Mechanisms of neuromuscular dysfunction in critical illness

Pathophysiological role of connexin and pannexin hemichannels in neuromuscular disorders

A growing body of research has provided evidence that de novo expression of connexin hemichannels and upregulation of pannexin hemichannels (Cx HCs and Panx HCs, respectively) in the cytoplasmic membrane of skeletal muscle (sarcolemma) are critical steps in the pathogenesis of muscle dysfunction of many genetic and acquired muscle diseases. This review provides an overview of the current understanding of the molecular mechanisms regulating the expression of Cx and Panx HCs in skeletal muscle, as well as their roles in both muscle physiology and pathologies. Additionally, it addresses existing gaps in knowledge and outlines future challenges in the field.

Clinical and Epidemiological Characteristics of Patients with COVID-19 Admitted to the Intensive Care Unit: A Two-Year Retrospective Analysis

In March 2020, COVID-19 was characterized as a pandemic by the World Health Organization. Hospitalized patients affected by COVID-19 presented with severe respiratory and motor impairment, especially those who required intensive treatment and invasive mechanical ventilation, with sequelae that extended after the period of hospitalization. Thus, the aim of the current study was to verify the clinical and epidemiological characteristics of patients with COVID-19 admitted to the Intensive Care Unit in 2020 and 2021, according to age group. Methods: A retrospective cohort study. Data were collected through the “ICUs Brasileiras” between March 2020 and November 2021 for severe acute respiratory syndrome (SARS) due to COVID-19. The following were analyzed: the number of hospital admissions, days in the ICU and hospital, clinical aspects (non-invasive or invasive ventilatory support, comorbidities, frailty, SAPS 3 and SOFA severity scales, use of amines and renal support), and ICU and hospital mortality rate. Results: A total of 166,966 ICU hospital admissions were evaluated over the evaluated quarters. The main results showed a peak in the number of hospitalizations between March and May 2021, with a higher percentage of males. The peak of ICU admissions for 7 days was between March and May 2021 and 21 days between March and May 2020. In addition, higher deaths were observed in the age groups between 40 and 80 years between 2020 and 2021, with the group above 81 being the age group with the highest mortality. Mortality in the ICU of ventilated patients was higher in the age group above 70 years. Another observation was the predominance of SAPS 3 and the peak of mechanical ventilation for more than 7 days between June and August 2021. Conclusion: The clinical and epidemiological characteristics of patients with COVID-19 were influenced by age group, showing higher mortality over 81 years and over 70 years in the ICU supported by mechanical ventilation, maintained for 7 days from June to August 2021. The years 2020 and 2021 also showed differences for patients with COVID-19, with greater hospitalization between March and May 2021, especially in the ICU for 7 days, and between March and May 2020 for the 21-day period.

Molecular Mechanisms Underlying Intensive Care Unit-Acquired Weakness and Sarcopenia

Skeletal muscle is a highly adaptable organ, and its amount declines under catabolic conditions such as critical illness. Aging is accompanied by a gradual loss of muscle, especially when physical activity decreases. Intensive care unit-acquired weakness is a common and highly serious neuromuscular complication in critically ill patients. It is a consequence of critical illness and is characterized by a systemic inflammatory response, leading to metabolic stress, that causes the development of multiple organ dysfunction. Muscle dysfunction is an important component of this syndrome, and the degree of catabolism corresponds to the severity of the condition. The population of critically ill is aging; thus, we face another negative effect-sarcopenia-the age-related decline of skeletal muscle mass and function. Low-grade inflammation gradually accumulates over time, inhibits proteosynthesis, worsens anabolic resistance, and increases insulin resistance. The cumulative consequence is a gradual decline in muscle recovery and muscle mass. The clinical manifestation for both of the above conditions is skeletal muscle weakness, with macromolecular damage, and a common mechanism-mitochondrial dysfunction. In this review, we compare the molecular mechanisms underlying the two types of muscle atrophy, and address questions regarding possible shared molecular mechanisms, and whether critical illness accelerates the aging process.

Protective Effects of Glutamine and Leucine Supplementation on Sepsis-Induced Skeletal Muscle Injuries

This study investigated the effects of l-glutamine (Gln) and/or l-leucine (Leu) administration on sepsis-induced skeletal muscle injuries. C57BL/6J mice were subjected to cecal ligation and puncture to induce polymicrobial sepsis and then given an intraperitoneal injection of Gln, Leu, or Gln plus Leu beginning at 1 h after the operation with re-injections every 24 h. All mice were sacrificed on either day 1 or day 4 after the operation. Blood and muscles were collected for analysis of inflammation and oxidative damage-related biomolecules. Results indicated that both Gln and Leu supplementation alleviated sepsis-induced skeletal muscle damage by reducing monocyte infiltration, calpain activity, and mRNA expression levels of inflammatory cytokines and hypoxia-inducible factor-1α. Furthermore, septic mice treated with Gln had higher percentages of blood anti-inflammatory monocytes and muscle M2 macrophages, whereas Leu treatment enhanced the muscle expressions of mitochondrion-related genes. However, there were no synergistic effects when Gln and Leu were simultaneously administered. These findings suggest that both Gln and Leu had prominent abilities to attenuate inflammation and degradation of skeletal muscles in the early and/or late phases of sepsis. Moreover, Gln promoted the switch of leukocytes toward an anti-inflammatory phenotype, while Leu treatment maintained muscle bioenergetic function.

Dynamic inhomogeneity of aeration along the vertical axis of the lung may predict weaning failure regardless of diaphragm dysfunction

PURPOSE

This study aimed to investigate dynamic changes of lung aeration during a spontaneous breathing trial (SBT) in patients with diaphragm dysfunction (DD) and to predict weaning failure using electrical impedance tomography (EIT).

MATERIALS AND METHODS

We enrolled 40 adult patients who received mechanical ventilation over 48 h and were eligible for SBT with a T-piece. All patients were screened for DD using ultrasonography before SBT. EIT data, including global inhomogeneity index (an off-site parameter), and temporal skew of aeration (TSA) (an on-site parameter) were collected.

RESULTS

Sixteen (40%) patients had DD. During SBT, the tidal impedance variation decreased by 32% from baseline in patients with DD and by 14% in those without DD (p = 0.001). The global inhomogeneity index in the SBT failure group (n = 9) was 0.92 (median), and that of the SBT success group was 0.65 (p = 0.004). The TSA along the vertical axis of the lung was 12.0% and 2.0%, respectively (p = 0.001). With a vertical TSA cutoff of ≥4.35%, SBT failure was predicted with a sensitivity of 88.9% and specificity of 96.9% (area under the curve: 0.955).

