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Oral Contrast for Abdominal Computed Tomography in Children: The Effects on Gastric Fluid Volume

Mahmoud, Mohamed MD*,§; McAuliffe, John MD, MBA*; Kim, Hwa-Young MD; Mishra, Pragnyadipta MD*; Salisbury, Shelia PhD; Schnell, Beverly PhD; Hirsch, Patricia BSN*; Arbabi, Shahriar MD*; Donnelly, Lane F. MD

doi: 10.1213/ANE.0b013e3181f1bd6f
Pediatric Anesthesiology: Research Reports
Chinese Language Editions

BACKGROUND: Oral enteric contrast medium (ECM) is frequently administered to achieve visualization of the gastrointestinal tract during abdominal evaluation with computed tomography (CT). Administering oral ECM less than 2 hours before sedation/anesthesia violates the nothing-by-mouth guidelines and in theory may increase the risk of aspiration pneumonia. In this study we measured the residual gastric fluid when using a protocol in which ECM is administered up to 1 hour before anesthesia/sedation. We hypothesized that patients receiving ECM 1 hour before anesthesia/sedation would have residual gastric fluid volume (GFV) >0.4 mL/kg.

METHODS: Anesthesia and radiology reports, CT images, and department incident reports were reviewed between January 2005 and June 2009 for all patients who required sedation/anesthesia for abdominal CT. For each patient, the volume of contrast or stomach fluid was calculated using a region of interest outlining the stomach portion containing high-attenuation fluid and low-attenuation of other gastric contents. Information obtained from anesthesia/sedation reports included demographic characteristics, presenting pathology, drugs used for anesthesia/sedation induction and maintenance, airway interventions, method for securing endotracheal tube, and complications related to ECM administration, including oxygen desaturation, vomiting, coughing, bronchospasm, laryngospasm, and aspiration.

RESULTS: We identified 365 patients (mean age = 32 months; range = 0.66 to 211.10 months) who received oral/IV contrast material before anesthesia/sedation for abdominal CT and 47 patients (mean age = 52 months; range = 0.63 to 215.84 months) who received only IV contrast material and followed the traditional fast. For those who received oral contrast, the mean contrast volume administered was 18.10 mL/kg (range = 1.5 to 82.76 mL/kg). The median GVF 1 hour after completing the oral contrast was significantly higher than that in patients who received only IV contrast (0.38 mL/kg vs. 0.15 mL/kg, P = 0.0049). GFV exceeded 0.4 mL/kg in 189 patients (178 of 365 [49%] in the oral contrast group vs. 11 of 47 [23%] in the IV contrast group) (χ2 = 10.7874, P = 0.0010). Among those who received oral contrast, 207 patients had general anesthesia and 158 patients had deep sedation. Two cases of vomiting were reported in the general anesthesia group with no evidence of pulmonary aspiration identified.

CONCLUSION: For children receiving an abdominal CT, the residual GFV exceeded 0.4 mL/kg in 49% (178/365) of those who received oral ECM up to 1 hour before anesthesia/sedation in comparison with 23% (11/47) of those who received IV-only contrast.

Published ahead of print August 24, 2010 Supplemental Digital Content is available in the text.

From the *Department of Anesthesiology, Department of Radiology, and Division of Biostatistics and Epidemiology, Tehran University Children's Hospital Medical Center, Tehran, Iran, and the §Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio.

Address correspondence to Mohamed Mahmoud, MD, Assistant Professor in Clinical Anesthesia and Pediatrics, Cincinnati Children's Hospital Medical Center, 3333 Burnet Avenue, MLC 2001, Cincinnati, OH 45229. Address e-mail to

Accepted June 28, 2010

Published ahead of print August 24, 2010

Standard protocols for pediatric abdominal computerized tomography (CT) imaging include both enteric contrast medium (ECM) and IV agents.1,2 Because of rapid transit time through the stomach and small bowel, ECM is best administered 1 hour before imaging for optimal evaluation.3,4 The timing of oral contrast administration before sedation/anesthesia presents a challenge because administering ECM less than 2 hours before sedation/anesthesia is at odds with the nothing- by-mouth (NPO) guidelines that apply to healthy populations and in theory may increase the risk of aspiration pneumonia. There are little or no data concerning gastric residual volumes after administration of ECM within 1 hour of anesthesia/sedation, nor is there any agreement on the volume of contrast to be administered for pediatric patients undergoing abdominal CT with ECM.

