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1 Department of Radiology, Cincinnati Children's Hospital Medical Center, 3333
Burnet Ave., Cincinnati, OH 45229-3039.
2 Department of Pediatrics, Cincinnati Children's Hospital Medical Center,
Cincinnati, OH 45229-3039.
3 Department of Surgery, Cleveland Clinic Foundation, Cleveland, OH 44195.
4 Center for Epidemiology and Biostatistics, Cincinnati Children's Hospital
Medical Center, Cincinnati, OH 45229-3039.
Received October 9, 2003;
accepted after revision December 1, 2003.
Address correspondence to M. J. Halsted.
Abstract
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MATERIALS AND METHODS. We performed a retrospective review of 74 CT scans obtained in infants and children who had received blunt abdominal trauma, scoring the quality of visualization of bowel structures, the presence of non–bowel-related findings, and the confidence level in making each assessment. The date range of the scans reviewed overlapped with the period in which the oral contrast material used for scanning such patients was switched from dilute Hypaque to water. Of the 74 CT scans that we reviewed, 53 were obtained with dilute Hypaque and 21 were obtained with water. The sex distribution between the two groups was compared using a chi-square test, whereas the mean age was compared using a two-sample two-sided Student's t test. A two-sample one-sided Student's t test of equivalence was used to analyze the data.
RESULTS. Sex distribution for the two groups of patients was not significantly different (69.81% of the group who received dilute Hypaque were boys; 68.18% of the group who received water were boys). Furthermore, the difference in the mean age for the two groups was not statistically significantly (dilute Hypaque group, 8.86 years; water group, 10.18 years). No statistically significant difference in performance of the contrast agents was found with respect to the detection of intraabdominal abnormality. As an oral contrast material, water performed as well as dilute Hypaque in facilitating visualization of all intraabdominal anatomic structures.
CONCLUSION. In defining anatomic details of the hollow gastrointestinal tract, water is as effective as dilute Hypaque as an oral contrast agent for CT in the setting of acute blunt abdominal trauma in pediatric patients.
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Negative agents also have been studied in adults, and water has been shown to be an effective negative contrast agent [5]. In a study evaluating water, dilute Calogen ([banana oil], Scientific Hospital Supplies; another negative contrast agent), and sodium diatrizoate (a positive agent), Calogen was found to be superior for showing the gastric wall and for evaluating the proximal duodenum, but all three agents had similar performances for evaluation of structures beyond the mid portion of the duodenum [2].
Use of any oral contrast agent poses a small risk of aspiration [6–8]. This risk is one reason that some have questioned whether it is necessary to use an oral contrast agent of any kind in the CT evaluation of patients with blunt abdominal trauma [9–11]. However, at our institution, we believe that the diagnostic usefulness of CT scans obtained for this indication is enhanced by the use of an oral contrast agent. We sought to minimize the risk of aspiration associated with the use of oral contrast material while maximizing the diagnostic usefulness of our scans.
Therefore, we designed a study to address whether water could substitute for dilute Hypaque Sodium ([diatrizoic acid dihydrate] Amersham Health) as an oral contrast agent for abdominal CT performed to evaluate children who had received blunt abdominal trauma. The hypothesis of our study was that, in this setting, water would be as effective as dilute Hypaque in defining anatomic details of the hollow gastrointestinal tract.
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A HiSpeed Advantage CT scanner was used (General Electric Medical Systems). Hypaque powder was diluted as directed on the package insert. The dose of oral contrast material for patients younger than 1 year was 4 oz (118 mL). Patients who were between 1 and 5 years old received 8 oz (237 mL), patients between 6 and 12 years old received 12 oz, (355 mL), and patients older than 12 years received 16 oz (473 mL). IV contrast material, 2 mL/kg of Optiray 320 ([ioversol] Mallinckrodt), was administered by hand injection. The slice thickness used for infants and for children up to 2 years old was 5 mm at a pitch of 1.3; for patients between 2 and 10 years old, 7 mm at a pitch of 1.3; and for patients 10 years of age and older, 10 mm at a pitch of 1.3. The milliamperage setting was varied depending on the weight of each patient. [12, 13] All other scanning parameters were based on departmental scanning protocols.
