Morbidity and mortality factors in the elective surgery of infrarenal abdominal aortic aneurysm: a case study with 134 patients

Abstracts

BACKGROUND: Conventional surgical treatment of infrarenal abdominal aortic aneurysm (AAA) can result in serious complications. To optimize treatment outcome it is important to identify patients at risk of having complications and implement prophylaxis. OBJECTIVES: To analyze early surgical mortality rate and postsurgical complications, and to identify risk factors related to morbidity and mortality. METHOD: A total of 134 patients with infrarenal AAA submitted to elective surgical correction from February 2001 to December 2005 were analyzed. RESULTS: The mortality rate (5.2%) was secondary mainly to acute myocardial infarction and intestinal ischemia. Heart-related complications were the most frequent, followed by lung and kidney complications. Presence of diabetes mellitus, congestive heart failure, coronary artery disease, and scintigraphy suggestive of ischemia were related to cardiac complications. Advanced age, chronic obstructive lung disease and reduced forced vital capacity were related to higher risks of atelectasis and pulmonary infection. Presence of renal failure, prolonged aortic clamping and high urea rates were related to acute renal failure. Smoking and advanced age were associated with lower limb ischemia. Presence of obstructive coronary insufficiency and prolonged aortic clamping and surgery time were associated with higher mortality rate. CONCLUSION: The morbidity and mortality rate was compatible with data found in the national and international literature, secondary to cardiac, pulmonary and kidney complications. Identified risk factors before and during the surgery were related to these complications.

Abdominal aortic aneurysm; morbidity; mortality; elective surgical procedures; risk factors

CONTEXTO: O tratamento cirúrgico convencional do aneurisma da aorta abdominal (AAA) infra-renal pode resultar em complicações graves. A fim de otimizar os resultados na evolução do tratamento, é importante que sejam identificados os pacientes predispostos a determinadas complicações e instituídas condutas preventivas. OBJETIVOS: Avaliar a taxa de mortalidade operatória precoce, analisar as complicações pós-operatórias e identificar os fatores de risco relacionados com a morbimortalidade. MÉTODO: Foram analisados 134 pacientes com AAA infra-renal submetidos a correção cirúrgica eletiva no período de fevereiro de 2001 a dezembro de 2005. RESULTADOS: A taxa de mortalidade foi de 5,2%, sendo secundária principalmente a infarto agudo de miocárdio (IAM) e isquemia mesentérica. As complicações cardíacas foram as mais freqüentes, seguidas das pulmonares e renais. A presença de diabetes melito (DM), insuficiência cardíaca congestiva (ICC), insuficiência coronariana (ICO) e cintilografia miocárdica positiva para isquemia estiveram associadas às complicações cardíacas. A idade avançada, a doença pulmonar obstrutiva crônica (DPOC) e a capacidade vital forçada reduzida aumentaram os riscos de atelectasia e pneumonia. História de nefropatia, tempo de pinçamento aórtico prolongado e níveis de uréia elevados aumentaram os riscos de insuficiência respiratória aguda (IRA). A isquemia dos membros inferiores esteve associada ao tabagismo e à idade avançada, e a maior taxa de mortalidade, à presença de coronariopatia, tempos prolongados de pinçamento aórtico e de cirurgia. CONCLUSÃO: A taxa de morbimortalidade esteve compatível com a literatura nacional e internacional, sendo secundária às complicações cardíacas, respiratórias e renais. Os fatores de risco identificados no pré e transoperatório estiveram relacionados com essas complicações.

Aneurisma da aorta abdominal; morbidade; mortalidade; procedimentos cirúrgicos eletivos; fatores de risco

ORIGINAL ARTICLE

Morbidity and mortality factors in the elective surgery of infrarenal abdominal aortic aneurysm: a case study with 134 patients

Aquiles Tadashi Ywata de Carvalho^I; Vanessa Prado dos Santos^II; Álvaro Razuk Filho^III; Walter Karakhaian^III; Henrique Jorge Guedes Neto^III; Valter Castelli Jr.^III; Roberto Augusto Caffaro^IV

