bloqueadores neuromusculares actualmente

1332 www.ccmjournal.org May 2013 Volume 41 Number 5

Intensivists use neuromuscular blocking agents for a variety of clin-ical conditions, including for emergency intubation, acute respira-tory distress syndrome, status asthmaticus, elevated intracranial pressure, elevated intra-abdominal pressure, and therapeutic hypothermia after ventricular fibrillationassociated cardiac arrest. The continued creation and use of evidence-based guidelines and protocols could ensure that neuromuscular blocking agents are used and monitored appropriately. A collaborative multidisciplinary approach coupled with constant review of the pharmacology, dos-ing, drug interactions, and monitoring techniques may reduce the adverse events associated with the use of neuromuscular block-ing agents. (Crit Care Med 2013; 41:13321344)Key Words: associated complications; ICU; monitoring; neuromuscular blockade; pharmacology; reversal; use

Currently, controversy surrounds the use of neuromus-cular blocking agents (NMBAs) in the ICU. Proposed adjunctive applications for NMBAs in the ICU include the following: improving chest wall compliance, eliminating ventilator dyssynchrony, reducing intra-abdominal pressures (IAPs), preventing and treating shivering, and preventing ele-vations in intracranial pressure (ICP) from airway stimulation. These relative indications are tempered by clinician concern for development of prolonged ICU-acquired weakness (ICU-AW); prolonged mechanical ventilation; the risk of patient awareness during paralysis; and an increased risk for deep venous throm-bosis (DVT), corneal abrasions, and anaphylaxis (1).

Today, NMBAs are being used much less frequently than in past years. A survey of 34 ICUs from the 1980s reported that 90% of mechanically ventilated patients received NMBAs

(2). A more recent international observational study reported that only 13% of patients on mechanical ventilation received NMBAs (3). A 2006 Canadian survey of critical care practitio-ner practices noted that the most important factors for choos-ing a specific NMBA were clinician experience, duration of action, mechanism of action, and patient-specific factors (4). A similar survey conducted in the United States reported that clinical experience and perception were the most common rea-sons for choosing a NMBA (5).

This review examines the anatomy of the NMJ and the physiology of neuromuscular transmission. The classification, pharmacology, reversal, monitoring, associated complications, and guidelines concerning NMBAs will also be reviewed. In addition, the use of NMBAs in critically ill patients during six clinical situations will be examined: emergency intubation, acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), status asthmaticus, elevated ICP, elevated IAP, and therapeutic hypothermia after out-of-hospital ventricular fibrillation (VF)-associated cardiac arrest (1, 68). A com-puterized literature search through MEDLINE and PubMed (January 1975September 2012) was performed to identify observational and interventional studies evaluating NMBAs for management of emergent/urgent intubation, ALI/ARDS, status asthmaticus, elevated ICP, elevated IAP, and therapeutic hypothermia. The following search terms were used: NMBAs, neuromuscular blockers, paralytics, paralysis, succinylcho-line, atracurium, cisatracurium, pancuronium, rocuronium, vecuronium, critical care, intensive care, mechanical ventila-tion, ALI, ARDS, status asthmaticus, ICP, traumatic brain injury, IAP, abdominal compartment syndrome (ACS), thera-peutic hypothermia, train-of-four (TOF), peripheral nerve stimulator, monitoring, complications, DVT, corneal abrasions, anaphylaxis and neuromuscular blockade, and reversal. We excluded articles published in languages other than English.

ANATOMY/PHYSIOLOGY OF NEUROMUSCULAR TRANSMISSIONThere are three major components involved in neuromuscular transmission: the neuron, the neurotransmitter (acetylcho-line), and the muscle fiber (9). Figure 1 depicts the relation-ship between these three major components of the NMJ. The NMJ marks the location where the axonal terminus lies in close

The Use of Neuromuscular Blocking Agents in the ICU: Where Are We Now?

Steven B. Greenberg, MD1,2; Jeffery Vender, MD, MBA, FCCP, FCCM1,2

1University of Chicago, Chicago, IL.2NorthShore University HealthSystem, Evanston, IL.

Dr. Vendor consulted for Pharmadiem. Dr. Greenberg has disclosed that he does not have any potential conflicts of interest.

For information regarding this article, E-mail: [email protected]

Critical Care Medicine

0090-3493

10.1097/CCM.0b013e31828ce07c

41

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Copyright 2013 by the Society of Critical Care Medicine and Lippincott Williams & Wilkins

DOI: 10.1097/CCM.0b013e31828ce07c

Esther

Concise Definitive ReviewSeries Editor, Jonathan E. Sevransky, MD, MHS

Concise Definitive Review

Critical Care Medicine www.ccmjournal.org 1333

proximity to the muscle membrane. The motor unit comprises a lower motor neuron and its associated innervated muscle. One nerve has the capability of innervating over 100 muscle fibers in the motor unit. Acetylcholine, a neurotransmitter, is produced and stored in vesicles at the NMJ and then released into the synapse once an action potential is generated (9, 10).

