Measurements of gastric emptying during continuous nasogastric infusion of liquid feed: electric impedance tomography versus gamma scintigraphy

Gastric functional monitoring by gastric electrical impedance tomography (gEIT) suit with dual-step fuzzy clustering

Gastric Function has been successfully estimated by gastric electrical impedance tomography (gEIT) Suit with dual-step fuzzy clustering. The gEIT Suit which are made of elastic cloth with dual-planar electrodes and compact data acquisition (DAQ) system measures gastric impedance Z to visualize the gastric conductivity distribution σ. The dual-step fuzzy clustering extracts the clustered gastric conductivity distribution ^kσ, which accurately estimates the gastric function. The gEIT Suit with dual-step fuzzy clustering are applied to eight healthy persons during liquid meal consumption to estimate the gastric function under gastric accommodation phase of 200, 400 and 600 mL based on the gastric emptying phase. As the results, the gEIT Suit successfully estimate the gastric function. By the measured impedance Z, the subjects have a mean temporal impedance [Formula: see text]= - 9.27 [Ohm] and p-value of that [Formula: see text] p(Z) = 0.0013[-]as the t-test result. In the case of gastric conductivity distribution σ, the subjects have a value of spatial mean conductivity distribution ⟨σ⟩ = 0.23[-] and p-value of that ⟨σ⟩ p(σ) = 0.0140[-]. Lastly, in the case gastric volume V, subjects have a gastric volume V = 12.44 [%] and p-value p(V) = 0.0664[-].

Suppressing interferences of EIT on synchronous recording EEG based on comb filter for seizure detection

Background and objective

The purpose of this study was to eliminate the interferences of electrical impedance tomography (EIT) on synchronous recording electroencephalography (EEG) for seizure detection.

Methods

The simulated EIT signal generated by COMSOL Multiphysics was superimposed on the clinical EEG signal obtained from the CHB-MIT Scalp EEG Database, and then the spectrum features of superimposed mixed signals were analyzed. According to the spectrum analysis, in addition to high-frequency interference at 51.2 kHz related to the drive current, there was also low-frequency interference caused by switching of electrode pairs, which were used to inject drive current. A low pass filter and a comb filter were used to suppress the high-frequency interference and low-frequency interference, respectively. Simulation results suggested the low-pass filter and comb filter working together effectively filtered out the interference of EIT on EEG in the process of synchronous monitoring.

Results

As a result, the normal EEG and epileptic EEG could be recognized effectively. Pearson correlation analysis further confirmed the interference of EIT on EEG was effectively suppressed.

Conclusions

This study provides a simple and effective interference suppression method for the synchronous monitoring of EIT and EEG, which could be served as a reference for the synchronous monitoring of EEG and other medical electromagnetic devices.

Electrical Impedance Tomography - Recent Applications and Developments

Electrical impedance tomography (EIT) is a low-cost noninvasive imaging method. The main purpose of this paper is to highlight the main aspects of the EIT method and to review the recent advances and developments. The advances in instrumentation and in the different image reconstruction methods and systems are demonstrated in this review. The main applications of the EIT are presented and a special attention made to the papers published during the last years (from 2015 until 2020). The advantages and limitations of EIT are also presented. In conclusion, EIT is a promising imaging approach with a strong potential that has a large margin of progression before reaching the maturity phase.

A new six-electrode electrical impedance technique for probing deep organs in the human body

Electrical impedance measurements of biological tissue have many potential applications and tetrapolar impedance measurement (TPIM) with four electrodes is traditionally used which eliminates high skin contact impedance. A linear array of four electrodes for TPIM on the horizontal plane of a cylindrical volume conductor of diameter D, where the length of the array is πD/2 with potential electrodes near the centre of the array, will give a high sensitivity near the surface which reduces rapidly with depth. A recently proposed six-electrode variation of TPIM uses an additional pair of potential electrodes on the opposite side of the volume conductor in the same horizontal plane around the circumference, with the expectation that the sensitivity of the deeper regions will thereby be enhanced. The present work carries out a finite element simulation (using COMSOL) and an experimental phantom study (saline phantom) to quantitatively evaluate the improvement obtained by this new method. The new configuration doubled the sensitivity at the central region, which was reasonably uniform over a wider zone, gradually increasing towards the potential electrodes on both sides. This would be useful for a range of biological studies of deep body organs such as lungs, stomach, and bladder. where the respective external body shapes may be approximated by an oval cylinder and where electrical impedance techniques have shown promise.

