Comparative effects on glucose absorption of intragastric and post-pyloric nutrient delivery in the critically ill

Assessment of physiological barriers to nutrition following critical illness

BACKGROUND & AIMS

Nutrition may be important for recovery from critical illness. Gastrointestinal dysfunction is a key barrier to nutrition delivery in the Intensive Care Unit (ICU) and metabolic rate is elevated exacerbating nutritional deficits. Whether these factors persist following ICU discharge is unknown. We assessed whether delayed gastric emptying (GE) and impaired glucose absorption persist post-ICU discharge.

METHODS

A prospective observational study was conducted in mechanically ventilated adults at 3 time-points: in ICU (V1); on the post-ICU ward (V2); and 3-months after ICU discharge (V3); and compared to age-matched healthy volunteers. On each visit, all participants received a test-meal containing 100 ml of 1 kcal/ml liquid nutrient, labelled with 0.1 g ¹³C-octanoic acid and 3 g 3-O-Methyl-glucose (3-OMG), and breath and blood samples were collected over 240min to quantify GE (gastric emptying coefficient (GEC)), and glucose absorption (3-OMG concentration; area under the curve (AUC)). Data are mean ± standard error of the mean (SEM) and differences shown with 95% confidence intervals (95%CI).

RESULTS

Twenty-six critically ill patients completed V1 (M:F 20:6; 62.0 ± 2.9 y; BMI 29.8 ± 1.2 kg/m²; APACHE II 19.7 ± 1.9), 15 completed V2 and eight completed V3; and were compared to 10 healthy volunteers (M:F 6:4; 60.5 ± 7.5 y; BMI 26.0 ± 1.0 kg/m²). GE was significantly slower on V1 compared to health (GEC difference: -0.96 (95%CI -1.61, -0.31); and compared to V2 (-0.73 (-1.16, -0.31) and V3 (-1.03 (-1.47, -0.59). GE at V2 and V3 were not different to that in health (V2: -0.23 (-0.61, 0.14); V3: 0.10 (-0.27, 0.46)). GEC: V1: 2.64 ± 0.19; V2: 3.37 ± 0.12; V3: 3.67 ± 0.10; health: 3.60 ± 0.13. Glucose absorption (3-OMG AUC_0-240) was impaired on V1 compared to V2 (-37.9 (-64.2, -11.6)), and faster on V3 than in health (21.8 (0.14, 43.4) but absorption at V2 and V3 did not differ from health. Intestinal glucose absorption: V1: 63.8 ± 10.4; V2: 101.7 ± 7.0; V3: 111.9 ± 9.7; health: 90.7 ± 3.8.

CONCLUSION

This study suggests that delayed GE and impaired intestinal glucose absorption recovers rapidly post-ICU. This requires further confirmation in a larger population. The REINSTATE trial was prospectively registered at www.anzctr.org.au.

TRIAL ID

ACTRN12618000370202.

Gut dysfunction in the ICU: diagnosis and management

PURPOSE OF REVIEW

Progress has been made in our understanding of gut dysfunction in critical illness. This review will outline new findings and give perspectives based on previous knowledge and concurrent advances in nutrition.

RECENT FINDINGS

The relationship between gut dysfunction and poor outcomes in critical illness has received considerable interest. It remains uncertain whether gut dysfunction is merely a marker of illness severity or if it is directly responsible for prolonged critical illness and increased mortality. This relationship is difficult to ascertain given there is no agreed method for identification and quantification; biomarkers such as intestinal fatty acid binding protein and citrulline show promise but require further study. Recent studies have investigated strategies to deliver enteral nutrition targets with impacts on gut function, including high calorie or protein formulae, intermittent regimes and novel prokinetics.

SUMMARY

Gut dysfunction is associated with poor outcomes, but it remains uncertain whether strategies to improve gut function will influence survival and recovery.

Postprandial rise of essential amino acids is impaired during critical illness and unrelated to small-intestinal function

Background

Postprandial rise of plasma essential amino acids (EAAs) determines the anabolic effect of dietary protein. Disturbed gastrointestinal function could impair the anabolic response in critically ill patients. Aim was to investigate the postprandial EAA response in critically ill patients and its relation to small‐intestinal function.

Methods

Twenty‐one mechanically ventilated patients and 9 healthy controls received a bolus containing 100 ml of a formula feed (Ensure) and 2 g of 3‐O‐Methyl‐d‐glucose (3‐OMG) via postpyloric feeding tube. Fasting and postprandial plasma concentrations of EAAs, 3‐OMG, total bile salts, and the gut‐released hormone fibroblast growth factor 19 (FGF19) were measured over a 4‐hour period. Changes over time and between groups were assessed with linear mixed‐effects analysis. Early (0–60 minutes) and total postprandial responses are summarized as the incremental area under the curve (iAUC).

