To snowblack or anyone who can help me - okt3

[ArchivalUser]

Thank you for posting this question and discussion with folks were intersting but I would like to ask you few basic definition about the concept.

I went through Goljan's notes you mentionned and I think we need to make the difference between:

PaO2, and SaO2.

Here is the question you posted:

Mr Joker was rushed into ER this afternoon with dyspnea, tachycardia and cyanosis.
Pulse Ox = 80% on arrival. No bleeding observed. Hct = 15%. PCO2 = 50%.
You, on duty, gave 100% O2 over 5 min but Joker's SaO2 remains at 80%.
Your diagnostic cause ?

a) ventilation defect
b) perfusion defect
c) myocardal infarction
d) hydronephrosis
e) anemia

PaO2=Pressure keeping O2 dissolved in plasma of arterial blood.

SaO2=Average percentage of O2 bound to Hb.

I-Ventilation defects
Impaired O2 delivery to alveoli
-----Example-respiratory distress syndrome with collapse of the distal airways
No O2 exchange in lungs that are perfused but not ventilated
Produces intrapulmonary shunting of blood

*******Administration of 100% O2 does not increase the Pao2.

II-Perfusion defects
Absence of blood flow to alveoli
----Example-pulmonary embolus
No O2 exchange in lungs that are ventilated but not perfused
Produces an increase in pathologic dead space
******Administration of 100% O2 increases the Pao2.

Source: Goljan RR


In my understanding, SaO2 decrease in case of CO poisoning and Methemoglobinemia with normal PaO2 and in case of respiratory acidosis with decrease PaO2.

I am confused do you mean PaO2 or SaO2 in this question?

Pulse oximetry measures SaO2, since Goljan talk about PaO2 change with 100% O2 make the difference between Perfusion-ventilation, can we use SaO2 to determine the level of PaO2 or arterial blood gases?

Thank you for your help and God Bless you All.

[ArchivalUser]

any1??????

[ArchivalUser]

okt3, honestly i do not understand the whole question. i dont know why 100% o2 does not increase Sao2.
even in ventilation defect. or intrapulmonary shunt.

[ArchivalUser]

I think the qs is made by snowblack while read Goljan notes, but the concept given by Papi is about PaO2 and 100% O2 to make the diff. between V-Q, not SaO2, anyway thank you for input.

[ArchivalUser]

i think the cause is anemia,So2 can decrease by 2 ways ,shift of o2 from bound form to the dissolved form or decrease the total no of
Hb molecules which happen here ......HC is very low
correct me if i am wrong

[ArchivalUser]

giving O2 via anything will definitely not increase O2 saturation in perfusion defect because the blood can't reach the smaller vessels in the alveoli for effective O2 loading so that Hb can't be as saturated as you want it to be.