Three-Dimensional Holographic Electromagnetic Imaging for Accessing Brain Stroke

The authors recently developed a two-dimensional (2D) holographic electromagnetic induction imaging (HEI) for biomedical imaging applications. However, this method was unable to detect small inclusions accurately. For example, only one of two inclusions can be detected in the reconstructed image if the two inclusions were located at the same XY plane but in different Z-directions. This paper provides a theoretical framework of three-dimensional (3D) HEI to accurately and effectively detect inclusions embedded in a biological object. A numerical system, including a realistic head phantom, a 16-element excitation sensor array, a 16-element receiving sensor array, and image processing model has been developed to evaluate the effectiveness of the proposed method for detecting small stroke. The achieved 3D HEI images have been compared with 2D HEI images. Simulation results show that the 3D HEI method can accurately and effectively identify small inclusions even when two inclusions are located at the same XY plane but in different Z-directions. This preliminary study shows that the proposed method has the potential to develop a useful imaging tool for the diagnosis of neurological diseases and injuries in the future.

Nerve localization techniques for peripheral nerve block and possible future directions

BACKGROUND

Ultrasound guidance is now a standard nerve localization technique for peripheral nerve block (PNB). Ultrasonography allows simultaneous visualization of the target nerve, needle, local anesthetic injectate, and surrounding anatomical structures. Accurate deposition of local anesthetic next to the nerve is essential to the success of the nerve block procedure. Due to limitations in the visibility of both needle tip and nerve surface, the precise relationship between needle tip and target nerve is unknown at the moment of injection. Importantly, nerve injury may result both from an inappropriately placed needle tip and inappropriately placed local anesthetic. The relationship between the block needle tip and target nerve is of paramount importance to the safe conduct of peripheral nerve block.

METHODS

This review summarizes the evolution of nerve localization in regional anesthesia, characterizes a problem faced by clinicians in performing ultrasound-guided nerve block, and explores the potential technological solutions to this problem.

RESULTS

To date, technology newly applied to PNB includes real-time 3D imaging, multi-planar magnetic needle guidance, and in-line injection pressure monitoring. This review postulates that optical reflectance spectroscopy and bioimpedance may allow for accurate identification of the relationship between needle tip and target nerve, currently a high priority deficit in PNB techniques.

CONCLUSIONS

Until it is known how best to define the relationship between needle and nerve at the moment of injection, some common sense principles are suggested.

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.

Gastric motility measurement and evaluation based on electrical-mechanical composite mechanism

Gastric motility and emptying are a composite course involving electrical activity and mechanical contraction. In the research of gastric motility, the electrical activity should be closely connected to the subsequent mechanical contraction based on the understanding of electrical-mechanical composite mechanism. Existing simulation research and clinical research suggest that electrogastrogram (EGG) signals can provide physiological time scales, and gastric motility can be extracted from impedance signals. According to the coupling of the myoelectric activity and the mechanical contraction of the stomach, the correlation analysis of multiple signals can be performed. And then the influence of various factors such as the range, time and transmission distance of the gastric contraction can be deeply explored. The method combining gastric impedance and synchronous EGG measurements is effective and promising for evaluating gastric motility.

Gastroesophageal reflux in critically ill patients

Gastroesophageal reflux (GER) is a common occurrence in critically ill, mechanically ventilated patients. Reflux can lead to pulmonary aspiration of gastric contents and subsequent pneumonia. Several characteristics of patients, interventions provided in the intensive care unit setting, and factors associated with feeding increase a patient's risk for reflux. Critical care nurses and clinical nurse specialists can identify patients at highest risk for GER by utilizing the patient's history, reviewing the medications, and assessing the current status to provide interventions to reduce the risk of GER and its sequelae of aspiration pneumonia. This article reviews the physiology of GER, risk factors, and interventions to decrease GER in the critically ill patient.

