Bench-to-bedside review: the gut as an endocrine organ in the critically ill

Inter-relationships between gastric emptying and glycaemia: Implications for clinical practice

Gastric emptying (GE) exhibits a wide inter-individual variation and is a major determinant of postprandial glycaemia in health and diabetes; the rise in blood glucose following oral carbohydrate is greater when GE is relatively more rapid and more sustained when glucose tolerance is impaired. Conversely, GE is influenced by the acute glycaemic environment acute hyperglycaemia slows, while acute hypoglycaemia accelerates it. Delayed GE (gastroparesis) occurs frequently in diabetes and critical illness. In diabetes, this poses challenges for management, particularly in hospitalised individuals and/or those using insulin. In critical illness it compromises the delivery of nutrition and increases the risk of regurgitation and aspiration with consequent lung dysfunction and ventilator dependence. Substantial advances in knowledge relating to GE, which is now recognised as a major determinant of the magnitude of the rise in blood glucose after a meal in both health and diabetes and, the impact of acute glycaemic environment on the rate of GE have been made and the use of gut-based therapies such as glucagon-like peptide-1 receptor agonists, which may profoundly impact GE, in the management of type 2 diabetes, has become commonplace. This necessitates an increased understanding of the complex inter-relationships of GE with glycaemia, its implications in hospitalised patients and the relevance of dysglycaemia and its management, particularly in critical illness. Current approaches to management of gastroparesis to achieve more personalised diabetes care, relevant to clinical practice, is detailed. Further studies focusing on the interactions of medications affecting GE and the glycaemic environment in hospitalised patients, are required.

Exendin-4 Exacerbates Burn-Induced Mortality in Mice by Switching to Th2 Response

INTRODUCTION

To determine if Exendin-4 could be a therapeutic agent for burn-induced hyperglycemia.

MATERIALS AND METHODS

Male Balb/c mice received a bolus of Exendin-4 intraperitoneally immediately after 15% total body surface area scald injury. Tail glucose levels were recorded and T-cell functions were analyzed at 4 h and 24 h postburn (pb). Pancreatic pathology was observed consecutively. The secretions of cytokines were detected in serum, spleen, and lung. Apoptosis of splenic CD3+ T-cells was examined by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling and flow cytometry.

RESULTS

Although Exendin-4 could attenuate burn-induced hyperglycemia in mice at 4 h pb, it accelerated their survival dose dependently with progressive depletion of splenocyte number. T-cell function underwent two-phasic changes following Exendin-4 treatment. Compared to placebo mice, T-cell from Exendin-4-treated mice was manifested with increased proliferation, while decreased IL-2 secretion and lower ratio of IL-4/IFN-γ at 4 h pb. However, at 24 h pb, it showed decreased proliferation, while increased IL-2 secretion and higher ratio of IL-4/IFN-γ. Exendin-4 could elicit higher circulating IL-6 and IL-10 levels at 4 h pb, which were pronounced in the lung at 24 h pb. In the meanwhile, severe inflammation could be found in the pancreas. At 24 h pb, the numbers of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling or caspase-3 positive cells and the apoptosis of CD3+ T-cells were significantly increased in the spleens of Exendin-4 mice relative to placebo mice.

CONCLUSIONS

These data support a pathogenic role of Exendin-4 signaling during thermal injury, warning against its clinical application in acute insults.

Perspective: Drawing on Findings From Critical Illness to Explain Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

We propose an initial explanation for how myalgic encephalomyelitis / chronic fatigue syndrome (ME/CFS) could originate and perpetuate by drawing on findings from critical illness research. Specifically, we combine emerging findings regarding (a) hypoperfusion and endotheliopathy, and (b) intestinal injury in these illnesses with our previously published hypothesis about the role of (c) pituitary suppression, and (d) low thyroid hormone function associated with redox imbalance in ME/CFS. Moreover, we describe interlinkages between these pathophysiological mechanisms as well as “vicious cycles” involving cytokines and inflammation that may contribute to explain the chronic nature of these illnesses. This paper summarizes and expands on our previous publications about the relevance of findings from critical illness for ME/CFS. New knowledge on diagnostics, prognostics and treatment strategies could be gained through active collaboration between critical illness and ME/CFS researchers, which could lead to improved outcomes for both conditions.

Enteral feeding, even when the gut does not feel very good?

PURPOSE OF REVIEW

To summarize knowledge on the gut function in relation to enteral nutrition.

RECENT FINDINGS

The gut is certainly suffering during critical illness but our understanding of the exact mechanisms involved is limited. Physicians at bedside are lacking tools to identify how well or bad the gut is doing and whether the gut is responding adequately to critical illness. Sensing nutrition as a signal is important for the gut and microbiome. Enteral nutrition has beneficial effects for the gut perfusion and function. However, early full enteral nutrition in patients with shock was associated with an increased number of rare but serious complications.

