Respiratory Therapy Study Guide: Lung Volumes, PFTs, and ABGs

ABG Interpretation and Respiratory Concepts

ABG Condition Characteristics

  • Respiratory Acidosis: High PaCO2.
  • Respiratory Alkalosis: Low PaCO2.
  • Metabolic Alkalosis: High HCO or low H+.
  • Metabolic Acidosis: Low HCO3- or high H+.

Buffers & Gas Regulation

  • Hemoglobin: The most important protein buffer in the body.
  • Respiratory System: Helps regulate CO2 levels in the blood, which affects pH balance.

Key Concepts to Remember

  • CO2 is acidic. More CO2 = lower pH (acidosis).
  • HCO3- is a base. More HCO3- = higher pH (alkalosis).
  • FRC is all the leftover air after you breathe out normally.
  • Peak flow is all about speed - how fast you can blow air out.

Key Respiratory Terms

  • Air Trapping: Air that stays in the lungs after exhaling because of airway narrowing (often in asthma or COPD).
  • Functional Residual Capacity (FRC): The air left in the lungs after a normal exhale.
    • FRC = Residual Volume (RV) + Expiratory Reserve Volume (ERV)

Pulmonary Function Tests (PFTs)

  • Peak Expiratory Flow (PEF): The fastest speed a person can blow air out.
  • Diffusion Capacity: Measures how well gases like oxygen and carbon dioxide move across the alveolar-capillary membrane.
  • Body Plethysmography: The most accurate test to measure FRC.
  • Other FRC Test Options:
    • Multibreath Nitrogen Washout
    • Helium Dilution

ABG Interpretation - Normal Values

  • pH: 7.35-7.45
  • PaCO2: 35-45 mm Hg (ABG), 40-52 mm Hg (VBG)
  • HCO3-: 22-26 mmol/L
  • PaO2: 80-100 mm Hg

ABG Interpretation - Examples

  • Example 1:
    • pH: 7.21
    • PaCO2: 94 mm Hg
    • HCO3-: 26
    • Diagnosis: Respiratory Acidosis (high CO2, low pH)
  • Example 2:
    • pH: 7.51
    • PaCO2: 23 mm Hg
    • HCO3-: 22
    • Diagnosis: Respiratory Alkalosis (low CO2, high pH)