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* From the Departments of Emergency Medicine, and
Community Health and Epidemiology,* Queen’s University, Kingston Ontario, Canada.
Address correspondence to: Dr. D. W. Howes, Empire 3, Department of Emergency Medicine, Kingston General Hospital, 76 Stuart St., Kingston, Ontario K7L 2V7, Canada. Phone: 613-549-6666 ext. 6367; Fax: 613-548-1374; E-mail: danielwilliamhowes{at}hotmail.com
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Abstract |
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Methods: A prospective study was conducted with patients presenting to a 21-bed medical-surgical intensive care unit. An adapter was developed using an endotracheal tube adapter to connect a colorimetric CO2 detector to a feeding tube in an airtight manner. In part I of the study a feeding tube connected to the colorimeter was inserted into the endotracheal tubes of ten ventilated patients to test the device’s ability to detect tracheal placement. In part II patients undergoing feeding tube insertion had tube position confirmed with the colorimeter as well as the reference standard two-step x-ray.
Results: In phase I the colorimeter correctly identified tracheal placement in all ten patients. In phase II 93/100 procedures ultimately were eligible; the colorimeter had a sensitivity of 0.88 (95% confidence interval: 0.65–1.00) and specificity of 0.99 (0.97–1.00). The device missed one of the eight tracheal placements. Agreement between the colorimeter and two-step x-ray interpretations was excellent (Kappa 0.86; standard error 0.10).
Conclusion: We describe a novel, convenient method to confirm esophageal feeding tube placement. The device is easily assembled and inexpensive, but should not be reused. Colorimetric determination of tracheal feeding tube placement with this device has excellent agreement with the reference standard two-step radiological technique.
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Introduction |
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Tracheal placement can result in significant morbidity, and is not prevented by a cuffed endotracheal tube.1 The complication rate for feeding tube placement may be as high as 4.4%.2 Complications include pneumothorax, atelectasis, pleural effusion, bronchopleural fistula, hydrothorax, empyema, mediastinitis, pneumonitis, esophageal perforation and pneumonia.3
Auscultation of air in the stomach has been classically used to confirm placement, but air infused into the pleural space can just as easily be heard over the upper abdomen.4 This method, as well as other tests that confirm placement after the tube is fully advanced takes place when the tube may already have perforated the bronchus. Further methods include fluoroscopy, endoscopy and direct visualization. These techniques are labour intensive, expensive, and add extra discomfort or radiation to the patient.5
The safest way to ensure esophageal placement of the feeding tube is the "two-step" technique, first described in 1989.2 The feeding tube is inserted part way, to a distance approximating a point a few centimetres past the carina (30 cm of tube length). An x-ray is taken to confirm midline position past divergence of the carina, after which the feeding tube is advanced and a second x-ray is taken to confirm position below the diaphragm. If the tube is in the bronchus, it is removed. If the tube is above the carina, bronchial or esophageal placement cannot be determined. The tube is advanced a short distance and the first-step x-ray is repeated. This technique is safe and accurate and is the reference standard for confirming feeding tube placement, however the technique is also time-consuming, expensive and inconvenient.
Electronic capnographs that use infrared absorption spectrometry, generally used to measure end-tidal CO2 and confirm endotracheal tube placement, have been used to confirm esophageal placement of feeding tubes.5,6 These devices are expensive and are not always available where feeding tubes are being inserted. Colorimetric end-tidal CO2 devices use a sulfonephthalein-impregnated pH-sensitive filter paper as an indicator that changes from purple to yellow in the presence of carbon dioxide.7 They were developed to confirm endotracheal tube placement, so unlike the electronic capnographs they have no adapters for feeding tubes and no sampling stream to ensure a flow of gases through the feeding tube. They are single use and disposable, and can be easily stocked anywhere in the hospital.
In 1998 Thomas et al. described a study of ten patients for whom colorimetric end-tidal CO2 detection was used to document proper feeding tube placement.8 In 2002 a larger study of 53 patients9 used a disposable tracheostomy tube inner cannula with a 15-mm snap-lock connecter to attach the feeding tube to the colorimeter. This study also reported 100% accuracy in determining tube placement. While showing impressive results, the sample size of these two studies was modest, and neither team attempted to overcome the potential problem of gas sampling.
We have developed an alternative method for using colorimetric CO2 detectors to confirm feeding-tube placement. Two types of adapters were developed (Figure
) using materials readily available in most intensive care units (ICU). In addition, suction was added to ensure gas sampling through the feeding tube.
