5 CREDITS 10 MARKS

Question 1

1. Draw and explain O2 dissociation curve for normal, methb

Answer 1

shift to the left
methemoglobin (Fe3+) is unable to bind to Hb
remaining normal hb (Fe2+) have higher affinity to O2
harder to release O2 to tissue

Question 2

a. What is SPO2 and PaO2
b. what are the difference in reading in methemoglobinemia and why
b. how does giving O2 supplement change the readings?

Answer 2

a. SPO2 is the measurament of O2 bound to Hb while PaO2 measures O2 in plasma.
b. SPO2 can be low/normal or high as methemoglobin interferes with pulse oxymetry. PaO2 should be normal or a bit high as methemoglobin does not interfears with O2 dissolved in plasma
c. O2 supplement does not help to increase SPO2 but will definitely increase PaO2

Question 3

name 10 substances that can cause methemoglobinemia

Answer 3

Drugs: Benzocaine, lidocaine, dapsone, sulfonamides, nitroglycerin, and nitroprussides
Chemicals: Aniline dyes, nitrobenzene, nitrites, and certain herbicides
Recreational drugs: Amyl nitrite (poppers), nitrous oxide (laughing gas), and local anesthetics or painkillers used to “cut” cocaine
Contaminated water: Well water contaminated with nitrates, especially in rural areas