Episode #107 Perioperative Blood Pressure: Past, Present, and Future

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. In November 2021, we discussed perioperative hypotension on Episodes 70 and 71. This is one of the most popular series of all time and it is a review of a very important topic for anesthesia patient safety during the perioperative period. Today, we are going to revisit episodes 70 and 71, but before we do that, we are heading into the APSF archives.

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!”

Before we revisit episode 71, let’s jump back in time and into the APSF Newsletter archives to the Summer 1990 APSF Newsletter to review the article, “BP Changes Tied to Complications” by Dean Tully. For this episode and future similar shows, we will take a look at past articles that were published in the APSF Newsletter that you can find on our website. Keep in mind that things may have changed a lot since the publication of these articles, but they are of interest from our archives.

Perioperative blood pressure management has been a critical topic for anesthesia patient safety for a long time. For this article from our archives segment, we are going to be looking at the flip side of the blood pressure coin including preop and post-op hypertension as well as intraoperative lability. What were our considerations in 1990? During the preoperative phase, our understanding was that medical management of hypertension was important to reduce morbidity associated with congestive heart failure, chronic renal failure, and cerebrovascular accidents, but there was limited evidence for the link between pre-operative hypertension and postoperative complications. One finding from the 1979 paper by Prys-Roberts was that patients with pre-op hypertension were more likely to have labile blood pressures during the surgery. Goldman and colleagues studied this in 1979 and published in Anesthesiology, “Risks of General Anesthesia and Elective Operation in the Hypertensive Patient. Tully points out that even though this study did not contain many patients with severe hypertension, one of the conclusions from the study related to patients with severe hypertension has become accepted clinical practice related to proceeding with elective surgery as long as the diastolic blood pressure is stable at a level less than 110 mmHg with close perioperative monitoring.

Let’s move into the operating room. The 1983 study by Rao and El Etra reported that postoperative reinfarction rates were higher in patients with labile blood pressures during the surgeries including hypertension, hypotension, and tachycardia. In addition, patients with intraoperative ischemia and  post-operative infarction were more likely to have perioperative episodes of hypertension, hypotension, or tachycardia. It appears that working to maintain stable hemodynamics in the operating room may help to decrease postoperative complications.

We made it out of the OR and into the PACU. When patients present with blood pressure changes in the PACU, it is important to create a differential diagnosis for the hypotension or hypertension and manage the patient appropriately. These are common events after surgery and during recovery from anesthesia. Patients with chronic hypertension are likely to develop hypertension after surgery requiring treatment after excluding other reversible causes of the hypertension. Labetalol is often used in the PACU for significant hypertension. The conclusion from our article from the archives is just as true today as it was in 1990. I will read it now. “Over-all, careful attention to blood pressure management can be an important component of maximizing anesthesia patient safety.”

And with that, let’s continue the conversation about careful attention to blood pressure management and take a listen as we revisit episode #71. First, we are going to hear from Dan Sessler, the author of our featured article and he is going to share with us why he is so passionate about this area and what he hopes to see going forward.

[Episode 70 Clip]

[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.”

[Episode 71 Clip]

[Sessler] “There’s clear evidence that hypotension is associated with myocardial injury, kidney injury, and death. The extent to which this association is causal remains largely unknown at this point. We very much need large robust randomized trials. Fortunately, these are in progress and the results should be available relatively soon. But in the meantime, clinicians would be well guided to keep mean arterial pressure above 65 mmHg during surgery and preferably above 75 mmHg postoperatively.”

[Bechtel] To follow along with us, head over to APSF.org and click on the Newsletter heading. Fifth one down is the Newsletter Archives. Then, scroll down until you get to October 2021. There you will find our featured article today, “Perioperative Hypotension” by Dan Sessler. And now, let’s revisit Episode 71.

[Episode 71 Segment]

“Hypotension in the OR is a big threat to anesthesia patient safety and the risk continues even after we leave the OR and into the postoperative time period as well. Last week, we reviewed the associations with hypotension during the perioperative period including myocardial injury and ischemia, acute kidney injury, and delirium. Today, we are going to discuss considerations for blood pressure management.

During the preoperative patient assessment, there are no patient risk factors or specific surgical procedures that can reliably predict which patients will go one to develop intraoperative hypotension. Unfortunately, we still do not know the best methods to prevent and treat hypotension during anesthesia care. Studies have evaluated the relationships between intraoperative cardiac index and blood pressure as well as intravascular volume status and prevention of hypotension which did not provide the easy answer for preventing or treating perioperative hypotension.

