art line vs cuff pressure

Why would an arterial line with a relatively good waveform be way off from a automatic cuff pressure. My cuff pressure was reading about 30 mm hg more on the SBP than the arterial line despite a good wave form; with arterial line being zeroed and leveled. I also checked my tubing to make sure all of my connections were tight. I took the cuff pressure on bilateral arms and it was very close in both arms but way off from my arterial line pressure. The patient was on multiple vasopressors so I was not sure which pressure to go by. The residents at the facility I work at wanted me to go by the arterial pressure. Looking back I obviously should have gotten a manual blood pressure and seen which was closest to that.
I'm not sure why either, especially seeing that you checked all your connections and such. I know from experience that NIBP monitors can give wacky readings. I remember once have a sepsis patient, she was not tachy, labs were off but not alarming, mental status unchanged but her NIBP kept saying 70 SPB. I mean like 2 other nurses plus the resident couldn't understand why her BP was so low, we all scratched our heads because it made no sense to us. We were so panicked by her BP we moved her from the main ED to the critical care bay where they took her BP and guess what it was..... 100/70. So yeah that taught me to do a good old fashioned manual lol, and to think no-one thought of doing a manual BP!So I mean if you had good waveform, zeroed line and everything I say the art line should be trusted over the NIBP and something was off with the NIBP.

I go by the arterial line. If the waveform is good and it's been zeroed and leveled to the phlebostatic axis the art line is more accurate than the cuff pressure. Also con side you may be using the wrong size BP cuff. A cuff that's too small gives a falsely elevated reading. A cuff that's too large gives a false low reading.

Also remember that with cuff pressure, the measured extremity needs to be at the level of the heart. Below the level of the heart, the reading can be falsely elevated, and above the level of the heart, you may get a false low reading.

MAP from the intra-arterial line would be the most reliable. There are many factors that could account for the difference, but generally we would go by the higher reading.

Disclosure: I'm still but a student... but I'm not inexperienced in taking manual BP's (about 24k of them, actually)I would expect that an A-line would be fairly accurate, as long as everything is appropriately set up. The NIBP autocuff could certainly read higher or lower if the cuff size isn't correct, the extremity isn't appropriately positioned, and so on. If you're getting that much of a difference between the A-line and the NIBP, I would suggest checking the cuff size, whether the cuff is at the same level as the heart, and also check the BP manually as sometimes patient movement artifact can appear to the machine to be an accurate measurement of BP. Don't forget to actually look at the patient and as long as the patient's doing OK, watch how the patient's BP's trend on the same machine, using the same equipment. Never be a stranger to manual BPs!

Absolutely. I hate the NIBP machines because: 1) they rely on excellent technique to give even vaguely reliable results, and much more often than not they get slapped on crooked, over gown or shirt sleeves, with a wrong size, with the microphone nowhere near the artery and the fit not snug enough to make for reliable compression, because users have no idea why these matter2) they are useless for any patient with arrhythmias, as they rely on the sounds of the blood at systole, and afib and others give irregular pulse pressure as well as irregular rate-- real ears can pick this up and/or correlate with the needle bouncing +/- concurrent visual on the EKG3) they are often not serviced regularlyPressure transducers do not drift; they fail, but they don't give false readings. Yes, they will give inaccurate readings if they aren't positioned at the phlebostatic axis (which changes when patient position changes, not just up and down but when turned to the side), but those aren't false readings. They also show you variable pulse pressures on afib, etc.