Episode #219 Optimizing Outcomes in Anesthesia Care: Spotlight on Intraoperative Hypotension

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. We hope you tuned in last week when we started the conversation about intraoperative hypotension, usually defined as mean arterial blood pressure less than 65mmHg, and the threat to anesthesia patient safety. An important part of every anesthesia plan should include minimizing the occurrence, severity, and duration of intraoperative hypotension.

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

Our featured article once again 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. The 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.

Let’s start with a quick review from last week. Here are some of the highlights:

Intraoperative hypotension is a big threat to anesthesia patient safety.

It is associated with postoperative complications including acute kidney injury, myocardial injury after non-cardiac surgery, delirium, and stroke as well as increased morbidity, mortality, and hospital readmissions.

Intraoperative hypotension occurs when the blood pressure drops below a safe threshold leading to end-organ hypoperfusion.

Here are some blood pressure thresholds to keep in mind: MAP less than 65mm Hg for longer periods of time or any MAP less than or equal to 55mmHg since these are associated with an increased risk for adverse postoperative outcomes.

Monitoring blood pressure may be done with intermittent non-invasive blood pressure cuffs which may allow hypotensive events to remain undetected for longer duration.

Continuous blood pressure monitors are available with an invasive intra-arterial line or a non-invasive finger cuff device. Benefits for continuous blood pressure monitoring include:

• 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.

And now, we are ready to get back into the article, right where we left off.

Remember, an important part of every anesthetic plan should be to minimize the occurrence, severity, and duration of intraoperative hypotension. At the same time, we must be careful to avoid inappropriate fluid and vasopressor administration which may lead to end-organ damage as well. This seems like a good time for a literature review. Check out the show notes for the citations.

First up we have the article by Ariyarathna and colleagues. This is a retrospective cohort study of elective non-cardiac surgery patients over the age of 65 years old who developed acute kidney injury within 48 hours of surgery. Intraoperative factors included intraoperative hypotension with mean arterial blood pressure less than 60 or systolic blood pressure less than 90 and intraoperative vasopressor use. The results revealed that the majority of the hypotensive episodes were short, lasting less than 10 minutes while vasopressors were used in the majority of cases at almost 85%. The authors concluded that high vasopressor use (greater than 20mg of any specific vasopressor) was associated with postoperative AKI in this cohort of patients and this was independent from hypotensive events.

Next up, we have the 2020 article by Anolik and colleagues that evaluated postoperative hypotension in patients  undergoing abdominal free flap breast reconstruction with ERAS protocol and fluid restriction compared to traditional management. The authors observed the following in ERAS patients:

• a higher rate of postoperative symptomatic hypotension
• less intraoperative IV fluid administration
• increased duration of intraoperative hypotension
• No differences in postoperative urine output and adverse events.

We are moving on to a bigger, multicenter study. Check out the 2022 study by Chiu and colleagues that evaluated over 32,000 abdominal surgery patients over a 5-year time period with the Multicenter Perioperative Outcomes Group or MPOG intuitions. Results included the following:

• Increased rates of AKI even with a reduction in intraoperative hypotension
• Decreased intraoperative fluid administration and increased vasopressor use which were both associated with increased incidence of AKI.
• Greater than 50% decreased risk for the development of AKI when the crystalloid administration increased from one to ten milliliters per kilogram per hour.

The big takeaway from this study is the idea that administration of vasopressors to treat or prevent intraoperative hypotension while minimizing IV fluid administration may lead to adverse effects including decreased splanchnic and renal perfusion leading to ileus, postoperative nausea and vomiting, surgical site infections, and AKI.

Now, it’s time to review the differential diagnosis for intraoperative hypotension. Here we go:

Reduced myocardial contractility, vasodilation, hypovolemia, bradycardia, extrinsic compression of heart chambers (from a pericardial effusion or pneumothorax) or a combination of these. We can turn to some of our more advanced monitoring to help prevent, diagnose, and treat hypotension. These monitors provide information about stroke volume, cardiac output, and stroke volume variation. This allows us to provide goal-directed therapy to treat intraoperative hypotension and work to keep patients safe, rather than just giving vasopressors to treat BP number.

Do you practice goal-directed therapy while providing anesthesia care? The authors define goal-directed therapy as the optimal administration at the most appropriate time of fluids, inotropes, and vasopressors while being guided by an advanced hemodynamic monitor. The goal is to optimize tissue oxygen delivery and prevent organ hypoperfusion with treatment for a specific endpoint. Check out Figure 1 in the article for a visual representation of a goal-directed therapy. The top of the chart is Goal-Directed Therapy. The next row branches into the two strategies of  goal directed hemodynamic therapy and goal directed fluid therapy. The next row includes the interventions of fluids, inotropes, and vasopressors for hemodynamic therapy and fluids for fluid therapy. The hemodynamic variables that can be used to help guide fluid therapy include stroke volume and stroke volume variation. You can use cardiac index to help guide inotrope administration and systemic vascular resistance to guide vasopressor administration.

