Electrophysiological Screening to Assess Foot Drop Syndrome in Severe Acquired Brain Injury in Rehabilitative Settings

BACKGROUND

Foot drop syndrome (FDS), characterized by severe weakness and atrophy of the dorsiflexion muscles of the feet, is commonly found in patients with severe acquired brain injury (ABI). If the syndrome is unilateral, the cause is often a peroneal neuropathy (PN), due to compression of the nervous trunk on the neck of the fibula at the knee level; less frequently, the cause is a previous or concomitant lumbar radiculopathy. Bilateral syndromes are caused by polyneuropathies and myopathies. Central causes, due to brain or spinal injury, mimic this syndrome but are usually accompanied by other symptoms, such as spasticity. Critical illness polyneuropathy (CIP) and myopathy (CIM), isolated or in combination (critical illness polyneuromyopathy, CIPNM), have been shown to constitute an important cause of FDS in patients with ABI. Assessing the causes of FDS in the intensive rehabilitation unit (IRU) has several limitations, which include the complexity of the electrophysiological tests, limited availability of neurophysiology consultants, and the severe disturbance in consciousness and lack of cooperation from patients.

OBJECTIVES

We sought to propose a simplified electrophysiological screening that identifies FDS causes, particularly PN and CIPNM, to help clinicians to recognize the significant clinical predictors of poor outcomes in severe ABI at admission to IRU.

METHODS

This prospective, single-center study included 20 severe ABI patients with FDS (11 females/9 males, mean age 55.10 + 16.26; CRS-R= 11.90 + 6.32; LCF: 3.30 + 1.30; DRS: 21.45 + 3.33), with prolonged rehabilitation treatment (≥2 months). We applied direct tibialis anterior muscle stimulation (DMS) associated with peroneal nerve motor conduction evaluation, across the fibular head (NCS), to identify CIP and/or CIM and to exclude demyelinating or compressive unilateral PN.

RESULTS

At admission to IRU, simplified electrophysiological screening reported four unilateral PN, four CIP and six CIM with a CIPNM overall prevalence estimate of about 50%. After 2 months, the CIPNM group showed significantly poorer outcomes compared to other ABI patients without CIPNM, as demonstrated by the lower probability of achieving endotracheal-tube weaning (20% versus 90%) and lower CRS-R and DRS scores. Due to the subacute rehabilitation setting of our study, it was not possible to evaluate the motor results of recovery of the standing position, functional walking and balance, impaired by the presence of unilateral PN.

CONCLUSIONS

The implementation of the proposed simplified electrophysiological screening may enable the early identification of unilateral PN or CIPNM in severe ABI patients, thereby contributing to better functional prognosis in rehabilitative settings.

Intensive Care Unit-Acquired Weakness after Liver Transplantation: Analysis of Seven Cases and a Literature Review

Intensive Care Unit (ICU)-Acquired Weakness (ICU-AW) is a generalized muscle weakness that is clinically detected in critical patients and has no plausible etiology other than critical illness. ICU-AW is uncommon in patients undergoing orthotopic liver transplantation (OLT). Our report sheds light on the highest number of ICU-AW cases observed in a single center on OLT patients with early allograft dysfunction. Out of 282 patients who underwent OLT from January 2015 to June 2023, 7 (2.5%) developed generalized muscle weakness in the ICU and underwent neurophysiological investigations. The neurologic examination showed preserved extraocular, flaccid quadriplegia with the absence of deep tendon reflexes in all patients. Neurophysiological studies, including electromyography and nerve conduction studies, showed abnormalities with fibrillation potentials and the rapid recruitment of small polyphasic motor units in the examined muscles, as well as a reduced amplitude of the compound muscle action potential and sensory nerve action potential, with an absence of demyelinating features. Pre-transplant clinical status was critical in all patients. During ICU stay, early allograft dysfunction, acute kidney injury, prolonged mechanical ventilation, sepsis, hyperglycemia, and high blood transfusions were observed in all patients. Two patients were retransplanted. Five patients were alive at 90 days; two patients died. In non-cooperative OLT patients, neurophysiological investigations are essential for the diagnosis of ICU-AW. In this setting, the high number of red blood cell transfusions is a potential risk factor for ICU-AW.

COVID-19-Induced Myopathy and Diaphragmatic Weakness: A Case Report

Coronavirus disease 2019 (COVID-19) is a respiratory illness caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus that can induce myopathy, which can evolve into potentially life-threatening muscle weakness, including diaphragmatic paralysis. We present a case report of a 57-year-old female treated in the medical ICU for acute respiratory distress syndrome (ARDS) triggered by active COVID-19 infection, who subsequently developed worsening respiratory weakness from underlying COVID-19 myopathy manifesting as respiratory muscle weakness. Our patient's muscle biopsy highlights the development of muscle atrophy without evidence of inflammatory myopathy, making the presence of pre-existing autoimmune myopathy unlikely. While literature cites different biochemical etiologies for the development of myopathy, the exact mechanism behind this phenomenon is not yet defined.

Neuromuscular Ultrasound in Intensive Care Unit-Acquired Weakness: Current State and Future Directions

Intensive care unit-acquired weakness (ICUAW) is one of the most common causes of muscle atrophy and functional disability in critically ill intensive care patients. Clinical examination, manual muscle strength testing and monitoring are frequently hampered by sedation, delirium and cognitive impairment. Many different attempts have been made to evaluate alternative compliance-independent methods, such as muscle biopsies, nerve conduction studies, electromyography and serum biomarkers. However, they are invasive, time-consuming and often require special expertise to perform, making them vastly impractical for daily intensive care medicine. Ultrasound is a broadly accepted, non-invasive, bedside-accessible diagnostic tool and well established in various clinical applications. Hereby, neuromuscular ultrasound (NMUS), in particular, has been proven to be of significant diagnostic value in many different neuromuscular diseases. In ICUAW, NMUS has been shown to detect and monitor alterations of muscles and nerves, and might help to predict patient outcome. This narrative review is focused on the recent scientific literature investigating NMUS in ICUAW and highlights the current state and future opportunities of this promising diagnostic tool.

