Mechanisms underlying feed intolerance in the critically ill: Implications for treatment

Malnutrition is associated with poor outcomes in critically ill patients. Although nutritional support is yet to be proven to improve mortality in non-malnourished critically ill patients, early enteral feeding is considered best practice. However, enteral feeding is often limited by delayed gastric emptying. The best method to clinically identify delayed gastric emptying and feed intolerance is unclear. Gastric residual volume (GRV) measured at the bedside is widely used as a surrogate marker for gastric emptying, but the value of GRV measurement has recently been disputed. While the mechanisms underlying delayed gastric emptying require further investigation, recent research has given a better appreciation of the pathophysiology. A number of pharmacological strategies are available to improve the success of feeding. Recent data suggest a combination of intravenous metoclopramide and erythromycin to be the most successful treatment, but novel drug therapies should be explored. Simpler methods to access the duodenum and more distal small bowel for feed delivery are also under investigation. This review summarises current understanding of the factors responsible for, and mechanisms underlying feed intolerance in critical illness, together with the evidence for current practices. Areas requiring further research are also highlighted.

Modulation of individual components of gastric motor response to duodenal glucose

AIM:To evaluate individual components of the antro-pyloro-duodenal(APD)motor response to graded small intestinal glucose infusions in healthy humans.METHODS:APD manometry was performed in 15healthy subjects(12 male;40±5 years,body mass index 26.5±1.6 kg/m2)during four 20-min intraduodenal infusions of glucose at 0,0.5,1.0 and 1.5 kcal/min,in a randomised double-blinded fashion.Glucose solutions were infused at a rate of 1 mL/min and separated by 40-min"wash-out"period.Data are mean±SE.Inferential analyses are repeated measure analysis of variance with Bonferroni post-hoc testing.RESULTS:At 0 kcal/min frequency of pressure waves were:antrum(7.5±1.8 waves/20 min)and isolated pyloric pressure waves(IPPWs)(8.0±2.3 waves/20min)with pyloric tone(0.0±0.9 mmHg).Intraduodenal glucose infusion acutely increased IPPW frequency(P<0.001)and pyloric tone(P=0.015),and decreased antral wave frequency(P=0.007)in a dosedependent fashion.A threshold for stimulation was observed at 1.0 kcal/min for pyloric phasic pressure waves(P=0.002)and 1.5 kcal/min for pyloric tone and antral contractility.CONCLUSION:There is hierarchy for the activation of gastrointestinal motor responses to duodenal glucose infusion.An increase in IPPWs is the first response observed.