Neuromuscular blocking agents in the intensive care unit: a two-edged sword

Propofol: Effects on the Central Nervous System

Propofol remains a popular agent for providing intraoperative anesthesia as well as sedation during mechanical ventilation in the intensive care unit (ICU) setting. In addition to its sedative/anxiolytic properties, propofol has been shown to have several beneficial effects on central nervous system (CNS) parameters such as cerebral metabolic rate for oxygen, cerebral blood flow, and intracranial pressure. These properties have been demonstrated in both laboratory animals and in clinical investigations In humans. This article reviews the available literature concerning the effects of propofol on CNS dynamics and discusses its possible application as a therapeutic agent in patients with altered intracranial compliance and/or increased intracranial pressure.

Diagnosis and management of critical illness polyneuropathy and critical illness myopathy

Newly acquired neuromuscular weakness commonly develops in the setting of critical illness. This weakness delays recovery and often causes prolonged ventilator dependence. An axonal sensory-motor polyneuropathy, critical illness polyneuropathy (CIP), is seen in up to a third of critically ill patients with the systemic inflammatory response syndrome (usually due to sepsis). As frequently, or more so, an acute myopathy, critical illness myopathy (CIM), develops in a similar setting, often in association with the use of corticosteroids and/or nondepolarizing neuromuscular-blocking agents. This paper reviews the clinical features, diagnostic approach, and treatment of CIP and CIM. There are no specific pharmacologic treatments for CIP or CIM, but recognizing the presence of one of these disorders often improves management. Prevention of CIP and CIM is feasible in part by avoiding risk factors and by aggressive medical management of critically ill patients. Intensive insulin therapy in intensive care unit patients appears to reduce the likelihood of developing CIP and/or CIM. Future treatments of sepsis may further reduce the incidence of these neuromuscular consequences of critical illness.

Danon disease with typical early-onset cardiomyopathy in a male: focus on a novel LAMP-2 mutation

We report a case of a 16-yr-old male with Danon disease caused by a novel mutation in the LAMP-2 gene. Mutations in the LAMP-2 gene result in the absence of LAMP-2 on immunohistochemical staining of muscle tissue, thus defining Danon disease, a rare X-linked myopathy. It is characterized clinically by HCM or left ventricular hypertrophy, a WPW pattern on ECG, variable degrees of muscular weakness (skeletal myopathy), mental retardation, and retinal changes. The patient presented with severe skeletal muscular weakness and respiratory failure. He also had a history of two OHTs, the first one for severe HCM and the second for allograft rejection. The patient's myopathy was initially presumed to be exclusively related to steroid-induced "critical care myopathy." However, further evaluation with a thigh muscle biopsy revealed autophagic vacuoles with sarcolemnal features suggestive of a lysosomal storage disorder. DNA analysis ultimately identified a previously unreported hemizygous IVS6+3_+6delGAGT splice site deletion mutation in the LAMP-2 gene located within the 5' splice site of intron 6, consistent with Danon disease.

Combination of histopathological and electromyographic patterns can help to evaluate functional outcome of critical ill patients with neuromuscular weakness syndromes

Introduction

The aim of the study was to describe patterns of neuromuscular weakness using a combination of electromyography and histology, and to evaluate functional outcome in patients following complicated cardiovascular surgery.

Methods

Fifteen adults requiring long-term mechanical ventilation (>15 days) following cardiovascular surgery associated with postoperative complications were prospectively included. Electrophysiological and histological analyses (muscle and nerve) were performed when failure to wean from mechanical ventilation associated with peripheral neuromuscular weakness was noticed. Functional disability was evaluated 12 months after surgery.

Results

Six patients had a predominantly axonal neuropathy, six presented with myopathy, and three patients had a combination of axonal neuropathy and myopathy. All of them presented with acute tetraparesis and failure to wean from mechanical ventilation. All of the study patients who received corticosteroids exhibited a myopathic pattern (with or without axonopathic changes) but never an axonopathic pattern only. Only two of the eight survivors at 12 months were not ambulatory. These two patients had no detectable compound muscle action potential on electrophysiological examination.