Intensive Care Unit-Acquired Weakness in Patients With Acute Kidney Injury: A Contemporary Review

Acute kidney injury (AKI) and intensive care unit-acquired weakness (ICU-AW) are 2 frequent complications of critical illness that, until recently, have been considered unrelated processes. The adverse impact of AKI on ICU mortality is clear, but its relationship with muscle weakness-a major source of ICU morbidity-has not been fully elucidated. Furthermore, improving ICU survival rates have refocused the field of intensive care toward improving long-term functional outcomes of ICU survivors. We begin our review with the epidemiology of AKI in the ICU and of ICU-AW, highlighting emerging data suggesting that AKI and AKI treated with kidney replacement therapy (AKI-KRT) may independently contribute to the development of ICU-AW. We then delve into human and animal data exploring the pathophysiologic mechanisms linking AKI and acute KRT to muscle wasting, including altered amino acid and protein metabolism, inflammatory signaling, and deleterious removal of micronutrients by KRT. We next discuss the currently available interventions that may mitigate the risk of ICU-AW in patients with AKI and AKI-KRT. We conclude that additional studies are needed to better characterize the epidemiologic and pathophysiologic relationship between AKI, AKI-KRT, and ICU-AW and to prospectively test interventions to improve the long-term functional status and quality of life of AKI survivors.

Statin-Induced Anti-3-Hydroxy-3-Methylglutaryl-Coenzyme A Reductase (Anti-HMGCR) Myopathy

Statins are known to pharmacologically target 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR). Several subtypes of anti-HMGCR autoimmune myopathies have been reported as a result of statin use. Although these types vary widely, a severe and rare form of statin-induced myopathy is immune-mediated necrotizing myopathy (IMNM), resulting in severe muscle injury that does not respond to statin cessation and is associated with poor outcomes. Diagnosis is confirmed through biopsy confirming the necrosis of biopsy fibers, in addition to elevated anti-HMGCR serum levels. Management lacks proper guidelines, however, immunosuppressive therapy has been proposed as a possible intervention. The aim of this report is to increase providers' knowledge of the presentation and possible treatment of statin-induced immune-mediated necrotizing myopathy.

A prospective clinical study on the mechanisms underlying critical illness myopathy-A time-course approach

BACKGROUND

Critical illness myopathy (CIM) is a consequence of modern critical care resulting in general muscle wasting and paralyses of all limb and trunk muscles, resulting in prolonged weaning from the ventilator, intensive care unit (ICU) treatment and rehabilitation. CIM is associated with severe morbidity/mortality and significant negative socioeconomic consequences, which has become increasingly evident during the current COVID-19 pandemic, but underlying mechanisms remain elusive.

METHODS

Ten neuro-ICU patients exposed to long-term controlled mechanical ventilation were followed with repeated muscle biopsies, electrophysiology and plasma collection three times per week for up to 12 days. Single muscle fibre contractile recordings were conducted on the first and final biopsy, and a multiomics approach was taken to analyse gene and protein expression in muscle and plasma at all collection time points.

RESULTS

(i) A progressive preferential myosin loss, the hallmark of CIM, was observed in all neuro-ICU patients during the observation period (myosin:actin ratio decreased from 2.0 in the first to 0.9 in the final biopsy, P < 0.001). The myosin loss was coupled to a general transcriptional downregulation of myofibrillar proteins (P < 0.05; absolute fold change >2) and activation of protein degradation pathways (false discovery rate [FDR] <0.1), resulting in significant muscle fibre atrophy and loss in force generation capacity, which declined >65% during the 12 day observation period (muscle fibre cross-sectional area [CSA] and maximum single muscle fibre force normalized to CSA [specific force] declined 30% [P < 0.007] and 50% [P < 0.0001], respectively). (ii) Membrane excitability was not affected as indicated by the maintained compound muscle action potential amplitude upon supramaximal stimulation of upper and lower extremity motor nerves. (iii) Analyses of plasma revealed early activation of inflammatory and proinflammatory pathways (FDR < 0.1), as well as a redistribution of zinc ions from plasma.

CONCLUSIONS

The mechanical ventilation-induced lung injury with release of cytokines/chemokines and the complete mechanical silencing uniquely observed in immobilized ICU patients affecting skeletal muscle gene/protein expression are forwarded as the dominant factors triggering CIM.

A Global Survey on Diagnostic, Therapeutic and Preventive Strategies in Intensive Care Unit-Acquired Weakness

Background and Objectives: Intensive care unit-acquired weakness (ICU-AW) is one of the most frequent neuromuscular complications in critically ill patients. We conducted a global survey to evaluate the current practices of diagnostics, treatment and prevention in patients with ICU-AW. Materials and Methods: A pre-survey was created with international experts. After revision, the final survey was endorsed by the European Society of Intensive Care Medicine (ESICM) using the online platform SurveyMonkey®. In 27 items, we addressed strategies of diagnostics, therapy and prevention. An invitation link was sent by email to all ESICM members. Furthermore, the survey was available on the ESICM homepage. Results: A total of 154 healthcare professionals from 39 countries participated in the survey. An ICU-AW screening protocol was used by 20% (28/140) of participants. Forty-four percent (62/141) of all participants reported performing routine screening for ICU-AW, using clinical examination as the method of choice (124/141, 87.9%). Almost 63% (84/134) of the participants reported using current treatment strategies for patients with ICU-AW. The use of treatment and prevention strategies differed between intensivists and non-intensivists regarding the reduction in sedatives (80.0% vs. 52.6%, p = 0.002), neuromuscular blocking agents (76.4% vs. 50%, p = 0.004), corticosteroids (69.1% vs. 37.2%, p < 0.001) and glycemic control regimes (50.9% vs. 23.1%, p = 0.002). Mobilization and physical activity are the most frequently reported treatment strategies for ICU-AW (111/134, 82.9%). The availability of physiotherapists (92/134, 68.7%) and the lack of knowledge about ICU-AW within the medical team (83/134, 61.9%) were the main obstacles to the implementation of the strategies. The necessity to develop guidelines for the screening, diagnosing, treatment and prevention of ICU-AW was recognized by 95% (127/133) of participants. Conclusions: A great heterogeneity regarding diagnostics, treatment and prevention of ICU-AW was reported internationally. Comprehensive guidelines with evidence-based recommendations for ICU-AW management are needed.

