Transperitoneal versus retroperitoneal approach for elective open abdominal aortic aneurysm repair

  • Protocol
  • Intervention

Authors


Abstract

This is a protocol for a Cochrane Review (Intervention). The objectives are as follows:

To assess the effectiveness and safety of the transperitoneal versus retroperitoneal approach for elective open abdominal aortic aneurysm repair on mortality, complications, hospital stay and blood loss.

Background

Description of the condition

Abdominal aortic aneurysm (AAA) is an abnormal enlargement in diameter of the aorta. With the ageing of the population, the prevalence of abdominal aortic aneurysm is increasing. The incidence rate is very high among men aged between 65 and 79 years, reaching 5% to 10% (Vardulaki 1999). Untreated AAAs are likely to increase in size and may eventually rupture. Rupture of the abdominal aorta is the most serious complication, which presents as a surgical emergency. Approximately 6000 men a year die from ruptured aortic aneurysm in England and Wales, accounting for about 2% of deaths in men (Earnshaw 2004). Elective surgical or endovascular repair of aortic aneurysms aims to prevent death from rupture.

Description of the intervention

Dubost performed the first successful excision of an abdominal aortic aneurysm via the retroperitoneal route in 1951 (Dubost 1952). However, the retroperitoneal approach, as it was reported by Oudot (Oudot 1951), offered limited exposure. In the following years, most surgeons preferred to use the transperitoneal approach or transabdominal aortic replacement for open infrarenal abdominal aortic aneurysm repair (Creech 1966). The retroperitoneal approach was not forgotten. In 1963, Rob wrote a detailed description of the retroperitoneal approach including its advantages, such as easier postoperative course, and its disadvantages, such as limited exposure (Rob 1963). In 1980, Williams reported an extended retroperitoneal approach, which offers a better exposure not only of the infrarenal but also of the pararenal and suprarenal aorta (Williams 1980). Endovascular repair is now the new choice method to treat abdominal aortic aneurysm as described by a number of reviews and meta-analyses comparing endovascular versus open surgery (Adriaensen 2002; Wilt 2006), although these reviews do not address the different approaches for open surgery. The 30 day mortality for elective endovascular aneurysm repair is lower than for open repair, but long-term mortality has been shown to be similar (Jetty 2010). Because endovascular repair is associated with higher costs, open surgical repair is still an important method for treating abdominal aortic aneurysms.

How the intervention might work

The transperitoneal approach is a very simple approach which allows surgical evaluation of the whole intra-abdominal cavity to deal with concomitant surgical disease such as colon carcinoma. The inferior mesenteric artery and eventually the polar renal arteries could also be repaired, which can be incorporated in an infrarenal aortic graft. The transperitoneal approach is thought to be better for venous anomalies (Nevelsteen 2005). An equal transperitoneal aortic approach to the abdominal aorta can be attained through midline and transverse abdominal incisions. Because there are no statistically significant differences in morbidity through transverse and midline abdominal incisions, the type of incision used can be left to the surgeon's preference (Lacy 1994). However, the transperitoneal approach usually involves intestinal manipulation, mesenteric traction, and blood contamination of the peritoneal cavity, all of which may lead to impaired intestinal motility (Arya 2009). In order to avoid these complications, many doctors prefer to use the retroperitoneal approach. Compared with the transperitoneal approach, the retroperitoneal approach does not require opening the whole intra-abdominal cavity, however it is time consuming and would not be better for emergency cases (Nevelsteen 2005). Although one study reported that respiratory function after aortic aneurysm repair was similar between the two groups (Volta 2003), other studies have reported that patients who had abdominal aortic aneurysm repair using the retroperitoneal approach had fewer postoperative respiratory complications, reduced incidence of intestinal obstruction, reduced intubation time, and decreased hospital stay and costs (Helsby 1975; Leather 1989; Taheri 1983). Moreover, several similar prospective randomized studies of the two approaches for aortic surgery have been performed, with conflicting results (Cambria 1990; Sieunarine 1997; Taheri 1983).

Why it is important to do this review

This review will draw together the available evidence to assess the advantages and disadvantages of the transperitoneal versus retroperitoneal approach for open abdominal aortic aneurysm repair.

Objectives

To assess the effectiveness and safety of the transperitoneal versus retroperitoneal approach for elective open abdominal aortic aneurysm repair on mortality, complications, hospital stay and blood loss.

Methods

Criteria for considering studies for this review

Types of studies

Randomized controlled trials (RCTs) will be considered. There will be no language and publication status restrictions.

Types of participants

We will include patients receiving elective open surgery for abdominal aortic aneurysm (including with iuxtarenal, pararenal, thoracoabdominal aneurysm). In addition, we will include all studies that meet the criteria even if a study does not report all of the pre-specified outcomes.

We plan to exclude patients undergoing endovascular repair.

