Neuromuscular manifestations of critical illness

Systemic inflammatory response syndrome increases immobility-induced neuromuscular weakness

OBJECTIVE

Inflammation and immobility are comorbid etiological factors inducing muscle weakness in critically ill patients. This study establishes a rat model to examine the effect of inflammation and immobilization alone and in combination on muscle contraction, histology, and acetylcholine receptor regulation.

DESIGN

Prospective, randomized, experimental study.

SETTING

Animal laboratory of a university hospital.

SUBJECTS

Sprague-Dawley rats.

INTERVENTIONS

To produce systemic inflammation, rats (n = 34) received three consecutive intravenous injections of Corynebacterium parvum on days 0, 4, and 8. Control rats (n = 21) received saline. Both groups were further divided to have one hind limb either immobilized by pinning of knee and ankle joints or sham-immobilized (surgical leg). The contralateral nonsurgical leg of each animal served as control (nonsurgical leg).

MEASUREMENTS AND MAIN RESULTS

After 12 days, body weight and muscle mass were significantly reduced in all C. parvum animals compared with saline-injected rats. Immobilization led to local muscle atrophy. Normalized to muscle mass, tetanic contraction was reduced in the surgical leg after immobilization (7.64 +/- 1.91 N/g) and after inflammation (8.71 +/- 2.0 N/g; both p < .05 vs. sham immobilization and saline injection, 11.03 +/- 2.26 N/g). Histology showed an increase in inflammatory cells in all C. parvum-injected animals. Immobilization in combination with C. parvum injection had an additive effect on inflammation. Acetylcholine receptors were increased in immobilized muscles and in all muscles of C. parvum-injected animals.

CONCLUSIONS

The muscle weakness in critically ill patients can be replicated in our novel rat model. Inflammation and immobilization independently lead to muscle weakness.

Endotoxin reduces availability of voltage-gated human skeletal muscle sodium channels at depolarized membrane potentials

OBJECTIVE

Critical illness myopathy is a common cause for difficulties in weaning from the respirator and prolonged rehabilitation of patients recovering from sepsis. Several studies have shown that the primary cause of acute generalized muscle weakness is loss of muscle membrane excitability. This study was designed to investigate a potential direct interaction of lipopolysaccharides from Escherichia coli with voltage-gated human skeletal muscle sodium channels (NaV1.4) in vitro.

DESIGN

In vitro laboratory investigation.

SETTING

University laboratory.

SUBJECTS

NaV1.4 sodium channel alpha-subunits stably expressed in human embryonic kidney (HEK293) cells.

INTERVENTIONS

We investigated the effect of lipopolysaccharide on voltage-dependent sodium channel gating by using two distinct modes of application: 1) acute perfusion (pharmacologic lipopolysaccharide concentrations between 5 ng/mL and 50 microg/mL) in order to establish a concentration-effect relationship; and 2) incubation with a clinically relevant concentration of lipopolysaccharide (300 pg/mL).

MEASUREMENTS AND MAIN RESULTS

Lipopolysaccharide did not alter the kinetics of sodium current activation or inactivation when depolarizations were started from hyperpolarized holding potentials. However, when either fast or slow inactivation was induced by membrane depolarization before the test pulse, lipopolysaccharide reversibly reduced channel availability during the test pulse at concentrations of > or = 50 ng/mL revealed by a maximum hyperpolarizing shift of -25 mV in the voltage dependence of fast and slow inactivation, respectively. Incubation with a lipopolysaccharide concentration of 300 pg/mL for 1 hr reproduced the effects on slow but not on fast inactivation. After 20 hrs of low-dose lipopolysaccharide, the peak sodium current was significantly reduced.

CONCLUSIONS

Our results show that lipopolysaccharide interacts with voltage-gated sodium channels, reducing channel availability at depolarized membrane potentials during acute application, independent of the membrane potential after chronic exposure. These effects may contribute to reduced muscle membrane excitability in sepsis.

Mechanisms of neurologic failure in critical illness

Critical illness frequently is associated with neurologic failure that may involve the central and peripheral nervous systems. Central nervous system failure is associated with a spectrum of neurobehavioral changes including delirium, coma, and long-term cognitive dysfunction. Peripheral neurologic failure, or critical illness neuromuscular abnormalities, is suggested by diffuse arreflexic weakness and protracted respiratory insufficiency, and may also persist long after the acute hospitalization. While the burden of neurological disease complicating critical illness is considerable, preventive or therapeutic options are limited. This article provides an overview of research evaluating the relationship between critical illness and neurologic function, with a special emphasis on underlying mechanisms.

