Specific intraluminal nutrients alter mucosal blood flow during gut ischemia/reperfusion

When can we start early enteral nutrition safely in patients with shock on vasopressors?

Shock is a common critical illness characterized by microcirculatory disorders and insufficient tissue perfusion. Patients with shock and hemodynamic instability generally require vasopressors to maintain the target mean arterial pressure. Enteral nutrition (EN) is an important therapeutic intervention in critically ill patients and has unique benefits for intestinal recovery. However, the initiation of early EN in patients with shock receiving vasopressors remains controversial. Current guidelines make conservative and vague recommendations regarding early EN support in patients with shock. Increasing studies demonstrates that early EN delivery is safe and feasible in patients with shock receiving vasopressors; however, this evidence is based on observational studies. Changes in gastrointestinal blood flow vary by vasopressor and inotrope and are complex. The risk of gastrointestinal complications, especially the life-threatening complications of non-occlusive mesenteric ischemia and non-occlusive bowel necrosis, cannot be ignored in patients with shock during early EN support. It remains a therapeutic challenge in critical care nutrition therapy to determine the initiation time of EN in patients with shock receiving vasopressors and the safe threshold region for initiating EN with vasopressors. Therefore, the current review aimed to summarize the evidence on the optimal and safe timing of early EN initiation in patients with shock receiving vasopressors to improve clinical practice.

Glucagon-like peptide-2 protects the gastric mucosa via regulating blood flow and metabolites

INTRODUCTION

Refractory peptic ulcers lead to perforation and hemorrhage, which are fatal. However, these remain a therapeutic challenge. Gastric mucosal blood flow is crucial in maintaining gastric mucosal health. It's reported that Glucagon-like peptide-2 (GLP-2), a gastrointestinal hormone, stimulated intestinal blood flow. However, the direct role of GLP-2 in gastric mucosal blood flow and metabolites remain unclear. Here, we speculated that GLP-2 might protect the gastric mucosa by increasing gastric mucosal blood flow and regulating metabolites. This study was conducted to evaluate the role of GLP-2 in gastric mucosal lesions and its underlying mechanism.

METHODS

We analyzed endogenous GLP-2 during gastric mucosal injury in the serum. Rats were randomly divided into two groups, with 36 rats in each group as follows: (1) normal control group (NC1); (2) ethanol model group (EC1); rats in EC1 and NC1 groups were intragastrically administered ethanol (1 ml/200 g body weight) and distilled water (1 ml/200 g body weight). The serum was collected 10 min before intragastric administration and 15, 30, 60, 90, and 120 min after intragastric administration. Furthermore, additional male Sprague-Dawley rats were randomly divided into three groups, with six rats in each group as follows: (1) normal control group (NC); (2) ethanol model group (EC); (3) 10 μg/200 g body weight GLP-2 group (GLP-2). Rats in the NC and EC groups were intraperitoneally injected with saline. Those in the GLP-2 group were intraperitoneally injected with GLP-2. Thirty minutes later, rats in the EC and GLP-2 groups were intragastrically administered ethanol (1 ml/200 g body weight), and rats in the NC group were intragastrically administered distilled water (1 ml/200 g body weight). After the intragastric administration of ethanol for 1 h, the animals were anesthetized and gastric mucosal blood flow was measured. Serum were collected for ultra performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS) metabolomics.

RESULTS

There were no significant change in endogenous GLP-2 during gastric mucosal injury (P<0.05). Pretreatment with GLP-2 significantly reduced ethanol-induced gastric mucosal lesions by improving the gastric mucosal blood flow, as examined using a laser Doppler flow meter, Guth Scale, hematoxylin-eosin staining, and two-photon microscopy. UPLC-MS/MS analyses showed that GLP-2 also maintained a steady state of linoleic acid metabolism.

CONCLUSIONS

Taken together, GLP-2 protects the gastric mucosa against ethanol-induced lesions by improving gastric mucosa blood flow and affecting linoleic acid metabolism.

