveoli are the site of gas exchange.
  • Pulmonary arteries bring deoxygenated blood to alveoli.
  • Pulmonary veins carry reoxygenated blood from alveoli.

Detailed Gas Exchange

  • Partial pressure in alveoli:
    • Oxygen: 100 mm Hg
    • Carbon Dioxide: 40 mm Hg
  • Pulmonary artery:
    • Oxygen: 40 mm Hg
    • Carbon Dioxide: 46 mm Hg
  • Gas Movement:
    • CO2 moves from blood to alveoli.
    • O2 moves from alveoli to blood.

Systemic Circulation

  • Oxygenated blood carried by systemic arteries to tissues.
  • In tissues:
    • O2: <40 mm Hg
    • CO2: >45 mm Hg
  • Oxygen moves into tissues; CO2 moves into blood (deoxygenated).

Arterial Blood Gas Analysis

  • Measures pH, O2, and CO2 in blood.
  • pH: Normal 7.35 - 7.45
    • Changes indicate acidosis or alkalosis.
  • Partial Pressure of Oxygen: 80 - 100 mm Hg
    • Below 80 mm Hg indicates cyanosis.
  • Partial Pressure of Carbon Dioxide: 35 - 45 mm Hg
    • Changes indicate respiratory issues.
  • Bicarbonate: 22 - 26 mEq/L
    • Changes indicate metabolic issues.
  • Hemoglobin Saturation with Oxygen: ~98%

Venous Blood Analysis

  • Venous blood more acidic due to higher CO2.
  • Normal ranges:
    • pH: 7.38 - 7.43
    • Oxygen: 35 - 40 mm Hg
    • Carbon Dioxide: 41 - 52 mm Hg
    • Bicarbonate: 24 - 28 mEq/L
    • Hemoglobin Saturation: ~75%

Conclusion

  • Venous blood returns to heart, pumped to lungs, reoxygenated.
  • CO2 exhaled and used by plants.
  • Cyclical process of gas exchange.

Note

  • Remember to combine all readings for a comprehensive diagnosis of acidosis or alkalosis.

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