Mechanisms of neuromuscular dysfunction in critical illness

The development of neuromuscular dysfunction (NMD) during critical illness is increasingly recognized as a cause of failure to wean from mechanical ventilation and is associated with significant morbidity and mortality. At times, it is difficult to identify the presence of NMD and distinguish the etiology of the weakness in patients with critical illness, but subtle clinical findings and bedside electrophysiologic testing are helpful in establishing the diagnosis. This article describes the clinical spectrum of acquired neuromuscular weakness in the setting of critical illness, provides an approach to diagnosis, and discusses its pathogenesis. Finally, a defective sodium channel regulation as a unifying mechanism underlying NMD in critically ill patients is proposed.

The role of future longitudinal studies in ICU survivors: understanding determinants and pathophysiology of weakness and neuromuscular dysfunction

PURPOSE OF REVIEW

The goals of this review are to discuss the pathophysiology and determinants of muscle weakness and neuromuscular dysfunction after critical illness, and to offer thoughts regarding the role of future longitudinal studies in this area.

RECENT FINDINGS

While recent studies support the finding that neuromuscular dysfunction is common and important after critical illness, reversible risk factors and approaches to prevention and treatment remain unproven. Pathophysiologic studies implicate disease and treatment associated factors in the development of nerve and muscle damage during critical illness; these factors may provide targets for future studies.

SUMMARY

Additional studies with improved methodology that address epidemiology and that test interventions are needed to understand and to improve neuromuscular function after critical illness.

Fulminant Guillain–Barré syndrome after closed head injury: a potentially reversible cause of an ominous examination

✓ Fulminant Guillain–Barré syndrome (GBS) is a rapidly progressive form of polyneuropathy in which patients demonstrate eventual flaccid quadriplegia and an absence of brainstem function. Most patients present after a mild upper respiratory or gastrointestinal illness and have nondiagnostic cerebral imaging studies. The authors present a case of fulminant GBS that developed in a 55-year-old alcoholic man 1 week after admission for a closed head injury. The details of this case and a discussion of GBS will be presented. This case provides evidence for combined central and peripheral nervous system involvement in severe cases of GBS. Recognition of fulminant GBS is important to prevent inappropriate declaration of brain death or withdrawal of support in the face of a potentially reversible process.

Role of endotoxin in the pathogenesis of critical illness polyneuropathy

Critical illness polyneuropathy (CIP) occurs in association with sepsis and multiple organ failure; however, little is known about the pathomechanisms of CIP and its therapy. In order to determine the parameters which interfere with development of CIP, electrophysiological investigations of peripheral nerves and biochemical measures were correlated to each other. The present study includes 20 consecutive patients in an intensive care unit developing severe sepsis or septic shock. Nerve conduction studies and electromyography were performed with occurring sepsis (day 1, 7, 14) and neurophysiological parameters were correlated with biochemical measures, especially indicators of infection and inflammation. It was found that all patients developed neurophysiological signs of axonal motor polyneuropathy. There was a significant correlation between serum concentrations of endotoxin and interleukin-2 receptors (IL2-R) and reduction of the amplitude of the compound motor action potentials. Other clinical and biochemical parameters showed no significant correlations with neurophysiological data. This finding apparently indicates that endotoxin damages nerve axons directly or indirectly, e.g. by activation of inflammatory cascades (IL2-R). Endotoxin appears to be an essential factor in the pathogenesis of CIP in sepsis, and therapeutic options neutralizing endotoxin may prevent development of CIP.

Mitochondrial function in sepsis: respiratory versus leg muscle

Patients with sepsis-induced multiple organ failure often experience muscle fatigue in both locomotive and respiratory muscles. Muscle fatigue extends intensive care unit stay, mostly in the form of prolonged weaning from the ventilator, and the recovery period after intensive care unit treatment due to general muscle fatigue. Muscle mitochondria are the main determinant of muscle fatigue and fatigability. Derangements in mitochondrial function in locomotive muscles have been described extensively both in animal models and patients with sepsis. Also, in respiratory muscle, mitochondrial function and content are impaired during sepsis. However, in septic patients with multiple organ failure, in locomotive muscle, lower levels of energy-rich compounds accompany the decreased mitochondrial content, whereas in respiratory muscle, the decreased mitochondrial content has no effect on cellular energy metabolism.

