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Corresponding author: Ellen H. Elpern, RN, APN, 1725 W Harrison, Ste 054, Chicago, IL 60612 (e-mail: Ellen_H_Elpern{at}rush.edu).
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Abstract |
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Objective To compare the accuracy of capnometry (colorimetric indicator of end-tidal carbon dioxide) and air insufflation/auscultation with the accuracy of radiography in detecting the location of gastric tubes.
Methods A prospective convenience sample of insertions of Salem sump gastric tubes was studied. Tubes were inserted by nurses according to the unit’s standard procedure, and air insufflation/auscultation, capnometry, and radiography were used to detect the position of the tubes. Results obtained with each of the methods were compared.
Results A total of 91 tube placements were studied in 69 patients. No radiographically documented instances of lung placement occurred. Capnometry incorrectly indicated 15 of 91 gastric placements (16%) as placements in the lung. Air insufflation/auscultation incorrectly indicated 5 of 91 gastric placements (5%) as placements in the lung.
Conclusions Neither air insufflation nor capnometry is a fail-safe method for determining placement of gastric tubes. Radiography remains the preferred method.
Notice to CE enrollees:A closed-book, multiple-choice examination following this article tests your understanding of the following objectives:
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Currently, radiography is the gold standard for confirming the position of enteral tubes. A 2-step process1 for radiographic confirmation has been advocated: (1) A radiograph is obtained after a feeding tube is inserted to a depth of 35 cm to establish that the tube is in the esophagus rather than in a main bronchus. (2) Once correct placement is determined, the tube is fully advanced, and enteral placement is verified by obtaining a second radiograph. Implementation of this protocol helps reduce procedure-related pneumothoraces.1 Disadvantages include the time required, delays in use of the tube, exposure to radiation, and expense.
Alternative methods of distinguishing between respiratory and gastrointestinal placement at initial insertion have been used (Table 1
). Some methods (eg, observing the patient for signs and symptoms of respiratory distress, air insufflation, visual inspection of aspirate) are unreliable, some are not readily available at the bedside (eg, detection of bilirubin, trypsin, or pepsin), and others (eg, air bubbling) have not been adequately investigated.4 Metheny et al5 conducted trials of pH testing of tube aspirate to predict tube placement upon initial insertion. Although the results were promising, pH testing is not recommended in place of radiographic confirmation because of the difficulty of obtaining aspirates; the overlap in pH values of lung, gastric, and intestinal aspirates; and possible effects of acid-inhibiting medications on pH values.
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| Lung intubation occurs in up to 27% of enteral tube placements in hospitalized patients.
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In 1994, a technique of capnographic sampling for CO2 during insertion of small-bore intestinal feeding tubes was tested in 20 adults.6 Capnographs were displayed whenever tubes were in the trachea or pharynx. CO2 was not detected when tubes were in the esophagus. In a subsequent study7 of 100 small-bore intestinal tube placements in an intensive care unit, capnography was 100% sensitive for detecting radiographically confirmed lung placement (11% of placements). No CO2 was detected in any of 89 enteral placements. Burns et al8 investigated capnography to determine initial placement of small- and large-bore feeding tubes in adults receiving mechanical ventilation. Radiographs confirmed proper placement of all small-bore tubes, and the capnographic findings agreed with the radiographic findings in all instances. Capnography indicated that 4 of 13 large-bore gastric tubes were misplaced in the lungs, but radiographic confirmation was not obtained.
| Aspirate pH testing should not replace radiographic confirmation of enteral placement.
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Capnometric confirmation of feeding tube placement was tested in several trials. Small-bore intestinal tubes were inserted deliberately into both the upper part of the airway and the gastrointestinal tract in 10 adults receiving mechanical ventilation.9 All tracheal insertions resulted in colorimetric indications of CO2. None of the nasoenteric insertions resulted in changes in the indicator color. With radiographs as the gold standard, similar results of 100% sensitivity and 100% specificity for capnometry were found in 53 blind small-bore tube placements in adults receiving ventilatory support. Further, capnometry revealed 20 of 20 instances of deliberate transient tracheal tube placements.10
Burns et al2 compared capnography and capnometry to evaluate initial blind placement of feeding tubes in critically ill adults. Agreement was consistent between the 2 methods for CO2 detection of presumed inadvertent lung intubations. Radiographs were not obtained to confirm tube location.