Development of an Anatomically Realistic Forward Solver for Thoracic Electrical Impedance Tomography

Electrical impedance tomography (EIT) has the potential to provide a low cost and safe imaging modality for clinically monitoring patients being treated with mechanical ventilation. Variations in reconstruction algorithms at different clinical settings, however, make interpretation of regional ventilation across institutions difficult, presenting the need for a unified algorithm for thoracic EIT reconstruction. Development of such a consensual reconstruction algorithm necessitates a forward model capable of predicting surface impedance measurements as well as electric fields in the interior of the modeled thoracic volume. In this paper, we present an anatomically realistic forward solver for thoracic EIT that was built based on high resolution MR image data of a representative adult. Accuracy assessment of the developed forward solver in predicting surface impedance measurements by comparing the predicted and observed impedance measurements shows that the relative error is within the order of 5%, demonstrating the ability of the presented forward solver in generating high-fidelity surface thoracic impedance data for thoracic EIT algorithm development and evaluation.

Electrical bioimpedance gastric motility measurement based on an electrical-mechanical composite mechanism

AIM: To introduce a bioimpedance gastric motility measurement method based on an electrical-mechanical composite concept and a preliminary clinical application.

METHODS: A noninvasive gastric motility measurement method combining electrogastrogram (EGG) and impedance gastric motility (IGM) test was used. Preliminary clinical application studies of patients with functional dyspepsia (FD) and gastritis, as well as healthy controls, were carried out. Twenty-eight FD patients (mean age 40.9 ± 9.7 years) and 40 healthy volunteers (mean age 30.9 ± 7.9 years) were involved. IGM spectrum was measured for both the healthy subjects and FD patients, and outcomes were compared in the FD patients before treatment and 1 wk and 3 wk after treatment. IGM parameters were obtained from 30 erosive gastritis patients (mean age 50.5 ± 13.0 years) and 40 healthy adults, and IGM and EGG results were compared in the gastritis patients before treatment and 1 wk after treatment.

RESULTS: There were significant differences in the IGM parameters between the FD patients and healthy subjects, and FD patients had a poorer gastric motility [percentage of normal frequency (PNF) 70.8 ± 25.5 in healthy subjects and 28.3 ± 16.9 in FD patients, P < 0.01]. After 1 wk administration of domperidone 10 mg, tid, the gastric motility of FD patients was not improved, although the EGG of the patients had returned to normal. After 3 wk of treatment, the IGM rhythm of the FD patients became normal. There was a significant difference in IGM parameters between the two groups (PNF 70.4 ± 25.5 for healthy subjects and 36.1 ± 21.8 for gastritis patients, P < 0.05). The EGG rhythm of the gastritis patients returned to normal (frequency instability coefficient 2.22 ± 0.43 before treatment and 1.77 ± 0.19 one wk after treatment, P < 0.05) after 1 wk of treatment with sodium rabeprazole tablets, 10 mg, qd, po, qm, while some IGM parameters showed a tendency toward improvement but had not reached statistical significance.

CONCLUSION: The electrical-mechanical composite measurement method showed an attractive clinical application prospect in gastric motility research and evaluation.

Gastric motility functional study based on electrical bioimpedance measurements and simultaneous electrogastrography

For some time now, the research on gastric motility and function has fallen behind in the amount of research on gastric endocrine, exocrine secretion, and gastric morphology. In this paper, a noninvasive method to study gastric motility was developed, taking bioimpedance measurements over the gastric area simultaneously with the electrogastrography (EGG). This is based on the concept of observing and analyzing simultaneously the intrinsic electrical gastric activity (basic electric rhythm) and the mechanical gastric activity. Additionally, preliminary clinical studies of healthy subjects and subjects with functional dyspepsia (FD) and gastritis were carried out. The impedance gastric motility (IGM) measurements of the healthy and FD subjects were compared, along with the studies of the FD subjects before treatment and after one week and three weeks of treatment. We also compared IGM measurements of healthy subjects and subjects with erosive gastritis, along with the studies of the subjects with erosive gastritis before treatment and after one week of treatment. Results show that FD subjects have poor gastric motility (P<0.01). After a week of treatment, the gastric motility of FD subjects was not yet improved although the EGG had returned to normal by this time. By three weeks of treatment, the regular IGM rhythm returned in FD subjects. There was a significant difference of IGM parameters between the gastritis and healthy subjects (P<0.05). The EGG rhythm of the gastritis subjects returned to normal at one week post-treatment, while IGM parameters showed a trend to improvement (P>0.05), These results suggest the possibility of clinic application of the proposed method.