The cardiac R-R variation and sympathetic skin response in the intensive care unit

BACKGROUND AND PURPOSE

The central and peripheral nervous systems are often affected in intensive care unit (ICU) patients, especially those with prolonged assisted ventilation and sepsis or systemic inflammatory response syndrome (SIRS). The autonomic nervous system, however, has been under-investigated in such patients. We evaluated autonomic nervous system (ANS) function in 29 ICU patients with various neurological disorders.

METHODS

Testing involved cardiac R-R variation (CRRV) as an index of parasympathetic function and the sympathetic skin response (SSR) for sympathetic assessment.

RESULTS

Only those 8 patients with sepsis-related neuropathy or encephalopathy had abnormal CRRV, while the SSR was absent in all but 2 patients.

CONCLUSIONS

Our preliminary study revealed a high incidence of autonomic dysfunction in ICU patients with various neurological disorders.

Chronic Escherichia coli infection induces muscle wasting without changing acetylcholine receptor numbers

OBJECTIVE

Muscle weakness in septic patients is a serious problem as it complicates and lengthens hospital stays, prolongs rehabilitation and increases costs. We examined the effects of a chronic infection with Escherichia coli on muscle function, muscle mass, and the expression of nicotinic acetylcholine receptors (AChRs).

DESIGN AND SETTING

Prospective, randomized animal study in an animal laboratory, university hospital.

SUBJECTS

Sprague-Dawley rats.

INTERVENTIONS

A catheter was implanted into the external jugular vein of anesthetized rats, and a dose of 3.2x10(8) CFU of E. coli bacteria was injected; the catheter was then sealed and tunneled subcutaneously.

MEASUREMENTS AND RESULTS

Animals injected with E. coli bacteria showed a significant decrease in body and muscle mass over the 14-day experimental period. Neuromuscular function was tested by mechanomyography on days 3, 7, and 14 following injection. Tetanic tension decreased over the time course of sepsis, without effecting tetanic fade. Serum levels of acute-phase protein, alpha1-acid glycoprotein, were increased by day 3, and remained significantly higher until day 14. AChRs were quantitated using 125I-labeled bungarotoxin and revealed no differences between groups.

CONCLUSIONS

Central venous injection of E. coli bacteria induces systemic inflammation evidenced as loss of body weight, muscle mass and increased alpha1-acid glycoprotein levels. The inflammation-induced muscle weakness is due to muscle atrophy and not to upregulated AChRs. This model may prove useful for studying maneuvers to prevent muscle wasting with inflammation.

Consensus guidelines for sustained neuromuscular blockade in critically ill children

BACKGROUND

The United Kingdom Paediatric Intensive Care Society Sedation, Analgesia and Neuromuscular Blockade Working Group is a multidisciplinary expert panel created to produce consensus guidelines on sedation, analgesia and neuromuscular blockade in critically ill children and forward knowledge in these areas. Neuromuscular blockade is recognized as an important element in the care of the critically ill and adult clinical practice guidelines in this area have been available for several years. However, similar clinical practice guidelines have not previously been produced for the critically ill pediatric patient.

METHODS

A modified Delphi technique was employed to allow the Working Group to anonymously consider draft recommendations in up to three Delphi rounds with predetermined levels of agreement. This process was supported by a total of four consensus conferences and once consensus had been achieved, a systematic review of the available literature was carried out.

RESULTS

A set of consensus guidelines was produced including six key recommendations. An evaluation of the existing literature supporting these recommendations is provided.

CONCLUSIONS

Multidisciplinary consensus guidelines for maintenance neuromuscular blockade in critically ill children (excluding neonates) have been successfully produced and are supported by levels of evidence. The Working Group has highlighted the paucity of high quality evidence in these important clinical areas and this emphasizes the need for further randomized clinical trials in this area.

[Critical illness myopathy in intensive care patients. Pathogenetic concepts and clinical management]

Intensive care patients are at increased risk of developing sepsis with multi-organ failure during treatment (severe sepsis) possibly leading to complications of the central and peripheral nervous system. Among these, septic encephalopathy, critical illness polyneuropathy (CIP) and critical illness myopathy (CIM) are the most important. Neuromuscular complications in particular are difficult to diagnose as they mostly become apparent only when sedation has ceased and the awakening patient experiences difficulties in weaning from the respirator and reduced voluntary strength. CIP and CIM are generally self-limiting, however, they greatly prolong ICU stay and rehabilitation, thus nowadays also imposing a real budget threat. The diagnostics, especially the differentiation between CIM and CIP is difficult and a multi-disciplinary approach involving ICU physicians, anesthetists and neurologists is needed. Our knowledge of the causes of the primary ICU myopathy, although rapidly evolving during recent years, is still in its infancy and specific treatment of CIM is not yet available. The present overview summarizes insights into clinical and new diagnostic strategies for early detection of neuromuscular dysfunction in ICU patients. This article focuses on current concepts and results revealing the pathomechanism(s) of CIM and some simple therapeutic or preventive measures have been deduced which are summarized and discussed.