In our institution, the ECM protocol stipulates that the entire volume of contrast be given over 1 hour and that the radiological examination can commence 1 hour after completion of contrast administration. There was no clear consensus among the anesthesiologists who care for these patients as to the best technique for anesthesia/sedation. A variety of sedation and anesthetic techniques are often used to facilitate these studies, with none being the standard of care.

The purpose of this retrospective study was to measure the residual gastric fluid by using a protocol with contrast administration ending 1 hour before anesthesia/deep sedation and to review our records for all complications that occurred with the different sedative/anesthetic techniques used. Animal studies showed that values larger than 0.4 and 0.8 mL/kg increase risk of aspiration,5,6 although there is no known gastric fluid volume (GFV) that places a particular patient at clinically relevant risk or eliminates all the risk. The hypothesis was that patients who received ECM 1 hour before anesthesia/deep sedation would have residual GFV exceeding 0.4 mL/kg.

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After IRB approval, the medical records of consecutive children who required sedation/anesthesia for abdominal CT and received contrast at Cincinnati Children's Hospital Medical Center between January 2005 and June 2009 were reviewed retrospectively. Candidate patients for review were identified from departmental anesthesia and radiology records by procedure code. The abdominal CT examinations were performed for various clinical indications. All of the examinations were scheduled; none were urgent or emergency scans. Children being evaluated for trauma and appendicitis do not receive ECM at our institution and therefore were not included in the study population. With the exception of the administration of ECM, the patients followed the standard fasting guidelines: no solids for at least 8 hours and clear liquids up until 2 hours before arrival to the radiology suite. In all cases, medical records including anesthesia and radiology reports were reviewed. Anesthesia/sedation reports were reviewed for the following: presenting pathology, demographic characteristics including age, sex, and ASA physical status, pre- or postinduction placement of IV line, and the drugs used for anesthesia/sedation induction and maintenance. Airway maintenance data were reviewed for the following: airway protection (including protected [endotracheal tube (ETT), and trachesostomy] or nonprotected [laryngeal mask airway (LMA) and native airway]) and the method of securing the ETT (including rapid sequence, modified rapid sequence, and none). Complications potentially related to the administration of ECM were also recorded (including oxygen desaturation in the radiology suite or recovery room, vomiting, coughing, bronchospasm, laryngospasm, and aspiration). Aspiration was considered to have occurred if any of the following events were documented: aspiration was described in the medical record; chest radiographs were obtained after the procedure to exclude aspiration and showed acute lung opacification; oxygen desaturation or respiratory distress occurred after an episode of vomiting; or the patient required unanticipated admission to the hospital or had other unanticipated changes in therapy related to changes in respiratory status after CT was performed.

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CT Contrast Protocol

All studies were performed with IV contrast and most were performed with ECM. CT studies and reports were reviewed for documentation of the administration of both ECM and the route used for administration (per oral, nasogtarstic tube, and gastric tube and nasojejunal tube).

Diluted isohexol 300 mgI/mL (Omnipaque 300, General Electric Healthcare, Princeton, New Jersey) was used for enteric contrast. The contrast is diluted to a final concentration of 6 mg/mL by diluting 1 mL of Omnipaque 300 in 50 mL of clear liquid (water, fruit punch, or pulp-free juice). The volume of administered diluted contrast is dependent upon age (Table 1). ECM was given by mouth, when possible. Drinking started 2 hours before and ended 1 hour before anesthesia and CT scanning.

Table 1

Table 1

All CT examinations were performed after administration of IV contrast as well. Ioversol 320 mg/mL (Optiray 320, Mallinckrodt Inc., Hazelwood, Missouri) was used as the contrast agent. For CT of the abdomen and pelvis, volume of administered IV contrast is based on child body weight, with 2 mL/kg up to a maximum of 100 mL. Contrast is injected via peripheral IV access by means of a power injector at a rate of 2 mL/s or by hand injection, depending upon the size of the peripheral IV access catheter.