Current progress of research on intestinal bacterial translocation

Under normal conditions, the intestinal flora and the body are in dynamic equilibrium. When the barrier function of the intestinal tract is damaged due to various reasons, changes in the number and proportion of bacteria or spatial displacement result in bacterial translocation (BT), which ultimately leads to multiple organ dysfunction syndrome (MODS). Endogenous infections and endotoxemia caused by intestinal flora and endotoxin translocation are the origins of inflammatory responses, and the intestinal tract is the organ in which MODS both initiates and targets. Only by ensuring the integrity of the intestinal mucosal barrier can intestinal BT be effectively prevented. Elimination of the primary disease and maintaining blood and oxygen supply to the intestine is the most basic treatment. Early initiation of the intestinal tract, establishment of enteral nutrition, and selective digestive decontamination are also highly effective treatments. Early diagnosis, intervention, or prevention of BT may be a new avenue or important connection in the treatment of various diseases. The mechanism of BT, detection techniques, prevention and treatment, and its interaction with parenteral diseases were reviewed.

Evaluation of the NMR-MOUSE as a new method for continuous functional monitoring of the small intestine during different perfusion states in a porcine model

Objective

The study aim was to evaluate a small low-field NMR (nuclear magnetic resonance) scanner, the NMR-MOUSE^®, for detecting changes in intestinal diffusion under different (patho-) physiological perfusion states.

Methods

Laparotomy was performed on 8 female landrace pigs (body weight 70±6 kg) and the feeding vessels of several intestinal loops were dissected. Successively, the intestinal loops were examined using O2C (oxygen to see, LEA Medizintechnik GmbH, Giessen, Germany) for microcirculatory monitoring and the NMR-MOUSE^® for diffusion measurement (fast and slow components). On each loop the baseline measurement (physiological perfusion) was followed by one of the following main procedures: method 1 –ischemia; method 2 –flow reduction; method 3 –intraluminal glucose followed by ischemia; method 4 –intraluminal glucose followed by flow reduction. Additionally, standard perioperative monitoring (blood pressure, ECG, blood gas analyses) and histological assessment of intestinal biopsies was performed.

Results

There was no statistical overall time and method effect in the NMR-MOUSE measurement (fast component: p_time = 0.6368, p_method = 0.9766, slow component: p_time = 0.8216, p_method = 0.7863). Yet, the fast component of the NMR-MOUSE measurement showed contrary trends during ischemia (increase) versus flow reduction (decrease). The slow-to-fast diffusion ratio shifted slightly towards slow diffusion during flow reduction. The O2C measurement showed a significant decrease of oxygen saturation and microcirculatory blood flow during ischemia and flow reduction (p < .0001). The local microcirculatory blood amount (rHb) showed a significant mucosal increase (p_{Clamping(method 1)} = 0.0007, p_{Clamping(method 3)} = 0.0119), but a serosal decrease (p_{Clamping(method 1)} = 0.0119, p_{Clamping(method 3)} = 0.0078) during ischemia. The histopathological damage was significantly higher with increasing experimental duration and at the end of methods 3 and 4 (p < .0001,Fisher-test).

Conclusion

Monitoring intestinal diffusion changes due to different perfusion states using the NMR-MOUSE is feasible under experimental conditions. Despite the lack of statistical significance, this technique reflects perfusion changes and therefore seems promising for the evaluation of different intestinal perfusion states in the future. Beforehand however, an optimization of this technology, including the optimization of the penetration depth, as well as further validation studies under physiological conditions and including older animals are required.

Feeding the Open Abdomen

BACKGROUND

The purpose of this study was to determine if early enteral nutrition improves outcome for trauma patients with an open abdomen (OA).

METHODS

Retrospective review was used to identify 78 patients who required an OA for >or=4 hospital days, survived, and had available nutrition data. Demographic data and nutrition data comprising enteral nutrition initiation day and daily % target goal were collected. Patients were divided into 2 groups: early enteral feeding (EEN), initiated <or=4 days within celiotomy; and late enteral feeding (LEN; >4 days). Outcomes included infectious complications, early closure of the abdominal cavity (<8 days from original celiotomy), and fistula formation.

RESULTS

Fifty-three of 78 (68%) patients were men, with a mean age of 35 years; 74% had blunt trauma. Forty-three of 78 (55%) patients had EEN, whereas 35 of 78 (45%) had LEN. There was no difference with respect to demographics, injury severity, or infectious complication rates. Thirty-two of 43 (74%) patients with EEN had early closure of the abdominal cavity, whereas 17 of 35 (49%) patients with late feeding had early closure (p = .02). Four of 43 (9%) patients with EEN demonstrated fistula formation, whereas 9 of 35 (26%) patients with late feeding formed fistulae (p = .05). The EEN group had lower hospital charges (p = .04) by more than $50,000.

