An update on muscle wasting in ICU

Abstract

Mortality rates from critical illness are decreasing worldwide, but survivors suffer from significant functional disability as a result of muscle wasting. In the short-term the functional effects are seen in increased time of mechanical ventilation, and increased length of stay. Muscle wasting is the most common complication of critical illness, occurring in 25-50% of patients. In a longitudinal observational study, daily loss of muscle mass averaged 2-3% over the first 10 days. The scale of wasting was related to the severity of organ failure and of acute lung injury. Changes in muscle mass are underpinned by alterations in muscle protein homeostasis. In stable isotope infusion experiments, muscle protein synthesis was reduced to levels of fasted controls despite the initiation of enteral feed. Protein synthetic levels recovered variably over the first week to levels comparable to fed controls. As a result, muscle protein breakdown was increased relative to muscle protein synthesis, leading to a net catabolic state. There is a need for secondary prevention measures to be instituted in current practise. Increased nutritional delivery cannot be recommended at this stage during acute critical illness and early mobilisation has been demonstrated to increase functional status. This is best achieved through the ABCDEF bundle. This bundle constitutes a co-ordinated package of care with sedation control to facilitate spontaneous breathing and decreasing delirium. This facilitates early mobilisation, which is currently the only preventative measure with an evidence base to decrease skeletal muscle wasting associated functional disability.