SUMMARY

Whenever synthesizing knowledge in physiology and available evidence in critically ill, we suggest that enteral nutrition has beneficial effects but may turn harmful if provided too aggressively. Contraindications to enteral nutrition are listed in recent guidelines. For patients with gastrointestinal dysfunction but without these contraindications, we suggest considering early enteral nutrition as a signal to the gut and to the body rather than an energy and protein provision. With this rationale, we think that low dose of enteral nutrition could and probably should be provided also when the gut does not feel very good. Understanding the feedback from the gut in response to enteral nutrition would be important, however, monitoring tools are currently limited to clinical assessment only.

Lessons From Heat Stroke for Understanding Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

We here provide an overview of the pathophysiological mechanisms during heat stroke and describe similar mechanisms found in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Both conditions are characterized by disturbed homeostasis in which inflammatory pathways play a central role. Splanchnic vasoconstriction, increased gut permeability, gut-related endotoxemia, systemic inflammatory response, central nervous system dysfunction, blood coagulation disorder, endothelial-cell injury, and mitochondrial dysfunction underlie heat stroke. These mechanisms have also been documented in ME/CFS. Moreover, initial transcriptomic studies suggest that similar gene expressions are altered in both heat stroke and ME/CFS. Finally, some predisposing factors for heat stroke, such as pre-existing inflammation or infection, overlap with those for ME/CFS. Notwithstanding important differences - and despite heat stroke being an acute condition - the overlaps between heat stroke and ME/CFS suggest common pathways in the physiological responses to very different forms of stressors, which are manifested in different clinical outcomes. The human studies and animal models of heat stroke provide an explanation for the self-perpetuation of homeostatic imbalance centered around intestinal wall injury, which could also inform the understanding of ME/CFS. Moreover, the studies of novel therapeutics for heat stroke might provide new avenues for the treatment of ME/CFS. Future research should be conducted to investigate the similarities between heat stroke and ME/CFS to help identify the potential treatments for ME/CFS.

Promotion of Regular Oesophageal Motility to Prevent Regurgitation and Enhance Nutrition Intake in Long-Stay ICU Patients. A Multicenter, Phase II, Sham-Controlled, Randomized Trial: The PROPEL Study

OBJECTIVES

To evaluate the effect of esophageal stimulation on nutritional adequacy in critically ill patients at risk for enteral feeding intolerance.

DESIGN

A multicenter randomized sham-controlled clinical trial.

SETTING

Twelve ICUs in Canada.

PATIENTS

We included mechanically ventilated ICU patients who were given moderate-to-high doses of opioids and expected to remain alive and ventilated for an additional 48 hours and who were receiving enteral nutrition or expected to start imminently.

INTERVENTIONS

Patients were randomly assigned 1:1 to esophageal stimulation via an esophageal stimulating catheter (E-Motion Tube; E-Motion Medical, Tel Aviv, Israel) or sham treatment. All patients were fed via these catheters using a standardized feeding protocol.

MEASUREMENTS AND MAIN RESULTS

The co-primary outcomes were proportion of caloric and protein prescription received enterally over the initial 7 days following randomization. Among 159 patients randomized, the modified intention-to-treat analysis included 155 patients: 73 patients in the active treatment group and 82 in the sham treatment group. Over the 7-day study period, the percent of prescribed caloric intake (± SE) received by the enteral route was 64% ± 2 in the active group and 65% ± 2 in sham patients for calories (difference, -1; 95% CI, -8 to 6; p = 0.74). For protein, it was 57% ± 3 in the active group and 60% ± 3 in the sham group (difference, -3; 95% CI, -10 to 3; p = 0.30). Compared to the sham group, there were more serious adverse events reported in the active treatment group (13 vs 6; p = 0.053). Clinically important arrhythmias were detected by Holter monitoring in 36 out of 70 (51%) in the active group versus 22 out of 76 (29%) in the sham group (p = 0.006).

CONCLUSIONS

Esophageal stimulation via a special feeding catheter did not improve nutritional adequacy and was associated with increase risk of harm in critically ill patients.

The effects of ulimorelin, a ghrelin agonist, on liquid gastric emptying and colonic transit in humans

BACKGROUND

Ulimorelin, a small molecule ghrelin agonist and prokinetic agent, was effective in animal models of gastroparesis and delayed transit. However, employing once daily administration, it failed in clinical trials of postoperative ileus (POI), a condition in which colonic motility recovers last. The aim of this study was to evaluate drug dosing and regional differences in drug activity between stomach and colon.

METHODS

Gastric emptying was assessed by scintigraphy in healthy adults at single doses of 600-1200 µg kg^-1 and multiple doses of 80-600 µg kg^-1 Q8H for 7 days. Colonic motility was assessed by 7-region scintigraphic analysis at a dose of 600 µg kg^-1 for 2 days. The primary endpoints were percent change in time to 50% (∆t₅₀ ) liquid gastric emptying on Days 1, 4, and 6 and the geometric mean center of colonic transit at 24 hours (GC₂₄ ). Plasma concentrations of free and total ulimorelin were measured for pharmacokinetic and exposure-response modeling.

