Given the following data, calculate a patient's tissue O2 ...

[Mr.Thesaxman]

Given the following data, calculate a patient's tissue O2 delivery. SaO2: 95 PaO2 90 mm Hg Hb: 14 g C.O.: 4.5 liters/minute
 
  A. 530 ml O2/minute
  B. 580 ml O2/minute
  C. 701 ml O2/minute
  D. 810 ml O2/minute

Question 2

In which of the following conditions does the arterial-mixed venous O2 content difference (aO2 difference) become misleading when it is used to assess tissue O2 extraction?
 
  A. cardiogenic shock
  B. septic shock
  C. neurogenic shock
  D. anaphylactic shock

[ndhahbi]

Answer to Question 1

ANS: D
A. Incorrect response: See explanation D.
B. Incorrect response: See explanation D.
C. Incorrect response: See explanation D.
D. Correct response: The calculation of the tissue O2 delivery (DO2) is as follows:
STEP 1: Determine the arterial O2 content.
Arterial O2 content = (SaO2  Hb  1.34 ml O2/g Hb) + (PaO2  0.003 vol/mm Hg)
= (0.95)(14 g Hb/100 ml blood)(1.34 ml O2/g Hb) + (90 mm Hg  0.003 vol/mm Hg)
= 18.09 volumes
= 18.09 ml O2/100 ml blood
STEP 2: Express the arterial O2 content 18.09 ml O2/100 ml blood as ml O2/ml blood.
18.09 ml O2/100 ml blood = 0.180 ml O2/ml blood
STEP 3: Calculate the DO2 using the formula below:
DO2 = (SaO2  Hb  1.34 ml O2/g Hb)C.O.
= (arterial O2 content)(C.O.)
= (0.180 ml O2/ml blood)(4500 ml blood/min)
= 810 ml O2/minute
Alternatively, the formula for the DO2 is:
DO2 = CaO2  C.O.  10

Answer to Question 2

ANS: B
A. Incorrect response: The aO2 difference is useful in managing patients with primary cardiovascular compromise. An aO2 difference of less than 5 volumes (i.e., 5 ml O2/dl) in a patient with cardiogenic shock suggests adequate O2 extraction from the blood.
B. Correct response: In septic shock, the capability to increase O2 extraction from the blood is lost because of systemic shunting. Therefore, using the aO2 difference as an index of the tissue O2 extraction during septic shock is misleading. An aO2 difference value of 5 ml O2/dl may be present in a patient with septic shock; however, this patient may have poor extraction capabilities from the systemic disease.
C. Incorrect response: See explanation B.
D. Incorrect response: See explanation B.