Gastric motility functional study based on electrical bioimpedance measurements and simultaneous electrogastrography

For some time now, the research on gastric motility and function has fallen behind in the amount of research on gastric endocrine, exocrine secretion, and gastric morphology. In this paper, a noninvasive method to study gastric motility was developed, taking bioimpedance measurements over the gastric area simultaneously with the electrogastrography (EGG). This is based on the concept of observing and analyzing simultaneously the intrinsic electrical gastric activity (basic electric rhythm) and the mechanical gastric activity. Additionally, preliminary clinical studies of healthy subjects and subjects with functional dyspepsia (FD) and gastritis were carried out. The impedance gastric motility (IGM) measurements of the healthy and FD subjects were compared, along with the studies of the FD subjects before treatment and after one week and three weeks of treatment. We also compared IGM measurements of healthy subjects and subjects with erosive gastritis, along with the studies of the subjects with erosive gastritis before treatment and after one week of treatment. Results show that FD subjects have poor gastric motility (P<0.01). After a week of treatment, the gastric motility of FD subjects was not yet improved although the EGG had returned to normal by this time. By three weeks of treatment, the regular IGM rhythm returned in FD subjects. There was a significant difference of IGM parameters between the gastritis and healthy subjects (P<0.05). The EGG rhythm of the gastritis subjects returned to normal at one week post-treatment, while IGM parameters showed a trend to improvement (P>0.05), These results suggest the possibility of clinic application of the proposed method.

Electrical bioimpedance and other techniques for gastric emptying and motility evaluation

The aim of this article is to identify non-invasive, inexpensive, highly sensitive and accurate techniques for evaluating and diagnosing gastric diseases. In the case of the stomach, there are highly sensitive and specific methods for assessing gastric motility and emptying (GME). However, these methods are invasive, expensive and/or not technically feasible for all clinicians and patients. We present a summary of the most relevant international information on non-invasive methods and techniques for clinically evaluating GME. We particularly emphasize the potential of gastric electrical bioimpedance (EBI). EBI was initially used mainly in gastric emptying studies and was essentially abandoned in favor of techniques such as electrogastrography and the gold standard, scintigraphy. The current research evaluating the utility of gastric EBI either combines this technique with other frequently used techniques or uses new methods for gastric EBI signal analysis. In this context, we discuss our results and those of other researchers who have worked with gastric EBI. In this review article, we present the following topics: (1) a description of the oldest methods and procedures for evaluating GME; (2) an explanation of the methods currently used to evaluate gastric activity; and (3) a perspective on the newest trends and techniques in clinical and research GME methods. We conclude that gastric EBI is a highly effective non-invasive, easy to use and inexpensive technique for assessing GME.

Sleeve Gastrectomy Surgical Assistive Instrument for Accurate Remnant Stomach Volume

Sleeve gastrectomy, which is based on reducing the size of the stomach, is one of the most successful bariatric surgeries and is yet to be standardized. One of the reasons is the lack of a method to obtain an accurate remnant stomach volume. The weight loss obtained postsurgery is highly correlated with the remnant stomach volume. Therefore, it is important to get consistently an accurate remnant stomach volume to be able to compare sleeve gastrectomy with other surgeries and in order to predict the weight loss. In addition, the measurement of the pyloric pressure is important for understanding the mechanism of weight loss and predicting complication postsurgery. A surgical assistive device for sleeve gastrectomy surgery is presented in this paper. The purpose of this instrument is to assist surgeons in obtaining an accurate remnant stomach volume and in measuring the pyloric pressure. The device consists of several inflatable compartments controllable by the surgeon. Prototype laboratory test results gave an accuracy of 96.7% and a repeatability of 97.6% for different desired volumes using air for compartment inflation, and an accuracy of 96.3% and a repeatability of 98.4% for different desired volumes using water for compartment inflation. The pressure measurement accuracies obtained are 96.8% using air and 99.7% using water. It is worth noting that these accuracies are expected to differ when the device is tested in vivo.

