Metabolic effects of intensive insulin therapy in critically ill patients

Could Exogenous Insulin Ameliorate the Metabolic Dysfunction Induced by Glucocorticoids and COVID-19?

The finding that high-dose dexamethasone improves survival in those requiring critical care due to COVID-19 will mean much greater usage of glucocorticoids in the subsequent waves of coronavirus infection. Furthermore, the consistent finding of adverse outcomes from COVID-19 in individuals with obesity, hypertension and diabetes has focussed attention on the metabolic dysfunction that may arise with critical illness. The SARS coronavirus itself may promote relative insulin deficiency, ketogenesis and hyperglycaemia in susceptible individuals. In conjunction with prolonged critical care, these components will promote a catabolic state. Insulin infusion is the mainstay of therapy for treatment of hyperglycaemia in acute illness but what is the effect of insulin on the admixture of glucocorticoids and COVID-19? This article reviews the evidence for the effect of insulin on clinical outcomes and intermediary metabolism in critical illness.

Endogenous Glucose Production in Critical Illness

Regulation of endogenous glucose production (EGP) by hormonal, neuronal, and metabolic signaling pathways contributes to the maintenance of euglycemia under normal physiologic conditions. EGP is defined by the generation of glucose from substrates through glycogenolysis and gluconeogenesis, usually in fasted states, for local and systemic use. Abnormal increases in EGP are noted in patients with diabetes mellitus type 2, and elevated EGP may also impact the pathogenesis of nonalcoholic fatty liver disease and congestive heart failure. In this narrative review, we performed a literature search in PubMed to identify recently published English language articles characterizing EGP in critical illness. Evidence from preclinical and clinical studies demonstrates that critical illness can disrupt EGP through multiple mechanisms including increased systemic inflammation, counterregulatory hormone and catecholamine release, alterations in the hypothalamic-pituitary axis, insulin resistance, lactic acidosis, and iatrogenic insults such as vasopressors and glucocorticoids administered as part of clinical care. EGP contributes to hyperglycemia in critical illness when abnormally elevated and to hypoglycemia when abnormally depressed, each of which has been independently associated with increased mortality. Increased EGP may also promote protein catabolism that could worsen critical illness myopathy and impede recovery. Better understanding of the mechanisms and factors contributing to dysregulated EGP in critical illness may help in the development of therapeutic strategies that promote euglycemia, reduce intensive care unit-associated catabolism, and improve patient outcomes.

Protein Requirements of the Critically Ill Pediatric Patient

This article includes a review of protein needs in children during health and illness, as well as a detailed discussion of protein metabolism, including nitrogen balance during critical illness, and assessment and prescription/delivery of protein to critically ill children. The determination of protein requirements in children has been difficult and challenging. The protein needs in healthy children should be based on the amount needed to ensure adequate growth during infancy and childhood. Compared with adults, children require a continuous supply of nutrients to maintain growth. The protein requirement is expressed in average requirements and dietary reference intake, which represents values that cover the needs of 97.5% of the population. Critically ill children have an increased protein turnover due to an increase in whole-body protein synthesis and breakdown with protein degradation leading to loss of lean body mass (LBM) and development of growth failure, malnutrition, and worse clinical outcomes. The results of protein balance studies in critically ill children indicate higher protein needs, with infants and younger children requiring higher intakes per body weight compared with older children. Monitoring the side effects of increased protein intake should be performed. Recent studies found a survival benefit in critically ill children who received a higher percentage of prescribed energy and protein goal by the enteral route. Future randomized studies should evaluate the effect of protein dosing in different age groups on patient outcomes, including LBM, muscle structure and function, duration of mechanical ventilation, intensive care unit and hospital length of stay, and mortality.

Insulin modulates energy and substrate sensing and protein catabolism induced by chronic peritonitis in skeletal muscle of neonatal pigs

BACKGROUND

Acute infection promotes skeletal muscle wasting and insulin resistance, but the effect of insulin on energy and substrate sensing in skeletal muscle of chronically infected neonates has not been studied.

METHODS

Eighteen 2-d-old pigs underwent cecal ligation and puncture (CLP) or sham surgery (CON) to induce a chronic infection for 5 d. On d 5, pancreatic-substrate clamps were performed to attain fasting or fed insulin levels but to maintain glucose and amino acids in the fasting range. Total fractional protein synthesis rates (K_s), translational control mechanisms, and energy sensing and degradation signal activation were measured in longissimus dorsi muscle.