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CT Image Evaluation

CT images were evaluated by using commercially available measurement tools from a picture archive computer system (PACS) (Centricity, General Electric Medical Systems, Milwaukee, Wisconsin); electronic regions of interest were hand-drawn using a computer mouse, outlining the portion of stomach that contained high-attenuation fluid, consistent with contrast, on each CT image, which demonstrated contrast in the stomach. The areas were multiplied by the slice thickness (5 mm) to create a volume and the volumes added together to create a total volume of contrast in the stomach (in milliliters). The resolution of the region of interest tool is determined by the resolution of the imaging study being measured. For CT, this resolution is submillimeter. Because there is sometimes nonmixing of oral contrast and other gastric contents, there are sometimes fluid–fluid levels with both high-attenuation contrast and low-attenuation of other gastric contents. In such cases, the volume of nonopacified fluid in the stomach was also calculated in a similar manner and added to calculate the total fluid volume in the stomach.

In patients who did not receive ECM, the volume of fluid in the stomach was calculated by use of a region of interest measuring the area of fluid density within the stomach on each image with fluid in the stomach. The areas were converted to volumes and added together to calculate the total volume as above.

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Statistical Analysis

Continuous data are presented as means ± SD for normally distributed variables and as medians (and interquartile range) plus minimum and maximum for nonnormally distributed data. Categorical variables are presented as frequencies and percentages.

Our primary outcome variable was GFV measured in milliliters per kilogram. The Wilcoxon Mann–Whitney test was used to determine whether there was a difference in the GFV between patients who received oral contrast and those who did not receive oral contrast.

Patients were placed in dichotomous groups on the basis of GFV: those having a zero volume and those with more than zero volume. A χ2 test was applied to determine whether there was any difference in the proportion of fasted patients with zero GFV in comparison with those who had ECM 1 hour before.

A χ2 test was performed to compare the 2 groups (had oral contrast vs. did not have oral contrast) with respect to the percentage of patients who had residual GFV exceeding 0.4 mL/kg.

We identified those who had a protected airway and then used the Wilcoxon Mann– Whitney test to examine whether there was a difference in GFV between those with a protected airway and those without a protected airway.

The presence or absence of ascites was observed, and the χ2 test (or Fisher's exact test, when appropriate) was used to see whether the incidence of ascites was associated with protected/unprotected airway or with outlier/nonoutlier values of GFV.

All analyses were done using SAS® software (Version 9.2, Cary, North Carolina). All tests were 2-sided, and P values ≤0.05 were considered statistically significant.

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There were 412 patients in the data set for analysis. A total of 365 subjects received oral contrast material for the CT scan; 207 had general anesthesia (GA), and 158 were sedated. We also identified 47 subjects who received only IV contrast material as a control group. The GFV range and the demographic characteristics—including age, sex, and ASA physical status—are reported in Table 2. The range for presenting pathology for patients who received ECM is shown in Table 3. The majority of patients (91%) were younger than 5 years old. All older patients were developmentally delayed; otherwise, patients in this age group do not receive GA/deep sedation. The median GFV was significantly higher for patients who received ECM than for those who received only IV contrast (P = 0.0049). The medians (interquartile ranges) were 0.38 mL/kg (0.01 to 2.99) for those who received oral contrast and 0.15 mL/kg (0.00 to 0.39) for those who did not receive oral contrast. The mean GFV 1 hour after completing the oral contrast was 2.10 ± 3.49 mL/kg and was 0.73 ± 1.56 mL/kg for patients who received only IV contrast. There was no difference in GFV between those with a protected airway and those without a protected airway (Wilcoxon Mann– Whitney test, P = 0.3887). The medians (and interquartile ranges) are 0.34 (0.00, 1.92) for a protected airway and 0.31 (0.016, 2.76) for an unprotected airway.

