The use of neuromuscular blocking drugs in intensive care practice

Clinical Practice Guideline of Acute Respiratory Distress Syndrome

There is no well-stated practical guideline for mechanically ventilated patients with or without acute respiratory distress syndrome (ARDS). We generate strong (1) and weak (2) grade of recommendations based on high (A), moderate (B) and low (C) grade in the quality of evidence. In patients with ARDS, we recommend low tidal volume ventilation (1A) and prone position if it is not contraindicated (1B) to reduce their mortality. However, we did not support high-frequency oscillatory ventilation (1B) and inhaled nitric oxide (1A) as a standard treatment. We also suggest high positive end-expiratory pressure (2B), extracorporeal membrane oxygenation as a rescue therapy (2C), and neuromuscular blockage for 48 hours after starting mechanical ventilation (2B). The application of recruitment maneuver may reduce mortality (2B), however, the use of systemic steroids cannot reduce mortality (2B). In mechanically ventilated patients, we recommend light sedation (1B) and low tidal volume even without ARDS (1B) and suggest lung protective ventilation strategy during the operation to lower the incidence of lung complications including ARDS (2B). Early tracheostomy in mechanically ventilated patients can be performed only in limited patients (2A). In conclusion, of 12 recommendations, nine were in the management of ARDS, and three for mechanically ventilated patients.

Do Sedation and Neuromuscular Blockade Influence the Outcome of Adult Intensive Care Patients? A Prospective Observational Study

A prospective observational study was conducted on patients admitted to an adult intensive care unit (ICU) to investigate the pattern of sedation, analgesia and neuromuscular blockade and to determine their relationship to patient outcomes. Data including age, gender, diagnoses, dosage of sedatives, analgesics and neuromuscular blocking agents (NMBA), duration of mechanical ventilation, admission and weaning sedation scores, ICU length of stay and outcomes were recorded; 1550 patient-days were studied from 140 mechanically ventilated patients, of which 52 (37%) received NMBA. The mean length of stay in patients receiving NMBA was 15.6 days compared to 11.7 in patients who did not receive them (p=0.08). Mean duration of mechanical ventilation was 12.5 days in patients receiving NMBA, while it was 10.2 days in patients who did not receive NMBA (p=0.21). Neuromuscular blockade did not significantly influence the duration of mechanical ventilation, length of stay and survival of ICU patients.

Exercise limitation following transplantation

Organ transplantation is one of the medical miracles or the 20th century. It has the capacity to substantially improve exercise performance and quality of life in patients who are severely limited with chronic organ failure. We focus on the most commonly performed solid-organ transplants and describe peak exercise performance following recovery from transplantation. Across all of the common transplants, evaluated significant reduction in VO2peak is seen (typically renal and liver 65%-80% with heart and/or lung 50%-60% of predicted). Those with the lowest VO2peak pretransplant have the lowest VO2peak posttransplant. Overall very few patients have a VO2peak in the normal range. Investigation of the cause of the reduction of VO2peak has identified many factors pre- and posttransplant that may contribute. These include organ-specific factors in the otherwise well-functioning allograft (e.g., chronotropic incompetence in heart transplantation) as well as allograft dysfunction itself (e.g., chronic lung allograft dysfunction). However, looking across all transplants, a pattern emerges. A low muscle mass with qualitative change in large exercising skeletal muscle groups is seen pretransplant. Many factor posttransplant aggravate these changes or prevent them recovering, especially calcineurin antagonist drugs which are key immunosuppressing agents. This results in the reduction of VO2peak despite restoration of near normal function of the initially failing organ system. As such organ transplantation has provided an experiment of nature that has focused our attention on an important confounder of chronic organ failure-skeletal muscle dysfunction.