Results

At baseline, fasting EAA levels were similar in both groups: 1181 (1055–1276) vs 1150 (1065–1334) μmol·L−1, P = .87. The early postprandial rise in EAA was not apparent in critically ill patients compared with healthy controls (iAUC₆₀, −4858 [−6859 to 2886] vs 5406 [3099–16,853] µmol·L⁻¹·60 minutes; P = .039). Impaired EAA response did not correlate with impaired 3‐OMG response (Spearman ρ 0.32, P = .09). There was a limited increase in total bile salts but no relevant FGF19 response in either group.

Conclusion

Postprandial rise of EAA is blunted in critically ill patients and unrelated to glucose absorption measured with 3‐OMG. Future studies should aim to delineate governing mechanisms of macronutrient malabsorption.

[Effect of hypocaloric versus standard enteral feeding on clinical outcomes in critically ill adults - A meta-analysis of randomized controlled trials with trial sequential analysis]

OBJECTIVES

To compare the effect of hypocaloric versus standard enteral feeding on clinical outcomes in critically ill adults, and to investigate the influence of protein intake upon the outcome effects of hypocaloric feeding.

DESIGN

A meta-analysis of randomized controlled trials (RCTs) and trial sequential analysis (TSA) were carried out.

SETTING

Intensive Care Unit (ICU).

PATIENTS

Or participants Critically ill adults.

INTERVENTIONS

Hypocaloric enteral feeding versus standard enteral feeding.

MAIN VARIABLES OF INTEREST

The primary outcomes were all-cause short-term mortality and the incidence of nosocomial infection.

RESULTS

Eleven RCTs met the inclusion criteria; of these trials, two were judged as having low risk of bias. Compared with standard enteral feeding, hypocaloric enteral feeding had no benefits in terms of reducing short-term mortality, the incidence of nosocomial infection, or long-term mortality, though it had a positive impact upon the incidence of gastrointestinal intolerance. The TSA further confirmed these results. In turn, hypocaloric enteral feeding had no effects upon the incidence of bloodstream infection, pneumonia, hypoglycemia or the duration of mechanical ventilation, ICU stay, or in-hospital stay. The above results remained unchanged in the sub-analysis of trials with a low risk of bias, trials administering a similar dose of protein, or trials administering different doses of protein.

CONCLUSIONS

Compared with standard enteral feeding, hypocaloric enteral feeding was not associated with better clinical outcomes in critically ill adults, except for a lower risk of gastrointestinal intolerance. The difference in protein intake between groups might have no influence on the outcome effects of hypocaloric enteral feeding. High quality randomized controlled trials are needed to confirm this, however.

The role of nutritional support in the physical and functional recovery of critically ill patients: a narrative review

The lack of benefit from randomised controlled trials has resulted in significant controversy regarding the role of nutrition during critical illness in terms of long-term recovery and outcome. Although methodological caveats with a failure to adequately appreciate biological mechanisms may explain these disappointing results, it must be acknowledged that nutritional support during early critical illness, when considered alone, may have limited long-term functional impact.This narrative review focuses specifically on recent clinical trials and evaluates the impact of nutrition during critical illness on long-term physical and functional recovery.Specific focus on the trial design and methodological limitations has been considered in detail. Limitations include delivery of caloric and protein targets, patient heterogeneity, short duration of intervention, inappropriate clinical outcomes and a disregard for baseline nutritional status and nutritional intake in the post-ICU period.With survivorship at the forefront of critical care research, it is imperative that nutrition studies carefully consider biological mechanisms and trial design because these factors can strongly influence outcomes, in particular long-term physical and functional outcome. Failure to do so may lead to inconclusive clinical trials and consequent rejection of the potentially beneficial effects of nutrition interventions during critical illness.

