Endovascular aortic repair has been shown to reduce postoperative morbidity and mortality compared to open aortic surgery (OAS) [1]. In the setting of aneurysmal or occlusive disease, it has even become the preferred treatment modality in patients with suitable anatomy ^[2][3][4][2,3,4]. These minimally invasive procedures allow for the treatment of high-risk patients who are not suitable for OAS by mitigating surgical stress. Despite this, OAS remains a proven treatment option in patients with extended occlusive aorto-iliac disease [5], complex aortic aneurysms defined as those with hostile infrarenal aortic neck features or extended aneurysms involving the renal and/or visceral arteries, or to salvage failure of previous endovascular treatment [6]. In these settings, OAS causes more physiological stress because of the invasive surgical approach and supra-renal cross-clamping requiring organ protection strategies [7]. These procedures are usually performed by experienced and high-volume teams and lend themselves to the implementation of measures to reduce associated morbidity. Nonetheless, the postoperative mortality rate remains as high as 4–8% in a contemporary series of OAS for complex AAA, mainly related to respiratory and cardiac events ^[8][9][10][8,9,10]. Analysis of a national registry showed that the proportion of patients treated by OAS for aorto-iliac occlusive disease declined by two thirds in the past 15 years, while no improvement in postoperative mortality was noted over the same period of time [11].

Prehabilitation refers to a combination of measures aiming to prepare patients for the physiological and psychological stress induced by surgery [12]. There is growing evidence that these programs confer benefits to patients [13] and promote enhanced recovery after surgery (ERAS). The ERAS evidence-based consensus statement based on this emerging knowledge and was initially described for colorectal surgery [14]. Based on various changes to overall care in this setting, similar guidelines were progressively integrated into other surgical specialties ^{[15][16][17][18][19]}[15,16,17,18,19] and, more recently, for OAS [20].

2. Physiological Consequences of OAS for Complex Aortic Surgery

The physiological response that occurs because of surgical injury is referred to as the surgical stress response. It is mediated by an endocrine/inflammatory response and reduces tissue damage, prevents or combats infection, and initiates the healing process ^[21][22][21,22]. The intensity of the stress response is proportional to the surgical wound, internal organ manipulation and tissue dissection, and is correlated with postoperative adverse events [23]. OAS can be performed through a transperitoneal or a retroperitoneal approach when the disease remains limited to the abdominal aorta. The transperitoneal approach leads to a severe alteration in pulmonary mechanics [24] and bowel motility, resulting in higher rates of postoperative pneumonia and prolonged ileus [25]. Pulmonary complications are even more likely if a thoraco-abdominal exposure is performed, because of the detrimental effect on lung volume via alveolar collapse and pleural effusion, respiratory muscles and diaphragmatic dysfunction, all encouraging pulmonary infection [26]. Owing to the up to 50% increase in oxygen consumption after major abdominal surgery related to the elevated global oxygen demand, pulmonary complications may lead to serious consequences [27]. Aortic cross-clamping results in major hemodynamic changes including increased blood pressure, changes in afterload and cardiac output variability [28]. Unclamping results in reperfusion syndrome that triggers a systemic inflammatory response. The intensity of this effect is related to the level and time of clamping [29], and can result in multiple organ dysfunction, which can vary in intensity. In parallel, postoperative ischemia/reperfusion injuries are closely related to pre-existing organ impairment and the patient’s medical history [29]. Coagulopathy can occur during open vascular surgery and is multifactorial. The underlying mechanisms are complex and not fully understood [30]. Major intraoperative bleeding is typically the starting point, leading to the consumption of platelets and coagulation factors. The dilution of the coagulation factors induced by fluid resuscitation, including red cell transfusion, worsens the coagulation disorders [31]. Furthermore, acidosis occurs secondary to tissue hypoperfusion and impairs the coagulation process, resulting in delays in clot formation and reducing the clot strength [32]. Hypothermia may also contribute to acquired coagulopathy by decreasing platelets’ aggregability and adhesion. Pre-existing platelet dysfunction secondary to chronic renal disease or antiplatelet therapy, in addition to the administration of heparin during vascular surgery, may contribute to exacerbations in the acquired coagulopathy consequences and challenge their management.