CONCLUSION

Dynamic inhomogeneity of aeration along the vertical axis of the lung as assessed using TSA predicts SBT failure regardless of DD.

TRIAL REGISTRATION

This trial was retrospectively registered at cris.nih.go.kr (identifier: KCT003567; release date February 27, 2019).

Characteristics, treatments, and prognosis of a critical illness polyneuromyopathy patient with positive anti-GM1 after severe traumatic brain injury: A case report

To investigate the clinical features, treatment and prognosis of critical illness polyneuromyopathy (CIPNM) in patients with severe traumatic brain injury (sTBI) who had positive anti-ganglioside GM1 (anti-GM1) antibody IgG. A case of CIPNM with positive anti-GM1 antibody IgG was retrospectively analysed and followed-up for 30 months. After 1 week of treatment with large dose of short-term glucocorticoid and human immunoglobulin, the muscle strength of both lower extremities was restored to grade 1. Three months later, the muscle strength and muscle tension of the patient's limbs returned to normal except for grade 3 of bilateral dorsal extensor muscle strength. In addition, the patient can walk alone with a waddling gait. After 30 months, there was no recurrence. The application of large dose of short-term glucocorticoid and human immunoglobulin to CIPNM that are positive for anti-GM1 antibodies may be an effective treatment.

Diaphragmatic speckle tracking imaging for 2D-strain assessment in mechanical ventilation weaning test

Ultrasound (US) is recognized as a useful tool for detecting lung physiology and pathology. Lung US is compared with standard techniques for evaluating lung structure and function such as computed tomography and pulmonary function tests. At present, markers of normal physiology and pathology are detected using expected image patterns. Detecting the latter depends on the experience of the operator. Diaphragmatic dysfunction is a particularly frequent problem in intensive care. Diaphragmatic dysfunction is easily assessed using lung US. Speckle tracking analysis, a known method for assessing tissue displacement and deformation in cardiology, is proposed to be utilized in lung US for detecting and quantifying lung sliding. Using speckle tracking analysis to diaphragmatic deformation quantification could be an informative and new tool for weaning from mechanical ventilation.

Evaluation on the effect of acupuncture on patients with sepsis-induced myopathy (ACU-SIM pilot study): A single center, propensity-score stratified, assessor-blinded, prospective pragmatic controlled trial

BACKGROUND

Sepsis-induced myopathy (SIM) is a disease that causes motor dysfunction in patients with sepsis. There is currently no targeted treatment for this disease. Acupuncture has shown considerable efficacy in the treatment of sepsis and muscle weakness. Therefore, our research aims to explore the effects of acupuncture on the improvement of muscle structure and function in SIM patients and on activities of daily living.

METHODS

The ACU-SIM pilot study is a single-center, propensity-score stratified, assessor-blinded, prospective pragmatic controlled trial (pCT) with a 1-year follow-up period. This study will be deployed in a multi-professional critical care department at a tertiary teaching hospital in Guangzhou, China. Ninety-eight intensive care unit subjects will be recruited and assigned to either the control group or the acupuncture group. Both groups will receive basic treatment for sepsis, and the acupuncture group will additionally receive acupuncture treatment. The primary outcomes will be the rectus femoris cross-sectional area, the Medical Research Council sum-score and time-to-event (defined as all-cause mortality or unplanned readmission to the intensive care unit due to invasive ventilation). The activities of daily living will be accessed by the motor item of the Functional Independence Measure. Recruitment will last for 2 years, and each patient will have a 1-year follow-up after the intervention.

DISCUSSION

There is currently no research on the therapeutic effects of acupuncture on SIM. The results of this study may contribute to new knowledge regarding early muscle atrophy and the treatment effect of acupuncture in SIM patients, and the results may also direct new approaches and interventions in these patients. This trial will serve as a pilot study for an upcoming multicenter real-world study.

TRIAL REGISTRATION

Chinese Clinical Trials Registry: ChiCTR-1900026308, registered on September 29th, 2019.

Related factors of the nursing diagnosis ineffective breathing pattern in an intensive care unit

OBJECTIVE

to identify the predicting factors and sensitivity, specificity, positive and negative related value of nursing diagnosis Ineffective Breathing Pattern among patients of an intensive care unit.

METHOD

cross-sectional study. A logistic regression was fitted to assess the simultaneous effects of related factors.

RESULTS

among the 120 patients, 67.5% presented Ineffective Breathing Pattern. In the univariate analysis, the related factors were: group of diseases, fatigue, obesity and presence of bronchial secretion, and the defining characteristics were: changes in respiratory depth, auscultation with adventitious sounds, dyspnea, reduced vesicular murmurs, tachypnea, cough and use of the accessory musculature to breathe. The mean age of patients with was higher than those without this diagnosis. The defining characteristics reduced murmurs had high sensitivity (92.6%), specificity (97.4%), negative related value (86.4%) and positive related value (98.7%). The related factors of Ineffective Breathing Pattern were the related factors fatigue, age and group of diseases.

CONCLUSION

fatigue, age and patients with a group of diseases were related factors of Ineffective Breathing Pattern in this study. Reduced vesicular murmurs, auscultation with adventitious sounds and cough may be defining characteristics to be added in the international classification, as well as the related factors bronchial secretion and group of diseases.

Effects of Neuromuscular Electrical Stimulation of the Quadriceps and Diaphragm in Critically Ill Patients: A Pilot Study

Background

Deep and respiratory muscle disorders are commonly observed in critically ill patients. Neuromuscular electrical stimulation (NMES) is an alternative to mobilize and to exercise that does not require active patient participation and can be used on bedridden patients.

Objective

Evaluate the effectiveness of the NMES therapy in quadriceps versus diaphragm subjects in mechanical ventilation (MV).

Methods

Sixty-seven subjects in MV were included, divided into 3 groups: (a) control group (CG, n=26), (b) stimulation of quadriceps (quadriceps group–QG, n=24), and (c) stimulation of diaphragm (diaphragm group–DG, n=17). The QG and DG patients received consecutive daily electrical stimulation sessions at specific points from the first day of randomization until ICU discharge. Respiratory and peripheral muscle strength, MV time, length of hospitalization, and functional independence score (the Functional Status Score-ICU) were recorded.

Results

There were studied n=24 (QG), n=17 (DG), and n=26 (CG) patients. Peripheral muscle strength improved significantly in the QG (p=0.030). Functional independence at ICU discharge was significantly better in QG (p=0.013), and the QG presented a better Barthel Index compared to DG and CG (p=0.0049) and also presented better FSS compared to CG (p=0.001).