CONCLUSIONS

EEN in the OA was associated with (1) earlier primary abdominal closure, (2) lower fistula rate, (3) lower hospital charges.

Defining and Assessing Tolerance in Enteral Nutrition

Nutrition support has become widely recognized as an essential component of optimal care for acutely ill patients. Enteral nutrition is preferred over parenteral routes when possible. However, prescribed enteral nutritional regimens are sometimes met with side effects and even complications. These adverse events have been collectively termed "intolerance," and forms of intolerance occur in a spectrum from bothersome at least to life threatening when most severe. Here we discuss nutritional access and its maintenance, introduce and define intolerance, and then review the current literature with regard to principal forms of enteral nutrition intolerance.

Nutrition Support in Adult Trauma Patients

Nutrition supplementation is paramount to the care of severely injured patients. Despite its widespread use in trauma patients, many areas of clinical practice remain controversial. The purpose of this paper is to critically review the literature studying the use of enteral vs parenteral nutrition (PN) and to provide the rationale for early enteral nutrition. Additional controversies confronting clinicians are reviewed, including the use of immune-enhancing agents and the optimal site for enteral nutrition delivery (gastric vs small intestinal). Evidence-based recommendations for clinical practice are presented when available.

Electroacupuncture at Zusanli (ST36) promotes gastric emptying and mucosal blood flow during oral resuscitation of scalded rats with a pyruvate-enriched ORS

AIM

The aim of this study was to investigate the effect of electroacupuncture at ST36 (EA ST36) on gastric emptying and mucosal blood flow during intragastric resuscitation with pyruvate-enriched oral rehydration solution (Pyr-ORS) in scalded rats.

METHODS

The rats were subjected to a 35% total body surface area (TBSA) of scald injury and randomly divided into five groups (N=24) and two subgroups (n=12) in each group. The Pyr-ORS was delivered intragastrically according to the Parkland formula immediately after scalding at a dose of 1 mL kg(-1) %TBSA(-1) in 1 h. In these animals, the bilateral Zusanli points (ST36) were electroacupunctured at a constant voltage (2 mA and 2-100 HZ) for 0.5 h immediately after intragastric resuscitation. At 2 and 4 h after scalding, the gastric emptying rate (GER) and gastric mucosal blood flow (GMBF) were determined, and the motilin levels of the plasma and gastric tissues were also analyzed at two time points, respectively.

RESULTS

GER and GMBF were markedly decreased in groups with scalding and resuscitation, compared with the sham groups at two time points (P<0.05), but they were greatly improved in groups byEAST36 at 2 and 4 h after sustaining scald injuries (P<0.05). Bilateral vagotomy further aggravated the reduction of GER and GMBF in scalded rats. EA after gastric vagotomy failed to raise GER and GMBF. Neither EA nor vagotomy had effects on the reduced motilin levels of plasma and gastric tissues in animals after scalding.

CONCLUSION

EA ST36 has a significant effect on improving gastric emptying and mucosal ischemia in the oral resuscitation of burn injury, possibly through the activation of a cholinergic nerve-dependent mechanism. In addition, EA ST36 showed no effects on motilin levels, but requires further investigations.

Early enteral nutrition in critically ill patients with hemodynamic instability: an evidence-based review and practical advice

Early enteral nutrition (EEN) in critically ill patients is associated with significant benefit as well as elevated risk of complications. Concomitant use of EEN with vasopressors has been associated with nonocclusive bowel necrosis in critically ill patients with hemodynamic instability. The decision when to initiate enteral nutrition in hemodynamically unstable patients that require vasoactive substances remains a clinical dilemma. This review summarizes the effect of EEN and vasoactive agents on gastrointestinal blood flow and perfusion in critically ill patients, based on current evidence. Animal and clinical data involving simultaneous administration of EEN and vasoactive agents for hemodynamic instability are reviewed, and the factors related to the safety and effectiveness of EEN support in this patient population are analyzed. Moreover, practical recommendations are provided. Additional randomized clinical trials are warranted to provide cutting-edge evidence-based guidance about this issue for practitioners of critical care.

