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Patient-Controlled Room Air Insufflation Versus Automated Carbon Dioxide Delivery for CT Colonography

¹ Department of Radiology, University of Wisconsin Medical School, Clinical Science Center, 600 Highland Ave., Madison, WI 53792.
² Ministry Health-St. Mary's Hospital, Rhinelander, WI 54501.
³ Department of Radiology, Uniformed Services University of the Health Sciences, Bethesda, MD.
⁴ Biostatistics Consulting Center, Uniformed Services University of the Health Sciences, Bethesda, MD.

Received March 8, 2005; accepted after revision April 6, 2005.

 
The opinions and assertions contained herein are those of the authors and should not be construed as official or as representing the opinions of the Department of the Navy or the Department of Defense.

Presented at the 2005 annual meeting of the American Roentgen Ray Society, New Orleans, LA.

Address correspondence to P. J. Pickhardt.

Abstract

Top Abstract Introduction Subjects and Methods Results Discussion References

 
OBJECTIVE. Our objective was to prospectively compare colonic distention and patient comfort at screening CT colonography (CTC) with patient-controlled room air (RA) insufflation versus automated carbon dioxide (CO₂) delivery.

SUBJECTS AND METHODS. Two hundred eight adults undergoing CTC were randomized to RA or CO₂ (104 per method). Colonic distention was prospectively assessed by segment using a 4-point scale (1 = optimal, 2 = adequate, 3 = inadequate, 4 = collapsed). Adequacy of combined supine/prone segmental evaluation was also recorded. Patients provided discomfort ratings on a 0-10 scale (0-1 = none/insignificant, 2-3 = minimal, 4-6 = intermediate, 7-10 = significant) before, during, and after the procedure.

RESULTS. No significant differences in segmental distention were observed in the prone position between techniques. In the supine position, CO₂ resulted in significantly greater distention in the sigmoid, descending, and transverse segments (p < 0.01). After combined supine/prone assessment, two/104 (1.9%) and three/104 (2.9%) patients were judged to have an inadequately evaluated segment on RA and CO₂, respectively (four sigmoid, one transverse). Mean discomfort scores for RA and CO₂ were 3.97 and 5.08 during the examination (p < 0.01); 0.91 and 0.42 immediately after (p < 0.01); 0.51 and 0.25 15 min later (p < 0.05); and 0.15 and 0.04 2 hours later (p < 0.01), respectively. During active distention, 19 (18.3%) and 33 (31.7%) patients reported significant transient discomfort with RA and CO₂, respectively (p < 0.05). Beyond 15 min, only two (1.9%) patients with RA and no patients with CO₂ had a discomfort level higher than 3.

CONCLUSION. Although patient-controlled RA insufflation and automated CO₂ delivery each resulted in negligible postprocedure discomfort and reliable colonic distention, CO₂ was better for both categories.

Keywords: colon • CT colonography • CT technique • screening

Introduction

Top Abstract Introduction Subjects and Methods Results Discussion References

 
Adequate colonic distention is critical for effective polyp detection when performing CT colonography (CTC). Collapsed or poorly distended segments lower the sensitivity for polyp or mass detection. These inadequately distended segments may also lead to an increased false-positive rate because they can mimic carcinoma [1]. Given that CTC is performed without sedation, this distention must be achieved with an acceptable level of patient discomfort if it is to be widely embraced. At our institution, we have used both patient-controlled room air (RA) and automated carbon dioxide (CO₂) methods for colonic distention. The purpose of this study was to compare these two techniques both in terms of their adequacy of colonic distention and levels of patient discomfort. Although manual RA insufflation performed by the CT technologist or physician has been compared with automated CO₂ [2-4], patient-controlled RA insufflation has not, to our knowledge, been compared with automated CO₂ delivery.

Subjects and Methods

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Study Protocol and Technique
This study was performed under a protocol approved by our institutional review board. Between May and October 2004, 222 consecutive adults underwent screening CTC examination, randomized to either patient-controlled RA or automated CO₂ delivery. Fourteen of 222 patients (7 RA and 7 CO₂) were excluded from further consideration because they reported baseline abdominal discomfort before colonic distention that was greater than 1, yielding 208 patients with 104 patients in each group (RA = 55 women, 49 men; mean age ± SD = 56.6 ± 9.2 years; CO₂ = 55 women, 49 men; mean age ± SD = 57.1 ± 7.8 years). For the purposes of this study, standard 2D multiplanar reconstruction views from CTC (axial, sagittal, and coronal) were prospectively interpreted by one of two gastrointestinal radiologists, each of whom had previously interpreted hundreds of CTC studies.

