Approach to neuromuscular disorders in the intensive care unit

Exploring the Muscle Metabolomics in the Mouse Model of Sepsis-Induced Acquired Weakness

Background/Aim

We aimed to identify the differentially expressing metabolites (DEMs) in the muscles of the mouse model of sepsis-induced acquired weakness (sepsis-AW) using liquid chromatography-mass spectrometry (LC-MS).

Materials and Methods

Sepsis by cecal ligation puncture (CLP) with lower limb immobilization was used to produce a sepsis-AW model. After this, the grip strength of the C57BL/6 male mice was investigated. The transmission electron microscopy was utilized to determine the pathological model. LC-MS was used to detect the metabolic profiles within the mouse muscles. Additionally, a statistically diversified analysis was carried out.

Results

Compared to the sepsis group, 30 DEMs, including 17 upregulated and 13 down-regulated metabolites, were found in the sepsis-AW group. The enriched metabolic pathways including purine metabolism, valine/leucine/isoleucine biosynthesis, cGMP-PKG pathway, mTOR pathway, FoxO pathway, and PI3K-Akt pathway were found to differ between the two groups. The targeted metabolomics analysis explored significant differences between four amino acid metabolites (leucine, cysteine, tyrosine, and serine) and two energy metabolites (AMP and cAMP) in the muscles of the sepsis-AW experimental model group, which was comparable to the sepsis group.

Conclusion

The present work identified DEMs and metabolism-related pathways within the muscles of the sepsis-AW mice, which offered valuable experimental data for diagnosis and identification of the pathogenic mechanism underlying sepsis-AW.

Weakness in the intensive care unit

When asked to assess patients in an intensive care unit (ICU) who have respiratory muscle weakness, oropharyngeal weakness and a vulnerable airway, our immediate thought may be of Guillain-Barré syndrome or myasthenia gravis, but there are many other possible causes. For example, previously unrecognised chronic neurological conditions may decompensate and require ICU admission. Clinicians can use various clinical clues to help recognise them and need to understand how patterns of weakness reflect differing causes of reduced consciousness on ICU. Additionally, patients admitted to ICU for any reason may develop weakness during their stay, the most likely cause being ICU-acquired weakness. Assessing patients in ICU is challenging, hampered by physical barriers (machines, tubes), medication barriers (sedatives) and cognitive barriers (delirium, difficulty communicating). Nonetheless, we need to reach a clinical diagnosis, organise appropriate tests and communicate clearly with both patients and ICU colleagues.

Corticosteroids and neuromuscular blockers in development of critical illness neuromuscular abnormalities: A historical review

Weakness is common in critically ill patients, associated with prolonged mechanical ventilation and increased mortality. Corticosteroids and neuromuscular blockade (NMB) administration have been implicated as etiologies of acquired weakness in the intensive care unit. Medical literature since the 1970s is replete with case reports and small case series of patients with weakness after receiving high-dose corticosteroids, prolonged NMB, or both. Several risk factors for weakness appear in the early literature, including large doses of steroids, the dose and duration of NMB, hyperglycemia, and the duration of mechanical ventilation. With improved quality of data, however, the association between weakness and steroids or NMB wanes. This may reflect changes in clinical practice, such as a reduction in steroid dosing, use of cisatracurium besylate instead of aminosteroid NMBs, improved glycemic control, or trends in minimizing mechanical ventilatory support. Thus, based on the most recent and high-quality literature, neither corticosteroids in commonly used doses nor NMB is associated with increased duration of mechanical ventilation, the greatest morbidity of weakness. Minimizing ventilator support as soon as the patient's condition allows may be associated with a reduction in weakness-related morbidity.