Transmural intestinal wall permeability in severe ischemia after enteral protease inhibition

In intestinal ischemia, inflammatory mediators in the small intestine's lumen such as food byproducts, bacteria, and digestive enzymes leak into the peritoneal space, lymph, and circulation, but the mechanisms by which the intestinal wall permeability initially increases are not well defined. We hypothesize that wall protease activity (independent of luminal proteases) and apoptosis contribute to the increased transmural permeability of the intestine's wall in an acutely ischemic small intestine. To model intestinal ischemia, the proximal jejunum to the distal ileum in the rat was excised, the lumen was rapidly flushed with saline to remove luminal contents, sectioned into equal length segments, and filled with a tracer (fluorescein) in saline, glucose, or protease inhibitors. The transmural fluorescein transport was determined over 2 hours. Villi structure and epithelial junctional proteins were analyzed. After ischemia, there was increased transmural permeability, loss of villi structure, and destruction of epithelial proteins. Supplementation with luminal glucose preserved the epithelium and significantly attenuated permeability and villi damage. Matrix metalloproteinase (MMP) inhibitors (doxycycline, GM 6001), and serine protease inhibitor (tranexamic acid) in the lumen, significantly reduced the fluorescein transport compared to saline for 90 min of ischemia. Based on these results, we tested in an in-vivo model of hemorrhagic shock (90 min 30 mmHg, 3 hours observation) for intestinal lesion formation. Single enteral interventions (saline, glucose, tranexamic acid) did not prevent intestinal lesions, while the combination of enteral glucose and tranexamic acid prevented lesion formation after hemorrhagic shock. The results suggest that apoptotic and protease mediated breakdown cause increased permeability and damage to the intestinal wall. Metabolic support in the lumen of an ischemic intestine with glucose reduces the transport from the lumen across the wall and enteral proteolytic inhibition attenuates tissue breakdown. These combined interventions ameliorate lesion formation in the small intestine after hemorrhagic shock.

Oxygen in the regulation of intestinal epithelial transport

The transport of fluid, nutrients and electrolytes to and from the intestinal lumen is a primary function of epithelial cells. Normally, the intestine absorbs approximately 9 l of fluid and 1 kg of nutrients daily, driven by epithelial transport processes that consume large amounts of cellular energy and O2. The epithelium exists at the interface of the richly vascularised mucosa, and the anoxic luminal environment and this steep O2 gradient play a key role in determining the expression pattern of proteins involved in fluid, nutrient and electrolyte transport. However, the dynamic nature of the splanchnic circulation necessitates that the epithelium can evoke co-ordinated responses to fluctuations in O2 availability, which occur either as a part of the normal digestive process or as a consequence of several pathophysiological conditions. While it is known that hypoxia-responsive signals, such as reactive oxygen species, AMP-activated kinase, hypoxia-inducible factors, and prolyl hydroxylases are all important in regulating epithelial responses to altered O2 supply, our understanding of the molecular mechanisms involved is still limited. Here, we aim to review the current literature regarding the role that O2 plays in regulating intestinal transport processes and to highlight areas of research that still need to be addressed.

Pyruvate-enriched oral rehydration solution improved intestinal absorption of water and sodium during enteral resuscitation in burns

AIM

To investigate alteration in intestinal absorption during enteral resuscitation with pyruvate-enriched oral rehydration solution (Pyr-ORS) in scalded rats.

METHODS

To compare pyruvate-enriched oral rehydration solution (Pyr-ORS) with World Health Organisation oral rehydration solution (WHO-ORS), 120 rats were randomly divided into 6 groups and 2 subgroups. At 1.5 and 4.5 h after a 35% TBSA scald, the intestinal absorption rate, mucosal blood flow (IMBF), Na(+)-K(+)-ATPase activity and aquaporin-1 (AQP-1) expression were determined (n = 10), respectively.

RESULTS

The intestinal Na(+)-K(+)-ATPase activity, AQP-1 expression and IMBF were markedly decreased in scald groups, but they were profoundly preserved by enteral resuscitation with WHO-ORS and further improved significantly with Pyr-ORS at both time points. Na(+)-K+-ATPase activities remained higher in enteral resuscitation with Pyr-ORS (Group SP) than those with WHO-ORS (Group SW) at 4.5 h. AQP-1 and IMBF were significantly greater in Group SP than in Group SW at both time points. Intestinal absorption rates of water and sodium were obviously inhibited in scald groups; however, rates were also significantly preserved in Group SP than in Group SW with an over 20% increment at both time points.