Table 2

Table 2

Table 3

Table 3

We also examined the distribution of GFV (in milliliters per kilogram) by age group. Among the 1- to 5-year-old and the 13-years-and-older age groups, the GFV was significantly lower for those who did not receive oral contrast than it was for those who did (medians 0.19 vs. 0.42 mL/kg, P = 0.0344 for the 1- to 5-year-old age group; medians 0.06 vs. 4.53, P = 0.0043 for the 13-and-older age group). There was no significant difference in GFV between those who did and those who did not receive oral contrast among the less-than-1-year-olds and the 6- to 12-year-olds.

Of the 365 patients who received oral contrast, 91 (25%) had zero GFV in comparison with 15 (32%) of the 47 who did not receive oral contrast (Fig. 1). The difference in incidence of zero volume between the groups was not significant (χ2 = 1.06; P = 0.3026).

Figure 1

Figure 1

There were 189 patients who had GFV that exceeded 0.4 mL/kg. Of the 365 patients who received oral contrast, 178 patients (49%) had GFV >0.4 mL/kg in comparison with 11 (23%) of the 47 in the IV contrast group (χ2 = 10.7874, P = 0.0010).

We also examined the relationship between volume of ECM administered and residual volume at 1 hour after ingestion. The data are shown as fraction of administered volume remaining as a function of the fraction of patients (Table 4). This enables one to estimate the GFV in milliliters per kilogram 1 hour after contrast administration if the volume of contrast given in milliliters per kilogram is known.

Table 4

Table 4

The distribution of contrast within the alimentary canal of the 365 children who received oral contrast was not uniform. Contrast was present in the small intestine in 328 (90%) and in the large intestine in 285 (78%) of the 365 patients studied. Contrast opacified both small and large intestines in 271 (74%).

The range for presenting pathology for patients with large residual GFV (outliers) is shown in Table 5. We also examined the presence or absence of ascites in these patients. Of the 34 outliers, 5 had ascites, giving an incidence of 14.71%. Of the 378 nonoutliers, only 22 had ascites, giving an incidence of 5.82%. Even though it looks like there is a difference of 14.71% versus 5.82%, we do not have enough evidence to say that outliers had a higher incidence of ascites because the Fisher's exact test has a P value = 0.0605.

Table 5

Table 5

The majority of patients who received ECM and had GA (207) were induced with propofol and anesthesia maintained with sevoflurane. The airway support for these patients was 99 (48%) ETT, 36 (17%) LMA, and 6 (3%) tracheotomy. For the remaining subjects, intermittent spontaneous mask ventilation with or without an oral airway was used. Rapid sequence induction was given to 65 patients among the 99 patients who had an ETT.

The most frequently used sedatives for patients who had sedation (178) were IV pentobarbital 154 (87%), dexmedetomidine 11 (6%), or a combination of midazolam, fentanyl with dexmedetomidine, and pentobarbital in 25 (14%). None of these patients required any airway support during imaging.

There was no evidence of pulmonary aspiration in any patient. Among patients who had GA the following complications occurred: one incident of vomiting after awake extubation (GFV was zero), and one incident of vomiting after the LMA was removed at deep plane of anesthesia (GFV was 7 mL/kg). Four patients had oxygen desaturation (<94%) in the postanesthesia care unit. All of these desaturations were related to airway obstruction, which improved with head positioning and oxygen administration. One patient had laryngospasm that was terminated by positive pressure ventilation during induction. Among patients who had deep sedation, 1 patient with a history of reactive airway had oxygen desaturation in the postanesthesia care unit and was treated successfully with albuterol. This patient was sedated with pentobarbital. None of the patients who had IV contrast had any complication related to contrast administration.

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The practice of administering ECM by mouth or enteric tube before sedating a child for CT has been a routine procedure at our institution and at most large pediatric institutions in the United States for decades.1,2 This practice is now being questioned on the basis of safety-related concerns because it violates fasting guidelines that are used to reduce the risk of rare pulmonary aspiration of gastric contents.7 Anesthesiologists are asked to accommodate the 1 hour prior ECM administration and design an appropriate anesthetic plan to obtain an accurate study. The use of ECM in close proximity to a GA creates a conflict for the anesthesia provider because the study cannot be cancelled because of a violation of fasting guidelines.

