This study aims to evaluate whether the reduction in the amount of intraoperative norepinephrine required to prevent hypotension, facilitated by processed electroencephalography (pEEG) -guided general anesthesia, will lead to a decrease in postoperative complications, particularly acute kidney injury (AKI).

In major abdominal surgery, intraoperative hypotension (IOH) remains a prevalent concern, contributing significantly to postoperative complications. These complications include acute kidney injury (AKI), myocardial injury, and even mortality. While IOH is multifactorial, its occurrence is frequently associated with the need for vasopressor support, particularly norepinephrine, which is widely used to manage and prevent IOH. However, it is important to note that vasopressors, including norepinephrine, are themselves implicated in promoting AKI .

The lack of consensus on a universal definition for IOH adds complexity to this issue. Currently, it remains unclear whether IOH should be defined based on absolute blood pressure thresholds or as a relative decrease from baseline. IOH is commonly defined as a systolic blood pressure of <90 mm Hg or a mean arterial pressure (MAP) of <65 mm Hg.

Ephedrine is often the first-line vasopressor administered to treat IOH, with norepinephrine as a second-line option. The hemodynamic effects of these two agents differ: norepinephrine increases cardiac preload without significantly increasing afterload, thereby raising cardiac output. Ephedrine, however, increases cardiac output but with a greater increase in afterload, often leading to tachycardia, which can be detrimental to patients. The variable effectiveness of ephedrine and its associated side effects have led clinicians to consider norepinephrine as a more appropriate option for managing IOH, potentially with fewer cardiovascular side effects.

Additionally, crystalloid fluid overload during abdominal surgery has been linked to poor postoperative outcomes, including anastomotic instability. Liberal fluid regimes may disrupt the physiological healing processes at surgical sites, suggesting that fluid management strategies aimed at minimizing overload could improve patient outcomes.

Recent studies propose that early norepinephrine administration to maintain MAP, even before the onset of hypotension, may help reduce the need for large fluid volumes.

One important factor contributing to IOH and vasopressor use is excessively deep general anesthesia. Processed electroencephalography (pEEG) can guide the optimization of anesthesia depth, potentially preventing overly deep anesthesia and, in turn, reducing the incidence of IOH and the need for vasopressor .

Inclusion Criteria:

1. Patients scheduled for major abdominal surgery lasting more than 2 hours under general anesthesia.
2. American Society of Anesthesiologists Physical Status (ASA) score I-III.
3. Age range of 18-70 years.
4. Both male and female patients.

Exclusion Criteria:

1. Emergency surgeries.
2. Uncontrolled hypertension (systolic blood pressure >150 mm Hg) despite medication.
3. Recent acute cardiovascular events, including heart failure or acute coronary syndrome.
4. Chronic kidney disease with a glomerular filtration rate <30 ml/min/1.73 m² or requiring renal replacement therapy.
5. Severe hepatic failure (ASAT/ALAT >2N, elevated bilirubin, or PT <50%).
6. Preoperative sepsis or septic shock.
7. Pregnancy.
8. Patient refusal to participate in the study.