Management of intracerebral hemorrhage--use of statins

Intracerebral hemorrhage (ICH) is a neurologic injury resulting in significant morbidity and mortality. Statins play a significant role in primary and secondary prevention of cardiovascular and cerebrovascular ischemic events. Despite clear benefits of statins in ischemic stroke, post hoc analyses of some studies suggest there may be a link between statin therapy and development of ICH. Direct pharmacologic effects of decreased serum levels of total cholesterol and low-density lipoproteins in conjunction with pleiotropic effects are thought to be linked to this possible increase in ICH risk. In the face of the potential of statins to increase the risk of ICH, recent evidence suggests that statins may also have beneficial effects on patient outcomes when continued or initiated following an ICH. This discordance in findings and the overall lack of well-designed prospective clinical trials increase the complexity of clinical decision making when utilizing statin therapy in patients with, or at risk for, ICH. This review evaluates the pharmacologic effects of statin therapy and describes how these effects translate to both risks and benefits in ICH. The current literature regarding the effects of statin therapy on clinical outcomes in ICH is evaluated to help guide clinicians with decisions regarding initiation, continuation, or discontinuation of statin therapy in patients with ICH.

Percutaneous Muscle Biopsies: Review of 900 Consecutive Cases at London Health Sciences Centre

Objective:

In the present study we review our experience with 900 consecutive percutaneous muscle biopsies over the period 1993 to 2007. We examined the advantages and limitations of the procedure, biopsy site preferences, diagnostic range, frequency of diagnoses and quality of histopathology. Demographics, referral patterns and patients' perceptions of the procedure were also assessed.

Methods:

Cases were identified through the London Health Sciences Centre Department of Pathology database. Standard biopsy procedures were followed using a manual trocar style instrument. With a neuropathology technologist in attendance at all biopsies, biopsies were oriented in the fresh state and snap frozen.

Results:

Most referrals for muscle biopsy were from neuromuscular neurologists. The procedure was found to be efficient, well-tolerated and produced high quality specimens in all diagnostic categories. No major complications occurred. Failure to obtain an adequate tissue sample, although uncommon (<2%), was usually due to marked obesity, edema or muscle wasting. Bleeding at the site was rarely problematic and no wound infections were reported.

Conclusions:

Needle muscle biopsies represent an efficient alternative to open biopsies when peripheral nerve sampling is not required and when large tissue samples are not needed for extensive biochemical analyses.

Delirium detection based on monitoring of blinks and eye movements

OBJECTIVE

To investigate whether delirious patients differ from nondelirious patients with regard to blinks and eye movements to explore opportunities for delirium detection.

METHODS

Using a single-center, observational study in a tertiary hospital in the Netherlands, we studied 28 delirious elderly and 28 age- and gender-matched (group level) nondelirious elderly, postoperative cardiac surgery patients. Patients were evaluated for delirium by a geriatrician, psychiatrist, or neurologist using the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition criteria. Blinks were automatically extracted from electro-oculograms and eye movements from electroencephalography recordings using independent component analysis. The number and duration of eye movements and blinks were compared between patients with and without delirium, based on the classification of the delirium experts described above.

RESULTS

During eyes-open registrations, delirious patients showed, compared with nondelirious patients, a significant decrease in the number of blinks per minute (median: 12 [interquartile range {IQR}: 5-18] versus 18 [IQR: 8-25], respectively; p = 0.02) and number of vertical eye movements per minute (median: 1 [IQR: 0-13] versus 15 [IQR: 2-54], respectively; p = 0.01) as well as an increase in the average duration of blinks (median: 0.5 [IQR: 0.36-0.95] seconds versus 0.34 [IQR: 0.23-0.53] seconds, respectively; p <0.01). During eyes-closed registrations, the average duration of horizontal eye movements was significantly increased in delirious patients compared with patients without delirium (median: 0.41 [IQR: 0.15-0.75] seconds versus 0.08 [IQR: 0.06-0.22] seconds, respectively; p <0.01).

CONCLUSION

Spontaneous eye movements and particularly blinks appear to be affected in delirious patients, which holds promise for delirium detection.

