Certified Pulmonary Function Technologist (CPFT) Practice Exam

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How can you quickly calculate CaO2?

Hgb/2 then add Hgb
Hgb/3 then add original Hgb
Hgb/3 then subtract 1
Hgb/4 then add 2

The correct answer is: Hgb/3 then add original Hgb

Calculating the arterial oxygen content (CaO2) is essential in assessing a patient's oxygenation status. The correct approach involves knowing how much oxygen is bound to hemoglobin (Hgb) and the amount dissolved in plasma. The formula to calculate the oxygen content is: CaO2 = (Hgb × 1.34 × SpO2) + (0.003 × PaO2) However, for a quick estimation, a commonly used shortcut is to take the hemoglobin value and divide it by 3, then add it back to the original hemoglobin value. This approximation works because it simplifies the 1.34 factor associated with hemoglobin saturation without needing the actual saturation percentage for a rough calculation. In this option, dividing hemoglobin by three gives a rough estimate of the grams of oxygen bound to hemoglobin, while adding the original hemoglobin value allows for estimating the total oxygen content when considering both the bound and the dissolved fractions. This method provides a practical way for healthcare providers to quickly assess a patient's oxygen delivery without extensive calculations. Consequently, the correct option is significant because it aligns with the clinical context of rapidly evaluating a patient's respiratory function using accessible data.