Gastric Versus Small Bowel Feeding in Critically Ill Adults

Critically ill patients often require enteral feedings as a primary supply of nutrition. Whether enteral nutrition (EN) should be delivered as a gastric versus small bowel feeding in the critically ill patient population remains a contentious topic. The Society of Critical Care Medicine (SCCM)/American Society for Parenteral and Enteral Nutrition (ASPEN), the European Society for Parenteral and Enteral Nutrition (ESPEN), and the Canadian Clinical Practice Guidelines (CCPG) are not in consensus on this topic. No research to date demonstrates a significant difference between the two feeding routes in terms of patient mortality, ventilator days, or length of stay in the intensive care unit (ICU); however, studies provide some evidence that there may be other benefits to using a small bowel feeding route in critically ill patients. The purpose of this paper is to examine both sides of this debate and review advantages and disadvantages of both small bowel and gastric routes of EN. Practical issues and challenges to small bowel feeding tube placement are also addressed. Finally, recommendations are provided to help guide the clinician when selecting a feeding route, and suggestions are made for future research.

Gastrointestinal dysfunction relating to the provision of nutrition in the critically ill

PURPOSE OF REVIEW

During critical illness, enteral nutrition remains central to clinical care and an understanding of gut dysfunction is therefore important. Contemporary data have contributed to our knowledge in this area and this review will concentrate on recently published studies.

RECENT FINDINGS

It is difficult to precisely measure gastric emptying and nutrient absorption as part of routine clinical care. However, techniques for the measurement of these parameters for research purposes have been refined, studied and validated. These methodologies allow the evaluation of novel treatments that modulate gastric emptying. Quantification and an understanding of the mechanisms of nutrient malabsorption may facilitate the development of therapeutic agents to improve absorption and/or formulae, which are more readily absorbed, thereby improving nutritional and clinical outcomes.

SUMMARY

Improved understanding of gut pathophysiology in critical illness provides opportunities for the development and testing of novel and targeted treatment strategies, with the objective to improve clinical outcomes in this group.

Human in vivo regional intestinal permeability: importance for pharmaceutical drug development

Both the development and regulation of pharmaceutical dosage forms have undergone significant improvements and development over the past 25 years, due primarily to the extensive application of the biopharmaceutical classification system (BCS). The Biopharmaceutics Drug Disposition Classification System, which was published in 2005, has also been a useful resource for predicting the influence of transporters in several pharmacokinetic processes. However, there remains a need for the pharmaceutical industry to develop reliable in vitro/in vivo correlations and in silico methods for predicting the rate and extent of complex gastrointestinal (GI) absorption, the bioavailability, and the plasma concentration-time curves for orally administered drug products. Accordingly, a more rational approach is required, one in which high quality in vitro or in silico characterizations of active pharmaceutical ingredients and formulations are integrated into physiologically based in silico biopharmaceutics models to capture the full complexity of GI drug absorption. The need for better understanding of the in vivo GI process has recently become evident after an unsuccessful attempt to predict the GI absorption of BCS class II and IV drugs. Reliable data on the in vivo permeability of the human intestine (Peff) from various intestinal regions is recognized as one of the key biopharmaceutical requirements when developing in silico GI biopharmaceutics models with improved predictive accuracy. The Peff values for human jejunum and ileum, based on historical open, single-pass, perfusion studies are presented in this review. The main objective of this review is to summarize and discuss the relevance and current status of these human in vivo regional intestinal permeability values.

Comparisons between intragastric and small intestinal delivery of enteral nutrition in the critically ill: a systematic review and meta-analysis

Introduction

The largest cohort of critically ill patients evaluating intragastric and small intestinal delivery of nutrients was recently reported. This systematic review included recent data to compare the effects of small bowel and intragastric delivery of enteral nutrients in adult critically ill patients.

Methods

This is a systematic review of all randomised controlled studies published between 1990 and March 2013 that reported the effects of the route of enteral feeding in the critically ill on clinically important outcomes.

Results

Data from 15 level-2 studies were included. Small bowel feeding was associated with a reduced risk of pneumonia (Relative Risk, RR, small intestinal vs. intragastric: 0.75 (95% confidence interval 0.60 to 0.93); P = 0.01; I² = 11%). The point estimate was similar when only studies using microbiological data were included. Duration of ventilation (weighted mean difference: -0.36 days (-2.02 to 1.30); P = 0.65; I² = 42%), length of ICU stay (WMD: 0.49 days, (-1.36 to 2.33); P = 0.60; I² = 81%) and mortality (RR 1.01 (0.83 to 1.24); P = 0.92; I² = 0%) were unaffected by the route of feeding. While data were limited, and there was substantial statistical heterogeneity, there was significantly improved nutrient intake via the small intestinal route (% goal rate received: 11% (5 to 16%); P = 0.0004; I² = 88%).

Conclusions

Use of small intestinal feeding may improve nutritional intake and reduce the incidence of ICU-acquired pneumonia. In unselected critically ill patients other clinically important outcomes were unaffected by the site of the feeding tube.