ICU Advantage: Arterial Blood Gases Interpretation

Introduction

• Presenter: Eddie Watson
• Series on arterial blood gases (ABG)
• Focus on ABG interpretation
• Importance of subscribing to stay updated

Body pH Basics

• Normal body pH: 7.4
• Mechanisms to maintain pH:
  • Bicarbonate buffering system
    • Involves blood, lungs, and kidneys
  • Key organs: Lungs and Kidneys

Lungs

• Breathe faster/larger tidal volume in acidosis → Blood becomes more alkaline
• Breathe slower/reduced tidal volume in alkalosis → Blood becomes more acidic
• Fast compensation mechanism

Kidneys

• Reabsorb more/less bicarbonate (HCO3)
  • More bicarbonate → Higher pH
  • Less bicarbonate → Lower pH
• Slow compensation mechanism, takes hours to days

Key Concepts

• CO2 (Carbon Dioxide): Acidic, influences respiratory disorders
• HCO3 (Bicarbonate): Alkaline, influences metabolic disorders
• Understanding CO2 and HCO3's impact on pH is crucial for ABG interpretation

Primary Alterations in Body pH

Respiratory Acidosis

• Increased CO2
• Decreased pH
• Lungs under-ventilating, CO2 buildup

Respiratory Alkalosis

• Decreased CO2
• Increased pH
• Lungs over-ventilating, CO2 loss

Metabolic Acidosis

• Decreased bicarbonate
• Lower pH
• Possible causes: GI, endocrine, renal, nutritional disorders

Metabolic Alkalosis

• Increased bicarbonate
• Higher pH
• Various causes

Normal ABG Values

• pH: 7.35 - 7.45
• PaO2 (Partial pressure of arterial oxygen): 80 - 100
• PaCO2 (Partial pressure of arterial CO2): 35 - 45
• HCO3 (Bicarbonate): 22 - 26

Steps for Basic ABG Interpretation

1. Check pH:
   • < 7.35 = Acidosis

   • 7.45 = Alkalosis

2. Assess CO2:

   • 45 = High

   • < 35 = Low
3. Assess Bicarb:
   • < 22 = Low

   • 26 = High

4. Determine Respiratory or Metabolic:
   • Abnormal CO2 = Respiratory
   • Abnormal Bicarb = Metabolic

ROAM Acronym

• Respiratory Opposite, Metabolic Equal
  • pH changes opposite to CO2 changes
  • pH changes equal to bicarbonate changes

Examples

Example 1

• pH = 7.38, PaCO2 = 42, HCO3 = 23
• Normal ABG

Example 2

• pH = 7.27, PaCO2 = 53, HCO3 = 24
• Respiratory Acidosis

Example 3

• pH = 7.51, PaCO2 = 29, HCO3 = 22
• Respiratory Alkalosis

Example 4

• pH = 7.30, PaCO2 = 37, HCO3 = 20
• Metabolic Acidosis

Example 5

• pH = 7.49, PaCO2 = 42, HCO3 = 29
• Metabolic Alkalosis

Conclusion

• Importance of understanding ABG interpretation
• Next lesson: Compensation mechanisms
• Encourage subscription and engagement with the channel
• Check out other related series on topics like Shock.