Blood Pressure Measurements: Arterial Line vs Oscillometric Cuffs

We all do this every single day. We measure target many of our interventions in the critically ill patients to blood pressure. Whether it’s fluids, vasopressors, or blood pressure lowering agents, we obsess over these parameters. We feel warm and fuzzy if it’s okay. But are we using the right tool to find out these numbers?

I’ve always harped on arterial lines, although invasive, being the most reliable method of evaluating the blood pressure in our patients. If someone is critically ill on jet fuel, they’re getting an a-line. This is a fun study where they compared the oscillometric BP cuffs to a-lines in 736 patients.

When you look at the mean differences they obtained, the numbers weren’t too bad.
Systolic: 0.8mmHg
Diastolic: -2.9mmHg
Mean Arterial pressure: -1mmHg

This wouldn’t drive any of us crazy, right? We’d be cool with these differences if it avoids invasive (painful) interventions on our patients. But wait, there’s more. There was a large amount of variability which could lead to additional interventions.
Systolic: ± 15.7mmHg
Diastolic: ± 11mmHg
MAP: ± 10.2mmHg

The article goes as far as to say that BP cuffs would not pass the Association for the Advancement of Medical Instrumentation standards. There’s no data as to how this changes outcomes.

This was a post hoc analysis (after the fact). This shouldn’t be too challenging to accomplish a prospective study looking at this in our critically ill patients. We have many patients who have a BP cuffs and an a-line in place. Why not just record cuff pressures every 15 minutes and obtain some data? Obviously it’s more complicated than that.

A hat tip to the authors.

T. Kaufmann, E.G.M. Cox, R. Wiersema, et al., Non-invasive oscillometric versus invasive arterial blood pressure measurements in critically ill patients: A post hoc analysis of a prospective observational study, Journal of Critical Care(2019)

Link to full article (not free)

Although great care has been taken to ensure that the information in this post is accurate, eddyjoemd, LLC shall not be held responsible or in any way liable for the continued accuracy of the information, or for any errors, omissions or inaccuracies, or for any consequences arising therefrom.

Oscillometric devices vs Arterial lines. New data.

Why is it important to stay up to date? There’s a pendulum in medicine but there’s a time when the pendulum swing is going to bite you in the butt and you’re going to be wrong. Seems like I’m wrong.

I have an extremely popular post and YouTube video regarding how oscillometric devices are correct with regards to their MAP but not their SBP and DBP. I hadn’t found any studies to validate how the SBP and DBP applied. Now we have data. And I may have to eat my words. I’m cool with that, though. This study was published earlier today. I cannot get my hands on it to take it apart, but the data is compelling. They did some fancy statistics that I can’t admit to understand including Bland-Altman and error grid analyses. Although the averages seem to be close, the variations are as follows:
SAP 0.8 mmHg (±15.7 mmHg, −30.2 to 31.7 mmHg)
DAP −2.9 mmHg (±11.0 mmHg, −24.5 to 18.6 mmHg)
MAP −1.0 mmHg (±10.2 mmHg, −21.0 to 18.9 mmHg)

The interesting part is that the ICU is a world of details and although the differences were small. The variation between the two, radial arterial line and oscillometric cuff, was enough though to cause additional treatment changes in more than 20% of patients.

I despise reading abstracts and coming to conclusions but at this point I have no choice. Maybe tomorrow I’ll be able to take this apart entirely.

Link to abstract

EJ

Kaufmann T, Cox EGM, Wiersema R, et al. Non-invasive oscillometric versus invasive arterial blood pressure measurements in critically ill patients: A post hoc analysis of a prospective observational study [published online ahead of print, 2020 Feb 22]. J Crit Care. 2020;57:118–123. doi:10.1016/j.jcrc.2020.02.013

Although great care has been taken to ensure that the information in this post is accurate, eddyjoemd, LLC shall not be held responsible or in any way liable for the continued accuracy of the information, or for any errors, omissions or inaccuracies, or for any consequences arising therefrom.

Brachial Arterial Catheterization

Since I've started working at my new institution, I've placed two brachial arterial lines and an axillary line. As any intensivist will admit, if you're looking elsewhere from the radial, it means that the patient is pretty sick and you need some results, quickly.

While performing this procedure, I've received strange looks from the nurses as they are unfamiliar with the location. Where I trained, I saw anesthesia commonly place these without any issues in the cardiac surgery population. I decided to do a bit of a search for the data behind the safety of this procedure.

First of all, why should we worry? The brachial artery lacks collateral circulation. As with any other line, we worry about clinical ischemia, nerve injury (which is the median nerve in the case of the brachial artery), and infection. What's the data behind these, though?

Here are some of the more recent studies. I'll let you all decide for yourselves after you read the articles. Thanks to the authors!

Clinical review: Complications and risk factors of peripheral arterial catheters used for haemodynamic monitoring in anaesthesia and intensive care medicine

Published in 2002 in Critical Care. This is an open access article. 

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC137445/pdf/cc1489.pdf

"Only one serious complication was found in a study of 1000 patients in which the brachial artery was used for invasive monitoring in ambulatory patients. This complication was an infected haematoma arising from a pseudoaneurysm. Another study that employed the brachial artery for arterial blood sampling in 6185 patients also showed a small number of complications (incidence 0.2%), mainly paresthesias." 

Brachial Arterial Pressure Monitoring during Cardiac Surgery Rarely Causes Complications

I cannot obtain full access to this study published in June of 2017 but it can be found here: 

http://anesthesiology.pubs.asahq.org/article.aspx?articleid=2618830

Review of their abstract shows that their study population was exclusively in cardiac surgery patients and they looked at vascular issues, nerve injury, and infections as complications

They concluded that "Among 21,597 qualifying patients, 777 had vascular or nerve injuries or local infections, but only 41 (incidence 0.19% [95% CI, 0.14 to 0.26%]) were potentially consequent to brachial arterial cannulation. Vascular complications occurred in 33 patients (0.15% [0.10 to 0.23%]). Definitely or possibly related infection occurred in 8 (0.04% [0.02 to 0.08%]) patients. There were no plausibly related neurologic complications."

Brachial Artery Catheterization: An Assessment of Use Patterns and Associated Complications

Published in 2012 in Anesthesia and Analgesia. This is open access so you can obtain a copy for yourself! 

http://journals.lww.com/anesthesia-analgesia/fulltext/2014/02000/Brachial_Artery_Catheterization___An_Assessment_of.9.aspx

This was a retrospective study with 858 patients. "the overall rate of vascular and neurologic complications was low in both brachial and radial artery catheterization groups (3 [0.35%] vs 1 [0.03%], brachial versus radial, respectively; P = 0.03). No cases of catheter-related bloodstream infection were identified in either cohort."

There are some older studies which I need to briefly glance at but I wanted to get this out there and I'll add some more goodies later. 

-EJ

Although great care has been taken to ensure that the information in this post is accurate, eddyjoemd, LLC shall not be held responsible or in any way liable for the continued accuracy of the information, or for any errors, omissions or inaccuracies, or for any consequences arising therefrom.