Effects of neuromuscular block on systemic and cerebral hemodynamics and bispectral index during moderate or deep sedation in critically ill patients

Neuromuscular Blockade in Adult Respiratory Distress Syndrome

Although current clinical practice guidelines have discordant conclusions, a judicious approach to using NMBA infusions may include reserving their use for patients with early severe ARDS who are already deeply sedated and for patients under light sedation who have significant ventilator dyssynchrony, despite attempts to adjust both ventilator settings and sedation requirements. Based on current evidence, the duration of NMBA use should be limited to 48 hours, whenever possible.

Management of Neuromuscular Blocking Agents in Critically Ill Patients with Lung Diseases

The use of neuromuscular blocking agents (NMBAs) is common in the intensive care unit (ICU). NMBAs have been used in critically ill patients with lung diseases to optimize mechanical ventilation, prevent spontaneous respiratory efforts, reduce the work of breathing and oxygen consumption, and avoid patient-ventilator asynchrony. In patients with acute respiratory distress syndrome (ARDS), NMBAs reduce the risk of barotrauma and improve oxygenation. Nevertheless, current guidelines and evidence are contrasting regarding the routine use of NMBAs. In status asthmaticus and acute exacerbation of chronic obstructive pulmonary disease, NMBAs are used in specific conditions to ameliorate patient-ventilator synchronism and oxygenation, although their routine use is controversial. Indeed, the use of NMBAs has decreased over the last decade due to potential adverse effects, such as immobilization, venous thrombosis, patient awareness during paralysis, development of critical illness myopathy, autonomic interactions, ICU-acquired weakness, and residual paralysis after cessation of NMBAs use. The aim of this review is to highlight current knowledge and synthesize the evidence for the effects of NMBAs for critically ill patients with lung diseases, focusing on patient-ventilator asynchrony, ARDS, status asthmaticus, and chronic obstructive pulmonary disease.

Comparative analysis of the effect of electromyogram to bispectral index and 95% spectral edge frequency under remimazolam and propofol anesthesia: a prospective, randomized, controlled clinical trial

Background

Bispectral index (BIS), an index used to monitor the depth of anesthesia, can be interfered with by the electromyogram (EMG) signal. The 95% spectral edge frequency (SEF95) also can reflect the sedation depth. Remimazolam in monitored anesthesia care results in higher BIS values than propofol, though in the same sedation level assessed by Modified Observers Assessment of Alertness and Sedation (MOAA/S). Our study aims to illustrate whether EMG is involved in remimazolam causing higher BIS value than propofol preliminarily and to explore the correlations among BIS, EMG, and SEF95 under propofol and remimazolam anesthesia.

Patients and methods

Twenty-eight patients were randomly divided into propofol (P) and remimazolam (RM) groups. Patients in the two groups received alfentanil 10 μg/kg, followed by propofol 2 mg/kg and remimazolam 0.15 mg/kg. Blood pressure (BP), heart rate (HR), and oxygen saturation (SpO2) were routinely monitored. The BIS, EMG, and SEF95 were obtained through BIS VISTATM. The primary outcomes were BIS, EMG, and the correlation between BIS and EMG in both groups. Other outcomes were SEF95, the correlation between BIS and SEF95, and the correlation between EMG and SEF95. And all the statistical and comparative analysis between these signals was conducted with SPSS 26.0 and GraphPad Prism 8.

Results

BIS values, EMG, and SEF95 were significantly higher in the RM group than in the P group (all p < 0.001). There was a strong positive correlation between BIS and EMG in the RM group (r = 0.416). Nevertheless, the BIS in the P group showed a weak negative correlation with EMG (r = -0.219). Both P (r = 0.787) and RM group (r = 0.559) had a reasonably significant correlation coefficient between BIS and SEF95. SEF95 almost did not correlate with EMG in the RM group (r = 0.101).

Conclusion

Bispectral index can be interfered with high EMG intensity under remimazolam anesthesia. However, EMG can hardly affect the accuracy of BIS under propofol anesthesia due to low EMG intensity and a weak negative correlation between EMG and BIS. Moreover, SEF95 may have a great application prospect in predicting the sedation condition of remimazolam.

Electroencephalography spectral edge frequency and suppression rate-guided sedation in patients with COVID-19: A randomized controlled trial

Background

Sedation in coronavirus disease 2019 (COVID-19) patients has been identified as a major challenge. We aimed to investigate whether the use of a multiparameter electroencephalogram (EEG) protocol to guide sedation in COVID-19 patients would increase the 30-day mechanical ventilation-free days (VFD).

Methods

We conducted a double-blind randomized clinical trial. We included patients with severe pneumonia due to COVID-19 who required mechanical ventilation (MV) and deep sedation. We randomized to the control (n = 25) or multiparameter group (n = 25). Sedation in the intervention group was administered following the standard institutional protocols together with a flow chart designed to reduce the propofol administration dose if the EEG suppression rate was over 2% or the spectral edge frequency 95 (SEF95) was below 10 Hz. We performed an intention-to-treat analysis to evaluate our primary outcome (30-day VFD).

