THE INFLUENCE OF RISK FACTORS ON MORTALITY RATES AFTER ELECTIVE OPEN
REPAIR OF ABDOMINAL AORTIC ANEURYSMS (AAA)
Ana Luísa Pinto (analuisapinto28@hotmail.com), Catarina Machado (menina.catarina@gmail.com),
Filipa Gomes (filipa56popcorn@hotmail.com), Hugo Sousa (hmlsbiff@hotmail.com), José Henrique
Messias (jham14@hotmail.com), Joana Teixeira (joanamnt@hotmail.com), Luís Miguel Lázaro
(miguel_lazaro@portugalmail.com),
Miguel
Quinta
e
Costa
(rafaela_parreira@hotmail.com),
Maria
Filipa
Figueiredo
(m.filipa.figueiredo@hotmail.com),
(miguelmascarenhascdf@hotmail.com),
Sérgio
Cardoso
(s3rgio13@gmail.com),
Rafaela
Sílvia
Parreira
Farraposo
(silvia@estg.ipleiria.pt), Sofia Figueiredo (sofia_b_figueiredo@hotmail.com).
MD PhD Sérgio Sampaio, Class 5
ABSTRACT
BACKGROUND: There are several risk factors that contribute for the development of Abdominal
Aortic Aneurysms (AAA). Despite recent advances in medical care, Elective Open Repair (EOR)
remains the main worldwide “gold standard” procedure for AAA repair and even with selected
patients’, overall mortality rate is roughly 5%. AIMS OF THE STUDY: This meta-analysis aims to
summarize the risk factors, postoperative complications and mortality rates of patients with AAA
undergoing EOR, and analyze the influence of risk factors on patients’ outcome, contributing to the
improvement of the prediction of patients’ outcome after EOR. METHODS: A total of 203 articles
were collected regarding AAA, elective open repair/surgery and mortality in the PubMed/Medline
database. From those, only 50 provided data related to clinical variables, risk factors exposition,
postoperative complications and clinical outcome. RESULTS: Our study revealed that Males with
advanced age (mean 71.0years old) and with a mean aneurysm diameter of 5.9 cm were the most
frequent patients with AAA among all studies. The most common risk factors found were
Hypertension (median 60.0%), Smoking Habits (median 54.2%), History of Cardiac Diseases
(median 44.3%), and History of Pulmonary Diseases (median 23.0%). Statistical analysis revealed a
median occurrence of morbidity events of 31.0%, while the median mortality rate was 4.0%. The
meta-analysis revealed that Hypertension (OR=2.95; p<0.001), Chronic Renal Failure (OR=2.78;
p<0.001), History of Cardiact Disease (OR=1.93; p<0.001), Female Gender (OR=1.58; p<0.001),
Aneurysm Diameter (OR=1.58; p<0.011) and Age (OR=1.07; p<0.001) were associated with
increased risk of death after EOR, while History of Pulmonary Disease (OR=1.32; p=0.112) and
11
Diabetes Mellitus (OR=1.28; p=0.309) did not provide strong data. Moreover, Smoking habits
revealed not to influence the patient’ outcome after EOR. CONCLUSIONS: Our study revealed
important findings that contribute to the prediction of patient’s outcome after EOR, which may help to
select patients that can be submitted to EOR and expect a good outcome.
KEY-WORDS: Abdominal Aortic Aneurysm (AAA); elective open repair (EOR); risk factors;
postoperative complications; mortality; morbidity; meta-analysis review.
INTRODUCTION
Abdominal Aortic Aneurysm (AAA) is a severe health condition that can lead to death if a rupture
occurs. In the United States, 40,000 patients are submitted to elective surgical repair of AAA each
year, nevertheless, preoperative mortality occurs in 2-8% of properly selected patients (1-4). Despite
the different options to prevent rupture, this condition is responsible for approximately 9,000 deaths
per year (1).
An AAA is considered to be an abnormal widening of 1.5-folds the normal diameter of the aorta below
the renal arteries, and it's development is related to several risk factors which are associated with the
weakening of the aortic wall, namely: smoking, diabetes, elevated cholesterol, family history,
hypertension and atherosclerosis (1). The incidence of AAA increases with age, rarely developing
before the age of 50, and is much more common in men (1, 4). As an aneurysm grows progressively,
rupture can occur at any moment, and even with an emergency repair the mortality remains to be
roughly 50%.