CONCLUSION

The Pyr-ORS may be superior to the standard WHO-ORS in the promotion of intestinal absorption of water and sodium during enteral resuscitation.

Removal of luminal content protects the small intestine during hemorrhagic shock but is not sufficient to prevent lung injury

The small intestine plays a key role in the pathogenesis of multiple organ failure following circulatory shock. Current results show that reduced perfusion of the small intestine compromises the mucosal epithelial barrier, and the intestinal contents (including pancreatic digestive enzymes and partially digested food) can enter the intestinal wall and transport through the circulation or mesenteric lymph to other organs such as the lung. The extent to which the luminal contents of the small intestine mediate tissue damage in the intestine and lung is poorly understood in shock. Therefore, rats were assigned to three groups: No-hemorrhagic shock (HS) control and HS with or without a flushed intestine. HS was induced by reducing the mean arterial pressure (30 mmHg; 90 min) followed by return of shed blood and observation (3 h). The small intestine and lung were analyzed for hemorrhage, neutrophil accumulation, and cellular membrane protein degradation. After HS, animals with luminal contents had increased neutrophil accumulation, bleeding, and destruction of E-cadherin in the intestine. Serine protease activity was elevated in mesenteric lymph fluid collected from a separate group of animals subjected to intestinal ischemia/reperfusion. Serine protease activity was elevated in the plasma after HS but was detected in lungs only in animals with nonflushed lumens. Despite removal of the luminal contents, lung injury occurred in both groups as determined by elevated neutrophil accumulation, permeability, and lung protein destruction. In conclusion, luminal contents significantly increase intestinal damage during experimental HS, suggesting transport of luminal contents across the intestinal wall should be minimized.

Nutritional support in patients following damage control laparotomy with an open abdomen

INTRODUCTION

Damage control laparotomy (DCL) and the open abdomen have been well accepted following either severe abdominal trauma or emergency surgical disease. As DCL is increasingly utilized as a therapeutic option, appropriate management of the post-DCL patient is important. Early caloric support by enteral nutrition (EN) in the critically ill patient improves wound healing and decreases septic complications, lung injury, and multi-system organ failure. However, following DCL, nutritional strategies can be challenging and, at times, even daunting.

CONCLUSIONS

Even though limited data exist, the use of early EN following DCL seems safe, provided that the patient is not undergoing active resuscitation or the bowel is not in discontinuity. It is unknown as to whether EN in the open abdomen reduces septic complications, prevents enterocutaneous fistula (ECF), or alters the timing of definitive abdominal wall closure. Future investigation in a prospective manner may help elucidate these important questions.

Nutrition and the open abdomen

Adequate nutrition support is critical in the management of patients with an open abdomen. Despite the literature supporting its use in trauma patients, provider concerns and clinical controversies remain regarding the early administration and long-term sequelae of enteral nutrition (EN) therapy in these patients. The purpose of this article is to review the clinical concepts behind the use of the open abdomen, as well as examine the altered nutrition requirements associated with the maintenance of a temporary laparostomy. The rationale for early EN is described, as well as the pros and cons surrounding the use of supplemental parenteral nutrition in those patients unable to meet nutrition goals enterally in a reasonable time frame. Finally, an open abdomen nutrition support algorithm is provided as part of the critical care plan in these patients who represent the sickest of surgical patients.

Carbachol promotes gastrointestinal function during oral resuscitation of burn shock

AIM

To investigate the effect of carbachol on gastrointestinal function in a dog model of oral resuscitation for burn shock.

METHODS

Twenty Beagle dogs with intubation of the carotid artery, jugular vein and jejunum for 24 h were subjected to 35% total body surface area full-thickness burns, and were divided into three groups: no fluid resuscitation (NR, n = 10), in which animals did not receive fluid by any means in the first 24 h post-burn; oral fluid resuscitation (OR, n = 8), in which dogs were gavaged with glucose-electrolyte solution (GES) with volume and rate consistent with the Parkland formula; and oral fluid with carbachol group (OR/CAR, n = 8), in which dogs were gavaged with GES containing carbachol (20 μg/kg), with the same volume and rate as the OR group. Twenty-four hours after burns, all animals were given intravenous fluid replacement, and 72 h after injury, they received nutritional support. Hemodynamic and gastrointestinal parameters were measured serially with animals in conscious and cooperative state.

