Measurement of gastric emptying in ICU patients with ¹³C-acetate

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Introduction

In clinical practice, gastric emptying and the success of gastric feeding is assessed by measurement of gastric residuals. A new setting easily allows bedside measurements in ventilated ICU-patients by ¹³C-technology to evaluate gastric transport.

Methods

¹³C-acetate added to tube feeding will be absorbed into the blood stream from the duodenum and oxidised to ¹³CO₂ in the liver. The ratio of ¹³CO₂/¹²CO₂ in the expired air can be determined by infrared isotope-selective spectrometry (IRIS). Increasing expiratory concentrations of ¹³CO₂ indicate transport of the applied tracer from the stomach to the duodenum. In 11 healthy volunteers breathing spontaneously via a tight CPAP mask on a Dräger Evita respirator system, ¹³CO₂ enrichment in the expired air was measured for two hours after ingestion of 150 mg ¹³C-acetate in 50 ml tube feeding. In nine ventilated ICU patients measurements were performed to determine expiratory ¹³CO2/¹²CO2 ratios after administration of the same amount of tracer and tube feeding via gastric tube. Gastric reflux and the total amount of tube feeding were recorded before measuring.

Figure

Cumulative recovery (mean ± SD) in volunteers (filled diamond) and ICU-patients (clear circle)

Results

The new setting was validated in volunteers. About 20 to 40 min after ingestion of the tracer, peak values (% of ¹³C dose/h) were recorded. Within two hours the cumulative recovery was 20%. In the ICU patients only a small quantity of the applied tracer (<5%) was recovered independent of reflux amounts.

Conclusion

We could not quantify gastric emptying by this new setting in ICU patients. Failure might be due to changes in transport mechanisms, resorption in the duodenum, metabolism and pool exchange compared to healthy volunteers.