Once the action potential reaches the motor terminus, the depolarization results in the release (in the presence of calcium) of approximately 4 million molecules of acetylcholine into the NMJ. Two acetylcholine molecules bind to a postsynaptic nico-tinic receptor on the muscle resulting in an excitatory postsyn-aptic end-plate potential. Once this endplate potential reaches its threshold, it produces a muscle action potential that results in muscle contraction. The muscle returns to its precontractile state once acetylcholine is broken down by the enzyme, ace-tylcholinesterase. The large amount of acetylcholine molecules released in the NMJ acts as a protective mechanism to ensure muscle contraction (911).

CLASSIFICATION OF NMBAs AND PHARMACODYNAMICSMuscle relaxants are typically classified by their mechanism of action (depolarizing vs nondepolarizing) and duration of action (short, intermediate, and long acting). Table 1 depicts the pharmacokinetics, pharmacodynamics, and data relating to dosing and mode of administration of commonly used NMBAs in the ICU (1114). Succinylcholine, the only avail-able depolarizing agent, binds to acetylcholine receptors and causes persistent depolarization (10). Succinylcholine pro-duces initial muscle fasciculations followed by flaccid paralysis (10). It is frequently used for urgent or emergent intuba-tion in the ICU. Nondepolarizing agents act as competitive antagonists of nicotinic receptors, blocking the action of ace-tylcholine (11). These nondepolarizing drugs can be further divided into two groups, aminosteroids (i.e., pancuronium,

vecuronium, and rocuronium) and benzylisoquinoliniums (i.e., atracurium, cisatracurium, doxacurium, and mivacu-rium). Each drug within these classifications has unique phar-macokinetic properties (1113).

PharmacologyAltered Physiology During Critical Illness. Critical illness is associated with altered physiology that may affect the pharma-cokinetics of NMBAs. A lack of understanding or recognition of these changes can result in clinical failures or adverse drug events (15). This section will discuss how age, hypothermia, and electrolytes/pH disturbances may alter the action of NMBAs.

Multiple factors may affect the pharmacokinetics of NMBAs in critically ill patients. Age-related changes (i.e., reduction in total body water, lean body mass, and serum albumin concen-tration) may result in a reduction in the volume of distribution of NMBAs (13). Increased age may contribute to a reduction in the rate of drug elimination via decreases in cardiac output, glo-merular filtration rate, and liver function (1215). Hypothermia may prolong the duration of action of nondepolarizing NMBAs (16, 17). The mechanisms underlying this prolongation include an altered sensitivity of the NMJ, a reduction in acetylcholine mobilization, decreased muscle contractility, reduced renal and hepatic excretion, changes in drug volumes of distributions, and pH-related changes at the NMJ (1618). Hypothermia may also slow the Hoffmann elimination process and prolong the effect of both cisatracurium and atracurium (1318).

Electrolyte and pH disturbances may alter the duration of action of NMBAs. Hypokalemia may augment the block-ade induced by nondepolarizing agents, while also reduc-ing the ability of neostigmine (and other anticholinesterase reversal agents) to reverse the blockade (12, 13). Magnesium prolongs the duration of neuromuscular blockade by inhibit-ing calcium channels in the presynaptic terminal and inhibit-ing postjunctional potentials. Calcium triggers acetylcholine

Figure 1. Depicts the major components of the neuromuscular junction: the neuron, acetylcholine, and the muscle. Acetylcholine is stored in vesicles within the neuron. When an action potential is generated, acetylcholine is released into the synapse in a process called exocytosis. Acetylcholine binds to receptors on the muscle cell to stimulate muscle contraction. (Reproduced with permission from Bargmann C: Neurosciences: Genomics reaches the synapse. Nature 2005; 436:473474.)

Greenberg and Vender


release, and therefore, hypercalcemia may both reduce the sen-sitivity to NMBA and decrease the duration of neuromuscular blockade. The blockade effect of nondepolarizing agents may be enhanced (although the mechanism is not clearly under-stood) by both respiratory and metabolic acidosis (12, 13). Antagonism of neuromuscular blockade by reversal agents may occur more slowly in the presence of a respiratory acidosis or metabolic alkalosis (12, 13).

Organ Dysfunction and NMBAs. Aminosteroid NMBA pharmacokinetics can be affected by liver dysfunction. Pan-curonium half-life is prolonged in patients with cirrhosis because of its increased volume of distribution (19). Similarly, vecuronium can also have a prolonged elimination half-life, reduced clearance, and enhanced blockade in the setting of cir-rhosis. However, the elimination and clearance of vecuronium may not be altered in less severe forms of liver disease (13). Severe hepatic dysfunction can also increase the volume of dis-tribution of rocuronium, which will prolong its elimination half-life and recovery time after reversal (13). Large intubating

doses (1.2 mg/kg) or repeated doses of rocuronium in the set-ting of severe liver disease typically prolong its effect (13).

Aminosteroid NMBAs have variable durations of action in the setting of severe renal disease (13, 19). Renal failure increases elimination half-life and decreases clearance most significantly for the long-acting aminosteroid muscle relaxants (i.e., pancuronium) (13). Vecuronium may have a prolonged effect due to its active metabolite, 3-desacetyl vecuronium, which accumulates to a significant degree with severe renal dis-ease (19). Rocuronium can have an increased volume of distri-bution and decreased plasma clearance in the setting of renal failure (21, 22). However, the duration of action of repeated or single doses of rocuronium is typically not affected by renal failure (13, 21, 22).

