Background: An abdominal aortic aneurysm (AAA) is a localized dilatation of the infrarenal aorta that, when it meets critical criteria, can rupture and cause a vital emergency, requiring immediate surgery with a mortality rate close to 85%(1). Also, symptomatic AAA and/or imminent rupture is a surgical emergency that should be recognized and treated promptly. Elective procedures are usually performed in patients with AAA with a diameter greater than 5.5 cm in men and 5.0 cm in women(2,3).

There are different techniques for the surgical repair of AAA, which are divided into two main groups: endovascular and open procedures. The endovascular procedure offers an early survival benefit, better postoperative recovery, and fewer incision-related complications as it is a minimally invasive procedure. However, it requires more re-interventions, but most are mainly minor endovascular procedures. In contrast, an open approach has a better 15-year late survival benefit, associated with greater graft durability, a lower rate of re-interventions, and the additional advantage of being more affordable (4-7).

Several risk factors have been established around surgical procedures that may affect the outcome, including preoperative and intraoperative hypotension. Preoperative hypotension is one of the most crucial factors, especially when talking about ruptured AAA, where it is present with a high frequency and has been seen as an association with mortality with an AOR of 3.28 (CI 1.75-5.41; P < .001) (8). For intraoperative hypotension, a study showed that it increased the 30-day mortality after an elective open repair of AAA with an OR of 6.61 (CI 0.71-61.07; p = 0.05). Also, it has been associated with liver dysfunction (p < 0.001) and colonic ischemia (P=0.021) (9-11).

However, the frequency and effects of postoperative hypotension in open and endovascular AAA surgery have not been described in the literature despite the everyday use of vasopressor medications (48%) in the immediate medical management following an open AAA repair(12). However, other studies have shown that postoperative hypotension in abdominal surgery is a significant complication that can have adverse effects on the patient. This condition is characterized by a decrease in blood pressure, which can lead to myocardial injury, acute kidney damage, and an increase in short-term mortality(13).

According to literature, postoperative hypotension is common after major abdominal surgeries, and its detection may be suboptimal if routine vital sign assessments are the sole monitoring method. A prospective observational study found that nearly one-quarter of patients experienced episodes of mean arterial pressure (MAP) below 70 mmHg for at least 30 minutes, many of which went undetected through routine evaluations(14). Another study highlighted that prolonged postoperative hypotension, defined by absolute MAP thresholds, is associated with myocardial injury, especially when MAP falls below 65 mmHg for extended periods (15).

In addition, in other vascular interventions like carotid endarterectomy, postoperative hypotension has been associated with increased risks of 30-day mortality, stroke, myocardial infarction, and length of stay(16).

Given the potential implications for adverse perioperative outcomes, it is essential to elucidate potential risk factors to tailor the perioperative management of AAA repair further. Thus, we aim to describe the mortality and determine the risk factors associated with peroperative and postoperative hypotension at 48 hours in patients who underwent an Infrarenal Abdominal Aortic Aneurysm Repair at the Rijnstate Hospital during the period 1-1-2013 until 31-12-2021.

Research question: What were the risk factors associated with postoperative hypotension in patients who underwent an Infrarenal Abdominal Aortic Aneurysm Repair at the Rijnstate Hospital during the period 2013 to 2021?

Hypothesis:

Alternate hypothesis: There are specific risk factors associated with postoperative hypotension in patients who underwent an Infrarenal Abdominal Aortic Aneurysm Repair at the Rijnstate Hospital during the period 2013 until 2021.

Research design: Observational, monocenter, retrospective cohort study.

Selection Criteria:

• Inclusion criteria: all patients treated open and endovascular for an abdominal aortic aneurysm in Rijnstate between 1-1-2013 and 31-12-2021.
• Exclusion criteria: Patients managed hybrid (EVAR + open) or expectantly.

Objectives:

General Objective: Determine the risk factors associated with per- and postoperative hypotension in patients who underwent an Infrarenal Abdominal Aortic Aneurysm Repair at the Rijnstate Hospital from 1-1-2013 until 31-12-2021.

• Specific Objectives:

• Characterize the sociodemographic and clinical variables of the patients who underwent an Infrarenal Abdominal Aortic Aneurysm Repair.
• Determine the risk factors associated with peroperative and postoperative hypotension in patients who underwent an Infrarenal elective open Abdominal Aortic Aneurysm Repair.
• Determine the risk factors associated with peroperative and postoperative hypotension in patients who underwent an Infrarenal elective endovascular Abdominal Aortic Aneurysm Repair.
• Describe the 30-day postoperative mortality associated with each type of management and postoperative hypotension in patients who underwent an Infrarenal Abdominal Aortic Aneurysm Repair.
• Describe the 30-day postoperative secondary clinical outcomes associated with each type of management and postoperative Hypotension in patients who underwent an Infrarenal Abdominal Aortic Aneurysm Repair.