RESULTS

In fasting conditions, CLP reduced K_s and sirtuin 1 (SIRT1) and increased AMP-activated protein kinase α (AMPKα) activation and muscle RING-finger protein-1 (MuRF1). Insulin treatment increased K_s and mitochondrial protein synthesis, enhanced translation activation, and reduced SIRT1 in CON. In contrast, in CLP, insulin treatment increased K_s, protein kinase B (PKB) and Forkhead box O1 phosphorylation, antagonized AMPK activation, and decreased peroxisome proliferator-activated receptor gamma coactivator 1-α (PGC-1α), MuRF1, and SIRT1.

CONCLUSION

Energy and substrate sensing in skeletal muscle by the PKB-AMPK-SIRT1-PGC-1α axis is impacted by chronic infection in neonatal pigs and can be modulated by insulin.

Moderate glucose control results in less negative nitrogen balances in medical intensive care unit patients: a randomized, controlled study

Introduction

Hyperglycemia and protein loss are common in critically ill patients. Insulin can be used to lower blood glucose and inhibit proteolysis. The impact of moderate insulin therapy on protein metabolism in critically ill patients has not been evaluated. We compared urinary nitrogen excretion, nitrogen balance, serum albumin concentrations, prealbumin concentrations, and clinical outcomes between patients receiving moderate insulin therapy (MIT) and conventional insulin therapy (CIT) in a medical ICU.

Methods

Patients were randomly divided into groups and treated with MIT (glucose target 120 to 140 mg/dl) or CIT (glucose target 180 to 200 mg/dl). Calories and protein intake were recorded each day. On days 3, 7 and 14, the 24-hour urinary nitrogen excretion, nitrogen balance, and serum albumin and prealbumin concentrations were measured. Clinical outcomes data were collected.

Results

A total of 112 medical ICU patients were included, with 55 patients randomized to the MIT group and 57 patients randomized to the CIT group. Patients treated with MIT showed a trend towards increased nitrogen balance (P = 0.070), significantly lower urinary nitrogen excretion (P = 0.027), and higher serum albumin (P = 0.047) and prealbumin (P = 0.001) concentrations than patients treated with CIT. The differences between the two groups were most significant on day 3, when all factors showed significant differences (P < 0.05).

Conclusions

Moderate glucose control results in less negative nitrogen balances in medical ICU patients. Differences are more significant in the early stages compared with the late stages of critical illness.

Trial registration

ClinicalTrial.Gov NCT 01227148

Current recommended parenteral protein intakes do not support protein synthesis in critically ill septic, insulin-resistant adolescents with tight glucose control

OBJECTIVE

To investigate the effects of insulin infusion and increased parenteral amino acid intakes on whole body protein balance, glucose kinetics, and lipolysis in critically ill, insulin-resistant, septic adolescents.

DESIGN

A single-center, randomized, crossover study.

SETTING

A medicosurgical intensive care unit in a tertiary university hospital.

PATIENTS

Nine critically ill, septic adolescents (age 15.0 ± 1.2 yrs, body mass index 20 ± 4 kg m(-2)) receiving total parenteral nutrition.

INTERVENTIONS

Patients received total parenteral nutrition with standard (1.5 g · kg(-1) · day(-1)) and high (3.0 g · kg(-1) · day(-1)) amino acid intakes in a 2-day crossover setting, randomized to the order in which they received it. On both study days, we conducted a primed, constant, 7-hr stable isotope tracer infusion with [1-(13)C]leucine, [6,6-(2)H(2)]glucose, and [1,1,2,3,3-(2)H(5)]glycerol, in combination with a hyperinsulinemic euglycemic clamp during the last 3 hrs.

MEASUREMENTS AND MAIN RESULTS

Insulin decreased protein synthesis at standard amino acid and high amino acid intakes (p < .01), while protein breakdown decreased with insulin at standard amino acid intake (p < .05) but not with the high amino acid intake. High amino acid intake improved protein balance (p < .05), but insulin did not have an additive effect. There was significant insulin resistance with an M value of ~3 (mg · kg(-1) · min(-1))/(mU · mL(-1)) which was 30% of reported normal values. At high amino acid intake, endogenous glucose production was not suppressed by insulin and lipolysis rates increased.

CONCLUSION

The current recommended parenteral amino acid intakes are insufficient to maintain protein balance in insulin-resistant patients during tight glucose control. During sepsis, insulin decreases protein synthesis and breakdown, and while high amino acid intake improves protein balance, its beneficial effects may be offset by enhanced endogenous glucose production and lipolysis, raising concerns that insulin resistance may have been exacerbated and that gluconeogenesis may have been favored by high amino acid intakes. Dose-response studies on the effect of the level of amino acid intakes (protein) on energy metabolism are needed.