In 2005, the American Association of Critical-Care Nurses issued a practice alert11 on verification of feeding tube placement. Radiography was specified as the only reliable method of confirming tube location. Although the results of other methods could be suggestive of enteral placement, clinicians were directed to obtain radiographic confirmation before administering formula or medications through feeding tubes. The possible role of CO2 monitoring as a method for detection of misplaced tubes was not mentioned.
In the medical intensive care unit at Rush University Medical Center, Chicago, Illinois, nurses are responsible for inserting Salem sump gastric feeding tubes. Our practice has been to use air insufflation/auscultation to verify tube placement. Radiographic confirmation has not been required. The purpose of the investigation reported here was to compare the accuracy of capnometry and gastric insufflation/auscultation with radiography for distinguishing pulmonary placement from enteral placement. In addition, we sought to determine occurrences of false-positives (erroneous indications of pulmonary placement) and false-negatives (failure to detect pulmonary placement) with air insufflation and capnometry.
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Methods |
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Each Salem sump tube was inserted per institutional procedure (Table 2). After each tube insertion, a bolus of air (typically 10 mL) was insufflated through the tube while auscultation was performed over the patient’s epigastrium. The presence or absence of the sound of air movement was noted. Next, an adapter was placed on the proximal end of the Salem sump tube to allow attachment of a capnometer (Easy Cap II, Nellcor Puritan Bennett LLC, Pleasanton, California; see Figure). After attachment, the capnometer was observed for 1 minute for any color change indicating exhaled CO2, and the results were recorded. Because capnometers are designed to detect CO2 emanating through the tube, capnometry was not used if any liquid was apparent in the Salem sump tube after insertion.
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Age and sex were recorded for each patient in the study. Salem sump tube size, route of insertion, the patient’s level of consciousness, type and size of artificial airway, and use of mechanical ventilation were noted for each instance of tube placement.
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Analysis |
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Results |
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Complete data sets (results of air insufflation, capnometry, and radiography) were available for 91 tube placements. A total of 11 patients had a Salem sump tube inserted twice, 4 patients had one inserted 3 times, and 1 patient had one inserted 4 times. Reinsertions were related mainly to inadvertent removal of the tube or removal and reinsertion with airway extubation and reintubation.
Tube insertions were incomplete and unacceptable for analysis for several reasons. In 4 instances, tubes were removed before radiography because the patient had respiratory distress and a nurse thought that respiratory placement had occurred. On 14 occasions radiographs were not obtained because of the patient’s self-extubation or transfer of the patient off the unit before the radiograph could be obtained. On at least 5 documented occasions, capnometry was not performed because secretions or blood was present in the lumen of the Salem sump tube.
| Capnometry incorrectly identified 16% of gastrointestinal placement as in the lung.
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Results obtained with the experimental methods were compared with radiographic findings. Chest radiographs were obtained to confirm tube location in 78 insertions, abdominal films in 12, and both chest and abdominal films in 1. All tubes were in the gastrointestinal tract; 3 tubes were at the gastroesophageal junction and 2 were in the duodenum. Radiographs showed no evidence of lung placements, so occurrences of false-negatives with air insufflation and capnometry could not be determined. For false-positives, capnometry incorrectly indicated that 15 of 91 gastrointestinal placements (16%) were in the lung, and air insufflation incorrectly indicated that 5 of 91 gastrointestinal placements (5%) were in the lung.
Because we had no confirmed lung placements, we could not determine conclusively whether false-negative results would have been obtained with the methods tested. Four data sets were incomplete because the Salem sump tubes were removed as a result of respiratory signs or symptoms before radiographs could be obtained. Of note, 2 of the 4 were for patients with endotracheal tubes who were receiving mechanical ventilation. The nurses who performed these insertions reported persistent coughing by the patients and, in the patients receiving mechanical ventilation, heard air movement through the tube with ventilator-delivered breaths. If these tubes were truly pulmonary placements, our rate of inadvertent lung intubation was 4.4% and capnometry and air insufflation correctly indicated lung placements in these instances.
| Neither air insufflation nor capnometry is a fail-safe indicator of proper tube placement.
