Predictive Factors of Complications Following Elective EVAR - Essay Example

Predictive factors of complications following elective endovascular abdominal aortic aneurysm repair (EVAR) Introduction Patency of blood vessels is an important factor which determines normal blood flow and ultimately the health. Any aberration, either occlusion or disruption of blood flow or the risk of leakage inside the intact body organs and tissues can pose an immediate life threatening situation. Thinning of either arterial or venous vessel walls, either due to anatomical defect, disease or aging can result in aneurysm development which immediately becomes prone to mechanical disruption due to its abnormality in size and shape as well as the thinning of the vessel wall. The aorta is the primary vessel carrying fresh blood to vital organs and any functional or structural defect can lead to a high risk situation. Abdominal Aortic Aneurysm (AAA) is a serious disorder which results in the permanent dilatation of the terminal portion of the abdominal aorta which is prone to rupture and a major cause of death in the developed countries encountered in recent years (Vorp, 2006). Aneurysm develops due to the degeneration of the aortic wall which results in the increased pressure of blood on the vessel wall and can result in its mechanical disruption and internal haemorrhage. Mostly such aneurysms are encountered in aging males but incidences in females have also occurred. The usual symptoms are abdominal and back pain as well as tenderness on palpation (Davis & Taylor, 2007). In case of rupture, the prognosis is usually grave with little chances of recovery after open surgery, as usually at such advanced ages comorbidities are the complicating factors. Regular monitoring and scanning in persons predisposed to such a condition is therefore absolutely essential and a surgical intervention can be undertaken before the rupture actually occurs. The usual approach employed for a long time was open surgery, but a new technique of endoluminal repair developed by Volodos and Parodi in 1991 subsequently named as endovascular abdominal aortic aneurysm repair (EVAR) revolutionized the treatment as a more successful and less invasive procedure (Davis & Taylor, 2007). The technique has received encouraging response from surgeons in different locations and is steadily being refined by making it less invasive through the use of newer innovations of technology as well as trying for a percutaneous access to the aorta. Elective surgery is indicated based on the prediction of an impending rupture when risk parameters such as the size and growth rate of the aneurysm are evaluated. When the aortic diameter increases to an extent > 5.5 cm in males or the growth rate exceeds by 1cm per year, surgery is usually recommended (Davis & Taylor, 2007). In females, elective surgery may be recommended at a lesser size of the aneurysm. In the past, open repair of the aneurysm using a graft involved the post peri-operative surgical risks of cardiovascular, respiratory and renal complications which worsened the patient’s condition and the complication rate remained at a steady value of between 15-30% for a number of years. This prompted the search for newer techniques and the endoluminal repair (EVAR) received encouraging response from the surgical community. In this technique, the operation is carried out under regional anaesthesia and an aortic stent graft is placed in the aortic lumen, which provides both radial and longitudinal support. Experience and technology led to the development of better material and techniques for this procedure as the implanted stent material was constantly improved due to complications of lower limb perfusion or dislodging as well as the incidents of a newly discovered complication, the ‘endoleaks’ which occurred in and around the stent, either due to end zone leakage or perfusion through the fabric of the stent. Complications arising out of the EVAR procedure are many and are being steadily recognized and classified which forms the basis for building a predictive model for complications after the procedure which is presently under intensive research and study. Methods A search was performed through various scientific databases like OIVDSP and Pubmed for published studies in the English language that had evaluated the clinical trials as well as the latest advances in EVAR as a procedure for abdominal aortic aneurysm. The keywords used were, “ EVAR”, “abdominal aortic aneurysm”, “endovascular aneurysm repair”, “predictive factors-EVAR”, “complications of EVAR” and “Infrarenal aortic aneurysm repair”. Full texts of all relevant articles were downloaded, analyzed and