Acute and severe trabecular bone loss in a rat model of critical illness myopathy

Prolonged mechanical ventilation for critically ill patients with respiratory distress can result in severe muscle wasting with preferential loss of myosin. Systemic inflammation triggered by lung mechanical injury likely contributes to this myopathy, although the exact mechanisms are unknown. In this study, we hypothesized that muscle wasting following mechanical ventilation is accompanied by bone loss. The objective was to determine the rate, nature, and extent of bone loss in the femora of rats ventilated up to 10 days and to relate the bone changes to muscle deterioration. We have developed a rat model of ventilator-induced muscle wasting and established its feasibility and clinical validity. This model involves pharmacologic paralysis, parenteral nutrition, and continuous mechanical ventilation. We assessed the hindlimb muscle and bone of rats ventilated for 0, 2, 5, 8, and 10 days. Routine histology, microCT, and biomechanical evaluations were performed. Hindlimb muscles developed changes consistent with myopathy, whereas the femurs demonstrated a progressive decline in trabecular bone volume, mineral density, and microarchitecture beginning Day 8 of mechanical ventilation. Biomechanical testing showed a reduction in flexural strength and stiffness on Day 10. The bone changes correlated with the loss of muscle mass and myosin. These results demonstrate that mechanical ventilation leads to progressive trabecular bone loss parallel to muscle deterioration. The results of our study suggest that mechanically ventilated patients may be at risk of compromised bone integrity and muscle weakness, predisposing to post-ventilator falls and fractures, thereby warranting interventions to prevent progressive bone and muscle decline.

COVID-19 Neuromuscular Involvement in Post-Acute Rehabilitation

Background: Coronavirus disease 2019 (COVID-19) is associated with muscle and nerve injuries as a consequence of prolonged critical illness or the infection itself. In this study, we evaluated neuromuscular involvement in patients who underwent post-acute intensive rehabilitation after COVID-19. Methods: Clinical and neurophysiological evaluations, including nerve conduction studies and electromyography, were performed on 21 consecutive patients admitted for rehabilitation after COVID-19. Results: Clinical signs suggesting muscle or nerve involvement (weakness, reduced deep tendon reflexes, impaired sensitivity, abnormal gait) were found in 19 patients. Neurophysiological examinations confirmed neuromuscular involvement in 17 patients: a likely association of critical illness myopathy (CIM) and critical illness polyneuropathy (CIP) was found in 5 patients; CIM alone was found in 4 patients; axonal sensory-motor polyneuropathy was found in 4 patients (CIP in 2 patients, metabolic polyneuropathy in 2 patients); Guillain-Barré syndrome was found in 2 patients (classical demyelinating sensory-motor polyneuropathy and acute motor axonal neuropathy, respectively); peroneal nerve injury was found in 1 patient; and pre-existing L4 radiculopathy was found in 1 patient. Conclusions: Neuromuscular involvement is a very common finding among patients admitted for rehabilitation after COVID-19, and proper investigation should be conducted when muscle or nerve injury is suspected for adequate rehabilitative strategy planning.

Intensive Care Unit-Acquired Weakness and Positioning-Related Peripheral Nerve Injuries in COVID-19: A Case Series of Three Patients and the Latest Literature Review

A subgroup of COVID-19 patients requires intensive respiratory care. The prolonged immobilization and aggressive treatments predispose these patients to develop intensive care unit-acquired weakness (ICUAW). Furthermore, this condition could increase the chance of positioning-related peripheral nerve injuries. On the basis of the latest literature review, we describe a case series of three patients with COVID-19 who developed ICUAW complicated by positioning-related peripheral nerve injuries Every patient presented sensorimotor axonal polyneuropathy and concomitant myopathy in electrophysiological studies. Furthermore, muscle MRI helped the diagnosis of ICUAW, showing massive damage predominantly in the proximal muscles. Notably, nerve ultrasound detected positioning-related peripheral nerve injuries, even though the concomitant ICUAW substantially masked their clinical features. During the acute phase of severe COVID-19 infection, most medical attention tends to be assigned to critical care management, and neuromuscular complications such as ICUAW and positioning-related peripheral nerve injuries could be underestimated. Hence, when starting post-ICU care for COVID-19 cases, the combination of electrophysiological and imaging studies will aid appropriate evaluation on the patients with COVID-19-related ICUAW.

Pathophysiology and management of critical illness polyneuropathy and myopathy

Critical illness-associated weakness (CIAW) is an umbrella term used to describe a group of neuromuscular disorders caused by severe illness. It can be subdivided into three major classifications based on the component of the neuromuscular system (i.e. peripheral nerves or skeletal muscle or both) that are affected. This includes critical illness polyneuropathy (CIP), critical illness myopathy (CIM), and an overlap syndrome, critical illness polyneuromyopathy (CIPNM). It is a common complication observed in people with critical illness requiring intensive care unit (ICU) admission. Given CIAW is found in individuals experiencing grave illness, it can be challenging to study from a practical standpoint. However, over the past 2 decades, many insights into the pathophysiology of this condition have been made. Results from studies in both humans and animal models have found that a profound systemic inflammatory response and factors related to bioenergetic failure as well as microvascular, metabolic, and electrophysiological alterations underlie the development of CIAW. Current management strategies focus on early mobilization, achieving euglycemia, and nutritional optimization. Other interventions lack sufficient evidence, mainly due to a dearth of large trials. The goal of this Physiology in Medicine article is to highlight important aspects of the pathophysiology of these enigmatic conditions. It is hoped that improved understanding of the mechanisms underlying these disorders will lead to further study and new investigations for novel pharmacologic, nutritional, and exercise-based interventions to optimize patient outcomes.