^IMSc. in Medicine, Faculdade de Ciências Médicas, Santa Casa de São Paulo, São Paulo, SP, Brazil. Specialist in Vascular and Endovascular Surgery, Sociedade Brasileira de Angiologia e de Cirurgia Vascular (SBACV). Member, SBACV

^IIPhD in Medicine, Faculdade de Ciências Médicas, Santa Casa de São Paulo, São Paulo, SP, Brazil

^IIIPhD. Associate professor, Faculdade de Ciências Médicas, Santa Casa de São Paulo, São Paulo, SP, Brazil

^IVPhD. Associate professor and head, Angiology, Vascular and Endovascular Surgery, Faculdade de Ciências Médicas, Santa Casa de São Paulo, São Paulo, SP, Brazil

Correspondence

ABSTRACT

INTRODUCTION: Conventional surgical treatment of infrarenal abdominal aortic aneurysm (AAA) can result in serious complications. To optimize treatment outcome it is important to identify patients at risk of having complications and implement prophylaxis.

OBJECTIVES: To analyze early surgical mortality rate and postsurgical complications, and to identify risk factors related to morbid and mortality.

METHOD: A total of 134 patients with infrarenal AAA submitted to elective surgical correction from February 2001 to December 2005 were analyzed.

RESULTS: The mortality rate (5.2%) was secondary mainly to acute myocardial infarction and intestinal ischemia. Heart-related complications were the most frequent, followed by lung and kidney complications. Presence of diabetes mellitus, congestive heart failure, coronary artery disease, and scintigraphy suggestive of ischemia were related to cardiac complications. Advanced age, chronic obstructive lung disease and reduced forced vital capacity were related to higher risks of atelectasis and pulmonary infection. Presence of renal failure, prolonged aortic clamping and high urea rates were related to acute renal failure. Smoking and advanced age were associated with lower limb ischemia. Presence of obstructive coronary insufficiency and prolonged aortic clamping and surgery time were associated with higher mortality rate.

CONCLUSION: The morbidity and mortality rate was compatible with data found in the national and international literature, secondary to cardiac, pulmonary and kidney complications. Identified risk factors before and during the surgery were related to these complications.

Keywords: Abdominal aortic aneurysm, morbidity, mortality, elective surgical procedures, risk factors.

Introduction

Abdominal aortic aneurysm (AAA) is a major disease in the practice of vascular surgeons, reaching 2-4% of the general population, in a ratio of five men to one woman.^1,2 With increased life expectancy, there is a higher incidence of AAA:^3-5 in the population over 65 years, the prevalence is 6%,^1.2 reaching 10%⁶ in the population above 80 years.

It is estimated that the annual incidence of AAA rupture is eight cases/100,000 inhabitants⁷ and that AAA accounts for 2% of deaths in the population above 60 years.⁵ Mortality in these patients may be related to AAA rupture, reaching rates between 23-63%,^2.8 whereas elective operative mortality is around 3-5%.^2,9

Conventional surgical treatment is characterized by substitution of the abdominal aortic aneurysmal segment by synthetic material grafts. Surgical access used for AAA repair can be through transperitoneal or extraperitoneal approach,^10,11depending on the anatomical and clinical characteristics of each case, with advantages and disadvantages according to the literature.^12,13

Nowadays, a less invasive procedure, by placement of stent grafts, is increasingly more present in the literature, with good outcomes for a certain group of patients.^14-19

Postoperative complications can be divided into early and late. Among early complications, some are related to the surgical procedure, and there are also clinical complications. The most common immediate complications, observed during the surgical procedure, comprise persistent bleeding with consumption of coagulation factors (disseminated intravascular coagulation), vascular lesions (especially venous lesions), lesion of parenchymal or hollow viscera, ureter lesions, distal embolism, distal thrombosis, among others. Late complications are characterized by anastomotic pseudoaneurysms, aortoenteric fistulas, thrombosis and graft infection.^14,20-22

Early postoperative complications are often responsible for elective AAA morbidity and mortality rates, and deserve special attention in our study for being a reflex of preoperative preparation and of the patient's general status. Patients with surgical indication should be submitted to preoperative evaluation, identifying risk factors, associated diseases, medications in use and previous surgeries, aiming at compensation of clinical conditions. In order to optimize the treatment of these patients, we believe it is essential to identify risk groups for certain complications and evaluate morbidity and mortality rates, applying specific preventive conducts for possible complications.