categorized according to the different facets of the condition as well as the suitability and complications involved in the procedure. The articles were categorized into five sections viz. case selection; factors affecting outcome; biology and pathophysiology; predictors & anatomical influences. Table 1 shows the details of the relevant articles of each category. Based upon the biology/pathophysiology, criteria adopted for elective surgery and the post surgery reviews an attempt was made to shortlist the predictive factors of complications after EVAR. Table 1 Categories Study Type Procedures Major Findings Case Selection Caron (2004) Anatomic considerations before surgery Review of anatomy of aorta & Iliac arteries. Unacceptable anatomical features: Desist from EVAR Richards (2009) Comparative study between ruptured & symptomatic aneurysms Comparison by Hardman’s Index (HI)and Univariate regression analysis Anatomical & Clinical guidelines should be strictly followed Barnes (2008) Development of predictive outcome models on a comparative basis Eight preoperative variables used for 17 outcomes were tested by regression analysis Preoperative measures can be adopted to decide the suitability for EVAR by an outcome based model Faizer (2007) Co-morbidity based objective scoring system for deciding between open surgery & EVAR Retrospective database review Patients with high medical risk for open repair benefitted with EVAR Sampaio (2004) Influence of gender in suitability for EVAR Evaluation of clinical data and CT scans Identical technical & clinical outcomes in both sexes, higher rate of neck dilatation in women& lower limb patency rates in men Jean-Baptiste E. (2007) Suitability of EVAR in high risk patients Statistical analysis of data from high risk patients over a 5 year span Technical success rate of 99% in high risk patients Sajid (2007) Outcome prediction evaluation by Glasgow Aneurysm Score (GAS) & Hardman’s index Retrospective statistical analysis GAS & HI poor predictors of outcome following EVAR Atkinson (2008) Risk stratification for anaesthesia & aortic surgery Treatise on risk evaluation techniques before surgery Cardiopulmonary exercise testing recommended before EVAR Factors Affecting Outcome Acosta (2007) Analysis of patient and management related predictors for outcome after open surgery & EVAR Data analysis from patients in a hospital spanning four years Age ,symptoms and blood Hb levels good markers for prediction of outcomes Peppelenbosch (2004) Effect of preoperative aneurysm diameter on clinical outcome following EVAR Life table analysis and log rank tests for three groups with different aneurysm size. Patients with large size aneurysms more likely to suffer from post surgical serious outcomes Timothy (2009) Identification of factors influencing stent acceptance and the implications of stent material Treatise on development of stent material used in EVAR and the mechanisms for avoidance of late occurring failure Follow up studies necessary after stent implant to prevent late occurring failures after EVAR Hertzer (2005) Evaluation of factors influencing survival after open surgery for AAA at a facility with a single surgeon Statistical evaluation of mortality data in patients undergoing open surgery for asymptomatic AAA after noninvasive/invasive procedures Patient age and other medical risk factors including comorbidities contribute to survival rates after open surgery for AAA Boult (2007) Effect of preoperative factors on mid-term survival in patients after undergoing EVAR Kaplan-Meier survival analysis Survival rate linked to ASA, aneurysm size and creatinine levels Biology & Pathophysiology Eckstein (2007) Effects of high volume case handling by open method of treating AAA & identification of perioperative predictors mortality Step wise logical regression analysis of data from German hospitals for the study of perioperative variables affecting outcomes. Significant predictors of perioperative mortality identified as age, AAA diameter, length of procedure, suprarenal clamping and blood transfusion Vorp (2007) Review on biomechanics of aortic aneurysm Treatise on biomechanical factors leading to aneurysm and the precipitating factors Less collagen and elastin the aneurysm blood vessel wall due to enzymatic degradation of structural proteins Davis (2008) Endovascular AAA repair Treatise on the development of the EVAR technique EVAR offers more advantage for survivability as compared to the open method Predictors Hassen (2007) Relationship between preoperative nutritional status and major vascular surgery Clinical assessment of preoperative nutrition prospectively in patients shortlisted for EVA, evaluation of body