Conclusion

The combination of electromyographic evaluation and neuromuscular histological abnormalities could help to identify the type and severity of neuromuscular weakness, in turn helping to evaluate the patient's potential functional prognosis.

Neuromuscular blocking agents in neurointensive care

INTRODUCTION

Intensive care treatment of patients with severe head injury is aimed at preventing secondary injury. One of the cornerstones in this treatment is sedation and ventilation. Use of Neuromuscular Blocking Agents (NBA) has gained widespread use as part of the protocol for maintaining normal intracranial pressure values, without class 1 evidence for the efficacy of the treatment.

METHODS

We examined data of the use of NBA as infusion during ventilator treatment, and IntraCranial Pressure (ICP) measurements in the database from the international multicenter randomized double blind trial of the NMDA receptor antagonist Selfotel. No specific mode of sedation was recommended in the study protocol.

RESULTS

Of the 427 patients enrolled in the study 326 had a full data set, 138 received NBA during their stay in the ICU. There were no statistical difference in demographic data between the two groups. During their stay in the ICU, patients who received NBA had a median of 13.5 hours with a recorded ICP above 20 mm Hg, patients who did not receive NBA had a median of 6.5 hours with ICP above 20 mm Hg (p < 0.05).

CONCLUSION

Our data challenges the concept of using NBA as part of a routine sedation strategy in treatment of patients with severe head injury.

Paralysis in the critically ill: intermittent bolus pancuronium compared with continuous infusion

OBJECTIVES

To compare recovery times from neuromuscular blockade between two groups of critically ill patients in whom pancuronium was administered by continuous infusion or intermittent bolus injection. To compare the mean pancuronium requirements (milligrams per kilogram per hour) and to assess the incidence of prolonged recovery times (>12 hrs) and residual muscle weakness.

DESIGN

Prospective, observational cohort.

SETTING

Intensive care unit in a university-affiliated hospital.

PATIENTS

A total of 30 mechanically ventilated patients who required pharmacologic paralysis. Patients were excluded if they had renal failure (creatinine clearance <30 mL/min), heart rate >130 beats/min, hepatic failure, peripheral nerve disease or myopathy, stroke, spinal cord damage, or myasthenia gravis.

INTERVENTIONS

Patients were assigned to receive pancuronium either by continuous infusion (n = 14) or intermittent bolus (n = 16). Depth of paralysis was titrated to maintain one or two responses to Train-of-Four stimulation with an accelerograph and desired clinical goals. Recovery time was defined as time from discontinuation of muscle relaxant until the amplitude of the fourth twitch, measured every 15-30 min using an accelerograph, was 70% the amplitude of the first twitch (Train-of-Four > or = 0.7).

MEASUREMENTS AND MAIN RESULTS

These patients included the only three patients with status asthmaticus in our study. The groups were similar with respect to age, sex, weight, Acute Physiology and Chronic Health Evaluation II score, mode of ventilation, creatinine clearance, indications for paralysis, and duration of pancuronium administration. The median time for patients to recover from paralysis was 3.5 hrs (95% confidence interval, 1.82-5.18) in the infusion group vs. 6.3 hrs (95% confidence interval, 3.40-9.19) in the intermittent bolus group (p = .10). Less drug was administered in the intermittent group (mean, 0.02+/-0.01 mg/kg/hr) than by infusion (mean, 0.04+/-0.01 mg/kg/hr; p < .001). Six patients (five in the infusion group and one in the intermittent group) developed persistent severe muscle weakness. In addition, six different patients (three from each group) had prolonged recovery >12 hrs.

CONCLUSIONS

Our study suggests that recovery time after paralysis with continuous infusion is faster than that after intermittent bolus injection. Although more pancuronium was administered in the continuous-infusion group, recovery time was not prolonged as a consequence. It is uncertain whether pancuronium given by infusion increases the risk of persistent muscle weakness.

Myopathy in critically ill patients

OBJECTIVE

To review myopathic changes occurring during intensive care treatment in the light of recent information about manifestation, clinical settings, pathophysiology, and histomorphologic changes.

DATA SOURCES

The computerized MEDLINE database, bibliography of pertinent articles, and the author's personal files.

STUDY SELECTION

Studies were selected according to their relevance to myopathic complications in critically ill patients.