Benzylisoquinoliniums may be preferable in ICU patients as they are not affected by renal or hepatic disease (13, 19). Hoffman degradation (a nonenzymatic degradation) accounts for most of the metabolism of both atracurium and cisatracurium (19). Cisatracurium ICU infusion studies (> 24-hr duration) suggest

TABLE 1. Drug Information on the Commonly Used Neuromuscular Blocking Agents in the ICU

NMBA Agent

NMBA Type

Pancuronium

A

Vecuronium

A

Rocuronium

A

Atracurium

B

Cisatracurium

B

Succinylcholine

D

Category (acting)

Long acting Intermediate Intermediate Intermediate Intermediate Short

Time to maximal blockade (min)

23 34 12 35 23 < 1

Duration of action (min)

60100 2035 2035, 6080 with rapid sequence dose

2035 3060 510

Dose

Bolus 0.050.1 mg/kg 0.080.1 mg/kg 0.61 mg/kg (11.2 mg/ kg for rapid sequence)

0.40.5 mg/kg 0.l0.2 mg/kg 1 mg/kg, dose higher in pediatrics

Continuous infusion dosing

0.81.7 mcg/ kg/min

0.81.7 mcg/ kg/min

812 mcg/ kg/min

520 mcg/ kg/min

13 mcg/kg/ min

Infusions no longer used commonly

Elimination 4570% renal, 1015% hepatic

50% renal, 3550% hepatic

33% renal, < 75% hepatic

510% renal, Hoffman elimination

510% renal, Hoffman elimination

Plasma cholinesterase

Active metabolites

3-OH and 17-OH pancuronium

3-Desacetyl- Vecuronium

None None (toxic metabolite- laudanosine)

None None

Side effects Vagal blockade, sympathetic stimulation, blocks muscarinic stimulation (bradycardia)

Vagal blockade at higher doses

Vagal blockade at higher doses, weakly blocks muscarinic stimulation (bradycardia)

Histamine release, minimal ganglionic blockade

None Minimal amount of histamine release, muscarinic stimulation (bradycardia)

NMBA = neuromuscular blocking agent, A = aminosteroid, B = benzylisoquinolinium, D = depolarizing agent.Information taken from references 1526.



that there is marginal accumulation of the drug. Several stud-ies suggest that the duration of action of cisatracurium is not affected by organ dysfunction (23). Laudanosine, a metabolite of atracurium, has central nervous system stimulating effects. Laudanosine levels have been reported to increase when using long-term atracurium infusions but are typically not high enough to promote seizure activity in humans (13, 19, 23).

Drug Interactions and NMBAs. Drug interactions may also alter the duration of action of NMBAs. Table 2 depicts some of the more common effects of drugs on neuromus-cular blockade. Certain antibiotics (i.e., aminoglycosides, clindamycin, and tetracycline) prolong the duration of NMBAs (24). Furosemide, calcium channel blockers, local anesthetics, and inhaled anesthetics can also potentiate neuromuscular blockade. Patients on chronic antiepileptic medications are typically resistant to aminosteroid NMBAs. This phenomenon may be due to increase clearance of these

NMBAs, an increase in binding to -1 acid glycoproteins, or an up-regulation of acetylcholine receptors. Participa-tion by a clinical pharmacist in the multidisciplinary ICU daily rounds coupled with the use of close neuromuscular monitoring may help prevent unwanted prolongation or reduction in neuromuscular blockade produced by drug interactions (1, 13, 24).

Reversal AgentsAnticholinesterase reversal agents (neostigmine, edropho-nium, or pyridostigmine) are only effective for nondepolariz-ing blockers and increase acetylcholine at the NMJ to reduce residual neuromuscular blockade (25). The duration of ace-tylcholinesterase inhibition is longer with pyridostigmine and neostigmine when compared with edrophonium, due to a strong covalent bond interaction between these two drugs and acetylcholinesterase (26, 27).

TABLE 2. Drug Interactions and Neuromuscular Blocking Agents

Drug Method

Causes resistance to NMB

Phenytoin Up-regulation of acetylcholine-R

Ranitidine Unknown

Carbamazepine Competes for acetylcholine receptors

Theophylline, caffeine Unknown

Calcium Antagonizes potentiating effect of magnesium on neuromuscular blockade

Prolongs NMB

Inhaled anesthetics Reduced postjunctional receptor sensitivity to acetylcholine

Magnesium Competes with calcium presynaptically

Potassium Low potassium enhances blockade and reduces ability of reversal by antagonists

Lithium Activation of potassium channels presynaptically

Immunosuppressant

Corticosteroids May decrease sensitivity of endplate to acetylcholine

Cyclosporine May inhibit neuromuscular blocking agent metabolism

Cardiovascular Reduces prejunctional acetylcholine release and decreases muscle contractility

Furosemide

-blockers and calcium channel blockers

Procainamide

Quinidine

Antibiotics Reduces prejunctional acetylcholine release, decreases postjunctional receptor sensitivity to acetylcholine, blocks acetylcholine receptors, or disrupts ion channels

Aminoglycosides

Tetracyclines

Clindamycin

Vancomycin

NMB = neuromuscular blocker.Information produced from references (15, 16, 23, 24).