Clinical, Neurophysiological and Neuroimaging Findings of Critical Illness Myopathy After COVID-19

Hypoxemic respiratory failure caused by coronavirus disease 2019 (COVID-19) may lead to prolonged intensive care unit stay and mechanical ventilation. Critically ill patients often develop intensive care unit acquired weakness (ICUAW), which is an umbrella term that encompasses critical illness polyneuropathy and critical illness myopathy. The aim of this paper is to report the clinical, neurophysiological, and radiological findings suggesting critical illness myopathy in three patients with critical COVID-19. Muscle magnetic resonance imaging may serve as a diagnostic tool for critical illness myopathy. Weaning failure and generalized muscle weakness with preserved sensation and cranial nerve function should alert physicians for ICUAW.

Case Report: Myopathy in Critically Ill COVID-19 Patients: A Consequence of Hyperinflammation?

Introduction: COVID-19-associated muscular complications may comprise myalgia, weakness, wasting, and rhabdomyolysis. Skeletal muscle damage in COVID-19 may be due to direct infection by the virus SARS-CoV-2 through interaction with the ACE2 receptor, systemic hyper-inflammatory state with cytokine release and homeostatic perturbation, an autoimmune process, or myotoxic drugs. Disclosing the cause of weakness in an individual patient is therefore difficult.

Case Description: We report two patients, who survived typical COVID-19 pneumonia requiring intensive care treatment and who developed early on myalgia and severe proximal weakness in all four limbs. Laboratory exams revealed elevated serum creatine kinase and markedly increased C-reactive protein and interleukin 6, concurring with a systemic inflammatory response. On admission in neurorehabilitation (4 and 7 weeks after COVID-19 onset, respectively), the patients presented with proximal flaccid tetraparesis and limb-girdle muscle atrophy. Motor nerve conduction studies showed decreased amplitude and prolonged duration of compound muscle action potentials (CMAPs) with normal distal motor latencies and normal conduction velocities in median and ulnar nerves. Needle electromyography in proximal muscles revealed spontaneous activity in one and myopathic changes in both patients.

Discussion: Clinical, laboratory, and electrodiagnostic findings in these patients were unequivocally consistent with myopathy. Interestingly, increased distal CMAP duration has been described in patients with critical illness myopathy (CIM) and reflects slow muscle fiber conduction velocity due to membrane hypo-excitability, possibly induced by inflammatory cytokines. By analogy with CIM, the pathogenesis of COVID-19-related myopathy might also depend on hyperinflammation and metabolic pathways that may affect muscles in a pathophysiological continuum from hypo-excitability to necrosis.

Guillain-Barré Syndrome as a Complication of COVID-19

Coronavirus disease 2019 (COVID-19) is associated with multiple neurological complications including Guillain-Barre syndrome (GBS). While there are reports of COVID-19 -related GBS cases, much remain unknown. We report two cases of GBS-associated COVID-19, which started about eight weeks after the initial COVID-19 infection. Such a long duration between infection and symptom onset of GBS is unusual for post-infectious GBS. Moreover, severely ill patients with COVID-19 may have prolonged hospital stay leading to critical illness myoneuropathy. Diagnosing superimposed GBS can be challenging in such cases. Clinical suspicion, nerve conduction studies with electromyography, and cerebrospinal fluid analysis can help in making the correct diagnosis. Both presented cases responded to intravenous immunoglobulin therapy.

Intensive Care Unit-Acquired Weakness: Not just Another Muscle Atrophying Condition

Intensive care unit-acquired weakness (ICUAW) occurs in critically ill patients stemming from the critical illness itself, and results in sustained disability long after the ICU stay. Weakness can be attributed to muscle wasting, impaired contractility, neuropathy, and major pathways associated with muscle protein degradation such as the ubiquitin proteasome system and dysregulated autophagy. Furthermore, it is characterized by the preferential loss of myosin, a distinct feature of the condition. While many risk factors for ICUAW have been identified, effective interventions to offset these changes remain elusive. In addition, our understanding of the mechanisms underlying the long-term, sustained weakness observed in a subset of patients after discharge is minimal. Herein, we discuss the various proposed pathways involved in the pathophysiology of ICUAW, with a focus on the mechanisms underpinning skeletal muscle wasting and impaired contractility, and the animal models used to study them. Furthermore, we will explore the contributions of inflammation, steroid use, and paralysis to the development of ICUAW and how it pertains to those with the corona virus disease of 2019 (COVID-19). We then elaborate on interventions tested as a means to offset these decrements in muscle function that occur as a result of critical illness, and we propose new strategies to explore the molecular mechanisms of ICUAW, including serum-related biomarkers and 3D human skeletal muscle culture models.

Refractory Acute Respiratory Distress Syndrome Secondary to COVID-19 Successfully Extubated to Average Volume-assured Pressure Support Non-invasive Ventilator

Coronavirus disease 2019 (COVID-19) is a respiratory illness caused by the highly infectious novel SARS-CoV-2 coronavirus spread by droplet transmission. Consequently, the use of respiratory devices that may potentially promote aerosolization like non-invasive positive pressure ventilation (NIPPV) for diseases such as obstructive sleep apnea (OSA), advanced chronic obstructive lung disease, pulmonary hypertension (PH), and neuromuscular respiratory disease has been called into question. We present a case of a patient with history of OSA and PH convalescing from refractory acute respiratory distress syndrome (ARDS) secondary to COVID-19 who was successfully extubated to average volume-assured pressure support (AVAPS).