Neuromuscular dysfunction acquired in critical illness: a systematic review

OBJECTIVE

To determine the prevalence, risk factors, and outcomes of critical illness neuromuscular abnormalities (CINMA).

DESIGN

Systematic review.

DATA SOURCES AND STUDY SELECTION

MEDLINE, EMBASE, CINAHL, and the Cochrane Library were searched for reports on adult ICU patients who were evaluated for CINMA clinically and electrophysiologically. Studies were included if they contained sufficient data to quantify the association between CINMA and relevant exposures and/or outcome variables.

MEASUREMENTS AND RESULTS

CINMA was diagnosed in 655 of 1421 [46% (95% confidence interval 43-49%)] adult ICU patients enrolled in 24 studies, all with inclusion criteria of sepsis, multi-organ failure, or prolonged mechanical ventilation. Diagnostic criteria for CINMA were not uniform, and few reports unequivocally differentiated between polyneuropathy, myopathy, and mixed types of CINMA. The risk of CINMA was associated with hyperglycemia (and inversely associated with tight glycemic control), the systemic inflammatory response syndrome, sepsis, multiple organ dysfunction, renal replacement therapy, and catecholamine administration. Across studies, there was no consistent relationship between CINMA and patient age, gender, severity of illness, or use of glucocorticoids, neuromuscular blockers, aminoglycosides, or midazolam. Unadjusted mortality was not increased in the majority of patients with CINMA, but mechanical ventilation and ICU and hospital stay were prolonged.

CONCLUSIONS

The risk of CINMA is nearly 50% in ICU patients with sepsis, multi-organ failure, or protracted mechanical ventilation. The association of CINMA with frequently cited CINMA risk factors (glucocorticoids, neuromuscular blockers) and with short-term survival is uncertain. Available data indicate glycemic control as a potential strategy to decrease CINMA risk.

Simplified electrophysiological evaluation of peripheral nerves in critically ill patients: the Italian multi-centre CRIMYNE study

Introduction

Critical illness myopathy and/or neuropathy (CRIMYNE) is frequent in intensive care unit (ICU) patients. Although complete electrophysiological tests of peripheral nerves and muscles are essential to diagnose it, they are time-consuming, precluding extensive use in daily ICU practice. We evaluated whether a simplified electrophysiological investigation of only two nerves could be used as an alternative to complete electrophysiological tests.

Methods

In this prospective, multi-centre study, 92 ICU patients were subjected to unilateral daily measurements of the action potential amplitude of the sural and peroneal nerves (compound muscle action potential [CMAP]). After the first ten days, complete electrophysiological investigations were carried out weekly until ICU discharge or death. At hospital discharge, complete neurological and electrophysiological investigations were performed.

Results

Electrophysiological signs of CRIMYNE occurred in 28 patients (30.4%, 95% confidence interval [CI] 21.9% to 40.4%). A unilateral peroneal CMAP reduction of more than two standard deviations of normal value showed the best combination of sensitivity (100%) and specificity (67%) in diagnosing CRIMYNE. All patients developed the electrophysiological signs of CRIMYNE within 13 days of ICU admission. Median time from ICU admission to CRIMYNE was six days (95% CI five to nine days). In 10 patients, the amplitude of the nerve action potential dropped progressively over a median of 3.0 days, and in 18 patients it dropped abruptly within 24 hours. Multi-organ failure occurred in 21 patients (22.8%, 95% CI 15.4% to 32.4%) and was strongly associated with CRIMYNE (odds ratio 4.58, 95% CI 1.64 to 12.81). Six patients with CRIMYNE died: three in the ICU and three after ICU discharge. Hospital mortality was similar in patients with and without CRIMYNE (21.4% and 17.2%; p = 0.771). At ICU discharge, electrophysiological signs of CRIMYNE persisted in 18 (64.3%) of 28 patients. At hospital discharge, diagnoses in the 15 survivors were critical illness myopathy (CIM) in six cases, critical illness polyneuropathy (CIP) in four, combined CIP and CIM in three, and undetermined in two.

Conclusion

A peroneal CMAP reduction below two standard deviations of normal value accurately identifies patients with CRIMYNE. These should have full neurological and neurophysiological evaluations before discharge from the acute hospital.