We plan to exclude studies which also include patients that undergo aorto-iliac and aorto-bifemoral bypasses unless the data for the AAA patients are stratified or obtained from the trialists.

Types of interventions

The transperitoneal approach versus retroperitoneal approach for elective open abdominal aortic aneurysm repair.

Types of outcome measures

Primary outcomes

1. Mortality

We will analyze in-hospital mortality, 30 day and late mortality separately.

2. Complications

We will include hematoma, abdominal wall hernia and chronic wound pain.

Secondary outcomes

1. Intensive care unit (ICU) or high dependency unit (HDU) stay

All patients are normally initially managed in the HDU or the ICU and transferred to the vascular surgery ward when deemed appropriate. ICU or HDU stay is defined as the time of patient stay in the ICU or HDU.

2. Hospital stay

Hospital stay is defined from the day of operation to the day when the patient leaves hospital.

3. Blood loss

Blood loss is defined as the total amount of blood obtained from suction, cell salvage and weighed swabs.

4. Aortic cross-clamp time

5. Operating time

Operating time is defined as the time from start of incision to the time of closure.

Search methods for identification of studies

Electronic searches

The Trials Search Co-ordinator (TSC) will search the Cochrane Peripheral Vascular Diseases (PVD) Group Specialised Register and the Cochrane Central Register of Controlled Trials (CENTRAL), part of The Cochrane Library (www.the cochranelibrary.com). See Appendix 1 for details of the search strategy which will be used to search CENTRAL. The Specialised Register is maintained by the TSC and is constructed from weekly electronic searches of MEDLINE, EMBASE, CINAHL and AMED, and through handsearching relevant journals. The full list of the databases, journals and conference proceedings which have been searched, as well as the search strategies used, are described in the Specialised Register section of the Cochrane Peripheral Vascular Diseases Group module in The Cochrane Library (www.thecochranelibrary.com).

In addition, the review authors will search PubMed, EMBASE and the China BioMedical Literature database (CBM) (from 1978) using the search strategies shown in Appendix 2 and Appendix 3. The CBM search will be based on the search terms used in the MEDLINE search strategy.

We will search for ongoing trials in the following databases:

Searching other resources

We will search the reference lists of retrieved articles and narrative and systematic reviews to find additional potentially relevant studies. We intend to contact experts and authors in the field for further information and for information about ongoing studies.

Data collection and analysis

Selection of studies

Two review authors (Yulong Zhang and Hui Pan) will independently select studies by screening the titles and abstracts using the pre-determined eligibility criteria to discard studies that are not applicable. If we cannot decide that the articles satisfy the inclusion criteria from the abstracts, the full texts of the trials will be obtained.

If there are two or more publications relating to one trial, only the publication with the most complete data or the pooled data from all publications will be included.

We will resolve disagreements regarding study inclusion by discussion between the two review authors and, if necessary, by the involvement of a third independent review author (Bin Ma).

Data extraction and management

Two authors (Yulong Zhang and Hui Pan) will independently extract data from the included trials using proformas designed by the Cochrane PVD Group. We will resolve disagreements through discussion with the third author (Bin Ma). We will seek additional information from trialists if this is required.

Assessment of risk of bias in included studies

Two authors (Bin Ma and Yulong Zhang) will independently assess the risk of bias for each study as described in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011).

The authors will assess the risk of bias for each of the following domains:

1. randomization;

2. allocation concealment;

3. blinding (outcome assessors);

4. completeness of data;

5. selective outcome reporting;

6. other sources of bias.

The authors will evaluate each criterion as 'low' risk of bias or 'high' risk of bias as described by Higgins 2011. If these criteria are not discussed, the authors will judge the risk of bias as 'unclear'.

Measures of treatment effect

For dichotomous outcomes, we will calculate a pooled estimate of the treatment effect for each outcome across trials as odds ratio (OR) with 95% confidence interval (CI). For continuous outcomes, we will calculate a pooled estimate of treatment effect by calculating the mean difference and 95% CI.

Unit of analysis issues

We do not intend to include non-standard designs, such as cross-over trials and cluster-randomized trials, in the analysis.

Dealing with missing data

We will contact the authors of the respective trials via email for clarification of any missing data. We will undertake sensitivity analyses to assess the impact of the quality of the studies, see section Sensitivity analysis.

Assessment of heterogeneity

We will use the Chi2 test on N-1 degrees of freedom with a significance level of 0.05, and the I2 statistic to examine the heterogeneity among trials. A guide to interpretation is as follows, as described in the Cochrane Handbook for Systematic Reviews of Interventions Version 5.1 (Higgins 2011). I2 values of 25%, 50% and 75% correspond to low, moderate and high levels of heterogeneity. If the I2 estimate is greater than 50%, the level of heterogeneity among trials will be regarded as moderate or high and the reasons will be investigated. We will present results separately and attempt to report the reasons if heterogeneity persists.