Colonic distention was prospectively assessed by segment on the 2D multiplanar reconstruction views using a 4-point scale (1 = optimal, 2 = adequate, 3 = inadequate, 4 = collapsed) for each of six segments (rectum, sigmoid, descending, transverse, ascending, and cecum). A segment was scored as a 4 if collapsed at any point, regardless of the degree of distention in the remainder of that segment. Distinction between adequate and inadequate distention was subjective. In general, inadequate distention implied that the presence of polyps 6 mm or larger could not be excluded in that segment. Distention scoring was done for both supine and prone scans, resulting in 12 segmental scores per patient. In addition, overall by-patient segmental adequacy for diagnosis was assessed from combined supine/prone evaluation. This subjective binary assessment (i.e., diagnostic or not) was performed for all segments that were inadequately distended or collapsed (i.e., 3 or 4) on at least one view. Combined adequacy indicates overall diagnostic quality of examination for the purposes of polyp detection.

Our protocol for colonic cleansing before CTC consists of oral sodium phosphate (45 mL) the evening before CTC; magnesium citrate is substituted for patients with renal or cardiac insufficiency. For the purposes of stool and fluid tagging, patients drink 2% CT barium (250 mL) and a water-soluble iodinated contrast agent (diatrizoate, 60 mL), respectively. Patients also follow a clear liquid diet on the day before examination and do not eat or drink after midnight.

Immediately before CT, colonic distention was achieved via a small flexible rectal catheter by either patient-controlled insufflation of RA using a standard handheld air bulb insufflator or by automated CO₂ delivery (PROTOCO₂L, E-Z-EM). Colonic distention for supine scanning was begun in the left lateral decubitus position. The patient then was instructed to roll gently into the supine position until completion. Prone scanning was performed after supine scanning for all patients. Colonic distention was assessed by an experienced CT technologist after obtaining scout images in both the supine and prone positions. In rare selected patients, the interpreting physician was consulted to assess distention adequacy while the patient remained on the table.

For RA technique, the CT technologists coached the patient on self-insufflation. For patients who were uncomfortable with self-insufflation, the technologist provided assistance as needed. Additional RA was added between supine and prone scanning, as tolerated. If the technologist decided distention was inadequate, additional RA was added as tolerated by the patient.

For CO₂ delivery, the manufacturer's recommended default settings were used. The dial for equilibrium pressure was set to 25 mm Hg with CO₂ delivered to the patient incrementally as follows: 1 L/min for 0-0.5 L of delivered volume, 2 L/min for 0.5-1.0 L, and a maximum 3 L/min for delivered volumes greater than 1 L. CO₂ was then delivered as needed to maintain a pressure up to 25 mm Hg throughout the examination. An electronic-controlled pressure relief valve was set at 50 mm Hg, and an independent redundant mechanical pressure relief valve was preset to 75 mm Hg. The volume and pressure were allowed to stabilize (typically 1-3 min) before scanning. If an initial 4-L bolus of CO₂ was administered to the patient with-out reaching pressure equilibrium, additional CO₂ (up to 2 L at a time) was added. Scout images were then acquired to assess adequacy of distention.

Patients verbally responded to a standard pain questionnaire using a 0-10 scale (0-1 = none/insignificant, 2-3 = minimal, 4-6 = intermediate, 7-10 = significant) for the level of abdominal discomfort experienced at five different times: immediately before the examination, during active distention, immediately after the examination, 15 min later, and 2 hr after the procedure.

Supine and prone MDCT images were obtained on 8-MDCT or 16-MDCT scanners (LightSpeed Series, GE Healthcare) with these parameters: 1.25-mm collimation, 1-mm reconstruction interval, 50-75 mAs, and 120 kVp.

Statistical Analysis
For each colonic segment, the Wilcoxon's rank sum test was used to test for associations between insufflation method and distention score for both supine and prone positions. Results for segments with significant differences were confirmed with Fisher's exact test. Generalized Cochran-Mantel-Haenszel statistics were used to assess the association between the method and distention score after stratifying by segment. Two tests were performed: a test for general association that examined whether the distribution of distention scores differed between the two methods and a test of row mean scores that examined whether the average scores differed between methods.

