Detection, localization and quantification of intracardiac shunts are one of the most important exercises in cardiac catheterization. In most cases a preliminary clinical evaluation will give us knowledge of the possible intracardiac shunt.
The pointers to the presence of a shunt are:
1) Unexplained arterial desaturation (arterial saturation < 95 per cent) suggestive of a right to left shunt and representing alveolar hypoventilation.
2) Unexpectedly high pulmonary artery saturation > 80 per cent-suggestive of a left to right shunt.
3) When data at catheterization does not confirm a particular lesion.
Detection of left to right intracardiac shunts—Measurement of blood oxygen saturation and content in the right heart (oximetry run)
Oximetry run is a basic technique for detecting and quantifying intracardiac shunts.The oxygen content or per cent saturation is measured in blood samples drawn sequentially from PA, RV, RA, SVC and IVC. A significant step-up is defined as an increase in the blood oxygen content or saturation that exceeds the normal variability that might be observed if multiple samples were drawn from that cardiac chamber. Oxygen content can be calculated from the knowledge of percentage saturation, the patient’s hemoglobin concentration and an assumed constant relationship for oxygen carrying capacity of hemoglobin (1.36mL O 2 /g hemoglobin).
Sites for Oximetry Run
Draw 2ml blood from the following recommended sites:
Left and/or right pulmonary artery
Main pulmonary artery
Right ventricular outflow tract
Right ventricle — mid
Right ventricle — tricuspid valveor apex
Right atrium — low or near tricuspid valve
Right atrium — mid
Right atrium — high
SVC — low — near junction with RA
SVC — high — near junction with innominate vein
IVC — high — just at or below the diaphragm
Left ventricle
Aorta - distal to insertion of ductus
Abbreviations:
SVS and IVC, superior and inferior vena cavae
RA, right atrium: RV, right venricule
PA, pulmonary artery
VSD, ventricular septal defect
TA, tricuspid regurgitation
PDA, patient ductus arteriosus
RP, pulmonic regurgitation
ASD, atrial septal defect
SBFI, systemic blood flow index
Q p /Q s , pulmonary to systemic flow ration.
To perform an oximetry run, an end hole catheter like Swan-Ganz balloon floatation catheter is used, and is positioned in the left or right pulmonary artery. Cardiac output is measured by the Fick method.
Calculation of Pulmonary Blood Flow (Q p )
Pulmonary blood flow is calculated by the formula:
O 2 consumption (mL/min)
PV O 2 PV O 2
content content
(mL/L) (mL/L)
Note that if the pulmonary vein has not been entered, systemic arterial oxygen content may be used, if systemic arterial oxygen saturation is > 95 per cent.
If the systemic oxygen saturation is < 95 per cent, it is necessary to determine the presence of a R Æ L shunt.
Calculation of Systemic Blood Flow (Q s )
The following formula is used for calculation of systemic blood flow:
The pointers to the presence of a shunt are:
1) Unexplained arterial desaturation (arterial saturation < 95 per cent) suggestive of a right to left shunt and representing alveolar hypoventilation.
2) Unexpectedly high pulmonary artery saturation > 80 per cent-suggestive of a left to right shunt.
3) When data at catheterization does not confirm a particular lesion.
Detection of left to right intracardiac shunts—Measurement of blood oxygen saturation and content in the right heart (oximetry run)
Oximetry run is a basic technique for detecting and quantifying intracardiac shunts.The oxygen content or per cent saturation is measured in blood samples drawn sequentially from PA, RV, RA, SVC and IVC. A significant step-up is defined as an increase in the blood oxygen content or saturation that exceeds the normal variability that might be observed if multiple samples were drawn from that cardiac chamber. Oxygen content can be calculated from the knowledge of percentage saturation, the patient’s hemoglobin concentration and an assumed constant relationship for oxygen carrying capacity of hemoglobin (1.36mL O 2 /g hemoglobin).
