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)