How to Write and Interpret ABG in Patient Chart

Understanding pO2 / FiO2 Ratio:

• pO2 (PaO2): Partial pressure of oxygen in arterial blood.
• FiO2: Fraction of inspired oxygen; the concentration of oxygen that a patient is breathing.

Calculation:

• The ratio is calculated by dividing the pO2 by the FiO2.
• For example, if pO2 is 190.1 mmHg and FiO2 is 0.40 (40% oxygen), the ratio is:
• P/F ratio = 190.1 / 0.40 = 475.25

Normal Range:

• A normal pO2 / FiO2 ratio is typically above 300.
• A ratio below 300 may indicate impaired oxygenation:
• 300-200: Mild ARDS
• 200-100: Moderate ARDS
• <100: Severe ARDS

Since the pO2 / FiO2 ratio helps in the evaluation of oxygenation status, it's crucial in critical care settings, particularly for patients on mechanical ventilation or with suspected ARDS.

Table with Normal Range:

Here’s the updated table with the pO2 / FiO2 ratio included:

Note that the pO2 / FiO2 value given (4.75) in the image might be an error or a different context measure, as the typical ratio should be much higher So don't forget to * 100 . For accurate clinical use, verify the exact FiO2 and appropriately calculate the ratio. If FiO2 is expressed as a percentage (like 40%), convert it to a fraction (0.40) for the ratio calculation.

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Detailed Guide for Interpreting ABG and Charting:

Step 1: Verify Patient Information and Sample Details

• Check the patient's name, ID, and sample collection time to ensure accuracy.

Step 2: Assess Acid-Base Status

• pH (Normal range: 7.35-7.45)
• pH 7.354: Slightly on the acidic side but within the normal range.
• Interpretation: Borderline acidosis.
• pCO2 (Normal range: 35-45 mmHg)
• pCO2 42.3 mmHg: Within the normal range, slightly leaning towards the upper limit.
• Interpretation: Normal respiratory function.
• HCO3- (Normal range: 22-26 mmol/L)
• HCO3- 23.0 mmol/L: Within the normal range.
• Interpretation: Normal metabolic function.
• Base Excess (BE) (Normal range: -2 to +2 mmol/L)
• BE (B) -2.5 mmol/L: Slightly negative, indicating mild metabolic acidosis.
• BE (ecf) -2.3 mmol/L: Similar to BE (B), suggesting mild metabolic acidosis.
• Interpretation: Mild metabolic acidosis.

Step 3: Evaluate Oxygenation Status

• pO2 (Normal range: 75-100 mmHg)
• pO2 190.1 mmHg: Elevated, likely due to supplemental oxygen.
• Interpretation: Hyperoxemia.
• O2 SAT (est) (Normal range: 95-100%)
• O2 SAT (est) 99.2%: Within normal limits.
• Interpretation: Normal oxygen saturation.

Step 4: Review Co-oximetry Results

• tHb (Normal range: 12-16 g/dL for females, 13-18 g/dL for males)
• tHb 8.0 g/dL: Low, indicating possible anemia.
• Interpretation: Anemia.
• FO2Hb (Normal range: 95-100%)
• FO2Hb 97.6%: Within normal limits.
• Interpretation: Normal oxygen-carrying capacity.
• FCOHb (Normal range: 0-1.5%)
• FCOHb 0.3%: Within normal limits.
• Interpretation: No significant carbon monoxide exposure.
• FMetHb (Normal range: 0-1.5%)
• FMetHb 0.6%: Within normal limits.
• Interpretation: No significant methemoglobinemia.

Step 5: Check Electrolyte Balance

• K+ (Normal range: 3.5-5.0 mmol/L)
• K+ 3.47 mmol/L: Slightly low.
• Interpretation: Mild hypokalemia.
• Ca++ (Normal range: 1.12-1.32 mmol/L)
• Ca++ 1.03 mmol/L: Low.
• Interpretation: Hypocalcemia.

Step 6: Note Temperature

• Temperature (Normal around 37°C)
• Temperature 36.9°C: Normal.
• Interpretation: Normothermia.

Charting in the Patient's Medical Record:

Here’s what should be documented in the patient's chart based on the ABG results:

Acid/Base Status:

• pH: 7.354
• pCO2: 42.3 mmHg
• HCO3-: 23.0 mmol/L
• BE (B): -2.5 mmol/L
• BE (ecf): -2.3 mmol/L

Oxygenation:

• pO2: 190.1 mmHg
• O2 SAT (est): 99.2%

Co-oximetry:

• tHb: 8.0 g/dL
• FO2Hb: 97.6%
• FCOHb: 0.3%
• FMetHb: 0.6%

Electrolytes:

• K+: 3.47 mmol/L
• Ca++: 1.03 mmol/L

Temperature:

• Temperature: 36.9°C

Interpretation Summary for Medical Record:

• Mild Metabolic Acidosis: Borderline low pH and slightly negative base excess values suggest a mild metabolic acidosis.
• Hyperoxemia: Elevated pO2 likely due to supplemental oxygen administration.
• Anemia: Low hemoglobin concentration indicating anemia.
• Electrolyte Imbalance: Mild hypokalemia and hypocalcemia detected.

Clinical Recommendations:

• Investigate the cause of metabolic acidosis: Assess for possible contributing factors such as renal function, lactate levels, and other metabolic conditions.
• Oxygen Therapy Management: Ensure the elevated pO2 is appropriate and adjust supplemental oxygen as necessary.
• Evaluate and Treat Anemia: Further evaluation and management for anemia, considering possible causes like blood loss, nutritional deficiencies, or chronic disease.
• Correct Electrolyte Imbalances: Monitor and correct potassium and calcium levels as needed.
• Follow-Up: Continuous monitoring and repeat ABG if clinically indicated to assess the response to interventions and adjust treatment accordingly.

By documenting and interpreting these ABG results in a structured and detailed manner, the clinical team can ensure accurate assessment and appropriate management of the patient’s condition.