In this context, if an aneurysm is detected at an early stage, clinicians may have to decide which
treatment options must be used, based on patient’s life expectancy and aneurysm’s size: active
surveillance, immediate/emergency repair, elective open repair (EOR) and endovascular repair
(EVAR) (4 – 6). EOR has been the most used approach to repair AAA, and is undertaken only when
the risk of rupture is considered to be high (11). EOR frequently faces with several postoperative
complications, such as: venous bleeding, resulting from iliac or left renal veins injury; gastrointestinal
ischemia, more likely to occur following ruptured AAA repair; cardiac complications, which constitute
the most serious threat to patients after AAA repair; pulmonary complications; and also renal failure.
AAA repair is, therefore a technically difficult procedure and despite later complications are
infrequent, mortality after EOR in properly selected patients still rounds 3 – 10% (2, 7).
The success rates of EOR depend on the patient’s condition and exposure to the different risk factors
(8-10). Thus, it is extremely important to evaluate the outcome considering the different risk factors.
Hence, we aimed to develop a systematic/meta-analysis review, including studies regarding patients
21
with AAA undergoing EOR, to summarize the risk factors, postoperative complications and mortality
rates, and also to analyse the influence of risk factors on patient’s outcome after EOR. Thus, by
summarizing these data we intend to contribute for the improvement of the prediction of patient’s
outcome after EOR.
PARTICIPANTS AND METHODS
Study participants and Sampling Methods
Studies were identified by searching the PUBMED/Medline database with the following query:
(("abdominal aortic aneurysm"[Text Word] OR "aortic aneurysm, abdominal"[MeSH Terms] OR
aaa[Text Word]) AND elective[All Fields] AND open[All Fields]) AND ((("wound healing"[TIAB] NOT
Medline[SB]) OR "wound healing"[MeSH Terms] OR repair[Text Word]) OR ("surgery"[Subheading]
OR "operative surgical procedures"[Text Word] OR "surgical procedures, operative"[MeSH Terms]
OR "surgery"[MeSH Terms] OR surgery[Text Word])) AND mortality[Text Word]. The endpoint of the
search was October 2007.
Study design
The query returned a total of 203 articles which were arbitrarily distributed among reviewers in order
to analyse the abstracts. In a first approach, studies had to fulfil the following criteria to be included in
this study: 1) patients must have been diagnosed with abdominal aortic aneurysms (AAA); 2) patients
must have been submitted to elective open repair/surgery; 3) the article has to provide data about
risk factors; and 4) provide data about clinical outcome after elective open repair of AAA.
Furthermore, studies were excluded if: 1) patients had other types or “mixed” aortic aneurysms; 2)
patients had been submitted to emergency repairs after ruptured AAA; 3) patients had been
submitted to EVAR; 4) studies had been performed considering special types of papers, such as
Reviews, Systematic Reviews, Meta-analysis, Letters or Editorials; 5) studies were presented in other
language than English, French, Spanish or Portuguese such as Swedish, Norwegian, Italian and
German; and 6) if there were no data related to the study design.
After the first selection step, 80 articles were selected and further request either online, by library
acquisition or by e-mail request to authors (Figure1). Only 67 articles were possible to obtain and
then submitted to a second triage step in order to select the articles that considered the variables of
interest for the study (Figure 2). This second triage step revealed that just 46 articles, which
represent 50 individual studies, had information about the variables of interest for the statistical
analysis (preoperative clinical variables, risk factors, postoperative complications, and patient's
outcome). These 50 studies were considered for the estimation of the frequency of all variables of
31
interest in the study. Finally we have selected only 17 studies that have considered differential
outcome values according to patient's risk factors in order to summarize its effect on patients’
outcome.
Variables description and data collection method
A complete random peer-review was performed in order to extract data from selected papers: 1)
general characteristics, such as: name of first author, year of publication, country of origin, type of
study, sample size; 2) clinical variables, such as: age, gender and aneurysm diameter; 3) risk factors
exposition: diabetis mellitus, history of cardiac disease, hypertension, history of pulmonary disease,
chronic renal failure, and smoking habits; 4) postoperative complications, such as: general morbidity,
venous bleeding, gastrointestinal ischemia, multiorgan failure, renal failure, general cardiac
complications, myocardial infarction, and respiratory complications; and 5) clinical outcome of the
patients. The clinical outcome of interest for this study was defined as 30 days after surgery. In cases
with different outcomes per report, each outcome was analyzed as an independent study.