Results

There was no difference in VFD at day 30 (median: 11 [IQR 0–20] days in the control group vs. 0 [IQR 0–21] days in the BIS multiparameter group, p = 0.87). Among secondary outcomes, we documented a 17% reduction in the total adjusted propofol administered during the first 5 days of the protocol [median: 2.3 (IQR 1.9–2.8) mg/k/h in the control group vs. 1.9(IQR 1.5–2.2) mg/k/h in the MP group, p = 0.005]. This was accompanied by a higher average BIS value in the intervention group throughout the treatment period.

Conclusion

A sedation protocol guided by multivariate EEG-derived parameters did not increase the 30-day VFD. However, the intervention led to a reduction in total propofol administration.

Effects of depth of neuromuscular blockade on the BIS-guided propofol requirement: A randomized controlled trial

BACKGROUND

Deep neuromuscular blockade is considered beneficial for improving the surgical space condition during laparoscopic surgery. Adequacy of the surgical space condition may affect the anesthetists' decision regarding titration of depth of anesthesia. We investigated whether deep neuromuscular blockade reduces the propofol requirement under bispectral index monitoring compared to moderate neuromuscular blockade.

METHODS

Adult patients undergoing elective laparoscopic colorectal surgery were randomly allocated to a moderate or deep group. A train-of-four count of 1-2 in the moderate group, and a post-tetanic count of 1-2 in the deep group, were maintained by continuous infusion of rocuronium. The induction and maintenance of anesthesia were achieved by target-controlled infusion of propofol and remifentanil. The dose of propofol was adjusted to maintain the bispectral index in the range of 40-50. The remifentanil dose was titrated to maintain the systolic blood pressure to within 20% of the ward values.

RESULTS

A total of 82 patients were included in the analyses. The mean±SD dose of propofol was 7.54 ± 1.66 and 7.42 ± 1.01 mg·kg-1·h-1 in the moderate and deep groups, respectively (P = .104). The mean±SD dose of remifentanil was 4.84 ± 1.74 and 4.79 ± 1.77 μg kg-1 h-1 in the moderate and deep groups, respectively (P = .688). In comparison to the moderate group, the deep group showed significantly lower rates of intraoperative patient movement (42.9% vs 22.5%, respectively, P = .050) and additional neuromuscular blocking agent administration (76% vs 53%, respectively, P = .007). Postoperative complications, including pulmonary complications, wound problems and reoperation, were not different between the two groups.

CONCLUSION

Deep neuromuscular blockade did not reduce the bispectral index-guided propofol requirement compared to moderate neuromuscular blockade during laparoscopic colon surgery, despite reducing movement of the patient and the requirement for a rescue neuromuscular blocking agent.

TRIAL REGISTRATION

Clinicaltrials.gov (NCT03890406).

Intravenous infusion of rocuronium bromide prolongs emergence from propofol anesthesia in rats

BACKGROUND

Neuromuscular blocking agents induce muscle paralysis via the prevention of synaptic transmission at the neuromuscular junction and may have additional effects at other sites of action. With regard to potential effects of neuromuscular blocking agents on the central nervous system, a definitive view has not been established. We investigated whether intravenous infusion of rocuronium bromide affects the emergence from propofol anesthesia.

METHODS

Using an in vivo rat model, we performed propofol infusion for 60 minutes, along with rocuronium bromide at various infusion rates or normal saline. Sugammadex or normal saline was injected at the end of the infusion period, and we evaluated the time to emergence from propofol anesthesia. We also examined the neuromuscular blocking, circulatory, and respiratory properties of propofol infusion along with rocuronium bromide infusion to ascertain possible factors affecting emergence.

RESULTS

Intravenous infusion of rocuronium bromide dose-dependently increased the time to emergence from propofol anesthesia. Sugammadex administered after propofol infusion not containing rocuronium bromide did not affect the time to emergence. Mean arterial pressure, heart rate, partial pressures of oxygen and carbon dioxide, and pH were not affected by rocuronium bromide infusion. Neuromuscular blockade induced by rocuronium bromide, even at the greatest infusion rate in the emergence experiment, was rapidly antagonized by sugammadex.

CONCLUSIONS

These results suggest that intravenous infusion of rocuronium bromide dose-dependently delays the emergence from propofol anesthesia in rats. Future studies, such as detection of rocuronium in the cerebrospinal fluid or central nervous system, electrophysiologic studies, microinjection of sugammadex into the brain, etc., are necessary to determine the mechanism of this effect.

