Questions regarding cardiac catheterisation and oxygen saturation levels can seem daunting at first but a few simple rules combined with logical deduction can usually produce the answer.
Let's start with the basics:
The table below shows the oxygen saturations that would be expected in different scenarios:
| Diagnosis & notes | RA | RV | PA | LA | LV | Aorta |
|---|---|---|---|---|---|---|
| Normal | 70% | 70% | 70% | 100% | 100% | 100% |
| **Atrial septal defect (ASD)**The oxygenated blood in the LA mixes with the deoxygenated blood in the RA, resulting in intermediate levels of oxygenation from the RA onwards | 85% | 85% | 85% | 100% | 100% | 100% |
| **Ventricular septal defect (VSD)**The oxygenated blood in the LV mixes with the deoxygenated blood in the RV, resulting in intermediate levels of oxygenation from the RV onwards. The RA blood remains deoxygenated | 70% | 85% | 85% | 100% | 100% | 100% |
| **Patent ductus arteriosus (PDA)**Remember, a PDA connects the higher pressure aorta with the lower pressure PA. This results in only the PA having intermediate oxygenation levels | 70% | 70% | 85% | 100% | 100% | 100% |
| VSD with Eisenmenger's | 70% | 70% | 70% | 100% | 85% | 85% |
| PDA with Eisenmenger's | 70% | 70% | 70% | 100% | 100% | 85% |
| ASD with Eisenmenger's | 70% | 70% | 70% | 85% | 85% | 85% |
Interpretation:
Normal Pattern
Left heart
Aorta-------120-140/70-90 ( pressure)---------98% (saturation)
LV------------120-140/5-10---------------98%
LA------------10-15/0-2------------------98%
Right heart
RA------------0-8 (mean pressure)------74%
RV-----------15-30/4-8----------------74%
PA-----------15-30/3-12---------------74%
SVC-----------------------------------74%
IVC------------------------------------70%
PCWP--------1-10 ( mean)