A total of 53 scans obtained with dilute Hypaque oral contrast material and 21 obtained with water were reviewed. Each scan was scored on a scale from 1 to 5 for the quality of visualization of the wall of seven bowel structures: the stomach wall, duodenal C-loop, duodenal–pancreatic interface, proximal small bowel, transverse duodenum, distal small bowel, and colon. Seven non–bowel-related abnormalities—free air, free fluid, contrast extravasation, bowel wall thickening, bowel wall enhancement, mesenteric edema or hemorrhage, and pancreatic trauma—were also assessed, and the degree of confidence in determining the presence or absence of these injuries was scored on a scale from 1 to 5. Finally, the presence of streak artifacts and their potential impact on the diagnostic quality of the study were assessed.
Statistical Analysis
A two-sample two-sided Student's t test was used to compare mean
age of children who received dilute Hypaque with the mean age of those who
received water. The gender distribution between the two different contrast
types was compared using a chi-square test. A two-sample one-sided Student's
t test of equivalence was used to assess whether differences in the
visualization of the anatomic structures were seen between the two agents. We
used SAS statistical software package (version 8.2, SAS Institute). To
determine power for equivalence, we ran the NQuery Advisor software package
(version 5.0, Statistical Solutions), which returned a 90% power to reject the
null hypothesis that the two types of contrast materials are not equivalent if
a maximum difference of 1.00 and a common standard deviation of 1.30 were
assumed. The maximum difference of 1.00 referred to the 5-point scale used to
assess visualization of structures and the presence of abnormal findings.
Therefore, a difference greater than one unit on this scale was considered
significant.
The number of normal versus abnormal cases among the group of patients who received water was compared with that in the group of patients who received dilute Hypaque using Fisher's exact test.
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Thus, although the precise incidence of oral contrast aspiration in the setting of acute abdominal trauma in pediatric patients remains unknown, it does seem clear that there is a small risk of aspiration in this setting. Because aspiration of dilute Hypaque can lead to chemical pneumonitis, the risk of pneumonia is higher if one aspirates dilute Hypaque than if one aspirates water. Moreover, water is cheaper and more readily available than Hypaque. Water can be obtained rapidly in the emergency department and requires no preparation. The time required to prepare dilute Hypaque could potentially delay scanning. These disadvantages of dilute Hypaque are compelling, given that the results of our study suggest that the diagnostic usefulness of water as an oral contrast agent is not significantly different from that of dilute Hypaque.
Some have questioned the value of oral contrast material in pediatric abdominal CT scanning [9, 10]. One study in the surgical literature was performed to determine whether the use of an oral contrast agent in CT of blunt abdominal trauma was necessary at all [11]. In this study, 492 adults with blunt abdominal trauma were given no oral contrast material before undergoing diagnostic CT. Forty-two of these patients underwent surgery. The reference standard consisted of a review of the CT report, surgical notes, and progress notes. Five bowel injuries were detected on CT. One case of ischemia of the small bowel was not detected on CT. In one patient, the CT scan was interpreted as showing a bowel injury, whereas at surgery a mesenteric hematoma was found. The conclusion of that study was that oral contrast material is not necessary for CT of patients who have received blunt abdominal trauma [11].
We found several potential problems with this study, however. The study was performed in adults and therefore may not accurately reflect the usefulness of oral contrast material in CT of the pediatric population. Because of the reference standard used in the study, subclinical bowel injuries, which potentially might have been detected on contrast-enhanced CT, may have been missed. Finally, on the basis of the CT scans obtained in that study, seven diagnostic errors—three involving bowel injury—were made. It is possible that use of oral contrast material might have prevented at least some of these diagnostic errors.
Pilot data and subsequent clinical experience have led Jamieson [10] to advocate the use of orally administered clear fluids rather than positive contrast agents for obtaining almost all pediatric abdominal CT scans except those obtained for evaluation of trauma. For CT of pediatric blunt abdominal trauma, he has abandoned the use of any oral contrast material and reserves use of positive oral contrast material for select cases such as the evaluation of enterocutaneous fistulas, for which direct injection of the agent may be most appropriate. In support of his recommendation that no contrast material be used for trauma patients, he argues that although there is less bowel distention in patients who have not received oral contrast material than in those who have received orally administered clear fluids, MDCT scans and multiplanar reformatted images can be used to overcome this limitation in the evaluation of the bowel [10].