Pulmonary complications of chronic neuromuscular diseases and their management

Chronic neuromuscular diseases may affect all major respiratory muscles groups including inspiratory, expiratory, and bulbar, and respiratory complications are the major cause of morbidity and mortality. Untreated, many of these diseases lead inexorably to hypercapnic respiratory failure, precipitated in some cases by chronic aspiration and secretion retention or pneumonia, related to impairment of cough and swallowing mechanisms. Many measures are helpful including inhibition of salivation, cough-assist techniques, devices to enhance communication, and physical therapy. In addition, ventilatory assistance is an important part of disease management for patients with advanced neuromuscular disease. Because of its comfort, convenience, and portability advantages, noninvasive positive pressure ventilation (NPPV) has become the modality of first choice for most patients. Patients to receive NPPV should be selected using consensus guidelines, and initiation should be gradual to maximize the chances for success. Attention should be paid to individual preferences for interfaces and early identification of cough impairment that necessitates the use of cough-assist devices. For patients considered unsuitable for noninvasive ventilation, invasive mechanical ventilation should be considered, but only after a frank but compassionate discussion between the patient, family, physician, and other caregivers.

Synthesis and neuromuscular blocking activity of 16beta-N-methylpiperazino steroidal derivatives

Steroidal quaternary ammonium compounds 12 and 13 with quaternised nitrogen at positions 3 and 16 of the steroidal nucleus in androstane series were synthesised and their neuromuscular blocking activities and ganglion blocking activities were studied using chick biventer and anaesthetised cat as the models. The bisquaternary compounds 12 and 13 have been found to be greater in potency than D-tubocurarine. Acetoxy derivative 13 has been found to be more potent than pipecuronium bromide taking D-tubocurarine as the standard compound indicating the need of acetoxy function at position 16.

Neuromuscular-blocking drugs. Use and misuse in the intensive care unit

The use of NMB agents for more than 24 to 48 hours in critically ill patients is associated with many potential complications. Neuromuscular-blocking drugs should be used only when their use is essential for optimal patient care. The indications for neuromuscular blockade must be defined clearly, and patients should be evaluated during treatment for the need for continued muscle relaxation. The smallest doses of NMB agents that will accomplish clinical goals should be used. This dosage can be determined through clinical evaluations and peripheral nerve monitoring. It is essential that all patients treated with NMB drugs receive appropriate sedation and analgesia. Myopathies, neuropathies, and alterations of the neuromuscular junction can occur in the ICU setting, and nondepolarizing muscle relaxants seem to be involved in the development of these disorders. Clinicians should be aware of risk factors that may predispose certain patients to neuromuscular complications, including sepsis and the use of high-dose steroids. Neuromuscular-blocking agents should be avoided in these patients if possible. Although not proved, early recognition and treatment of iatrogenic neuromuscular complications may improve patient outcome.

Pharmacokinetic-pharmacodynamic modeling of atracurium in intensive care patients

The authors have studied 10 critically ill patients with acute respiratory distress syndrome who required a neuromuscular blocking drug to assist mechanical ventilation. Patients received a bolus dose of 1 mg/kg of atracurium followed by a constant infusion rate of 1 mg/kg/h of this drug for 72 hours. Neuromuscular block was monitored using an accelerograph. Blood samples were obtained over a 96-hour period. A preliminary independent analysis was done to estimate the individual pharmacokinetic parameters; data were consistent with a one-compartment model. The pharmacodynamic data analysis was then performed using the changes in train-of-four (TOF) count as an index of the therapeutic effect of atracurium. Pharmacokinetic-dynamic variables were calculated using the Sheiner model and the Hill equation. The elimination half-life of atracurium averaged 22 minutes. Mean volume of distribution and plasma clearance were 217 ml/kg and 550 ml/min, respectively. There was a significant hysteresis loop when the TOF count was plotted against predicted plasma atracurium concentrations. The mean sigmoidicity factor, gamma, was 4.04. The concentration producing 50% of the Emax was 1.36 micrograms/mL, and the mean ke0 was 0.059 min-1. Recovery time ranged from 30 to 80 minutes, and none of the patients of this study had residual paralysis.