A 74-year-old male with medical history notable for OSA on NIPPV, PH, and hypertension presented with respiratory failure secondary to COVID-19 confirmed on polymerase chain reaction (PCR) test. His respiratory status worsened leading to ARDS requiring intubation. He was initially extubated to high flow nasal cannula (HFNC) due to hospital policy to avoid NIPPV due to concerns of viral dissemination. He did not tolerate HFNC and required re-intubation for prolonged period. He was then medically optimized for a second attempt and extubated two days later to AVAPS with an anti-viral filter and negative pressure room with a goal of optimizing his critical illness myopathy and pre-existing OSA and PH. He tolerated extubation well, and over the next five days was weaned from alternating AVAPS/HFNC to eventually requiring two liters nasal cannula in the day and AVAPS mode at night.

This case highlights a potential therapeutic option for patients with severe respiratory failure secondary to COVID-19. This patient’s pre-existing comorbidities of OSA and PH markedly increased his risk for extubation failure on HFNC. The use of AVAPS after his second extubation attempt helped ensure ventilation and oxygenation non-invasively. COVID-19 can lead to prolonged dependence on mechanical ventilation. This pandemic has the potential to create medical resource scarcities, especially in rural areas where ventilators and trained personnel are already in short supply. By using AVAPS mode, this patient was able to rehabilitate his myopathy and participate in intermittent weaning of HFNC to ultimately simple nasal cannula.

AVAPS is useful tool to facilitate extubation, as it allows non-invasive support of respiratory dynamics, particularly in those with co-morbidities such as OSA and PH. Further, larger scale studies are needed to determine its exact role during the COVID-19 pandemic.

Chronic muscle weakness and mitochondrial dysfunction in the absence of sustained atrophy in a preclinical sepsis model

Chronic critical illness is a global clinical issue affecting millions of sepsis survivors annually. Survivors report chronic skeletal muscle weakness and development of new functional limitations that persist for years. To delineate mechanisms of sepsis-induced chronic weakness, we first surpassed a critical barrier by establishing a murine model of sepsis with ICU-like interventions that allows for the study of survivors. We show that sepsis survivors have profound weakness for at least 1 month, even after recovery of muscle mass. Abnormal mitochondrial ultrastructure, impaired respiration and electron transport chain activities, and persistent protein oxidative damage were evident in the muscle of survivors. Our data suggest that sustained mitochondrial dysfunction, rather than atrophy alone, underlies chronic sepsis-induced muscle weakness. This study emphasizes that conventional efforts that aim to recover muscle quantity will likely remain ineffective for regaining strength and improving quality of life after sepsis until deficiencies in muscle quality are addressed.

Diaphragm Weakness in the Critically Ill: Basic Mechanisms Reveal Therapeutic Opportunities

The diaphragm is the primary muscle of inspiration. Its capacity to respond to the load imposed by pulmonary disease is a major determining factor both in the onset of ventilatory failure and in the ability to successfully separate patients from ventilator support. It has recently been established that a very large proportion of critically ill patients exhibit major weakness of the diaphragm, which is associated with poor clinical outcomes. The two greatest risk factors for the development of diaphragm weakness in critical illness are the use of mechanical ventilation and the presence of sepsis. Loss of force production by the diaphragm under these conditions is caused by a combination of defective contractility and reduced diaphragm muscle mass. Importantly, many of the same molecular mechanisms are implicated in the diaphragm dysfunction associated with both mechanical ventilation and sepsis. This review outlines the primary cellular mechanisms identified thus far at the nexus of diaphragm dysfunction associated with mechanical ventilation and/or sepsis, and explores the potential for treatment or prevention of diaphragm weakness in critically ill patients through therapeutic manipulation of these final common pathway targets.

No association between systemic complement activation and intensive care unit-acquired weakness

Background

The main risk factors for intensive care unit-acquired weakness (ICU-AW) are sepsis, the systemic inflammatory response syndrome (SIRS) and multiple organ dysfunction. These risk factors are associated with systemic complement activation. We hypothesized that critically ill patients who develop ICU-AW have increased systemic complement activation compared to critically ill patients who do not develop ICU-AW.

Methods

Complement activation products C3b/c, C4b/c and C5a were measured in plasma of ICU patients with mechanical ventilation for ≥48 hours. Samples were collected at admission to the ICU and for 6 consecutive days. ICU-AW was defined by a mean Medical Research Council (MRC) score <4. We compared the level of complement activation products between patients who did and who did not develop ICU-AW.

Results

Muscle strength measurements and complement assays were available in 27 ICU patients, of whom 13 patients developed ICU-AW. Increased levels of C4b/c were seen in all patients. Neither admission levels, nor maximum, minimum and mean levels of complement activation products were different between patients who did and did not develop ICU-AW.

Conclusions

Complement activation is seen in critically ill patients, but is not different between patients who did and who did not develop ICU-AW.

Muscle membrane properties in A pig sepsis model: Effect of norepinephrine

INTRODUCTION

Sepsis-induced myopathy and critical illness myopathy are common causes of muscle weakness in intensive care patients. This study investigated the effect of different mean arterial blood pressure (MAP) levels on muscle membrane properties following experimental sepsis.

METHODS

Sepsis was induced with fecal peritonitis in 12 of 18 anesthetized and mechanically ventilated pigs. Seven were treated with a high (75-85 mmHg) and 5 were treated with a low (≥60 mmHg) MAP target for resuscitation. In septic animals, resuscitation was started 12 h after peritonitis induction, and muscle velocity recovery cycles were recorded 30 h later.

RESULTS

Muscles in the sepsis/high MAP group showed an increased relative refractory period and reduced early supernormality compared with the remaining septic animals and the control group, indicating membrane depolarization and/or sodium channel inactivation. The membrane abnormalities correlated positively with norepinephrine dose.

DISCUSSION

Norepinephrine may contribute to sepsis-induced abnormalities in muscle by impairing microcirculation. Muscle Nerve 57: 808-813, 2018.