Normative values for SedLine-based processed electroencephalography parameters in awake volunteers: a prospective observational study

Processed electroencephalography (pEEG) is used to monitor depth of anaesthesia and/or sedation. A novel device (SedLine®) has been recently introduced into clinical practice. However, there are no published data on baseline SedLine values for awake adult subjects. We aimed to determine baseline values for SedLine-derived parameters in eyes-open and eyes-closed states. We performed a prospective observational study in healthy volunteers. SedLine EEG-derived parameters were recorded for 2 min with eyes closed and 8 min with eyes open. We determined the overall reference range for each value, as well as the reference range in each phase. We investigated changes in recorded parameters between the two phases, and the interaction between EMG, baseline characteristics, and Patient State Index (PSI). We collected data from 50 healthy volunteers, aged 23-63 years. Median PSI was 94 (92-95) with eyes open and 88 (87-91) with eyes closed (p < 0.001 for open versus close). EMG activity decreased from 47.2% (46.6-47.9) with eyes open to 28.6% (28.0-29.3) with eyes closing (p < 0.001). There was a significant positive correlation between EMG and PSI with eyes closed (p = 0.01) but not with eyes open, which was confirmed with linear regression analysis (p = 0.01). In awake volunteers, keeping eyes open induces significant changes to SedLine-derived parameters, most likely due to increased EMG activity (e.g. eye blinking). These findings have implications for the clinical interpretation of PSI parameters and for the planning of future research.

Minimal alveolar concentration for deep sedation (MAC-DS) in intensive care unit patients sedated with sevoflurane: A physiological study

BACKGROUND

Volatile anaesthetic agents, especially sevoflurane, could be an alternative for sedating ICU patients. In the operating theatre, volatile anaesthetic agents are monitored using minimal alveolar concentration (MAC). In ICU, MAC may be used to assess sedation level and may replace clinical scale especially when they are unusable. Therefore, we sought to investigate the minimal sevoflurane end-tidal concentration to achieved deep sedation in critical ill patients: MAC-deep sedation (MAC-DS).

METHODS

In a prospective interventional study, we included patients with a Richmond Assessment Sedation Score (RASS) of 0 without any sedation. We stepwise increased sevoflurane concentration level before assessing for deep sedation (RASS≤-3). MAC-DS was defined as the minimal sevoflurane MAC fraction or sevoflurane expiratory fraction (FeSevo) to get 90% and 95% of patients in deep sedation (MAC-DS 90 and MAC-DS 95, respectively).

RESULTS

Between June and November 2014, 30 patients were included (median age=60 years [interquartile range: 47-69]). Increasing sevoflurane MAC was correlated with a decrease in RASS values (r=-0.83, P<0.001). MAC-DS 90 and MAC-DS 95 were achieved at 0.42 MAC (CI 95 [0.38-0.46]) and 0.46 MAC (CI 95 [0.42-0.51]), respectively. FeSevo to achieve MAC-DS 90 and MAC-DS 95 was 0.72 (CI 95 [0.65-0.79]) and 0.80 (CI 95 [0.72-0.89]), respectively.

CONCLUSION

In this physiological study involving 30 ICU patients, MAC-DS, end-tidal sevoflurane concentration to get 95% of patients in deep sedation determined over more than 500 observations, is achieved at 0.8% of expired fraction of sevoflurane or at 0.5 age-adjusted MAC.

Effect of neuromuscular blockade on the bispectral index in critically ill patients

INTRODUCTION

It has been suggested that neuromuscular blockade (NMB) affects the capacity of bispectral index (BIS) monitoring to measure consciousness in sedated children. Our aim was to analyse the impact of NMB on BIS values in critically ill children.

METHODS

We conducted a prospective observational study of children monitored with a BIS system that received a continuous infusion of vecuronium. We analysed data on clinical, diagnostic and haemodynamic variables, sedatives, analgesics, muscle relaxants, and BIS parameters. We compared BIS parameters before the use of a muscle relaxant, during its administration, before its discontinuation and for the 24h following the end of the infusion.

RESULTS

The analysis included 35 patients (median age, 30 months). The most common diagnosis was heart disease (85%). The most frequent indication for initiation of NMB was low cardiac output (45%), followed by adaptation to mechanical ventilation (20%). Neuromuscular blockade did not produce a significant change in BIS values. We found a decrease was observed in electromyography (EMG) values at 6h (34.9±9.4 vs 31.2±7; P=.008) and 12h after initiation of NMB (34.9±9.4 vs 28.6±4.8; P =.006). We observed a small significant increase in BIS after discontinuation of NMB (from 42.7±11 to 48.4±14.5, P=.001), and 6 and 12h later (51.3±16.6; P=.015). There were no differences in the doses of sedatives or analgesics except for fentanyl, of which the dose was lowered after discontinuation of vecuronium.

CONCLUSION

Continuous NMB produces small changes on BIS values that are not clinically significant and therefore does not interfere with BIS consciousness monitoring in critically ill children.

Effects of Neuromuscular Blockages on Entropy Monitoring During Sevoflurane Anesthesia

Background

There are no data available on the effects of different degrees of neuromuscular blockade on spectral entropy during sevoflurane anesthesia. This study aimed to observe the effects of different degrees of neuromuscular blockade on state and response entropy during sevoflurane anesthesia.