Duration of action of atracurium when given by infusion to critically ill children

The aim of the study was to investigate the offset time of atracurium when given by continuous infusion on a paediatric intensive care unit and to look for evidence of tolerance. Over a period of 8 months, 20 mechanically ventilated children had a steady-state infusion of atracurium discontinued to enable the assessment of their level of sedation. The offset time of atracurium was assessed by train-of-four (TOF) stimulation of the ulnar nerve. The initial TOF reading was documented as was the time taken to reach a TOF ratio of 0.9. Thirty-five assessments were carried out. The mean offset time of atracurium was 28.7 min (SEM 1.76 min, range 8-56 min). There was no correlation between the dose of atracurium at discontinuation and the offset time of the infusion. The duration of infusion was negatively correlated with the offset time of atracurium, and this effect was most prominent in children who had received infusions for longer than 48 h. When given by continuous infusion, the offset time of atracurium is very variable between individual patients. Infusions administered for longer than 48 h are associated with a significant reduction in the offset time as a result of increasing tolerance.

The effect of induced hypothermia on the duration of action of atracurium when given by infusion to critically ill children

The aim of the study was to investigate the effect of induced hypothermia on the offset time of atracurium when given by continuous infusion to critically ill children. Over a period of 8 months, six mechanically ventilated children had a steady-state infusion of atracurium discontinued. The offset time of atracurium was assessed by train-of-four (TOF) stimulation of the ulnar nerve; recording the time taken to reach a TOF ratio of 0.9. Nine assessments were carried out. The mean offset time of atracurium was 82 min. This was significantly longer than in patients with temperatures within the normal physiological range. When considering all assessments, performed both in hypothermic and normothermic patients, there is a strong correlation between rectal temperature and the offset time of atracurium. Prolonged moderate hypothermia has a very significant effect on the offset time of atracurium when given by infusion to critically ill children.

[The use of curare-like agents in resuscitation]

OBJECTIVE

To analyse current data on use of neuromuscular blocking agents (NBA) in the intensive therapy unit (ITU) patients and to propose practice guidelines.

DATA SOURCES

We did a Medline search of French and English language articles on NBA administration in ITU patients from 1960 to 1998. Data were also selected from our own collection of articles and books.

STUDY SELECTION

Original articles, clinical cases, letters to the editor and review articles were considered.

DATA EXTRACTION

Data on pharmacology of NBA in the ITU patient were extracted, as well as data on administration patterns and cost.

DATA SYNTHESIS

The indications for myorelaxation in ITU patients include either short term use, as in anaesthesia, or long term administration for facilitation of mechanical ventilation, control of increased intracranial pressure, status epilepticus, tetanus and oxygen demand in case of muscular hyperactivity, diagnostic and therapeutic procedures facilitation. A beneficial effect of NBA on the prognosis of the disease for which these agents have been used is not yet proven. Suxamethonium, because for its short onset time and duration of action, is the agent of choice for endotracheal intubation if myorelaxation is required. Among the benzylisoquinolines, atracurium and besilate of cisatracurium are convenient agents in ITU patients, whereas mivacurium is of no special interest. Among the aminosteroids, pancuronium and vecuronium are the most often used agents in the ITU. Rocuronium has not yet been extensively assessed. Myorelaxants carry risks for morbidity and mortality. The difficulty to assess the neurological status and the level of sedation is a recognised adverse effect. An accidental disconnection from the circuit and the resulting asphyxia is nowadays recognised without delay by the ventilator. NBAs increase the rate of bronchopulmonary infections. Cardiovascular complications include extreme bradycardia or sinus arrest following vecuronium administration, and cardiac arrest after suxamethonium injection mainly in burned or traumatised patients. Conversely to anaesthesia, NBAs do not carry a significant risk for anaphylactic or anaphylactoid complications in the ITU. Tachyphylaxis occurs mainly in burns and other pathologies modifying acetylcholine receptors. Neuromuscular complications include myopathy from steroids, postparalytic syndrome, deconditioning syndrome and intensive care polyneuropathy. Prolonged curarisation after discontinuation of NBA administration has a multifactorial origin and must be differentiated from neuromuscular complications. For prolonged neuromuscular blockade, pancuronium, vecuronium and atracurium are the agents of choice. The association with an adequate sedation is essential. Assessment of depth of neuromuscular blockade is not based on clinical symptoms but on train-of-four (TOF) twitch monitoring. A convenient basic relaxation is usually obtained with the suppression of the two last responses to TOF.