Concomitant use of antimuscarinics (glycopyrrolate or atropine) with anticholinesterases is recommended to coun-teract side effects of increasing acetylcholine at muscarinic sites (i.e., bradycardia, bradyarrhythmias, increased secretions, and bronchoconstriction) (26, 27). Atropine (0.0050.01 mg/kg) is typically used with edrophonium (0.51.5 mg/kg) as they both have similar onsets of action (27). Glycopyrrolate (0.0070.015 mg/kg) is used to counteract the cholinergic effects of neostigmine (0.040.07 mg/kg). Alternatively, 0.2 mg of glycopyrrolate (IV) for each 1.0 mg of neostigmine or 5.0 mg of pyridostigmine can be given (27).

Clinicians should recognize that muscle weakness can occur when anticholinesterases are given to patients with full neu-romuscular recovery (2529). Clinical studies have demon-strated that administration of anticholinesterases in the setting of near complete neuromuscular recovery (TOF 0.9) resulted in a decrease in minute ventilation, upper airway muscle tone, and diaphragmatic function (28, 29).

Newer drugs that selectively encapsulate aminosteroid non-depolarizing agents (sugammadex-a modified A-cyclodextrin) provide more rapid reversal of aminosteroid NMBAs (3034). Sugammadex acts by forming tight complexes with these agents. Plasma steroidal neuromuscular blockers are quickly removed. The subsequent drop in plasma aminosteroid agent concentration produces a concentration gradient that allows for more aminosteroid to move from the NMJ into plasma. This remaining NMBA rapidly forms inactive complexes with the available plasma sugammadex (30). Sugammadex is cur-rently not available in the United States (but is available in Europe), nor has it been tested in the critically ill (3034). However, it may allow for the use of steroidal agents for urgent/emergent intubation in those patients in which succinylcho-line administration is contraindicated (see urgent/emergent intubation section). Furthermore, it may serve as a life-saving measure in those patients who receive aminosteroidal agents for intubation and who cannot be ventilated or intubated. Ongoing investigations may also address whether sugamma-dex can be used to reliably mitigate aminosteroid agent-asso-ciated anaphylaxis (35). Studies are warranted to validate its clinical use in the ICU.

MonitoringRepeated clinical, qualitative, and quantitative evaluation of the depth of neuromuscular blockade may result in a reduction of NMBA dose and a subsequent decrease risk of complica-tions from residual neuromuscular blockade (36). Intensivists may look to achieve the absence of spontaneous ventilation to improve patient-ventilator synchrony. Clinical signs (such as the presence of spontaneous ventilation, eye opening, sus-tained hand grip, leg lift, or sustained 5-s head lift), used alone to determine the extent of muscle relaxation, are poor deter-minants in predicting the presence of residual neuromuscular blockade (37). In addition, these signs are not useful in those patients who are uncooperative.

Peripheral nerve stimulators can facilitate appropriate titra-tion of NMBAs (94). TOF monitoring is the primary qualitative

method used for assessment of neuromuscular blockade and involves four supramaximal electrical impulses every 0.5 sec-onds applied to the ulnar, facial, or posterior tibial nerve (1, 13). Figure 2 depicts a peripheral nerve stimulator eliciting a TOF response. Stimulation of these nerves will produce four visualized muscle twitches from the associated muscles (typi-cally muscles of the thumb or eye) that are innervated by the nerves. Fade of the twitch response occurs with increasing neuromuscular blockade (37) (Fig. 2C). Evaluation of fade can be performed by comparing the strength (TOF ratio) of the fourth twitch to that of the first twitch (25, 37).

Several factors play a role in the assessment of TOF moni-toring. The loss of electrode skin adhesion, incorrect electrode placement, peripheral edema, and hypothermia (dampens peripheral stimulator twitch responses) can all contribute to inaccuracies in interpreting the TOF response (37, 38). TOF monitoring coupled with clinical evaluation has been shown to be insensitive for predicting residual neuromuscular weakness (25, 37). Patients with residual neuromuscular weakness can

On/Off

DBS Sustainedtetanus

Train- of-Four

SingleTwitch

- mA+

2a. TOF pattern (0.5 seconds each)

2b. Response in absence of NMB

2c. Response with partial NMB

Figure 2. Depicts a peripheral nerve stimulator applied to stimulate the ulnar nerve and the train-of-four (TOF) stimulation pattern with no neu-romuscular blockade (NMB) and partial blockade. A, TOF pattern (0.5 s each). B, Response in absence of NMB. C, Response with partial NMB. DBS = double burst suppression.



present with difficulty swallowing, rapid shallow breathing, nasal flaring, and overuse of accessory muscles (39). Studies suggest that residual neuromuscular blockade may lead to postoperative complications, including aspiration, atelectasis, pneumonia, and acute respiratory failure (25, 3740).