KEY RESULTS

Ulimorelin 150-600 µg kg^-1 every 8 hours resulted in statistically significant improvements (∆t₅₀  = 23% to 46% (P < .05)) in gastric emptying from baseline that were sustained through Day 6. However, no effects on GC₂₄ were observed. Pharmacokinetic analyses suggested that the free concentrations of ulimorelin achieved in POI trials and dosing frequency may have been inadequate.

CONCLUSIONS AND INFERENCES

Ulimorelin is a potent gastric prokinetic but lacks evidence of activity in the human colon, pointing to the stomach as the predominant site of action of ghrelin in humans; ClinicalTrials.gov NCT02993055.

Gallbladder Dyskinesia Is Associated With an Impaired Postprandial Fibroblast Growth Factor 19 Response in Critically Ill Patients

Critical illness is associated with a disturbed regulation of gastrointestinal hormones resulting in functional and metabolic anomalies. Fibroblast growth factor 19 (FGF19) is an ileum-derived metabolic hormone induced by bile salts upon gallbladder emptying after enteral nutrient stimulation. Our aim was to study the nutrient-stimulated FGF19 response in 24 patients admitted to the intensive care unit (ICU) compared with 12 healthy controls. All subjects received intraduodenal high-lipid nutrient infusion for 120 minutes. Blood was collected every 30 minutes until 1 hour after infusion, and gallbladder emptying was studied by ultrasound. Serum levels of bile salts and FGF19 were assessed. ICU patients had significantly higher fasting bile salt serum levels compared with controls, whereas FGF19 serum levels were similar. In both groups, nutrient infusion elicited substantial bile salt elevations (P < 0.001), peaking at 90 minutes, albeit with a significantly lower peak in the ICU patients (P = 0.029). In controls, FGF19 was significantly elevated relative to baseline from 120 minutes onward (P < 0.001). In ICU patients, the FGF19 response was blunted, as reflected by significantly lower FGF19 elevations at 120, 150, and 180 minutes (P < 0.05) and significantly lower area under the curve (AUC) values compared with controls (P < 0.001). Gallbladder dysmotility was associated with the impaired FGF19 response in critical illness. The gallbladder ejection fraction correlated positively with FGF19 AUC values (ρ = +0.34, P = 0.045). In 10 of 24 ICU patients, gallbladder emptying was disturbed. These patients had significantly lower FGF19 AUC values (P < 0.001). Gallbladder emptying and the FGF19 response were respectively disturbed or absent in patients receiving norepinephrine. Conclusion: The nutrient-stimulated FGF19 response is impaired in ICU patients, which is mechanistically linked to gallbladder dysmotility in critical illness. This may contribute to disturbed liver metabolism in these patients and has potential as a nutritional biomarker.

Gastrointestinal Sensing of Meal-Related Signals in Humans, and Dysregulations in Eating-Related Disorders

The upper gastrointestinal (GI) tract plays a critical role in sensing the arrival of a meal, including its volume as well as nutrient and non-nutrient contents. The presence of the meal in the stomach generates a mechanical distension signal, and, as gastric emptying progresses, nutrients increasingly interact with receptors on enteroendocrine cells, triggering the release of gut hormones, with lipid and protein being particularly potent. Collectively, these signals are transmitted to the brain to regulate appetite and energy intake, or in a feedback loop relayed back to the upper GI tract to further adjust GI functions, including gastric emptying. The research in this area to date has provided important insights into how sensing of intraluminal meal-related stimuli acutely regulates appetite and energy intake in humans. However, disturbances in the detection of these stimuli have been described in a number of eating-related disorders. This paper will review the GI sensing of meal-related stimuli and the relationship with appetite and energy intake, and examine changes in GI responses to luminal stimuli in obesity, functional dyspepsia and anorexia of ageing, as examples of eating-related disorders. A much better understanding of the mechanisms underlying these dysregulations is still required to assist in the development of effective management and treatment strategies in the future.

From dysmotility to virulent pathogens: implications of opioid use in the ICU

PURPOSE OF REVIEW

Gastrointestinal dysmotility occurs frequently in the critically ill. Although the causes underlying dysmotility are multifactorial, both pain and its treatment with exogenous opioids are likely causative factors. The purpose of this review is to describe the effects of pain and opioids on gastrointestinal motility; outline the rationale for and evidence supporting the administration of opioid antagonists to improve dysmotility; and describe the potential influence opioids drugs have on the intestinal microbiome and infectious complications.

RECENT FINDINGS

Opioid drugs are frequently prescribed in the critically ill to alleviate pain. In health, opioids cause gastric dysmotility, yet the evidence for this in critical illness is inconsistent and limited to observational studies. Administration of opioid antagonists may improve gastrointestinal motility, but data are sparse, and these agents cannot be recommended outside of clinical trials. Although critical illness is associated with alterations in the microbiome, the extent to which opioid administration influences these changes, and the subsequent development of infection, remains uncertain.