The objectives of the present study were to evaluate early operative mortality rate, analyze the patients' main preoperative complications (morbidities) and identify risk factors related to morbidity and mortality.

Method

Patients with infrarenal AAA submitted to elective surgical treatment by the Vascular Surgery Course of Santa Casa de São Paulo, São Paulo, SP, Brazil were consecutively included in the study.

Patients underwent surgery when the upper transverse diameter of their aneurysm reached 5 cm or when there was a growth > 0.5 cm in 6 months. Patients at very high surgical risk in outpatient follow-up were not submitted to conventional elective surgical treatment due to status of hard-to-treat congestive heart failure (CHF), acute myocardial infarction (AMI) less than 6 months ago, angina pectoris, terminal chronic renal failure, dyspnea at rest, oxygen-dependent patients and other diseases with life expectancy shorter than 2 years.

For the purposes of this investigation, information was obtained from the groups of patients as to the pre-, trans- and preoperative periods. An outpatient follow-up was performed up to 2 months after hospital discharge.

The factors present before and during the surgery were then correlated with occurrence of complications or death in the postoperative period, with the aim of determining which factors implied higher mortality and higher local and systemic morbidity.

The logistic regression technique was used for intra- and postoperative complications,²³ where the response variable is the likelihood a given patient has of having or not a certain complication, and the explanatory variables comprise varied possible risk factors. The analysis tested variables of possible complicating factors, and only statistically significant factors were reported. A significance level of 0.05 was used to differentiate strongly relevant factors.

Population

The data of 134 patients diagnosed with infrarenal AAA and consecutively submitted to elective surgical repair at the Vascular Surgery Course of Santa Casa de São Paulo from February 2001 to December 2005 were analyzed. Mean age was 66.1 years (54 and 85), and the male gender accounted for 76.1% (n = 102) of patients.

Most patients (73.1%) were asymptomatic at diagnosis, and abdominal pain was the most reported symptom, present in 26.9% of cases (n = 36).

The most frequent associated comorbidities were hypertension (73.9%), peripheral occlusive arterial disease (64.2%), smoking (56%), diabetes mellitus (39.6%), dyslipidemia (20.1%), chronic obstructive pulmonary disease (15.7%), congestive heart failure (14.9%), heart disease (14.2%), obesity (9.7%) and nephropathy (9%).

Mean aneurysm transverse diameter was 6 cm (4.5-10), and hospital stay ranged between 3-60 days.

Left extraperitoneal approach was used as surgical access in 88% of cases, followed by transverse transperitoneal in 5.3%, right extraperitoneal in 4.5%, and median in 2.2%.

Aortoaortic graft was performed in 43.2% of cases, followed by common aortobiiliac graft in 25.4%, common aortoiliac and external iliac graft in 15% and aortobifemoral graft in 9%. At least one of the internal iliac arteries was preserved in 97% of patients.

Surgical time ranged between 4-8 hours, mean of 5 hours, and anesthesia time ranged between 4.5-8.5 hours, mean of 5.9 hours. Mean aortic clamping was 1 hour (0.5-1.8).

Results

Postoperative morbidities are listed in Table 1.

The most frequent independent complication was atelectasis, affecting 36 patients (26.9%), followed by cardiac arrhythmia in 21 patients (15.7%) and hypertensive crisis in 20 patients (14.9%). On the other hand, cardiac complications were the most prevalent (43.2%).

Two patients that had AMI (28.5% of deaths) evolved to cardiogenic shock and death, and the third had good outcome and was discharged after 28 days of hospital stay. Sixty-six percent of individuals that had complications with AMI died.

Statistical analysis showed that patients with history of diabetes mellitus (p = 0.032), heart disease (p = 0.014), congestive heart failure (p = 0.008) and electrocardiographic changes in the ST segment, suggestive of myocardial ischemia (p = 0.033) had high rates of cardiac arrhythmia in the postoperative period. Similarly, patients that had ejection fraction < 40 (p = 0.011), myocardial scintigraphy positive for ischemia (p = 0.02) and congestive heart failure (p = 0.045) were associated with higher acute pulmonary edema rates in the postoperative period (Table 2).