Because maximum discomfort was indicated on a 10-point ordinal scale, the Wilcoxon's rank sum test was used to compare differences between the two groups at each time point. The chi-square test was used to compare proportions of patients at the various discomfort levels (i.e., 0-1 = none/insignificant, 2-3 = minimal, 4-6 = intermediate, 7-10 = significant).

Results

Top Abstract Introduction Subjects and Methods Results Discussion References

 
Colonic Distention
Mean segmental distention scores ranged from 1.05 (prone rectum) to 2.01 (supine sigmoid) for RA and from 1.10 (prone rectum) to 1.67 (supine sigmoid) for CO₂ (Fig. 1 and 2). Per our grading definition, the lower scores indicate better distention. In the supine position, patients with CO₂ had significantly better distention compared with RA in the sigmoid, descending, and transverse segments (p < 0.01). In the prone position, no significant differences in segmental distention were observed between the two techniques (p = 0.078 and p = 0.898, respectively).

View larger version (32K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1 —Mean segmental distention scores on supine positioning with patient-controlled room air (RA) and automated carbon dioxide (CO2). Lower scores represent greater distention. Mean segmental distention was better for CO2 compared with RA in all segments, but differences were statistically significant only for sigmoid, descending, and transverse segments. Sigmoid segment on supine had worst mean distention score among all segments (supine or prone) for both RA and CO2.

View larger version (30K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2 —Mean segmental distention scores on prone positioning with patient-controlled room air (RA) and automated carbon dioxide (CO2). Lower scores represent greater distention. Mean segmental distention showed no clear preference between CO2 and RA on prone, with no statistically significant differences. Rectum on prone had best mean segmental distention score among all segments (supine or prone) for both RA and CO2.

View larger version (23K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3 —Histogram of segmental distention scores (supine and prone combined). Note that most colonic segments were deemed adequate for evaluation (distention score of 1 or 2). Lower scores represent greater distention.

Patient Discomfort Scores
The differences between mean patient discomfort scores for RA and CO₂ were statistically significant at all time periods during and after examination (Fig. 4). Compared with RA, the mean discomfort score with CO₂ was significantly higher during active distention but was significantly lower at all times after distention. Improved patient comfort after distention with CO₂ may be related to more rapid resorption, as shown in Figures 5A, 5B, 5C and 5D.

View larger version (22K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4 —Mean patient discomfort scores during and after CT colonography examination. Significantly greater discomfort during active distention was reported by patients receiving automated carbon dioxide (CO2), whereas reverse trend was seen after examination, with greater discomfort reported with patient-controlled room air.

View larger version (110K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5A —Supine scout films in 52-year-old man undergoing CT colonography (CTC) screening. Patient volunteered to space out supine and prone scanning to allow distention with both carbon dioxide (CO2) and room air (RA), with additional scout films 15 min after each. Supine scout films using CO2 for distention immediately before supine CTC (A) and 15 min later (B) show significant resorption of colonic gas.

View larger version (105K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5B —Supine scout films in 52-year-old man undergoing CT colonography (CTC) screening. Patient volunteered to space out supine and prone scanning to allow distention with both carbon dioxide (CO2) and room air (RA), with additional scout films 15 min after each. Supine scout films using CO2 for distention immediately before supine CTC (A) and 15 min later (B) show significant resorption of colonic gas.

View larger version (110K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5C —Supine scout films in 52-year-old man undergoing CT colonography (CTC) screening. Patient volunteered to space out supine and prone scanning to allow distention with both carbon dioxide (CO2) and room air (RA), with additional scout films 15 min after each. Supine scout films using RA for distention immediately before prone CTC (A) and 15 min later (B) show significant retention of colonic gas. Patient noted no discomfort with CO2 at 15 min but intermediate discomfort with RA at 15 min.

View larger version (110K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5D —Supine scout films in 52-year-old man undergoing CT colonography (CTC) screening. Patient volunteered to space out supine and prone scanning to allow distention with both carbon dioxide (CO2) and room air (RA), with additional scout films 15 min after each. Supine scout films using RA for distention immediately before prone CTC (A) and 15 min later (B) show significant retention of colonic gas. Patient noted no discomfort with CO2 at 15 min but intermediate discomfort with RA at 15 min.

