Catabolism in Critical Illness: A Reanalysis of the REducing Deaths due to OXidative Stress (REDOXS) Trial

Dietary protein in the ICU in relation to health outcomes

PURPOSE OF REVIEW

Critical care nutrition guidelines recommend provision of higher protein doses than recommended in health. These recommendations have been predominately based on lower quality evidence and physiological rationale that greater protein doses may attenuate the significant muscle loss observed in critically ill patients. This review discusses the mechanistic action of protein in the critically ill, details results from recent trials on health outcomes, discusses considerations for interpretation of trial results, and provides an overview of future directions.

RECENT FINDINGS

Two recent large clinical trials have investigated different protein doses and the effect on clinical outcome. Important findings revealed potential harm in certain sub-groups of patients. This harm must be balanced with the potential for beneficial effects on muscle mass and physical function given that two recent systematic reviews with meta-analyses demonstrated attenuation of muscle loss with higher protein doses. Utilizing biological markers such as urea: creatinine ratio or urea levels may prove useful in monitoring harm from higher protein doses.

SUMMARY

Future research should focus on prospectively investigating biological signatures of harm as well as taking into the consideration elements that will likely enhance the effectiveness of protein dose.

Ammonia and urea metabolism in acute liver failure: A multicentre cohort study

BACKGROUND & AIMS

Ammonia is metabolized into urea in the liver. In acute liver failure (ALF), ammonia has been associated with survival. However, urea variation has been poorly studied.

METHODS

Observational cohort including ALF patients from Curry Cabral Hospital (Lisbon, Portugal) and Clinic Hospital (Barcelona, Spain) between 10/2010 and 01/2023. The United States ALF Study Group cohort was used for external validation. Primary exposures were serum ammonia and urea on ICU admission. Primary endpoint was 30-day transplant-free survival (TFS). Secondary endpoint was explanted liver weight.

RESULTS

Among 191 ALF patients, median (IQR) age was 46 (32; 57) years and 85 (44.5%) were males. Overall, 86 (45.0%) patients were transplanted and 75 (39.3%) died. Among all ALF patients, following adjustment for age, sex, body weight, and aetiology, higher ammonia or lower urea was independently associated with higher INR on ICU admission (p < .009). Among all ALF patients, following adjustment for sex, aetiology, and lactate, higher ammonia was independently associated with lower TFS (adjusted odds ratio (95% confidence interval [CI]) = 0.991 (0.985; 0.997); p = .004). This model predicted TFS with good discrimination (area under receiver operating curve [95% CI] = 0.78 [0.75; 0.82]) and reasonable calibration (R2 of 0.43 and Brier score of 0.20) after external validation. Among transplanted patients, following adjustment for age, sex, actual body weight, and aetiology, higher ammonia (p = .024) or lower (p < .001) urea was independently associated with lower explanted liver weight.

CONCLUSIONS

Among ALF patients, serum ammonia and urea were associated with ALF severity. A score incorporating serum ammonia predicted TFS reasonably well.

The kidney: the critical organ system for guiding nutrition therapy in the ICU-patient?

Most randomized controlled studies on nutrition in intensive care patients did not yield conclusive results or were neutral or negative concerning the primary endpoints but also in most secondary endpoints. However, there is a consistent observation that in several of these studies there was a negative effect of the nutrition intervention on the kidneys in one of the study arms. During the early phase and in unstable periods during further course of disease an inadequate clinical nutrition can damage the kidneys, can elicit or aggravate acute kidney injury and/ or increase requirements of renal replacement therapy (RRT). This relates to total energy intake, glucose intake/hyperglycemia and protein/ amino acid intake at various stages of renal dysfunction. The kidney could present a critical organ system for guiding nutrition therapy, a close monitoring of kidney function should be observed and nutrition therapy may need to be adapted accordingly. The long-held dogma of performing full nutrition and accept an otherwise not necessary RRT is definitely to be refuted.