If we look a little closer at goal-directed fluid therapy, we see that the goal is to identify which patients are preload dependent and will respond to a fluid bolus with an optimized position on the Frank-Starling curve. We can use advanced hemodynamic monitors to assess fluid responsiveness. According to the 2020 Perioperative Quality Initiative consensus statement on intraoperative fluid management, assessment of fluid responsiveness is the safest and most effective way to guide fluid therapy. It is vital to optimize stroke volume with appropriate administration of IV fluids to maintain circulating volume and gut perfusion to help decrease postoperative complications. If we look a little closer at goal-directed hemodynamic therapy, the goal is to maintain mean arterial blood pressure and avoid intraoperative hypotension. Goal directed therapies have been shown to decrease morbidity, mortality, and postoperative complications. This is an important step for helping to keep patients safe during anesthesia care. Let’s turn our attention to the FEDORA trial. This prospective, multicenter randomized controlled study looked at postoperative complications within the first 180 days after surgery in adult patients undergoing major elective surgery.  Esophageal doppler monitor-guided goal-directed hemodynamic therapy was used to guide administration of fluids, inotropes, and vasopressors with hemodynamic variables of stroke volume, mean arterial blood pressure, and cardiac index compared to IV fluid administration with traditional principles. Intraoperative goals in the goal-directed hemodynamic therapy group included maximal stroke volume, MAP >70mmHg, and cardiac index greater than or equal to 2.5. Now, for the results, Drumroll please…450 patients were included and there were less complications and shorter hospital length of stay in the goal-directed hemodynamic therapy group as well as less acute kidney injury, pulmonary edema, respiratory distress syndrome, and wound infections. There was no significant difference in mortality between the groups.

When high-risk patients are managed with goal-directed hemodynamic therapy protocols, there was a decreased risk for postoperative organ dysfunction. Elderly patients undergoing spine surgery can also benefit from goal-directed therapy with less intraoperative hypotension, postoperative nausea and vomiting, and delirium according to the 2018 study by Zhang and colleagues. Multiple studies have demonstrated that goal-directed therapy can be used to decrease intraoperative hypotensive events and benefit patients undergoing surgery and anesthesia care from low risk to high-risk.

The authors highlight that intraoperative hypotension is a serious public health issue and should be avoided in all age groups and for any length of time. We have tackled the problem by treating hypotension after it has already occurred. This is likely too late, placing patients at risk for end-organ damage. Going forward, we need to harness technology of artificial intelligence and machine learning in order to predict intraoperative hypotensive events and then reduce and prevent them. Have you heard of the Hypotension Prediction Index or HPI. The HPI provides a unitless number on a scale from 0 to 100 which indicates the likelihood that a hypotensive event will take place. The monitor also provides information about the likely underlying cause of the impending hypotensive events so that the correct intervention may be performed. Studies evaluating HPI have shown that this technology has the potential to decrease the occurrence, duration, and severity of IOH during non-cardiac surgery. For this monitor to work, protocols must be followed to provide appropriate management. This is an example of how reducing practice variation with protocols can help to decrease IOH.

Anesthesia professionals are charged with minimizing intraoperative hypotension. How can we do this? Check out Figure 2 in the article for a next step guide to help us achieve. These are actionable items.

• It starts with a call to action
• then we must measure postop AKI
• reporting is important and facilities must report outcomes to frontline anesthesia professionals
• continued education on intraoperative hypotension
• Increased and routine use of continuous hemodynamic monitoring when available/applicable
• Use predictive algorithms for hemodynamic management
• Protocolization to reduce practice variation.

The authors leave us with the call to action that intraoperative hypotension is a modifiable risk that we simply should not continue to tolerate. Keep in mind that it is more than just treating the number on the monitor with vasopressors. Goal-directed therapy is an important part of safe anesthesia care to treat the underlying cause of the hypotension and provide adequate end-organ perfusion.

We made it to the end of the article, but before we wrap up for today, we are going to hear from Yerdon again. I also asked her what she hopes to see going forward. Let’s take a listen to what she had to say.

[Yerdon] “Our hope is to raise awareness of the importance of appropriate intraoperative hemodynamic management. Going forward, we want to emphasize that it’s not just about blood pressure. It’s about flow and perfusion to the organs. There has been much focus on intraoperative hypotension or IOH, but we need to recognize that hemodynamic instability is the most important issue and strive to correct the cause of the instability.

IOH is just a symptom of the true problem. We need to treat the cause of hemodynamic instability, not just the numbers on the monitor. I envision intraoperative anesthesia care transitioning to continuous blood pressure monitoring, so we can minimize hemodynamic instability, so that no patient may be harmed by anesthesia care.

This would also allow for advanced hemodynamic monitoring and the potential for predicting and therefore preventing hemodynamic instability in IOH.”

[Bechtel] Thank you to Yerdon for contributing to the show today. We are looking forward to improved intraoperative blood pressure and advanced hemodynamic monitoring as we work toward ultimately the prevention of intraoperative hypotension.

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.

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

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