About

In critical care settings, interpreting Arterial Blood Gas (ABG) results is a fundamental skill that directly impacts patient outcomes. The balance of pH, carbon dioxide (PaCO2), and bicarbonate (HCO3) reveals the body's acid-base status and oxygenation efficiency. However, the interplay between these values can be complex, especially when the body attempts to compensate for an imbalance.

This ABG Analyzer is designed for medical students, nurses, and respiratory therapists. It goes beyond simple identification of Acidosis or Alkalosis; it analyzes the relationship between the respiratory and metabolic components to determine if the condition is compensated, partially compensated, or uncompensated. Understanding these nuances is critical for identifying the underlying pathology—whether it's respiratory failure requiring ventilation or a metabolic issue like diabetic ketoacidosis requiring insulin and fluids.

Formulas

The relationship between pH, bicarbonate, and carbon dioxide is governed by the Henderson-Hasselbalch equation:

pH = 6.1 + log(HCO₃0.03 × PaCO₂)

Logic Rules:

Step 1. Determine pH status: Acid (< 7.35), Normal, or Base (> 7.45).
Step 2. Determine PaCO2 status: Acid (> 45), Normal, or Base (< 35).
Step 3. Determine HCO3 status: Acid (< 22), Normal, or Base (> 26).
Match. The system matching the pH determines the primary problem (Respiratory vs Metabolic).

Reference Data

Parameter	Normal Range (Adult)	Interpretation of Low	Interpretation of High
pH (Acidity)	7.35 - 7.45	Acidemia (Acidosis)	Alkalemia (Alkalosis)
PaCO₂ (Respiratory)	35 - 45 mmHg	Respiratory Alkalosis (Hyperventilation)	Respiratory Acidosis (Hypoventilation)
HCO₃ (Metabolic)	22 - 26 mEq/L	Metabolic Acidosis	Metabolic Alkalosis
PaO₂ (Oxygenation)	80 - 100 mmHg	Hypoxemia	Hyperoxemia
SaO₂ (Saturation)	95 - 100%	Hypoxia	Normal

Frequently Asked Questions

In 'Partial Compensation', the pH is still abnormal, but the opposing system (e.g., kidneys for a respiratory problem) has started to shift outside the normal range to counteract the imbalance. In 'Full Compensation', the opposing system has worked enough to return the pH to the normal range (7.35-7.45), even though PaCO2 and HCO3 remain abnormal.

ROME stands for Respiratory Opposite, Metabolic Equal. In Respiratory disorders, pH and PaCO2 move in Opposite directions (pH down, PaCO2 up). In Metabolic disorders, pH and HCO3 move in Equal directions (pH down, HCO3 down).

This tool identifies the primary disorder and compensation status. Complex mixed disorders (where both respiratory and metabolic systems cause acidosis simultaneously) require advanced analysis, often involving the Anion Gap, which is not calculated here.

PaO2 measures the partial pressure of oxygen dissolved in the blood. While it doesn't directly affect the acid-base calculation (pH), it is crucial for determining if the patient has hypoxemia (low blood oxygen).