Episode #70 Perioperative Hypotension and Postoperative Mortality

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. The October 2021 APSF Newsletter is here. Raise your hands if you are excited! We sure are and that’s why today we are going to dive into the newest issue.

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

Now, before we get into the Newsletter and our featured article, we are going to here from the author. Today, we will be discussing the article, “Perioperative Hypotension” by Daniel Sessler. Sessler is the chair of the department of outcomes research at Cleveland Clinic. To kick off the show today, I asked Sessler “Why do you feel so passionate about this topic?” Let’s take a listen to what he had to say.

[Sessler] “Postoperative mortality remains strikingly common. About 2% of surgical inpatients die within 30days of surgery. In fact, if the 30 days within surgery were considered a disease, it would be the 3^rd leading cause of death in the United States. The only potentially modifiable factor that we know about that’s associated with  myocardial injury after noncardiac surgery is hypotension. Multiple studies show that mean arterial pressure less than 65mmHg is associated with myocardial injury, acute kidney injury, and death.”

[Bechtel] What a great way to kick off the show today. Don’t worry we are going to here from Sessler again so don’t turn that dial. But you may want to make some clicks because here is how to get to the featured article today. Head over to APSF.org and click on the Newsletter heading. First one down is the current issue. Then, click on our featured article today, “Perioperative Hypotension.” Have you ever seen hypotension in the OR? Have you ever discussed blood pressure goals during the perioperative time period? This is such an important topic for anesthesia patient safety.

Sessler opens the article with several sobering facts about perioperative outcomes since the mortality during the first 30 days after surgery is over 100 times greater than intraoperative mortality. The majority of postoperative mortality occurs during the initial hospitalization for the surgery with the most common causes  of mortality following non-cardiac surgery being from major bleeding and myocardial injury. This is a crucial concept. Just because we can get our patients safely through the surgery and out of the operating room does not mean that we have been successful in keeping them completely safe during anesthesia care.

Let’s take a closer look at what we mean when we talk about myocardial injury. First, it’s time for some definitions. Myocardial infarction or MI occurs when there is troponin elevation and either symptoms or signs of myocardial ischemia. Myocardial injury after non-cardiac surgery occurs when there is troponin elevation most likely due to myocardial ischemia and this includes myocardial infarction and any other events associated with myocardial ischemia that does not meet the criteria of MI. The etiology of these events during the perioperative time period is often due to an imbalance between myocardial supply and demand. It is not usually due to plaque rupture. The important thing here is that patients who have myocardial injury after non-cardiac surgery have a higher mortality at 30 days and up to one year after surgery and the mortality from a perioperative myocardial injury is greater than infarctions that occur outside of the operating room.

So, how can we identify patients who are at risk for higher postoperative mortality due to myocardial injury? We can check troponins and the good news is that there are thresholds for troponin assays for determining when myocardial injury following non-cardiac surgery has occurred. Being able to screen for this with an available lab test is important since over 90% of these events are asymptomatic and even patients who are asymptomatic are at risk for increased mortality. It may be appropriate to screen patients by drawing troponins preoperatively and then for the first 3 days postoperatively. Sessler describes some of the thresholds that may be used to identify myocardial injury after noncardiac surgery which include the following:

1. Non-high-sensitivity troponin T ≥0.03 ng/ml⁴;
2. High-sensitivity troponin T ≥65 ng/L; or high-sensitivity troponin T=20–64 ng/L and an increase ≥5 ng/L from baseline¹²;
3. High-sensitivity troponin I ≥60 ng/L¹³;
4. High-sensitivity troponin I ≥75 ng/L (Borges, unpublished);
5. Troponin I measures at least twice local 99th percentiles;
6. And finally, an increase of at least 20% in patients who have preoperative high-sensitivity troponin concentrations that exceed 80% of the relevant thresholds that I just mentioned.

You also will want to check out the article to look at the first figure which shows the 30-day mortality rate depending on the postoperative peak high-sensitivity troponin T concentration. This should come as no surprise that as the peak troponin level increases, so does the30-day mortality.

When we evaluate what can be done to keep patients safe, we need to recognize the unmodifiable factors. For myocardial injury after non-cardiac surgery and MI, these include age, diabetes, cardiovascular history and studies have shown that we cannot prevent a perioperative MI with beta-blocker, clonidine, or aspirin administration or by avoiding nitrous oxide.