Conclusions

Electrical stimulation of quadriceps had best outcomes for peripheral muscle strength compared with controls or electrical stimulation of diaphragm among mechanically ventilated critically ill subjects and promoted functional independence and decreased length of hospitalization.

Diaphragmatic ultrasonography for predicting ventilator weaning: A meta-analysis

BACKGROUND

Weaning failure is common in mechanically ventilated patients. Whether ultrasound can predict weaning outcome remains controversial. This meta-analysis was performed to assess the accuracy of diaphragmatic ultrasonography for predicting reintubation within 48 hours of extubation.

METHODS

Literature search was performed in PubMed, Embase, and Cochrane Library to identify all the relevant papers, published in English up to July 16, 2017. Eligible studies were included if data were in adequate details to rebuild 2 × 2 contingency tables. Methodological quality of the included studies was evaluated using the Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2) in Review Manager 5.3. The sensitivity, specificity, positive likelihood ratio (PLR), negative likelihood ratio (NLR), diagnostic odds ratio (DOR), and summary receiver operating characteristic (SROC) curve were pooled using the fixed or random effects model, meanwhile, the heterogeneity was evaluated using Cochran Q test and I statistics in Meta-DiSc 1.4. Publication bias was assessed using Deeks funnel plot in Stata 12.0.

RESULTS

Thirteen studies with 742 subjects were included in this meta-analysis. The pooled sensitivities for diaphragm excursion (DE) and diaphragm thickness fraction (DTF) were 0.786 and 0.893, and the pooled specificities were 0.711 and 0.796, respectively. The area under curve (AUC) for DE and DTF were 0.8590 and 0.8381. The DORs for DE and DTF were 10.623 and 32.521. No publication bias was observed among these studies.

CONCLUSIONS

Diaphragmatic ultrasonography is a promising tool for predicting reintubation within 48 hours of extubation. However, due to heterogeneities among the included studies, large-scale studies are warranted to confirm our findings.

Using M-mode ultrasonography to assess diaphragm dysfunction and predict the success of mechanical ventilation weaning in elderly patients

Background

Ultrasonography (US) is a non-invasive and commonly available bedside diagnostic tool. The aim of this study was to assess the utility of M-mode US on ventilator weaning outcomes in elderly patients.

Methods

This was a single center, prospective, observational study in patients aged 80 years or older who were in the medical intensive care unit, had undergone mechanical ventilation for >48 hours, and met the criteria for a spontaneous breathing trial (SBT). For 30 minutes at the start of SBT, each hemi-diaphragmatic movement and the velocity of contraction were evaluated by M-mode US. The the area under the receiver operating characteristic curve (AUROC) was calculated to determine the ability for measured variables to predict successful ventilator weaning.

Results

Forty patients were enrolled and assessed, grouped by those who had US-diagnosed diaphragm dysfunction (DD; 30/40; 75%) and those who did not (10/40; 25%). Patients with DD had a significantly longer total mechanical ventilation duration (536.4±377.05 vs. 250±109.02 hours, P=0.02) and weaning time (425.9±268.31 vs. 216.0±134.22 hours, P=0.002) than patients without DD. Patients with DD also had a higher incidence of weaning failure than patients without DD (24/30 vs. 4/10, P=0.017). Analysis of the receiver operating characteristic (ROC) curve (ROC) curve showed that the optimal cut-off values to predict weaning success were >10.7 mm for the right diaphragmatic movement, and >21.32 mm/s for the right diaphragmatic velocity of contraction; AUROC were 0.839 (95% CI, 0.689-0.936) and 0.833 (95% CI, 0.682-0.932), respectively. The sensitivity, specificity, positive and negative likelihood ratios for predicting weaning success were 83.33% vs. 66.67%, 75.00% vs. 92.86%, 3.33 vs. 9.33, and 0.22 vs. 0.36, for right diaphragmatic movement and diaphragmatic contraction velocity, respectively.

Conclusions

When assessed by M-mode US, DD appeared to be common in ventilated patients aged 80 years or older and was associated with a higher incidence of weaning failure. Larger right diaphragmatic movements or faster right diaphragmatic contraction velocity appeared to be good predictors of mechanical ventilation weaning success in elderly patients.

Review of Critical Illness Myopathy and Neuropathy

Critical illness myopathy (CIM) and neuropathy are underdiagnosed conditions within the intensive care setting and contribute to prolonged mechanical ventilation and ventilator wean failure and ultimately lead to significant morbidity and mortality. These conditions are often further subdivided into CIM, critical illness polyneuropathy (CIP), or the combination-critical illness polyneuromyopathy (CIPNM). In this review, we discuss the epidemiology and pathophysiology of CIM, CIP, and CIPNM, along with diagnostic considerations such as detailed clinical examination, electrophysiological studies, and histopathological review of muscle biopsy specimens. We also review current available treatments and prognosis. Increased awareness and early recognition of CIM, CIP, and CIPNM in the intensive care unit setting may lead to earlier treatments and rehabilitation, improving patient outcomes.

[Critical illness polyneuropathy and myopathy as neurological complications of sepsis]

Intensive care unit acquired weakness (ICUAW) is a frequent and severe complication of intensive care management. Within ICUAW critical illness polyneuropathy (CIP) and myopathy (CIM) can be differentiated. The major symptom of ICUAW is progressive quadriparesis, which makes weaning from the respirator more difficult, can appear early after admission to an ICU and can often be detected several months after discharge from the ICU. The pathophysiology of ICUAW is multifactorial and complex. Potential therapeutic approaches are the early and sufficient therapy of mulitorgan dysfunction, optimal control of glucose levels as well as early and intensive physiotherapy. This review article discusses the data on incidence, pathophysiology, diagnostic approaches and prognosis of ICUAW.