Material/Methods

Eighty-one female patients were randomized to 9 groups (n=9 per group) according to the concentration of sevoflurane and degree of neuromuscular blockade. Response and state entropy were monitored. The endpoints were: 1) impact of neuromuscular blockade on state entropy and response entropy, and the difference between response entropy and state entropy; and 2) the response of entropy after cutaneous tetanic electrical noxious stimulation to the ulnar nerve under different degrees of neuromuscular blockade and concentrations of sevoflurane.

Results

These were no significant differences in response entropy or state entropy, or differences between response entropy and state entropy among the groups in the awake state (P>0.05). Without noxious stimulation, sevoflurane concentrations and neuromuscular blockade had no significant effects on response entropy or state entropy, or on the difference between response entropy and state entropy (all P>0.05), but sevoflurane concentrations showed a significant effect on state entropy (P<0.05). After noxious stimulation, sevoflurane concentrations and neuromuscular blockade had significant effects on response entropy and state entropy, and on the difference between response entropy and state entropy.

Conclusions

Response entropy and state entropy decreased with increasing sevoflurane concentration. Neuromuscular blockade did not affect entropy without noxious stimulation. With stimulation, muscle relaxants significantly reduced the changes in entropy, and there were significant effects of neuromuscular blockade and sevoflurane on entropy.

Current Use of Neuromuscular Blocking Agents in Intensive Care Units

Neuromuscular blocking agents can be used for purposes such as eliminating ventilator-patient dyssynchrony, facilitating gas exchange by reducing intra-abdominal pressure and improving chest wall compliance, reducing risk of lung barotrauma, decreasing contribution of muscles to oxygen consumption by preventing shivering and limiting elevations in intracranial pressure caused by airway stimulation in patients supported with mechanical ventilation in intensive care units. Adult Respiratory Distress Syndrome (ARDS), status asthmaticus, increased intracranial pressure and therapeutic hypothermia following ventricular fibrillation-associated cardiac arrest are some of clinical conditions that can be sustained by neuromuscular blockade. Appropriate indication and clinical practice have gained importance considering side effects such as ICU-acquired weakness, masking seizure activity and longer durations of hospital and ICU stays. We mainly aimed to review the current literature regarding neuromuscular blockade in up-to-date clinical conditions such as improving oxygenation in early ARDS and preventing shivering in the therapeutic hypothermia along with summarising the clinical practice in adult ICU in this report.

Neuromuscular blocking agents for acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is an acute inflammatory process that impairs the ability of the lungs to oxygenate thereby resulting in respiratory failure. Treatment of ARDS is often a multimodal approach using both nonpharmacologic and pharmacologic treatment strategies in addition to trying to reverse the underlying cause of ARDS. Neuromuscular blocking agents (NMBAs) have been prescribed to patients with ARDS as they are thought to decrease inflammation, oxygen consumption, and cardiac output and help facilitate ventilator synchrony. NMBAs have only been evaluated in patients with early, severe ARDS in three multicenter, randomized, controlled trials (n = 432), but have resulted in decreased inflammation and improved oxygenation, ventilator-free days, and mortality. Despite reports of NMBAs being associated with adverse effects like postparalytic quadriparesis, myopathy, and prolonged recovery, these effects have not been seen in patients receiving short courses of NMBAs for ARDS. A large multicenter, prospective, randomized, placebo-controlled trial is ongoing to confirm benefit of NMBAs in early, severe ARDS when adjusting for limitations of the previous studies. The current available literature suggests that 48 h of NMBA therapy in patients with early, severe ARDS improves mortality, without resulting in additional patient harm.

Clinical Practice Guidelines for Sustained Neuromuscular Blockade in the Adult Critically Ill Patient

OBJECTIVE

To update the 2002 version of "Clinical practice guidelines for sustained neuromuscular blockade in the adult critically ill patient."

DESIGN

A Task Force comprising 17 members of the Society of Critical Medicine with particular expertise in the use of neuromuscular-blocking agents; a Grading of Recommendations Assessment, Development, and Evaluation expert; and a medical writer met via teleconference and three face-to-face meetings and communicated via e-mail to examine the evidence and develop these practice guidelines. Annually, all members completed conflict of interest statements; no conflicts were identified. This activity was funded by the Society for Critical Care Medicine, and no industry support was provided.

METHODS

Using the Grading of Recommendations Assessment, Development, and Evaluation system, the Grading of Recommendations Assessment, Development, and Evaluation expert on the Task Force created profiles for the evidence related to six of the 21 questions and assigned quality-of-evidence scores to these and the additional 15 questions for which insufficient evidence was available to create a profile. Task Force members reviewed this material and all available evidence and provided recommendations, suggestions, or good practice statements for these 21 questions.

