Simons, Shellie Robin PhD, RN; Abdallah, Lisa M. PhD, RN, CNE
Enteral feeding is superior to parenteral nutrition in maintaining intestinal structure and function, is associated with fewer possible complications, and is less costly.1 Generally, enteral feeding tube insertion and maintenance (including the verification of tube placement) are under the purview of RNs, but current practice in this area is seldom evidence based, and the consequences can be deadly.
Even if a tube is correctly inserted and initial gastric placement is confirmed by X-ray, continued assessment is required. Vomiting, coughing, retching, or suctioning can cause the distal tip to migrate upward into the esophagus or downward into the duodenum. It's also possible for a portion of the tube to become coiled in the pharynx. The severity of resulting complications depends on whether the malpositioned tube has been used to deliver feedings or medication, but possible outcomes include aspiration, pneumothorax, and sepsis.
A study of patients treated in an ICU between 1993 and 1995 found that 14 (nearly 2%) of 740 small-bore enteral feeding tubes were unintentionally placed in the tracheopulmonary system, causing major complications in five patients, two of whom died as a direct result—one from a tension pneumothorax and the other from sepsis precipitated by the delivery of alimentary fluid into the pleural space.2 In 2004, a large-scale study found that 87 (2%) of 4,190 patients with a nasoenteric feeding tube had the tube inadvertently placed in the bronchus.3 Thirty-four (39%) of these had endotracheal tubes in place, but the inflated cuffs didn't protect the airway in the nine patients who sustained a pneumothorax when the rigid stylet perforated the lung. A four-year review of small-bore nasogastric feeding tube insertions in a 690-bed medical center in Philadelphia revealed that in 50 (2.4%) of 2,079 patients with chest radiographic reports that mentioned feeding tubes, the tubes had been positioned in the pulmonary cavity.4
Risk, however, is not limited to respiratory complications. In an unusual case, a patient sustained a cerebral hemorrhage after a nurse inadvertently inserted a nasogastric tube through the sphenoid sinus into the lateral ventricle of her brain.5 To protect patients from such life-threatening errors, nurses need to follow a consistently reliable procedure for placing and assessing the placement of enteral feeding tubes.
ASSESSMENT AFTER BLIND INSERTION: A DECADES-OLD CHALLENGE
Accounts differ as to when the nasogastric tube was first used to deliver enteral feeding. Some say the Italian surgeon Aquapendente used a silver nasogastric tube in the 1600s, while others attribute the first use to John Hunter, who fed a patient using a flexible, hollow leather nasogastric tube in 1790.6 Levin introduced a flexible, rubber nasogastric tube in 1921,6 and since that time, nasogastric tubes made of polyvinyl chloride, silicone, and polyurethane have become available, with polyurethane and silicone preferred because they remain soft, flexible, and nonreactive over time.7 But such structural improvements in enteral feeding tubes have not eliminated a major challenge in their use: reliably assessing placement after blind insertion.
A long history of discredited methods. From the 1930s through the 1960s, many clinicians assumed that if a feeding tube was blindly inserted into the lungs, it would separate the vocal cords, preventing vocalization. During this period, nursing textbooks taught that feeding tube placement could be assessed by asking the patient to speak or hum; if the patient could do so, this was thought to indicate that the tube was in the alimentary, rather than the respiratory, tract.8, 9 This assumption was found to be untrue in 1983, when it was reported that a feeding tube inadvertently placed in the pleural space of an alert elderly man neither interrupted his speech nor caused him to cough.10
Textbooks of this era also suggested placing the end of the tube in water because it was believed that tracheal insertion would cause bubbles to appear in the water when the patient exhaled.8, 9 But the absence of bubbling is not a reliable indicator of gastric placement: if the feeding tube is kinked or occluded by respiratory secretions, it will produce no bubbles; likewise, air within the stomach may produce bubbles when a tube is properly placed.11
During the 1980s, nurses were taught to assess enteral tube placement by quickly injecting 10 to 20 mL of air into the tube while auscultating the patient's left upper abdominal quadrant.12 If the tube was in the stomach, the air was expected to enter the stomach without resistance, producing a “loud whooshing sound,” whereas if the tube was in a lung or the trachea, the air was expected to produce a muffled sound.12 The effectiveness of this practice was called into question in 1990, when a landmark study of 85 acutely ill adults found that the auscultatory method correctly predicted feeding tube location in only 34.2% of cases, with some degree of whooshing sounds being heard in all subjects.13 In another study, auscultation incorrectly predicted that 15 of 16 tubes had been placed in the stomach.14
Since that time, significant evidence supporting the discontinuation of this practice has emerged. Most nasogastric feeding tubes are small-bore tubes that limit the amount of air that can be injected and make it difficult to hear the whooshing sound, and normal bowel sounds may be misinterpreted as evidence that the tube is properly placed.15 Furthermore, auscultation is unlikely to reveal a malpositioned tube because nurses rarely auscultate over the lungs or the epigastrium to check the type and proximity of sound, and few nurses have actually heard the sound created by a malpositioned feeding tube.16, 17 Nevertheless, a 2002 survey of British nurses who specialized in nutrition found that 26% of the 47 respondents used auscultation alone to confirm nasogastric tube placement after blind insertion.18
COMPARING RESEARCH AND CURRENT PRACTICE
To examine current practice regarding confirmation of enteral tube placement, we telephoned a convenience sample of hospitals and skilled nursing facilities in Massachusetts and New Hampshire to request a copy of their current policies and procedures for confirming placement of feeding tubes. A total of 28 health care facilities agreed to share their policies.
