The enteroendocrine axis and its effect on gastrointestinal function, nutrition, and inflammation

PURPOSE OF REVIEW

Gastrointestinal (GI) dysfunction limits enteral nutrition (EN) delivery in critical illness and contributes to systemic inflammation. The enteroendocrine (EE) axis plays an integral role in this interface between nutrition, inflammation, and GI function in critical illness. In this review, we present an overview of the EE system with a focus on its role in GI inflammation and function.

RECENT FINDINGS

Enteroendocrine cells have been primarily described in their role in macronutrient digestion and absorption. Recent research has expanded on the diverse functions of EE cells including their ability to sense microbial peptides and metabolites and regulate immune function and inflammation. Therefore, EE cells may be both affected by and contribute to many pathophysiologic states and interventions of critical illness such as dysbiosis , inflammation, and alternative EN strategies. In this review, we present an overview of EE cells including their growing role in nonnutrient functions and integrate this understanding into relevant aspects of critical illness with a focus on EN.

SUMMARY

The EE system is key in maintaining GI homeostasis in critical illness, and how it is impacted and contributes to outcomes in the setting of dysbiosis , inflammation and different feeding strategies in critical illness should be considered.

A scoping review considering potential biomarkers or functional measures of gastrointestinal dysfunction and enteral feeding intolerance in critically ill adults

BACKGROUND & AIM

Enteral feeding intolerance (EFI) as a result of gastrointestinal (GI) dysfunction in critically ill adults can lead to suboptimal nutritional delivery, increasing the risk of hospital acquired malnutrition. There are no validated measures of EFI or consensus as to which measures could be used to define EFI. The aim of this scoping review is to explore the validity of biomarkers, physiological or functional measures of GI dysfunction and EFI in critically ill adults characterising their use in routine clinical practice to identify those with GI dysfunction to better guide nutritional support.

METHODS

Database searches were completed in Ovid MEDLINE, Embase, CINAHL and Web of Science using the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) guidelines. The search was performed until June 2022. Articles were included if they reported original studies that identify potential biomarkers or functional measures of EFI in critically ill adults. A nine-stage process was completed to extract and complete data synthesis.

RESULTS

139 unique articles were identified. Following review of titles and abstracts, 114 of these articles were excluded, three further articles were excluded after full text review and 22 articles met the inclusion criteria. A thematic analysis of the articles included identified three overarching themes of GI dysfunction: (1) Serum biomarkers, (2) Physiological markers, and (3) Functional markers. Within the category of serum biomarkers, a further three sub-categories were identified: (i) enterohormones, (ii) markers of enterocyte function, and iii) cytokines and neurotransmitters. Some associations were seen between EFI and heparin binding protein, intra-abdominal pressure, cholecystokinin and acetylcholine levels but no markers are currently suitable for daily clinical use.

CONCLUSIONS

Further larger studies are required to characterise the relationships between serum biomarkers, physiological and functional makers of GI dysfunction in critically ill adults. A robust definition of GI dysfunction should be included in any future research.

The Role of Inflammatory Mediators in the Development of Gastrointestinal Motility Disorders

Feeding intolerance and the development of ileus is a common complication affecting critically ill, surgical, and trauma patients, resulting in prolonged intensive care unit and hospital stays, increased infectious complications, a higher rate of hospital readmission, and higher medical care costs. Medical treatment for ileus is ineffective and many of the available prokinetic drugs have serious side effects that limit their use. Despite the large number of patients affected and the consequences of ileus, little progress has been made in identifying new drug targets for the treatment of ileus. Inflammatory mediators play a critical role in the development of ileus, but surprisingly little is known about the direct effects of inflammatory mediators on cells of the gastrointestinal tract, and many of the studies are conflicting. Understanding the effects of inflammatory cytokines/chemokines on the development of ileus will facilitate the early identification of patients who will develop ileus and the identification of new drug targets to treat ileus. Thus, herein, we review the published literature concerning the effects of inflammatory mediators on gastrointestinal motility.

Oropharyngeal Dysphagia and Impaired Motility of the Upper Gastrointestinal Tract-Is There a Clinical Link in Neurocritical Care?