Clinical practice guidelines for nutritional assessment and monitoring of adult ICU patients in China

The Chinese Society of Critical Care Medicine (CSCCM) has developed clinical practice guidelines for nutrition assessment and monitoring for patients in adult intensive care units (ICUs) in China. This guideline focuses on nutrition evaluation and metabolic monitoring to achieve optimal and personalized nutrition therapy for critically ill patients. This guideline was developed by experts in critical care medicine and evidence-based medicine methodology and was developed after a thorough review of the system and a summary of relevant trials or studies published from 2000 to July 2023. A total of 18 recommendations were formed and consensus was reached through discussions and reviews by expert groups in critical care medicine, parenteral and enteral nutrition, and surgery. The recommendations are based on currently available evidence and cover several key fields, including screening and assessment, evaluation and assessment of enteral feeding intolerance, metabolic and nutritional measurement and monitoring during nutrition therapy, and organ function evaluation related to nutrition supply. Each question was analyzed according to the Population, Intervention, Comparison, and Outcome (PICO) principle. In addition, interpretations were provided for four questions that did not reach a consensus but may have potential clinical and research value. The plan is to update this nutrition assessment and monitoring guideline using the international guideline update method within 3-5 years.

Persistent inflammation, immunosuppression, and catabolism syndrome (PICS): a review of definitions, potential therapies, and research priorities

Persistent Inflammation, Immunosuppression, and Catabolism Syndrome (PICS) is a clinical endotype of chronic critical illness. PICS consists of a self-perpetuating cycle of ongoing organ dysfunction, inflammation, and catabolism resulting in sarcopenia, immunosuppression leading to recurrent infections, metabolic derangements, and changes in bone marrow function. There is heterogeneity regarding the definition of PICS. Currently, there are no licensed treatments specifically for PICS. However, findings can be extrapolated from studies in other conditions with similar features to repurpose drugs, and in animal models. Drugs that can restore immune homeostasis by stimulating lymphocyte production could have potential efficacy. Another treatment could be modifying myeloid-derived suppressor cell (MDSC) activation after day 14 when they are immunosuppressive. Drugs such as interleukin (IL)-1 and IL-6 receptor antagonists might reduce persistent inflammation, although they need to be given at specific time points to avoid adverse effects. Antioxidants could treat the oxidative stress caused by mitochondrial dysfunction in PICS. Possible anti-catabolic agents include testosterone, oxandrolone, IGF-1 (insulin-like growth factor-1), bortezomib, and MURF1 (muscle RING-finger protein-1) inhibitors. Nutritional support strategies that could slow PICS progression include ketogenic feeding and probiotics. The field would benefit from a consensus definition of PICS using biologically based cut-off values. Future research should focus on expanding knowledge on underlying pathophysiological mechanisms of PICS to identify and validate other potential endotypes of chronic critical illness and subsequent treatable traits. There is unlikely to be a universal treatment for PICS, and a multimodal, timely, and personalised therapeutic strategy will be needed to improve outcomes for this growing cohort of patients.

Association between urea trajectory and protein dose in critically ill adults: a secondary exploratory analysis of the effort protein trial (RE-EFFORT)

BACKGROUND

Delivering higher doses of protein to mechanically ventilated critically ill patients did not improve patient outcomes and may have caused harm. Longitudinal urea measurements could provide additional information about the treatment effect of higher protein doses. We hypothesised that higher urea values over time could explain the potential harmful treatment effects of higher doses of protein.

METHODS

We conducted a reanalysis of a randomised controlled trial of higher protein doses in critical illness (EFFORT Protein). We applied Bayesian joint models to estimate the strength of association of urea with 30-day survival and understand the treatment effect of higher protein doses.

RESULTS

Of the 1301 patients included in EFFORT Protein, 1277 were included in this analysis. There were 344 deaths at 30 days post-randomisation. By day 6, median urea was 2.1 mmol/L higher in the high protein group (95% CI 1.1-3.2), increasing to 3.0 mmol/L (95% CI 1.3-4.7) by day 12. A twofold rise in urea was associated with an increased risk of death at 30 days (hazard ratio 1.34, 95% credible interval 1.21-1.48), following adjustment of baseline characteristics including age, illness severity, renal replacement therapy, and presence of AKI. This association persisted over the duration of 30-day follow-up and in models adjusting for evolution of organ failure over time.

CONCLUSIONS

The increased risk of death in patients randomised to a higher protein dose in the EFFORT Protein trial was estimated to be mediated by increased urea cycle activity, of which serum urea is a biological signature. Serum urea should be taken into consideration when initiating and continuing protein delivery in critically ill patients.

CLINICALTRIALS

gov Identifier: NCT03160547 (2017-05-17).