3. Preoperative Risk Assessment

These physiological consequences require physicians to conduct thorough risk stratification and optimise the treatment of pre-existing medical conditions. Cardiac complications account for up to 40% of adverse events after OAS [33]. Cardiac preoperative risk assessment usually includes recording the patient’s cardiovascular risk factors, and imaging or functional examinations including transthoracic echocardiography and a non-invasive stress testing. However, preoperative coronary revascularisation remains a matter of debate. According to the current guidelines, it should be considered only in patients with unstable coronary disease or in high-cardiac-risk patients [34]. To assess pulmonary risk, pulmonary function testing should not be used routinely, except in patients with previously diagnosed chronic obstructive pulmonary disease (COPD) or asthma [35]. Some authors advocate the liberal use of pulmonary function testing to detect undiagnosed COPD, allowing for a better selection of patients that would benefit from the implementation of medical therapy and prehabilitation [34]. Although pulmonary function testing can highlight undiagnosed pulmonary disease such as COPD, obesity hypoventilation syndrome or pulmonary artery hypertension, the results are poorly correlated with the patient’s functional status [36]. It is acknowledged that good functional status is correlated with a better prognosis, even in patients with numerous risk factors [37]. Therefore, other tools should be used for the identification of patients who may benefit the most from prehabilitation programs. Functional capacity is expressed in metabolic equivalents (MET), which reflect the ability to perform and cope with activities of daily living and the physiological capacity to increase cardiac output to meet elevated post-surgical oxygen demands [26]. Although chronic renal insufficiency is a surrogate marker for all-cause postoperative mortality after OAS, there are currently no effective strategies besides hydration to prevent post-operative kidney injury. However, preoperative serum creatinine concentration should be measured, and patients referred to specialist renal services, when creatinine clearance is <60 mL/min/1.73 m². [34] Malnutrition, estimated by a serum albumin level < 30–35 g/L, negatively correlates with pulmonary complications after non-cardiac major surgery ^[35][38][35,42], and surgical site infection in general surgery ^[39][43]. In the context of OAS, a multi-institutional study pooled analysis of 4956 patients undergoing OAS for AAA highlighted a detrimental severity-dependent association between preoperative serum albumin level and outcomes (30-day mortality, pulmonary complications, and length of stay) ^[40][44]. This study emphasized the need for the routine screening of preoperative serum albumin, allowing for poor nutritional status to be adequately corrected. Current guidelines also recommend that nutritional risk screening includes a record of body mass index (BMI), the percentage of weight loss within three months, and documentation of food intake ^[41][45]. The diagnosis and management of preoperative anaemia is of relevance before major vascular surgery, taking into consideration the high risk of major blood loss and the high cardiovascular risk of the involved population. The World Health Organization (WHO) defines anaemia as a hemoglobin (Hb) count <12.0 g/dL in female and <13.0 g/dL in male subjects ^[42][46]. Teams should adequately address preoperative anaemia in all patients undergoing OAS and define a transfusion plan. To allow for adequate time to optimize erythrocyte mass, laboratory testing should be completed 4–6 weeks prior to the operative date ^[43][44][47,48]. Frailty is a multifactorial state of impaired functional reserve and decreased resistance to stressors, and better predicts surgical risk compared to age itself in elderly patients. Frailty is also associated with delayed recovery and decline function after major surgery. ^[45][49] Thus, frailty screening appears to be of particular interest to implement interventions aiming to mitigate these risks ^[46][50]. Comprehensive geriatric assessment is the gold standard for frailty assessment but is limited by medical resources and is not relevant in all elderly surgical patients. Thus, numerous screening scores exist, including the Clinical Frailty Scale. This is a quick nine-point scale that does not require physical performance test. The feasibility of the test is particularly important when considering the limited time attributed to outpatient care ^[47][51]. Among selected patients, comprehensive geriatric assessment enables the identification and remediation of contributors to frailty (physical performance, nutrition, cognition, polypharmacy, and mental health) ^[47][51]. However, the beneficial impact of dedicated prehabilitation programs on frail patients still needs to be investigated ^[48][52].