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Methods |
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The authors developed two methods for attaching the feeding tube to a colorimetric CO2 indicator (Easy Cap II, Nellcor Puritan Bennett, Pleasanton, CA, USA) from materials readily available in the hospital (Figure
). The adapter from a 3.5-French endotracheal tube (Mallinckrodt, St. Louis, MO, USA) connects to the intake of the colorimeter and forms a snug fit in to the feeding tube (Entriflex, Sherwood Davis & Geck, St. Louis, MO, USA). For institutions without pediatric endotracheal tubes, the body of a 3-mL syringe has a Luer-Lok (Becton Dickinson & Co, Franklin Lakes, NJ, USA) to connect to the feeding tube while the adapter from a 7-French endotracheal tube (Mallinckrodt, St. Louis, MO, USA) connects to the intake port of the colorimeter and fits into the body of the syringe. Low-wall suction is briefly applied to the outflow of the colorimeter by using a 15-mm nipple tip adapter.
Phase I – ten endotracheal placements
For the first phase of the study, we wanted to ensure the device could detect tracheal placement. A convenience sample of ten intubated patients who would not suffer from a brief disconnection from positive pressure ventilation was selected. Feeding tubes were inserted into the endotracheal tube and the device was attached to the feeding tube. Low wall suction was applied to the opposite end of the detector for approximately five seconds. A change in indicator colour from purple to tan or yellow was considered a positive result.
Phase II – evaluation in 100 intubated patients
In the second stage of the study 100 consecutive intubated patients were enrolled. Any adult patient admitted to the ICU who was being ventilated and required a small-bore feeding tube was considered eligible. Exclusion criteria were patient or decision maker’s refusal of a feeding tube, contraindication to feeding tube placement, or difficult insertion requiring direct laryngoscopy. Patients who for any reason required repeated insertions (most often accidental tube removal) could be enrolled more than once. The unit of analysis was procedures performed.
For each procedure a feeding tube was inserted in the standard manner as for the two-step radiological technique, which served as the reference standard. Twenty-five centimetres approximates the distance from the lips to the carina in most patients, so the tube was inserted a distance of approximately 30 cm, adjusted to patient size. Before the first x-ray was taken, the device was attached to the feeding tube and a colorimetric determination of placement was made. This result was recorded on the study form. After recording the result, the first chest roentgenogram was obtained. If the feeding tube had passed distal to the carina, the position (esophageal or tracheal) was recorded on the study form. If the feeding tube was proximal to the carina and position could not be determined, it was advanced the required distance and the x-ray repeated without redoing the CO2 detection. If there were difficulties in repositioning requiring withdrawal of the tube, the device was connected again and recorded before taking another chest roentgenogram.
Clinical intervention (removal of a tracheal feeding tube vs advancement) was based solely on roentgenogram interpretation, not on colorimetric measurement.
Statistical analysis
For the ten intubated patients in phase I, the percentage that the colorimetric detector changed colour (from purple to tan or yellow) was calculated as an indication of the frequency of correct detection of endotracheal placement.
In phase II, each eligible procedure was classified according to the results of the CO2 based determination of feeding tube placement and the chest roentgenogram determination of tube placement. The latter was considered the reference standard in these analyses. The kappa statistic10 was used to describe agreement between the CO2 based and chest roentgenogram determinations. Kappa coefficients were interpreted according to the following a priori criteria: 
> 0.75 indicated excellent agreement, 0.40 
0.75 good agreement, and 0.40 marginal agreement.10 Standard measures of diagnostic validity (sensitivity, specificity) with exact confidence intervals were also calculated.10
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Phase II
One hundred procedures were involved in the study. Seven of the encounters were excluded from the analysis because of failure to complete the form indicating radiologic result (six) or breach in protocol (one; x-ray prior to colorimetric determination). The colorimeter agreed with the radiologic interpretation in the case of the protocol breach.
Results from the remaining 93 patient procedures are shown in the Table. Eight of the encounters (8.6%) involved tracheal placement, the remaining 85 (91.4%) were esophageal. There was one incorrect result in each category, giving a sensitivity of 0.88 (95% confidence interval 0.65–1.00) and a specificity of 0.99 (0.97–1.00). The Kappa was 0.86 (excellent agreement) with a standard error of 0.10.
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Discussion |
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For this study, the guide wire (stylet) of the feeding tube was removed during CO2 determination. Although the risk is extremely low when reinsertion of the wire is undertaken properly, perforation of the wall of the feeding tube with the wire has been described.11 The adapter described allows connection of the device with or without the wire in place.
Unlike the two previous trials on colorimetric CO2 detectors used for this purpose,3,8 our study addressed the issue of gas sampling. Leaving the device attached to the feeding tube and relying on patient ventilation to move CO2 through the tube to the detector will work in most patients, but not all. During the initial development and in the first phase of this trial we found that some patients had to have the device connected to suction to detect tracheal placement. The use of suction gives an immediate result, removes the need for waiting and the uncertainty of whether a negative result is due to correct placement or insufficient waiting time.