Sites for Oximetry Run
Draw 2ml blood from the following recommended sites:
Left and/or right pulmonary artery
Main pulmonary artery
Right ventricular outflow tract
Right ventricle — mid
Right ventricle — tricuspid valveor apex
Right atrium — low or near tricuspid valve
Right atrium — mid
Right atrium — high
SVC — low — near junction with RA
SVC — high — near junction with innominate vein
IVC — high — just at or below the diaphragm
Left ventricle
Aorta - distal to insertion of ductus
Abbreviations:
SVS and IVC, superior and inferior vena cavae
RA, right atrium: RV, right venricule
PA, pulmonary artery
VSD, ventricular septal defect
TA, tricuspid regurgitation
PDA, patient ductus arteriosus
RP, pulmonic regurgitation
ASD, atrial septal defect
SBFI, systemic blood flow index
Q p /Q s , pulmonary to systemic flow ration.
To perform an oximetry run, an end hole catheter like Swan-Ganz balloon floatation catheter is used, and is positioned in the left or right pulmonary artery. Cardiac output is measured by the Fick method.
Calculation of Pulmonary Blood Flow (Q p )
Pulmonary blood flow is calculated by the formula:
O 2 consumption (mL/min)
PV O 2 PV O 2
content content
(mL/L) (mL/L)
Note that if the pulmonary vein has not been entered, systemic arterial oxygen content may be used, if systemic arterial oxygen saturation is > 95 per cent.
If the systemic oxygen saturation is < 95 per cent, it is necessary to determine the presence of a R Æ L shunt.
Calculation of Systemic Blood Flow (Q s )
The following formula is used for calculation of systemic blood flow:
O 2 consumption (mL/min)
SA O 2 MV O 2
content content
(mL/L) (mL/L)
Mixed Venous Oxygen Content (MVO 2 )
For Mixed Venous Oxygen content, the formula validated by Flamm and associates is used:
(3 SVC O 2 + 1 IVC O 2)/4
Calculation of Left to Right Shunt
The formula used for calculation of left to right shunt is:
L Æ R Shunt = Q p - Q s
(L/min)
Flow Ratio
The ratio of Qp/Qs gives us the important physiologic information of the magnitude of left to right shunt.
Q p (SA O 2 - MV O 2
Q s ( PV O 2 - PA O 2 )
A QP/Qs value of <1.5 signifies a small left to right shunt and often may not require surgical correction. However, a Qp/Qs value of e” 2 indicates a large left to right shunt requiring surgical correction. Shunts of 1.5-2 are intermediate and surgery is recommended if the operative risk is low. A shunt of <1.0 indicates the presence of right to left shunt and irreversible pulmonary vascular disease.
Bidirectional Shunts
The formula used for calculating bidirectional shunts is:
O 2 consumption (mL/min)
PV O 2 MV O 2
content content
(mL/L) (mL/L)
The approximate left to right shunt is Qp – Q eff and the approximate right to left shunt is Qs –Qeff
SA O 2 MV O 2
content content
(mL/L) (mL/L)
Mixed Venous Oxygen Content (MVO 2 )
For Mixed Venous Oxygen content, the formula validated by Flamm and associates is used:
(3 SVC O 2 + 1 IVC O 2)/4
Calculation of Left to Right Shunt
The formula used for calculation of left to right shunt is:
L Æ R Shunt = Q p - Q s
(L/min)
Flow Ratio
The ratio of Qp/Qs gives us the important physiologic information of the magnitude of left to right shunt.
Q p (SA O 2 - MV O 2
Q s ( PV O 2 - PA O 2 )
A QP/Qs value of <1.5 signifies a small left to right shunt and often may not require surgical correction. However, a Qp/Qs value of e” 2 indicates a large left to right shunt requiring surgical correction. Shunts of 1.5-2 are intermediate and surgery is recommended if the operative risk is low. A shunt of <1.0 indicates the presence of right to left shunt and irreversible pulmonary vascular disease.
Bidirectional Shunts
The formula used for calculating bidirectional shunts is:
O 2 consumption (mL/min)
PV O 2 MV O 2
content content
(mL/L) (mL/L)
The approximate left to right shunt is Qp – Q eff and the approximate right to left shunt is Qs –Qeff
No comments:
Post a Comment
Note: Only a member of this blog may post a comment.