Quantitative neuromuscular monitoring allows clini-cians to both stimulate the peripheral nerve and quantify the response to nerve stimulation (37). These devices are not rou-tinely used in the ICU. Acceleromyography is available and has been used in the operating room (37). Acceleromyography modules have been integrated in some bedside monitoring systems and can be used in the operating room and ICU. Figure 3 depicts how this monitor is applied on the patient. This device may help reduce signs and symptoms of residual neuromuscular weakness along with respiratory complica-tions (hypoxemia and airway obstruction) (41, 42). Research is needed regarding quantitative monitoring and its utiliza-tion in the ICU.

A limited number of studies demonstrate a significant clini-cal benefit of neuromuscular monitoring for ICU patients (43, 44). An early open-label study using qualitative neuromuscular monitoring and adequate sedation showed that ICU patients did not experience prolonged paralysis, weakness, or other neuromuscular sequelae (45). Rudis et al (46) observed that neuromuscular monitoring decreased the amount of drug per hour, reduced the total drug used, and improved recovery time from neuromuscular blockade. Follow-up studies using a similar comparison with either atracurium or cisatracurium did not find this positive effect (47, 48). A more recent double-blinded randomized trial in a pediatric ICU found that neuro-muscular monitoring did not eliminate prolonged recovery in patients on vecuronium infusions (49). Trials are warranted to determine which patient populations will derive benefits from neuromuscular monitoring.

NMBAs AND ASSOCIATED COMPLICATIONS

ICU-Acquired WeaknessThe causes for ICU-acquired skeletal muscle weakness (ICU-AW) remain controversial. ICU-AW is classified as critical ill-ness polyneuropathy, critical illness myopathy, or critical illness neuromyopathy based on different electrophysiologic test find-ings (43, 50, 51). Proposed mechanisms for ICU-AW include disturbances in the microcirculation, protein malnutrition, systemic inflammation, and prolonged immobility (43, 50).

More than 40 case reports have implicated NMBAs as a possi-ble cause for ICU-AW (43, 52, 53). However, there is a paucity of well-designed trials that confirm this relationship (43). The exist-ing studies examine a heterogeneous critically ill patient popu-lation and are methodologically compromised by variability in data collection (43). Other proposed risk factors, such as the use of high-dose corticosteroids, hyperglycemia, variation in age among studied populations, amount of sedation used, and type and duration of NMBAs administration, were not consistently controlled (43, 50, 51). Inconsistent use of electrophysiologic and manual muscle testing complicates interpretation of the pub-lished studies. Some investigators have suggested that these tests do not correlate with muscle function or outcome (43, 50, 51).

Two recent trials did not identify an increased prevalence of ICU-AW in ARDS patients administered a 48-hour cisatracu-rium infusion (54, 55). Future investigations should examine the impact of other factors associated with ICU-AW, such as corticosteroids, sedation use, type and duration of NMBAs, or immobility. Trials should be performed on additional popu-lations (non-ARDS) to investigate whether limited use of NMBAs is associated with ICU-AW (43).

Awareness During Induced ParalysisA recent case series reported 11 ICU patients who had been aware during pharmacologic paralysis (56). The common themes reported were thoughts of life and death, weird dreams, fear, and resisting being tied down. It is imperative to achieve a deep sedative state with sedatives and analgesics prior to the initiation of an NMBA to mitigate the risk of awareness. The authors suggest that strict adherence to sedation guidelines and protocols may facilitate appropriate titration of drugs while reducing awareness during paralysis. They also recom-mended that monitors should be developed to help clinicians appropriately titrate NMBAs, sedatives, and hypnotics as seda-tion titration protocols are not adequate enough to eliminate awareness (5661).

No continuous bedside monitor has been universally used to alert clinicians of the potential for awareness. Processed electro-encephalogram models, such as the bispectral index (BIS mon-itor-Aspect Medical Systems, Covidien, Mansfield, MA), have been introduced into ICUs that may quantitatively monitor the level of consciousness (62). A recent ICU study suggested a satisfactory correlation between BIS values and validated sedation scales (63), whereas others have refuted it (6265). Well-designed clinical trials are needed to validate a correlation between sedation scales and continuous bedside monitors.

Piezoelectric sensor

Figure 3. Illustration of how the hand-held acceleromyography device is applied to a patient. This device stimulates the ulnar nerve producing thumb movement. A piezoelectric sensor is fixed onto the thumb and senses the acceleration of thumb movement. This acceleration is then sensed by the displayed monitor.



DVT and Corneal AbrasionsNMBA administration to ICU patients may lead to nosocomial complications, such as DVT and corneal abrasions. Immobil-ity achieved by paralysis increases stasis of flow leading to an increase in DVT rate (66). A recent study reported that the use of NMBAs is the strongest predictor for the development of ICU-related DVTs (67). The same trial reported that educa-tional initiatives to promote DVT prophylaxis (both mechani-cal and pharmacologic) significantly reduced the prevalence of DVTs (67). Closer neuromuscular monitoring coupled with protocols to guide titration of NMBAs may also contribute to reducing the DVT prevalence by reducing the time to recovery from neuromuscular blockade (67).

NMBAs also increase the risk of corneal abrasions in criti-cally ill patients. Paralysis abolishes eyelid closure and the blink reflex, which may result in cornea drying, scarring, ulceration, and infection (66). The prevalence of corneal abrasions in the adult critically ill varies from 8% to 60%, depending on the study design (68). Prophylactic eye protection (i.e., artificial ointments, eye covers, or methylcellulose drops) may reduce the prevalence of this ophthalmic complication (68).