Patients in the neurological ICU are at risk of suffering from disorders of the upper gastrointestinal tract. Oropharyngeal dysphagia (OD) can be caused by the underlying neurological disease and/or ICU treatment itself. The latter was also identified as a risk factor for gastrointestinal dysmotility. However, its association with OD and the impact of the neurological condition is unclear. Here, we investigated a possible link between OD and gastric residual volume (GRV) in patients in the neurological ICU. In this retrospective single-center study, patients with an episode of mechanical ventilation (MV) admitted to the neurological ICU due to an acute neurological disease or acute deterioration of a chronic neurological condition from 2011–2017 were included. The patients were submitted to an endoscopic swallowing evaluation within 72 h of the completion of MV. Their GRV was assessed daily. Patients with ≥1 d of GRV ≥500 mL were compared to all the other patients. Regression analysis was performed to identify the predictors of GRV ≥500 mL/d. With respect to GRV, the groups were compared depending on their FEES scores (0–3). A total of 976 patients were included in this study. A total of 35% demonstrated a GRV of ≥500 mL/d at least once. The significant predictors of relevant GRV were age, male gender, infratentorial or hemorrhagic stroke, prolonged MV and poor swallowing function. The patients with the poorest swallowing function presented a GRV of ≥500 mL/d significantly more often than the patients who scored the best. Conclusions: Our findings indicate an association between dysphagia severity and delayed gastric emptying in critically ill neurologic patients. This may partly be due to lesions in the swallowing and gastric network.

Intermittent or continuous feeding: any difference during the first week?

PURPOSE OF REVIEW

To balance theoretical pros and cons of intermittent feeding, in light of the current nutritional management early during critical illness.

RECENT FINDINGS

Less aggressive nutrient administration is clinically superior in acute critical illness. This counterintuitive clinical finding may be explained by nutrient restriction activating autophagy, a process that clears intracellular damage. Intermittent feeding holds numerous theoretical benefits, such as activation of autophagy, preservation of the circadian rhythm, increased protein synthesis, and enhanced endogenous fatty acids release. RCTs investigating intermittent feeding in the ICU, however, are the most often limited to evaluation of gastrointestinal complications. Current guidelines advocate against the use of intermittent feeding, based on lack of benefit and increased risk of diarrhea, as revealed by a meta-analysis.

SUMMARY

Benefits of intermittent feeding in the ICU are today speculative, yet its potential impact may reach far beyond the gastrointestinal tract. Only adequately powered RCTs, evaluating both gastrointestinal tolerance, metabolic impact and patient-centered effects of intermittent feeding will allow to adopt or abort this nutritional strategy.

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.

The GH Axis in Relation to Accepting an Early Macronutrient Deficit and Outcome of Critically Ill Patients

CONTEXT

Changes in the GH axis during critical illness resemble fasting in healthy adults and contribute to hypercatabolism, which potentially affects outcome. Accepting macronutrient deficits by withholding parenteral nutrition (PN) during the first week in the intensive care unit (ICU; late PN) reduced complications and accelerated recovery as compared with early use of PN (early PN).

OBJECTIVE

To investigate how late PN affects the GH axis in relation to its clinical outcome benefits.

DESIGN

Preplanned subanalysis of the Early Parenteral Nutrition Completing Enteral Nutrition in Adult Critically Ill Patients randomized controlled trial.

PARTICIPANTS

A total of 1128 patients for time-course study, 20 patients investigated for nocturnal GH pulsatility, and 600 patients investigated for muscle weakness, with early PN and late PN patients having comparable baseline characteristics.

INTERVENTION

Withholding PN during the first ICU week (late PN) vs early PN.

MAIN OUTCOME MEASURES

Changes in serum GH, IGF-I, IGF-binding protein (IGFBP) 3, and IGFBP1 concentrations from ICU admission to day 4 or last ICU day for patients with a shorter ICU stay (d4/LD) and association in multivariable analyses with likelihood of earlier live ICU discharge, risk of new infection, and muscle weakness.

RESULTS

Late PN attenuated a rise in serum GH and IGF-I (P < 0.0001), did not affect IGFBP3, and attenuated a decrease in IGFBP1 concentrations from admission to d4/LD (P < 0.0001) as compared with early PN. Late PN decreased nonpulsatile (P = 0.005), but not pulsatile, GH secretion. Adjusting the multivariable models for the observed GH axis alterations increased the independent benefit of late PN for all outcomes. GH axis alterations induced by late PN were independently associated with adverse outcomes (P ≤ 0.03).

CONCLUSION

Accepting macronutrient deficits early during critical illness further suppressed the GH axis, which statistically attenuated its clinical outcome benefits.

