BOF: 3.44
In which of the following
people would the oxygen-haemoglobin dissociation curve be shifted to the left?
a)
A person living at high altitude
b)
An insulin dependent diabetic who has been admitted with signs of salt
and water depletion and Kussmaul’s respiration
c)
A patient brought into casualty having attempted suicide by shutting
himself in his garage and turning on the car engine
d)
A person who has been engaging in unaccustomed strenuous physical
exercise
e)
A patient in the febrile phase of vivax malaria
Answer: c)
The oxygen haemoglobin
dissociation curve is the curve relating percentage oxygen saturation of
haemoglobin to the partial pressure of oxygen. It is an S shaped curve.
The factors that cause the
curve to shift to the right and thereby increase oxygen delivery to tissues
are:
§
Increased 2,3 PG levels, which occur in people living at high
altitude and in people within 60 minutes of engaging in exercise. The rise may
not occur in trained athletes.
§
Acidosis causes the curve to shift to the right and this would
be the cause of the shift to the right in the diabetic patient who has salt
and water depletion and Kussmaul’s respiration or deep sighing respiration,
which indicates metabolic acidosis. These features suggest the patient has
diabetic ketoacidosis.
§
High temperature too causes the curve to shift to the right and
this would occur in the patient who has high fever in vivax malaria.
The factors that cause the curve to shift to the
left are as follows:
§
Carboxyhaemoglobin causes the curve to shift to the left and
this would have occurred in the patient who attempted suicide, as he would
have carbon monoxide poisoning.
§
Methaemoglobin
§
Haemoglobin F
§
High pH
§
Low temperature
§
Low 2,3 DPG levels
Revision Tip
Revise internal abnormalities of red cells ACES for
PACES page 363