composition & systemic inflammatory response syndrome (SIRS) Nutritional status did not influence SIRS outcome, free fat mass & skeletal muscle mass (SMM) affected SIRS and SMM affected length of stay Clin. Res. (2005) Evaluation of long term outcome after EVAR in USA Statistical analysis of national registry EVAR a safe procedure if FDA approved devices were used Matsumura (2008) Comparative study of predictors of survival by open method and EVAR Multicentre clinical trial of patients undergoing either method of aneurysm repair by Cox modelling Independent risks of mortality identified irrespective of technique used Patterson (2008) Review paper on pre-operative risk prediction Review of 68 articles on comparison of risk prediction methods GAS found to be the most appropriate method but further refinement suggested Anatomical Influences AbuRahma (2009) Correlation of aortic neck length to early/late outcomes after EVAR Postoperative ultrasound an CT imaging studies by estimation of endoleak incidence, need for reintervention & survival Short aortic neck length patients suitable for carrying out EVAR procedure despite higher incidence of endoleaks Abbruzzese (2008) Anatomic & device specific evaluation of outcomes after EVAR Kaplan Meier analysis of outcomes by morphological examination of aneurysms No significant difference due to device specificity. Recommended specific instructions for use (IFUs) vital for reducing negative outcomes Ellen (2003) Outcomes of using EVAR in hostile neck anatomical situations Anatomic evaluation through CT scans Endografts can be successfully used in hostile neck patients after careful evaluation Choke (2006) Outcomes of using EVAR in hostile neck anatomical situations Correlation of prospective data and retrospective analysis of comparative data from good aortic neck/bad neck patients Endografts can be successfully used in hostile neck patients after careful evaluation Results & Discussion Although initial recommendations do not advocate the use of EVAR for repair of AAA, careful following of anatomical & clinical guidelines can lead to better outcomes as compared to the open method. Preoperative measures can be adopted to decide the suitability for EVAR by an outcome based model and patients with high medical risk for open repair benefitted hugely through the new technique of EVAR. There was no significant difference in clinical outcomes based on sex although there was higher rate of neck dilatation in case of women and lower limb patency rates in men. The studies conducted on the evaluation of pre as well as post operative outcomes following EVAR used GAS and HI methods which give a fair degree of accuracy but better evaluative criteria need to be developed for a truer picture. In high risk patients, EVAR had a better success rate as compared to the open method by grafting. Besides age, symptoms, blood Hb levels, ASA, aneurysm size, creatinine levels, AAA diameter, length of procedure, suprarenal clamping and blood transfusion, evaluation of comorbidities served as good markers for the prediction of outcomes. It was found that patients with large size aneurysms were more likely to suffer from post surgical serious outcomes. Therefore follow up studies were necessary after stent implant to prevent late occurring failures after EVAR. EVAR offers more advantage for survivability as compared to the open method. Differences in nutritional status did not influence systemic inflammation response syndrome (SIRS) outcome though free fat mass (FFM) & skeletal muscle mass (SMM) did affect SIRS length of stay in the hospital, respectively. In the United States, it was discovered that EVAR was a safer procedure if the FDA approved stents were used. However, mortality outcome was independent of the surgical mode employed for aneurysm removal. Short aortic neck length (hostile neck) patients were found to be suitable for carrying out EVAR procedure after careful evaluation despite higher incidence of endoleaks. Only the recommended specific instructions for use (IFUs) should be employed for reducing negative outcomes. References 1. Rockman Caron, Reducing Complications by Better Case Selection: Anatomic Considerations, j.semvascsurg.2004.09.006 2. 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AbuRahma Ali F. , Campbell John, Stone Patrick A. et. al., The correlation of aortic neck length to early and late outcomes in endovascular aneurysm repair patients, J Vasc Surg 2009;50:738-48 26. Abbruzzese Thomas A., Kwolek Christopher J. , Brewster David C. et. al., Outcomes following endovascular abdominal aortic aneurysm repair (EVAR): An anatomic and device-specific analysis, J Vasc Surg 2008;48:19-28 Read More