There are several points that are important in balancing the concerns of the radiologist in terms of obtaining a diagnostically accurate study with those of the anesthesiologist caring for the patient. The data in this study show that the timing of ECM administration is appropriate from a diagnostic imaging standpoint. Seventy-four percent of patients in which this protocol was used had opacification of the small and large intestines. Children often have a very rapid small intestine transit time. Waiting several hours after administration of contrast will often result in inadequate opacification of the small intestine.4 Small intestine transit time can be as fast as 15 minutes and on average is 1 hour and 24 minutes.3 In 83% of cases, small intestine transit time is <2 hours.3 Inadequate opacification of the small intestine can lead to diagnostic confusion between small intestine loops and fluid collections or masses.4

In 1974, Roberts and Shirley published a report regarding acid aspiration during cesarean delivery.5 The investigators reported that 0.4 mL/kg is the maximum acid aspirate that does not produce significant changes in the lungs. Numerous subsequent studies considered this value of 0.4 mL/kg as a risk factor for aspiration in humans. In 1988, however, Raidoo et al.6 found that in a primate model, the maximum acid aspirate volume that will not cause damage to the lungs is 0.8 mL/kg. Although increased gastric contents theoretically increase the risk of aspiration pneumonia, there is no known GFV that places a particular patient at clinically relevant risk or eliminates all the risk.8 GFV has been used as a surrogate marker for pulmonary aspiration risk in studies evaluating fasting protocol safety.9 11 These studies relied on assuring small preoperative GFV when clear liquids were ingested up to 2 hours before surgery.

Eight studies with approximately 1000 children from numerous centers investigated the ingestion of clear fluids by healthy children before elective surgery. A variety of clear fluids, of variable volumes (as much as 65 mL/kg), were ingested 2 to 3 hours before surgery, and the range of GFV was between 0.24 ± 0.31 and 0.57 ± 0.38 mL/kg.9,10,12 17 Cook-Sather et al. recently examined body mass index percentile and fasting duration effect on GFV and gastric fluid pH in children 2 to 12 years old and concluded that overweight/obese children may be allowed clear liquids 2 hours before surgery as GFV (ideal body weight) averages 1 mL/kg regardless of body mass index and fasting interval.18 Splinter et al. showed that in the same age group (2 to 12 years old) after a prolonged fast (mean fast of 14 hours), GFV was 0.39 · 0.37 mL/kg, and after unlimited clear fluids up to 3 hours before surgery, GFV was 0.34 · 0.28 mL/kg.14 Even in the fasting state, it is expected that one will find some fluid in the stomach, given ongoing salivary (1 mL/kg/h) and gastric (0.6 mL/kg/h) secretions.19 It is worth noting that although average GFV was demonstrably small in most of the fasting patients, some patients had larger residual GFV even when they followed the traditional fasting guidelines.

Previous studies measured estimated GFV by using blind aspiration through multiorificed catheters while the patient was placed in the supine, left, and right decubitus positions.11,18 With this method, 96%–97% of GFV is recovered.11,20 In our study we took a different approach in measuring the GFV by using the CT images as was previously described. Using the CT images to compute GFV, we found that the mean value for GFV was 2.10 ± 3.49 mL/kg. The median value for the same measurement was 0.38 mL/kg with the 25th percentile at 0.01 mL/kg and the 75th percentile at 2.99 mL/kg (Fig. 2). The large difference between the mean and median for the oral contrast group suggests that the distribution of GFV is very nonnormal, which was confirmed by performing the Shapiro–Wilk test (z = 10.35, P < 0.00, 001).

Figure 2

Figure 2

For the patients included in this study, the volume of diluted contrast administered was dependent on the age of the patient; the same volume is given to patients at both ends of an age range. The patients at the low end of the age range would get a larger volume on a per kilogram basis than would the patients at the upper end of the age range and thus have larger GFV. This practice causes a discontinuous relationship between age and residual GFV. As a result of this study, the contrast administration protocol is currently being revised to administer the contrast on a weight basis to reduce the probability of patients with large GFV.

