The incidence and immediate respiratory consequences of pulmonary aspiration of enteral feed

Introduction

The cause of a respiratory deterioration in a critically ill patient frequently remains unknown. Pulmonary aspiration of enteral feed during tracheal intubation may be recognised at the bedside by the appearance of feed in the tracheal aspirate but is commonly unrecognised. To reduce aspiration it is important to be able to detect it at the bedside and hence alter management to reduce risk factors. Techniques to detect feed aspiration using food colouring have poor sensitivity and are linked with mortality in septic patients [1]. The standard glucose oxidase strip method for detecting aspiration is also insensitive because the glucose levels in feeds are similar to those of normal tracheal aspirates. We have previously described a modified glucose oxidase test strip method with an improved sensitivity [2] whereby the glucose concentration of the feed is markedly increased.

Method

The glucose concentration of the feed was increased by adding 10 g of glucose to 500 ml of feed. This increased the carbohydrate load by only 14% from 68 g to 78 g, but markedly increased the glucose concentration by 1000% from 11 mmol/l to 120 mmol/l. Testing tracheal secretions with standard glucose oxidase strips allowed the detection of tracheal aspiration (when tracheal glucose exceeds blood glucose). Ten patients were studied and PaO₂/FiO₂ data were collected prospectively prior to and after each aspiration episode.

Results

Five of the 10 patients aspirated enteral feed on one or more occasion (incidence 50%). There were seven episodes of aspiration detected in 55 patient days studied (prevalence 13% per day ventilation). Following an aspiration there was a fall in PaO₂/FiO₂ from a mean of 29.2 to 20.7 kPa (Fig. 1; P < 0.017; Wilcoxon rank sum test).

Figure 1

Deterioration in gas exchange associated with feed aspiration (mean/2 SEM).

Conclusion

Aspiration of feed in the critically ill is common and is associated with a fall in PaO₂/FiO₂.