SUMMARY

Replication of clinical studies from ambulant populations in critical care is required to ascertain the independent influence of opioid administration on gastrointestinal motility and infectious complications.

A multicenter, randomized, double-blind study of ulimorelin and metoclopramide in the treatment of critically ill patients with enteral feeding intolerance: PROMOTE trial

PURPOSE

Enteral feeding intolerance (EFI) is a frequent problem in the intensive care unit (ICU), but current prokinetic agents have uncertain efficacy and safety profiles. The current study compared the efficacy and safety of ulimorelin, a ghrelin agonist, with metoclopramide in the treatment of EFI.

METHODS

One hundred twenty ICU patients were randomized 1:1 to ulimorelin or metoclopramide for 5 days. EFI was diagnosed by a gastric residual volume (GRV) ≥ 500 ml. A volume-based feeding protocol was employed, and enteral formulas were standardized. The primary end point was the percentage daily protein prescription (%DPP) received by patients over 5 days of treatment. Secondary end points included feeding success, defined as 80% DPP; gastric emptying, assessed by paracetamol absorption; incidences of recurrent intolerance (GRV ≥ 500 ml); vomiting or regurgitation; aspiration, defined by positive tracheal aspirates for pepsin; and pulmonary infection.

RESULTS

One hundred twenty patients were randomized and received the study drug (ulimorelin 62, metoclopramide 58). Mean APACHE II and SOFA scores were 21.6 and 8.6, and 63.3% of patients had medical reasons for ICU admission. Ulimorelin and metoclopramide resulted in comparable %DPPs over 5 days of treatment (median [Q1, Q3]: 82.9% [38.4%, 100.2%] and 82.3% [65.6%, 100.2%], respectively, p = 0.49). Five-day rates of feeding success were 67.7% and 70.6% when terminations unrelated to feeding were excluded, and there were no differences in any secondary outcomes or adverse events between the two groups.

CONCLUSIONS

Both prokinetic agents achieved similar rates of feeding success, and no safety differences between the two treatment groups were observed.

Role of Nutrition Support in Inflammatory Conditions

This review intends to summarize recent development on the potential nutrition implications of acute inflammation encountered during critical illness. Different aspects of the inflammatory response and their impact on nutrition management during critical illness will be discussed: the timing of the postinjury metabolic response, the integration of regulatory mechanisms involved in the metabolic response to stress, the oxidative stress, the metabolic and clinical consequences in terms of energy expenditure, use of energy, changes in body composition, and behavior.

Pathophysiology and Treatment of Gastrointestinal Motility Disorders in the Acutely Ill

Gastrointestinal dysmotility causes delayed gastric emptying, enteral feed intolerance, and functional obstruction of the small and large intestine, the latter functional obstructions being frequently termed ileus and Ogilvie syndrome, respectively. In addition to meticulous supportive care, drug therapy may be appropriate in certain situations. There is, however, considerable variation among individuals regarding what gastric residual volume identifies gastric dysmotility and would encourage use of a promotility drug. While the administration of either metoclopramide or erythromycin is supported by evidence it appears that, dual-drug therapy (erythromycin and metoclopramide) reduces the rate of treatment failure. There is a lack of evidence to guide drug therapy of ileus, but neither erythromycin nor metoclopramide appear to have a role. Several drugs, including ghrelin agonists, highly selective 5-hydroxytryptamine receptor agonists, and opiate antagonists are being studied in clinical trials. Neostigmine, when infused at a relatively slow rate in patients receiving continuous hemodynamic monitoring, may alleviate the need for endoscopic decompression in some patients.

[Gastrointestinal motility in critically ill patients]

Up to 80% of all critically ill patients develop gastrointestinal dysfunction, predominantly gastrointestinal motility disorder. In critically ill patients, gastrointestinal dysfunction or gastrointestinal failure is associated with increased morbidity and mortality. Correct diagnosis and early start of treatment are essential and can influence the outcome. Therapeutic options are normal potassium and magnesium levels, restrictive fluid balance, improved gastrointestinal microcirculation, individual sedoanalgetic concepts and early enteral nutrition. In addition, numerous target-oriented medical therapeutic options are available.

Gastrointestinal failure in the ICU

PURPOSE OF REVIEW

The current review summarizes different aspects of assessment of gastrointestinal function and provides a practical approach to management of adult patients with gastrointestinal dysfunction in the ICU.

RECENT FINDINGS

Different ways to define gastrointestinal failure have been used in the past. Recently, the term 'acute gastrointestinal injury (AGI)' has been proposed to specifically describe gastrointestinal dysfunction as a part of multiple organ dysfunction syndrome. Possible pathophysiological mechanisms and different aspects in assessment of gastrointestinal function in adult ICU patients are presented. Currently, there is no single marker that could reliably describe gastrointestinal dysfunction. Therefore, monitoring and management is still based on complex assessment of different gastrointestinal symptoms and feeding intolerance, even though this approach includes a large amount of subjectivity. The possible role of biomarkers (citrulline, enterohormones, etc.) and additional parameters like intra-abdominal pressure remains to be clarified.

