Episode #218 Unmasking the Risks: The Dangers of Low Blood Pressure During Surgery

Hello and welcome back to the Anesthesia Patient Safety Podcast. My name is Alli Bechtel, and I am your host. Thank you for joining us for another show. Let’s open the June 2024 APSF Newsletter once again. We have an important public safety announcement for you today.

Before we dive into the episode today, we’d like to recognize BD, a major corporate supporter of APSF. BD has generously provided unrestricted support to further our vision that “no one shall be harmed by anesthesia care”. Thank you, BD – we wouldn’t be able to do all that we do without you!”

Our featured article today is “Intraoperative Hypotension: A Public Safety Announcement for Anesthesia Professionals” by Amy Yerdon, Matt Sherrer, and Desiree Chappell. To follow along with us, head over to APSF.org and click on the Newsletter heading. First one down is the Current Issue. Then scroll down until you get to our featured article today. I will include a link in the show notes as well.

To help kick off the show today, we are going to hear from one of the authors. Let’s take a listen now.

[Yerdon] “Hi, my name is Amy Yurden, and I am a certified registered nurse anesthetist, and I’m also an assistant professor and the assistant program director of the nurse anesthesia program at the University of Alabama in Birmingham in the United States.  And I also work clinically at Huntsville Hospital in Huntsville, Alabama.”

[Bechtel] I asked Yerdon why she wrote this article. Here is her response.

[Yerdon] “My co-authors, Matt Scherer and Desiree Chappell and I believe that there’s an urgent need to raise awareness for all anesthesia professionals on this important issue. We wrote this review article to highlight the associations between intraoperative hemodynamic management or potential mismanagement and patient morbidity and mortality.

There’s a lack of reporting postoperative patient outcomes to frontline anesthesia professionals which further complicates the potential knowledge gap. Without up to date education or post op data, many anesthesia professionals do not believe their patients ever experience any adverse effects of their anesthetic care.

When talking with colleagues about this issue, I often hear them say, I’ve never had a patient experience any post op issues because of hypotension.  We felt it was time to sound the alarm on this important patient safety issue. As one of the most read journals by all types of anesthesia professionals, we felt the APSF newsletter was the best place to publish this article to impact the most patients by reaching the most anesthesia professionals.”

[Bechtel] Thank you so much for Yerdon for helping to introduce this important article and topic. Let’s get into the article.

Intraoperative hypotension is a big threat to anesthesia patient safety. Intraoperative hypotension is associated with a variety of postoperative outcomes including acute kidney injury, myocardial injury after non-cardiac surgery, and mortality. There may also be associations between intraoperative hypotension and delirium, stroke, and hospital readmissions. There are significant risks associated with intraoperative hypotension and this is something that anesthesia professionals may be able to do something about to help keep patients safe.

Monitoring blood pressure is required during anesthesia care and blood pressure management is part of the job for anesthesia professionals. And it is a very important part of the job since intraoperative hypotension may have significant adverse effects even after the patient leaves the operating room. There is evidence to support the association between intraoperative hypotension and acute kidney injury, myocardial injury after non-cardiac surgery, and mortality as well as delirium, stroke, and hospital readmissions. These adverse outcomes may continue to have a big impact on patient safety during the postoperative period. For example, patients who develop acute kidney injury are at risk for additional complications including stroke, myocardial injury, chronic kidney disease, in-hospital mortality, and one-year mortality. Acute kidney injury may also involve increases in length of stay, health care resource utilization, and health care costs. Anesthesia professionals may not be aware of the downstream effects from intraoperative hypotension once the patient leaves the recovery room and this is an important area where anesthesia professionals can work to decrease intraoperative hypotension to avoid future harm and to keep patients safe.

Let’s start with some definitions. Intraoperative hypotension occurs when the blood pressure drops below a safe threshold leading to end-organ hypoperfusion. When evaluating the incidence of intraoperative hypotension, it depends on the reduction of blood pressure and the duration of the reduction.

First, we are going to look at the study by Salmasi and colleagues published in Anesthesiology in 2017, “Relationship between intraoperative hypotension, defined by either reduction from baseline or absolute thresholds, and acute kidney and myocardial injury after noncardiac surgery: a retrospective cohort analysis.” Check out the show notes for the citation. This study used a 20% reduction from preoperative baseline blood pressure and an absolute threshold to define intraoperative hypotension. The authors discovered that using the relative threshold or the absolute threshold had a similar ability to differentiate between patients with myocardial and kidney injury and those without. Thus, it may be possible to use an absolute threshold to determine intraoperative hypotension. The results revealed that mean arterial blood pressure less than 65mmHg for one minute was associated with an increased risk of AKI and myocardial injury. The risk increased as the duration of the hypotension increased as well. Following this study, intraoperative hypotension was defined as MAP less than 65 mmHg for at least one minute.