ICU-Acquired Weakness

Observational studies of patients receiving prolonged mechanical ventilation and other forms of critical care support have determined acquired neuromuscular disorders to be extremely common. Early studies used electrophysiologic investigations to diagnose critical illness polyneuropathy (CIP) and muscle biopsy to confirm critical illness myopathy (CIM). More recent approaches seek to obviate these invasive techniques and build on a standardized bedside neuromuscular examination to identify patients with acquired weakness syndromes. Serial examination in the alert patient may serve as a reasonable prognosticator for most patients. The importance of ICU-acquired weakness syndromes is supported by the observation that muscle wasting and weakness are among the most prominent long-term complications of survivors of ARDS. In addition, a strong association appears to exist between acquired weakness and protracted ventilator dependence, an important determinant of ICU length of stay. Multivariate analysis has identified several risk factors associated with increased incidence for ICU-acquired weakness, including severe systemic inflammation, medications (specifically, corticosteroids and neuromuscular blocking agents), glycemic control, and immobility. We advocate an approach to this common syndrome that identifies risk factors early in the hope of minimizing their impact.

[Neuromuscular complications in transplant recipients]

Neuromuscular complications in transplant recipients are common and contribute to morbidity and mortality. Complications such as acute and chronic inflammatory demyelinating polyneuropathies and toxic myopathies are related to the changes in immune modulation that occur after transplantation or result from immunosuppressive treatment toxicity. Alternatively, other complications such as myositis, myasthenia gravis, and mononeuropathy multiplex may result from a dysimmune systemic disorder such as post-transplant lymphoproliferative disorder, graft-versus-host disease or hepatitis C virus or hepatitis B virus chronic infection. Lastly, some of these complications, e.g., compression or stretch of individual nerves or plexus, are commonly seen in a postoperative setting and are not specific of patients with organ transplantation. This review focuses on the characteristic features, management, prognosis and pathophysiology of common and immune-related neuromuscular complications in organ transplant recipients.

Effects of chronic sepsis on rat motor units: Experimental study of critical illness polyneuromyopathy

Critical illness polyneuromyopathy (CIP) leads to major muscle weakness correlated with peripheral nerve and/or muscle alterations. Because sepsis seems to be the main factor, we used an experimental model of chronic sepsis in rats to study the localization of the first alterations on isolated motor units of soleus muscle. Seven days of chronic sepsis leads to a decrease in muscle force and an increase in muscle fatigability. Muscle twitch contraction time is also slower and all the motor units exhibit a slow profile in septic rats. Motor axon conduction velocity remains normal. We observed a significant increase in the latency between nerve and muscle action potentials but no modifications in the electromechanical delay. The first action of sepsis on motor units seems to be a delayed trigger of muscle action potential along with a muscle weakness but without nerve conduction impairment.

The syndrome of rhabdomyolysis: Pathophysiology and diagnosis

Rhabdomyolysis is defined as a pathological condition of skeletal muscle cell damage leading to the release of toxic intracellular material into the blood circulation. Its major causes include trauma, ischemia, drugs, toxins, metabolic disorders, and infections. The pathophysiological hallmark of the syndrome is an increase in intracellular free ionized calcium due to either cellular energy depletion, or direct plasma membrane rupture. The increased intracellular calcium activates several proteases, intensifies skeletal muscle cell contractility, induces mitochondrial dysfunction, and increases the production of reactive oxygen species, ultimately resulting in skeletal muscle cell death. Clinically, the syndrome presents with severe muscular pain, weakness and myoglobinuria. Increased myoglobin and creatine phosphokinase as a consequence of muscular cell death are the major laboratory findings, which, in combination with the clinical presentation, lead the clinician to the final diagnosis of the syndrome.

Critical illness polyneuropathy and myopathy in pediatric intensive care: A review

OBJECTIVE

To review the medical literature on critical illness polyneuropathy and myopathy in childhood.

DATA SOURCE

Medline and EMBASE were searched using the following terms: critical illness (neuropathy, polyneuropathy, and myopathy), critical care (neuropathy, polyneuropathy, and myopathy), acute myopathy, acute necrotizing myopathy, children, and pediatric. The references listed in publications thus identified were also reviewed.

STUDY SELECTION AND DATA EXTRACTION

All studies relating to pediatric critical illness polyneuropathy and myopathy were included. The adult literature was also reviewed as to the current understanding of critical illness polyneuropathy and myopathy.