RESULTS

The Task Force developed a single strong recommendation: we recommend scheduled eye care that includes lubricating drops or gel and eyelid closure for patients receiving continuous infusions of neuromuscular-blocking agents. The Task Force developed 10 weak recommendations. 1) We suggest that a neuromuscular-blocking agent be administered by continuous intravenous infusion early in the course of acute respiratory distress syndrome for patients with a PaO2/FIO2 less than 150. 2) We suggest against the routine administration of an neuromuscular-blocking agents to mechanically ventilated patients with status asthmaticus. 3) We suggest a trial of a neuromuscular-blocking agents in life-threatening situations associated with profound hypoxemia, respiratory acidosis, or hemodynamic compromise. 4) We suggest that neuromuscular-blocking agents may be used to manage overt shivering in therapeutic hypothermia. 5) We suggest that peripheral nerve stimulation with train-of-four monitoring may be a useful tool for monitoring the depth of neuromuscular blockade but only if it is incorporated into a more inclusive assessment of the patient that includes clinical assessment. 6) We suggest against the use of peripheral nerve stimulation with train of four alone for monitoring the depth of neuromuscular blockade in patients receiving continuous infusion of neuromuscular-blocking agents. 7) We suggest that patients receiving a continuous infusion of neuromuscular-blocking agent receive a structured physiotherapy regimen. 8) We suggest that clinicians target a blood glucose level of less than 180 mg/dL in patients receiving neuromuscular-blocking agents. 9) We suggest that clinicians not use actual body weight and instead use a consistent weight (ideal body weight or adjusted body weight) when calculating neuromuscular-blocking agents doses for obese patients. 10) We suggest that neuromuscular-blocking agents be discontinued at the end of life or when life support is withdrawn. In situations in which evidence was lacking or insufficient and the study results were equivocal or optimal clinical practice varies, the Task Force made no recommendations for nine of the topics. 1) We make no recommendation as to whether neuromuscular blockade is beneficial or harmful when used in patients with acute brain injury and raised intracranial pressure. 2) We make no recommendation on the routine use of neuromuscular-blocking agents for patients undergoing therapeutic hypothermia following cardiac arrest. 3) We make no recommendation on the use of peripheral nerve stimulation to monitor degree of block in patients undergoing therapeutic hypothermia. 4) We make no recommendation on the use of neuromuscular blockade to improve the accuracy of intravascular-volume assessment in mechanically ventilated patients. 5) We make no recommendation concerning the use of electroencephalogram-derived parameters as a measure of sedation during continuous administration of neuromuscular-blocking agents. 6) We make no recommendation regarding nutritional requirements specific to patients receiving infusions of neuromuscular-blocking agents. 7) We make no recommendation concerning the use of one measure of consistent weight over another when calculating neuromuscular-blocking agent doses in obese patients. 8) We make no recommendation on the use of neuromuscular-blocking agents in pregnant patients. 9) We make no recommendation on which muscle group should be monitored in patients with myasthenia gravis receiving neuromuscular-blocking agents. Finally, in situations in which evidence was lacking or insufficient but expert consensus was unanimous, the Task Force developed six good practice statements. 1) If peripheral nerve stimulation is used, optimal clinical practice suggests that it should be done in conjunction with assessment of other clinical findings (e.g., triggering of the ventilator and degree of shivering) to assess the degree of neuromuscular blockade in patients undergoing therapeutic hypothermia. 2) Optimal clinical practice suggests that a protocol should include guidance on neuromuscular-blocking agent administration in patients undergoing therapeutic hypothermia. 3) Optimal clinical practice suggests that analgesic and sedative drugs should be used prior to and during neuromuscular blockade, with the goal of achieving deep sedation. 4) Optimal clinical practice suggests that clinicians at the bedside implement measure to attenuate the risk of unintended extubation in patients receiving neuromuscular-blocking agents. 5) Optimal clinical practice suggests that a reduced dose of an neuromuscular-blocking agent be used for patients with myasthenia gravis and that the dose should be based on peripheral nerve stimulation with train-of-four monitoring. 6) Optimal clinical practice suggests that neuromuscular-blocking agents be discontinued prior to the clinical determination of brain death.

Cerebral hyperaemia after isoflurane anaesthesia for craniotomy of patients with supratentorial brain tumour

BACKGROUND

Few studies look into cerebral blood flow (CBF) changes during emergence from general anaesthesia for craniotomy. The purpose of this study was to assess CBF changes during emergence from general anaesthesia for craniotomy, through monitoring blood oxygen saturation of jugular vein bulb (SjvO2 ) and transcranial Doppler (TCD).

METHODS

We enrolled 30 patients undergoing selective craniotomy (group C) for supratentorial brain tumour resection and 30 patients undergoing selective abdominal surgery (group A). Mean velocity of middle cerebral artery (Vmca), mean arterial pressure (MAP), SjvO2 (only measured in group C), and arterial CO2 partial pressure were measured before anaesthesia, at tracheal extubation, and 30, 60, 90, 120 min after extubation.