Artificial intelligence identified peptides modulate inflammation in healthy adults

Dietary bioactive peptides have been, among many functionalities, associated with immune modulation and thereby may improve resolution of inflammation. The goals of this research were to assess (1) whether specific peptides with immune-modulating activity consumed as part of a rice protein hydrolysate could be absorbed into blood and (2) whether they modulate inflammation markers. Artificial intelligence algorithms were applied to target, predict and unlock inflammation-modulating peptides from rice protein. A food application was developed containing four bioactive peptides. Protein docking simulation studies revealed high binding energies of these peptides with inflammation markers. In a small kinetic study 10 healthy subjects consumed the peptides with a single bolus of 20 g protein hydrolysate. Although absorption of the four predicted peptides at plasma concentrations deemed biologically relevant could not be confirmed (quantitative LC-MS/MS), several cytokines responded (ELISA kits). The 24-hour kinetic study revealed a slight suppression of pro-inflammatory TNF-α, IP-10 and NOx, whereas IL-6 increased temporarily (timepoints 2-12 hours). These markers returned to the baseline after 24 hours whereas others were not affected significantly (IL-10, hs-CRP, IL-8, and MCP-1). Consumption of a single dose protein hydrolysate containing immune modulatory peptides induced a mild temporary response most likely through intestinal signaling. Forthcoming studies will examine dietary supplementation in situations of stress.

Gastrointestinal Hormone Profiles Associated With Enteral Nutrition Tolerance and Gastric Emptying in Pediatric Critical Illness: A Pilot Study

BACKGROUND

Enteral nutrition (EN) intolerance and delayed gastric emptying are prevalent in pediatric critical illness and limit EN delivery. Gastrointestinal (GI) hormones may be associated with EN intolerance and delayed gastric emptying in this cohort.

METHODS

We determined GI hormone levels, time to achieve 50% of EN goal, and gastric emptying in critically ill children. Total amylin, active ghrelin, total glucagon-like peptide-1 (GLP-1), total gastric inhibitory polypeptide, glucagon, and total peptide-YY (PYY) were measured by multiplex assay and cholecystokinin by ELISA. Lower concentrations of acetaminophen at 1 hour (C1h, µg/mL) using the acetaminophen absorption test defined delayed gastric emptying. Correlation, regression analyses, and a principal component analysis were used to examine the association between GI hormones and time to 50% EN goal and C1h.

RESULTS

GI hormones were measured in 14 of 21 patients with gastric emptying testing; median age of 11.2 years (6.74-16.3) and 50% male. Increasing hormone levels from GI hormone profile 1 (GLP-1, glucagon, and amylin) correlated with greater time to reach 50% EN goal (R² = 0.296, P = 0.04). Decreasing hormone levels from GI hormone profile 2 (PYY and ghrelin) correlated with lower C1h and slower gastric emptying (R² = 0.342, P = 0.02).

CONCLUSION

GI hormone profiles are associated with time to achieve 50% of EN goal and gastric emptying in critically ill children. We have described a feasible model to study the role of GI hormones in this cohort, including the potential clinical applicability of GI hormone measurement in the management of delayed gastric emptying.

A Comparison of Gastric and Jejunal Feeding in Hypercatabolism Associated With Hypothalamic AMPK-Autophagy-POMC in Endotoxemic Rats

BACKGROUND

Hypercatabolism is associated with increased infectious rates and mortality in critically ill patients. Enteral nutrition (EN) is usually used to counteract hypercatabolism. However, the impact of different routes of EN on hypercatabolism remains unknown. Here, we compared the impact of gastric feeding (GF) and jejunal feeding (JF) on gastrointestinal hormones and hypercatabolism, which is associated with hypothalamic adenosine 5'-monophosphate-activated protein kinase (AMPK)-autophagy-proopiomelanocortin (POMC).

METHODS

Sixty adult male Sprague-Dawley rats were divided into 5 groups: Sham and lipopolysaccharide (LPS) groups fed a standard chow diet, a pair-fed group that was a subset of saline-treated rats pair-fed with the LPS group, and LPS + JF and LPS + GF groups (received EN via jejunal and gastric tube, respectively, for 3 days [100 kcal/kg/d]). Hypercatabolism was measured by insulin resistance, muscle protein synthesis, and atrophy. Serum gastrointestinal hormones, hypothalamic ghrelin, growth hormone secretagogue receptor-1α (GHS-R1α), and AMPK-autophagy-POMC markers were also detected.