Electrodiagnostic studies in the intensive care unit: A comparison study 2 decades later

INTRODUCTION

Since the late 1980s, critical illness myopathy (CIM) and critical illness polyneuropathy (CIP) have been increasingly recognized in the intensive care unit (ICU). We explored whether these causes of ICU weakness were now more likely to lead to electrodiagnostic studies (EDX) at our institution than they were 19-20 years earlier.

METHODS

We reviewed 100 consecutive ICU patients who underwent EDX from 2009 to 2015 and compared them to a previously reported study population from 1990-1995.

RESULTS

Thirty-seven (39%) had CIM, CIP, or both versus 55% in the previous study (P = 0.04). Thirty-four (36%) were diagnosed with "traditional" pre-ICU causes of weakness, such as motor neuron disease or Guillain-Barre syndrome, versus 29% in the earlier study (P = 0.3).

DISCUSSION

CIM and CIP continue to be common disorders that lead to ICU EDX, but their proportion declined compared with 19-20 years earlier, possibly due to the perceived role and selective use of EDX in the ICU. Muscle Nerve 57: 772-776, 2018.

Compound muscle action potential duration in critical illness neuromyopathy

INTRODUCTION

We sought to determine the specificity of compound muscle action potential (CMAP) durations and amplitudes in a large critical illness neuromyopathy (CINM) cohort relative to controls with other neuromuscular conditions.

METHODS

Fifty-eight patients with CINM who had been seen over a 17-year period were retrospectively studied. Electrodiagnostic findings of the CINM cohort were compared with patients with axonal peripheral neuropathy and myopathy due to other causes.

RESULTS

Mean CMAP durations were prolonged, and mean CMAP amplitudes were severely reduced both proximally and distally in all nerves studied in the CINM cohort relative to the control groups. The specificity of prolonged CMAP durations for CINM approached 100% if they were encountered in more than 1 nerve.

DISCUSSION

Prolonged, low-amplitude CMAPs occur more frequently and with greater severity in CINM patients than in neuromuscular controls with myopathy and axonal neuropathy and are highly specific for the diagnosis of CINM. Muscle Nerve 57: 395-400, 2018.

Optimizing testing methods and collection of reference data for differentiating critical illness polyneuropathy from critical illness MYOPATHIES

INTRODUCTION

In severe acute quadriplegic myopathy in intensive care unit (ICU) patients, muscle fibers are electrically inexcitable; in critical illness polyneuropathy, the excitability remains normal. Conventional electrodiagnostic methods do not provide the means to adequately differentiate between them. In this study we aimed to further optimize the methodology for the study of critically ill ICU patients and to create a reference database in healthy controls.

METHODS

Different electrophysiologic protocols were tested to find sufficiently robust and reproducible techniques for clinical diagnostic applications.

RESULTS

Many parameters show large test-retest variability within the same healthy subject. Reference values have been collected and described as a basis for studies of weakness in critical illness.

CONCLUSIONS

Using the ratio of neCMAP/dmCMAP (response from nerve and direct muscle stimulation), refractory period, and stimulus-response curves may optimize the electrodiagnostic differentiation of patients with critical illness myopathy from those with critical illness polyneuropathy.

ICU-Acquired Weakness

Survivorship after critical illness is an increasingly important health-care concern as ICU use continues to increase while ICU mortality is decreasing. Survivors of critical illness experience marked disability and impairments in physical and cognitive function that persist for years after their initial ICU stay. Newfound impairment is associated with increased health-care costs and use, reductions in health-related quality of life, and prolonged unemployment. Weakness, critical illness neuropathy and/or myopathy, and muscle atrophy are common in patients who are critically ill, with up to 80% of patients admitted to the ICU developing some form of neuromuscular dysfunction. ICU-acquired weakness (ICUAW) is associated with longer durations of mechanical ventilation and hospitalization, along with greater functional impairment for survivors. Although there is increasing recognition of ICUAW as a clinical entity, significant knowledge gaps exist concerning identifying patients at high risk for its development and understanding its role in long-term outcomes after critical illness. This review addresses the epidemiologic and pathophysiologic aspects of ICUAW; highlights the diagnostic challenges associated with its diagnosis in patients who are critically ill; and proposes, to our knowledge, a novel strategy for identifying ICUAW.

Mechanical Signaling in the Pathophysiology of Critical Illness Myopathy

The complete loss of mechanical stimuli of skeletal muscles, i.e., the loss of external strain, related to weight bearing, and internal strain, related to the contraction of muscle cells, is uniquely observed in pharmacologically paralyzed or deeply sedated mechanically ventilated intensive care unit (ICU) patients. The preferential loss of myosin and myosin associated proteins in limb and trunk muscles is a significant characteristic of critical illness myopathy (CIM) which separates CIM from other types of acquired muscle weaknesses in ICU patients. Mechanical silencing is an important factor triggering CIM. Microgravity or ground based microgravity models form the basis of research on the effect of muscle unloading-reloading, but the mechanisms and effects may differ from the ICU conditions. In order to understand how mechanical tension regulates muscle mass, it is critical to know how muscles sense mechanical information and convert stimulus to intracellular biochemical actions and changes in gene expression, a process called cellular mechanotransduction. In adult skeletal muscles and muscle fibers, this process may differ, the same stimulus can cause divergent response and the same fiber type may undergo opposite changes in different muscles. Skeletal muscle contains multiple types of mechano-sensors and numerous structures that can be affected differently and hence respond differently in distinct muscles.

ICU-Acquired Weakness Is Associated With Differences in Clinical Outcomes in Critically Ill Children

OBJECTIVE

ICU-acquired weakness, comprised critical illness myopathy and critical illness neuropathy, occurs in a significant proportion of critically ill adults and is associated with high morbidity and mortality. Little is known about ICU-acquired weakness among critically ill children. We investigated the incidence of ICU-acquired weakness among PICUs participating in the Virtual PICU Systems database. We also sought to identify associated risk factors for ICU-acquired weakness and evaluate the hypothesis that ICU-acquired weakness is associated with poor clinical outcomes.