RESULTS

Vmca of the same side of tumour was significantly higher than contralateral Vmca before anaesthesia and at all times after extubation in group C. The ipsilateral Vmca increased significantly (95.7 ± 16.9 cm/s vs. 63.7 ± 6.7 cm/s, P < 0.01) at extubation in group C, then declined but still above baseline significantly in the first 2 h after extubation. While Vmca of the right side changed only slightly (63.6 ± 7.7 cm/s vs. 61.8 ± 8.1 cm/s, P < 0.01) but significantly at extubation in group A. SjvO2 increased significantly (81.4% ± 7.4% vs. 60.9% ± 3.7%, P < 0.01) at extubation in group C, and remained above baseline significantly for 2 h. There was no significant correlation between Vmca and MAP at any time.

CONCLUSIONS

Cerebral hyperaemia occurs after supratentorial brain tumour resection surgery. The hyperaemia is more pronounced on the same side as the tumour.

The role of neuromuscular blockers in ARDS: benefits and risks

PURPOSE OF REVIEW

Neuromuscular blocking agents (NMBAs) are part of the pharmaceutical arsenal employed to treat acute respiratory distress syndrome (ARDS). However, their use remains controversial because the potential benefits of these agents are counterbalanced by possible adverse effects. This review summarizes advantages and risks of NMBAs based on the most recent literature.

RECENT FINDINGS

NMBAs have been shown to improve oxygenation during severe ARDS in three randomized controlled trials. The most recent results demonstrated that NMBAs decrease 90-day in-hospital mortality, particularly in the most hypoxaemic patients. NMBAs have not been shown to be an independent risk factor of neuromyopathy in most studies.

SUMMARY

NMBAs are commonly used in ARDS (25-55% of patients), but the benefits and the risks of using these agents are controversial. Recent data suggest that a continuous infusion of cisatracurium during the first 48  h of ARDS, particularly for patients with a P(a)O(2)/F(i)O(2) ratio less than 120, can decrease 90-day in-hospital mortality. NMBAs do not appear to be an independent risk factor for ICU-acquired weakness if they are not given with corticosteroids or in patients with hyperglycaemia.

Sedation for critically ill or injured adults in the intensive care unit: a shifting paradigm

As most critically ill or injured patients will require some degree of sedation, the goal of this paper was to comprehensively review the literature associated with use of sedative agents in the intensive care unit (ICU). The first and selected latter portions of this article present a narrative overview of the shifting paradigm in ICU sedation practices, indications for uninterrupted or prolonged ICU sedation, and the pharmacology of sedative agents. In the second portion, we conducted a structured, although not entirely systematic, review of the available evidence associated with use of alternative sedative agents in critically ill or injured adults. Data sources for this review were derived by searching OVID MEDLINE and PubMed from their first available date until May 2012 for relevant randomized controlled trials (RCTs), systematic reviews and/or meta-analyses and economic evaluations. Advances in the technology of mechanical ventilation have permitted clinicians to limit the use of sedation among the critically ill through daily sedative interruptions or other means. These practices have been reported to result in improved mortality, a decreased length of ICU and hospital stay and a lower risk of drug-associated delirium. However, in some cases, prolonged or uninterrupted sedation may still be indicated, such as when patients develop intracranial hypertension following traumatic brain injury. The pharmacokinetics of sedative agents have clinical importance and may be altered by critical illness or injury, co-morbid conditions and/or drug-drug interactions. Although use of validated sedation scales to monitor depth of sedation is likely to reduce adverse events, they have no utility for patients receiving neuromuscular receptor blocking agents. Depth of sedation monitoring devices such as the Bispectral Index (BIS©) also have limitations. Among existing RCTs, no sedative agent has been reported to improve the risk of mortality among the critically ill or injured. Moreover, although propofol may be associated with a shorter time to tracheal extubation and recovery from sedation than midazolam, the risk of hypertriglyceridaemia and hypotension is higher with propofol. Despite dexmedetomidine being linked with a lower risk of drug-associated delirium than alternative sedative agents, this drug increases risk of bradycardia and hypotension. Among adults with severe traumatic brain injury, there are insufficient data to suggest that any single sedative agent decreases the risk of subsequent poor neurological outcomes or mortality. The lack of examination of confounders, including the type of healthcare system in which the investigation was conducted, is a major limitation of existing pharmacoeconomic analyses, which likely limits generalizability of their results.

[EEG in intensive care unit: which indications, which material?]

There is a growing development of continuous EEG monitoring (cEEG) in the intensive care unit (ICU) management of neurological patients. Its main objective is the detection of epileptic seizures or status epilepticus because the sensitivity of standard short-duration EEG recording in the ICU is poor. The aim of monitoring is to allow rapid recognition and treatment of epileptic complications in order to decrease secondary insults to the brain and improve outcome. Several studies have demonstrated that a large proportion of patients has epileptic crisis after subarachnoid haemorrhage, stroke or brain trauma, without any clinical manifestation. The EEG feature has also demonstrated a prognosis value but its value for clinical management needs further studies. Another application of EEG in the ICU is monitoring depth of anaesthesia or barbiturate treatment. Due to artifacts contamination, this is possible only in deeply sedated of paralyzed patients. The impact or cEEG monitoring on clinical management and its indications have to be further defined.