Use of electrical bioimpedance for gastric motility measurement and evaluation

Electrical bioimpedance technology is a measurement method to extract biomedical information associated with the physiological and pathological states of human body according to the electrical properties of tissue and organs. It has many outstanding advantages such as noninvasiveness, cheapness, convenience and rich function information. According to the electrical properties of the stomach tissue or the food in the stomach and the characteristics of food digestion, electrical bioimpedance methods permit to extract physiological and pathological information associated with gastric motility, investigate gastric contraction, peristalsis, transmission and emptying, and measure and evaluate gastric motility function noninvasively. In this article, we reveiw the development history of electrical bioimpedance technology and the characteristics of gastric motility impedance signal, and introduce the bioimpedance methods for measurement of gastric motility based on the concept of electrical-mechanical coupling. Besides, we also summarize the application of bioimpedance methods in the basic research of gastric motility, in the measurement of gastric motility in patients with functional dyspepsia, in the evaluation of gastric motility in patients with erosive gastritis, and in the detection and screening of gastric cancer. Moreover, we put forward some suggestions on the future development directions of bioimpedance methods for measurement of gastric motility.

Effects of metoclopramide on gastric motility measured by short-term bio-impedance

AIM: To analyze the accuracy of short-term bio-impedance as a means of measuring gastric motility.

METHODS: We evaluated differences in the short-term electrical bio-impedance signal from the gastric region in the following conditions: (1) fasting state, (2) after the administration of metoclopramide (a drug that induces an increase in gastric motility) and (3) after food ingestion in 23 healthy volunteers. We recorded the real component of the electrical impedance signal from the gastric region for 1000 s. We performed a Fast Fourier Transform (FFT) on this data and then compared the signal among the fasting, medicated, and postprandial conditions using the median of the area under the curve, the relative area under the curve and the main peak activity.

RESULTS: The median of the area under the curve of the frequency range in the region between 2-8 cycles per minute (cpm) decreased from 4.7 cpm in the fasting condition to 4.0 cpm in the medicated state (t = 3.32, P = 0.004). This concurred with the decrease seen in the relative area under the FFT curve in the region from 4 to 8 cpm from 38.3% to 26.6% (t = 2.81, P = 0.012) and the increase in area in the region from 2 to 4 cpm from 22.4% to 27.7%, respectively (t = -2.5, P = 0.022). Finally the main peak position also decreased in the region from 2 to 8 cpm. Main peak activity in the fasting state was 4.72 cpm and declined to 3.45 cpm in the medicated state (t = 2.47, P = 0.025). There was a decrease from the fasting state to the postprandial state at 3.02 cpm (t = 4.0, P = 0.0013).

CONCLUSION: Short-term electrical bio-impedance can assess gastric motility changes in individuals experiencing gastric stress by analyzing the area medians and relative areas under the FFT curve.

Methods for the assessment of gastric emptying in critically ill, enterally fed adults

Critically ill patients may experience delayed gastric emptying. Patients receiving enteral feeding are monitored closely to detect a delay of gastric emptying, assess feeding tolerance, and prevent aspiration pneumonia. The most common practice for assessing gastric emptying is to measure the aspirated gastric residual volume; however, this is an unreliable method that lacks standardization, fails to differentiate normal digestive secretions from enteral formula, and results in unnecessary interruptions of enteral nutrition. The aim of this review is to identify an alternative method to assess gastric emptying, which should be reliable, sensitive, harmless, feasible, and inexpensive. Several techniques are discussed: scintigraphy, paracetamol absorption test, breath tests, refractometry, ultrasound, and gastric impedance monitoring. Refractometry seems to be the most appropriate tool for the regular assessment of enteral nutrition; however, standardization and validation of this method are needed before it can be routinely used to monitor critically ill patients receiving enteral nutrition.