RESULTS

GF increased serum total, acylated, desacylated, and hypothalamic ghrelin and decreased glucagon-like peptide-1 (GLP-1). But no effect on pancreatic polypeptide (PYY) and hypothalamic GHS-R1α was observed. JF showed no effect on hypothalamic ghrelin, GHS-R1α, and serum total, acylated, and desacylated ghrelin and even further aggravated GLP-1 and PYY. GF could effectively augment hypothalamic AMPK-autophagy-POMC and hypercatabolism. However, JF showed no effect on hypothalamic AMPK-autophagy-POMC and hypercatabolism.

CONCLUSIONS

GF could activate hypothalamic AMPK-autophagy and suppress POMC expression via gastrointestinal hormones to ameliorate hypercatabolism compared with JF, which suggested that GF may be the preferred route of EN in endotoxemic rats.

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.

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.

Is There a Role for Enterohormones in the Gastroparesis of Critically Ill Patients?

OBJECTIVES

Delayed gastric emptying occurs in critically ill patients and impairs the delivery, digestion, and absorption of enteral feeding. A pathophysiologic role of the enterohormones peptide YY and ghrelin is supported by preclinical data. To compare the circulating plasma levels of peptide YY and ghrelin in control subjects and in critically ill patients, during feeding and fasting, and to search for a correlation with gastric emptying.

DESIGN

A prospective observational trial.

SETTINGS

Mixed ICU of an academic hospital.

SUBJECTS

Healthy volunteers and patients expected to stay in ICU for at least 3 days in whom enteral nutrition was indicated.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Plasma peptide YY and ghrelin (enzyme-linked immunosorbent assay) were measured once in 10 fasting volunteers (controls) and daily from admission until day 5 of the ICU stay in 30 critically ill patients (median [interquartile range] age 63 [57-67] yr, median [interquartile range] Acute Physiology and Chronic Health Evaluation II score 21 [14-24]). Eight patients could not be fed (fasting group). In fed patients, 13 never had a gastric residual volume higher than 250 mL (low gastric residual volume group), in contrast to the high gastric residual volume group (n = 9). The plasma levels of peptide YY did not differ between patients (6.4 [0-18.1] pg/mL) and controls (4.8 [0.3-17.7] pg/mL). Ghrelin levels were lower in patients than in control (213 [54.4-522.7] vs 1,435 [1,321.9-1,869.3] pg/mL; p < 0.05). Plasma peptide YY or ghrelin did not differ between fasting and fed patients or between the high and low gastric residual volume groups.

CONCLUSIONS

In critically ill patients, plasma concentration of ghrelin significantly differs from that of controls, irrespective of the feeding status. No correlation was found between the temporal profile of ghrelin or peptide YY plasma concentration with bedside functional assessment of gastric emptying.

Gastric Dysmotility in Critically Ill Children: Pathophysiology, Diagnosis, and Management

OBJECTIVE

We aimed to review gastric dysmotility in critically ill children: 1) its pathophysiology, with a focus on critical care diseases and therapies that affect gastric motility, 2) diagnostic methodologies, and 3) current and future potential therapies.

DATA SOURCES

Eligible studies were identified from PubMed and MEDLINE.

STUDY SELECTION

Literature search included the following key terms: "gastric emptying," "gastric motility/dysmotility," "gastrointestinal motility/dysmotility," "nutrition intolerance," and "gastric residual volume."

DATA EXTRACTION

Studies since 1995 were extracted and reviewed for inclusion by the authors related to the physiology, pathophysiology, diagnostic methodologies, and available therapies for gastric emptying.

DATA SYNTHESIS

Delayed gastric emptying, a common presentation of gastric dysmotility, is present in up to 50% of critically ill children. It is associated with the potential for aspiration, ventilator-associated pneumonia, and inadequate delivery of enteral nutrition and may affect the efficacy of enteral medications, all of which may be result in poor patient outcomes. Gastric motility is affected by critical illness and its associated therapies. Currently available diagnostic tools to identify gastric emptying at the bedside have not been systematically studied and applied in this cohort. Gastric residual volume measurement, used as an indirect marker of delayed gastric emptying in PICUs around the world, may be inaccurate.

CONCLUSIONS

Gastric dysmotility is common in critically ill children and impacts patient safety and outcomes. However, it is poorly understood, inadequately defined, and current therapies are limited and based on scant evidence. Understanding gastric motility and developing accurate bedside measures and novel therapies for gastric emptying are highly desirable and need to be further investigated.

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.

Gastric residual volume in critically ill patients: a dead marker or still alive?

