Introduction
Colonoscopy is a routinely performed procedure essential for colorectal cancer screening, surveillance of polyps and inflammatory bowel disease, and the diagnosis and management of lower gastrointestinal symptoms [1-3]. Each year, approximately 14 million colonoscopies are performed in the United States [4,5]. Conventionally, the left lateral (LL) decubitus position has been the preferred starting position for colonoscopy. Facilitating the insertion process not only decreases procedural difficulty but may reduce time pressure during withdrawal, allowing more time for adenoma detection [6,7].
To facilitate efficient colonoscopic insertion, several ancillary strategies have been studied, including the application of external abdominal pressure and changes to the patient’s physical position [8]. Uddin et al compared LL with prone positioning in 101 patients [9]. The study reported that prone positioning resulted in significantly shorter cecal intubation times (424 vs. 550 sec, P=0.03) and less need for patient repositioning (8% vs. 28%, P=0.009). However, a larger study by Vergis et al had contrasting results and failed to show any benefit from prone positioning [10]. Other body positions have been proposed, including tilt down and supine, though with limited results [11-14].
The right lateral (RL) position has been proposed as an alternative starting body position for colonoscopy. RL has been most studied compared to other starting positions. Recently, Greene et al randomized 94 patients to RL and 91 patients to LL starting positions for colonoscopy [15]. It was proposed that air would preferentially fill the left colon with an RL starting position, thus increasing luminal distention and improving navigation through the large bowel. However, the study failed to show an association between cecal intubation time and patient position (RL 542.6±360.7 sec vs. LL 497.85±288.3 sec, P=0.354). Pain scores were also comparable (P=0.078). To evaluate the current evidence further, we conducted a systematic review and meta-analysis to compare the effect of LL and RL starting positions on colonoscopy outcomes.
Materials and methods
Search strategy
We conducted a comprehensive search of several databases and conference proceedings, including Medline and EMBASE, through Sept 2020. An experienced medical librarian helped with the literature search, using inputs from the study authors. We followed the Preferred Reporting items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines by using a predefined protocol to identify publications that reported studies comparing LL and RL starting position for colonoscopy [16,17].
Key words used in the literature search included a combination of “left lateral”, “right lateral”, “colonoscopy”, “cecal intubation”, “body position”, “decubitus position”, and “starting position”. The search was restricted to studies in human subjects published in peer-reviewed journals. Two authors (DR, OB) independently reviewed the title and abstract of studies identified in the primary search and excluded studies that did not address the research question, based on pre-specified exclusion and inclusion criteria. The full texts of the remaining articles were reviewed to determine whether they contained relevant information. Any discrepancy in article selection was resolved by consensus, and in discussion with a co-author.
The bibliographic section of the selected articles, as well as the systematic and narrative articles on the topic were manually searched for additional relevant articles. Details on the search strategy are presented in Supplementary Table 1.
Study selection
In this meta-analysis, we included only randomized control trials (RCTs) that evaluated and compared RL and LL starting positions for colonoscopy. Pediatric studies (age <18 years) were excluded. Studies were eligible for inclusion, irrespective of their sample-size, inpatient/outpatient setting and geography, as long as they provided data needed for the analysis. In the event of multiple publications from the same cohort and/or overlapping cohorts, data from the most recent and/or most appropriate comprehensive report were retained.
Data abstraction and quality assessment
Study references and citations were collected in EndNote X9 (Thomson Reuters, New York, NY). Covidence systematic review software (Veritas Health Innovation, Melbourne, Australia) was used to further screen and extract relevant studies. The full text of each selected article was reviewed to verify that it contained relevant information. To identify other potentially eligible publications, the bibliographic sections of the selected articles were manually searched for additional relevant articles. Data on study-related outcomes in the individual studies were abstracted by 2 authors (DR, JS), and 2 authors (DR, JS) did the quality scoring independently. The Jadad scale for RCTs was used to assess the study quality [18].
Outcomes assessed in study cohorts
The primary outcome was pooled cecal intubation rate, defined as colonoscope cannulation of the cecum. The secondary outcome included pooled cecal intubation time and procedure-related adverse events, including pain or discomfort evaluated using a visual analog scale.
Statistical analysis
We used meta-analysis techniques to calculate pooled estimates using a random-effects model [19-22]. We assessed heterogeneity between study-specific estimates using the Cochran Q statistical test for heterogeneity and the I2 statistic [23-26], where values of <30%, 30-60%, 61-75%, and >75% were suggestive of low, moderate, substantial, and considerable heterogeneity, respectively. Publication bias was ascertained qualitatively, by visual inspection of a funnel plot and quantitatively, by the Egger test. A P-value <0.05 was considered statistically significant [27-29]. Statistical analyses were conducted using STATA software, version 16.0 (College Station, TX: StataCorp LLC).