RESULTS

The mean arterial pressure, cardiac output and plasma volume dropped markedly, and gastrointestinal tissue perfusion was reduced obviously after the burn injury in all the three groups. Hemodynamic parameters and gastrointestinal tissue perfusion in the OR and OR/CAR groups were promoted to pre-injury level at 48 and 72 h, respectively, while hemodynamic parameters in the NR group did not return to pre-injury level till 72 h, and gastrointestinal tissue perfusion remained lower than pre-injury level until 120 h post-burn. CO(2) of the gastric mucosa and intestinal mucosa blood flow of OR/CAR groups were 56.4 ± 4.7 mmHg and 157.7 ± 17.7 blood perfusion units (BPU) at 24 h post-burn, respectively, which were significantly superior to those in the OR group (65.8 ± 5.8 mmHg and 127.7 ± 11.9 BPU, respectively, all P < 0.05). Gastric emptying and intestinal absorption rates of GES were significantly reduced to the lowest level (52.8% and 23.7% of pre-injury levels) in the OR group at about 2 and 4 h post-burn, and did not return to 80% of pre-injury level until 24 h. In the first 24 h post-burn, the rate of gastric emptying and intestinal water absorption were elevated by a mean 15.7% and 11.5%, respectively, in the OR/CAR group compared with the OR group. At 5 days, the mortality in the NR group was 30% (3/10), 12.5% in the OR group (1/8), and none in the OR/CAR group.

CONCLUSION

Carbachol had a beneficial effect on oral resuscitation of burn shock by promoting gastric emptying and intestinal absorption in our canine model.

Effect of carbachol on intestinal mucosal blood flow, activity of Na+-K+-ATPase, expression of aquaporin-1, and intestinal absorption rate during enteral resuscitation of burn shock in rats

We investigated the effect of carbachol (CAR, a cholinergic agent) on intestinal mucosal blood flow (IMBF), activity of Na-K-ATPase, expression of aquaporin (AQP)-1, and intestinal absorption rate during enteral resuscitation of a 35%TBSA scald in rats with a glucose electrolyte solution (GES). One hundred male Wistar rats were randomly divided into five groups: sham scald (N group); scald without fluid resuscitation (S group); scald resuscitated with enteral GES alone (GES group); scald resuscitated with enteral CAR alone (CAR group); and scald resuscitated with enteral CAR plus GES (GES/CAR group). The rats were inflicted 35%TBSA third degree of scald injury on the back with boiling water (100 degrees C, 15 seconds) in all groups, except the sham scald group. A catheter was inserted into the proximal duodenum (5 cm distal to pylorus) and distal ileum (5 cm proximal to cecum), of each rats through laparotomy, thus a segment of intestine was virtually isolated to form a loop for inlet and outlet of introduced fluid. In N, GES, and GES/CAR groups, fluids were introduced 30 minutes after scald injury. The speed of fluid infusion was 4 ml/kg/1%TBSA for 4 hours. CAR (60 microg/kg) was injected into the intestinal lumen at 30-minute after injury in CAR and GES/CAR groups. At 2 and 4 hours after scald, intestinal absorption rate of water and Na, and IMBF were determined, respectively. Then, animals were killed, and specimens of intestinal tissue were obtained for the determination of the activity of Na-K-ATPase, hematoxylin-eosin coloring, and expression of AQP-1. The intestinal absorption rate was reduced markedly in GES group compared with sham scald group at 2 and 4 hours after scald, and absorption rate of small intestine in GES/CAR was significantly higher than that in GES group (P < .05). It was also found that there was significant decrease in IMBF, activity of Na-K-ATPase, and expression of AQP-1 in scald group compared with the sham group. However, in GES/CAR group, the levels of these parameters were significantly increased compared with scald groups (P < .05). The results indicate that CAR promotes intestinal absorption rate of water and Na by improving IMBF, ATPase activity, and AQP-1 expression in gut mucosa during resuscitation with enteral GES of burn shock in rats.

