Chapter 14: ICU-Acquired Weakness and Early Mobilization in the Intensive Care Unit

KEY POINTS

INTRODUCTION

The decreasing mortality from critical illness over recent decades has led to an increasing number of intensive care unit (ICU) survivors.^1,2,3 As a result, there has been a shift in focus from short-term mortality to longer-term morbidities within the field of critical care. Neuromuscular complications, leading to ICU-acquired weakness (ICUAW) and impaired physical function, are common in survivors of critical illness, with a prevalence ranging from 9% to 87%.⁴ Furthermore, these complications are frequently severe and persistent, contributing to functional decline and significant decrements in health-related quality of life.^{5,6,7,8,9,10,11}

Reasons for muscle weakness following critical illness are multifactorial, including premorbid weakness associated with chronic diseases. Recently, there has been growing recognition that both critical illness and its associated treatments are toxic to muscles and nerves and contribute to the development of ICUAW.^1,2 Unfortunately, there are limited interventions to prevent or treat ICUAW. There is currently evidence from observational studies and small randomized controlled trials that establishes proof-of-principle that early mobilization (EM) may improve patient outcomes. This chapter will focus on the development, detection, and outcomes of ICUAW, with a particular emphasis on the role of EM in the critically ill. We will also discuss the barriers to EM in the ICU, the safety considerations for EM, strategies for measuring outcomes, and setting goals that include both the patient and their families.

ETIOLOGY AND PATHOPHYSIOLOGY OF WEAKNESS IN THE ICU

Bed Rest, Immobilization, and Disuse Muscle Atrophy

Prolonged bed rest and immobilization is common in many ICU patients and may contribute to the development of ICUAW.³ A meta-analysis of 39 randomized trials examining the effects of bed rest on 15 different medical conditions and procedures demonstrated that bed rest was not beneficial, and may be associated with harm.⁴

Prolonged bed rest leads to decreased muscle protein synthesis, increased muscle catabolism, and decreased muscle mass, especially in the lower extremities.^5,6 In healthy volunteers, muscle atrophy can begin within hours of immobility,⁷ resulting in a 4% to 5% loss of muscle strength for each week of bed rest.⁸ Immobility results in the activation of specific biochemical pathways that lead to enhanced proteolysis and decreased protein synthesis, resulting in a net loss in muscle mass, cross-sectional muscle area, and contractile strength.^9,10,11,12 Moreover, there is a general shift from slow twitch (type I) to fast twitch (type II) muscle fibers, with ...