Results
Search results and study characteristics
From an initial total of 558 studies, 535 records were screened after deduplication and 16 full-length articles were assessed. Five studies were included in the final meta-analysis [15,30-33]. Fig. 1 shows a schematic diagram of the study selection.
Figure 1 Study flow chart
A total of 809 patients (408 LL vs. 401 RL) were included in the final analysis. Additional details of study characteristics with patient demographics are summarized in Table 1. Four studies [15,30-32] were published as full manuscript publications while 1 study [33] was published in abstract format. Each study was from a geographically different location: the United Kingdom [30], Mexico [31], Canada [15], Indonesia [32], and Portugal [33]. A detailed assessment of study quality is given in Supplementary Table 2.
Table 1 Characteristics of studies included in meta-analysis
Cecal intubation
When all 5 studies were analyzed using a random effects model, RL and LL body positions had comparable rates of cecal intubation (odds ratio [OR] 1.3, 95% confidence interval [CI] 0.8-2.3; P=0.3; I2=0%) (Fig. 2). Upon analysis of cecal intubation time, the standardized mean difference was not statistically different between RL and LL positions (OR 0.08, 95%CI -0.09 to 0.26; P=0.4; I2=0%) (Fig. 3).
Figure 2 Forest plot for cecal intubation rate
CI, confidence interval
Figure 3 Forest plot for cecal intubation time
CI, confidence interval; Std diff, standard difference
Patient discomfort and adverse events
Discomfort was assessed according to a visual analog scale that is a validated and reliable pain-related scale used to assess patient discomfort [34]. Vergis et al reported the RL starting position was more comfortable for patients than the LL (2 vs. 3, P=0.02). However, a study with a similar sample size by Bayupurnama et al [32] reported comparable pain scores (RL 4.10 vs. LL 4.42, P=0.59). Mocanu et al [33] reported no significant difference in pain scores (RL 3.92 vs. LL 3.94, P=0.05). Greene et al [15] also reported no significant difference in pain scores (RL 3.20 vs. LL 2.55, P=0.078), though this study used the Nurse-Assessed Patient Comfort Score. None of the studies reported any adverse outcomes following RL or LL starting body positions.
Validation of meta-analysis results
Heterogeneity
We assessed the dispersion of the calculated rates using I2 percentage values. We found no significant heterogeneity in the reported pooled outcomes.
Publication bias
A publication bias analysis was not done, as the total number of studies included in the analysis was less than 10.
Discussion
This is the first systematic review and meta-analysis to compare LL and RL starting positions for colonoscopy. We found that neither the LL or RL patient position resulted in higher rates of cecal intubation. Cecal intubation times were comparable between both positions. Additionally, both positions were associated with similar patient-reported pain scores.
The Right Or Left in COLonoscopy (ROLCOL) trial by Vergis et al [30] reported a 30% better cecal intubation time starting from the RL position [30]. The study also reported better patient comfort using the RL starting position. It was thought that the RL position would optimize visualization and improve adenoma detection rate by potentially filling air in the left colon [35,36]. However, our findings disagree with those of Vergis et al and are in agreement with Greene et al [15], Mocanu et al [33] and Bayupurnama et al [32], who failed to show a benefit of RL over LL.
It was noted that the RL position may be useful in negotiating an acute sigmoid angle in female patients [37]. However, the RL position carries risks and certain patients may not be good candidates for this position. Patients are potentially at risk for gastroesophageal reflux and aspiration in the RL position [38,39].
The strengths of our review are as follows: systematic literature search with well-defined inclusion criteria, careful exclusion of redundant studies, inclusion of good quality studies with detailed extraction of data, rigorous evaluation of study quality, and statistics to establish and/or refute the validity of the results of our meta-analysis. We reported results based on current standards of quality measures in colonoscopy, as put forth by gastrointestinal societies such as the American Society of Gastrointestinal Endoscopy and the American College of Gastroenterology.
There were also several limitations to this study, most of which are inherent to any meta-analysis. We were unable to perform pooled analysis of adenoma detection rate as most studies did not report this outcome. Unlike the other studies included for meta-analysis, the Bayupurnama et al [32] article involved water-immersion, which may have affected outcomes. Additionally, most studies lack blinding, although it would be difficult or impossible to blind endoscopists to starting position.
This study is the most comprehensive review comparing the RL and LL body starting positions for colonoscopy. Ultimately, the RL starting position was comparable to the LL starting position and offered no additional benefit in terms of cecal intubation time, intubation rate or patient discomfort.
What is already known:
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Changes to the patient’s physical position may facilitate efficient colonoscopic insertion
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The left lateral (LL) decubitus starting position is most used during colonoscopy
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Previous studies have investigated other starting positions on colonoscopy outcomes
What the new findings are:
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This study compares the right lateral (RL) and LL starting positions for colonoscopy
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The mean difference in cecal intubation time was comparable
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RL offers no additional benefit in cecal intubation rate
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Patient discomfort was comparable between RL and LL starting positions