Statistical analysis
All collected data was inserted on a database using Statistical Package for Social Sciences (SPSS)
Version 16.0 for Windows (SPSS Inc). We have used the SPSS software to summarize the median
frequencies, range of values and standard deviations of all clinical variables, risk factors exposition
and postoperative complications, as well as to summarize the mortality rates of all studies. The Epi
Info™ Version 6 was used to perform a Χ2 analysis in order to determine the Odds Ratio (OR) and its
95% confidence interval, when the information was not available in the article. The meta-analysis of
data was made with the open access program R Version 2.6.2 to elaborate the Forest Plot graphics
in order to combine the information about the influence of risk factors on patients’ outcome
RESULTS
The first approach to this study was performed by summarizing the data about the risk factors and
postoperative complications, as well as to summarize the mortality rate within all studies (Table I).
The systematic review revealed an increased frequency of Male Gender (median 86.9%) among AAA
patients, which is consistent with the literature. Moreover, patients were diagnosed with advanced
age, with a mean of 71.4 years old among all studies, and with a mean aneurysm diameter of 5.9 cm.
The most common risk factors found were History of Hypertension (median 60.0%), Smoking Habits
(median 54.2%), History of Cardiac Diseases (median 44.3%), and History of Pulmonary Diseases
(median 23.0%). There was also a relative high frequency of patients with Diabetes Mellitus and
41
Chronic Renal Failure (9.5%).
In what concerns to the occurrence of postoperative complications, the most frequent were:
Respiratory Complications (median 7.5%), Cardiac Complications (median 5.7%), Bleeding (median
3.8%), and Multi Organ Failure (median 3.7%). We have also observed that the morbidity and
mortality rates varied a lot among studies, and statistical analysis revealed a median occurrence of
morbidity events of 31.0%, while the median mortality rate was 4.0%, varying between 0-17%.
The meta-analysis review of data combining the influence of risk factors on patients’ outcome after
EOR revealed that there is a differential influence according to the risk factor (Figure 1) (11 - 28).
While Hypertension, Chronic Renal failure, History of Cardiact Disease, Female Gender and Age
revealed statistical significant data that show they are associated with increased risk of death after
EOR, History of Pulmonary Disease and Diabetes Mellitus did not provide strong data according to
the statistical analysis. Moreover, Smoking habits revealed not to influence the patient’ outcome after
EOR.
Statistical analysis revealed that Hypertension and Chronic Renal Failure represent an almost 3-folds
increased risk for death after EOR; Cardiac Disease History represent an increased risk of almost 2folds; Female Gender and increment of 1cm in the Aneurysm Diameter revealed a 58% increased
risk; and Age has also proved to influence the risk of death after EOR, with an increment of 7% per
year.
DISCUSSION
Limits of the study
Despite all the preoccupations in the design of the study, we are aware that the study may have
some limitations. Firstly, we have found difficulties in the definition of the most sensitive query, mainly
due to the absence of a unique term to define “elective open repair”. Furthermore, we were forced to
apply the query without any reference to any risk factor or postoperative complications since there is
a wide variety and many of them are expressed differently, and therefore, the application of
inclusion/exclusion criteria might have not been as accurate as we aimed. He have also observed
that studies where extremely heterogenic and the majority of them failed to shown some of the
demographic and preoperative clinical variables, as well as risk factors exposition, that could be of
interest to perform a more accurate systematic review. Moreover, only few studies have shown the
outcome categorized by risk factor, which was extremely important to this study.
For all these reasons, we recognize the limits of this study and we are conscious that some data may
compromise our conclusions and the overview capacity of the results obtained.
Epidemiological Data
51
The systematic review of epidemiological data revealed that AAA was significantly more frequent in
Male Gender (median 86.9%), in patients with advanced age (mean of 71.4 years old), and with a
mean aneurysm diameter of 5.9 cm – Table I. Our results show similar distribution to those shown in
literature which refer that AAA are more common in men with age ranging 65-75 y.o. and diagnosed
with a diameter of the aorta below the renal arteries of >3.0 cm (1, 26, 29, 30).
Our study revealed that besides gender, age and aneurysm diameter, the most common risk factors
found were Hypertension (median 60.0%), Smoking Habits (median 54.2%) and History of Cardiac
Diseases (median 44.3%) – Tabe I. The great majority of review studies refer age, smoking, and
gender as the most significant AAA risk factors, although, hypertension and history of cardiac disease
should be also considered important (10, 30).