DATA EXTRACTION

All applicable data were extracted.

DATA SYNTHESIS

Myopathic changes occur frequently in patients treated in the intensive care unit (ICU). Three main types have been identified: critical illness myopathy, myopathy with selective loss of myosin filaments, and acute necrotizing myopathy of intensive care. These histologic types probably represent variable expressions of a toxic effect not yet identified. Candidates for such myotoxic effects are the mediators of the systemic response in sepsis and high-dose administration of corticosteroids and muscle relaxants. The influence of these latter agents appears to be particularly important in the pathogenesis of myosin loss and myonecrosis. Experimental studies suggest that axonal damage attributable to critical illness neuropathy can be an additional factor triggering myopathies in the ICU. Muscle membrane inexcitability was recently identified as an alternative mechanism of severe weakness in ICU patients.

CONCLUSIONS

Myopathic changes are surprisingly frequent in critically ill patients. The clinical importance of this finding is still unknown, but it is likely that weakness caused by myopathy prolongs ICU stay and rehabilitation. Because corticosteroids and muscle relaxants appear to trigger some types of ICU myopathy, they should be avoided or administered at the lowest doses possible. Sepsis, denervation, and muscle membrane inexcitability may be additional factors. Studies addressing the pathophysiology of myopathy in critically ill patients are urgently needed.

Monitoring neuromuscular blockade in the intensive care unit: the peripheral nerve stimulator

Traditionally, neuromuscular blocking agents (NMBAs) have been administered in the operating room as an adjunct to anesthetics. Recent studies in the United States have indicated that 98% of the anesthesiologists and critical care nurses surveyed use NMBAs at least occasionally. When monitoring the use of NMBAs, a combination of clinical monitoring and peripheral nerve stimulator monitoring has been recommended. However, the most effective techniques have yet to be described. Understanding the complexities of NMBAs and the absolute need for accurate monitoring techniques is imperative for clinicians. The purpose of this literature review is to evaluate current literature regarding monitoring techniques of NMBAs and to guide the advanced practice nurse's role in critical care.

Patterns of neurophysiological abnormality in prolonged critical illness

OBJECTIVE

To describe the various patterns of neurophysiological abnormalities which may complicate prolonged critical illness and identify possible aetiological factors.

DESIGN

Prospective case series of neurophysiological studies, severity of illness scores, organ failures, drug therapy and hospital outcome. Some patients also had muscle biopsies.

SETTING

General intensive care unit (ICU) in a University Hospital.

PATIENTS

Forty-four patients requiring intensive care unit stay of more than 7 days. The median age was 60 (range 27-84 years), APACHE II score 19 (range 8-33), organ failures 3 (range 1-6), and mortality was 23%.

RESULTS

Seven patients had normal neurophysiology (group I), 4 had a predominantly sensory axonal neuropathy (group II), 11 had motor syndromes characterised by markedly reduced compound muscle action potentials and sensory action potentials in the normal range (group III) and 19 had combinations of motor and sensory abnormalities (group IV). Three patients had abnormal studies but could not be classified into the above groups (group V). All patients had normal nerve conduction velocities. Electromyography revealed evidence of denervation in five patients in group III and five in group IV. There was no obvious relationship between the pattern of neurophysiological abnormality and the APACHE II score, organ failure score, the presence of sepsis or the administration of muscle relaxants and steroids. A wide range of histological abnormalities was seen in the 24 patients who had a muscle biopsy; there was no clear relationship between these changes and the neurophysiological abnormalities, although histologically normal muscle was only found in patients with normal neurophysiology. Only three of the eight patients from group III in whom muscle biopsy was performed had histological changes compatible with myopathy.

CONCLUSIONS

Neurophysiological abnormalities complicating critical illness can be broadly divided into three types -- sensory abnormalities alone, a pure motor syndrome and a mixed motor and sensory disturbance. The motor syndrome could be explained by an abnormality in the most distal portion of the motor axon, at the neuromuscular junction or the motor end plate and, in some cases, by inexcitable muscle membranes or extreme loss of muscle bulk. The mixed motor and sensory disturbance which is characteristic of 'critical illness polyneuropathy' could be explained by a combination of the pure motor syndrome and the mild sensory neuropathy. More precise identification of the various neurophysiological abnormalities and aetiological factors may lead to further insights into the causes of neuromuscular weakness in the critically ill and ultimately to measures for their prevention and treatment.

