The impact of hypotension in surgical and critically-ill patients

Recent studies show associations between intraoperative hypotension and increased risk of myocardial infarction (MI) and acute kidney injury (AKI) in non-cardiac surgical patients.1-3 Prolonged exposures below mean arterial pressure (MAP) thresholds of 65 mmHg and lower are associated with increased risk of MI and AKI in non-cardiac surgical patients.3 Additionally, studies show an increased risk of 30-day mortality associated with lower mean arterial pressure (MAP) in post non-cardiac surgery,4 and a significant increase in in-hospital mortality for patients experiencing post intubation hypotension (PIH) when compared to those not affected with PIH (35% vs. 20%).5

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Highlights from the Salmasi Analysis: “Relationship between Intraoperative Hypotension, Defined by Either Reduction from Baseline or Absolute Thresholds, and Acute Kidney and Myocardial Injury after Noncardiac Surgery”

In a comprehensive study conducted by the Cleveland Clinic, researchers found that intraoperative hypotension may be an important factor in the development of postoperative complications.

MAP below absolute thresholds of 65 mmHg and lower or relative thresholds of 20% or more below baseline were progressively related to both myocardial and kidney injury. At any given threshold, prolonged exposure was associated with increased odds.

There were no clinically important interactions between preoperative blood pressures and the relationship between hypotension and myocardial or kidney injury at intraoperative mean arterial blood pressures less than 65 mmHg. Absolute and relative thresholds had comparable ability to discriminate patients with myocardial or kidney injury from those without.

The lowest mean arterial pressure (MAP) thresholds for AKI. Univariable and multivariable relationship between AKI and absolute and relative lowest MAP thresholds. (A) and (C) Estimated probability of AKI were from the univariable moving-window with the width of 10% data; (B) and (D) were from multivariable logistic regression smoothed by restricted cubic spline with three degrees and knots at 10th, 50th, and 90th percentiles of given exposure variable. (A) and (B) show that there was a change point (i.e., decreases steeply up and then flattens) around 65 mmHg, but 20% was not a change point from (C) and (D).

Interaction between effects on myocardial injury after noncardiac surgery (MINS). (A) and (C) Estimated probability of MINS were from the univariable moving-window with the width of 10% data; (B) and (D) were from multivariable logistic regression smoothed by restricted cubic spline with three degrees and knots at 10th, 50th, and 90th percentiles of given exposure variable. Multivariable models adjusted for covariates in full paper, Salmasi Analysis. The interaction P values between the lowest mean arterial pressure (MAP) and baseline were < 0.001 and 0.84 between the lowest % MAP decrease and baseline, respectively. However, (A) and (B) plots show that there were no strong interaction effects as long as MAP is less than 65 mmHg.

With increasing evidence of the risks associated with hypotension during surgery, the HPI feature offers the ability to detect and respond to potentially developing hypotension by recognizing trends and receiving alerts before they occur.

Highlights from the Sun paper: “Association of Intraoperative Hypotension with Acute Kidney Injury after Elective Noncardiac Surgery”

The magnitude and duration of Intraoperative Hypotension (IOH) are an important risk factor for both Stage I and II AKI:

  • It has been proposed that in adult human, renal blood flow remains constant between MAP of 75 and 170 mmHg, but becomes pressure dependent beyond this range.16
  • Patients become susceptible to AKI when MAP decreases below the lower threshold of the autoregulation curve, but AKI could occur in the presence of adequate MAP but poor cardiac output.17
  • An increased risk of postoperative stage I AKI when intraoperative MAP was less than 60 mmHg for more than 20 min and less than 55 mmHg for more than 10 min. This study provides an impetus for clinical trials to determine whether interventions that promptly treat IOH and are tailored to individual patient physiology could help reduce the risk of these events

Highlights from the Mascha paper: “Intraoperative Mean Arterial Pressure Variability and 30-day Mortality in Patients Having Noncardiac Surgery”

Lower mean arterial pressure is strongly associated with mortality, lower intraoperative blood pressure variability per se is only mildly associate with postoperative mortality after surgery.

  • Average mean arterial pressure and mean pressure variability were nonlinearly related to 30-day mortality in noncardiac surgical patients. 
  • Anesthesiologists might thus pay more attention to overall trends in the mean blood pressure for a case than in the minute-to-minute variation.
References
* A hypotensive event is defined as MAP < 65 mmHg for a least one minute in duration.
1. Walsh, M., Devereaux, P. J., Garg, A. X., Kurz, A., Turan, A., Rodseth, R. N., . . . Sessler, D. I. (2013). Relationship between Intraoperative Mean Arterial Pressure and Clinical Outcomes after Noncardiac Surgery. Anesthesiology, 119(3), 507-515.
2. Sun, L. Y., Wijeysundera, D. N., Tait, G. A., & Beattie, W. S. (2015). Association of Intraoperative Hypotension with Acute Kidney Injury after Elective Noncardiac Surgery. Anesthesiology, 123(3), 515-523.
3. Salmasi, V., Maheshwari, K., Yang, G., Mascha, E. J., Singh, A., Sessler, D. I., & Kurz, A. (2017). Relationship between intraoperative hypotension, defined by either reduction from baseline or absolute thresholds, and acute kindney injury and myocardial injury. Anesthesiology,
4. Mascha, E. J., Yang, D., Weiss, S., & Sessler, D. I. (2015). Intraoperative Mean Arterial Pressure Variability and 30-day Mortality in Patients Having Noncardiac Surgery. Anesthesiology, 123(1), 79-91.
5. Heffner, A. C., Swords, D. S., Nussbaum, M. L., Kline, J. A., & Jones, A. E. (2012). Predictors of the complication of postintubation hypotension during emergency airway management. Journal of Critical Care, 27(6), 587-593.
Acumen Hypotension Probability Indicator Software

