Development of a reliable and valid bedside test for bilirubin and its utility for improving prediction of feeding tube location.

BACKGROUND

The addition of laboratory bilirubin readings to an algorithm based on pH alone improves prediction of feeding tube location; although reliable pH-teststrips are available, there is no bedside test to measure bilirubin in feeding tube aspirates.

OBJECTIVES

This study was designed to test the efficacy of a bilirubin teststrip with a newly developed scale in measuring the bilirubin content in feeding tube aspirates, and to determine the effectiveness of a combination of readings from pH and bilirubin teststrips in predicting feeding tube location.

METHODS

A total of 631 gastrointestinal specimens for concurrent pH and bilirubin testing were obtained from adult, acutely ill patients with newly inserted feeding tubes (nasogastric, n = 328; nasointestinal, n = 303) within 5 minutes of radiographs taken to determine tube location. In addition, 225 respiratory specimens were tested. Bilirubin was measured with a teststrip incorporating a newly developed colorimetric visual bilirubin (VBIL) scale, and by a laboratory assay. pH was measured with a teststrip and a pH-meter. Results from the bilirubin and pH tests were read by research assistants and staff nurses and compared with tube location as determined by radiography.

RESULTS

The correlation between readings made from the 5-point VBIL scale and the trimmed laboratory bilirubin was 0.93, with dichotomized readings correlating 0.87 and kappa equal to 0.86. A pH greater than 5 and a bilirubin less than 5 mg/dL successfully identified 100% of the 225 respiratory cases. In the category of pH 5 or less and bilirubin less than 5 mg/dL, 98% of the cases were gastric cases. In the category of pH greater than 5 and bilirubin 5 or higher mg/dL, nearly 88% of the cases were intestinal cases.

CONCLUSIONS

The newly developed VBIL scale is effective in determining the bilirubin content in feeding tube aspirates. Furthermore, compared with predicting tube location from pH-paper alone, dichotomized readings from the VBIL scale/bilirubin teststrip used in combination with a pH-teststrip improved the ability to differentiate between respiratory and gastrointestinal tube placement, as well as between gastric and intestinal tube placement. Refinement of the VBIL scale is indicated to increase its accuracy.