Aerial blood gas of a 5 year old child done at sea level gives the following results: pH 7.41, Pa02100 mmHg, and PaCO2 40 mm Hg. The child is being ventilated with 80% oxygen. What is the (A-a) P02
Correct Answer: 420.4 mm Hg
Description: D i.e. 420. 4 mm Hg PAO2 can be calculated by alveolar gas equation PAO2 = FIO2 x (Po - PH2O) - PaCO2 R Where: PA02 1,102 PB PH2O PaCO2 R = P02 of the alveolar air = Fraction of 02 in the air Barometric pressure (N-760 mm Hg) Water vapour pressure (N- 47 mm H20) Paial pressure of CO2 (N - 40 mm Hg) Respiratory quotient (CO2output= 200 ml 0 8 02 uptake 250 ml The data provided in the question is: Pa02 100 mm Hg PaCO2 * 40 mm Hg Fi02 * 8 mm Hg Fi02 - Fraction of inspired Oxygen At sea level (760 mm Hg pressure), the composition of air - 02 = 20%; N2 = 80% 20 So Fi02 is - = 0.2 100 In this question, the child is being ventilated with 80% 02 80 So Fi02 is ___ = 0.8 100 Substituting these values PAO2 = 0.8 x (760-47) - 40/0.8 = 520.4 mm Hg Therefore PAO2 - Pa02 = (520.4 mm Hg - 100 mm Hg) = 420.4 mm Hg.
Category:
Physiology
Get More
Subject Mock Tests
Practice with over 200,000 questions from various medical subjects and improve your knowledge.
Attempt a mock test nowMock Exam
Take an exam with 100 random questions selected from all subjects to test your knowledge.
Coming SoonGet More
Subject Mock Tests
Try practicing mock tests with over 200,000 questions from various medical subjects.
Attempt a mock test now