Give the equations for shunt (QS/QT) and dead space/tidal volume (VD/VT). What are their normal values?
Answer:
where CcO2, CaO2, and C
O2 are oxygen contents in pulmonary capillary, arterial, and mixed venous blood, respectively; QT is cardiac output; QS is shunt blood; and PaCO2 and PCO2 are partial pressures of CO2 in arterial blood and the mixed expired gases, respectively.
Normal QS/QT is 4% to 5%, and VD/VT is approximately 0.3.
Reference(s):
- Barash PG, Cullen BF, Stoelting RK, et al, eds. Clinical Anesthesia. 8th ed. Philadelphia, PA: Wolters Kluwer; 2017:374-376.
- Lumb AB. Nunn’s Applied Respiratory Physiology. 8th ed. Philadelphia, PA: Elsevier; 2017:122-124.