DESIGN

Retrospective cohort study.

SETTING

PICU.

MEASUREMENTS AND MAIN RESULTS

Virtual PICU System was queried for critical illness myopathy and critical illness neuropathy between January 2009 and November 2013. Demographic, admission, and clinical outcome variables including mechanical ventilation days, PICU length of stay, and discharge disposition were analyzed. The Pediatric Index of Mortality-2 was used to evaluate and control for illness severity and risk of mortality. Among 203,875 admissions, there were 55 cases of critical illness myopathy reported and no cases of critical illness neuropathy, resulting in an incidence of 0.02%. Mechanical ventilation days were higher among patients with ICU-acquired weakness versus those who did not develop ICU-acquired weakness (31.6 ± 28.9 vs 9.3 ± 20.6; p < 0.001). In our multivariable analysis, when controlling for Pediatric Index of Mortality-2, ICU-acquired weakness was more frequently reported in those with admission diagnoses of respiratory illness and infection and the need for mechanical ventilation, renal replacement therapy, extracorporeal life support, and tracheostomy. ICU-acquired weakness was associated with a longer PICU length of stay, episodes requiring mechanical ventilation, and discharge to an intermediate, chronic care, and rehabilitation care unit. ICU-acquired weakness was not independently associated with mortality.

CONCLUSIONS

ICU-acquired weakness is uncommonly diagnosed among PICU patients reported in Virtual PICU System. ICU-acquired weakness is associated with critical care therapies, invasive procedures, and resource utilization. Limitations of our retrospective study include underrecognition of ICU-acquired weakness and lack of standardized diagnostic criteria within Virtual PICU System. Prospective studies are needed to better understand the true incidence, risk factors, and clinical course for patients who develop ICU-acquired weakness.

Assessment of intensive care unit-acquired weakness in young and old mice: An E. coli septic peritonitis model

INTRODUCTION

There are few reports of in vivo muscle strength measurements in animal models of ICU-acquired weakness (ICU-AW). In this study we investigated whether the Escherichia coli (E. coli) septic peritonitis mouse model may serve as an ICU-AW model using in vivo strength measurements and myosin/actin assays, and whether development of ICU-AW is age-dependent in this model.

METHODS

Young and old mice were injected intraperitoneally with E. coli and treated with ceftriaxone. Forelimb grip strength was measured at multiple time points, and the myosin/actin ratio in muscle was determined.

RESULTS

E. coli administration was not associated with grip strength decrease, neither in young nor in old mice. In old mice, the myosin/actin ratio was lower in E. coli mice at t = 48 h and higher at t = 72 h compared with controls.

CONCLUSIONS

This E. coli septic peritonitis mouse model did not induce decreased grip strength. In its current form, it seems unsuitable as a model for ICU-AW.

Hospital-level factors associated with report of physical activity in patients on mechanical ventilation across Washington State

RATIONALE

Use of physical and/or occupational therapy in the intensive care unit (ICU) is safe, feasible, and demonstrates improvements in functional status with early administration. Access to physical and/or occupational therapy in the ICU is variable, with little known regarding its use in community ICUs.

OBJECTIVES

Determine what proportion of hospitals across Washington State report use of physical activity in mechanically ventilated patients and investigate process of care factors associated with reported activity delivery.

METHODS

Cross-sectional telephone interview survey study of nurse managers in hospitals caring for patients on mechanical ventilation across Washington State in 2013. Survey responses were linked with hospital-level data available in the Washington State Department of Health Comprehensive Hospital Abstract Reporting System database. Chi-square testing was used to explore unadjusted associations between potential process of care factors and report on activity delivery. Two multivariable logistic regression models were developed to explore the association between presence of a mobility protocol and report on delivery of activity.

MEASUREMENTS AND MAIN RESULTS

We identified 54 hospitals caring for patients on mechanical ventilation; 47 participated in the survey (response rate, 85.5%). Nurse managers from 36 (76.6%) hospitals reported use of physical activity in patients on mechanical ventilation, with 22 (46.8%) reporting use of high-level physical activity (transferring to chair, standing or ambulating) and 24 (51.1%) reporting use in high-severity patients (patients requiring mechanical ventilation and/or vasopressors). Presence of a written ICU activity protocol (odds ratio [OR], 5.54; 95% confidence interval [CI], 1.60-19.18; P = 0.006), hospital volume (OR, 5.33; 95% CI, 1.54-18.48; P = 0.008), and academic affiliation (OR, 4.40; 95% CI, 1.23-15.63; P = 0.02) were associated with report of higher level activity. Presence of a written ICU activity protocol (OR, 6.00; 95% CI, 1.69-21.14; P = 0.005) and academic affiliation (OR, 4.50; 95% CI, 1.21-16.46; P = 0.02) were associated with report of delivery of physical activity to high-severity patients.

CONCLUSIONS

Nurse managers at three-fourths (76.6%) of eligible hospitals across Washington State reported use of physical activity in patients on mechanical ventilation. Hospital-level factors including hospital volume, academic affiliation, and presence of a mobility protocol were associated with report of higher level activity and delivery of activity to high-severity patients.

Quantitative neuromuscular ultrasound in intensive care unit-acquired weakness: A systematic review

Intensive care unit-acquired weakness (ICU-AW) causes significant morbidity and impairment in critically ill patients. Recent advances in neuromuscular ultrasound (NMUS) allow evaluation of neuromuscular pathology early in critical illness. Here we review application of ultrasound in ICU-AW. MEDLINE-indexed articles were searched for terms relevant to ultrasound and critical illness. Two reviewers evaluated the resulting abstracts (n = 218) and completed full-text review (n = 13). Twelve studies and 1 case report were included. Ten studies evaluated muscle thickness or cross-sectional area (CSA): 8 reported a decrease, and 2 reported no change. Two studies reported preservation of muscle thickness in response to neuromuscular electrical stimulation, and 1 found no preservation. One study found decreases in gray-scale standard deviation, but no change in echogenicity. One study described increases in echogenicity and fasciculations. Ultrasound reliability in ICU-AW is not fully established. Further investigation is needed to identify ultrasound measures that reliably predict clinical, electrodiagnostic, and pathologic findings of ICU-AW.