Reduced motor neuron excitability is an important contributor to weakness in a rat model of sepsis

The mechanisms by which sepsis triggers intensive care unit acquired weakness (ICUAW) remain unclear. We previously identified difficulty with motor unit recruitment in patients as a novel contributor to ICUAW. To study the mechanism underlying poor recruitment of motor units we used the rat cecal ligation and puncture model of sepsis. We identified striking dysfunction of alpha motor neurons during repetitive firing. Firing was more erratic, and often intermittent. Our data raised the possibility that reduced excitability of motor neurons was a significant contributor to weakness induced by sepsis. In this study we quantified the contribution of reduced motor neuron excitability and compared its magnitude to the contributions of myopathy, neuropathy and failure of neuromuscular transmission. We injected constant depolarizing current pulses (5s) into the soma of alpha motor neurons in the lumbosacral spinal cord of anesthetized rats to trigger repetitive firing. In response to constant depolarization, motor neurons in untreated control rats fired at steady and continuous firing rates and generated smooth and sustained tetanic motor unit force as expected. In contrast, following induction of sepsis, motor neurons were often unable to sustain firing throughout the 5s current injection such that force production was reduced. Even when firing, motor neurons from septic rats fired erratically and discontinuously, leading to irregular production of motor unit force. Both fast and slow type motor neurons had similar disruption of excitability. We followed rats after recovery from sepsis to determine the time course of resolution of the defect in motor neuron excitability. By one week, rats appeared to have recovered from sepsis as they had no piloerection and appeared to be in no distress. The defects in motor neuron repetitive firing were still striking at 2weeks and, although improved, were present at one month. We infer that rats suffered from weakness due to reduced motor neuron excitability for weeks after resolution of sepsis. To assess whether additional contributions from myopathy, neuropathy and defects in neuromuscular transmission contributed to the reduction in force generation, we measured whole-muscle force production in response to electrical stimulation of the muscle nerve. We found no abnormality in force generation that would suggest the presence of myopathy, neuropathy or defective neuromuscular transmission. These data suggest disruption of repetitive firing of motor neurons is an important contributor to weakness induced by sepsis in rats and raise the possibility that reduced motor neuron excitability contributes to disability that persists after resolution of sepsis.

Critical Illness Neuromyopathy Complicating Akinetic Crisis in Parkinsonism: Report of 3 Cases

Akinetic crisis (AC) is a life-threatening complication of parkinsonism characterized by an acute severe akinetic-hypertonic state, consciousness disturbance, hyperthermia, and muscle enzymes elevation. Injectable dopaminomimetic drugs, high-dose methylprednisolone, and dantrolene are advocated as putative specific treatments. The course of the illness is frequently complicated by infections, pulmonary embolism, renal failure, disseminated intravascular coagulation, and cardiac arrhythmias. Critical illness neuromyopathy (CINM) is an acquired neuromuscular disorder characterized by flaccid quadriparesis and muscle enzyme elevation, often occurring in intensive care units and primarily associated with inactivity, sepsis, multiorgan failure, neuromuscular blocking agents, and steroid treatment. In 3 parkinsonian patients, during the course of AC we observed disappearance of rigidity but persistent hypoactivity. In all, neurological examination showed quadriparesis with loss of tendon reflexes and laboratory investigation disclosed a second peak of muscle enzymes elevation, following the first increment due to AC. Electrophysiological studies showed absent or reduced sensory nerve action potentials and compound muscular action potentials, myopathic changes, and fibrillation potentials at electromyography recordings, and reduced excitability or inexcitability of tibialis anterior at direct muscle stimulation, leading to a diagnosis of CINM in all 3 patients. In 1 patient, the diagnosis was also confirmed by muscle biopsy. Outcome was fatal in 2 of the 3 patients. Although AC is associated with most of the known risk factors for CINM, the cooccurrence of the 2 disorders may be difficult to recognize and has never been reported. We found that CINM can occur as a severe complication of AC, and should be suspected when hypertonia-rigidity subsides despite persistent akinesia. Strict monitoring of muscle enzyme levels may help diagnosis. This finding addresses possible caveats in the use of putative treatments for AC.

Physical activity, muscle strength, and exercise capacity 3 months after severe sepsis and septic shock

PURPOSE

To quantify the physical activity in daily life (PADL), muscle strength, and exercise capacity in the short and medium term in survivors of severe sepsis and septic shock.

METHODS

Prospective cohort study with a follow-up from hospital admission to 3 months after hospital discharge. Seventy-two patients admitted to the ICU for severe sepsis or septic shock and a control group of healthy sedentary subjects (n = 50) were enrolled. All patients had their PADL quantified by an accelerometer during their hospital stay and 3 months after. Exercise capacity and handgrip and quadriceps muscle strength were also evaluated.

RESULTS

During hospitalization, patients spent the majority of their time inactive in a lying or sitting position (90 ± 34% of daily time). Physical inactivity was partially reduced 3 months after (58 ± 20% of daily time). However, the time patients spent walking was only 63% of the time reported for healthy subjects. Patients also showed lower movement intensity when compared with controls (2.1 ± 0.3 vs 2.5 ± 0.4 m/s(2)). At hospital discharge, muscle strength and exercise capacity were approximately 54% of the predicted value, and these parameters showed significant increase in patients 3 months after (70% of predicted value). Multivariable analysis demonstrated that the use of systemic corticosteroids and hospitalization time negatively influenced quadriceps strength and exercise capacity at the time of hospital discharge.

CONCLUSION

Our results suggest that survivors of sepsis admitted to the ICU have a substantial reduction in physical activity, exercise capacity, and muscle strength compared to healthy subjects that persist even 3 months after hospital discharge.

The impact of extended bed rest on the musculoskeletal system in the critical care environment

Prolonged immobility is harmful with rapid reductions in muscle mass, bone mineral density and impairment in other body systems evident within the first week of bed rest which is further exacerbated in individuals with critical illness. Our understanding of the aetiology and secondary consequences of prolonged immobilization in the critically ill is improving with recent and ongoing research to establish the cause, effect, and best treatment options. This review aims to describe the current literature on bed rest models for examining immobilization-induced changes in the musculoskeletal system and pathophysiology of immobilisation in critical illness including examination of intracellular signalling processes involved. Finally, the review examines the current barriers to early activity and mobilization and potential rehabilitation strategies, which are being, investigated which may reverse the effects of prolonged bed rest. Addressing the deleterious effects of immobilization is a major step in treatment and prevention of the public health issue, that is, critical illness survivorship.

Neuromuscular complications of critical illness

Neuromuscular sequelae are common in the critically ill. Critical illness polyneuropathy and critical illness myopathy are neuromuscular complications of sepsis or iatrogenic complications of treatments required in intensive care. This article discusses the diagnosis, treatment, and prognosis of these disorders based on a literature review. This review found that glycemic control, early mobilization, and judicious use of steroids and neuromuscular blocking agents are the primary approaches to reduce the incidence and severity of neuromuscular complications in affected patients.