SUMMARY

Defining gastrointestinal failure remains challenging but broad consensus needs to be reached and disseminated soon to allow conduct of interventional studies. A systematic approach to management of gastrointestinal problems is recommended.

Energy-Dense Formulae May Slow Gastric Emptying in the Critically Ill

BACKGROUND

Enteral feed intolerance occurs frequently in critically ill patients and can be associated with adverse outcomes. "Energy-dense formulae" (ie, >1 kcal/mL) are often prescribed to critically ill patients to reduce administered volume and are presumed to maintain or increase calorie delivery. The aim of this study was to compare gastric emptying of standard and energy-dense formulae in critically ill patients.

METHODS

In a retrospective comparison of 2 studies, data were analyzed from 2 groups of patients that received a radiolabeled 100-mL "meal" containing either standard calories (1 kcal/mL) or concentrated calories (energy-dense formulae; 2 kcal/mL). Gastric emptying was measured using a scintigraphic technique. Radioisotope data were collected for 4 hours and gastric emptying quantified. Data are presented as mean ± SE or median [interquartile range] as appropriate.

RESULTS

Forty patients were studied (n = 18, energy-dense formulae; n = 22, standard). Groups were well matched in terms of demographics. However, patients in the energy-dense formula group were studied earlier in their intensive care unit admission (P = .02) and had a greater proportion requiring inotropes (P = .002). A similar amount of calories emptied out of the stomach per unit time (P = .57), but in patients receiving energy-dense formulae, a greater volume of meal was retained in the stomach (P = .045), consistent with slower gastric emptying.

CONCLUSIONS

In critically ill patients, the administration of the same volume of a concentrated enteral nutrition formula may not result in the delivery of more calories to the small intestine over time because gastric emptying is slowed.

What's Next for Gastrointestinal Disorders: No Needles?

A myriad of pathologies affect the gastrointestinal tract, citing this affected area as a significant target for therapeutic intervention. One group of therapeutic agents, antisense and oligonucleotides and small interfering RNAs, offer a promising platform for treating a wide variety of diseases ranging from cancer to auto-immune diseases. Current delivery methods are carried out either systemically or locally into diseased areas, both of which involve needles. The challenge in orally administering this type of treatment lies in the complications that arise due to the vast environmental extremes found within the gastrointestinal tract, owing to the fact that, as the drug travels down the gastrointestinal tract, it is subjected to pH changes and interactions with bacteria and a variety of digestive and protective enzymes including proteases, DNAses, and RNAses. Overcoming these challenges to allow the practical application of these drugs is a priority that has invoked a multitude of research in the chemical, biological, and material sciences. In this review, we will address common gastrointestinal pathologies, the barriers to oral-based therapies and antisense-interfering technologies, the approaches that have already been applied for their delivery, and the current status of antisense drug therapy clinical trials for gastrointestinal-related disorders.

Chronic critical illness: the price of survival

BACKGROUND

The evolution of the techniques used in the intensive care setting over the past decades has led on one side to better survival rates in patients with acute conditions and severely impaired vital functions. On the other side, it has resulted in a growing number of patients who survive an acute event, but who then become dependent on one or more life support techniques. Such patients are called chronically critically ill patients.

MATERIALS & METHODS

No absolute definition of the disease is currently available, although most patients are characterized by the need for prolonged mechanical ventilation. Mortality rates are still high even after dismissal from intensive care unit (ICU) and transfer to specialized rehabilitation care settings.

RESULTS

In recent years, some studies have tried to clarify the pathophysiological characteristics underlying chronic critical illness (CCI), a disease that is also characterized by severe endocrine and inflammatory impairments, partly accounting for the almost constant set of symptoms.

DISCUSSION

Currently, no specific treatment is available. However, a strategic early therapeutic approach on ICU admission might try to prevent the progress of the acute disease towards chronic critical illness.

Update on Severe Burn Management for the Intensivist

Thermal injury of humans causes arguably the most severe perturbations in physiology that can be experienced. These physiologic derangements start immediately and can persist in some form until months or even years after the burn wounds are healed. Burn shock, marked activation of the systemic inflammatory response, multiple-organ failure, infection, and wound failure are just a few of the insults that may require management by the intensivist. The purpose of this article is to review recent advances in the critical care management of thermally injured patients.

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.