A statistically significant difference was noted in the number of patients experiencing "significant" [5-8] transient discomfort during active distention, with 19 (18.3%) of 104 patients with RA versus 33 (31.7%) of 104 patients with CO₂ (p < 0.05). "Intermediate" [4, 9, 10] scores during active distention were reported by 41 (39.9%) of 104 patients with RA and 47 (45.2%) of 104 patients with CO₂ (p = 0.49). Immediately after the procedure, "significant" discomfort was reported by two (1.9%) of 104 patients with RA and none of 104 patients with CO₂ (p = 0.50), and "intermediate" scores were reported by five (4.8%) of 104 patients with RA and one (0.9%) of 104 patients with CO₂ (p = 0.21). At 15 min after the procedure, no discomfort scores were rated as "significant" in either group, and "intermediate" scores were reported in two (1.9%) patients with RA and none with CO₂ (p = 0.50). At 2 hr after the procedure, no scores were "significant" or "intermediate" in either group.

Discussion

Top Abstract Introduction Subjects and Methods Results Discussion References

 
The potential for widespread use of CTC as a screening method for the detection of colorectal neoplasia is currently a topic of intense discussion and investigation [9]. Along with adequate preparation, diagnostic colonic distention is a critical component of technical success in CTC [1]. Patient discomfort, during and after the examination, must also be acceptable if CTC is to be widely embraced. The most commonly used methods of colonic distention for CTC include manual RA controlled by the medical staff (technologist or physician), manual RA controlled by the patient, and automated CO₂. In our experience, patient-controlled RA insufflation is better tolerated and generally results in better distention compared with staff-controlled RA [9]. Both patient-controlled RA insufflation and automated CO₂ delivery for CTC are safe techniques. To our knowledge, no perforations resulting from either technique in asymptomatic patients undergoing CTC evaluation have been reported. Rare perforations in symptomatic patients have occurred, however, when the patient did not control the insufflation [5, 10].

Relatively few studies have been presented or published that compare RA and CO₂ techniques [2-4]. To our knowledge, no study to date has compared patient-controlled RA insufflation with automated CO₂ delivery, which we believe represent the two best approaches currently available. Relative advantages of RA include its obvious availability, ease of use, and low cost. CO₂, however, may be better tolerated because of its rapid resorption through the colon wall (up to 150 times faster than RA) and may result in better colonic distention [1, 2].

Studies evaluating the effect of spasmolytics on colonic distention at CTC have found mixed but largely negative results. In two separate studies, glucagon provided no apparent benefit [5, 10]. In one study, N-butylscopolammonium bromide (Buscopan, Boehringer Ingelheim) was found to improve distention, but a second study found no diagnostic benefit [8, 11]. For several reasons, we do not advocate the routine use of Buscopan for CTC screening. First, only 5 (2.4%) of 208 patients in our series had an inadequately distended segment after combined assessment of supine and prone scans. Second, administration of an IV drug adds to patient discomfort, creates an opportunity for possible new side effects, increases examination duration, and increases cost. Third, even if diagnostic benefit had been shown conclusively, this agent is not available for use in the United States [8, 11].

Earlier studies comparing manual RA and manual CO₂ at double-contrast barium enema found the latter achieved reduced levels of discomfort during and after examination [12, 13] but also resulted in significantly decreased colonic distention, presumably because of its rapid resorption (automated delivery systems were not in use) [14]. Use of CO₂ has also been studied for conventional colonoscopy [15-18]. A more recent CTC study found that automated, pressure-controlled CO₂ delivery resulted in improved colonic distention compared with manual CO₂, without increased discomfort [19]. Further-more, using an increasing CO₂ delivery rate, with the settings used in our protocol improves distention over a constant inflow rate, without increasing discomfort [20]. Automated CO₂ versus manual staff-controlled RA was recently compared and improved distention was found with CO₂ [3].

Our results show that, in the supine position, automated CO₂ delivery resulted in significantly better distention in the sigmoid, descending, and transverse segments. Whether this increased segmental distention actually resulted in improved diagnostic performance was beyond the scope of this study because such an analysis would require an even larger sample size. In the prone position, no significant differences in segmental distention were observed between the two techniques. On combined supine/prone analysis, only two patients using RA and three patients using CO₂ had a segment rated inadequate for diagnosis resulting in an incomplete evaluation. Not surprisingly, the sigmoid colon accounted for most (four of five) of the failed segments. As a result of this study, we now take additional steps to decrease further the number of nondiagnostic segments. Subjectively, we are currently finding that overall distention with CO₂ is now clearly more consistent and superior to what we were achieving previously with either technique, and it seems to be associated with decreased patient discomfort.