Acute and long-term dysphagia in critically ill patients with severe sepsis: results of a prospective controlled observational study

Dysphagia is a major risk factor for morbidity and mortality in critically ill patients treated in intensive care units (ICUs). Structured otorhinolaryngological data on dysphagia in ICU survivors with severe sepsis are missing. In a prospective study, 30 ICU patients with severe sepsis and thirty without sepsis as control group were examined using bedside fiberoptic endoscopic evaluation of swallowing after 14 days in the ICU (T1) and 4 months after onset of critical illness (T2). Swallowing dysfunction was assessed using the Penetration-Aspiration Scale (PAS). The Functional Oral Intake Scale was applied to evaluate the diet needed. Primary endpoint was the burden of dysphagia defined as PAS score >5. At T1, 19 of 30 severe sepsis patients showed aspiration with a PAS score >5, compared to 7 of 30 in critically ill patients without severe sepsis (p = 0.002). Severe sepsis and tracheostomy were independent risk factors for severe dysphagia with aspiration (PAS > 5) at T1 (p = 0.042 and 0.006, respectively). 4-month mortality (T2) was 57 % in severe sepsis patients compared to 20 % in patients without severe sepsis (p = 0.006). At T2, more severe sepsis survivors were tracheostomy-dependent and needed more often tube or parenteral feeding (p = 0.014 and p = 0.040, respectively). Multivariate analysis revealed tracheostomy at T1 as independent risk factor for severe dysphagia at T2 (p = 0.030). Severe sepsis appears to be a relevant risk factor for long-term dysphagia. An otorhinolaryngological evaluation of dysphagia at ICU discharge is mandatory for survivors of severe critical illness to plan specific swallowing rehabilitation programs.

Neuromuscular complications in intensive care patients

Increased survival of critically ill patients has focused the attention on secondary complications of intensive care unit (ICU) stay, mainly ICU-acquired weakness (ICUAW). ICUAW is relatively common with significant impact on recovery. Prolonging mechanical ventilation and overall hospitalization time, increased mortality, and persistent disability are the main problems associated with ICUAW. The chapter deals mainly with the differential diagnosis of neuromuscular generalized weakness that develops in the ICU, but focal ICUAW is reviewed too. The approach to the diagnosis and the yield of various techniques (mainly electrophysiological and histological) is discussed. Possible therapeutic interventions of this condition that modify the course of this deleterious situation and lead to better rehabilitation are discussed. The current postulated mechanisms associated with ICUAW (mainly the more frequent critical illness neuropathy and myopathy) are reviewed.

Critical illness myopathy

PURPOSE OF REVIEW

To describe the incidence, major risk factors, and the clinical, electrophysiological, and histological features of critical illness myopathy (CIM). Major pathogenetic mechanisms and long-term consequences of CIM are also reviewed.

RECENT FINDINGS

CIM is frequently associated with critical illness polyneuropathy (CIP), and may have a relevant impact on patients' outcome. CIM has an earlier onset than CIP, and recovery is faster. Loss of myosin filaments on muscle biopsy is important to diagnose CIM, and has a good prognosis. Critical illness, use of steroids, and immobility concur in causing CIM.

SUMMARY

A rationale diagnostic approach to CIM using clinical, electrophysiological, and muscle biopsy investigations is important to plan adequate therapy and to predict recovery.

A 17 year-old girl with a demyelinating disease requiring mechanical ventilation: a case report

Background

Demyelinating diseases cause destruction of the myelin sheath, while axons are relatively spared. Pathologically, demyelination can be the result of an inflammatory process, viral infection, acquired metabolic derangement and ischemic insult. Three diseases that can cause inflammatory demyelination of the CNS are: Multiple sclerosis (MS), Acute disseminated encephalomyelitis (ADEM) and Acute hemorrhagic leucoencephalitis. Differentiation is not always easy and there is considerable overlaping. Data about adults with acute demyelination requiring ICU admission is limited.

Case presentation

A 17 year old Greek female was hospitalised in the ICU because of acute respiratory failure requiring mechanical ventilation. She had a history of febrile disease one month before, acute onset of paraplegia, diplopia, progressive arm weakness and dyspnea. Her consciousness was not impaired. A demyelinating central nervous system (CNS) disease, possibly post infectious encephalomyelitis (ADEM) was the underlying condition. The MRI of the brain disclosed diffused expanded cerebral lesions involving the optic nerve, basal ganglia cerebellum, pons and medulla oblongata. There was also extended involvement of the cervical and thoracic part of the spinal cord. CSF leukocyte count was elevated with lymphocyte predominance. The patient required mechanical ventilation for two months. Then she was transferred to a rehabilitation centre. Three years later she remains paraplegic. Since then she has not suffered any other demyelination attack.

Conclusions

Demyelinating diseases can cause acute respiratory failure when the spinal cord is affected. Severe forms of these diseases, making necessary ICU admission, is less frequently reported. Intensivists should be aware of the features of these rare diseases.

Reduced motoneuron excitability in a rat model of sepsis

Many critically ill patients in intensive care units suffer from an infection-induced whole body inflammatory state known as sepsis, which causes severe weakness in patients who survive. The mechanisms by which sepsis triggers intensive care unit-acquired weakness (ICUAW) remain unclear. Currently, research into ICUAW is focused on dysfunction of the peripheral nervous system. During electromyographic studies of patients with ICUAW, we noticed that recruitment was limited to few motor units, which fired at low rates. The reduction in motor unit rate modulation suggested that functional impairment within the central nervous system contributes to ICUAW. To understand better the mechanism underlying reduced firing motor unit firing rates, we moved to the rat cecal ligation and puncture model of sepsis. In isoflurane-anesthetized rats, we studied the response of spinal motoneurons to injected current to determine their capacity for initiating and firing action potentials repetitively. Properties of single action potentials and passive membrane properties of motoneurons from septic rats were normal, suggesting excitability was normal. However, motoneurons exhibited striking dysfunction during repetitive firing. The sustained firing that underlies normal motor unit activity and smooth force generation was slower, more erratic, and often intermittent in septic rats. Our data are the first to suggest that reduced excitability of neurons within the central nervous system may contribute to ICUAW.