It is difficult to compare our results with previous studies because we measured the GFV after 1 hour of fasting. Previous studies did premedicate with oral acetaminophen or midazolam, and these drugs are known to be associated with increased GFV. Our approach to measuring the GFV, which is standard and accepted technique for volume measurement in the radiology literature,21 was different from that in previous studies, which measured estimated GFV by using blind aspiration of the gastric contents. Lastly, the patient populations in the cited studies were ASA I or II, and they presented for elective surgery, which requires tracheal intubation. Most of our patients have coexisting diseases that might affect the gastrointestinal motility, but we did not find any correlation between ASA status and GFV. We were also unable to demonstrate increased residual GFV with specific coexisting disease.

A death related to the aspiration of contrast material has been reported in an adult who was undergoing CT.22 In addition several cases of aspiration from contrast material leading to adverse affects in children who underwent CT have been well documented.23,24 These described cases have occurred in patients who were being imaged for trauma23,24 and spurred much debate concerning the safety of administering ECM for the CT examination of trauma patients. The safety of administering ECM for CT before sedation has been studied. Ziegler et al. examined the safety records of 367 patients who received oral contrast material before sedation for abdominal CT. Chloral hydrate was given to 30 patients and pentobarbital to 337. The results showed that in 4 cases (1%), vomiting occurred as the patient was awakening from sedation; however, there were no associated events. All 4 patients had been sedated with pentobarbital.25

The multicenter Pediatric Sedation Research Consortium, which collected data on 49,836 propofol sedations in children, showed that vomiting occurred 49 times (0.1%) and aspiration occurred 4 times during these 10,000 sedation/anesthesia encounters (0.04%).26 A retrospective study by Sanborn et al. of 16,467 sedations during imaging procedures in children using chloral hydrate, midazolam, fentanyl, or pentobarbital found 70 (0.4%) respiratory incidents that included aspiration in 2 patients (aspiration incidence of 0.012%).27 The low incidence of aspiration pneumonia with sedation and anesthesia might be attributed to the fact that the stomach is a very distensible organ that accommodates large amount of fluids before the resting intragastric pressure increases.28 Gastric pressure must exceed the barrier pressure of the lower esophageal sphincter for regurgitation to occur. The barrier pressure of the lower esophageal sphincter does not appear to be as easily overcome under GA as is generally believed.28

The administration of an oral contrast is generally accepted as useful in the CT evaluation of the abdomen, especially in children, who lack the inherent internal contrast. There is, however, debate over whether CT examinations can be performed without oral contrast. When contrast is to be administered, there is no uniform practice as to the time between contrast administration and the start of the CT examination.29 31 Consequently, there is likely to be considerable variation in sedation/anesthesia practices and airway management. This variation was shown in a national survey developed and conducted by radiologists in 1988 to document the current practice for sedating children for CT at that time.2 Twenty percent of hospitals (16% of the caseload) claimed that all of their abdominal CT studies were performed on sedated patients who had been given ECM. On average, 68% of all CT studies involved children who had been sedated and given ECM; in 47% of cases the radiologist was responsible for the sedation, in 37% the primary care physician, and in only 3% was the anesthesiologist responsible. Most responders stated that the time was <1 hour (mean for all hospitals was 39 minutes). Use of intubation during CT with oral ECM was rare. Orally administered chloral hydrate was the most frequently used first-line drug for sedation in most types of CT studies.2

Limitations of our report include its retrospective nature and small sample size. We relied on chart review to detect evidence of aspiration. This procedure relies on the anesthesia provider correctly documenting all events; if a significant aspiration event had occurred, it would have been picked up as an unanticipated admission.

In conclusion, children who received EMC up to 1 hour before anesthesia/sedation had larger GVF than did those who did not receive ECM (P = 0.0049). The residual GFV exceeded 0.4 mL/kg in 49% of these patients. However, there was no evidence of increased complications in this study group. The data sample is small in relation to the reported incidence of aspiration in the literature. Therefore, we cannot make any firm recommendation on the safety of a technique for anesthesia/sedation for patients who receive ECM 1 hour before their CT exams.

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