Respiratory complications were much frequent, affecting 57 patients (42.5%). The risk factors for these complications are found in Table 3.

In this series, 11 patients (8.2%) evolved with non-dialytic acute renal failure, and nine patients (6.7%) with acute renal failure requiring dialysis. Statistical analysis showed that individuals with history of nephropathy, i.e., with creatinine and urea levels > 1.6 mg/dL and 55 mg/dL, respectively (p = 0.001) had higher risk of developing renal dysfunction, requiring dialysis in the postoperative period. Therefore, patients with high levels of urea (> 55 mg/dL) in the preoperative period (p = 0.001), with aortic clamping time > 1.5 hour (p = 0.014) and with diuresis < 40 mL/hour in the intraoperative period (p = 0.014) had higher risk of developing non-dialytic renal dysfunction in the postoperative period.

Surgical wound complications present in 17 individuals (12.7%) mainly occurred in patients with surgical access involving the inguinal region (p < 0.05), a fact that had statistical significance. Body mass index (BMI) > 30 kg/m² (p = 0.004) and surgical time > 5 hours (p = 0.045) were associated with surgical wound infection (3.7%). BMI > 30 kg/m² (p = 0.001) was related to presence of surgical wound hematoma (Table 4).

There was lower limb ischemia in eight patients (6.0%). The causes were embolism in five (3.7%) and thrombosis in three (2.3%). Patients with lower limb embolism were treated with embolectomy, with good resolution of ischemia. Two patients with lower limb arterial thrombosis had mild and distal ischemia (foot and toes), and a clinical treatment was chosen, with good evolution. The third patient with arterial thrombosis had severe ischemia of the lower limb, and local revascularization was performed using a femoropopliteal graft. This patient evolved with graft thrombosis and irreversible ischemia and subsequent limb loss.

In this population, age > 70 years (p = 0.043) and history of smoking (p = 0.045) were related to higher risk of ischemic complications of the lower limbs, a fact that had statistical significance.

Mortality rate in this study was 5.2% (n = 7), according to the following specification: two patients died due to AMI, two patients due to mesenteric ischemia, one patient due to lower limb ischemia, one patient due to acute renal failure, and one patient due to bronchopneumonia.

When the influence of risk factors on mortality was analyzed (Table 5), there was a statistically significant increase in mortality in patients with history of heart disease (p = 0.029), with aortic clamping time > 1.5 hour (p = 0.014) and surgical time > 5 hours (p = 0.013).

There was no relationship between mortality rate and aneurysm transverse diameter, choice of surgical access, losses and replacement of blood volume in the intraoperative period.

Discussion

Fifty-eight patients (43.2%) had heart events, which accounted for the main complications. This fact is in agreement with Anacleto et al., who showed high rates of morbidity and mortality due to congestive heart failure (CHF) and tachyarrhythmia, and with Johnston et al., who included heart ischemia as the main postoperative complication.^24,25 Of 134 patients who underwent surgery at Vascular Surgery Course of Santa Casa de São Paulo throughout the study period, three (2.2%) evolved with AMI, and two evolved with cardiogenic shock and death (28.5% of deaths) and the third had good evolution, being discharged after 28 days of hospital stay. Statistical analysis showed that patients with history of heart disease, CHF and electrocardiographic changes in the ST segment had high rates of cardiac arrhythmia, a fact that has been reported by Johnston et al., who mention a higher incidence of arrhythmias in cardiac patients.²⁶

According to Hertzer et al., history of heart disease is a risk factor for AMI.²⁷ In this study, presence of AMI was not related to preoperative factors with statistical significance, a fact that could be explained by the sample size.

Pulmonary events are very frequent and contribute to higher rates of postoperative complications. Johnstonet al. reported rates of significant postoperative pulmonary dysfunction of about 9%, including atelectasis, pneumonia and pulmonary embolism.²⁶ In the present case, respiratory complications were much frequent, affecting 42.5% of the individuals. One patient had sepsis due to respiratory infection followed by death, while another patient with pulmonary embolism had good evolution, being discharged on the 8th postoperative day.