Intensive care unit-related generalized neuromuscular weakness due to critical illness polyneuropathy/myopathy in critically ill patients

Thirty to fifty percent of critically ill patients admitted to the intensive care unit suffer from generalized neuromuscular weakness due to critical illness polyneuropathy, critical illness myopathy, or a combination of them, thus prolonging mechanical ventilation and their intensive care unit stay. A distinction between these syndromes and other neuromuscular abnormalities beginning either before or after ICU admission is necessary. These intensive care unit-related diseases are associated with both elevated mortality rates and increased morbidity rates. Generally, over 50 % of patients will completely recover. Most of them recover after 4-12 weeks, but some patients have been reported to keep on suffering from muscle weakness for at least 4 months. Prevention has a key role in the management of critical illness neuromuscular disorders, as no specific therapy has been suggested. Either prevention or aggressive treatment of sepsis can prevent critical illness polyneuropathy and critical illness myopathy. The dose and duration of the administration of neuromuscular blocking drugs should be limited, and their concurrent administration with corticosteroids should be avoided. Intensive insulin therapy has also been proven to reduce their incidence. Finally, early mobilization via active exercise or electrical muscle stimulation plays a significant role in their prevention.

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.

Utility of cystatin C for renal function in amyotrophic lateral sclerosis

OBJECTIVES

Creatinine (Cr) as a marker of renal function has limited value in amyotrophic lateral sclerosis (ALS) because patients with ALS have reduced muscle mass. Thus, there is a need for alternative methods of assessing renal function. Cystatin C (CysC), which is unaffected by muscle mass, is potentially an ideal biomarker of nephrotoxicity in ALS; however, its utility requires validation.

MATERIAL AND METHODS

One hundred and six subjects were recruited for the study: 76 ALS patients and 30 healthy controls. We compared the Cr-based estimated glomerular filtration rate (eGFR) with the CysC-based eGFR in the ALS patients and healthy controls. The results were further analysed according to the severity of ALS in the patients.

RESULTS

The mean Cr-based eGFRs were 257.2 ± 383.1 ml/min/1.73 m(2) in the ALS group and 98.1 ± 34.9 in the control group; however, the mean CysC-based eGFRs were not significantly different between both groups. Thus, the Cr-based eGFR in the ALS group was markedly higher than any of the other values. Although serum CysC levels did not correlate with the severity of ALS according to the ALS Functional Rating Scale-Revised, strong simple correlations were observed between serum Cr levels and the severity of ALS (correlation coefficient = 0.734, P < 0.001).

CONCLUSIONS

This study demonstrates the potential usefulness of CysC as a biomarker of renal function in ALS patients. Furthermore, its applicability could be extended to other neuromuscular diseases.

Neurophysiological testing in neurocritical care

PURPOSE OF REVIEW

To summarize a consensus of European authorities about the applications of clinical neurophysiology in the ICU and, particularly, for a clinically useful management of individual patients.

RECENT FINDINGS

Clinical neurophysiology is useful for diagnosis (epilepsy, brain death, and neuromuscular disorders), prognosis (anoxic ischemic encephalopathy, head trauma, and neurological disturbances of metabolic and toxic origin), and follow-up. The prognostic significance of each test varies as a function of coma etiology. A distinction should be made between tests whose abnormalities are indicative of a poor prognosis (bilateral absence of N20 in anoxic coma, abnormalities suggesting pontine involvement in head trauma) and those whose relative normalcy constitutes an argument for a good prognosis (integrity of brainstem conductions in head trauma, presence of cognitive evoked potentials - mismatch negativity, P300 - irrespective of coma etiology).The highlights of the recent literature mainly concern continuous neuromonitoring for early detection of nonconvulsive seizures, both in adult and neonatal ICU, brain entry into the ischemic penumbra zone, and neuronal functional consequences of intracranial hypertension.

SUMMARY

The domain of clinical neurophysiology is similar to that of clinical examination and complementary to that of imaging techniques. It substantially improves the individual management of ICU patients.