AnaphylaxisAllergic reactions associated with NMBAs are typically IgE-mediated (69). The ammonium ion in many NMBAs is the likely allergic component, which is also seen in many com-mon household products. Patients may develop anaphylaxis after the first dose of NMBA due to cross reactivity with other inciting agent exposures. Seven consecutive large French sur-veys over an 18-year period suggested that NMBAs are the most frequent perioperative agents (more than sedatives, hypnotics, latex, antibiotics, and colloids) involved in allergic reactions (70, 71).

A diagnostic approach to suspected cases of anaphylaxis may include the following: obtaining a detailed medical his-tory, observing clinical signs (under deep sedation-pulseless-ness, oxygen desaturation, bronchospasm, and difficulty in ventilating), performing mediator release assays at the time of the reaction (i.e., tryptase levels), quantifying specific IgE immediately or during the first 6 months after the event, and performing skin tests and other biologic assays, such as hista-mine release tests or basophil activation (69, 71). The mainstay for diagnosis is the combination of obtaining the appropri-ate history with skin testing. Skin prick (SPT) or intradermal testing (IDT) are typically performed within 6 weeks of the reaction. Skin tests for NMBA usually remain positive for years following the exposure. Control testing (with saline) should be performed to ensure an accurate result. Skin testing has a high reported sensitivity (9497%) (69). SPT is preferred when investigating an NMBA anaphylactic reaction, whereas IDT is recommended to investigate a cross reaction (69, 71).

GuidelinesCritical Care Medicine published ICU guidelines in 2002 stat-ing that NMBAs should be used for an adult patient in an ICU to manage ventilation, manage increased ICP, treat muscle

spasms, and decrease oxygen consumption only when all other means have been tried without success (Grade C recommen-dation) (72). Both clinical and TOF monitoring was also rec-ommended (Grade B) so that the least amount of drug is used for the shortest duration (72). Guidelines have been developed for the titration of sedation and analgesics (7376). Clinicians should evaluate the reason for (at least daily) and depth of neu-romuscular blockade (continuously) so that mobility may be achieved faster, which may decrease the prevalence of delirium, increase functional independence, and increase ventilator-free days (77, 78).

NMBA ICU Applications: Urgent/Emergent IntubationSuccinylcholine (11.5 mg/kg) is typically used to establish control of the airway to reduce the risk of aspiration due to its rapid onset (3060 s) and short duration of action (510 min) (79, 81). A 2008 Cochrane Database meta-analysis (37 stud-ies included) suggested that succinylcholine administration was associated with superior intubating conditions when compared with rocuronium (82). When rocuronium (1.2 mg/kg) was used, it was associated with similar intubating con-ditions when compared with succinylcholine. However, suc-cinylcholine was still reported to be clinically superior due to its shorter duration of action (82). A more recent randomized controlled trial in the ICU compared rocuronium (0.6 mg/kg) with succinylcholine (83). This trial suggested that there was no difference between the two drugs with regard to intubating conditions, prevalence and severity of oxygen desaturations, and prevalence of failed intubation attempts (83). Succinyl-choline should be avoided in the following clinical conditions where its depolarizing effect can cause a substantial increase in extracellular potassium: sustained muscle weakness, prolonged immobility, massive trauma with significant muscle injury, severe abdominal infections, concomitant acidosis and severe hypovolemia, or burns. Patients with renal failure can develop an increase in plasma potassium (approximately 0.5 mEq/L1 mEq/L) with use of succinylcholine, and therefore, it is rela-tively contraindicated in these patients (7981).

Nondepolarizing NMBAs are the alternatives to succinyl-choline for endotracheal intubation. High-dose rocuronium (11.2 mg/kg) is commonly used for rapid intubation due to its relative short onset (12 min) of action (79). However, the duration of action is much longer with this dose (approxi-mately 6080 min) when compared with the standard intubating dose of rocuronium 0.6 mg/kg (2035 min). Rocuronium has a significant longer duration of action when compared with succinylcholine, and therefore, it may not be the appropriate drug for an anticipated difficult intuba-tion or mask ventilation as hypoxemia may occur (79, 82). Caution should also be used in patients with aminosteroid allergies (anaphylaxis has been reported with rocuronium) (71). Cisatracurium may be advantageous for intubation in patients with both liver and renal dysfunction. However, its onset of action is longer than rocuronium and its duration of action is comparable or somewhat longer than rocuronium. This does not make it an ideal drug for securing the airway



emergently (47, 81). A recent study investigated the use of NMBAs for emergent endotracheal intubation in 566 patients from two major tertiary care centers (84). The use of NMBAs was associated with an improvement in intubating condi-tions and a reduction in both the prevalence of hypoxemia and procedure-related complications (aspiration, traumatic intubation, esophageal intubation, dental injury, and endo-bronchial intubation) (84).

