Hypotension Prediction Index and Intraoperative Hypotension Incidence

Intraoperative hypotension (IOH) is common, a study involved 34,045 surgical patients in elective, emergency, and intensive care unit (ICU) found that the incidence of hypotension (defined as systolic blood pressure below 80mmHg) greater than 5 minutes and 10 minutes was 25.7% and 14.6%, respectively. In another large sample size study of 22,109 patients with ASA grade 3 to 4 undergoing surgery with duration of ≥180 minutes found that 88% of patients experienced at least one episode of intraoperative hypotension, defined as a fall in mean arterial pressure (MAP) below 65 mmHg lasting at least 1 min. A multicenter retrospective cohort study from the U.S. electronic health record database conducted between 2008 and 2017 and including 368222 noncardiac surgeries reported that the incidence of MAP ≤65 mmHg during surgery was 19.3%.

IOH was significantly associated with postoperative complications and poor outcomes. Meta-analysis suggests that IOH increases the incidence of acute kidney injury, myocardial injury, and 30-day mortality after noncardiac surgery. Intraoperative MAP below 70 mmHg is an independent risk factor for increased mortality at 30 days postoperatively, while intraoperative MAP below 65 mmHg is an independent risk factor for myocardial injury after noncardiac surgery. Studies of non-cardiac, non-obstetric surgery have found that intraoperative MAP events below 55 mmHg is associated with persistent renal impairment up to 90 days postoperatively. In addition, intraoperative MAP reductions of more than 30% are associated with postoperative ischemic stroke.

China is experiencing an aging population, the number of elderly patients receiving surgical anesthesia is increasing year by year. Based on the 5-items frailty assessment scale shown that old age is closely related to the development of frailty. The prevalence of frailty among patients over 65-year-old was 7%, and 26% in patients with age over 85 years. Frailty refers to a state in which the functions of multiple systems are cumulatively reduced, leading to a decline in the body's reserve capacity and resistance. Frail patients have decreased organ reserve function, decreased response ability to surgical stress, reduced cardiac stroke volume, impaired cardiac autonomic nervous system function, and decreased albumin levels, resulting in increased blood concentration of anesthetic drugs, at risk for persistent hypotension and severe postoperative complications. In addition, the occurrence of intraoperative hypotension may further aggravate organ dysfunction on the impaired functionality of ischemia-sensitive organs such as the kidneys. The postoperative complications in frail patients undergoing abdominal surgery is as high as 45.5-57.1%. Therefore, it is important to strengthen intraoperative blood pressure management and prevent hypotensive events in frail patients.

IOH is preventable and may potential to improvement in postoperative outcomes. Futier et al highlighted management targeting an individualized systolic blood pressure, compared with standard management, reduced the risk of postoperative organ dysfunction 30 days after surgery. Current treatment of intraoperative hypotensive episodes is not proactive and rather occurs with some delay. For elderly frail populations undergoing major surgery, there is need for a novel method to prevent hypotension.

Edwards Lifesciences has developed an algorithm that by applying machine learning methods analyzing continuously invasively measured arterial waveforms with the Acumen lQ is able to predict hypotension, defined as a mean arterial pressure (MAP) below 65 mmHg lasting for at least 1 min. The Hypotension Prediction Index (HPI) ranges from 0 to 100, and higher values reflect a higher likelihood of hypotension and shorter intervals between periods of hypotension. In major abdominal surgery, HPI demonstrated a sensitivity of 85.8%, 81.7%, and 80.6% respectively to predict a hypotensive event at 5, 10, and 15 minutes before a hypotensive event. The HPI enable the treating anesthetist to proactive treat the predicted hypotension. Various studies have shown that HPI ability in reducing TWA-MAP < 65mmHg and significantly reduction in the incidence of IOH in major noncardiac surgery such as abdominal surgery, gastrointestinal surgery, spinal surgery, in elderly populations undergoing orthopedics surgery.

This study aim to implement intraoperative hemodynamic monitoring and management guided with HPI algorithm in frail patients undergoing elective abdominal surgery. Investigators hypothesize that the use of this algorithm will alter treatment of hypotension and reduces the amount of hypotension as measured by the time weighted average (TWA) during non-cardiac surgery and to anticipate a reduction of postoperative AKI incidents, to explore the clinical benefits of impact of Acumen guided algorithm hemodynamic management in postoperative intestinal function recovery, and postoperative cardiac complications.