CLINICAL CASES
161
[17.2] Which of the following treatment strategies is the most effective reme-
diation for CO poisoning?
A. Removal from CO source
B. Removal from CO source and administration of 100 percent O2
C. Administration of 5 to 7 percent CO2 to stimulate respiration followed
by 100 percent O2
D. Administration of 5 to 7 percent CO2 to stimulate respiration
E. Removal from CO source and administration of 5 to 7 percent CO2
to stimulate respiration
[17.3] In addition to forming carboxyhemoglobin, the toxic effects of CO
include inhibition of which of the following enzymes involved in
oxidation-reduction reactions?
A. NADPH dehydrogenase
B. Coenzyme Q reductase
C. Cytochrome c reductase
D. Succinate dehydrogenase
E. Cytochrome oxidase
A nsw ers
[17.1]
C. Carbon monoxide binds to hemoglobin with 220 times the affinity
of O2. Thus CO displaces O2 from oxyhemoglobin to form carboxy-
hemoglobin. Carbon monoxide has no appreciable effect on pH such
as CO2 may have. It does not change the valence state of iron or inter-
fere with O2 transport across membranes. CO binding does not
change myoglobin to hemoglobin.
[17.2]
B. Removal from the CO is always the first step. Increasing the O2
concentration serves to displace the CO to hemoglobin and
cytochrome oxidase. Adding CO2 may stimulate respiration rate, but
it also causes an additional pH perturbation.
[17.3]
E. Carbon monoxide binds to cytochrome oxidase but not to the other
enzymes listed.
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