ALI/ARDSALI/ARDS is managed by treating the underlying cause of respiratory failure while reducing the risk of ventilator-induced lung injury (6, 85, 86). Induction of paralysis may increase chest wall compliance, eliminate patient-ventilator dyssynchrony, facilitate lung recruitment, reduce inflam-matory mediator release, decrease lung hyperinflation, and reduce oxygen consumption (albeit controversial) (6, 87). At least eight clinical trials have assessed the use of NMBAs for managing ALI/ARDS (Table 3) (1). Two small observational trials in ALI/ARDS patients prior to the year 2000 reported no effect on oxygenation when using a pancuronium bolus (88, 89). A large retrospective study by Arroliga et al (3) in

2005 noted that 13% of patients were administered NMBAs for at least 1 day. NMBA use was associated with prolonged duration of mechanical ventilation, ICU length of stay, and an increase in mortality (3). A small randomized crossover trial in severe sepsis patients reported that oxygen consumption or delivery was not improved in patients randomized to receive NMBAs (90).

Short-term use of cisatracurium in patients with ALI/ARDS has been associated with beneficial outcomes. Two small ran-domized controlled trials using cisatracurium in patients with ARDS demonstrated an improvement in oxygenation (91, 92). Another randomized trial in ARDS patients demonstrated that the early use of cisatracurium for 48 hours improved oxy-genation and reduced concentrations of pulmonary inflam-matory mediators (54). A larger multicenter trial in patients with severe ARDS (PaO

2/FIO

2 < 150 mm Hg) reported that

early administration of cisatracurium for 48 hours increased adjusted 90-day survival, ventilator-free days, organ failurefree days, and reduced barotrauma (55). Further studies are required to define the appropriate combination of sedation and NMBAs and to identify when NMBA use will improve outcomes in patients with ALI/ARDS.

TABLE 3. Use of Neuromuscular Blocking Agents for Acute Respiratory Distress Syndrome in the ICU

Citation Study Design NMBA Regimen Conclusions

Papazian et al (54) RCT (n = 340), severe ARDS Cisatracurium infusion 48 hr vs placebo

Improved adjusted 90-d survival (p = 0.04), increased ventilator-free days (p = 0.03), increased organ dysfunctionfree days (p = 0.01), decreased barotrauma (p = 0.03)

Arroliga et al (7) Retrospective (n = 549), ALI/ARDS

High PEEP group, 45% had NMBA; low PEEP group, 33% had NMBA

No difference in 60-d mortality or length of mechanical ventilation

Forel et al (55) RCT (n = 36), ARDS Cisatracurium infusion 48 hr vs placebo

Significant reduction in pulmonary/systemic cytokines (p = 0.005, p = 0.04) and increased oxygenation (p < 0.001)

Arroliga et al (3) Retrospective (n = 5183), patient with mechanical ventilation 12 hr

13% of patients given NMBA

Significant increase in ICU mortality (p < 0.001), duration of mechanical ventilation (p < 0.001), and ICU length of stay (p < 0.001)

Gainnier et al (91) RCT (n = 56), severe ARDS Cisatracurium infusion 48 hr vs placebo

Improvement in oxygenation (p = 0.021), decrease in FIO2 (p < 0.001), and decrease in PEEP (p = 0.036)

Lagneau et al (92) RCT (n = 102), ARDS Cisatracurium (2-hr infusion) used train-of-four to titrate NMBA

Increase in oxygenation in groups with NMBA (p = 0.0014)

Conti et al (89) Prospective, open label (n = 13); ALI/ARDS

1 bolus-pancuronium No difference in oxygenation

Bishop (88) Prospective, open label (n = 9); ALI/ARDS

1 bolus-pancuronium No difference in oxygenation

NMBA = neuromuscular blocking agent, RCT = randomized controlled trial, ALI = acute lung injury, ARDS = acute respiratory distress syndrome, PEEP = positive end-expiratory pressure.



Status AsthmaticusNMBAs are used sparingly for patients with status asthmati-cus to minimize ventilator asynchrony, lung hyperinflation, and barotrauma (44). Table 4 presents several trials examin-ing NMBA use in patients with status asthmaticus. ICU-AW is reported in this population (93) and appears to be more commonly associated with the use of concomitant high-dose steroids (9498). A recent retrospective study in mechani-cally ventilated patients with status asthmaticus suggested that patients who require deep sedation with persistent immobiliza-tion are still at risk for weakness, despite a decline in the dura-tion of induced paralysis (97). The risk of prolonged weakness may be reduced by using the minimal doses of sedation, corti-costeroids, and NMBAs required to achieve the desired effect and to withdraw these drugs as soon as possible (97, 98).

Increased ICPNMBAs are typically reserved for patients with intracranial hypertension in whom sedation alone does not reduce ICP

(99). Few studies have evaluated the use of NMBAs for the management of elevations in ICP due to coughing, suctioning, or movement (100107) (Table 5). Hsiang et al (100) suggested that while NMBAs may reduce mortality, they may increase severe disability. The routine use of NMBAs for elevated ICP does not appear to be indicated at this time (106, 107). Patients who receive extended neuromuscular blockade as a second tier therapy for elevated ICP can be monitored with peripheral nerve stimulation to potentially avoid unwanted side effects (see Monitoring section) (99).