Analysis unit

The unit of analysis for this study will be mortality as the dependent variable and the presence of peropertive and postoperative hypotension at 48 hours, defined as an SBP less than 90 mmHg, a MAP less than 60 mmHg, or a difference of more than 30 mmHg compared to pre-operative blood pressure (17).

Additionally, the secondary outcomes will include the occurrence of acute kidney injury, acute myocardial infarction, prolonged mechanical ventilation, spinal cord ischemia, stroke, and mesenteric ischemia (13).

Statistical Analysis: The description of the variables will be done by calculating absolute and relative frequencies for qualitative variables and the use of measures of central tendency and dispersion for quantitative variables; parametric and nonparametric statistics will be used depending on the normal distribution of the data, which will be evaluated using Kolmogorov-Smirnov or Shapiro-Wilk.

Bivariate analysis will be performed, the student t-test will be used for normally distributed data, and the Mann-Whitney U and Kruskal-Wallis H tests will be used for non-normally distributed data. Rates and differences in proportions will be estimated using Pearson's c2 test and Fisher's exact test.

Subsequently, a Kaplan-Meier survival analysis will be performed to evaluate mortality up to 30 days after the surgical procedure or until discharge. Sensitivity analyses will be used to calculate survival. Missing values will be excluded from the analysis. A P value of < 0.05 will be considered statistically significant.

A univariate and multivariate logistic regression analysis will study the association between hypotension and risk factors.

Data management:

Each investigator involved in this research project will be responsible for ensuring the protection and security of patient data. Once the final research products have been generated, the principal investigator will be responsible for the final custody of the database and directory of variables.

Bias control: The potential measures of bias for this study and the control strategy for each are:

• Information bias: The possibility that patients do not have all the information necessary to complete the database and incur loss of information should be contemplated. If the clinical history does not contain all the information needed to complete the database, Missing values will be excluded from the analysis.
• Observer bias: This bias can occur when the researcher, knowing the expected outcome, tends to find more cases of this event in a particular cohort. A non-existent association may appear. To avoid this, only the information found in the clinical history or reliable and objective sources of information will be included without interpretation of any variable by the investigators.
• Confounding bias: All results derived from observational studies are potentially influenced by confounding bias. In this type of study confounding bias is understood as a comparability problem whose origin is linked to the impossibility of randomly assigning the exposure of the study subjects. Thus, confounding variables are not equally distributed among the contrast groups, and subjects are exposed for different reasons that depend on cultural and socioeconomic patterns. To reduce the risk of the presence of this bias, different risk factors associated with worse outcomes have been included so that the analysis can control for these factors in case there is a greater presence of these factors in some of the groups that could affect the results.

Expected Results and Impact: Publish one paper with the institutional experience to generate knowledge on this pathology's multidisciplinary management and present an abstract at an international congress.

• Determine the risk factors associated with postoperative hypotension in patients who underwent an Infrarenal Abdominal Aortic Aneurysm Repair.
• Describe the mortality and secondary clinical outcomes associated with each type of treatment and postoperative hypotension in patients undergoing infrarenal abdominal aortic aneurysm repair.

Ethical aspects: The study is conducted within the ethical principles for medical research on human subjects according to the Declaration of Helsinki - 59th General Assembly, Seoul, Korea, October 2008. CIOMS Guidelines, the Good Clinical Practice Guidelines of the International Conference on Harmonization (GCP/ICH). The present research is classified within the category of no risk. Since it is a retrospective study in which no intervention will be performed.

Access to the research instruments will be limited only to the investigators, who will be ready to give information about the study to organized, approved, and interested entities if they are of an academic and scientific nature, preserving the accuracy of the results. Absolute confidentiality will be maintained, and a good professional, institutional name will be preserved.

Inclusion Criteria:

• Age > 18 years
• Elective AAA repair between 2013 and 2022 (endovascular and open)

Exclusion Criteria:

• Data from the blood pressure monitoring system were only available from 2013, so patients treated before January 1th 2013 were excluded.
• Patients were also excluded from the study if registered objection to use their data for research,
• absence of blood pressure data,
• revision surgery after previous endovascular or open repair,
• ruptured aneurysm,
• mycotic aneurysm, or
• treatment with endovascular aneurysm sealing.

Patients with an abdominal aortic aneurysm treated electively between 2013 and 2022.

The raw data supporting the conclusions of this article will be made available by the authors upon request and can only be shared anonymously. This restriction is due to hospital policies, which prohibit data sharing without clearly defined purposes. Data transfer agreements must be in place before data can be shared.