To answer your question, not all pts are able to have a pulm caths. It has to be maintained by nurses who are trained to use them. However, you can get a CVP reading from other things (not just pulm catheters). Most pts who have a central line (non-valved) can have CVP readings. So, if you have a jugular central line, a subclavian central line, or even a non-valved PICC line, you can get CVP readings. A CVP reading equals your right atrial pressure. PICCs, subclavians, and jugular lines terminate in the superior vena cava, or the junction of the vena cava and the atrium, so all you do is hook-up a CVP transducer and you can get the reading. (Sometimes, a CVP reading from a non-valved PICC isn't really that accurate, but it's better than nothing!). So, if a pt has a central line and they become septic, go into shock, or have issues with volume overload or depletion, you can get a reading without inserting a pulm cath. It can give you a good idea of their volume status or give some hints to right side of the heart.
And remember that pulmonary artery catheters not only look at the left side of the heart, but the right side as well (where as a CVP only looks at the right). PA caths give readings for the right side of the heart and the pulmonary artery. After you inflate the balloon and "wedge" it, you are able to get a reading for the left side of the heart b/c the balloon occludes the pressure behind it (basically). So, you get the right and the left. And, if you have any pulmonary issue like COPD or a PE, it can through off some of the readings. That one of the things the nurses are trained to do. They have to be able to pick out, interpret, and trouble shoot issues that can happen with PA caths.
Arterial lines not only have the ability to get real time B/P's and abg blood draws, they can also be hooked up to certain monitors that can read cardiac output, stroke volume, and systemic vascular resistance. It's a lot of great information for just a simple peripheral line. So, if a pt can't have a pulm cath, they can have a central line for CVPs and an a-line for b/p and cardiac output, which are much more minimally invasive compared to a PA cath.