Neuromuscular blockers in surgery and intensive care, Part 1

Vecuronium bromide and its advanced intermediates: A crystallographic and spectroscopic study

Vecuronium bromide (Piperidinium, 1-[(2β,3α,5α,16β,17β)-3,17-bis(acetyloxy)-2-(1-piperidinyl)androstan-16-yl]-1-methyl-, bromide; Norcuron®) has been extensively used in anesthesiology practice as neuromuscular blocking agent since its launch on the market in 1982. However, a detailed crystallographic and NMR analysis of its advanced synthetic intermediates is still lacking. Hence, with the aim of filling this literature gap, vecuronium bromide was prepared starting from the commercially available 3β-hydroxy-5α-androstan-17-one (epiandrosterone), implementing some modifications to a traditional synthetic procedure. A careful NMR study allowed the complete assignment of the ¹H, ¹³C, and ¹⁵N NMR signals of vecuronium bromide and its synthetic intermediates. The structural and stereochemical characterization of 2β,16β-bispiperidino-5α-androstane-3α,17β-diol, the first advanced synthetic intermediate carrying all the stereocenters in the final configuration, was described by means of single-crystal X-ray diffraction and Hirshfeld surface analysis, allowing a detailed conformational investigation.

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.

Review of Continuous Infusion Neuromuscular Blocking Agents in the Adult Intensive Care Unit

The use of continuous infusion neuromuscular blocking agents remains controversial. The clinical benefit of these medications may be overshadowed by concerns of propagating intensive care unit-acquired weakness, which may prolong mechanical ventilation and impair the inability to assess neurologic function or pain. Despite these risks, the use of neuromuscular blocking agents in the intensive care unit is indicated in numerous clinical situations. Understanding pharmacologic nuances and clinical roles of these agents will aid in facilitating safe use in a variety of acute disease processes. This article provides clinicians with information regarding pharmacologic differences, indication for use, adverse effects, recommended doses, ancillary care, and monitoring among agents used for continuous neuromuscular blockade.

Sedation Analgesia and Neuromuscular Blockade in Pediatric Critical Care: Overview and Current Landscape

Sedation is a mainstay of therapy for critically ill children. Although necessary in the care of the critically ill child, sedative drugs are associated with adverse effects, such as disruption of circadian rhythm, altered sleep, delirium, potential neurotoxicity, and immunosuppression. Optimal approaches to the sedation of the critically ill child should include identification of sedation targets and sedation interruptions, allowing for a more individualized approach to sedation. Further research is needed to better understand the relationship between critical illness and sedation pharmacokinetics and pharmacodynamics, the impact of sedation on immune function, and the genetic implications on drug disposition and response.

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.

Rapid-sequence intubation: a review of the process and considerations when choosing medications

OBJECTIVE

To summarize published data regarding the steps of rapid-sequence intubation (RSI); review premedications, induction agents, neuromuscular blockers (NMB), and studies supporting use or avoidance; and discuss the benefits and deficits of combinations of induction agents and NMBs used when drug shortages occur.

DATA SOURCE

A search of Medline databases (1966-October 2013) was conducted.

STUDY SELECTION AND DATA EXTRACTION

Databases were searched using the terms rapid-sequence intubation, fentanyl, midazolam, atropine, lidocaine, phenylephrine, ketamine, propofol, etomidate thiopental, succinylcholine, vecuronium, atracurium, and rocuronium. Citations from publications were reviewed for additional references.

DATA SYNTHESIS

Data were reviewed to support the use or avoidance of premedications, induction agents, and paralytics and combinations to consider when drug shortages occur.

CONCLUSIONS

RSI is used to secure a definitive airway in often uncooperative, nonfasted, unstable, and/or critically ill patients. Choosing the appropriate premedication, induction drug, and paralytic will maximize the success of tracheal intubation and minimize complications.