Anesthesia with propofol induces insulin resistance systemically in skeletal and cardiac muscles and liver of rats

Hyperglycemia together with hepatic and muscle insulin resistance are common features in critically ill patients, and these changes are associated with enhanced inflammatory response, increased susceptibility to infection, muscle wasting, and worsened prognosis. Tight blood glucose control by intensive insulin treatment may reduce the morbidity and mortality in intensive care units. Although some anesthetics have been shown to cause insulin resistance, it remains unknown how and in which tissues insulin resistance is induced by anesthetics. Moreover, the effects of propofol, a clinically relevant intravenous anesthetic, also used in the intensive care unit for sedation, on insulin sensitivity have not yet been investigated. Euglycemic hyperinsulinemic clamp study was performed in rats anesthetized with propofol and conscious unrestrained rats. To evaluate glucose uptake in tissues and hepatic glucose output [(3)H]glucose and 2-deoxy[(14)C]glucose were infused during the clamp study. Anesthesia with propofol induced a marked whole-body insulin resistance compared with conscious rats, as reflected by significantly decreased glucose infusion rate to maintain euglycemia. Insulin-stimulated tissue glucose uptake was decreased in skeletal muscle and heart, and hepatic glucose output was increased in propofol anesthetized rats. Anesthesia with propofol induces systemic insulin resistance along with decreases in insulin-stimulated glucose uptake in skeletal and heart muscle and attenuation of the insulin-mediated suppression of hepatic glucose output in rats.

Long-term neuromuscular sequelae of critical illness

In this observational study, we analyzed the long-term neuromuscular deficits of survivors of critical illness. Intensive care unit-acquired muscular weakness (ICU-AW) is a very common complication of critical illness. Critical illness polyneuropathy (CIP) and critical illness myopathy (CIM) are two main contributors to ICU-AW. ICU-AW is associated with an increased mortality and leads to rehabilitation problems. However, the long-term outcome of ICU-AW and factors influencing it are not well known. We analyzed the medical records of 490 survivors of critical illness, aged 18-75 years and located in the area of the study center. Intensive care unit (ICU) survivors with comorbidities that might influence neuromuscular follow-up examinations, muscle strength, or results of nerve conduction studies, such as renal or hepatic insufficiency, diabetes mellitus, or vitamin deficiency were excluded. A total of 51 patients were finally included in the study. Six to 24 months after discharge from the ICU, we measured the Medical Research Council (MRC) sum score, the Overall Disability Sum score (ODSS), and also performed nerve conduction studies and EMG. For all ICU survivors, the median MRC sum score was 60 (range 47-60) and the median ODSS score was 0 (range 0-8). CIP was diagnosed in 21 patients (41 %). No patient was diagnosed with CIM. Patients with diagnosis of CIP showed a higher median ODSS scores 1 (range 0-8) versus 0 (range 0-5); p < 0.001 and lower median MRC sum scores 56 (range 47-60) versus 60 (range 58-60); p < 0.001. The three main outcome variables MRC sum score, ODSS score and diagnosis of CIP were not related to age, gender, or diagnosis of sepsis. The MRC sum score (r = -0.33; p = 0.02) and the ODSS score (r = 0.31; p = 0.029) were correlated with the APACHE score. There was a trend for an increased APACHE score in patients with diagnosis of CIP 19 (range 6-33) versus 16.5 (range 6-28); p = 0.065. Patients with the diagnosis of CIP had more days of ICU treatment 11 days (range 2-74) versus 4 days (range 1-61); p = 0.015, and had more days of ventilator support 8 days (range 1-59) versus 2 days (range 1-46); p = 0.006. The MRC sum score and the ODSS score were correlated with the days of ICU treatment and with the days of ventilator support. The neuromuscular long-term consequences of critical illness were not severe in our study population. As patients with concomitant diseases and old patients were excluded from this study the result of an overall favorable prognosis of ICU-acquired weakness may not be true for other patient's case-mix. Risk factors for the development of long-term critical illness neuropathy are duration of ICU treatment, duration of ventilator support, and a high APACHE score, but not diagnosis of sepsis. Although ICU-AW can be serious complication of ICU treatment, this should not influence therapeutic decisions, given its favorable long-term prognosis, at least in relatively young patients with no concomitant diseases.

[Intensive care unit-acquired weakness in the critically ill : critical illness polyneuropathy and critical illness myopathy]

Intensive care unit-acquired weakness (ICUAW) is a severe complication in critically ill patients which has been increasingly recognized over the last two decades. By definition ICUAW is caused by distinct neuromuscular disorders, namely critical illness polyneuropathy (CIP) and critical illness myopathy (CIM). Both CIP and CIM can affect limb and respiratory muscles and thus complicate weaning from a ventilator, increase the length of stay in the intensive care unit and delay mobilization and physical rehabilitation. It is controversially discussed whether CIP and CIM are distinct entities or whether they just represent different organ manifestations with common pathomechanisms. These basic pathomechanisms, however, are complex and still not completely understood but metabolic, inflammatory and bioenergetic alterations seem to play a crucial role. In this respect several risk factors have recently been revealed: in addition to the administration of glucocorticoids and non-depolarizing muscle relaxants, sepsis and multi-organ failure per se as well as elevated levels of blood glucose and muscular immobilization have been shown to have a profound impact on the occurrence of CIP and CIM. For the diagnosis, careful physical and neurological examinations, electrophysiological testing and in rare cases nerve and muscle biopsies are recommended. Nevertheless, it appears to be difficult to clearly distinguish between CIM and CIP in a clinical setting. At present no specific therapy for these neuromuscular disorders has been established but recent data suggest that in addition to avoidance of risk factors early active mobilization of critically ill patients may be beneficial.

Diaphragm dysfunction assessed by ultrasonography: influence on weaning from mechanical ventilation

OBJECTIVE

To determine the prevalence of diaphragmatic dysfunction diagnosed by M-mode ultrasonography (vertical excursion <10 mm or paradoxic movements) in medical intensive care unit patients and to assess the influence of diaphragmatic dysfunction on weaning outcome.

DESIGN

Prospective, observational study.

SETTING

Twenty-eight-bed medical intensive care unit in a university-affiliated hospital.

PATIENTS

Eighty-eight consecutive patients in the medical intensive care unit who required mechanical ventilation over 48 hrs and met the criteria for a spontaneous breathing trial were assessed. Patients with a history of diaphragmatic or neuromuscular disease or evidence of pneumothorax or pneumomediastinum were excluded.

INTERVENTIONS

During spontaneous breathing trial, each hemidiaphragm was evaluated by M-mode ultrasonography using the liver and spleen as windows with the patient supine. Rapid shallow breathing index was simultaneously calculated at the bedside.

MEASUREMENTS AND MAIN RESULTS

The prevalence of ultrasonographic diaphragmatic dysfunction among the eligible 82 patients was 29% (n = 24). Patients with diaphragmatic dysfunction had longer weaning time (401 [range, 226-612] hrs vs. 90 [range, 24-309] hrs, p < .01) and total ventilation time (576 [range, 374-850] hrs vs. 203 [range, 109-408] hrs, p < .01) than patients without diaphragmatic dysfunction. Patients with diaphragmatic dysfunction also had higher rates of primary (20 of 24 vs. 34 of 58, p < .01) and secondary (ten of 20 vs. ten of 46, p = .01) weaning failures than patients without diaphragmatic dysfunction. The area under the receiver operating characteristics curve of ultrasonographic criteria in predicting weaning failure was similar to that of rapid shallow breathing index.