Intensive care unit-acquired weakness: clinical phenotypes and molecular mechanisms

Intensive care unit-acquired weakness (ICUAW) begins within hours of mechanical ventilation and may not be completely reversible over time. It represents a major functional morbidity of critical illness and is an important patient-centered outcome with clear implications for quality of life and resumption of prior work and lifestyle. There is heterogeneity in functional outcome related to ICUAW across various patient populations after an episode of critical illness. This state-of-the art review argues that this observed heterogeneity may represent a clinical spectrum of disability in which there are recognizable clinical phenotypes for outcome according to age, burden of comorbid illness, and ICU length of stay. It further argues that these functional outcomes are modified by mood, cognition, and caregiver physical and mental health. This proposed construct of clinical phenotypes will be used as a framework for a review of the current literature on the molecular biology of muscle and nerve injury. This translational approach for the development of models pairing clinical phenotypes for different functional outcomes after critical illness with molecular mechanism of injury may offer unique insights into the diagnosis and treatment of muscle and nerve lesions.

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.

Influence of critical illness on axonal loss in Guillain-Barré syndrome

In this study we sought to determine whether axonal damage in severe Guillain-Barré syndrome (GBS) was secondary to critical illness polyneuropathy (CIP) in the intensive care unit (ICU) by reviewing comorbidities in patients who had initial and follow-up electromyographic (EMG) studies. Patients were classified as demyelinating (EMG-D) or axonal (EMG-A) according to findings on the second EMG. A critical illness (CI) score, derived from components of the APACHE II score, assessed the severity of critical illness in the ICU. Forty-one patients were admitted to the ICU and had a follow-up EMG. Of these, 28 (68%) developed an EMG-A pattern. There was no difference in the timing of the second EMG (mean, 23 days) between the two groups. The mean CI score (10.7 for EMG-A vs. 9.2 for EMG-D, P = 0.47) and frequency of sepsis (89% vs. 77%, P = 0.36) were similar between the groups. Mean strength (0-100, Medical Research Council scale) and Hughes disability scores for the EMG-A group were significantly worse at admission, nadir, and discharge. EMG-A patients had significantly more days on the ventilator (25 vs. 11), in the ICU (26 vs. 15), and in the hospital (29 vs. 18). Sixty-eight percent of patients with GBS in the ICU developed axon loss, but this was not related to the usual precipitants of CIP.

Guillain-Barré syndrome following thoracic spinal cord trauma

PURPOSE

Guillain-Barré syndrome (GBS) is an acute immunologic attack of the peripheral nerves causing rapidly ascending weakness and areflexia. Occasionally, weakness is severe enough to leave patients paralyzed and without adequate respiratory function. In such patients, intensive care unit (ICU) admission is required. Infrequently, GBS occurs in patients already admitted to the ICU. When this occurs, it can be difficult to distinguish GBS from critical illness neuropathy (CIN). However, it is important to consider GBS in these cases, since treatment options are available, and early treatment is associated with significantly improved outcome.

CLINICAL FEATURES

A 28-yr-old man involved in a motor vehicle collision sustained multiple injuries, including T6-T7 thoracic vertebrae fracture. Magnetic resonance imaging identified spinal cord compression at T6-T7, without brain or cervical cord injury. Shortly after admission, the patient developed marked autonomic instability with fluctuating temperatures and severe hypotension. Lower extremity weakness rapidly worsened to paraplegia and new weakness developed affecting bilateral upper extremities and face. Electrodiagnostic studies showed severe axonal polyneuropathy, with denervation in all extremities. The cerebrospinal fluid protein concentration was 5.03 g.L(-1). The patient was treated empirically for the possibility of GBS. Six months later, the patient recovered significant strength in his face and extremities, including his legs.

CONCLUSIONS

Guillain-Barré syndrome in trauma patients is rare and is limited to case reports following head trauma. This case also highlights the similarities and the subtle differences between GBS and CIN. Ultimately, definitive diagnosis of GBS may not be possible; however, an empiric course of intravenous immunoglobulins or plasma-exchange may be warranted, if GBS is a reasonable possibility.

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.