Overview
This lecture explains how to determine compensation in arterial blood gas (ABG) problems using the Tic Tac Toe method, focusing on identifying metabolic or respiratory imbalances and compensation status.
Tic Tac Toe Method for ABG Analysis
- Use a Tic Tac Toe grid to categorize pH, PaCO₂, and HCO₃⁻ (bicarb) as acidic, normal, or basic.
- Identify which values align vertically (three in a row) to diagnose the primary acid-base imbalance.
- If there is no vertical three in a row, suspect full compensation.
Determining Compensation Levels
- Uncompensated: pH is abnormal, the value not causing the imbalance is normal, so compensation has not started.
- Partially Compensated: pH is abnormal, but the value not causing the imbalance shifts in the opposite direction, indicating partial compensation.
- Fully Compensated: pH is normal, but PaCO₂ and HCO₃⁻ are both abnormal; use pH direction to determine underlying disorder.
Interpreting Blood pH in Compensation
- Normal blood pH range is 7.35–7.45, with 7.40 as the absolute normal.
- pH between 7.35–7.40 indicates compensated acidosis; 7.40–7.45 indicates compensated alkalosis.
- Assess pH side (acidic or alkalotic) to identify the underlying process during full compensation.
Example Walkthroughs
- Metabolic Acidosis, Uncompensated: pH acidic, low HCO₃⁻ (acidic), normal PaCO₂.
- Metabolic Acidosis, Partially Compensated: pH acidic, low HCO₃⁻, low PaCO₂ (basic).
- Metabolic Acidosis, Fully Compensated: pH is normal but on the acidic side, HCO₃⁻ acidic, PaCO₂ basic.
Key Terms & Definitions
- Arterial Blood Gas (ABG): Test that measures blood pH, PaCO₂, and HCO₃⁻ to assess acid-base status.
- PaCO₂: Partial pressure of carbon dioxide (respiratory component), normal: 35–45 mmHg.
- HCO₃⁻: Bicarbonate (metabolic component), normal: 22–26 mEq/L.
- Compensation: Body’s adjustment to restore normal blood pH during acid-base imbalance.
Action Items / Next Steps
- Practice using the Tic Tac Toe method with sample ABG values.
- Review the table of normal lab ranges for ABG interpretation.
- Watch the comprehensive acid-base balance video if further clarification is needed.