Given the potential diagnostic benefit afforded by oral contrast agents and the lack of a large prospective randomized study with a definitive finding that oral contrast agents are not useful for CT of pediatric blunt abdominal trauma, our institution continues to administer oral contrast agents to our pediatric patients as part of our blunt abdominal trauma CT protocol. However, we recognize that there are several potential problems with the use of dilute Hypaque in this setting. If Hypaque is incorrectly diluted, the resulting mixture can be hypertonic, and its use can cause fluid shifts, which can be significant in infants, potentially causing serious morbidity. Dilute Hypaque can also cause streak artifacts that can limit detail in the region of the liver, spleen, and pancreas, organs that are often injured in blunt abdominal trauma. Theoretically at least, oral contrast material can be aspirated, and this risk might be greater in the compromised trauma patient. Because water compares favorably to other oral contrast agents and the morbidity rate associated with aspiration of water is clearly lower than that associated with aspiration of dilute Hypaque, water seems preferable to dilute Hypaque as a contrast agent. Moreover, water is inexpensive, readily available, and requires no dilution [9].
No known diagnostic problems arose from streak artifacts associated with the use of dilute Hypaque, although these artifacts may potentially limit the evaluation of the stomach wall and adjacent structures, organs that are commonly injured in blunt abdominal trauma. In our study, streak artifacts occurred in 28% of the scans obtained with dilute Hypaque. There is no risk of contrast-induced streak artifact when water is used as the contrast agent. The results of our study clearly suggest that water is not significantly less effective as an oral contrast agent than dilute Hypaque for defining anatomic details of the hollow gastrointestinal tract on CT in pediatric patients with acute blunt abdominal injuries.
We are aware of several limitations in our study. We used the observations of a single radiologist to compare the performance of the two contrast agents. Perhaps other radiologists would draw different conclusions from the same CT scans; however, their observations might also be subject to significant interobserver variability, and they might not reach a consensus as to the superiority of either agent. The reviewing radiologist could not have been blinded as to whether water or dilute Hypaque was used as the oral contrast material because these agents are readily distinguished on inspection of the images. We used subjective measures of the radiologist's ability to visualize bowel structures and his confidence in excluding non–bowel-related injuries. Although the quality of visualization and confidence in assessment of structures were rated on a quantitative scale, these measurements are inherently subjective rather than objective, rendering the data qualitative rather than quantitative. This inherent subjectivity introduces the possibility of observer bias. We did not perform true internal comparisons: No patient was scanned twice, once with water and once with dilute Hypaque, to compare directly the quality of evaluation of gastrointestinal structures and to determine whether non–bowel-related injuries were more easily detected with one agent versus the other in precisely identical contexts. However, we believe that the additional radiation exposure to patients in such a study would not be justifiable. We performed no clinical or surgical correlative follow-up as a reference standard. Such follow-up might reveal unsuspected differences in the outcomes of patients who received water rather than dilute Hypaque. Finally, although the selection of subjects was randomized, the study was retrospective, not prospective.
In conclusion, water offers multiple advantages over dilute Hypaque: water is as effective, less expensive, and more immediately available; it requires no preparation (enabling more rapid administration); and it is safer if aspirated. We found that water performs as well as dilute Hypaque as an oral contrast agent for CT of children who had sustained blunt abdominal trauma. At our institution, the abdominal CT trauma protocol now calls for water instead of dilute Hypaque as an oral contrast agent.
Although some radiologists would argue that an oral contrast agent of some type is useful in the CT evaluation of pediatric blunt abdominal trauma, others perform such CT evaluations without using oral contrast agents of any kind. A prospective blinded randomized trial comparing CT scans obtained with water as an oral contrast agent with CT scans obtained with no oral contrast agent would help to establish an optimal standard of practice.
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