Muscle relaxants allergy

The most common agents that are responsible for intraoperative anaphylaxis are muscle relaxants. In fact, neuromuscular blocking agents (NMBAs) contribute to 50-70 percent of allergic reactions during anaesthesia. The main mechanism of hypersensitivity reactions to NMBAs is represented by acute type I allergic reactions and the most severe form is anaphylaxis. The rate of non IgE mediated immediate hypersensitivity reactions usually varies between 20 percent and 35 percent of the reported cases in most large series. In a recent report, non allergic suspected reactions to NMBAs occurred with almost the same frequency as did those with an allergic component. Although the precise mechanisms of these reactions remain difficult to ascertain, they usually result from direct non specific mast cell and basophil activation. After diagnostic procedures, regardless of the specific IgE results, NMBAs are contraindicated if the skin tests were positive. In view of the constantly evolving anesthesiologic practices, and of the complexity of allergy investigation, an active policy to identify patients at risk and to provide any necessary support to anaesthetists and allergologists should be promoted. The high frequency of IgE anaphylactic reactions and the feasibility of skin tests in children justify systematic allergy testing whenever hypersensitivity reaction occurs during general anaesthesia.

Pharmacokinetics and pharmacodynamics in the critically ill child

An understanding of pharmacokinetics and pharmacodynamics can allow for a rational approach to prescribing medications for critically ill children. Absorption, distribution, metabolism, elimination, and the response to medications are affected by age and disease state. Various medications are used in the care of critically ill children. Many medications are prescribed for children based on dosing guidance from adult studies, however. Care providers must be cautious of the high risk for drug interactions and adverse reactions in the intensive care setting.

Drugs, their targets and the nature and number of drug targets

What is a drug target? And how many such targets are there? Here, we consider the nature of drug targets, and by classifying known drug substances on the basis of the discussed principles we provide an estimation of the total number of current drug targets.

Reversed Ipsilateral Acoustic Reflex: A Study on Subjects Treated With Muscle Relaxants

OBJECTIVES

To rule out any possible involvement of the middle ear muscles in the genesis of the reversed ipsilateral acoustic reflex (RIAR).

DESIGN

Prospective study to evaluate the effects of muscle relaxants on the RIAR of otosclerotic ears as well as on the acoustic reflex of individuals with normal middle ear function. Admittance recording during ipsilateral acoustic stimulation was performed in patients undergoing pharmacological treatment for surgical procedures. Fentanyl, propofol, and a muscle relaxant were sequentially administered intravenously. Ipsilateral acoustic reflexes were recorded before and after each drug injection. Three patients were affected from otosclerosis, whereas 14 individuals had normal middle ear function. Moreover, the ipsilateral acoustic reflex obtained in normal subjects after their treatment with muscle relaxants was compared with that of 10 otosclerotic patients who were not treated pharmacologically.

RESULTS

The RIAR of three otosclerotic ears was not inhibited by muscle relaxants as well as by fentanyl and propofol. Moreover, muscle relaxants, when administered in normal subjects, always induced the block of the stapedial reflex that was replaced by a reversed reflex strictly similar to the RIAR of the 10 otosclerotic patients not treated pharmacologically. Propofol could also induce, in most of the cases, the reduction and in some occasion even the reversal of the stapedial reflex, whereas fentanyl did not affect it significantly.

CONCLUSION

The RIAR does not appear to be related to the contraction of the middle ear muscles.

Adverse reactions to neuromuscular blocking agents

Neuromuscular blocking agents (NMBAs) play a predominant role in the incidence of severe adverse reactions occurring during anesthesia. Most hypersensitivity reactions are of immunologic origin (IgE-mediated) or are related to direct stimulation of histamine release. The incidence of IgE-mediated hypersensitivity or anaphylaxis is estimated between 1 in 10,000 and 1 in 20,000 anesthesias, and NMBAs represent the most frequently involved substances, with a range of 50% to 70%. Any suspected anaphylactic reaction must be extensively investigated using combined perioperative and postoperative testing. Because of the frequent cross-reactivity observed with muscle relaxants, every available NMBA should be tested. This should help provide documented advice for future administration of anesthesia. There is no demonstrated evidence for systematic preoperative screening in the general population at this time. Other well-known adverse effects have been described, such as the succinylcholine-triggered cytotoxic effects on muscle cells, but these are responsible for characteristic clinical symptoms, which are usually easy to distinguish from anaphylactic reactions