Enteral glutamine: a novel mediator of PPARgamma in the postischemic gut

Early enteral nutrition supplemented with glutamine, arginine, omega-3 fatty acids, and nucleotides has been shown to decrease infection complications in critically injured patients. Concern has been raised, however, that under conditions of hyperinflammation, these diets may be injurious through the induction of inducible NO synthase by enteral arginine. In a rodent model of gut ischemia/reperfusion, inflammation and injury are intensified by enteral arginine and abrogated by glutamine. These findings correlate with the degree of metabolic stress imposed upon the gut by hypoperfusion. Glutamine is metabolized by the gut and therefore, can contribute back energy in the form of ATP, whereas arginine is a nonmetabolizable nutrient, using but not contributing energy. Recent data suggest that one of the molecular mechanisms responsible for the gut-protective effects of enteral glutamine is the activation of peroxisome proliferator-activated receptor gamma. This anti-inflammatory transcription factor belongs to the family of nuclear receptors, plays a key role in adipocyte development and glucose homeostasis, and has been recognized as an endogenous regulator of intestinal inflammation. Preliminary clinical studies support the use of enteral glutamine in patients with gut hypoperfusion.

Enteral glutamine during active shock resuscitation is safe and enhances tolerance of enteral feeding

BACKGROUND

Feeding the hemodynamically unstable patient is increasingly practiced, yet few data exist on its safety. Because enteral glutamine is protective to the gut in experimental models of shock and improves clinical outcomes, it may benefit trauma patients undergoing shock resuscitation and improve tolerance if administered early. This pilot study aimed to evaluate gastrointestinal tolerance and safety of enteral feeding with glutamine, beginning during shock resuscitation in severely injured patients.

METHODS

In a prospective randomized trial, 20 patients were randomly assigned to either an enteral glutamine group (n = 10) or a control group (n = 10). Patients with severe trauma meeting standardized shock resuscitation criteria received enteral glutamine 0.5 g/kg/d during the first 24 hours of resuscitation and 10 days thereafter. Immune-enhancing diet began on postinjury day 1, with a target of 25 kcal/kg/d. Control patients received isonitrogenous whey powder plus immune-enhancing diet. Tolerance (vomiting, nasogastric output, diarrhea, and distention) was assessed throughout the study.

RESULTS

Glutamine was well tolerated and no adverse events occurred. Treated patients had significantly fewer instances of high nasogastric output (5 vs 23; p = .010), abdominal distention (3 vs 12; p = .021), and total instances of intolerance (8 vs 42; p = .011). Intensive care unit (ICU) and hospital length of stay were comparable. Control patients required supplemental parenteral nutrition (PN) to meet goals at day 7.

CONCLUSIONS

Enteral glutamine administered during active shock resuscitation and through the early postinjury period is safe and enhances gastrointestinal tolerance. A large clinical trial is warranted to determine if enteral glutamine administered to the hemodynamically unstable patient can reduce infectious morbidity and mortality.

The role of macronutrients in gastrointestinal blood flow

PURPOSE OF REVIEW

The presence of luminal nutrients after a meal increases gastrointestinal blood flow in a phenomenon called postprandial hyperemia. In many conditions related to splanchnic hypoperfusion, enteral nutrition may play a role in counterbalancing the installed splanchnic low-flow state by producing intestinal hyperemia. However, when the gut is hypoperfused there is a chance of enteral nutrition producing a mismatch of the oxygen demand: supply ratio with subsequence gut ischemia. This article aims to review the effects of macronutrients on gastrointestinal blood flow in both health and critical conditions, especially those related to hepatosplanchnic hypoperfusion.

RECENT FINDINGS

Splanchnic blood flow is related not only to the route (intravenous or enteral) and timing of nutritional support (during the course of the insult) but also to the composition of the formula. Critically ill patients with gut hypoperfusion may tolerate enteral nutrition, but this effect may be restricted to the early post-injury phase. During ischaemia reperfusion injury, immune nutrients may promote different outcomes: glutamine may protect whereas arginine may deteriorate the mucosal barrier and enhance permeability.

SUMMARY

Understanding the relationship between macronutrients and gastrointestinal blood flow is a major challenge. Ongoing research in nutritional support in hypoperfused, catecholamine-dependent patients will open the door to optimize the recovery of patients in critical care.