CONCLUSIONS

Using M-mode ultrasonography, diaphragmatic dysfunction was found in a substantial number of medical intensive care unit patients without histories of diaphragmatic disease. Patients with such diaphragmatic dysfunction showed frequent early and delayed weaning failures. Ultrasonography of the diaphragm may be useful in identifying patients at high risk of difficulty weaning.

Early rehabilitation in critical care (eRiCC): functional electrical stimulation with cycling protocol for a randomised controlled trial

INTRODUCTION

Intensive care-acquired weakness is a common problem, leads to significant impairment in physical functioning and muscle strength, and is prevalent in individuals with sepsis. Early rehabilitation has been shown to be safe and feasible; however, commencement is often delayed due to a patient's inability to co-operate. An intervention that begins early in an intensive care unit (ICU) admission without the need for patient volition may be beneficial in attenuating muscle wasting. The eRiCC (early rehabilitation in critical care) trial will investigate the effectiveness of functional electrical stimulation-assisted cycling and cycling alone, compared to standard care, in individuals with sepsis.

METHODS AND ANALYSIS

This is a single centre randomised controlled trial. Participants (n=80) aged ≥18 years, with a diagnosis of sepsis or severe sepsis, who are expected to be mechanically ventilated for ≥48 h and remain in the intensive care ≥4 days will be randomised within 72 h of admission to (1) standard care or (2) intervention where participants will receive functional electrical muscle stimulation-assisted supine cycling on one leg while the other leg undergoes cycling alone. Primary outcome measures include: muscle mass (quadriceps ultrasonography; bioelectrical impedance spectroscopy); muscle strength (Medical Research Council Scale; hand-held dynamometry) and physical function (Physical Function in Intensive Care Test; Functional Status Score in intensive care; 6 min walk test). Blinded outcome assessors will assess measures at baseline, weekly, at ICU discharge and acute hospital discharge. Secondary measures will be evaluated in a nested subgroup (n=20) and will consist of biochemical/histological analyses of collected muscle, urine and blood samples at baseline and at ICU discharge.

ETHICS AND DISSEMINATION

Ethics approval has been obtained from the relevant institution, and results will be published to inform clinical practice in the care of patients with sepsis to optimise rehabilitation and physical function outcomes.

TRIAL REGISTRATION

Australian and New Zealand Clinical Trials Registry ACTRN12612000528853.

Critical illness polyneuropathy and myopathy: a major cause of muscle weakness and paralysis

Critical illness polyneuropathy (CIP) and myopathy (CIM) are complications of critical illness that present with muscle weakness and failure to wean from the ventilator. In addition to prolonging mechanical ventilation and hospitalisation, CIP and CIM increase hospital mortality in patients who are critically ill and cause chronic disability in survivors of critical illness. Structural changes associated with CIP and CIM include axonal nerve degeneration, muscle myosin loss, and muscle necrosis. Functional changes can cause electrical inexcitability of nerves and muscles with reversible muscle weakness. Microvascular changes and cytopathic hypoxia might disrupt energy supply and use. An acquired sodium channelopathy causing reduced muscle membrane and nerve excitability is a possible unifying mechanism underlying CIP and CIM. The diagnosis of CIP, CIM, or combined CIP and CIM relies on clinical, electrophysiological, and muscle biopsy investigations. Control of hyperglycaemia might reduce the severity of these complications of critical illness, and early rehabilitation in the intensive care unit might improve the functional recovery and independence of patients.

Miscellaneous neurologic or neuromuscular disorders in horses

NMD is an important cause of morbidity in horses. Signs of dysfunction could be variable depending on the specific area affected. NM disease can go unrecognized if a thorough evaluation is not performed in diseased horses. Electrodiagnostic testing is an area that has the potential to document and improve our understanding of NM disease yet is uncommonly performed. Keeping an open and observant mind will enhance our ability to search and find answers.

Tumor necrosis factor-α downregulates sodium current in skeletal muscle by protein kinase C activation: involvement in critical illness polyneuromyopathy

Sepsis is involved in the decrease of membrane excitability of skeletal muscle, leading to polyneuromyopathy. This effect is mediated by alterations of the properties of voltage-gated sodium channels (Na(V)), but the exact mechanism is still unknown. The aim of the present study was to check whether tumor necrosis factor (TNF-α), a cytokine released during sepsis, exerts a rapid effect on Na(V). Sodium current (I(Na)) was recorded by macropatch clamp in skeletal muscle fibers isolated from rat peroneus longus muscle, in control conditions and after TNF-α addition. Analyses of dose-effect and time-effect relationships were carried out. Effect of chelerythrine, a PKC inhibitor, was also studied to determine the way of action of TNF-α. TNF-α induced a reversible dose- and time-dependent inhibition of I(Na). A maximum inhibition of 75% of the control current was observed. A shift toward more negative potentials of activation and inactivation curves of I(Na) was also noticed. These effects were prevented by chelerythrine pretreatment. TNF-α is a cytokine released in the early stages of sepsis. Besides a possible transcriptional role, i.e., modification of the channel type and/or number, we demonstrated the existence of a rapid, posttranscriptional inhibition of Na(V) by TNF-α. The downregulation of the sodium current could be mediated by a PKC-induced phosphorylation of the sodium channel, thus leading to a significant decrease in muscle excitability.

Maximum inspiratory pressure, a surrogate parameter for the assessment of ICU-acquired weakness

BACKGROUND

Physical examination has been advocated as a primary determinant of ICU-acquired weakness (ICU-AW). The purpose of the study is to investigate ICU-AW development by using Maximum Inspiratory Pressure (MIP) as a surrogate parameter of the standardized method to evaluate patients' peripheral muscle strength.

METHODS

Seventy-four patients were recruited in the study and prospectively evaluated in a multidisciplinary university ICU towards the appearance of ICU-AW. APACHE II admission score was 16 ± 6 and ICU stay 26 ± 18 days. ICU-AW was diagnosed with the Medical Research Council (MRC) scale for the clinical evaluation of muscle strength. MIP was measured using the unidirectional valve method, independently of the patients' ability to cooperate.