Now, if we scan the literature on intraoperative hypotension between that first definition in 2017 until 2022, we can see that the most common definitions of intraoperative hypotension include the following:

• Any MAP <65 mmHg
• Or MAP < 65mmHg for at least one minute

With these definitions, it becomes clear that this is a very common event. How common? Well, if we look at a recent retrospective observational multicenter study of over 22,000 patients by Shah and colleagues, over 88% of noncardiac surgery patients had at least one episode of intraoperative hypotension for greater than or equal to one minute and 33% for at least 10 minutes. The mean duration of the hypotensive events was found to be about 28 minutes. Check out Table 1 in the article for a comparison of the different incidences of IOH with MAP less than 65mmHg reported in the literature. In these studies of thousands of patients, the incidence of IOH ranged from 19.3% to 88% and the mean duration of IOH was between 22-36 minutes. What about in your practice? Do you see intraoperative mean arterial blood pressure values of less than 65mmHg when you are providing anesthesia care?

Intraoperative hypotension is getting more attention and is recognized as a new quality measure by the Centers for Medicare and Medicaid Services. MAP less than 65mmHg for greater than 15 minutes is a new criterion in the Merit-Based Incentive Payment System or MIPS. The Merit-Based Incentive Payment System total score depends on quality, cost, promoting interoperability, and improvement activities. For this specific measure, a lower intraoperative hypotension score means that the patient spent less time with a mean arterial blood pressure less than 65mmHg. This is one of six different anesthesia measures that may be submitted for the quality part of the MIPS score and the final MIPS score is used to determine payment adjustments for Medicare Part B claims.

Using this quality measure, we can continue to evaluate the incidence of intraoperative hypotension.

Let’s check out the 2023 article, “Incidence of intraoperative hypotension during non-cardiac surgery in community anesthesia practice: a retrospective observational analysis. I will include the citation in the show notes as well. In this study, the incidence of hypotension was found to be 29% during non-cardiac procedures and there was varying incidence among clinicians which signifies practice variation. This is an area where if we can reduce practice variation with quality improvement initiatives, we hope to improve intraoperative hypotension management and reduce the incidence of this modifiable risk.

If we continue to look into the threat of intraoperative hypotension, we see that more severe hypotensive events and longer cumulative duration are associated with increased risk for morbidity and mortality. Keep in mind that MAP less than 65mm Hg for longer periods of time or any MAP less than or equal to 55mmHg is associated with an increased risk for adverse postoperative outcomes. Anesthesia professionals are charged with minimizing the occurrence, severity, and duration of intraoperative hypotension as part of every anesthesia plan. An important step for keeping patients safe involves careful blood pressure monitoring. We often use non-invasive intermittent oscillometric blood pressure monitoring with an arm cuff. However, this type of blood pressure monitoring may lead to delayed or missed detection of blood pressure changes or hypotensive events, inaccurate measurements with extremes, and overestimation of blood pressure during hypotension leading to more severe hypotensive events then what is recognized by the anesthesia professional. We may even be missing hypotensive events with non-invasive BP cuff measurements depending on the frequency of the monitoring and the default settings of the monitor. The most common frequencies for this monitoring are every two to five minutes. Without constant monitoring, there may be a longer duration of hypotension or a period of time when hypotension remains undetected which increases the threat to patient safety.

There are several benefits for continuous blood pressure monitoring including the following:

• Less BP variability
• Improved hemodynamic stability
• Detection of hypotensive episodes that are missed by intermittent BP monitoring
• Earlier recognition and treatment of IOH
• And overall reduction in IOH.

Continuous BP monitoring may be done with invasive intra-arterial BP monitoring. The risks for this procedure include infection, nerve damage, thrombus, and pseudoaneurysm. Non-invasive continuous BP monitoring may be done with a finger cuff which avoids the risks of an invasive procedure, but is limited by the additional cost of this technology compared to a BP cuff and the potential for less accuracy in older patients and patients with atherosclerosis. Do you have a non-invasive finger cuff available at your institution? This device uses volume clamp technology using varying cuff pressure over the finger arteries to maintain constant volume. Then the finger arterial BP is reconstructed into an arterial waveform which can be used for pulse wave analysis and the resultant advanced hemodynamic variables of stroke volume, cardiac output, and stroke volume variation. These variable may be help to determine the cause of the hypotension so that you can provide the necessary treatment. This is an excellent monitoring choice when you want a continuous BP monitor, but you do not need to collect samples of arterial blood during the surgical procedure.

We have made it to the end of the show, but not the end of the article. We hope that you tune in next week as we continue the conversation about intraoperative hypotension and the threat to anesthesia patient safety. The big takeaway for today is the following:

“Clinicians Should Minimize the Occurrence, Severity, and Duration of IOH.”

We hope that you will make this your new mantra and incorporate it into your anaesthesia practice to help keep patients safe.

If you have any questions or comments from today’s show, please email us at [email protected]. Please keep in mind that the information in this show is provided for informational purposes only and does not constitute medical or legal advice. We hope that you will visit APSF.org for detailed information and check out the show notes for links to all the topics we discussed today.

It has been a couple months since the last APSF Newsletter was published and we are eagerly awaiting the next release in October. In the meantime, we hope that you will check out the articles between issues over on our website. Recent articles include:

• Can We Apply the Lessons We Have Learned (or not) From Our Recent Pandemic to Mass Casualty Readiness?
• Perioperative Handoff Education Resources
• Case Report: Needle Thoracostomy: The Right Equipment for the Job?

So, what are you waiting for? Check out the link in the show notes or head over to ASPF.org and click on the Newsletter heading. Second one down is Articles Between Issues.

Until next time, stay vigilant so that no one shall be harmed by anesthesia care.

© 2024, The Anesthesia Patient Safety Foundation