Increased IAPIntra-abdominal hypertension (IAH) is defined as a repeated elevation in IAP of at least 12 mm Hg (108110). ACS is defined as continued IAH of greater than 20 mm Hg with end-organ dysfunction or failure (109, 110). Reduced abdominal wall compliance due to third spaced fluids, tense abdominal closures, and pain or inadequate sedation can lead to further increases in IAPs and subsequent organ failure (110). NMBAs

TABLE 4. Use of Neuromuscular Blocking Agents for Status Asthmaticus in ICU

Author Study Design% of patient receiving NMBA Results

Kesler et al (97) Retrospective (n = 170) 67% before 1995, 77% after 1995

No statistically significant difference in weakness between NMBA group and sedation-only group

Adnet et al (96) Retrospective (n = 118) 54% Higher prevalence of muscle weakness, longer mechanical ventilation, longer ICU stay, and increase prevalence of pneumonia in NMBA group

Behbehani et al (130) Retrospective (n = 86) 35% Increase myopathies with NMBAs

Leatherman et al (94) Retrospective (n = 107) 65% Increase prevalence of muscle weakness with steroids + NMBAs, but no increase muscle weakness with use of benzylisoquinoliniums

Griffin et al (131) Case series (n = 3), reviewed (n = 18) case reports

100% All patients received both steroids and steroidal NMBA and all patients developed severe muscle weakness

NMBA = neuromuscular blocking agent.

TABLE 5. The Use of Neuromuscular Blocking Agents in Neurointensive Care

Author Study Design% of NMBA Used or Type of NMBA Results

Schramm et al (103) Randomized controlled trial (n = 14), neurosurgery

Cisatracurium or atracurium bolus

Atracurium-transient decrease in ICP, MAP, CPP, CBF; cisatracurium, no effect on MAP, ICP, CPP, CBF

Schramm et al (101) Prospective, open label (n = 24)

Cisatracurium bolus No effect on MAP, ICP, CPP, CBF

Prielipp et al (102) Prospective, open label (n = 6)

Doxacurium bolus and infusion

No effect on MAP, ICP, no prolonged weakness

Hsiang et al (100) Retrospective (n = 514) traumatic brain injury

NMBA used in < 50% patients

Decrease mortality with NMBA but increase prevalence of severely disabled patients, pneumonia, and ICU stay

NMBA = neuromuscular blocking agent, ICP = intracranial pressure, MAP = mean arterial pressure, CPP = cerebral perfusion pressure, CBF = cerebral blood flow.



have been reported to improve elevated IAPs by reducing abdominal muscle tone (110113).

Neuromuscular blockade may provide clinicians with more time to remove fluid or treat the underlying cause of IAH and avoid surgical decompression (113115). Table 6 presents a few studies examining the use of NMBA in the treatment of IAH. A small prospective trial suggested that a bolus dose of cisatracu-rium was effective in significantly decreasing mild elevations in IAP (111). A recent case report describing a patient undergoing adrenalectomy who had ACS reported that a prolonged NMBA infusion of 48 hours was effective in reducing IAPs and provid-ing a good recovery (114). It has been recommended (Grade 2C) by the International ACS Consensus Definitions Conference Committee that NMBAs can be used in selected patients to reduce mild-to-moderate elevations of IAP (109, 110).

Therapeutic Hypothermia After Out-of-Hospital VF-Associated Cardiac ArrestIn 2002, two landmark trials demonstrated that using mild hypothermia (3234 C) for 1224 hours in unconscious patients after out-of-hospital VF cardiac arrest improved neu-rologic outcomes, with one trial suggesting a survival benefit (116, 117). This therapy has been validated in other random-ized studies and meta-analyses (8, 118127). NMBAs were primarily used to prevent shivering (8, 116, 117) in the two original trials (and others).

The optimal combination of sedatives, analgesics, and paralytics during hypothermia after VF-associated cardiac arrest is unknown. Chamorro et al (127) performed a sys-tematic review of 44 studies (68 international ICUs, primar-ily European) examining intensivists preferences for the administration of sedatives, analgesics, and NMBAs during therapeutic hypothermia after VF cardiac arrest. A significant variability in the protocolized use of all medications for these patients was found. Fifty-four ICUs routinely used NMBAs to prevent shivering, whereas eight ICUs used NMBAs to treat shivering (127). Pancuronium was the primary agent used in 24 international ICUs surveyed, whereas cisatracurium was the second most common agent used. A minority of ICUs used neuromuscular monitoring to guide NMBA dosing and therapy (127). Studies are required to elucidate the optimal type, dose, and mode of administration of NMBAs, as well

as optimal combination of sedatives and analgesics in this patient population (128, 129).

CONCLUSIONIntensivists use NMBAs for a variety of clinical conditions. Constant review and exploration of pharmacology, dosing, drug interactions, and monitoring techniques may reduce the unwanted side effects of NMBAs. Adoption of a collabora-tive ICU team effort coupled with the use of evidence-based guidelines may improve patient outcomes when using NMBAs. These measures may ensure that NMBAs are used and moni-tored appropriately.

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TABLE 6. Studies Involving Neuromuscular Blocking Agent and Intra-Abdominal Hypertension

Author Study Design NMBAs Results

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