4. Management of Postoperative Risk with an Active Preoperative Program

4.1. Prehabilitation

It stands to reason that patients with a higher functional capacity are more likely to have an uneventful postoperative course ^[37][49][50][37,41,53]. Thus, prehabilitation presents the opportunity to prevent postoperative adverse events by improving patients’ functional capacity through a combination of measures. Prehabilitation also aims to promote the enhanced and full recovery of preoperative functional capacity by increasing physiological reserve. Prehabilitation has evolved from unimodal intervention (exercise or nutrition alone) to a multimodal and multidisciplinary preoperative approach ^[51][54]. Despite the lack of a consistent definition, prehabilitation is known as a combination of exercise interventions aiming to improve conditioning before surgery. These programs usually include aerobic exercises (cycling and walking), resistance training, and specific deep-breathing training and exercises. Multimodal prehabilitation encompasses this exercise training, along with dietary interventions, psychological support, smoking and alcohol cessation, and medical optimization. Primarily, physicians encourage compliance through counselling and education. In the context of upper abdominal surgery, the benefit of a 30 min preoperative physiotherapy session including education and breathing exercise training has been demonstrated in a randomized control trial (RCT) ^[52][55]. The absolute reduction risk of postoperative pulmonary complications was as high as 15% in the intervention group. Patients should commit to smoking cessation through a dedicated road map in connection with addiction specialists and psychologists ^[53][56]. This decreases the rate of pulmonary complications by more than 20% if initiated for 4 weeks before surgery ^[54][57] and reduces the risk of postoperative infections ^[55][58].

4.2. Enhanced Recovery Pathways

ERAS is a perioperative care pathway aiming to accelerate patients’ recovery and discharge while reducing postoperative complications. Based on RCTs, fast-track surgery programs have become the standard of care in colorectal surgery ^[54][56][57,76]. The benefits in the setting of AAA open repair were also evaluated in an RCT in the late 2000s ^[57][77]. This study showed encouraging results, with decreased postoperative assisted mechanical ventilation, fewer medical complications and faster recovery of gastrointestinal function. A recently published meta-analysis found benefits of ERAS in OAS in terms of hospital stay and postoperative complications, while no difference was found in 30-day mortality ^[58][78]. There is no available standardized ERAS protocol, but it is acknowledged that the positive influence on outcomes mainly depends on a combination of measures, with the isolated effect of individual elements being less important ^[59][79]. Integral components that should be considered and protocoled in all enhanced recovery pathways are fasting and carbohydrate loading, multimodal analgesia, prevention of postoperative nausea and vomiting, patient warming, anaesthetic protocols, postoperative fluid management, catheter/drain removal, early mobilization, and chest physiotherapy ^[20][58][20,78]. Patient blood management (PBM) is a recently defined multidisciplinary multimodal approach to limit the use and need of allogenic blood transfusions in at-risk patients. Preoperative anaemia is present in as many as 40% of surgical patients ^[60][80] and can have multiple aetiologies, including iron deficiency, occult blood loss, chronic kidney disease, cancer, or chronic inflammatory state. Intuitively, anaemia should be associated with an increased incidence of postoperative adverse events given the first principles of physiology regarding the balance between organ oxygen supply and demand. In addition, patients with vascular conditions are at higher risk because of the disseminated nature of the atherosclerotic disease. An increased risk of postoperative major adverse cardiac events was found in patients with preoperative anaemia in a vascular surgery population, with a severity-dependant association ^[61][81]. A meta-analysis pooled the results of 949,445 patients from 24 studies undergoing all types of surgery and highlighted that preoperative anaemia tripled the risk of in-hospital mortality ^[62][82]. Nonetheless, a multicentre study demonstrated that transfusion itself was an independent predictor of postoperative morbidity and mortality in 2946 patients undergoing major vascular surgery ^[63][83]. The uncertainty of whether allogeneic red cell transfusion is associated with harm or benefit in anaemic patients remains unsolved ^[64][84]. Transfusion exposes the patient to a higher risk of infections including surgical-site infections and pneumonia ^[65][66][67][85,86,87] related to its immunosuppressive effects ^[42][46], and additionally incurs considerable costs ^[68][88].