To compare these practices with recently published findings and recommendations, we conducted a comprehensive online review of nursing literature published between 1980 and 2010 and included in the Cumulative Index to Nursing and Allied Health Literature (CINAHL), MEDLINE, or the Health Reference Center Academic. We searched these databases using the following keywords and phrases: “enteral feeding,” “enteral nutrition,” “feeding tubes,” and “verification of feeding tube placement.” We then searched the reference lists of the articles we obtained for additional sources. We considered all English-language, research-based articles pertaining to the practice of placing enteral feeding tubes or assessing enteral feeding tube placement in adult patients. We applied no other inclusion criteria.
Our initial literature search yielded a total of 102 English-language articles, 44 of which were specifically related to enteral tube placement in adults. Of these, 20 were research-based studies. We reviewed those 20 studies for evidence that could shape practice. In addition, we reviewed 20 nursing textbooks published between 2002 and 2010 for their current practice recommendations on the subject.
In our convenience sample, hospital and skilled nursing facility policies for assessing enteral feeding tube placement varied considerably, with some simply referring nurses to a current nursing textbook (see Table 1). The majority recommended the auscultatory method, with four using it as the sole means of verifying tube placement, though its unreliability is well established (see Table 2 15-31). Only 12 policies specified a frequency at which tubes should be assessed for correct placement, and five hospitals that admitted both adult and pediatric patients had no formal policy for assessing enteral feeding tube placement in adult patients, one of which also had no formal policy for assessing enteral feeding tube placement in pediatric patients.
Auscultation. In 2005, the National Patient Safety Agency of the United Kingdom issued a patient safety alert in which they reported that, over a two-year period, 11 deaths and one case of serious harm resulted from malpositioned small-bore nasogastric feeding tubes.31 The alert clearly stated that “auscultation of air insufflated through the feeding tube (‘whoosh test’)” must not be used to assess placement of nasogastric feeding tubes and emphasized that use of this method had, in several cases, wrongly suggested that a tube was correctly placed, resulting in significant harm when feedings were initiated. Even so, this method continues to be widely promulgated and used.
In fact, several current nursing textbooks and manuals continue to recommend the use of auscultation, either by itself,32 in combination with aspiration of gastric contents,33, 34 or as a preliminary check prior to X-ray to avoid “ordering an X-ray when the tube is clearly incorrectly placed”35—the latter being a practice that can falsely suggest improper placement, resulting in unnecessary removal of the tube. In our survey of policies and procedures, auscultation proved to be the most widely practiced means of assessing enteral feeding tube placement, with 17 of 28 New England hospitals using this method.
pH testing. In 1989, investigators testing the effectiveness of measuring the pH of aspirated secretions to assess placement of a feeding tube found that 80.8% of aspirates from enteral feeding tubes placed in the stomach had pH paper readings of 1 to 4, while 87.4% of aspirates from tubes placed in the intestines had pH paper readings of 6 to 9.21 Although X-rays revealed seven cases of pulmonary placement, only one aspirate of the seven was tested; it had a pH paper reading of 8. Numerous studies support the use of aspiration and pH testing of aspirates to confirm proper placement of enteral feeding tubes.17, 22, 23, 36
At first glance, aspirating a small amount of tube secretions and testing the pH of the aspirate seems to be an easy and highly reliable method for confirming enteral feeding tube placement, and it is recommended for this purpose in a number of current nursing texts.29, 37-42 There are, however, significant limitations to this method. Medications, such as H2-receptor antagonists or proton pump inhibitors, which are frequently prescribed to prevent stress ulcers and gastric reflux, can raise gastric pH as high as 6.24 And in one study of 52 patients fed by nasogastric (50) or nasoenteric (2) tubes, 42% of patients were receiving one or the other of these medications.17
Likewise, commercially prepared feeding formulas, which typically have a pH close to 6.6, have an alkalizing effect on stomach secretions.25 In a 1986 study of 366 gastric aspirates from 20 patients receiving nasoenteral feeding with Osmolite or Isocal and no other gastric acid buffering, 96% of aspirates from the 10 patients receiving gastric feeding and 43% from the 10 patients receiving intestinal feeding had a gastric pH greater than 3.5.26 In a 2002 study of 80 patients receiving continuous tube feeding, the mean pH of gastric aspirate as measured by pH test strips was 5.7.25
Because the pH level of gastric aspirate is often elevated by either medication or enteral feeding formulas, pH testing isn't always a reliable indicator of gastric placement and may lead the examiner to falsely suspect that the feeding tube is in the lung or small intestines. To prevent alkalizing enteral feeding formulas or medication from confounding pH testing, wait at least one hour after administering feedings or medications before assessing pH, and flush the tube with 30 mL of air immediately before aspiration to clear it of other substances.43
Another limitation of pH testing may explain why so few hospitals in our convenience survey included it as part of their policy: at many hospitals, pH testing is considered a point of care procedure, which, like blood glucose testing, requires annual evaluation of staff skill and competency. It is, therefore, more expensive and resource intensive to allow this practice at the bedside.
