NI FEATURE: THE EDITORIAL DEBATE-- PROS AND CONS
|Year : 2016 | Volume
| Issue : 4 | Page : 604--605
Stuck to the ventilator: The neuromyopathy of critical illness
Department of Neurology, Fortis Hospital, Jaipur, Rajasthan, India
Department of Neurology, Fortis Hospital, Jaipur, Rajasthan
|How to cite this article:|
Ramrakhiani N. Stuck to the ventilator: The neuromyopathy of critical illness.Neurol India 2016;64:604-605
|How to cite this URL:|
Ramrakhiani N. Stuck to the ventilator: The neuromyopathy of critical illness. Neurol India [serial online] 2016 [cited 2020 Sep 28 ];64:604-605
Available from: http://www.neurologyindia.com/text.asp?2016/64/4/604/185385
Critical illness polyneuropathy (CIP) and critical illness myopathy (CIM) are conditions which are often associated with a critically ill patient in the intensive care unit (ICU) and lead to a flaccid paralysis with involvement of limb and respiratory muscles. The loss of “flesh and strength” was described in critically ill patients in the nineteenth century. However, it took another century before this term was coined by Bolton et al., in 1984, who attributed the characteristic axonal loss of motor and sensory fibers to the toxic effect of sepsis. More recently, a new term called ICU acquired weakness (ICUAW) has been coined to address this entity, which is practically useful. This condition occurs in between 20 - 50 percent of critically ill patients who have been on mechanical ventilation for more than one week in an ICU and is usually identified by the failure to wean the patient from the ventilator.
This condition is typically recognized when withdrawal of sedation reveals a weak patient with flaccid quadriparesis, who grimaces on deep painful stimuli, with decreased or minimal limb movement. Deep tendon reflexes (DTR) are depressed or absent in CIP and normal or hypoactive in CIM. Diaphragmatic weakness is also very common and is responsible for ventilatory dependence. In conscious patients, CIP and CIM are arbitrarily diagnosed if the Medical Research Council sum score is less than 48 after evaluating three muscle in both upper and lower limbs on both right and left side on a scale of 0 to 5. Other diagnostic criteria  for CIP are difficulty in weaning from the ventilator, which is not related to any cardiopulmonary cause, possible limb weakness, and electrophysiological evidence of axonal motor and sensory polyneuropathy. On electrophysiology, sensory and motor amplitude of <80% of the lower limit of normal in two or more nerves, absence of conduction block or prolonged F waves, absence of decremental response and reduced recruitment of long duration high amplitude motor unit potential (MUP) are the characteristic features. Supportive diagnostic features of CIP are normal cerebrospinal fluid (CSF) protein and a normal serum creatine kinase. The mechanics of axonal injury in CIP is not known. Possibility of injury to the microcirculation of distal nerves causing ischemia and axonal degeneration is postulated. Also, during sepsis, reversible but prolonged electrical non-excitability of nerve may be triggered. In a septic rat model, there were reduced motor and sensory tail nerve amplitudes which indicated that sodium channels were inactivated. It is possible that all these mechanisms may represent the entire range of pathophysiological spectrum.
In the case of CIM, usually flaccid paralysis with normal or reduced DTRs are seen in the setting of glucocorticoid use. In conscious patients, the sensory examination is normal and electrophysiology reveals moderately reduced CMAPS with normal sensory potentials and a myopathic pattern on electromyography (EMG). Muscle biopsy, although rarely justified in clinical practice, reveals a selective loss of thick (myosin) filament with varying degree of necrosis, which is a marker of disease severity.
Previous studies by Khan et al., revealed an abnormal baseline nerve conduction study upon enrolment in 63% of patients (31/48), which was predictive of the hospital mortality (55% vs 0% for patients with a normal baseline nerve conduction study) suggesting that changes in nerve conduction occur early in the course of severe sepsis, and that majority of patients have both critical illness myopathy and neuropathy. Another study, Critical Illness to Monitor for CIM and/or CIP (CRIMYNE) showed that in 92 patients who had normal nerve conduction studies at 24 hours after their ICU admission, serial electro-diagnostic studies were useful in predicting the development of CIM/CIP and a reduction of more than 25% in the peroneal compound muscle action potential was the most useful method in diagnosing the development of these entities.
The treatment of this condition is mainly supportive, although treatment of hyperglycaemia and early mobilization of patients has been found to be beneficial. Minimizing of sedation also may have a beneficial effect. Mobilization of patients should be started while the patient is still on mechanical ventilation which calls for a change in ICU culture and a strong multidisciplinary approach. CIM has a relatively better prognosis than CIN. There are a number of ongoing trials exploring the potential preventive pharmacological agents for ICUAW. These agents are primarily anti-inflammatory and metabolic agents aimed at decreasing the severity of ICUAW and include 5 hydroxytryptamine (2C) agonist, hydroxymethybutyrate and intravenous immunoglobulins.
In this edition of Neurology India, an interesting and elegant study is published by Gupta and Mishra, of over 100 patients in the ICU in whom the development of CIP was evaluated and the two groups of patients (those with CIM/CIP and those without this entity) were evaluated for their disease severity using the Acute Physiology and Chronic Health Evaluation II (APACHE 2) score. An APACHE 2 score of more than 15 and the use of neuromuscular blocking agents were found to have a significant correlation with the development of CIP by the authors in their study. The strength of their study includes a well-planned study design with repeated nerve conduction studies for those patients who developed CIP late in the course of their illness, the exclusion of other causes of preexistent neuropathy (which must have been a difficult task to perform), and the grading of the severity of illness through a multi-modality score like the APACHE 2 score. They have only included patients of SIRS of presumptive microbiological etiology. Most of the patients were found to develop CIP early in the course of their illness. The practical significance of this study would be to keep a hawk-like alertness for these conditions in patients who are at risk and have higher scores, and to pre-emptively institute measures like sedation-free interval for measurement of muscle strength in suitable candidates with a good glycemic control. Considering the practical difficulties of performing electrophysiology in an ICU setting on a ventilated patient, those patients who have decreased MRC scores or are difficult to clinically evaluate could be subjected to nerve conduction studies. However, the lack of clinical data and an exclusive reliance on electrophysiology for diagnosis are the drawbacks of this study. The significance of electrophysiological involvement in the absence of weakness makes the diagnosis of ICUAW uncertain. The electrophysiological data, if also analyzed in detail, would have given additional insights into the pattern of nerve involvement.
To conclude, ICUAW is common in the critical care setting and is often under-reported. The avoidance of risk factors or their modification, and an early activity of the patients may reduce the severity of this condition. More studies and newer therapeutic approaches may help us in treating this debilitating condition.
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