CONCLUSION

The use of NBA in ITU patient should result from a rational decision making procedure, the blockade titrated with a TOF monitor and maintained as superficially and shortly as possible.

Vecuronium dose requirement and pupillary response in a patient with olivopontocerebellar atrophy (OPCA)

PURPOSE

Olivopontocerebellar atrophy (OPCA), a variant of spinocerebellar degeneration (Shy-Drager syndrome), is a systemic degenerative disorder affecting the neurons of multiple nuclei. We investigated the sensitivity to vecuronium and the pupillary responses to various stresses in a patient with OPCA.

CLINICAL FEATURES

A 65-yr-old woman with a six-month history of OPCA underwent a left upper lobectomy for lung cancer under propofol-N2O anaesthesia. She had symptoms of dysarthria, bulbar palsy, cerebellar ataxia, Parkinsonism, myosis, pyramidal signs and muscular atrophy of the distal extremities. A cumulative dose-response curve for vecuronium was constructed, and pupillary changes in response to various noxious stimuli were evaluated with concomitant recording of the Spectral-Edge-Frequency 90% (SEF90; the frequency below which 90 percent of the EEG power is located). The dose-response curve for vecuronium and the estimated ED50 value (the 50% blocking dose of vecuronium) in this patient with OPCA were almost identical with those of five ASA I-II patients (27 micrograms.kg-1 vs 31 micrograms.kg-1). The pupil size and the SEF90 did not change after tracheal intubation or surgical stimulation in this patient, while in the control subjects (n = 3), these measures increased in response to both stresses.

CONCLUSIONS

The absence of pupillary and SEF90 responses to noxious stimuli suggests a sensitivity to propofol and/or central autonomic dysfunction in patients with OPCA. Although the dose requirement of vecuronium in this patient was similar to that of the control patients, the effects of neuromuscular blockers may vary depending on the severity of muscle atrophy.

Pharmacokinetics of drugs used in critically ill adults

Critically ill patients exhibit a range of organ dysfunctions and often require treatment with a variety of drugs including sedatives, analgesics, neuromuscular blockers, antimicrobials, inotropes and gastric acid suppressants. Understanding how organ dysfunction can alter the pharmacokinetics of drugs is a vital aspect of therapy in this patient group. Many drugs will need to be given intravenously because of gastrointestinal failure. For those occasions on which the oral route is possible, bioavailability may be altered by hypomotility, changes in gastrointestinal pH and enteral feeding. Hepatic and renal dysfunction are the primary determinants of drug clearance, and hence of steady-state drug concentrations, and of efficacy and toxicity in the individual patient. Oxidative metabolism is the main clearance mechanism for many drugs and there is increasing recognition of the importance of decreased activity of the hepatic cytochrome P450 system in critically ill patients. Renal failure is equally important with both filtration and secretion clearance mechanisms being required for the removal of parent drugs and their active metabolites. Changes in the steady-state volume of distribution are often secondary to renal failure and may lower the effective drug concentrations in the body. Failure of the central nervous system, muscle, the endothelial system and endocrine system may also affect the pharmacokinetics of specific drugs. Time-dependency of alterations in pharmacokinetic parameters is well documented for some drugs. Understanding the underlying pathophysiology in the critically ill and applying pharmacokinetic principles in selection of drug and dose regimen is, therefore, crucial to optimising the pharmacodynamic response and outcome.