This is why it is so important to identify any modifiable factors that we may be able to address during anesthesia, which brings us to the next topic of…perioperative hypotension. Sessler describes what we know about the association between hypotension and myocardial injury and MI. Intraoperative hypotension with a mean arterial pressure below 65mmHg is associated with myocardial injury and MI. We need to remain vigilant in the postoperative period as well since there is an association between postop hypotension and MI even in patients who were not hypotensive intraoperatively. Just because we leave the operating room and turn off the anesthesia, does not mean that it is time to let down our guard according data from the Vascular events In noncardiac Surgery patIents cOhort evaluation or VISION cohort.  This study looked at the relationship between holding or continuing ACE-inhibitors or ARBs in patients undergoing noncardiac surgery and the risk of death, stroke, and myocardial injury at 30 days with the secondary outcomes of intraoperative and postoperative hypotension and was published in Anesthesiology in 2017 by Roshanov and colleagues. It revealed that postoperative hypotension was common with 19.5% of patients in the cohort having at least one episode of hypotension. Postop hypotension occurred in almost 12% of patients on post-op day 1 and the majority of these events occurred in the first 3 days after surgery. Going one step further, these relatively common episodes of postoperative hypotension were associated with major vascular events and were even more strongly associated with MI or death than intraoperative hypotension. Another association includes perioperative hypotension and an increased risk of stroke. Check out figures 2-5 in the article to see these association and results.

Are there any other modifiable factors associated with myocardial injury and infarction? Postoperative anemia has a strong association and this exists even when adjusting for baseline patient characteristics including preoperative anemia. A couple of other factors, heart rate of 100 beats/min and systolic hypertension up to 200mmHg were not associated with postoperative myocardial injury. Even though hypoxemia is a common event it is not clear if this contributes to myocardial injury at this time.

If hypotension is associated with myocardial injury, are there any other end-organs that could be affected in a similar way? To help answer this question, we need to look closer at acute kidney injury following non-cardiac surgery. Here’s what we know: It is common. Stage 2-3 AKI occurs in 1% of patients and stage 1 AKI occurs in up to 7.4% of patients and there is an association between hypotension and the development of AKI. In fact, there is evidence that mean arterial levels less than 55mmHg for less than 5 minutes was associated with an 18% increase in the risk for AKI. The important point here is that the degree of hypotension as well as the length of time that the patient experiences hypotension are important factors for the development of AKI. Once patients develop perioperative AKI, they go on to have a higher 1-year mortality or even if they start with mild Stage 1 AKI, these patients may develop worsening kidney function in the next 1-2 years following their non-cardiac surgery. This data comes from the 2020 study by Turan and colleagues published in Anesthesiology, Mild acute kidney injury after noncardiac surgery is associated with long-term renal dysfunction: a retrospective cohort study. I will include the references in the show notes as well.

Next up, let’s look at delirium following noncardiac surgery and the impact and associations. There is a 10% reported incidence of delirium following major noncardiac surgery with a higher incidence in patients over the age of 65 years old. The development of postoperative delirium is multifactorial. One important consideration is the impact of hypotension when the mean arterial pressure falls below the lower limit of cerebral autoregulation leading to decreased cerebral perfusion. Cerebral autoregulation refers to the maintenance of stable cerebral blood flow within the cerebral vasculature with a range of blood pressures as a result of changes in the arteriolar diameter and cerebral vascular resistance. Cerebral autoregulation helps to ensure that the brain is perfused despite some changes in blood pressure which may occur during induction of anesthesia or at other periods during the surgery and anesthetic. It is important to keep in mind that we do not know the threshold for cerebral autoregulation and it is likely different for each patient. What we do know though is that this is an association between hypotension and delirium and cognitive decline with a small randomized control trial in cardiac surgery patients revealing that hypotension may cause delirium. There are 2 other important components to the development of delirium following surgery. First, patients with acute postoperative delirium are more likely to have long-term cognitive impairment. Second, is that there is likely a relationship between hypotension and strokes and patients who have a stroke are at higher risk for developing delirium.

We still have a lot more to talk about when it comes to perioperative hypotension, but we are just about out of time for today. You will have to tune in next time. We will hear from Sessler again and talk about considerations for blood pressure management.

Before we go, are there any researchers in the audience?! Don’t be shy! We hope that you will consider applying for the Joint APSF and Foundation of Anesthesia Education and Research Mentored Research Training Grant. This is an exciting opportunity for the next generation of perioperative patient safety scientists. This is a two-year, $300,000 award with a goal for anesthesiologists within 10 years of their first faculty appointment to develop skills and collect preliminary data to go on an become independent investigators in the field of anesthesia patient safety. Mark your calendars for December 1, 2021 and be ready to submit your letter of intent. The submission period will close on January 1, 2022. For more information, head over to APSF.org and click on Grants and Awards Heading. I will include the link in the show notes as well.

If you have any questions or comments from today’s show, please email us at [email protected].

Visit APSF.org for detailed information and check out the show notes for links to all the topics we discussed today.  Please keep in mind that the information in this show is provided for informational purposes only and does not constitute medical or legal advice. Thanks for tuning in and if you liked this show, please share it with your friends and colleagues, and leaders at your institution. Plus, if you get a chance, can you leave us a 5 star review. This helps our show to stay visible so that every interested in perioperative patient safety is able to tune in.

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

© 2021, The Anesthesia Patient Safety Foundation