RESULTS

A significant correlation was found between MIP and MRC (r = 0.68, p < 0.001). Patients that developed ICU-AW (MRC<48) had a longer weaning period compared to non ICU-AW patients (12 ± 14 versus 2 ± 3 days, p < 0.01). A cut-off point of 36 cmH2O for MIP was defined by ROC curve analysis for ICU-AW diagnosis (88% sensitivity,76% specificity). Patients with MIP below the cut-off point of 36 cmH2O had a significant greater weaning period (10 ± 14 versus 3 ± 3 days, p = 0.004) also shown by Kaplan-Meier analysis (log-rank:8.2;p = 0.004).

CONCLUSIONS

MIP estimated using the unidirectional valve method may be a potential surrogate parameter for the assessment of muscle strength compromise, useful for the early detection of ICU-AW.

Factors underlying the early limb muscle weakness in acute quadriplegic myopathy using an experimental ICU porcine model

The basic mechanisms underlying acquired generalized muscle weakness and paralysis in critically ill patients remain poorly understood and may be related to prolonged mechanical ventilation/immobilization (MV) or to other triggering factors such as sepsis, systemic corticosteroid (CS) treatment and administration of neuromuscular blocking agents (NMBA). The present study aims at exploring the relative importance of these factors by using a unique porcine model. Piglets were all exposed to MV together with different combinations of endotoxin-induced sepsis, CS and NMBA for five days. Peroneal motor nerve conduction velocity and amplitude of the compound muscle action potential (CMAP) as well as biceps femoris muscle biopsy specimens were obtained immediately after anesthesia on the first day and at the end of the 5-day experimental period. Results showed that peroneal nerve motor conduction velocity is unaffected whereas the size of the CMAP decreases independently of the type of intervention, in all groups after 5 days. Otherwise, despite a preserved size, muscle fibre specific force (maximum force normalized to cross-sectional area) decreased dramatically for animals exposed to MV in combination with CS or/and sepsis. These results suggest that the rapid declines in CMAP amplitude and in force generation capacity are triggered by independent mechanisms with significant clinical and therapeutic implications.

Neuromuscular disorders in critically ill patients: review and update

Neuromuscular disorders that are diagnosed in the intensive care unit (ICU) usually cause substantial limb weakness and contribute to ventilatory dysfunction. Although some lead to ICU admission, ICU-acquired disorders, mainly critical illness myopathy (CIM) and critical illness polyneuropathy (CIP), are more frequent and are associated with considerable morbidity. Approximately 25% to 45% of patients admitted to the ICU develop CIM, CIP, or both. Their clinical features often overlap; therefore, nerve conduction studies and electromyography are particularly helpful diagnostically, and more sophisticated electrodiagnostic studies and histopathologic evaluation are required in some circumstances. A number of prospective studies have identified risk factors for CIP and CIM, but their limitations often include the inability to separate CIM from CIP. Animal models reveal evidence of a channelopathy in both CIM and CIP, and human studies also identified axonal degeneration in CIP and myosin loss in CIM. Outcomes are variable. They tend to be better with CIM, and some patients have longstanding disabilities. Future studies of well-characterized patients with CIP and CIM should refine our understanding of risk factors, outcomes, and pathogenic mechanisms, leading to better interventions.

Critical illness polyneuropathy and myopathy in the intensive care unit

Critical illness polyneuropathy (CIP) and critical illness myopathy (CIM) are major complications that occur in severely ill patients who require intensive care treatment. CIP and CIM affect the limb and respiratory muscles, and, as a consequence, they characteristically complicate weaning from the ventilator, increase the length of stay on the intensive care unit, and prolong physical rehabilitation. The basic pathophysiology of both disorders is complex and involves metabolic, inflammatory and bioenergetic alterations. It is unclear at present whether CIP and CIM are distinct entities, or whether they just represent different 'organ' manifestations of a common pathophysiological mechanism. This article provides an overview of the clinical and diagnostic features of CIP and CIM and discusses current pathophysiological and therapeutic concepts relating to these neuromuscular disorders.

Sepsis-induced myopathy

Sepsis is a major cause of morbidity and mortality in critically ill patients, and despite advances in management, mortality remains high. In survivors, sepsis increases the risk for the development of persistent acquired weakness syndromes affecting both the respiratory muscles and the limb muscles. This acquired weakness results in prolonged duration of mechanical ventilation, difficulty weaning, functional impairment, exercise limitation, and poor health-related quality of life. Abundant evidence indicates that sepsis induces a myopathy characterized by reductions in muscle force-generating capacity, atrophy (loss of muscle mass), and altered bioenergetics. Sepsis elicits derangements at multiple subcellular sites involved in excitation contraction coupling, such as decreasing membrane excitability, injuring sarcolemmal membranes, altering calcium homeostasis due to effects on the sarcoplasmic reticulum, and disrupting contractile protein interactions. Muscle wasting occurs later and results from increased proteolytic degradation as well as decreased protein synthesis. In addition, sepsis produces marked abnormalities in muscle mitochondrial functional capacity and when severe, these alterations correlate with increased death. The mechanisms leading to sepsis-induced changes in skeletal muscle are linked to excessive localized elaboration of proinflammatory cytokines, marked increases in free-radical generation, and activation of proteolytic pathways that are upstream of the proteasome including caspase and calpain. Emerging data suggest that targeted inhibition of these pathways may alter the evolution and progression of sepsis-induced myopathy and potentially reduce the occurrence of sepsis-mediated acquired weakness syndromes.

Inactivation of sodium channels underlies reversible neuropathy during critical illness in rats

Neuropathy and myopathy can cause weakness during critical illness. To determine whether reduced excitability of peripheral nerves, rather than degeneration, is the mechanism underlying acute neuropathy in critically ill patients, we prospectively followed patients during the acute phase of critical illness and early recovery and assessed nerve conduction. During the period of early recovery from critical illness, patients recovered from neuropathy within days. This rapidly reversible neuropathy has not to our knowledge been previously described in critically ill patients and may be a novel type of neuropathy. In vivo intracellular recordings from dorsal root axons in septic rats revealed reduced action potential amplitude, demonstrating that reduced excitability of nerve was the mechanism underlying neuropathy. When action potentials were triggered by hyperpolarizing pulses, their amplitudes largely recovered, indicating that inactivation of sodium channels was an important contributor to reduced excitability. There was no depolarization of axon resting potential in septic rats, which ruled out a contribution of resting potential to the increased inactivation of sodium channels. Our data suggest that a hyperpolarized shift in the voltage dependence of sodium channel inactivation causes increased sodium inactivation and reduced excitability. Acquired sodium channelopathy may be the mechanism underlying acute neuropathy in critically ill patients.