The metabolic effects of intermittent versus continuous feeding in critically ill patients

Intermittent (or bolus) feeding regimens in critically ill patients have been of increasing interest to clinicians and scientists. Changes in amino acid, fat and carbohydrate metabolites over time might yet deliver other benefits (e.g. modulation of the circadian rhythm and sleep, and impacts on ghrelin secretion, insulin resistance and autophagy). We set out to characterise these changes in metabolite concentration. The Intermittent versus Continuous Feeding in Critically Ill paitents study (NCT02358512) was an eight-centre single-blinded randomised controlled trial. Patients were randomised to received a continuous (control arm) or intermittent (6x/day, intervention arm) enteral feeding regimen. Blood samples were taken on trial days 1, 7 and 10 immediately before and 30 min after intermittent feeds, and at equivalent timepoints in the control arm. A pre-planned targeted metabolomic analysis was performend using Nuclear Resonance Spectroscopy. Five hundred and ninety four samples were analysed from 75 patients. A total of 24 amino acid-, 19 lipid based-, and 44 small molecule metabolite features. Across the main two axes of variation (40-60% and 6-8% of variance), no broad patterns distinguished between intermittent or continuous feeding arms, across intra-day sampling times or over the 10 days from initial ICU admission. Logfold decreases in abundance were seen in metabolites related to amino acids (Glutamine - 0.682; Alanine - 0.594), ketone body metabolism (Acetone - 0.64; 3-Hydroxybutyric Acid - 0.632; Acetonacetic Acid - 0.586), fatty acid (carnitine - 0.509) and carbohydrate metabolism ( Maltose - 0.510; Citric Acid - 0.485). 2-3 Butanediol, a by-product of sugar-fermenting microbial metabolism also decreased (- 0.489). No correlation was seen with change in quadriceps muscle mass for any of the 20 metabolites varying with time (all p > 0.05). Increasing severity of organ failure was related to increasing ketone body metabolism (3 Hydroxybutyric Acid-1 and - 3; p = 0.056 and p = 0.014), carnitine deficiency (p = 0.002) and alanine abundancy (p - 0.005). A 6-times a day intermittent feeding regimen did not alter metabolite patterns across time compared to continuous feeding in critically ill patients, either within a 24 h period or across 10 days of intervention. Future research on intermittent feeding regimens should focus on clinical process benefits, or extended gut rest and fasting.

Characterising biological mechanisms underlying ethnicity-associated outcomes in COVID-19 through biomarker trajectories: a multicentre registry analysis

BACKGROUND

Differences in routinely collected biomarkers between ethnic groups could reflect dysregulated host responses to disease and to treatments, and be associated with excess morbidity and mortality in COVID-19.

METHODS

A multicentre registry analysis from patients aged ≥16 yr with SARS-CoV-2 infection and emergency admission to Barts Health NHS Trust hospitals during January 1, 2020 to May 13, 2020 (wave 1) and September 1, 2020 to February 17, 2021 (wave 2) was subjected to unsupervised longitudinal clustering techniques to identify distinct phenotypic patient clusters based on trajectories of routine blood results over the first 15 days of hospital admission. Distribution of trajectory clusters across ethnic categories was determined, and associations between ethnicity, trajectory clusters, and 30-day survival were assessed using multivariable Cox proportional hazards modelling. Secondary outcomes were ICU admission, survival to hospital discharge, and long-term survival to 640 days.

RESULTS

We included 3237 patients with hospital length of stay ≥7 days. In patients who died, there was greater representation of Black and Asian ethnicity in trajectory clusters for C-reactive protein and urea-to-creatinine ratio associated with increased risk of death. Inclusion of trajectory clusters in survival analyses attenuated or abrogated the higher risk of death in Asian and Black patients. Inclusion of C-reactive protein went from hazard ratio (HR) 1.36 [0.95-1.94] to HR 0.97 [0.59-1.59] (wave 1), and from HR 1.42 [1.15-1.75]) to HR 1.04 [0.78-1.39] (wave 2) in Asian patients. Trajectory clusters associated with reduced 30-day survival were similarly associated with worse secondary outcomes.

CONCLUSIONS

Clinical biochemical monitoring of COVID-19 and progression and treatment response in SARS-CoV-2 infection should be interpreted in the context of ethnic background.