The EEG signal: a window on the cortical brain activity

The accurate assessment of the depth of anesthesia, allowing a more accurate adaptation of the doses of hypnotics, is an important end point for the anesthesiologist. It is a particularly crucial issue in pediatric anesthesia, in the context of the recent controversies about the potential neurological consequences of the main anesthetic drugs on the developing brain. The electroencephalogram signal reflects the electrical activity of the neurons in the cerebral cortex. It is thus the key to assessment of the level of hypnosis. Beyond visual analysis, several monitoring devices allow an automated treatment of the electroencephalographic (EEG) signal, combining time and frequency domain analysis. Each of these monitors focuses on a specific combination of characteristics of the signal and provides the clinician with useful information that remains, however, partial. For a comprehensive approach of the EEG-derived indices, the main features of the normal EEG, in adults and children, will be presented in the awake state and during sleep. Age-related modifications accompanying cerebral maturation during infancy and childhood will be detailed. Then, this review will provide an update on how anesthetic drugs, particularly hypnotics, influence the EEG signal, and how the main available monitors analyze these drug-induced modifications. The relationships between pain, memory, and the EEG will be discussed. Finally, this review will focus on some specific EEG features such as the electrical epileptoid activity observed under sevoflurane anesthesia. The EEG signal is the best window we have on cortical brain activity and provides a fair pharmacodynamic feedback of the effects of hypnotics. However, the cortex is only one of several targets of anesthesia. Hypnotics and opiates, have also subcortical primary targets, and the EEG performances in the evaluation or prediction of nociception are poor. Monitoring subcortical structures in combination with the EEG might in the future allow a better evaluation and a more precise adaptation of balanced anesthesia.

Monitoring sedation in the critically ill child

Sedation is an essential part of the management of the critically ill child, and its monitoring must be individualised and continuous in order to adjust drug doses according to the clinical state. There is no ideal method for evaluating sedation in the critically ill child. Haemodynamic variables have not been found to be useful. Clinical scales are useful when sedation is moderate, but are limited by their subjective nature, the use of stimuli, and the impossibility of evaluating profoundly sedated patients or those receiving neuromuscular blocking drugs; in addition, many of these scales have not been evaluated in children. The COMFORT scale is the most appropriate, as it was designed and validated for critically ill children requiring mechanical ventilation. Electroencephalography-derived methods permit continuous monitoring, provide an early indication of changes in the level of sedation, and facilitate a rapid adjustment of medication. However, these methods were designed and validated for patients under anaesthesia and their results cannot be fully extrapolated to the critically ill patient; in addition, some of them have not been validated in small children and there is still little experience in critically ill children. The main indications for the use of these methods are in patients with deep sedation and/or neuromuscular blockade. The bispectral index is the most widely used method at the present time. Analysis and comparison of the efficacy of the different methods for evaluating sedation in the critically ill child is required.

Cerebral blood flow monitoring using a novel laser Doppler flowmeter in asphyxiated infants

BACKGROUND

The aim of the present study was to investigate the role of early changes in cerebral blood flow (CBF) predicting the severity of neurological outcome in asphyxiated infants.

METHOD

Serial monitoring of CBF was performed using a newly developed laser Doppler flowmeter (LDF) in parallel with conventional hemodynamic monitoring, such as mean arterial blood pressure (mABP) or heart rate (HR) in 11 asphyxiated infants (five infants with neurological sequelae and six infants without sequelae) during the first 4 days of life. Psychomotor development was followed up to 20 months.

RESULTS

No differences in average CBF, mABP, average HR, or Apgar scores were found between infants with neurological sequelae and those without (P > 0.1). Significant difference was found only in average stability index during the first 48 h of life (SI48), defined as a coefficient of variation of CBF during the corresponding period (P= 0.04). An SI48 > or = 0.24 had positive predictive value of 100% for neurological sequelae while that <0.24 had a negative predictive value of 66.7%.

CONCLUSION

SI48, an average stability index of CBF during the first 48 h of life, can be a useful index to predict neurological outcome in asphyxiated infants.

Responsiveness to stimuli of bispectral index, middle latency auditory evoked potentials and clinical scales in critically ill children

SUMMARY

We performed simultaneous recordings of Bispectral Index (BIS) and middle latency auditory evoked potentials. We also recorded two clinical scales, the Modified Ramsay scale and the COMFORT scale. Heart rate and blood pressure were measured once a day, for a maximum of 5 days, in 81 critically ill children. Changes with tactile, auditory, and painful stimuli were analysed. All the stimuli significantly increased the BIS value, the painful stimulus having the greatest effect. The painful stimulus was the only one that altered the middle latency auditory evoked potentials. Although the responses of the clinical scales to stimuli were statistically significant, they were of little clinical relevance. None of the stimuli used significantly altered the heart rate or blood pressure. We conclude that tactile, auditory and painful stimuli produced changes of little relevance in the clinical scales, BIS or middle latency auditory evoked potentials. We found the BIS was the most sensitive method and the painful stimulus had the greatest effect.

