Calculation of Bidirectional Shunts Cross road both for examinee and examiner
May 07, 2015
Calculation of Bidirectional ShuntsCross road both for examinee and examiner
Shunt Run• “Shunt Run” is performed if a difference of 8% or more is noted in
blood sampling between chambers
Smaller physical, biggest physiological
Flamm’s
Flamm’s MVO2• Average Oxygen Content in Chambers proximal to the Shunt
• Method to calculate Mixed Venous Oxygen content
• Need to factor in Contribution from IVC and SVC which is not equal
• Flamm Equation:
3xSVC Oxygen Content + IVC Oxygen Content
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4
Dissolved O2
Fick Equation to Calculate Oxygen Content• Assumes in steady state that…
that rate of substance entering (C in x Qflow) is equal to the rate of substance leaving
(C out x Qflow) + the rate at which indicator, V, is added.
Flow= Oxygen consumption/Arterial-Venous oxygen content difference
• Where oxygen content is determined by automated methods
• oxygen consumption is assumed based on patient’s age, gender and body surface area when not directly measured
Fick’s
Puzzles of 6
• MVO2
• PAO2
• PVO2
• SAO2
• QP
• QS
Pulmonary Blood Flow
Systemic Blood flow
Qeff
In the Absence of Shunt in series•PBF=SBF=EBF
Left-to-right shunt• The approximate left-to-right shunt then = Q p - Q eff
Left to Right shunt
Left to right shunt
Effective Blood Flow• Fraction of Mixed Venous blood received by the lungs without
contamination from shunt(from left to right)
Right-to-left shunt• the approximate right-to-left shunt equals Q s- Q eff
Right to left shunt
Just understand ,do not mug it up