Disposable NIBP Protector

Mitigate NIBP and auscultation errors by observing the plethysmographic waveform on the pulse oximeter and noting the mean arterial pressure
"If there's a place you want to go, I can take you there, I know, I'm the map. If there's a place you need to go, I bet I can take you there, and I'm the map. I'm the map, I am the map, I am the map!" - Dora the Explorer
Many millennial medical staff may happily sing along while reading this, while their parents and older colleagues with children may still be using cheese graters on the forebrain to erase memories.
Don't worry, baby boomer medics, I won't start singing the "Barney" theme song next, but I do want to show a little love for an often overlooked vital sign parameter, mean arterial pressure (map).We need to pay more attention to the small number in parentheses next to the NIBP reading, as it is one of the more reliable measurements of perfusion that we can assess.
Back in 2011, I wrote a column titled "Tips and Tricks for EMS Blood Pressure Readings."This column, along with Mike McEvoy's "Five Mistakes That Are Causing Your Blood Pressure Readings to Be Inaccurate," appears frequently on social media and EMS blogs whenever a new EMT seeks help on how to get an accurate blood pressure while moving to an ambulance.
And always in those comment threads, some wise old paramedics point out that NIBP readings are notoriously inaccurate and that you should "treat the patient, not the monitor".Usually, he would suggest that if they don't completely abandon the NIBP machine, they should at least get the first pressure manually.He's right, NIBP machines are notoriously inaccurate.Even device makers say so.Read your heart monitor's operator's manual and hide a disclaimer somewhere in it that in our patients who need accurate BP the most - patients on both ends of the scale - the NIBP reading on your screen may not be, um, actual blood pressure.
If I had a dollar for every EMT who confidently declared a BP ending in zero (150/90, 120/80, 110/70, every time) or a BP who pulled the stethoscope out of his ear and stuttered hesitantly Ended up with an odd number read on a meter with an even hash mark... well, I'd have a lot of dollars.Maybe not enough to buy the trendy double wide I've been eyeing for a long time, but it happens so often that I call a manual blood pressure monitor a paramedic polygraph.
If it were easy to auscultate blood pressure, we wouldn't be posting tips and tricks about how to do it every year or so.
However, although the NIBP cuff tends to significantly overestimate systolic blood pressure in shock, it achieves nearly the same MAP as invasive arterial monitoring.
In a study of 4,957 adult ICU patients in a tertiary care center, more than 27,000 blood pressure values ​​were obtained simultaneously with the NIBP and catheter-of-arterial sensors.Acute kidney injury and mortality were higher in the systolic NIBP-measured group than in the group with arterial systolic blood pressure in the same range (< 70 mmHg).1
When comparing acute kidney injury prevalence and ICU mortality between arterial MAP and noninvasive MAP, the differences were small, and the lead study authors concluded that NIBP overestimated systolic blood pressure in the state of shock, but not by the noninvasive blood pressure cuff. The obtained MAP correlations were very close to arterial MAP (Figures 1 and 2).
So why are NIBP machines so accurate at measuring MAP but so unreliable at measuring systolic blood pressure?The answer is that what the NIBP machine actually measures is MAP.Their calculated blood pressure.
This is the exact opposite of how we do it manually; we auscultate Korotkoff to determine systolic and diastolic blood pressure, and then mathematically derive mean arterial pressure from the following equation:
Many of us learned this calculation in nursing school and then quickly forgot, because most of our treatment parameters are related to systolic blood pressure, and because we hate math.It turns out that NIBP machines that derive blood pressure from MAP and pulse rate are not much better at math than we are.
Most people who have been in the back seat of an ambulance for more than five minutes realize that a smiling, pink grandma who weighs 90 pounds and has a blood pressure of 84/60 is nothing like a man who weighs 250 pounds and has a blood pressure of 90./40.For grandma, it could be her daily blood pressure, her vital organs are well perfused.For the burly, gray-skinned, sweaty truck driver, despite his high systolic blood pressure, he was under-perfused.
Most sources consider a MAP of 65 mmHg to be the lowest threshold for vital organ perfusion, with a normal MAP range of 70-110 mmHg.Human kidneys are more sensitive to hypoperfusion, although some animal studies have shown that bleeding rats (did you know rats have the same MAP as humans?) can tolerate MAPs as low as 50 mmHg for up to 90 minutes.Acute kidney injury begins within 20 minutes with a MAP below 60 mmHg.
So the next time you're wondering if your patient is a quart low but blood pressure isn't that bad, watch the plethysmographic waveform on your pulse oximeter, if you're believing NIBP blood pressure in between Indecisive doesn't really match the patient's clinical presentation, or your partner's lying ear, pay more attention to that little number in parentheses next to your NIBP reading.MAP will not lead you in the wrong direction.
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Kelly Grayson, NRP, CCP, is a critical care paramedic in Louisiana.For the past 24 years, he has served as a field paramedic, critical care transport paramedic, field supervisor and educator.He is the president of the Louisiana EMS Educators Association and a board member of the Los Angeles National Registered EMT Association.
He holds an associate degree in general studies from Nunez Community College, Louisiana State University Eunice.Kelly was recognized as the 2016 Louisiana Paramedic of the Year, the 2002 Louisiana EMS Instructor of the Year, and the 2002 Louisiana AHA District Teacher of the Year, and was the recipient of the 2012 Best Regular Featured Web Column/Industry Maggie Award and 2014 Best Online Column at the Annual Folio Eddie Awards.He is a frequent speaker at EMS conferences, has contributed to various EMS training materials, and is the author of the popular blog A Day In a Day In a Ambulance Driver, "En Route: A Paramedic's Stories of Life, Death and Everything Inbetween" and "Live: More Stories About Life, Death, and What's In Between".You can follow him on Twitter (@AmboDriver), Facebook, LinkedIn, or email kelly@ambulancedriverfiles.com.Kelly is a member of the EMS1 Editorial Advisory Board.
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