DATA SYNTHESIS

Critical illness polyneuropathy and critical illness myopathy are well recognized in adults, in whom they commonly cause generalized weakness and muscle wasting, with failure to wean from mechanical ventilation. Critical illness polyneuropathy and critical illness myopathy are reported in 32-100% of critically ill adult patients ventilated for >3 days. There is significant clinical and neurophysiologic overlap between the two conditions, such that the term critical illness polyneuropathy and myopathy (CIPNM) is often used. Critical illness polyneuropathy and critical illness myopathy have only occasionally been reported in childhood, and little is known of their prevalence or clinical significance in this population. This article summarizes the pediatric literature on critical illness polyneuropathy and critical illness myopathy and highlights areas for future research in critically ill children.

CONCLUSIONS

Critical illness polyneuropathy and myopathy may cause significant morbidity in critically ill children. These conditions seem to be clinically and electrophysiologically similar in children and adults, but prospective studies of these entities are required to better characterize their frequency, natural history, and clinical significance in pediatric practice.

Neuromuscular Sequelae in Survivors of Acute Lung Injury

Pulmonary function improves rapidly in most survivors of ALI, yet most have profound and life-altering physical impairment. critical illness polyneuropathy and myopathy (CIPM) are complications that may account for most long-term disability. Short-term morbidity includes difficulty weaning from mechanical ventilation, return to assisted breathing after weaning, and delayed return home after hospital discharge. Therapies that reduce sepsis and prolonged mechanical ventilation may minimize CIPM, as in intensive insulin treatment of ICU hyperglycemia. CIPM identification is important for ALI patients' care and prognostication. Observational studies are needed to understand the epidemiology and natural history of CIPM; interventional studies with CIPM and functional outcomes as major endpoints are essential for improvement of ALI patients' health and quality of life.

Impact of intensive insulin therapy on neuromuscular complications and ventilator dependency in the medical intensive care unit

RATIONALE

Critical illness polyneuropathy/myopathy causes limb and respiratory muscle weakness, prolongs mechanical ventilation, and extends hospitalization of intensive care patients. Besides controlling risk factors, no specific prevention or treatment exists. Recently, intensive insulin therapy prevented critical illness polyneuropathy in a surgical intensive care unit.

OBJECTIVES

To investigate the impact of intensive insulin therapy on polyneuropathy/myopathy and treatment with prolonged mechanical ventilation in medical patients in the intensive care unit for at least 7 days.

METHODS

This was a prospectively planned subanalysis of a randomized controlled trial evaluating the effect of intensive insulin versus conventional therapy on morbidity and mortality in critically ill medical patients. All patients who were still in intensive care on Day 7 were screened weekly by electroneuromyography. The effect of intensive insulin therapy on critical illness polyneuropathy/myopathy and the relationship with duration of mechanical ventilation were assessed.

MEASUREMENTS AND MAIN RESULTS

Independent of risk factors, intensive insulin therapy reduced incidence of critical illness polyneuropathy/myopathy (107/212 [50.5%] to 81/208 [38.9%], p = 0.02). Treatment with prolonged (> or = 14 d) mechanical ventilation was reduced from 99 of 212 (46.7%) to 72 of 208 (34.6%) (p = 0.01). This was statistically only partially explained by prevention of critical illness polyneuropathy/myopathy.

CONCLUSION

In a subset of medical patients in the intensive care unit for at least 7 days, enrolled in a randomized controlled trial of intensive insulin therapy, those assigned to intensive insulin therapy had a reduced incidence of critical illness polyneuropathy/myopathy and were treated with prolonged mechanical ventilation less frequently.

Acute neuromuscular weakness in the intensive care unit

INTRODUCTION

Patients in the intensive care unit develop generalized weakness due to a number of factors. Neuromuscular weakness is a common cause of failure to wean from the ventilator and decreased limb movements. A rational approach to evaluation of weakness will help to identify most of the common causes of neuromuscular weakness in the intensive care unit.

AIMS

This review provides an analysis of neuromuscular weakness and a practical algorithm to assist in diagnostic evaluation.

CONCLUSIONS

The most common acquired causes of weakness in the critically ill patient in the intensive care unit are critical illness polyneuropathy and critical illness myopathy. In the intensive care unit setting, electrophysiological studies, biopsies, and imaging studies are often necessary to complement the clinical impression.