Nutrition rehabilitation in the intensive care unit

The maintenance of homeostasis after severe injury requires the restoration of the physiological regulation of food intake. A wide array of functional alterations can hinder the intake of adequate amounts of nutrients to support the recovery from critical illness. These alterations encompass changes in the preprandial phase, reflected by a loss of appetite; changes in the prandial phase, yielding swallowing disorders; and changes in the postprandial phase, including impairments of gastric emptying, gut motility, and satiety. This tutorial aims to review these often overlooked features and to suggest recommendations for the nutrition rehabilitation of the critically ill.

Definition, prevalence, and outcome of feeding intolerance in intensive care: a systematic review and meta-analysis

Clinicians and researchers frequently use the phrase 'feeding intolerance' (FI) as a descriptive term in enterally fed critically ill patients. We aimed to: (1) determine what is the most accepted definition of FI; (2) estimate the prevalence of FI; and (3) evaluate whether FI is associated with important outcomes. Systematic searches of peer-reviewed publications using PubMed, MEDLINE, and Web of Science were performed with studies reporting FI extracted. We identified 72 studies defining FI. In 33 studies, the definition was based on large gastric residual volumes (GRVs) together with other gastrointestinal symptoms, while 30 studies relied solely on large GRVs, six studies used inadequate delivery of enteral nutrition (EN) as a threshold, and three studies gastrointestinal symptoms without reference to GRV. The median volume used to define a 'large' GRV was 250 ml (ranges from 75 to 500 ml). The pooled proportion (n = 31 studies) of FI was 38.3% (95% CI 30.7-46.2). Five studies reported outcomes, all of them observed adverse outcome in FI patients. In three studies, respectively, FI was associated with increased mortality and ICU length-of-stay. In summary, FI is inconsistently defined but appears to occur frequently. There are preliminary data indicating that FI is associated with adverse outcomes. A standard definition of FI is required to determine the accuracy of these preliminary data.

Severe acute malnutrition in childhood: hormonal and metabolic status at presentation, response to treatment, and predictors of mortality

OBJECTIVE

Malnutrition is a major cause of childhood morbidity and mortality. To identify and target those at highest risk, there is a critical need to characterize biomarkers that predict complications prior to and during treatment.

METHODS

We used targeted and nontargeted metabolomic analysis to characterize changes in a broad array of hormones, cytokines, growth factors, and metabolites during treatment of severe childhood malnutrition. Children aged 6 months to 5 years were studied at presentation to Mulago Hospital and during inpatient therapy with milk-based formulas and outpatient supplementation with ready-to-use food. We assessed the relationship between baseline hormone and metabolite levels and subsequent mortality.

RESULTS

Seventy-seven patients were enrolled in the study; a subset was followed up from inpatient treatment to the outpatient clinic. Inpatient and outpatient therapies increased weight/height z scores and induced striking changes in the levels of fatty acids, amino acids, acylcarnitines, inflammatory cytokines, and various hormones including leptin, insulin, GH, ghrelin, cortisol, IGF-I, glucagon-like peptide-1, and peptide YY. A total of 12.2% of the patients died during hospitalization; the major biochemical factor predicting mortality was a low level of leptin (P = .0002), a marker of adipose tissue reserve and a critical modulator of immune function.

CONCLUSIONS

We have used metabolomic analysis to provide a comprehensive hormonal and metabolic profile of severely malnourished children at presentation and during nutritional rehabilitation. Our findings suggest that fatty acid metabolism plays a central role in the adaptation to acute malnutrition and that low levels of the adipose tissue hormone leptin associate with, and may predict, mortality prior to and during treatment.

Incretins and the intensivist: what are they and what does an intensivist need to know about them?

Hyperglycaemia occurs frequently in the critically ill, even in those patients without a history of diabetes. The mechanisms underlying hyperglycaemia in this group are complex and incompletely defined. In health, the gastrointestinal tract is an important modulator of postprandial glycaemic excursions and both the rate of gastric emptying and the so-called incretin hormones, glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide, are pivotal determinants of postprandial glycaemia. Incretin-based therapies (that is, glucagon-like peptide- 1 agonists and dipeptidyl-peptidase-4 inhibitors) have recently been incorporated into standard algorithms for the management of hyperglycaemia in ambulant patients with type 2 diabetes and, inevitably, an increasing number of patients who were receiving these classes of drugs prior to their acute illness will present to ICUs. This paper summarises current knowledge of the incretin effect as well as the incretin-based therapies that are available for the management of type 2 diabetes, and provides suggestions for the potential relevance of these agents in the management of dysglycaemia in the critically ill, particularly to normalise elevated blood glucose levels.

Endogenous amylin and glucagon-like peptide-1 concentrations are not associated with gastric emptying in critical illness

BACKGROUND

In health, the hormones amylin and glucagon-like peptide-1 (GLP-1) slow gastric emptying (GE) and modulate glycaemia. The aims of this study were to determine amylin and GLP-1 concentrations in the critically ill and their relationship with GE, glucose absorption and glycaemia.

