How far to the right atrium?
As one shoves the catheter deeper and deeper, the distal lumen is transduced; the resulting pressure waveforms are one's guide to the catheter's position
- 10-15cm from the subclavian vein, 15-20cm from the jugular vein, 30-40cm from the femoral vein
- The right ventricle is another 10cm, and the pulmonary artery is another 10 cm after that.
In the Superior Vena Cava and the right atrium
The introducer sheath goes in first. Before the PA catheter is threaded in, the distal lumen is connected to a CVP transducer, so the pressure wave can be observed. The pressure here will be 1-6mmHg.
Atrial fibrillation may be encountered at this stage as the catheter tip tickles the atrium.
In the right ventricle
Once you are past the tricuspid valve, you suddenly get a nice pulsatile waveform, which is the right ventricular contraction.
The systolic pressure here should be between 15 and 30mmHg. The diastolic should be same as right atrial pressure, about 1-6mmHg (makes sense given that the right ventricle fills from the right atrium).
Not always is the waveform so pretty; mitral regurgitation may give a large v-wave, which may be confused for a pulmonary atrial wave. Additionally, a normal RV waveform may come and go, as the catheter tip flicks in and out of the ventricle. Its not a common place occurrence, but ventricular arrhythmias may be expected to happen here.
As soon as you are in the RV, and are seeing the pulse waveform, you can inflate the balloon with air. The volume is 1.5ml.
In the pulmonary artery
Past the pulmonary valve, one can now see the PA waveform, which resembles the waveform of any other artery. At this stage the diastolic pressure rises to about 6-12mmHg (due to flow resistance in the pulmonary arterial network) This is the fabled PA diastolic pressure, the PADP, which maintains a stable and reliable relationship with the PAWP.
Now, we wedge the catheter
The catheter with the inflated balloon is advanced further, until the PA waveform disappears, and a venous-looking waveform appears. This is the wedge waveform. It indicates that the pulmonary artery is occluded.
The pressure here should also be 6-12 mmHg, like the PA diastolic pressure. If it is different, it shouldn't be far off ( about 5mmHg) and this relationship should persists for some hours, so you can just use the PADP (this way you don't have to wedge repeatedly). Once you have found this wedging point, deflate the balloon passively, and fix the catheter in position.
DO NOT KEEP IT INFLATED. Bad things will happen.