Critical illness polyneuropathy and myopathy: a systematic review

Critical illness polyneuropathy and critical illness myopathy are frequent complications of severe illness that involve sensorimotor axons and skeletal muscles, respectively. Clinically, they manifest as limb and respiratory muscle weakness. Critical illness polyneuropathy/myopathy in isolation or combination increases intensive care unit morbidity via the inability or difficulty in weaning these patients off mechanical ventilation. Many patients continue to suffer from decreased exercise capacity and compromised quality of life for months to years after the acute event. Substantial progress has been made lately in the understanding of the pathophysiology of critical illness polyneuropathy and myopathy. Clinical and ancillary test results should be carefully interpreted to differentiate critical illness polyneuropathy/myopathy from similar weaknesses in this patient population. The present review is aimed at providing the latest knowledge concerning the pathophysiology of critical illness polyneuropathy/myopathy along with relevant clinical, diagnostic, differentiating, and treatment information for this debilitating neurological disease.

Long-term recovery In critical illness myopathy is complete, contrary to polyneuropathy

INTRODUCTION

Muscle weakness in critically ill patients after discharge varies. It is not known whether the electrophysiological distinction between critical illness myopathy (CIM) and critical illness polyneuropathy (CIP) during the early part of a patient's stay in the intensive care unit (ICU) predicts long-term prognosis.

METHODS

This was a prospective cohort study of mechanically ventilated ICU patients undergoing conventional nerve conduction studies and direct muscle stimulation in addition to neurological examination during their ICU stay and 1 year after ICU discharge.

RESULTS

Twenty-six patients (7 ICU controls, 8 CIM patients, and 11 CIM/CIP patients) were evaluated 1 year after discharge from the ICU. Eighty-eight percent (n = 7) of CIM patients recovered within 1 year compared with 55% (n = 6) of CIM/CIP patients. Thirty-six percent (n = 4) of CIM/CIP patients still needed assistance during their daily routine (P = 0.005).

CONCLUSIONS

Early electrophysiological testing predicts long-term outcome in ICU survivors. CIM has a significantly better prognosis than CIM/CIP.

Neuromuscular complications of critical illness

Patients admitted to intensive care units (ICUs) suffer from a wide range of neurological disorders. Some develop within the ICU rendering weakness and difficulty in weaning patients from ventilator support. ICUAW, or ICU acquired weakness, is a broad term that includes several more specific neuromuscular problems. After exclusion of other causes of weakness, ICUAW includes critical illness polyneuropathy (CIP), first described by Charles Bolton, critical illness myopathy (CIM), and disorders of neuromuscular junction transmission. This chapter reviews the clinical, electrophysiological, and pathological features of these conditions and provides clinicians with approaches toward diagnosing and investigating ICUAW.

Intensive care unit acquired weakness in children: Critical illness polyneuropathy and myopathy

BACKGROUND AND AIMS

Intensive care unit acquired weakness (ICUAW) is a common occurrence in patients who are critically ill. It is most often due to critical illness polyneuropathy (CIP) or to critical illness myopathy (CIM). ICUAW is increasingly being recognized partly as a consequence of improved survival in patients with severe sepsis and multi-organ failure, partly related to commonly used agents such as steroids and muscle relaxants. There have been occasional reports of CIP and CIM in children, but little is known about their prevalence or clinical impact in the pediatric population. This review summarizes the current understanding of pathophysiology, clinical presentation, diagnosis and treatment of CIP and CIM in general with special reference to published literature in the pediatric age group.

SUBJECTS AND METHODS

Studies were identified through MedLine and Embase using relevant MeSH and Key words. Both adult and pediatric studies were included.

RESULTS

ICUAW in children is a poorly described entity with unknown incidence, etiology and unclear long-term prognosis.

CONCLUSIONS

Critical illness polyneuropathy and myopathy is relatively rare, but clinically significant sequelae of multifactorial origin affecting morbidity, length of intensive care unit (ICU) stay and possibly mortality in critically ill children admitted to pediatric ICU.

Intensive care unit-acquired weakness (ICUAW) and muscle wasting in critically ill patients with severe sepsis and septic shock

Sepsis presents a major health care problem and remains one of the leading causes of death within the intensive care unit (ICU). Therapeutic approaches against severe sepsis and septic shock focus on early identification. Adequate source control, administration of antibiotics, preload optimization by fluid resuscitation and further hemodynamic stabilisation using vasopressors whenever appropriate are considered pivotal within the early-golden-hours of sepsis. However, organ dysfunction develops frequently in and represents a significant comorbidity of sepsis. A considerable amount of patients with sepsis will show signs of severe muscle wasting and/or ICU-acquired weakness (ICUAW), which describes a frequently observed complication in critically ill patients and refers to clinically weak ICU patients in whom there is no plausible aetiology other than critical illness. Some authors consider ICUAW as neuromuscular organ failure, caused by dysfunction of the motor unit, which consists of peripheral nerve, neuromuscular junction and skeletal muscle fibre. Electrophysiologic and/or biopsy studies facilitate further subclassification of ICUAW as critical illness myopathy, critical illness polyneuropathy or critical illness myoneuropathy, their combination. ICUAW may protract weaning from mechanical ventilation and impede rehabilitation measures, resulting in increased morbidity and mortality. This review provides an insight on the available literature on sepsis-mediated muscle wasting, ICUAW and their potential pathomechanisms.