Critical illness polyneuropathy and myopathy: clinical features, risk factors and prognosis

Acquired neuromuscular weakness due to critical illness polyneuropathy and myopathy (CIPNM) frequently develops in patients hospitalized in the intensive care unit for more than 1 week. CIPNM may present with muscle weakness and failure to wean from mechanical ventilation, but is discovered more often and earlier by electrophysiological examination. In this review, the incidence, clinical and electrophysiological features, differential diagnosis and prognosis of CIPNM will be described. Risk factors for CIPNM are sepsis or systemic inflammatory response syndrome and the severity of multi-organ failure. Presence of CIPNM is associated with higher mortality rate, prolonged duration of mechanical ventilation and prolonged rehabilitation. The majority of survivors with CIPNM have persistent functional disabilities and a reduced quality of life. There is need for new therapeutic strategies to prevent or minimize CIPNM in critically ill patients.

Brief review: Nondepolarizing neuromuscular blocking drugs and critical illness myopathy

PURPOSE

Critically-ill patients who receive nondepolarizing neuromuscular blocking drugs (NMBDs) may be at risk of developing profound muscle weakness that may last for months after the NMBD is discontinued, especially when large cumulative doses of NMBDs and corticosteroids are co-administered to septic, mechanically ventilated patients. This review focuses on the etiology and clinical features of critical illness myopathy (CIM), summarizes specific risk factors for its development, and discusses strategies that might be used to attenuate or even prevent the development of this potentially devastating syndrome.

CLINICAL FEATURES

The etiology of CIM is unknown. Whether it can develop in at-risk patients who undergo lengthy operations during which they receive NMBDs is also unknown. In some patients following exposure to NMBDs their motor systems are impaired secondary to loss of thick (myosin) filaments that render the muscle unexcitable to direct electrical stimulation, while the sensory system is spared. Management of patients who develop NMBD myopathy is supportive, consisting of nutritional support, physical therapy, and daily trials of decreased ventilatory support.

CONCLUSION

Recent guidelines recommend that NMBDs be used in critically ill patients only when absolutely necessary, that the depth of muscle paralysis be monitored to avoid overdosing and metabolite accumulation, and that drug administration be curtailed periodically to allow interruption of sustained NMBD effect.

Acute rhabdomyolysis complicating status asthmaticus in children: case series and review

OBJECTIVES

To describe a case series of 4 children who developed acute rhabdomyolysis as a complication of acute respiratory failure secondary to status asthmaticus.

METHODS

A retrospective review of all children who were admitted to our pediatric intensive care unit (PICU) with status asthmaticus from November 1998 through July 2004 was performed and all children who developed acute rhabdomyolysis, defined as a 5-fold increase above the upper limit of normal in the serum creatine phosphokinase (CPK) concentration (CPK > or = 1250 IU/L), were identified. Demographic and clinical data were abstracted from the medical record.

RESULTS

During the study period, 108 children with status asthmaticus were admitted to our PICU (3.6% of all admissions). Four children (age 12-19 years) developed acute respiratory failure requiring mechanical ventilation, and all 4 of these children (3.7% of all children with status asthmaticus admitted to the PICU) developed acute rhabdomyolysis. The 4 children who developed acute rhabdomyolysis were older than the children with status asthmaticus, without rhabdomyolysis (median age 15 years vs. 5 years).

CONCLUSIONS

Acute rhabdomyolysis complicating status asthmaticus may be more common than previously ascertained. We therefore suggest that CPK levels should be followed closely in all children with status asthmaticus and acute respiratory failure. The early presentation of rhabdomyolysis in the current series suggests that factors other than corticosteroids and neuromuscular blockers are potentially involved. Mechanical ventilation and older age seem to be significant risk factors for rhabdomyolysis, perhaps implicating a mechanism similar to the pathogenesis of severe exercise-related rhabdomyolysis. Further clinical study of the incidence and causative factors of rhabdomyolysis in this population is warranted.

Dysregulation of sodium channel gating in critical illness myopathy

Critical illness myopathy (CIM) is the most common caused of acquired weakness in critically ill patients. While atrophy of muscle fibers causes weakness, the primary cause of acute weakness is loss of muscle excitability. Studies in an animal model of CIM suggest that both depolarization of the resting potential and a hyperpolarized shift in the voltage dependence of sodium channel gating combine to cause inexcitability. In active adult skeletal muscle the only sodium channel isoform expressed is Nav1.4. In the animal model of CIM the Nav1.5 sodium channel isoform is upregulated, but the majority of sodium current is still carried by Nav1.4 sodium channels. Experiments using toxins to selectively bock the Nav1.4 isoform demonstrated that the cause of the hyperpolarized shift in sodium channel inactivation is a hyperpolarized shift in inactivation of the Nav1.4 isoform. These data suggest that CIM represents a new type of ion channel disease in which altered gating of sodium channels is due to improper regulation of the channels rather than mutation of channels or changes in isoform expression. The hypothesis that dysregulation of sodium channel gating underlies inexcitability of skeletal muscle in CIM raises the possibility that there maybe dysregulation of sodium channel gating in other tissues in critically ill patients. We propose that there is a syndrome of reduced electrical excitability in critically ill patients that affects skeletal muscle, peripheral nerve, the heart and central nervous system. This syndrome manifests as CIM, critical illness polyneuropathy, reduced cardiac contractility and septic encephalopathy.