Visualizing gastric aspirates. Aspiration of recognizable gastric content is often part of the process used to confirm placement of an enteral feeding tube. Gastric aspirates are described as being grassy green or colorless, often with sediment. Intestinal aspirates are often yellow or bile stained and either clear or cloudy. Pleural aspirates are described as watery and straw colored, while tracheobronchial fluid is off-white or tan and often mixed with mucus.27 Unfortunately, the overlapping color and physical characteristics ascribed to the aspirates limit this method significantly. In a study of 880 aspirates from nasally placed feeding tubes, observers found it difficult to agree on the aspirates' specific color and clarity characteristics.28 Researchers concluded that the visual characteristics of feeding tube aspirate can be helpful in distinguishing between gastric and intestinal content but is of little value in differentiating between gastrointestinal and respiratory placement.
Gastric contents are also aspirated to assess tolerance to the feeding and risk of aspiration. But in a 2005 randomized trial, risk of aspiration couldn't be determined from measuring residual volume.44 Of the hospital policies we evaluated, it was unclear whether gastric contents were aspirated as a means of checking tube placement or of monitoring gastric emptying.
Measuring feeding tube length. Current practice dictates that at the time of radiographic confirmation of tube site location, the tube should be marked with indelible ink or adhesive tape where it exits the nares.29, 30 On subsequent feedings, if the nurse notes that more of the tube is exposed, the position of the tip should be questioned. But this method should never be the sole means of determining tube placement, because tubes that appear to be securely taped can still migrate.27 Migration is more likely with the commonly used small-bore tubes.
OTHER METHODS OF ASSESSING PLACEMENT
Bilirubin aspirated from a feeding tube is useful in determining placement because bilirubin is normally found in intestinal fluid and, in small amounts, within the stomach if bile is refluxed from the duodenum. Bilirubin is rarely present in tracheobronchial or pleural fluid.22, 45 A colorimetric test for detecting bilirubin is not yet available for use at the bedside.23, 45
Another method that has been investigated for use in mechanically ventilated patients is carbon dioxide measurement, using capnometry at the proximal end of the feeding tube. The color change that indicates the presence of carbon dioxide is considered a sign of pulmonary tube placement.46 In some studies, capnometry has proved remarkably reliable for verifying enteral feeding tube placement in mechanically ventilated patients.15, 47 But in one study of 69 mechanically ventilated patients, capnometry incorrectly identified 16% of tubes as being in the lung, suggesting that the technology needs to be refined.48
Despite decades of research on the subject, primarily by Metheny and colleagues, our literature review uncovered no formal guidelines or practice recommendations from any professional association for inserting and verifying placement of blindly inserted enteral feeding tubes. In 2009, however, the American Association of Critical-Care Nurses (AACN) issued a practice alert on the subject, containing a number of evidence-based proposals.19
During the blind insertion of any feeding tube, the AACN recommends using several methods to assess tube location. These include watching for signs of respiratory distress, visually assessing aspirate, and using pH testing, if available. Before the tube is used to administer feeding or medication, the AACN recommends confirming placement by X-ray.19 Radiographic confirmation is particularly important when small-bore tubes are used because they may produce no symptoms when incorrectly placed and usually require a stylet for insertion, which introduces the risk of tissue perforation if the tube is not correctly positioned.11
Once initial proper placement is confirmed by X-ray, mark the tube's exit site clearly with tape or a permanent marker.19 Since all bedside methods of assessing feeding tube placement have limited efficacy, the AACN suggests that nurses should assess feeding tube placement at four-hour intervals, using the following methods19:
* measure the external portion of the tube
* review routine chest and abdominal X-ray reports
* observe changes in the volume and appearance of feeding tube aspirates
* test the pH of aspirates (if pH strips are available)
* obtain X-rays if tube placement is in doubt
Despite the plethora of evidence that's been available since 1989, nurses continue to use the auscultatory method to assess enteral feeding tube placement, whether out of habit or because of a lack of resources and time. Until a completely reliable, simple, and cost-effective means of assessing placement is available, nurses must be vigilant in using the best evidence to date.
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