Free Acid Base Calculator

Acid‑Base Calculator: Arterial Blood Gas (ABG) Interpretation

The arterial blood gas (ABG) calculator serves as a practical tool for interpreting the acid‑base status of a patient. By entering the results of a blood sample, healthcare professionals can quickly assess the patient’s pH, partial pressures of oxygen and carbon dioxide, bicarbonate level, and compute the anion gap. This free online blood gas analyzer is designed to aid in the evaluation of respiratory and metabolic disorders, offering a preliminary interpretation that can be used alongside clinical judgment.

Understanding Acid‑Base Balance

In a healthy individual, acid‑base homeostasis is maintained through the coordinated action of the lungs and kidneys. When this system is disrupted, the blood pH may fall below 7.35 (acidosis) or rise above 7.45 (alkalosis). The underlying cause can be either respiratory—originating from altered lung function—or metabolic, arising from kidney‑related issues. Often, the body attempts to compensate: respiratory acidosis may trigger a metabolic compensation, while metabolic acidosis may prompt a respiratory adjustment. The ABG interpretation tool helps identify whether a patient has a pure imbalance or a compensated state.

Key Arterial Blood Gas Parameters

An ABG test provides direct measurements of several critical values:

Parameter	Normal Range
pH	7.35 – 7.45
PaO₂ (partial pressure of oxygen)	75 – 100 mmHg
PaCO₂ (partial pressure of carbon dioxide)	35 – 45 mmHg
HCO₃⁻ (bicarbonate)	22 – 26 mEq/L

These values form the basis for determining whether the patient is experiencing acidosis or alkalosis and whether the origin is respiratory, metabolic, or combined.

Anion Gap Calculation

The anion gap (AG) quantifies the difference between the most abundant cation (Na⁺) and the sum of the major anions (Cl⁻ and HCO₃⁻). The standard formula is:

$$\text{AG} = \text{Na}^+ - (\text{Cl}^- + \text{HCO}_3^-)$$

The normal range for the anion gap is between 8 and 16 mEq/L. However, this calculated value should be adjusted for serum albumin concentration because albumin contributes to the anionic charge. The acid‑base calculator often incorporates this correction to provide a more accurate assessment.

How the Acid‑Base Calculator Works

To use this acid‑base balance calculator, you need the following lab values:

• pH
• PaCO₂ (partial pressure of carbon dioxide)
• HCO₃⁻ (bicarbonate)
• Chloride (Cl⁻)
• Sodium (Na⁺)
• Albumin (optional, for corrected AG)

From the first three parameters, the tool determines whether the patient is in acidosis, alkalosis, or a normal pH range and suggests whether the pattern is metabolic, respiratory, or a mixed disorder. The anion gap is then computed from the electrolyte levels, optionally corrected for albumin.

Clinical Example: Applying the Calculator

Consider an 86‑year‑old man with severe COPD who presents with fatigue and shortness of breath, and a saturation of approximately 85%. An arterial blood gas test yields:

• pH: 7.1
• PaCO₂: 56 mmHg
• HCO₃⁻: 24 mEq/L
• Chloride: 108 mEq/L
• Sodium: 140 mEq/L
• Albumin: 3.3 g/dL

The low pH (7.1) and elevated PaCO₂ (56 mmHg) with a normal bicarbonate indicate uncompensated respiratory acidosis. The anion gap computed from the electrolyte panel is:

$$\text{AG} = 140 \, \text{mEq/L} - (108 \, \text{mEq/L} + 24 \, \text{mEq/L}) = 8 \, \text{mEq/L}$$

This value falls within the normal range (8–16 mEq/L). The ABG interpretation tool thus confirms the presence of respiratory acidosis without a significant anion gap metabolic disturbance, guiding further clinical management.

Important Considerations

While this blood gas analyzer offers valuable insights, it remains a decision‑support tool and is not a substitute for professional medical evaluation. The results should always be reviewed by a qualified healthcare provider who can integrate them with the patient’s full clinical picture. This information is provided for educational and reference purposes only.