Literature suggests a wide variety of postoperative complications, and most of them are correlated
with the healthy condition of the patient prior to the surgery, or also to the experience of the surgical
team. It is comonly accepted that between 5-25% of all patients will at least suffer one postoperative
complication prior to 30 days after surgery (3, 10). Our study showed that the median occurrence of
Morbidity events was of 31.0%, which seems to be very high. Nevertheless, this value has vary a lot
among all studies, ranging from 0.3 – 68.1%, therefore, we may assume that these differences might
be correlated with the healthy condition of patients. The most frequent postoperative complications
found were Respiratory (median 7.5%) and Cardiac (median 5.7%), followed by Bleeding (median
3.8%), and Multi Organ Failure (median 3.7%) – Table I. The main conclusion to take form these
data, and according to some studies, is that patients might need to stay at a Intensive Care Unit
(ICU) for a few time in order to reestablish the optimal conditions for the patient go to home and
complete the recover without any more complication (8).
Another curious finding was that like morbidity, mortality rates varied a lot among studies between 017% and statistical analysis revealed a median mortality rate of 4.0% – Table I. Mortality rates prior to
30days after surgery for patients undergoing EOR ranges between 1-5%, although in some surgical
teams this can be 0%. Despite the differential conditions of patients, in-hospital care conditions are
extremely important to prevent higher mortality rates. Our result is similar to those found in the
majority of the published studies (1, 3, 7, 30). Moreover, mortality rates seem to be influenced by
patients’ risk factor exposition and therefore can vary within studies (7-9).
Influence of risk factor on patient’s outcome after EOR
Although there were only 17 studies which provide the necessary data, the meta-analysis revealed
interesting data which consider the role of risk factors on patient’s outcome after EOR (Figure 1).
Statistical analysis revealed no significant data, when considering the influence of Smoking Habits ,
Pulmonary Disease History (PDH) and Diabetes Mellitus (DM) and their influence on patients’
61
outcome after EOR. Despite Smoking is considered to represent a significant risk marker for AAA
development, statistical analysis revealed that patient’s outcome was not influenced by Smoking
Habits (OR=1.00; p=0.987). Nevertheless, the analysis showed that PDH and DM might reveal an
increase of 32% and 28%, respectively, in the risk for death after EOR if present. Nevertheless, these
two risk factors require more studies to clarify its effect on patients’ outcome.
The first significant data that came out from the analysis was the fact that Hypertension (HT) or
Chronic Renal Failure (CRF) were responsible for an almost 3-folds increased risk for death after
EOR (OR=2.95, p<0.001; OR=2.78, p<0.001, respectively). These 2 risk factors are well correlated
with patients’ health condition and are extremely important for the recovery after any surgical
procedure, thus, it was not a surprise to observe that they might increase the risk of death. There is
also an important remark, CRF has been assumed as a significant risk marker, but the way authors
considered present or absent is not actually uniform. Despite the majority of authors used the
creatinine levels to assume the CRF, the “cut-off” value was not uniform, and while used values
>1.5mg/dL as the cut-off, many of them used 2.0mg/dL. This data might be extremely useful in the
future, but authors nedd to provide more uniform values in order to establish a clear role.
As we were expecting, Cardiac Disease History (CDH) has proven to be an increased risk factor for
death after EOR (OR=1.93 with p<0.001). Death after any invasive surgical procedure in patients who
had previous CDH is more frequent, since it is common that people who suffered cardiac events may
have repetitions shortly in time and mainly after surgeries.
Epidemiological data, such as Age, Aneurysm Diameter and Gender, had also provide significant
data. Statistical analysis revealed that Female gender increases the risk of death after EOR in 58%
when compared to Male gender, which represent a significant risk factor for AA. However, it is well
known that when females develop AAA, usually it has more severe consequences and death can
occur shortly after surgery. A similar effect was shown when we observed that an increment of 1cm of
the Aneurysm Diameter represents a 58% increase risk of death after EOR. Finally we observed that
despite not very notorious, Age has proved to influence the risk of death after EOR, with an
increment of 7% per year.
Conclusions
Despite the fact that EOR has been substituted by Endovascular Repair, EOR has proven to have
good results in AAA management, but may require experienced surgeons and good in-hospital
intensive care unites in order to contribute for the improvement of AAA management.
Our study revealed important findings that contribute to the prediction of patient’s outcome after EOR,
by simple analysis of risk factor exposition. Moreover, it may allow the development of a decision tree
for the selection of patients that can be submitted to EOR and expect a good outcome.
71
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Table I - Risk factors, postoperative complications, morbidity and mortality rates
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Figure 1 – Forest plots of the influence of risk factors on patients’ outcome.
Mean Age
Hipertension
Mean Aneurysm Diameter
Diabetes Mellitus
Female Gender
History of Pulmonary Disease
History of Cardiac Disease
History of Pulmonary Disease
Smoking
131