Arterial Line Accuracy - help!

[MarySunshine]

Hi Everyone,

I come from an ICU that used arterial lines frequently and I considered myself competent and knowledgable on them. I have encountered a new practice on my traveling assignment and I need advice and further arterial line insight from you all.

While it was considered common knowledge at my old ICU that art lines must remain at a fixed point (heart level is where we put them) in order to be consistent and accurate, they do NOT do that on this unit. They actually tape the transducer (which in this set up is only about 6 inches from the insertion site) to the patient's arm. I've always had a set up where the tranducer was about 2 feet from the insertion site and I would fix it at heart level to the bed or to a standing pole in the room.

It was considered common knowledge about my unit that if the tranducer was too low then it was an inaccurately high reading and it was was too high it was an inaccurately low reading.

I've checked the protocol and it says NOTHING about setting the transducer to a fixed point.

When checking for a cuff pressure correlation the MAPS often do correlate fairly well, even with the tranducer lying in the patient's lap. But the systolics vary and I just can't get used to this. I had a patient last night whose BP was apparently higher than his set parameters when he arm was on the bed but when I raised his arm to heart level MAGICALLY he was within parameters! But apparently, the arm lying wherever it may lie is the set up that they use.

What am I missing here? This is a MAJOR teaching hospital and my unit is full of experienced ICU nurses.

[RNperdiem, RN]

Unless the transducer is dangling over the side of the bed, the readings should be fine. If the patient's arm is resting on the bed, it will be at heart level, even as the bed is raised and lowered. I have seen both ways-on the patient or mounted on a block.

[cardiacRN2006, ADN, RN]

We tape our transducers to a little pad (hunk of rolled up washcloths) and lay it as close to the phlebostatic axis as we can. If it moves around in bed then it's no biggie, but the numbers will be inaccurate. So if it's not staying where it should, then every hour I replace it to get an accurate reading. But usually it doesn't move.

[ChelleChelle]

MarySunshine,

It sounds to me like you are describing the difference between "pole-mount" transducers mounted on an IV pole in a transducer holder with the transducer stop-cock at the level of the phlebostatic axis and "patient-mount"............where the transducer is attached to the patient usually via a garter belt type system or taped either to the patient or to a small towel roll. In EITHER case...........you are correct in that the transducer stop-cock is supposed to be leveled to the phlebostatic axis when you are recording readings. (We rezero every 4 hours.......or whenever the readings are "iffy".

I haven't noticed a great difference in the patients that I care for between pole-mount and patient mount, but personally I prefer patient mount............as "extra tubing" could tend to increase or amplify catheter whip, spike or overshoot and error.

However amongst the 4 ICU's in my hospital, there is GREAT debate whether pole mount or patient mount is better..........and folks who are convinced that one or the other is ABSOLUTELY the only way to go.

Currently our cardiac unit is the only unit that insists on pole mount, the other 3 all go with patient mounts.

If the transducer is high the reading could be FALSELY low; if the transducer is low, the reading could be FALSELY high........why bother with numbers you can't trust??? I make sure I can trust the numbers by keeping the transducers at the phlebostatic axis and by determining the following the trend between cuff and art line.

We handle arterial lines the same as PA lines in the following expected practices:

See attached PA practice alert.

Meaning the expected practice is:

1. The RN does a square wave test at the beginning of each shift and whenever the art line appears dampened or distorted

2. The transducer stop-cock is level with the phlebostatic axis and the patient is supine with the HOB up no greater than 60 degrees when readings are recorded.

3. I also correlate the arterial line with a manual pressure in both arms at the beginning of my shift; manual pressure in the arm without the art line in it; occlusion pressure in the arm in which the art line is placed. Or manual pressure in both arms if the art line is somewhere other than a brachial or radial artery.

I'll try to look it up in the AACN procedure manual and get back to you tomorrow................ about whether it mentions anything about pole mount versus patient mount, but I doubt it does.

PA Catheter Practice Alerts.pdf

[MarySunshine]

Thanks everyone! So, in the case of this particular set-up, I should physically walk into the room and raise the patient's arm so that the transducer is level with the phlebostatic axis each time I want a blood pressure reading? That seems ridiculous. It's NOT continuous blood pressure monitoring if I have to go in there and do that every time I want a pressure! Also, no one else does this so the monitoring won't be consistent at all. Everyone else just goes "Okay, the MAPS are the same when we take a cuff pressure!" and then just takes the reading at face value with the transducer IN THE BED.

RNPerDiem, in this case it is not at heart level because the transducer is actually right by the patient's wrist, so if the patient's HOB is at 30 degrees there's at least a foot of distance to heart level.

[cardiacRN2006, ADN, RN]

I should physically walk into the room and raise the patient's arm so that the transducer is level with the phlebostatic axis each time I want a blood pressure reading? That seems ridiculous.

No, you don't have to do it every hour. You have to do that if your transducer is not staying put in bed and it's giving you inaccurate readings. That's pretty rare. Usually my towel/washcloth bundle stays put.

Plus, I don't know about everybody else, but I'm in my patient's room way more than just once every hour, so it's no bid deal to just re-adjust the transducer if needed...