Prolonged weakness after cisatracurium infusion: a case report

OBJECTIVE

To present the first documented case report of myopathy persisting for >48 hrs in a patient treated with cisatracurium and concomitant high-dose corticosteroids.

DESIGN

Anecdotal observations in one patient.

SETTING

Medical-respiratory intensive care unit (ICU) at a tertiary care, university teaching hospital.

PATIENT

A 45-yr-old female admitted status for post-bilateral total knee replacement complicated by aspiration pneumonitis and acute respiratory distress syndrome (ARDS).

INTERVENTIONS

The patient required pressure control ventilation and sedation with midazolam and fentanyl infusions. On ICU day 2, the patient was placed on inverse ratio ventilation and paralyzed with cisatracurium. On ICU day 6, methylprednisolone 125 mg i.v. every 6 hrs was initiated for fibroproliferative ARDS. On ICU day 11, methylprednisolone was reduced to 60 mg i.v. every 6 hrs and tapered over several weeks. Cisatracurium infusion rates ranged from 6.3 to 10.5 microg/kg/min, with an average of 8.0 microg/kg/min.

MEASUREMENTS AND MAIN RESULTS

Train-of-Four was assessed before initiation of therapy and every 4 hrs, thereafter. Train-of-Four values were maintained from 1 to 4 throughout therapy and a value of 4 was recorded when therapy was discontinued. On day 13, neuromuscular blocking agent therapy was discontinued, but severe proximal and distal muscle weakness was observed bilaterally. Creatinine kinase concentrations on 3 and 13 days after discontinuation of the paralytic agent were 181 and 96 units/L, respectively. On day 24, the patient moved her fingertips. On ICU day 30, the patient was weaned from the mechanical ventilator. The patient was transferred to the ward on day 33. Extensive rehabilitation with physical and occupational therapy was required for several months.

CONCLUSION

Clinicians should remember that irrespective of chemical structural, neuromuscular blocking agents might produce prolonged paralysis in predisposed patients.

Oxygen delivery, oxygen consumption, and gastric intramucosal pH are not improved by a computer-controlled, closed-loop, vecuronium infusion in severe sepsis and septic shock

OBJECTIVE

To investigate the influence of the neuromuscular blocking agent vecuronium on oxygen delivery (DO2), oxygen consumption (VO2), oxygen extraction ratio, and gastric intramucosal pH in heavily sedated patients with severe sepsis or septic shock.

DESIGN

Prospective, randomized, placebo-controlled, cross-over trial.

SETTING

University hospital intensive care unit.

PATIENTS

Eighteen mechanically ventilated patients with severe sepsis or septic shock.

INTERVENTIONS

All patients were heavily sedated. After baseline measurement, a computer-controlled, closed-loop infusion of either vecuronium or saline was initiated and further measurements were made at 40 and 60 mins. The procedure was repeated with the alternative agent after return of neuromuscular function.

MEASUREMENTS AND MAIN RESULTS

DO2, VO2, intramucosal pH were monitored using pulmonary artery catheters, a gas exchange monitor, and gastric tonometers. Changes from baseline were compared (paired t-test, p = .05). The vecuronium closed-loop infusion achieved T1 between 5% and 15% at 40 mins. There was a significant difference in the changes from baseline for static respiratory compliance in the vecuronium closed-loop infusion group compared with the saline closed-loop infusion group. There was no significant difference in the change from baseline for systemic or pulmonary vascular resistance, DO2, VO2, oxygen extraction ratio, or intramucosal pH.

CONCLUSIONS

In these patients, vecuronium infusion achieved the targeted level of paralysis and improved respiratory compliance but did not alter intramucosal pH, VO2, DO2, or oxygen extraction ratios. With deep sedation, neuromuscular blockade in severe sepsis/septic shock does not significantly influence oxygen flux and should be abandoned as a routine method of improving tissue oxygenation in these patients.