Thompson et al. showed that pneumopathy and smoking were associated with a higher rate of pulmonary complications.²⁸ Similarly, preoperative factors, such as chronic obstructive pulmonary disease (COPD), smoking and obesity (BMI > 30 kg/m²) were associated with a higher risk of developing respiratory complications in the postoperative period. This fact is in accordance with Goldstone, who considers smokers and patients with COPD with high PO₂ < 50 and/or PCO₂²⁹ as patients of high surgical risk.

Renal complications are important causes in the increase in morbidity and mortality after aneurysm surgeries. Patients with history of chronic nephropathy, with high creatinine levels in the preoperative period or that needed suprarenal aortic clamping in the intraoperative period had a higher risk of renal failure.³⁰

Ligation of the left renal vein as operative tactics may determine a certain degree of transient loss of renal function and, when necessary, should be performed preserving the gonadal and adrenal veins.³¹ In this study, ligation of the left renal vein was performed in one individual after occurrence of inadvertent lesion. There was no worsening of postoperative renal function.

Eleven patients (8.2%) evolved with non-dialytic acute renal failure, and nine patients (6.7%) with acute renal failure requiring dialysis. Statistical analysis showed that individuals with history of nephropathy had higher risk of developing renal dysfunction in the postoperative period, requiring dialysis, a fact that has been observed by Batt et al., who reported presence of higher renal complication rates in patients with previous renal failure.²⁰ Similarly, patients with high urea levels in the preoperative period, with prolonged aortic clamping time and with reduced diuresis in the intraoperative period had higher risk of developing non-dialytic renal dysfunction in the postoperative period, which has been reported in the literature.^30-32

Complications regarding surgical wound increase surgical morbidity and mortality, especially when there is involvement of vascular graft. In vascular graft infection, its removal and suture of the aortic stump using axillary-bifemoral may be required.⁹

Hallett et al. reported 1.3% of vascular graft infection and anastomotic bleeding.³³ In this series, five (3.7%) patients had superficial surgical wound infection when choice was for conservative treatment with endovenous wide-spectrum antibiotic therapy, with good evolution. Short follow-up of these patients (2 months), performed by laboratory and imaging examinations, did not show involvement of synthetic graft or indications of infection in this plane.

Statistical analysis showed that individuals with BMI > 30 kg/m,² surgical time > 5 hours and surgical incision involving the inguinal region had higher rates of hematomas and surgical wound infection, which has been reported by Szilagyi et al.³⁴

Presence of peripheral occlusive arterial disease (POAD) was remarkable in this series (64.2%). Johnston et al. also indicated a high occurrence of peripheral vascular disease in patients with AAA and emphasized the possibility of ischemic complications of the lower limbs, with risk of limb loss.²⁶ There are several factors contributing to a high rate of POAD and its complications in this study; among them are the increasing prevalence of hypertension, diabetes mellitus, smoking, dyslipidemia, and patient's age. This sample proved to be comprised of individuals with many risk factors for atherosclerosis.^35-37

There was a higher occurrence of lower limb ischemia in individuals with old age (> 70 years) and in smokers, both due to embolism and arterial thrombosis, suggesting a population formed by patients with risk factors for thromboembolic phenomena.^38,39 On the other hand, presence of preoperative POAD, evaluated by palpation of peripheral pulses, was not related to a higher risk of lower limb ischemia.

In a study conducted by Becker et al., events or deaths after AAA surgery with gastrointestinal causes basically occur due to interruption of intestinal vascularization, and mesenteric ischemia contributed to 10% of deaths.⁹ This complication can be avoided by preserving one of the internal iliac arteries and with left colon revascularization by reimplantation of the inferior mesenteric artery when it had preserved caliber and absence of intraoperative reflux.^26,33,40,41

There was mesenteric ischemia in two patients (1.5%), a finding that is compatible with Anacleto et al., who showed a 2.3% rate of this disease after AAA surgery.²⁴ However, Hallett et al., in a study of 307 patients, reported an 0.7% incidence of colon ischemia.³³ In our sample, preservation of internal iliac arteries and reimplantation of the inferior mesenteric artery were not performed in both patients mentioned earlier, a situation that may justify unfavorable evolution.^40,41

