Shunt calculations

Question 1

O2 content of blood: depend on

Answer 1

Depend on O2 saturation and O2 carrying capacity

Question 2

Formula calc O2 content

Answer 2

O_(2 ) content= % saturation x [Hb] x 1.36 x 10

Question 3

How to detect cardiac shunting

Answer 3

Oximetry run

Calculation of pulmonary and systemic blood flow: Qp/Qs

Question 4

How to do oximetry run

Answer 4

• O2 content or saturation measured in blood samples drawn from PA → RV → RA → CrVC → CaVC
  o Shunt localized if significant step up (>normal variability) in O2 saturation/content
   RA: receives blood from 3 different venous sources: CrVC, CaVC, CS
• Can vary up to 2 vol%
   RV: max variation 1vol%
   PA: max variation 0.5vol%
  o If difference >8% btw PA and CrVC: L to R shunt is present
• Depending on location of step up, shunt can be localized

Question 5

Fick principle

Answer 5

At rest: O2 in - O2 out = O2 organ has used

CO = O2 consumption/arteriovenous difference

• O2 consumption: compare O2 content from arterial to venous blood
  o Arteriovenous O2 difference: arterial O2 – venous O2
  o Consumption of O2 by certain organ of body → in this case the lungs

Question 6

Shunt ratio calc

Answer 6

• L → R shunt: Qp – Qs (L/min)
  o Qp = SV or CO from RV
  o Qs = SV or CO from LV

Question 7

Qp equation

Answer 7

Qp=(O2 consumption (ml/min))/(PV O2 content (ml/L)-PA O2 content (ml/L))

Question 8

Qs equation

Answer 8

Qs=(O2 consumption (ml/min))/(SA O2 content (ml/L)-MV O2 content (ml/L))

Question 9

Shunt ratio Qp/Qs equation

Answer 9

Qp/Qs=((SA O2-MV O2))/((PV O2 -PA O2))

• SA O2: systemic arterial O2 saturation
• MV O2: mixed venous O2 saturation
• PV O2: pulmonary venous O2 saturation
• PA O2: pulmonary arterial O2 saturation

Question 10

Qeff equation

Answer 10

Qeff=(O2 consumption (ml/min))/(PV O2 content (ml/L)-MV O2 content (ml/L))

Question 11

What info is provided w/ Qp/Qs

Answer 11

• Important information about magnitude of shunting
  o <1.5 → small L to R shunt
  o >2 → large L to R shunt

Question 12

When is Qeff calculation useful

Answer 12

• Simultaneous R → L and L → R shunt
• Effective blood flow: flow that would exist in absence of shunting