Immune-enhancing enteral nutrients differentially modulate the early proinflammatory transcription factors mediating gut ischemia/reperfusion

BACKGROUND

Recent reports suggest that enteral diets enriched with arginine may be harmful by enhancing inflammation. This is consistent with our gut ischemia/reperfusion (I/R) model in which arginine induced the proinflammatory mediator inducible nitric oxide synthase and resulted in injury and inflammation whereas glutamine was protective. We now hypothesize that arginine and glutamine differentially modulate the early proinflammatory transcription factors activated by gut I/R.

METHODS

At laparotomy, jejunal sacs were filled with either 60 mmol/L glutamine, arginine, or an iso-osmotic control followed by 60 minutes of superior mesenteric artery occlusion and 6 hours of reperfusion and compared with shams. Jejunum was harvested for nuclear factor (NF)-kappaB and activator protein-1 (AP-1) measured by electrophoretic mobility shift assay and c-jun and c-fos (AP-1 family) by supershift.

RESULTS

Both NF-kappaB and AP-1 were activated by gut I/R. Arginine and glutamine had no differential effect on NF-kappaB, whereas AP-1 expression (c-jun but not c-fos) was markedly enhanced by arginine and significantly lessened by glutamine.

CONCLUSION

Arginine enhanced expression of the early proinflammatory transcription factor AP-1 but not NF-kappaB. This represents a novel mechanism by which arginine may be harmful when administered to critically ill patients.

Superior mesenteric artery occlusion models shock-induced gut ischemia-reperfusion

INTRODUCTION

Superior mesenteric artery occlusion (SMAO) is a simple and reproducible model of shock-induced gut ischemia/reperfusion, but some argue that it is not clinically relevant. The purpose of the current study was to compare SMAO to a standard model of controlled hemorrhage (CH) and uncontrolled hemorrhage (UH).

METHODS

Rats had femoral lines and a jejunal mucosal laser Doppler placed followed by SMAO (60 min of ischemia, no resuscitation), controlled hemorrhage (40 mm Hg for 60 min, 2:1 resuscitation shed blood and lactated Ringers), or uncontrolled hemorrhage (liver injury, 3:1 resuscitation with lactated Ringers). Base deficit, lactate, and jejunal mucosal flow (as a percentage of baseline) were recorded during ischemia and for 120 min after reperfusion. Jejunal tissue was harvested for morphological evaluation. Comparison among groups was by analysis of variance (ANOVA), and significance was set at P < 0.05.

RESULTS

Mucosal blood flow was similar among groups at the onset of reperfusion (CH, 16.9 +/- 5.0% versus UH, 10.9 +/- 3.1% versus SMAO, 13.9 +/- 6.2%) and during the initial period of reperfusion. By 120 min, however, flow in CH (75.4 +/- 2.5%) was significantly higher that in either UH (36.4 +/- 13.1%) or SMAO (31.7 +/- 8.4%). Histological injury was less with CH, while base deficit was significantly higher in CH at the onset of reperfusion (-24 +/- 2 versus UH, -10 +/- 3 and SMAO, -6 +/- 3 mM/L) but comparable by the end (CH, -17 +/- 4 versus UH, -16 +/- 3 and SMAO, -17 +/- 2 mM/L).

CONCLUSIONS

SMAO is a clinically relevant model of shock-induced gut ischemia/reperfusion.

Non-occlusive mesenteric ischaemia: a common disorder in gastroenterology and intensive care

Non-occlusive mesenteric ischaemia is characterized by gastrointestinal ischaemia with normal vessels. In gastroenterology it is recognized as rare disease occasionally causing acute bowel infarction or ischaemic colitis. From intensive care literature this disorder is recognized as an early phenomenon during circulatory stress. This early mucosal ischaemia then leads to increased permeability, bacterial translocation, and further mucosal hypoperfusion. The damage is produced mainly during reperfusion following ischaemia with fresh inflow of oxygen and outflow of waste products into the systemic circulation. The mechanisms underlying non-occlusive mesenteric ischaemia include macrovascular vasoconstriction, hypoperfusion of the tips of the villi and shunting. It is very common in critically ill and perioperative patients, but also occurs in pancreatitis, renal failure and sepsis. Treatment options include aggressive fluid resuscitation and careful choice of vasoactive drugs. Control of reperfusion damage and new endothelin-antagonists are potentially useful new treatment options.