METHODS

In fasted critically ill and healthy subjects (n = 26 and 23 respectively), liquid nutrient, containing 100 mg (13) C-sodium octanoate and 3 g 3-O-methlyglucose (3-OMG), was administered via a nasogastric tube. Amylin, GLP-1, glucose and 3-OMG concentrations were measured in blood samples taken during fasting, and 30 min and 60 min after the 'meal'. Breath samples were taken to determine gastric emptying coefficient (GEC). Intolerance to intragastric feeding was defined as a gastric residual volume of ≥ 250 ml and/or vomiting within the 24 h prior to the study.

RESULTS

Although GE was slower (GEC: critically ill 2.8 ± 0.9 vs. health, 3.4 ± 0.2; P = 0.002), fasting blood glucose was higher (7.0 ± 1.9 vs. 5.7 ± 0.2 mmol/l; P = 0.005) and overall glucose absorption was reduced in critically ill patients (3-OMG: 9.4 ± 8.0 vs. 17.7 ± 4.9 mmol/l.60 min; P < 0.001), there were no differences in fasting or postprandial amylin concentrations. Furthermore, although fasting [1.7 (0.4-7.2) vs. 0.7 (0.3-32.0) pmol/l; P = 0.04] and postprandial [3.0 (0.4-8.5) vs. 0.8 (0.4-34.3) pmol/l; P = 0.02] GLP-1 concentrations were increased in the critically ill and were greater in feed intolerant when compared with those tolerating feed [3.7 (0.4-7.2) vs. 1.2 (0.7-4.6) pmol/l; P = 0.02], there were no relationships between GE and fasting amylin or GLP-1 concentrations.

CONCLUSION

In the critically ill, fasting GLP-1, but not amylin, concentrations are elevated and associated with feed intolerance. Neither amylin nor GLP-1 appears to substantially influence the rate of GE.

The effects of critical illness on intestinal glucose sensing, transporters, and absorption

OBJECTIVES

Providing effective enteral nutrition is important during critical illness. In health, glucose is absorbed from the small intestine via sodium-dependent glucose transporter-1 and glucose transporter-2, which may both be regulated by intestinal sweet taste receptors. We evaluated the effect of critical illness on glucose absorption and expression of intestinal sodium-dependent glucose transporter-1, glucose transporter-2, and sweet taste receptors in humans and mice.

DESIGN

Prospective observational study in humans and mice.

SETTING

ICU and university-affiliated research laboratory.

SUBJECTS

Human subjects were 12 critically ill patients and 12 healthy controls. In the laboratory 16-week-old mice were studied.

INTERVENTIONS

Human subjects underwent endoscopy. Glucose (30 g) and 3-O-methylglucose (3 g), used to estimate glucose absorption, were infused intraduodenally over 30 minutes. Duodenal mucosa was biopsied before and after infusion. Mice were randomized to cecal ligation and puncture to model critical illness (n = 16) or sham laparotomy (control) (n = 8). At day 5, mice received glucose (100 mg) and 3-O-methylglucose (10 mg) infused intraduodenally prior to mucosal tissue collection.

MEASUREMENTS AND MAIN RESULTS

Quantitative polymerase chain reaction was performed to measure absolute (human) and relative levels of sodium-dependent glucose transporter-1, glucose transporter-2, and taste receptor type 1 member 2 (T1R2) transcripts. Blood samples were assayed for 3-O-methylglucose to estimate glucose absorption. Glucose absorption was three-fold lower in critically ill humans than in controls (p = 0.002) and reduced by a similar proportion in cecal ligation and puncture mice (p = 0.004). In critically ill patients, duodenal levels of sodium-dependent glucose transporter-1, glucose transporter-2, and T1R2 transcript were reduced 49% (p < 0.001), 50% (p = 0.009), and 85% (p = 0.007), whereas in the jejunum of cecal ligation and puncture mice sodium-dependent glucose transporter-1, glucose transporter-2, and T1R2 transcripts were reduced by 55% (p < 0.001), 50% (p = 0.002), and 69% (p = 0.004).

CONCLUSIONS

Critical illness is characterized by markedly diminished glucose absorption, associated with reduced intestinal expression of glucose transporters (sodium-dependent glucose transporter-1 and glucose transporter-2) and sweet taste receptor transcripts. These changes are paralleled in cecal ligation and puncture mice.

Neonatal intestinal physiology and failure

The neonatal intestine is a complex organ that regulates the absorption of nutrients essential for growth and development. Intestinal failure results from insufficient or functionally inadequate bowel and can lead to failure of neonatal growth and development. Current literature on neonatal intestinal physiology and failure was reviewed and summarized. A homeostatic interplay of electrolytes, enzymes, and hormonal regulators is essential to achieve the physiologic balance needed for adequate intestinal performance. Physiologic consequences of intestinal failure are dependent on the length and anatomic location of the diseased or surgically resected bowel. Intestinal failure leads to disruption of normal intestinal physiology and may have long-term consequences for growth and development if inadequately treated. Parenteral nutrition remains the mainstay of treatment for neonatal intestinal failure.