Elevated Serum Urea-to-Creatinine Ratio and In-Hospital Death in Patients with Hyponatremia Hospitalized for COVID-19

Hyponatremia is associated with adverse outcomes in hospitalized patients. An elevated value of the serum urea-to-creatinine ratio (UCR) has been proposed as a proxy of hypovolemia. The aim of this study was to investigate the relationship between the UCR and in-hospital death in patients hospitalized with COVID-19 and hyponatremia. We studied 258 patients admitted for COVID-19 between January 2020 and May 2021 with serum sodium at < 135 mmol/L. The primary end-point was all-cause mortality. A 5-unit increase in the serum UCR during hospital stays was associated with an 8% increase in the hazard of all-cause death (HR = 1.08, 95% CI: 1.03-1.14, p = 0.001) after adjusting for potential confounders. In patients with a UCR > 40 at baseline, a > 10 mmol/L increase in serum sodium values within the first week of hospitalization was associated with higher odds of in-hospital death (OR = 2.93, 95% CI: 1.03-8.36, p = 0.044) compared to patients who experienced a < 10 mmol/L change. This was not observed in patients with a UCR < 40. Hypovolemia developing during hospital stays in COVID-19 patients with hyponatremia detected at hospital admission bears an adverse prognostic impact. Moreover, in hypovolemic patients, a > 10 mmol/L increase in serum sodium within the first week of hospital stays may further worsen the in-hospital prognosis.

Females have a different metabolic response to critical illness, measured by comprehensive amino acid flux analysis

BACKGROUND

The trajectory from healthy to critical illness is influenced by numerous factors, including metabolism, which differs substantially between males and females. Whole body protein breakdown is substantially increased in critically ill patients, but it remains unclear whether there are sex differences that could explain the different health outcomes. Hence, we performed a secondary analysis of a study, where we used a novel pulse isotope method in critically ill and matched healthy males and females.

METHODS

In 51 critically ill ICU patients (26 males, 15 females) and 49 healthy controls (36 males and 27 females), we assessed their general and disease characteristics and collected arterial(ized) blood in the postabsorptive state after pulse administration of 8 ml of a solution containing 18 stable AA tracers. In contrast to the original study, we now fitted the decay curves and calculated non-compartmental whole body amino acid production (WBP) and compartmental measurements of metabolism, including intracellular amino acid production. We measured amino acid enrichments and concentrations by LC-MS/MS and derived statistics using AN(C)OVA.

RESULTS

Critically ill males and females showed an increase in the WBP of many amino acids, including those related to protein breakdown, but females showed greater elevations, or in the event of a reduction, attenuated reductions. Protein breakdown-independent WBP differences remained between males and females, notably increased glutamine and glutamate WBP. Only severely ill females showed a lower increase in WBP of many amino acids in comparison to moderately ill females, suggesting a suppressed metabolism. Compartmental analysis supported the observations.

CONCLUSIONS

The present study shows that females have a different response to critical illness in the production of several amino acids and changes in protein breakdown, observations made possible using our innovative stable tracer pulse approach.

CLINICAL TRIAL REGISTRY

Data are from the baseline measurements of study NCT02770092 (URL: https://clinicaltrials.gov/ct2/show/NCT02770092) and NCT03628365 (URL: https://clinicaltrials.gov/ct2/show/NCT03628365).

Novel nutritional strategies to prevent muscle wasting

PURPOSE OF REVIEW

Muscle wasting in critical illness has proven to be refractory to physical rehabilitation, and to conventional nutritional strategies. This presents one of the central challenges to critical care medicine in the 21st century. Novel strategies are needed that facilitate nutritional interventions, identify patients that will benefit and have measurable, relevant benefits.

RECENT FINDINGS

Drug repurposing was demonstrated to be a powerful technique in the coronavirus disease 2019 pandemic, and may have similar applications to address the metabolic derangements of critical illness. Newer biological signatures may aid the application of these techniques and the association between changes in urea:creatinine ratio and the development of skeletal muscle wasting is increasing. A core outcome set for nutrition interventions in critical illness, supported by multiple international societies, was published earlier this year should be adopted by future nutrition trials aiming to attenuate muscle wasting.

SUMMARY

The evidence base for the lack of efficacy for conventional nutritional strategies in preventing muscle wasting in critically ill patients continues to grow. Novel strategies such as metabolic modulators, patient level biological signatures of nutritional response and standardized outcome for measurements of efficacy will be central to future research and clinical care of the critically ill patient.