Assessment of reporting biases

We will construct a funnel plot to investigate publication bias.

Data synthesis

We plan to only use a random-effects model in the meta-analysis because of the likely heterogenous population.

Subgroup analysis and investigation of heterogeneity

No subgroup analysis is planned.

Sensitivity analysis

We will conduct sensitivity analyses by analyzing the following categories of studies separately: trials with and without adequate randomization and concealment of treatment allocation; trials with and without intention-to-treat analysis; trials with a drop-out rate of more than 20% and less than 20%. For sensitivity analyses we will describe both the main effects within strata and a coefficient (and 95% CI) describing the interaction between them.

Acknowledgements

The review authors would like to thank the following people for commenting on the draft protocol: Ming Guo, Bobo Zheng.

Appendices

Appendix 1. CENTRAL search strategy

#1MeSH descriptor: [Aortic Aneurysm, Abdominal] explode all trees
#2aneurysm* near/4 (abdom* or thoracoabdom* or thoraco-abdom* or aort*) 
#3(aort* near/3 (ballon* or dilat* or bulg* or expan*)) 
#4AAA or TAAA 
#5MeSH descriptor: [Aorta] explode all trees and with qualifiers: [Surgery - SU]
#6MeSH descriptor: [Peritoneum] explode all trees and with qualifiers: [Surgery - SU]
#7MeSH descriptor: [Retroperitoneal Space] explode all trees and with qualifiers: [Surgery - SU]
#8MeSH descriptor: [Blood Vessel Prosthesis Implantation] explode all trees
#9MeSH descriptor: [Blood Vessel Prosthesis] explode all trees
#10#1 or #2 or #3 or #4 or #5 or #6 or #7 or #8 or #9 
#11transperitoneal or transabdominal:ti,ab,kw  (Word variations have been searched)
#12retroperitoneal:ti,ab,kw  (Word variations have been searched)
#13#11 and #12 
#14#10 and #13 

Appendix 2. Authors' PubMed search strategy

1 randomized controlled trial [pt]

2 controlled clinical trial [pt]

3 randomized [ti/ab]

4 placebo [ti/ab]

5 drug therapy [sh]

6 randomly [ti/ab]

7 trial [ti/ab]

8 groups [ti/ab]

9 1 OR 2 OR 3 OR 4 OR 5 OR 6 OR 7 OR 8

10 animals [mh] not (humans [mh] and animals [mh])

11 9 not 10

12 aortic aneurysm [MeSH]

13 blood vessel prosthesis implantation [MeSH]

14 blood vessel prosthesis [MeSH] 

15 aneurysm OR AAA [Title/Abstract]

16 12 OR 13 OR 14 OR 15

17 transperitoneal [Title/Abstract] OR transabdominal [Title/Abstract]

18 retroperitoneal [Title/Abstract]

19 retroperitoneal space [MeSH] OR peritoneum [MeSH]

20 18 OR 19

21 11 and 16 and 17 and 20

Appendix 3. Authors' EMBASE search strategy

1 random*

2 placebo*

3 doubl* adj blind*

4 singl* adj blind*

5 assign*

6 allocat*

7 "double-blind procedure"/exp

8 "randomized controlled trial"/exp

9 "single-blind procedure"/exp

10 1 or 2 or 3 or 4 or 5 or 6 or 7 or 8 or 9

11 abdominal aortic aneurysm/exp

12 "aortic aneurysm"

13 blood vessel prosthesis/exp

14 "blood vessel prosthesis"

15 blood vessel transplantation

16 blood vessel prosthesis implantation

17 11 or 12 or 13 or 14 or 15 or 16

18 retroperitoneum/exp

19 "Retroperitoneal Space"

20 "retroperitoneal approach"

21 19 or 20

22 "transperitoneal approach"

23 "transperitoneal Space"

24 22 or 23

25 10 and 17 and 21 and 24

Contributions of authors

Draft the protocol: Bin Ma and Yulong Zhang
Develop and run the search strategy: Bin Ma
Obtain copies of studies: Hui Pan
Select which studies to include: Bin Ma and Yulong Zhang
Extract data from studies: Hui Pan and Yulong Zhang
Enter data into RevMan: Bin Ma and Yulong Zhang
Carry out the analysis: Bin Ma and Yulong Zhang
Interpret the analysis: KeHu Yang and Bin Ma
Draft the final review: Bin Ma and Yulong Zhang
Update the review: Bin Ma and Yulong Zhang

Declarations of interest

None known

Sources of support

Internal sources

  • No sources of support supplied

External sources

  • Chief Scientist Office, Scottish Government Health Directorates, The Scottish Government, UK.

    The PVD Group editorial base is supported by the Chief Scientist Office.

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