Glucose content of tracheal aspirates: implications for the detection of tube feeding aspiration

Abstract

Objective: To determine, using a sensitive glucose assay, whether monitoring of tracheal aspirate glucose concentration could serve as a marker of aspiration of enteral feedings.

Design: Prospective, controlled trial.

Setting: Intensive care units of a tertiary care hospital.

Patients: Fifteen enterally fed and 15 nonenterally fed, tracheally intubated patients who had normal lung fields on a routine chest radiograph.

Interventions: Patients with endotracheal tubes undergoing routine tracheal suctioning had tracheal secretions collected three times per day with a minimum of 4 hrs between samples for up to 5 days. Daily chest radiographs were reviewed for evidence of the development of pneumonitis using defined criteria.

Measurements and main results: Glucose concentrations in five commonly used commercial feeding formulas, as well as in the medications patients were receiving enterally or as an oral wash, were measured. Tracheal secretion glucose concentrations were 66 +/- 54 (SD) mg/dL (3.7 +/- 3.0 mmol/L) and 105 +/- 70 mg/dL (5.8 +/- 3.9 mmol/L) in the enterally fed and nonenterally fed patients, respectively (p = NS). Of the medications administered, the majority contained negligible glucose, but ten had > 3 mg/dose of glucose. However, there was no correlation between administration of these medications and the tracheal glucose concentrations. Tracheal glucose concentrations were similar in patients who received medications containing glucose and patients who received either no medications or medications with negligible glucose content. A small but significant correlation between blood glucose and tracheal secretion glucose concentrations (r2 = .15, p < .05) was observed. None of the patients developed aspiration pneumonitis. Glucose concentrations in widely used commercial formulas (44 to 202 mg/dL; 2.4 to 11.2 mmol/L) overlapped considerably with glucose concentrations in tracheal secretions in the absence of aspiration and were for the most part within 2 SD of mean values in tracheal secretions.

Conclusions: Tracheal secretions contain high glucose concentrations, both in enterally fed patients without evidence of aspiration pneumonitis and in nonenterally fed patients. The concentration of glucose in tracheal secretions appears to be determined, in part, by ambient extracellular glucose concentrations. We conclude that measurement of glucose in tracheal secretions is unlikely to be useful in monitoring for tube feeding aspiration in tracheally intubated, enterally fed patients.