Arterial Blood Gas Interpretation Calculator

Step 1: Gather Patient Data

Before using the calculator, collect the following patient data:

• pH: Indicates the acidity or alkalinity of the blood.
• PaCO₂: Partial pressure of carbon dioxide, reflecting respiratory function.
• HCO₃⁻: Bicarbonate level, indicating metabolic function.
• Sodium (Na⁺), Chloride (Cl⁻), and Albumin: Electrolytes used to calculate the anion gap.

Step 2: Input Validation

Ensure that the input values fall within the physiological ranges:

• pH: 6.8 to 7.8
• PaCO₂: 15 to 130 mmHg
• HCO₃⁻: 3 to 45 mEq/L
• Sodium: 110 to 170 mEq/L
• Chloride: 70 to 130 mEq/L
• Albumin: 0.1 to 7 g/dL

Step 3: pH Analysis

• Acidemia: pH < 7.35
• Alkalemia: pH > 7.45
• Normal pH: 7.35 ≤ pH ≤ 7.45

Step 4: Identify Primary Disorders

• Metabolic Acidosis: HCO₃⁻ < 22 mEq/L
  • Calculate expected PaCO₂: (1.5 × HCO₃⁻) + 8
  • Check for respiratory compensation or additional disorders.
• Metabolic Alkalosis: HCO₃⁻ > 26 mEq/L
  • Calculate expected PaCO₂: (0.7 × (HCO₃⁻ − 24)) + 40
  • Check for respiratory compensation or additional disorders.
• Respiratory Acidosis: PaCO₂ > 45 mmHg
  • Acute: HCO₃⁻ increases by 1 for every 10 mmHg increase in PaCO₂.
  • Chronic: HCO₃⁻ increases by 3.5 for every 10 mmHg increase in PaCO₂.
• Respiratory Alkalosis: PaCO₂ < 35 mmHg
  • Acute: HCO₃⁻ decreases by 2 for every 10 mmHg decrease in PaCO₂.
  • Chronic: HCO₃⁻ decreases by 5 for every 10 mmHg decrease in PaCO₂.

Step 5: Determine Compensation Status

• Evaluate if the compensation is appropriate based on the expected values.
• Identify any additional metabolic or respiratory disorders.

Step 6: Calculate Anion Gap

• Uncorrected Anion Gap: Na⁺ − (Cl⁻ + HCO₃⁻)
• Corrected Anion Gap: Adjust for albumin if provided.
  • Normal albumin is 4 g/dL. For each 1 g/dL albumin is below 4, add 2.5 to the anion gap.
• Interpretation:
  • High anion gap (>12) suggests the presence of unmeasured anions, often seen in metabolic acidosis.
  • Normal anion gap indicates no significant unmeasured anions.

Step 7: Interpret Results

Combine the findings from the pH analysis, primary disorder identification, compensation status, and anion gap calculation to form a comprehensive interpretation.

Display the results, including primary disorders, compensation status, and anion gap, to guide clinical decision-making.