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 15 healthy 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/20 min) 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 dose-dependent 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.

The gut-brain axis in the critically ill: is glucagon-like peptide-1 protective in neurocritical care?

Enteral nutrient is a potent glucagon-like peptide-1 (GLP-1) secretagogue. In vitro and animal studies indicate that GLP-1 has immune-modulatory and neuroprotective effects. To determine whether these immune-modulatory and neuroprotective effects of GLP-1 are beneficial in the critically ill, studies achieving pharmacological GLP-1 concentrations are warranted.

Reg IV is differently expressed in enteroendocrine cells of human small intestine and colon

Reg IV is a 17 kD secreted C-type lectin physiologically found in selected enteroendocrine cells (EEC). It is thought be involved in the regulation of normal and pathological intestinal and/or neuroendocrine differentiation and proliferation but its ultimate functional role(s) is still unclear. We used immunostaining and compared the cellular expression of Reg IV with a panel of neuroendocrine markers in human GI-tract tissue samples. Reg IV showed cellular co-distribution with serotonin and chromogranin A in all parts of GI-tract. Co-localization of Reg IV with somatostatin was seen in colon and with substance P in ileum. Subpopulations of cells expressing Reg IV overlapped with EECs containing GLP-1, GLP-2, secretin, PYY, and ghrelin, depending on the anatomical localization of the samples. The results further underscore the high degree of diversity among EECs and suggest that Reg IV may be involved in the finetuning of functions exerted by the neuroendocrine cells in the GI-tract.

Exogenous glucagon-like peptide-1 attenuates the glycaemic response to postpyloric nutrient infusion in critically ill patients with type-2 diabetes

INTRODUCTION

Glucagon-like peptide-1 (GLP-1) attenuates the glycaemic response to small intestinal nutrient infusion in stress-induced hyperglycaemia and reduces fasting glucose concentrations in critically ill patients with type-2 diabetes. The objective of this study was to evaluate the effects of acute administration of GLP-1 on the glycaemic response to small intestinal nutrient infusion in critically ill patients with pre-existing type-2 diabetes.

METHODS

Eleven critically ill mechanically-ventilated patients with known type-2 diabetes received intravenous infusions of GLP-1 (1.2 pmol/kg/minute) and placebo from t = 0 to 270 minutes on separate days in randomised double-blind fashion. Between t = 30 to 270 minutes a liquid nutrient was infused intraduodenally at a rate of 1 kcal/min via a naso-enteric catheter. Blood glucose, serum insulin and C-peptide, and plasma glucagon were measured. Data are mean ± SEM.

RESULTS

GLP-1 attenuated the overall glycaemic response to nutrient (blood glucose AUC30-270 min: GLP-1 2,244 ± 184 vs. placebo 2,679 ± 233 mmol/l/minute; P = 0.02). Blood glucose was maintained at < 10 mmol/l in 6/11 patients when receiving GLP-1 and 4/11 with placebo. GLP-1 increased serum insulin at 270 minutes (GLP-1: 23.4 ± 6.7 vs. placebo: 16.4 ± 5.5 mU/l; P < 0.05), but had no effect on the change in plasma glucagon.

CONCLUSIONS

Exogenous GLP-1 in a dose of 1.2 pmol/kg/minute attenuates the glycaemic response to small intestinal nutrient in critically ill patients with type-2 diabetes. Given the modest magnitude of the reduction in glycaemia the effects of GLP-1 at higher doses and/or when administered in combination with insulin, warrant evaluation in this group.

TRIAL REGISTRATION

ANZCTR:ACTRN12610000185066.

Waking up the gut in critically ill patients

Multiorgan failure frequently develops in critically ill patients. While therapeutic efforts in such patients are often focused on the lungs, on the cardiovascular system as well as on the kidneys, it is important to also consider the functional alterations in gut motility and hormone secretion. Given the central regulatory functions of many gut hormones, such as glucagon-like peptide 1, glucagon-like peptide 2, ghrelin and others, exogenous supplementation of some of these factors may be beneficial under conditions of critical illness. From a pragmatic point of view, the most feasible way towards a restoration of gut hormone secretion in critically ill patients is to provide enteral nutritional supply as soon as possible.

The therapeutic potential of a venomous lizard: the use of glucagon-like peptide-1 analogues in the critically ill

Glucagon-like peptide-1 (GLP-1), a principal mediator of the postprandial insulinotropic response in health, has a half-life of minutes. The saliva of the Gila monster contains exendin-4, a structural analogue of human GLP-1, but with a much longer half-life. A synthetic preparation of exendin-4, exenatide, is suitable for human use and effectively lowers glucose in ambulant type 2 diabetic patients. When compared with insulin, exenatide therapy is associated with a reduction in hypoglycaemic episodes and postprandial glycaemic excursions in this group. Accordingly, GLP-1 analogues are appealing therapies for hyperglycaemia in the critically ill patient and warrant further study.