Use of short-term bio-impedance for gastric motility assessment

Gastric motility (GM) has been assessed using bio-impedance (BI) techniques in the time domain using short term recordings and analyzing mainly the median of the area under the fast Fourier transform (FFT) spectra. The BI technique has been applied to the gastric system mainly for gastric emptying (GE) studies. However, gastric motility evaluation using BI has not been fully implemented. In this study, we propose the use of the BI technique for the evaluation of gastric motility considering global features of the fast FFT spectra. The study was performed in eleven healthy subjects who were evaluated in fasting and postprandial conditions. The results indicate that the use of the median of the area under the FFT spectra is equivalent to the use of the main peak of the spectra to determine the changes in gastric motility from the fasting to the postprandial state. This demonstrates that BI is a valid technique for gastric motility evaluation in short time recordings.

An appraisal of the strengths and weaknesses of newborn and juvenile rat models for researching gastrointestinal development

Research on the impact of bioactive compounds on the development and functional maturation of the gastrointestinal (GI) tract using newborn and juvenile rats has greatly contributed to the knowledge of GI physiology and to the improved clinical management of both premature and full-term newborns. Of the animal models available, two types have been described for use with young rats – maintenance models and substitution models. Maintenance models are those in which the young are reared with the dam and therefore benefit from continuation of natural nutrition and maternal care. Substitution models are those in which the young are reared in the absence of the dam using artificially formulated milk delivered by various means into specific GI sites. In this review, we describe these models and their operation, and discuss the strengths and weaknesses of each. Attention is also given to questions of scientific validity and some animal welfare issues raised by the use of these models.

Electrical impedance tomography measuring gastric emptying and gastric motility

Electrical impedance tomography (EIT) is a novel medical imaging technology, which comes forth in recent 20 years following morphology imaging and structure imaging. EIT has the outstanding advantages of noninvasive, functional imaging and medical image monitoring. It has been mostly used in gastroenterology to assess flow of ingesta through the gastric region as an alternative to radionuclide studies. In vitro, EIT can accurately measure the volume of glass rods/balloons in a phantom. In humans, EIT can accurately measure gastric volume (balloons) in experimental conditions. Gastric emptying measurement of EIT has good correlations with dye dilution, gastric residuals and scintigraphy. By electrode array located on body surface, gastric motility measurement using EIT realizes noninvasive measurement and directly displays shrink and motility conditions of stomach in body by images of real time. This is going to be a great progress of gastric motility measurement and evaluation method. EIT gastric motility measurement has shown seductive application prospect.

Nutritional interventions in critical illness

The metabolism of critical illness is characterised by a combination of starvation and stress. There is increased production of cortisol, catecholamines, glucagon and growth hormone and increased insulin-like growth factor-binding protein-1. Phagocytic, epithelial and endothelial cells elaborate reactive oxygen and nitrogen species, chemokines, pro-inflammatory cytokines and lipid mediators, and antioxidant depletion ensues. There is hyperglycaemia, hyperinsulinaemia, hyperlactataemia, increased gluconeogenesis and decreased glycogen production. Insulin resistance, particularly in relation to the liver, is marked. The purpose of nutritional support is primarily to save life and secondarily to speed recovery by reducing neuropathy and maintaining muscle mass and function. There is debate about the optimal timing of nutritional support for the patient in the intensive care unit. It is generally agreed that the enteral route is preferable if possible, but the dangers of the parenteral route, a route of feeding that remains important in the context of critical illness, may have been over-emphasised. Control of hyperglycaemia is beneficial, and avoidance of overfeeding is emphasised. Growth hormone is harmful. The refeeding syndrome needs to be considered, although it has been little studied in the context of critical illness. Achieving energy balance may not be necessary in the early stages of critical illness, particularly in patients who are overweight or obese. Protein turnover is increased and N balance is often negative in the face of normal nutrient intake; optimal N intakes are the subject of some debate. Supplementation of particular amino acids able to support or regulate the immune response, such as glutamine, may have a role not only for their potential metabolic effect but also for their potential antioxidant role. Doubt remains in relation to arginine supplementation. High-dose mineral and vitamin antioxidant therapy may have a place.