The colorimetric CO2 detector was incorrect on two occasions. Incorrect results are of the greatest concern when tracheal placement has occurred (false negative result), and complications can ensue. In retrospect, it was found that the particular colorimeter that was used for that patient had been reused for a number of patients, and it was unclear if was still functioning. For that reason and for proper infection control the authors recommend using a new colorimeter for each test of tube placement.
The results of this study are encouraging. The Kappa values of 0.883 and 0.933 show excellent agreement with the reference standard.10 The sensitivity of 94.4 and specificity of 98.8 are high. Previous studies have both reported 100% sensitivity and specificity, but with more modest sample sizes.
The cost of using the CO2 detector technique is significantly less than the cost of the two-step x-ray technique. A true cost analysis is beyond the scope of this article, but at our centre the cost of the CO2 detector ($11.93 Can) and the connecter ($1.21 Can) are less than the cost of a single chest roentgenogram, estimated to cost anywhere from $25 to $75 Canadian. Capnometry is much faster and less labour intensive than radiological interpretation, and it occurs at the bedside with the results available as the procedure is being performed. Fewer delays and ease of use should lead to greater compliance with a safe technique. Sampling tubing for electronic capnographers costs $19.02 to our institution and are recommended for single use only, making them more expensive than colorimetric capnometers.
The practical disadvantage of performing the two-step radiologic confirmation is that it is time consuming, taking a median of 159 min.5 While the complications from feeding tube insertion can be severe, the majority of them are minor (when detected before feeding) and easily corrected, so clinicians often choose not to bother. Capnographic tube confirmation could save up to one hour and 45 min over the radiologic method.5 For critical care units without electronic capnography, the colorimetric device offers a simple and relatively inexpensive alternative.
This study has some limitations. We used a convenience sample of patients receiving a feeding tube, and although there were incentives for physicians enrolling patients and minimal inconvenience in performing the study, it is quite possible that some patients receiving feeding tubes in the ICU were not enrolled. Because both the colorimetric CO2 detector technique and x-ray confirmation were performed on all patients, the results should be generalizable. To our best knowledge, the technique is applicable to any patient producing CO2.
In summary, we describe a novel, convenient method to confirm esophageal feeding tube placement. The device is easily assembled and inexpensive, but should not be reused. Colorimetric determination of tracheal feeding tube placement with this device has excellent agreement with the reference standard two-step radiological technique.
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Acknowledgments |
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Footnotes |
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Assessed February 20, 2004. Revision accepted September 2, 2004. Final revision accepted January 19, 2005.
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References |
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2 Roubenhoff R, Ravich WJ. Pneumothorax due to nasogastric feeding tubes. Report of four cases, review of the literature, and recommendations for prevention. Arch Intern Med 1989; 149: 184–8.[Abstract]
3 Araujo-Preza CE, Melhado ME, Gutierrez FJ, Maniatis T, Castellano MA. Use of capnometry to verify feeding tube placement. Crit Care Med 2002; 30: 2255–9.[Medline]
4 Leschke RR. Nasogastric intubation In: Reichman EF, Simon RR (Eds). Emergency Medicine Procedures. New York: McGraw-Hill; 2004: 413–9.
5 Kindopp AS, Drover JW, Heyland DK. Capnography confirms correct feeding tube placement in intensive care unit patients. Can J Anesth 2001; 48: 705–10.
6 D’Souza CR, Kilam SA, D’Souza U, Janzen EP, Sipos RA. Pulmonary complications of feeding tubes: a new technique of insertion and monitoring malposition. Can J Surg 1994; 37: 404–8.[Medline]
7 Frakes MA. Measuring end-tidal carbon dioxide: clinical applications and usefulness. Crit Care Nurse 2001; 21: 23–6.[Medline]
8 Thomas BW, Falcone RE. Confirmation of nasogastric tube placement by calorimetric indicator detection of carbon dioxide: a preliminary report. J Am Coll Nutr 1998; 17: 195–7.
9 Rosner B. Fundamentals of Biostatistics. CA: Duxbury Press, Wadsworth Publishing Company; 1989: 655.
10 Saltzberg DM, Goldstein M, Levine GM. Feeding tube-induced pneumothorax. JPEN J Parenter Enteral Nutr 1984; 8: 714–6.[Abstract]
This article has been cited by other articles:
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S. Roberts, P. Echeverria, and S. A. Gabriel Devices and Techniques for Bedside Enteral Feeding Tube Placement Nutr Clin Pract, August 1, 2007; 22(4): 412 - 420. [Abstract] [Full Text] [PDF]
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 J. E. de Aguilar-Nascimento and K. A. Kudsk Clinical Costs of Feeding Tube Placement JPEN J Parenter Enteral Nutr, July 1, 2007; 31(4): 269 - 273. [Abstract] [Full Text] [PDF]
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