The effects of electromyographic activity on the accuracy of the Narcotrend monitor compared with the Bispectral Index during combined anaesthesia

The Narcotrend is a monitor system for the assessment of depth of anaesthesia. The objective of this trial was to investigate the susceptibility of the Narcotrend to electromyographic (EMG) activity when compared with the Bispectral Index (BIS). We enrolled 33 patients undergoing major urological procedures under combined anaesthesia (thoracic epidural analgesia and general anaesthesia). Anaesthetic depth was assessed simultaneously by the BIS XP and Narcotrend. The intended anaesthetic depth ranged between 40 and 55 in the BIS and between D2 and D0 in the Narcotrend. BIS, but not Narcotrend, values correlated significantly (p < 0.0001) with EMG. BIS values between 70 and 80 occurred intermittently above an EMG activity of 35 dB, whereas the Narcotrend and the clinical signs remained unchanged during the period of elevated BIS values. None of the patients reported intra-operative awareness. Increased electromyographic activity does not affect Narcotrend values. Under combined anaesthesia, the Narcotrend monitor is more reliable when compared with the BIS regarding susceptibility to increased EMG activity.

An assessment of the validity of spectral entropy as a measure of sedation statein mechanically ventilated critically ill patients

OBJECTIVE

To assess whether the Entropy Module (GE Healthcare, Helsinki, Finland), a device to measure hypnosis in anesthesia, is a valid measure of sedation state in critically ill patients by comparing clinically assessed sedation state with Spectral Entropy

DESIGN

Prospective observational study.

SETTING

Teaching hospital general ICU.

PATIENTS AND PARTICIPANTS

30 intubated, mechanically ventilated patients without primary neurological diagnoses or drug overdose receiving continuous sedation.

INTERVENTIONS

Monitoring of EEG and fEMG activity via forehead electrodes for up to 72h and assessments of conscious level using a modified Ramsay Sedation Scale.

MEASUREMENTS AND RESULTS

475 trained observer assessments were made and compared with concurrent Entropy numbers. Median State (SE) and Response (RE) Entropy values decreased as Ramsay score increased, but wide variation occurred, especially in Ramsay 4-6 categories. Discrimination between different sedation scores [mean (SEM) P(K) value: RE 0.713 (0.019); SE 0.710 (0.019)] and between lighter (Ramsay 1-3) vs.deeper (Ramsay 4-6) sedation ranges was inadequate [P(K): RE 0.750 (0.025); SE 0.748 (0.025)]. fEMG power decreased with increasing Ramsay score but was often significant even at Ramsay 4-6 states. Frequent "on-off" effects occurred for both RE and SE, which were associated with fEMG activity. Values switched from low to high values even in deeply sedated patients. High Entropy values during deeper sedation were strongly associated with simultaneous high relative fEMG powers.

CONCLUSIONS

Entropy of the frontal EEG does not discriminate sedation state adequately for clinical use in ICU patients. Facial EMG is a major confounder in clinical sedation ranges.

Entropy is more resistant to artifacts than bispectral index in brain-dead organ donors

OBJECTIVE

To evaluate the usefulness of entropy and the bispectral index (BIS) in brain-dead subjects.

DESIGN AND SETTING

A prospective, open, nonselective, observational study in the university hospital.

PATIENTS AND PARTICIPANTS

16 brain-dead organ donors.

INTERVENTIONS

Time-domain electroencephalography (EEG), spectral entropy of the EEG, and BIS were recorded during solid organ harvest.

MEASUREMENTS AND RESULTS

State entropy differed significantly from 0 (isoelectric EEG) 28%, response entropy 29%, and BIS 68% of the total recorded time. The median values during the operation were state entropy 0.0, response entropy 0.0, and BIS 3.0. In four of 16 organ donors studied the EEG was not isoelectric, and nonreactive rhythmic activity was noted in time-domain EEG. After excluding the results from subjects with persistent residual EEG activity state entropy, response entropy, and BIS values differed from zero 17%, 18%, and 62% of the recorded time, respectively. Median values were 0.0, 0.0, and 2.0 for state entropy, response entropy, and BIS, respectively. The highest index values in entropy and BIS monitoring were recorded without neuromuscular blockade. The main sources of artifacts were electrocauterization, 50-Hz artifact, handling of the donor, ballistocardiography, electromyography, and electrocardiography.

CONCLUSION

Both entropy and BIS showed nonzero values due to artifacts after brain death diagnosis. BIS was more liable to artifacts than entropy. Neither of these indices are diagnostic tools, and care should be taken when interpreting EEG and EEG-derived indices in the evaluation of brain death.