Neuromuscular disorders in medical and surgical ICUs: case studies in critical care neurology

The differential diagnosis of generalized weakness in ICU patients is quite broad. Although neuromuscular disorders are the most common causes of generalized weakness, a thorough evaluation is necessary to delineate the underlying cause of weakness. Biochemical studies, neuroimaging, and electrophysiologic studies help to delineate most of the common disorders associated with weakness. Prompt identification of a neurologic disorder and initiation of therapy speeds up recovery and reduces morbidity and mortality in these patients.

High dexamethasone concentration prevents stimulatory effects of TNF-alpha and LPS on IL-6 secretion from the precursors of human muscle regeneration

A frequent finding in patients surviving critical illness myopathy is chronic muscle dysfunction. Its pathogenesis is mostly unknown; one explanation could be that muscle regeneration, which normally follows myopathy, is insufficient in these patients because of a high glucocorticoid level in their blood. Glucocorticoids can prevent stimulatory effects of proinflammatory factors on the interleukin (IL)-6 secretion, diminishing in this way the autocrine and paracrine IL-6 actions known to stimulate proliferation at the earliest, myoblast stage of muscle formation. To test this hypothesis, we compared the effects of major proinflammatory agents [tumor necrosis factor (TNF)-alpha and endotoxin lipopolysaccharide (LPS)] on the IL-6 secretion from the muscle precursors and then studied the influence of dexamethasone (Dex) on these effects. Mononuclear myoblasts, which still proliferate, were compared with myotubes in which this capacity is already lost. For correct interpretation of results, cultures were examined for putative apoptosis and necrosis. We found that constitutive secretion of IL-6 did not differ significantly between myoblasts and myotubes; however, the TNF-alpha- and LPS-stimulated IL-6 release was more pronounced (P < 0.001) in myoblasts. Dex, applied at the 0.1-100 nM concentration range, prevented constitutive and TNF-alpha- and LPS-stimulated IL-6 release at both developmental stages but only at high concentration (P < 0.01). Although there are still missing links to it, our results support the concept that high concentrations of glucocorticoids, met in critically ill patients, prevent TNF-alpha- and LPS-stimulated IL-6 secretion. This results in reduced IL-6-mediated myoblast proliferation, leading to the reduced final mass of the regenerated muscle.

Critical illness myopathy: what is happening?

PURPOSE OF REVIEW

The current review focuses on recent studies, both clinical and from basic sciences, which approach possible pathomechanisms of critical illness myopathy in order to better derive potential clinical strategies for a preventive or curative clinical setting. Trends and concepts of clinical diagnosis and handling will be evaluated and their implications for muscle physiology and nutritional/metabolic intervention discussed.

RECENT FINDINGS

Conventional electrophysiology was combined with direct muscle stimulation to better differentiate critical illness myopathy from other neuromuscular disorders in critical illness. Muscle weakness was the result of impaired excitation-contraction-coupling at the level of the sarcolemma and the sarcoplasmic reticulum membrane. Critical illness may alter sodium and ryanodine receptor calcium-release channels. Also, increased muscle proteolysis contributes to weakness in critical illness myopathy. Myosin loss is due to the risk factors systemic inflammatory response syndrome/sepsis, steroids and neuromuscular blocking agents. Steroids can also induce necrosis and apoptosis in muscle. Inflammatory mediators aggravated muscle metabolic failure in critical illness myopathy. Ubiquitin-proteasome pathways, cyclooxygenase activation, altered glucose transporter expression, MyoD suppression, impaired respiratory chain enzymes, ATP depletion, glucose toxicity and insulin resistance can all contribute to the critical illness myopathy pathomechanism.

SUMMARY

The search for pathomechanisms is an important task for both clinical and basic sciences. Targets for treatment or prevention of critical illness myopathy include systemic inflammatory response, increased proteolysis and reduced antioxidative capacitance in critically ill patients.