We have since refined our protocol for CO₂ delivery. The equilibrium pressure is now set initially at 20 mm Hg, which appears to result in decreased patient discomfort during active distention compared with 25 mm Hg. Patient positioning now entails left lateral decubitus for the initial 1.5 L, followed by right lateral decubitus to 2.5 L, followed by supine positioning thereafter. More recently, we found that the CT scout image is less reliable for assessing distention of the sigmoid and descending colon [21]. As a result, we now have the CT technologists review priority reconstructions of the 2D axial images while the patient remains on the gantry to evaluate left colonic distention in difficult cases. If sigmoid distention is clearly inadequate on both supine and prone scans, a third set of images is obtained with the patient in a right lateral decubitus position. This maneuver is necessary in less than 5% of cases. If incomplete segmental evaluation persists despite all of the efforts just described, we generally refer the patient for same-day unsedated flexible sigmoidoscopy to complete the screening examination, which is analogous to completion CTC performed when conventional colonoscopy fails to reach the cecum. This has occurred in much less than 1% of cases to date.

An acceptable level of patient discomfort during and after the examination is critical for CTC to be embraced by the general screening population. In our study, patients reported significantly less discomfort during active distention with RA versus CO₂, particularly among patients with "significant" discomfort (pain score, 7-10). This may be due in part to the patient's ability to control the rate of distention with RA, perhaps avoiding rectal spasm. As noted earlier, it appears that lowering the targeted equilibrium pressure may in fact decrease the number of patients experiencing significant discomfort during active distention with CO₂. Other steps that could potentially reduce discomfort further include slowing the rate of flow rise and decreasing the maximum flow rate. Although our data show greater discomfort during active distention with CO₂ compared with RA, this trend reversed after the examination, most likely related to the increased rate of CO₂ resorption (Figs. 5A, 5B, 5C and 5D). The differences in patient discomfort after the examination, although statistically significant in favor of CO₂, were less apparent clinically because the discomfort level dropped off rather precipitously with both methods. Most patients had negligible discomfort and were able to resume normal activities shortly after examination completion. This differs from conventional colonoscopy, which requires longer recovery secondary to conscious sedation.

This study has its limitations. A small number of patients (seven with RA and seven with CO₂) were excluded because of baseline discomfort scores greater than 1 before colonic insufflation. These patients were excluded because we decided the actual contribution of colonic distention to overall abdominal discomfort would be difficult to separate from baseline discomfort. In addition, assessment of colonic distention at CTC is subjective and may change with reviewer experience and also among different reviewers. Finally, self-assessment of discomfort by patients can be highly subjective. Although the absolute discomfort scores are of limited value, the relative scores between RA and CO₂ are more meaningful, particularly given the relatively large study group (to our knowledge, the largest to date).

Two additional factors that we did not specifically evaluate in our study but are nonetheless worthy of consideration when comparing RA and CO₂ are cost issues and technologist preference. A CTC program must determine whether the increased cost associated with automated CO₂ is more than offset by gains in colonic distention and postprocedure discomfort. Another important component that should be considered is the preference of CT technologists. We conducted an anonymous survey of our CT technologists and found that they clearly preferred the automated CO₂ technique over patient-controlled RA. The main reason was that more time and energy are required to coach each individual patient to self-insufflate adequately with RA, whereas automated CO₂ entails relatively little explanation to achieve similar results. In addition, determination of an adequate endpoint to colonic distention is often more easily obtained using automated CO₂. From the radiologist's perspective, the decreased operator dependence with the automated CO₂ technique results in more consistent distention and less variability from technologist to technologist.

Given the small but definite improvement in colonic distention, the improved patient comfort postprocedure, and the better overall acceptance by CT technologists, we have switched over to automated CO₂ as the frontline distention technique for our CTC screening program. In our current experience, CO₂ is highly reliable if continuous delivery at the equilibrium pressure is assured during imaging and if the steps outlined earlier are followed. Patient-controlled RA insufflation, however, remains a viable alternative and serves as a trusted backup. It is our hope that the manufacturers of automated CO₂ delivery systems will continue to strive for further improvements on their design, leading to even less patient discomfort during active distention.

In conclusion, although patient-controlled RA insufflation and automated CO₂ delivery each resulted in negligible postprocedure discomfort and reliable colonic distention, CO₂ was better for both categories. The decision of which technique to use should be individualized to best suit a given CTC program.

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