Longitudinal Changes in Muscle Mass After Intensive Care

Critical Illness, Muscle Loss

Critically ill patients often suffer from dramatic muscle loss while in the ICU. Recovery of muscle structure and function have been proposed as core outcome measures for interventional studies in ICU survivors. Ultrasound is an accessible and validated tool to monitor muscle mass over time, with quadriceps muscle layer thickness (MLT) corresponding well to more invasive or cumbersome modalities. In order to design adequately powered studies investigating the effects of nutritional or metabolic interventions on post-ICU recovery, an estimate of the population standard deviation in MLT change over time is required. Currently there is a paucity of data describing changes in muscle mass during the subsequent period of hospitalization in ICU survivors. The aim of this study is to estimate the mean change and standard deviation in quadriceps MLT over time, in patients discharged alive from intensive care. Patients will be followed until hospital discharge or up to 28 days after ICU discharge. Interactions with nutritional intake, inflammation and metabolic rate will be analyzed for hypothesis-generating purposes.

Background Rapid and severe muscle loss is a common feature in intensive care \[1\]. Nutritional support is provided with the intention of preventing excessive muscle protein breakdown, but the evidence that higher energy or protein intake can mitigate muscle wasting in the ICU is limited \[2\]. A potential explanation to these findings is the proinflammatory and catabolic state often associated with critical illness \[3\]. As long as a patient remains critically ill, the potential to promote anabolism and recovery may be limited. It is well-documented that patients discharged from ICU often suffer from poor oral intake during hospital stay \[4,5\]. Optimizing nutritional support in the post-ICU period may therefore be a simple and cost-effective way of counteracting sarcopenia and improving health-related outcomes \[6\]. Currently there is a lack of published studies investigating the effect of nutritional interventions on lean body mass after intensive care. This may be due to the cumbersome and resource-intensive methods previously available for measuring body composition. In recent years, bedside ultrasound has become increasingly popular as a research tool for monitoring muscle loss over time. It has been validated against other radiological modalities, is non-invasive and accessible \[7\]. As there is a lack of literature describing sonographic changes in muscle mass over time in the post-ICU phase, data is needed to support a formal power calculation for interventional studies assessing muscle loss as a primary outcome measure. We therefore plan an observational longitudinal study to describe the change in quadriceps muscle layer thickness over time between ICU and hospital discharge. Aim The aims of this project are to 1) estimate the standard deviation of the change in quadriceps muscle layer thickness (MLT) over time, and 2) determine the feasibility of performing a longitudinal follow-up of MLT and energy expenditure in hospitalized patients after ICU discharge. Hypothesis In patients discharged alive from the ICU, there is a decrease in mean MLT over time during hospitalization

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