CASE FILES: BIOCHEMISTRY
A N SW E R S TO C A SE 17: C A R B O N M O N O X ID E
PO ISO N IN G
Two elderly patients, with no medical problems present with acute
mental status change, fatigue, red lips, and nausea after being snowed in their
home during a blizzard with warmth provided by a furnace. The carboxyhe-
moglobin level is elevated.
Most likely cause: Carbon monoxide poisoning (increase
Rationale for treatment: Administration of 100 percent O2 displaces
CO from hemoglobin.
C L IN IC A L C O R R E L A T IO N
Carbon monoxide, a molecule with one carbon and one O2 atom, binds very
avidly to hemoglobin. It is a colorless and odorless gas and may arise from
internal combustion engines, fossil-fueled home appliances (heaters, furnaces,
stoves), and incomplete combustion of almost all natural and synthetic materials.
Because it does not give warning signs, CO is considered a significant hazard.
The patient generally has confusion and symptoms of O2 deprivation, but not
the symptoms of dyspnea, since the hemoglobin is saturated. The lips are a
distinct red color as a result of the hemoglobin being “oxygenated.” However,
because CO binds so avidly to the hemoglobin, no transfer of O2 occurs in the
peripheral tissue. Carbon monoxide also disrupts the O2-dependent steps of the
electron transport chain, leading to unavailability of ATP. Treatment is thus 100
percent O2 to displace the CO from the hemoglobin, and in severe cases, hyper-
baric therapy to increase the amount of O2 available to “drive out” the CO.
A PPR O A C H TO E L E C T R O N T R A N SF E R C H A IN (E T C )
A N D C A R B O N M O N O X ID E
Understand the process by which CO causes symptoms.
Know how CO disrupts O2 transport and uncouples the ETC.
Oxidase: An enzyme requiring molecular O2 as a substrate to produce
water as a reduced product. In the case of cytochrome oxidase, water is
the only product of oxygen reduction. With some other oxidases (called
mixed function oxidases), one atom of molecular oxygen is converted to
water, whereas the other atom of oxygen may be a hydroxylated product.