Studies evaluating intraoperative hypotension have revealed some of the following concerns:

• About one third of hypotensive episodes occur after induction of anesthesia and before surgical incision. This is often due to anesthetic drug effects. We cannot let our guard down after induction of anesthesia because hypotension during this time period has the same associations that we talked about last week as hypotension that occurs during the surgery.
• How we monitor blood pressure is important for being able to detect hypotension. Continuous blood pressure monitoring with an arterial line will detect more hypotensive episodes than non-invasive blood pressure monitoring at 5-minute intervals. Sessler mentions an algorithm to predict hypotension from an arterial waveform. This is The Hypotension Prediction Index which uses the arterial pressure waveform trace to generate a unitless number and higher numbers may predict increased risk for hypotension with MAP <65mmHg for at least 1 minute, in the future. For more information about this algorithm, check out the February 2020 article by Davies and colleagues in Anesthesia and Analgesia, “Ability of an Arterial Waveform Analysis–Derived Hypotension Prediction Index to Predict Future Hypotensive Events in Surgical Patients.” I will include the reference in the show notes as well. Studies using this prediction tool have shown either less hypotension or no benefit. Further studies with larger patients and more diverse patient populations are needed going forward.
• What medication do you reach for first to treat intraoperative hypotension? The most common medications include vasopressors such as phenylephrine or norepinephrine. In the United States, phenylephrine is the most common vasopressor used. Phenylephrine can be used to treat hypotension because it is an alpha agonist which increases the systemic vascular resistance often with a compensatory decrease in heart rate and cardiac output. Norepinephrine is a strong alpha agonist with weak beta-adrenergic agonism as well resulting in increased blood pressure with maintenance of cardiac output. Norepinephrine is the vasopressor of choice in septic shock since phenylephrine administration may lead to decreased splanchnic blood flow and decreased oxygen delivery to end-organs. At this time, there is little evidence regarding differences in outcomes for surgical patients based on the choice of vasopressor and phenylephrine and norepinephrine are often used depending on clinical preference and availability. What about the evidence for running a low-dose vasopressor infusion during the surgery and anesthesia care to prevent and treat intraoperative hypotension? Studies have not shown this practice to be harmful. Norepinephrine may be administered safely through a peripheral IV or central line. This is good news since there was concern that norepinephrine needed to be given through a central line only in the past. Check out the 2019 article in A & A, “Risk of Major Complications After Perioperative Norepinephrine Infusion Through Peripheral Intravenous Lines in a Multicenter Study” for more information. Spoiler alert: this study included over 14,000 patients and there were only 5 extravasation events and zero events of local tissue injury.

Remeber, the patient’s risk for hypotension remains even after leaving the OR. Sessler tells us that hypotension on the hospital floor is common, prolonged, and profound and this may be when damage to end-organs from hypoperfusion occurs. Going forward considerations for monitoring blood pressure as well as oxygen levels more often or even continuously may be needed. Another important consideration includes the timing for holding and restarting home blood pressure medications. For example, holding angiotensin converting enzyme inhibitors and angiotensin receptor blockers on the morning of surgery may help to prevent hypotension in the OR. Restarting home antihypertensive medications after surgery needs to be done carefully in order to decrease the risk for postoperative hypotension.

Studies have revealed that intraoperative hypotension with a MAP of less than 65 mmHg occurs in over 25% of surgical patients. Patients may develop hypotension postoperatively and even severe and prolonged events may go undetected due to the long intervals between routine vital sign monitoring on the hospital wards. These postoperative events are concerning and contribute to the development of myocardial and renal injury. Have we been able to delineate between an association and causality? A small randomized trial found that prevention of intraoperative hypotension decreased the risk of major complications by 25%. Going forward, we will be able to return to the literature to evaluate the results from the POISE-3 trail and the GUARDIAN trial which may help to determine causality of these associations. So, stay tuned.

In the meantime, we need to keep in mind that intraoperative and postoperative hypotension are associated with myocardial and renal injury with some evidence for an association between hypotension and delirium as well. While we are waiting for these large trials and further evidence, we need to remain vigilant with blood pressure monitoring and treatment. It may be that we discover interventions to prevent myocardial and renal injury from perioperative hypotension in the future. For now, it appears that an appropriate intraoperative strategy may include maintenance of MAP > 65mmHG with adjustments to anesthesia medication administration dose and timing, fluid management, and vasopressor administration. Once we leave the OR, the challenge continues due to monitoring ability. Keep in mind that patients may benefit from delaying restarting home antihypertensive medications in the early postoperative time period when they remain at risk for hypotension and the associated myocardial and renal injury. Sessler leaves us with a call to action that I am going to read now:

“Blood pressure—specifically hypotension prevention—is a modifiable factor that may reduce cardiovascular complications. Pending the results of robust trials, reasonable efforts to avoid perioperative hypotension seem prudent.”]

Thank you for joining us today as we talked all about perioperative blood pressure management, past, present and future. 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. Have you joined the conversation on twitter? If so, we would love for you to tag us in a tweet using #APSF podcast and share your patient safety related story. Thanks for listening and we can’t wait to hear from you soon!

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

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