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Discussion |
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Our results indicate that neither air insufflation nor capnometry is a fail-safe method for determining tube placement. Both methods indicated pulmonary placement of tubes that were actually in the gastrointestinal tract. In 2 instances of inaccurate results with air insufflation, radiographs showed that the tip of the Salem sump tube was at or near the gastroesophageal junction. In another false-positive result with air insufflation, the patient was morbidly obese. In these instances, the ability to clearly auscultate air sounds over the epigastrium may have been compromised.
We can only speculate on the 16% of capnometric results that incorrectly indicated pulmonary placement. We selected capnometry for detecting CO2 because of staff members’ familiarity with this method and its convenience and ease of use. In the capnometers in our study, pH-sensitive paper is used to indicate CO2. Manufacturers of these capnometers warn of false results related to air in the stomach before tube placement and to refluxed gastric contents, mucus, or edema fluid.12 Misleading capnometric color changes in patients with esophageal intubations have been reported.13,14 Although our protocol dictated that capnometric results were to be recorded only when no liquid was present in the tube, contamination of the acid-sensitive paper could have occurred that was not apparent to the tester. Also, coughing during or after intubation may have caused acidic gastric secretions to reflux into the Salem sump and contaminate the capnometer. This explanation was suggested in at least 3 instances when the capnometer changed color suddenly when the patient coughed.
| Inadvertent lung placement does not always evoke signs of respiratory obstruction or distress.
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Because asymptomatic airway placement of feeding tubes is common, we anticipated that we would encounter such placements. However, we think that all the lung placements in our sample were symptomatic. In order to minimize patients’ discomfort and complications, tubes were removed immediately if placement was associated with respiratory discomfort and/or respiratory compromise even before radiographs could be obtained. However, we emphasize that lack of respiratory signs and symptoms is not a reliable indicator for intended gastric placement. On the contrary, inadvertent lung placement does not always evoke signs and symptoms of respiratory obstruction or distress,15,16 and the unpredictability of clinical indications is precisely why alternative methods of ascertaining tube placements are so important.
We plan to explore further the accuracy of capnometry in detecting lung placements. We anticipate that investigation of a larger sample will include instances of radiographically confirmed lung placements. If capnometry correctly detects all lung placements, capnometry may provide a screening test for ruling out lung placement of Salem sump tubes; that is, a negative color change may make a confirmatory radiograph unnecessary. A positive color change in an asymptomatic patient would require radiographic documentation of tube location.
We recognize limitations in extending our findings to other situations and settings. We studied a convenience sample of adults in 2 units of a single medical center. We investigated placement of Salem sump tubes exclusively and cannot draw any conclusions about placement of other enteral tubes, such as intestinal tubes or gastrostomy tubes. We examined initial tube placement, and we cannot comment on methods for subsequent checks of tube position. Capnometers were used exclusively for CO2 detection, and we cannot know if our results might have been different if we had used capnography. We used radiography as the standard method for determining tube placement and compared radiographic findings with the findings of the other 2 methods studied. Possibly, radiographic evidence of placement could have been interpreted incorrectly.
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This investigation was supported by a grant from the Gamma Phi chapter of Sigma Theta Tau International and the Professional Nursing Staff Organization of Rush University Medical Center.
Now that you’ve read the article, create or contribute to an online discussion about this topic using eLetters. Just visit www.ajcconline.org and click "Respond to This Article" in either the full-text or PDF view of the article.
To learn more about enteral feeding and proper tube placement, visit http://ccn.aacnjournals.org and read the article by Bourgault and colleagues, "Development of Evidence-Based Guidelines and Critical Care Nurses’ Knowledge of Enteral Feeding" (Critical Care Nurse, August 2007).
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REFERENCES |
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