With increasing evidence of the risks associated with hypotension during surgery, the Acute Hypotension Probability Indicator Software (HPI) offers the ability to detect and respond to developing hypotension by recognizing trends and providing alerts before they impact your patients. Enabling you to react earlier and positively impact patient outcomes.

Part of the Acumen decision support software suite, HPI is compatible with the IQ family of hemodynamic solutions - including the FloTrac IQ sensor.

Know Before It's Low

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Hypotension Probability Indicator Brochure

Acumen Hypotension probablility indicator software

Three elements of the Acumen Hypotension Probability Indicator software

Hypotension Probability Parameter

Hypotension Probability Parameter

The hypotension probability parameter, P(↓BP), indicates the possibility that a patient may be trending toward a hypotensive event*. The proprietary algorithm - developed using data from almost 13,000 past hypotensive events and over 12,000 non-hypotensive events* - coupled with machine learning techniques, detects potential hypotensive trending of a patient's mean arterial pressure (MAP)2. P(↓BP) is calculated every 20 seconds enabling you to visually track hypotension probability in real-time, before an event occurs.

High-Alert Hypotension Probability Pop-Up

High-Alert Hypotension Probability Pop-Up

Once P(↓BP) exceeds 85%, an audible alarm sounds. When that probability exceeds the upper limit for two consecutive calculations, a pop-up window appears with a "high" alert - prompting you to investigate using the secondary screen's advanced hemodynamic parameters.

Secondary Screen for Physiologic Clarity

Secondary Screen for Physiologic Clarity

HPI also includes the Hypotension Probability Secondary Screen, which is easily accessed from any EV1000 clinical platform monitoring screen. It visually links pressure and flow parameters that are arranged by preload, contractility, and afterload. This allows you to investigate potential hemodynamic factors as they relate to high hypotension probability.

*A hypotensive event is defined as MAP < 65 mmHg for a least one minute duration.
Hypotension and hemodynamics

Uncovering the Possible Root Cause and Treatment Paths

Understanding the root cause of hypotension requires investigation of pressure and flow parameters.

Preload

  • Stroke Volume Variation (SVV) – the percent difference between minimum and maximum SV during a respiratory cycle. Serves as an accurate marker of position status on the Frank-Starling curve.

Contractility

  • Cardiac Output (CO) – can be used (in combination with SaO2 and hemoglobin) to monitor and optimize DO2 with fluid and inotropic agents.
  • Stroke Volume (SV) – enables an individualized approach to administering fluid until SV reaches a plateau on the Frank-Starling curve, in order to prevent hypovolemia and excessive fluid administration.
  • New - dP/dt – maximal dP/dt of an arterial pressure waveform is a measure of left ventricular contractility.

Afterload

  • Systemic Vascular Resistance (SVR) – the resistance to blood flow offered by all of the systemic vasculature, excluding the pulmonary vasculature.
  • New - Dynamic Arterial Elastance (Eadyn) – the ratio of pulse pressure variation to stroke volume variation (PPV/SVV). It is an estimate of arterial elastance, Ea.

Real-World Case

In this example, P(BP) successfully predicted a hypotensive event in a patient undergoing tumor debulking. With research indicating that even a one-minute drop in MAP below 65 mmHg significantly increases the risk of acute kidney injury (AKI) and myocardial infarction (MI), this foresight has the potential to help real-time clinical decision-making to manage intraoperative hypotension.**

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**Data on File.
The FloTrac IQ Sensor unlocks the Acumen hypotension probability indicator software

The FloTrac IQ sensor unlocks the Hypotension Probability Indicator feature that is part of the Acumen decision support software suite. The HPI feature gives you the intelligence to detect and respond to potentially developing hypotensive events* before they occur. The proprietary algorithm was developed using data from almost 13,000 past hypotensive events* and over 12,000 non-hypotensive events*, coupled with machine learning techniques, to detect potential hypotensive trending of a patient’s mean arterial pressure (MAP).

Improved volume management with the added intelligence of the Hypotension Probability Indicator feature, the FloTrac IQ system automatically updates advanced parameters every 20 seconds. This reflects rapid physiological changes in moderate to high-risk surgery more accurately. Advanced hemodynamic parameters provided by the FloTrac IQ sensor offer you continuous insight to more accurately determine your patient’s fluid status. The minimally-invasive FloTrac IQ sensor connects to any existing radial arterial line.

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*A hypotensive event is defined as MAP < 65 mmHg for a least one minute in duration.
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