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#1
07-10-2010
 USMLE Forums Veteran Steps History: 1 + CS Posts: 209 Threads: 34 Thanked 119 Times in 52 Posts Reputation: 149
High Hemoglobin Saturation yet low Oxygen content!

An adult Hb is 98% saturated with oxygen but his arterial oxygen content is decreased . The most likely cause of this condition is

A) anemia
B) an AV shunt
c) hemoglobinopathy
D) high altitude hypoxia
E) pulmonary diffusion defect
 The above post was thanked by: sm3356 (06-16-2015)

#2
07-10-2010
 USMLE Forums Scout Steps History: Step 1 Only Posts: 82 Threads: 8 Thanked 116 Times in 49 Posts

i think its option A. Anemia
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#3
07-10-2010
 USMLE Forums Veteran Steps History: 1 + CS Posts: 209 Threads: 34 Thanked 119 Times in 52 Posts Reputation: 149

can u explain /???

#4
07-10-2010
 USMLE Forums Addict Steps History: 1+CK+CS Posts: 187 Threads: 4 Thanked 408 Times in 130 Posts Reputation: 438

The formula for oxygen content is as follows:

1.34 x Hb x SaO2 / 100 + 0.0031 x PaO2.

The two most important determinants of this equation are Hb and SaO2, because PaO2 has a minor coefficient and affects the equation only when referring to high depths (where the high atmospheric pressure results to a coefficient much larger than 0.0031).

Given that SaO2 is high (by the question stem), the only variable that may affect the equation is Hb.

Hb levels fall in blood loss and hemoglobinopathy. But in hemoglobinopathy, SaO2 would also be affected (contrary to what the question stem gives), because mutated hemoglobins don't have the same affinity for O2 as HbA does. Furthermore, one wouldn't expect to diagnose a hemoglobinopathy in an adult for the first time.

So, the most probable cause of low Hb levels, that in turn lead to low O2 content, is anemia indeed.
 The above post was thanked by: abeeraltaf (11-03-2010), drHubaishi (12-07-2013), Sabio (07-10-2010), sm3356 (06-16-2015)
#5
07-10-2010
 USMLE Forums Newbie Steps History: Not yet Posts: 2 Threads: 0 Thanked 0 Times in 0 Posts Reputation: 10

An adult Hb is 98% saturated with oxygen but his arterial oxygen content is decreased . The most likely cause of this condition is

A) anemia

 Tags Hematology-, Physiology-, Step-1-Questions

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