Predicting Postoperative Myocardial Injury: A Retrospective Cohort Study Comparing Absolute Versus Relative Definitions of Intraoperative Hypotension

The investigators are conducting an important study aimed at better understanding and predicting a potential complication after non-cardiac surgery: myocardial injury. This research is crucial for enhancing surgical safety and improving patient outcomes.

Simply put, postoperative myocardial injury (PMI) means that heart muscle cells are damaged after non-cardiac surgery. While it might not cause obvious chest pain like a heart attack, it can show up as abnormalities on an electrocardiogram (ECG) or in blood tests (like elevated troponin levels). This type of injury is a significant factor contributing to postoperative complications and even mortality.

During surgery, hypotension-or low blood pressure-is a common occurrence. The investigators know that maintaining adequate blood pressure is essential for the heart to receive a sufficient blood supply. If blood pressure drops too low, the heart's blood supply can be reduced, potentially leading to oxygen deprivation and damage to heart muscle cells.

While it's widely accepted that low blood pressure is linked to myocardial injury, precisely defining "low blood pressure" during surgery has been a persistent challenge.

• Historically, the investigators have focused on the "absolute value" of blood pressure, such as a fixed mean arterial pressure (MAP) threshold (e.g., below 65 mmHg). Many studies have indeed shown that MAP below 65 mmHg, especially for extended periods, increases the risk of PMI.
• However, recent research is starting to challenge this perspective. Some studies have found that even maintaining a relatively higher blood pressure during surgery (e.g., MAP above 75 mmHg) didn't significantly reduce the incidence of PMI. This suggests that simply looking at a fixed blood pressure number might not tell the whole story.

Our preliminary research uncovered an intriguing finding: even if a patient's absolute blood pressure value during surgery seemed acceptable (e.g., above 60 mmHg), their risk of postoperative myocardial injury significantly increased if that pressure had dropped by more than 40% from their individual "normal" pre-operative blood pressure. Based on this discovery, our study proposes a novel hypothesis: the percentage drop in MAP from an individual's baseline might be more strongly correlated with postoperative myocardial injury and a better predictor of risk than the absolute MAP value.

The investigators will be reviewing patient data from non-cardiac surgeries performed at China-Japan Friendship Hospital between 2020 and 2025. The investigators will meticulously analyze these patients' intraoperative blood pressure changes (considering both absolute values and the percentage change from their pre-operative baseline) and compare these findings with whether they developed myocardial injury after surgery.

Our study's goal is to determine which definition of low blood pressure (absolute value or percentage drop from baseline) is more closely related to postoperative myocardial injury.

The investigators will collect detailed patient information, including demographics, past medical history, pre- and post-operative test results, intraoperative vital signs (blood pressure, heart rate, oxygen saturation, etc., recorded every 15 seconds), and intraoperative medications. All data will undergo rigorous statistical analysis to ensure the scientific validity and reliability of our findings.

The results of this study will help us more accurately identify patients at high risk for postoperative myocardial injury. If our hypothesis is confirmed, it means that during surgery, doctors, in addition to monitoring absolute blood pressure values, will pay closer attention to the degree of blood pressure drop relative to a patient's own normal baseline. This will help to:

• Improve understanding of individual patient differences: Recognizing that what's "normal" for one patient might be too low for another.
• Enable more precise adjustments in anesthesia and surgical management: Allowing for timely interventions to maintain optimal heart muscle perfusion, thereby reducing the incidence of postoperative myocardial injury.
• Ultimately, enhance patient safety during surgery and improve their recovery and long-term outcomes.