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pH and Concentration of Bilirubin in Feeding Tube Aspirates As Predictors of Tube Placement

Metheny, Norma A.; Stewart, Barbara J.; Smith, Lisa; Yan, Hua; Diebold, Marilyn; Clouse, Ray E.


Background: Currently available bedside methods for determining feeding tube placement often provide inconclusive results. Therefore, additional data are needed to assist nurses in making decisions regarding tube location.

Objectives: To describe the usual concentration of bilirubin in aspirates from newly inserted feeding tubes and to determine the extent to which these measures can contribute to pH alone in correctly predicting feeding tube location.

Methods: Gastrointestinal samples for concurrent pH and bilirubin testing were obtained from adult, acutely ill patients with newly inserted small-bore feeding tubes (nasogastric, n = 209; nasointestinal, n = 228) within 5 minutes of radiographs taken to determine tube location. Respiratory samples were tested (tracheobronchial, n = 126; pleural, n = 24). pH was measured with a pH meter, and bilirubin content was assayed spectrophotometrically. Results from the pH and bilirubin tests were compared with tube location as determined by radiography.

Results: Mean pH levels in the lung (7.73) and intestine (7.35) were significantly higher than the mean pH level in the stomach (3.90; p < .001 for each comparison). Mean bilirubin levels in the lung (.08 mg/dl) and stomach (1.28 mg/dl) were significantly lower than the mean bilirubin level in the intestine (12.73 mg/dl; p < .001 for each). By visually inspecting distribution overlap and mean differences by tube site, results were dichotomized so that a combination of pH and bilirubin values could be used to develop a predictive algorithm. A pH of >5 and a bilirubin value of <5 mg/dl correctly identified all respiratory cases, whereas a pH >5 coupled with a bilirubin level of ≥5 mg/dl correctly identified three fourths of the intestinal cases. A pH of ≤5 coupled with a bilirubin value of <5 correctly identified more than two thirds of the gastric cases.

Conclusions: Preliminary laboratory-based data indicate that appropriate use of the proposed algorithm could significantly reduce the number of x-rays needed to exclude respiratory placement and to distinguish between gastric and intestinal placement.

Norma A. Metheny, PhD, FAAN, is a Professor, Saint Louis University School of Nursing, St. Louis, MO.

Barbara J. Stewart, PhD, is a Professor, Oregon Health Sciences University, Portland, OR.

Lisa Smith, RN, MSN, was a Research Associate, Saint Louis University School of Nursing, St. Louis, MO.

Hua Yan, PhD, was a Research Associate, Saint Louis University School of Nursing, St. Louis, MO.

Marilyn Diebold, MSN, RN, was a Research Associate, Saint Louis University School of Nursing, St. Louis, MO.

Ray E. Clouse, MD, is a Professor, Washington University School of Medicine, St. Louis, MO.

Accepted for publication January 12, 1998.

This study was funded by the National Institute of Nursing Research, RO1-NRO-1669, 1991-1994, 1995-1998.

The authors gratefully acknowledge the expert guidance offered by Dr. Barbara C. Hansen throughout this study.

Address reprint requests to Norma A. Metheny, PhD, FAAN, School of Nursing, Saint Louis University, 3525 Caroline Mall, St. Louis, MO 63104-1099; e-mail:

© 1999 Lippincott Williams & Wilkins, Inc.