Early enteral nutrition (EN) is consistently recommended as first-line nutrition therapy in critically ill patients since it favorably alters outcome, providing both nutrition and nonnutrition benefits. However, critically ill patients receiving mechanical ventilation are at risk for regurgitation, pulmonary aspiration, and eventually ventilator-associated pneumonia (VAP). EN may increase these risks when gastrointestinal (GI) dysfunction is present. Gastric residual volume (GRV) is considered a surrogate parameter of GI dysfunction during the progression of enteral feeding in the early phase of critical illness and beyond. By monitoring GRV, clinicians may detect patients with delayed gastric emptying earlier and intervene with strategies that minimize or prevent VAP as one of the major risks of EN. The value of periodic GRV measurements with regard to risk reduction of VAP incidence has frequently been questioned in the past years. Increasing the GRV threshold before interrupting gastric feeding results in marginal increases in EN delivery. More recently, a large randomized clinical trial revealed that abandoning GRV monitoring did not negatively affect clinical outcomes (including VAP) in mechanically ventilated patients. The results have revived the discussion on the role of GRV monitoring in critically ill, mechanically ventilated patients receiving early EN. This review summarizes the most recent clinical evidence on the use of GRV monitoring in critically ill patients. Based on the clinical evidence, it discusses the pros and cons and further addresses whether GRV is a dead marker or still alive for the nutrition management of critically ill patients.

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.

Review article: the role of gastrointestinal hormones in the treatment of delayed gastric emptying in critically ill patients

BACKGROUND

Delayed gastric emptying limits the administration of enteral nutrition, leading to malnutrition, which is associated with higher mortality and morbidity. Currently available prokinetics have limitations in terms of sustained efficacy and side effects.

AIM

To summarise the mechanisms of action and to discuss the possible utility of gastrointestinal hormones to prevent or treat delayed gastric emptying in critically ill patients.

METHODS

We searched PubMed for articles discussing 'delayed gastric emptying', 'enteral nutrition', 'treatment', 'gastrointestinal hormones', 'prokinetic', 'agonist', 'antagonist' and 'critically ill patients'.

RESULTS

Motilin and ghrelin receptor agonists initiate the migrating motor complex in the stomach, which accelerates gastric emptying. Cholecystokinin, glucagon-like peptide-1 and peptide YY have an inhibiting effect on gastric emptying; therefore, antagonising these gastrointestinal hormones may have therapeutic potential. Other gastrointestinal hormones appear less promising.

CONCLUSIONS

Manipulation of endogenous secretion, physiological replacement and administration of gastrointestinal hormones in pharmacological doses is likely to have therapeutic potential in the treatment of delayed gastric emptying. Future challenges in this field will include the search for candidates with improved selectivity and favourable kinetic properties.

Gastrointestinal dysmotility: evidence and clinical management

PURPOSE OF REVIEW

Gastrointestinal dysmotility and dysfunction underlie our difficulties in providing adequate nutrition by the enteral route to our critically ill patients.

RECENT FINDINGS

Recent studies have quantified gastric emptying and nutrient absorption. Slow gastric emptying is common and probably mediated by cholecystokinin and reduced active ghrelin concentrations. The cause of impaired nutrient absorption is not yet fully understood but may be related to small intestinal blood flow and/or mucosal factors. The absorption of the different macronutrients may be affected in different ways both by critical illness and by therapies. A better understanding of this may optimize the design of nutrient formulations in the future. New treatment modalities for gastrointestinal dysfunction are being investigated and include small intestinal feeding, nonpharmacological options such as acupuncture, and drugs including novel motilin receptor agonists, and opioid antagonists.

SUMMARY

We are gradually developing a better understanding of how the gut works during critical illness, which has implications for optimizing the delivery of nutrition and thereby improving nutritional and clinical outcomes.

Nutrition support in the critically ill

PURPOSE OF REVIEW

To highlight the recent developments in nutritional support for critically ill patients.

RECENT FINDINGS

Increasing data support the benefits of early initiation of enteral nutrition, with improvements in small intestinal absorption and clinical outcomes. In contrast to the previous belief, recent data suggest caloric administration of greater than 65-70% of daily requirement is associated with poorer clinical outcomes, especially when supplemental parenteral nutrition is used to increase the amount of caloric delivery. The role of supplementary micronutrients and anti-inflammatory lipids has been further evaluated but remains inconclusive, and is not currently recommended.

SUMMARY

Together, current findings indicate that intragastric enteral nutrition should be initiated within 24 h of admission to ICU and supplementary parenteral nutrition should be avoided. Future research should aim to clarify the optimal energy delivery for best clinical outcomes, and the role of small intestinal function and its flora in nutritional care and clinical outcomes.