Among the most frequent immediate complications, vascular lesions, especially venous lesions, resulted in a significant increase in mortality of patients who underwent surgery due to aortic aneurysms. Johnston et al. reported 4.8% of operative bleeding, requiring blood transfusion; Diehl et al. observed increase in morbidity and mortality in patients with intraoperative hemorrhagic complications.^26,30 With the aim to reduce incidence of vascular lesions, control of iliac arteries was performed with minimal dissection, avoiding manipulation of the posterior aspect and a possible venous lesion.⁴²

Venous lesions occurred in six patients (4.5%), and the left renal vein was involved in one case, the inferior vena cava in two, and the iliac common vein in three cases. Under these conditions, there was an increase in surgical, anesthesia and infused volume times, but with no increase in complication rate.

Mortality rate was 5.2%, similar to that reported in the international literature.^{2,8,20,24,28,30,43,44} In Brazil, Becker et al., in a study of 600 patients submitted to elective surgery due to infrarenal AAA, found early mortality rate of 3.3%.⁹

Age above 80 years has been considered by Dardik et al. as a major concern factor in patients submitted to AAA surgery, as it causes a mortality rate around 7-10%.⁴³ Treiman et al., in a study of abdominal aneurysmectomy in 52 octogenarian patients, concluded that criteria for surgical indication should be similar in octogenarian patients with good functional capacity and in younger patients.⁴⁵ In this sample there was no difference in mortality between octogenarians and younger patients.

In this series the main causes of death were AMI in two patients and mesenteric ischemia in two patients. In agreement with this fact, Ruby et al. consider AMI as the main cause of immediate postoperative and long-term death,⁴⁶ while Thompson et al., in a study of 108 cases of AAA submitted to elective surgical election, considered heart and pulmonary complications²⁸ as the main cause of death. On the other hand, differently from our experience, in which sepsis due to bronchopneumonia represented one of the causes of death, Anacleto et al. showed that pulmonary complications are a major cause of morbidity.²⁴

Presence of heart failure is mentioned by many authors as a risk factor for mortality,^8,27,30,47 and our findings showed that presence of heart disease caused a significantly higher rate of death due to AMI (cardiogenic shock). Similarly, there was a higher mortality rate for patients with prolonged aortic clamping and surgical time, which has been reported by Johnston et al., who attributed this occurrence to a higher cardiac overload.²⁶

Two patients that did not have their internal iliac arteries preserved had mesenteric ischemia followed by death, a situation that has been reported by Cronenwettet al. and Longo et al.^40,41Such occurrence showed that 100% of our patients with intestinal ischemia died.However, there was no association with statistical significance as a result of sample size.

Similarly to what was observed by Becker et al.,when the participation of other risk factors in mortality was analyzed, there was no statistically significant increase in mortality of patients with renal failure, hypertension, chronic obstructive pulmonary disease, smoking, diabetes mellitus, and stroke.⁹

Conclusion

In conclusion, mortality rate was compatible with data from the literature, especially following AMI and mesenteric ischemia. In addition, the most frequent complications were cardiac, followed by pulmonary and renal complications.

It was also possible to observe the following associations:

- Diabetes mellitus, CHF, HF, ECG changes suggestive of ischemia, ejection fraction < 40 and positive myocardial scintigraphy for ischemia were associated with heart complications in the postoperative period, such as arrhythmias and acute pulmonary edema.

- Old age, COPD, smoking, alcoholism, BMI > 30 and reduced forced vital capacity increased risks of atelectasis, pleural effusion and bronchopneumonia.

- History of nephropathy, reduced diuresis in the intraoperative period, prolonged aortic clamping time and high urea levels increased risks of ARF.

- Incision involving the inguinal region, BMI > 30 and high surgical time increase rates of surgical wound infection and hematoma.

- Smoking and old age are associated with lower limb ischemia.

- Heart failure and prolonged aortic clamping and surgery time proved to be associated with higher mortality rate.

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Publication Dates

• Publication in this collection
  08 Dec 2008
• Date of issue
  Sept 2008

History

• Received
  14 Mar 2007
• Accepted
  16 Apr 2008