Protein Turnover and Metabolism in the Elderly Intensive Care Unit Patient

Abstract

Many intensive care unit (ICU) patients do not achieve target protein intakes particularly in the early days following admittance. This period of iatrogenic protein undernutrition contributes to a rapid loss of lean, in particular muscle, mass in the ICU. The loss of muscle in older (aged >60 years) patients in the ICU may be particularly rapid due to a perfect storm of increased catabolic factors, including systemic inflammation, disuse, protein malnutrition, and reduced anabolic stimuli. This loss of muscle mass has marked consequences. It is likely that the older patient is already experiencing muscle loss due to sarcopenia; however, the period of stay in the ICU represents a greatly accelerated period of muscle loss. Thus, on discharge, the older ICU patient is now on a steeper downward trajectory of muscle loss, more likely to have ICU-acquired muscle weakness, and at risk of becoming sarcopenic and/or frail. One practice that has been shown to have benefit during ICU stays is early ambulation and physical therapy (PT), and it is likely that both are potent stimuli to induce a sensitivity of protein anabolism. Thus, recommendations for the older ICU patient would be provision of at least 1.2-1.5 g protein/kg usual body weight/d, regular and early utilization of ambulation (if possible) and/or PT, and follow-up rehabilitation for the older discharged ICU patient that includes rehabilitation, physical activity, and higher habitual dietary protein to change the trajectory of ICU-mediated muscle mass loss and weakness.

Macronutrients in Parenteral Nutrition: Amino Acids

“…For adult patients in intensive care units (ICU), complete PN mixtures with a high protein/energy ratio would be recommended [32,33]. Unfortunately, most all-in-one industrialized mixtures generally do not guarantee sufficient AA supply to restore nitrogen losses [22,[34][35][36][37]. In these selected cases, personalized all-in-one PN mixtures represent the best solution to satisfy patient needs and prevent possible complications (i.e., overfeeding or refeeding in case of over-calorie supply).…”

Effects of protein supplementation on muscle wasting disorders: A brief update of the evidence

“…32 Isolated EAA such as leucine and its downstream metabolite, β-hydroxy β-methylbutyrate (HMB), have also been used in experimental models of SMM loss (i.e., bed rest/ casting) 21 due to their ability to stimulate MPS 38 and replete the increasing need in muscle protein metabolism observed in states of ageing, inactivity and disease. 16,39 This short, narrative review provides an overview of the latest evidence, with an emphasis on randomised controlled trials known to the authors and available on PubMed, related to the effects of protein supplementation on SMM, strength and function in individuals at risk of muscle wasting disorders, including those residing in long-term care facilities, admitted to hospital, and other clinical populations such as those with chronic obstructive pulmonary disease, heart disease, type 2 diabetes or cancer.…”

“…14 A hallmark of these states are reduced levels of physical activity or in some cases complete muscle disuse due to illness, surgery or immobilisation. 15,16 Indeed, it has been documented that older adults residing in residential aged care facilities spend approximately 12.5 hours per day sitting or lying, 17 and hospitalised patients may spend about 17 hours a day bed-ridden, 18 which markedly increases the risk of SMM loss. In community-dwelling older adults, 14 days of reduced physical activity in the form of a reduction in the number of steps performed daily (from 5962 ± 695 to 1413 ± 110 steps per day) resulted in a 2.8% loss of leg lean mass.…”

“…28 This is particularly concerning as in addition to the low levels of physical activity in nursing home residents and hospitalised patients, these individuals often have acute and chronic illnesses which accelerates the loss of SMM due, in part, to a pro-inflammatory status which favours muscle protein catabolism. 16 To prevent or attenuate SMM loss, a positive protein balance must be achieved. That is, muscle protein synthesis must exceed muscle protein breakdown rates over a daily cycle to promote muscle protein accretion.…”

Experimental and Outcome‐Based Approaches to Protein Requirements in the Intensive Care Unit

“…However, for older adults, the WHO had recommended 0.8 g/kg/d since 1985 4 . While the nitrogen balance data that were used for this recommendation indicated higher protein requirements, 5 only recently has expert consensus suggested that protein recommendations for older adults should be higher: 1.0–1.2 g/kg when healthy and up to 1.2–1.5 g/kg when combined with acute disorders, chronic disease, or physical training 7 – 9 …”