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:
Category | Parameter | Value | Normal Range | Units |
Acid/Base Status | pH | 7.354 | 7.35-7.45 | - |
pCO2 | 42.3 | 35-45 | mmHg | |
HCO3- (act) | 23.0 | 22-26 | mmol/L | |
HCO3- (std) | 22.5 | 22-26 | mmol/L | |
ctCO2 | 24.3 | - | mmol/L | |
Co-oximetry | tHb | 8.0 | 12-16 (females), 13-18 (males) | g/dL |
FO2Hb | 97.6 | 95-100 | % | |
FMetHb | 0.3 | 0-1.5 | % | |
Oxygenation | pO2 | 190.1 | 75-100 | mmHg |
O2 SAT (est) | 99.2 | 95-100 | % | |
pO2 / FiO2 | 475 | >300 | mmHg / % | |
Electrolytes | K+ | 3.47 | 3.5-5.0 | mmol/L |
Ca++ | 1.03 | 1.12-1.32 | mmol/L | |
Temperature | Temperature | 36.9 | Around 37 | °C |
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.
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.
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