Quiz #23 Answer: Shunt Calculcation (VSD with Eisenmenger)

Answers are in red fonts against the questions.

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Hypothetical case: 32 year old male with VSD and Eisenmenger syndrome. Necessary data are given.

Questions:

1)      What is the overall Qp/Qs?...1.0

2)      Calculate the effective pulmonary blood flow (Qep)….1.17 L/min/m²

3)      Calculate the amount of right to left shunt….0.35 L/min/m²

4)      Calculate the amount of left to right shunting….0.35 L/min/m²

(From Science and Practice of Pediatric Cardiology, 1990 ed. Page 921)

·         O2 content at 100% saturation is 17 g x 1.36 = 23.12 g%.

·         Qp:

=  (0.95 – 0.60) g% = 120/8.0 (x10 to convert to L/min/m2)

= 120/80 = 1.5 L/min/m².

·         Qs:

Qs = 120/23.1 (0.85-0.50) g% = 120/8.0*10 = 1.5 L/min/m².

Qp/Qs = 1.0

·         Effective PBF  (Qep):

Qep – 120/23.1(0.95-0.50) g% = 120/10.4 (x10 to convert to L/min/m²)

= 120/104 = 1.17 L/min/m².

(Both 1.15 and 1.17 are correct depending upon the calculation step at which you round the numbers. 1.15 is more correct than 1.17)!

·         R-L shunt:

(Qp – Qep) = 1.5 – 1.15 = 0.35 L/min/m²

(Pulmonary blood flow includes Qep + R-L shunt via VSD. Therefore, R-L shunt is Qp – Qep)

·         L-R shunt:

(Qs – Qep) = 1.5 – 1.15 = 0.35 L/min/m².

(Systemic blood flow includes Qep + L-R shunt via VSD. Therefore, L-R shunt is Qs – Qep).