Postoperative residual curarization (PORC) or residual neuromuscular blockade (RNMB) is a residual

paresis In medicine, paresis () is a condition typified by a weakness of voluntary movement, or by partial loss of voluntary movement or by impaired movement. When used without qualifiers, it usually refers to the limbs, but it can also be used to desc ...

after emergence from

general anesthesia General anaesthesia (UK) or general anesthesia (US) is a medically induced loss of consciousness that renders the patient unarousable even with painful stimuli. This effect is achieved by administering either intravenous or inhalational general ...

that may occur with the use of

neuromuscular-blocking drugs Neuromuscular-blocking drugs block neuromuscular transmission at the neuromuscular junction, causing paralysis of the affected skeletal muscles. This is accomplished via their action on the post-synaptic acetylcholine (Nm) receptors. In cli ...

. Today residual neuromuscular blockade is defined as a train of four ratio of less than 0.9 when measuring the response to

ulnar nerve In human anatomy, the ulnar nerve is a nerve that runs near the ulna bone. The ulnar collateral ligament of elbow joint is in relation with the ulnar nerve. The nerve is the largest in the human body unprotected by muscle or bone, so injury is ...

stimulation at the

adductor pollicis muscle In human anatomy, the adductor pollicis muscle is a muscle in the hand that functions to adduct the thumb. It has two heads: transverse and oblique. It is a fleshy, flat, triangular, and fan-shaped muscle deep in the thenar compartment beneath ...

using mechanomyography or

electromyography Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph to produce a record called an electromyogram. An electromyo ...

. A meta-analysis reported that the incidence of residual neuromuscular paralysis was 41% in patients receiving intermediate neuromuscular blocking agents during anaesthesia. It is possible that > 100,000 patients annually in the USA alone, are at risk of adverse events associated with undetected residual neuromuscular blockade. Neuromuscular function monitoring and the use of the appropriate dosage of

sugammadex Sugammadex, sold under the brand name Bridion, is a medication for the reversal of neuromuscular blockade induced by rocuronium and vecuronium in general anaesthesia. It is the first selective relaxant binding agent (SRBA). It is marketed by Mer ...

to reverse blockade produced by

rocuronium Rocuronium bromide (brand names Zemuron, Esmeron) is an aminosteroid non-depolarizing neuromuscular blocker or muscle relaxant used in modern anaesthesia to facilitate tracheal intubation by providing skeletal muscle relaxation, most commonly r ...

can reduce the incidence of postoperative residual curarization. In this study, with usual care group receiving reversal with

neostigmine Neostigmine, sold under the brand name Bloxiverz, among others, is a medication used to treat myasthenia gravis, Ogilvie syndrome, and urinary retention without the presence of a blockage. It is also used in anaesthesia to end the effects of n ...

resulted in a residual blockade rate of 43%.

Incidence

Multiple studies have demonstrated that incomplete reversal of NMBDs is an important risk factor for postoperative morbidity and mortality. Multiple studies have shown that postoperative residual curarization in the post-anesthesia care unit (PACU) is a common complication, with 40% of patients exhibiting signs of residual paralysis. The incidence of this complication continues to be high and does not seem to be decreasing over time.

Types of neuromuscular blocking agents

Classified into two main groups: •Depolarizing NMBDs: produces skeletal muscle relaxation by binding directly with nAChRs to cause prolonged depolarization. •Non-depolarizing NMBDs: competitive antagonists (competing with acetylcholine Chfor the binding sites at the nAChRs), preventing the initiation of action potential.

Non-depolarizing neuromuscular blocking agents

Non-depolarizing NMBAs are classified based on their duration of action (short, intermediate, or long-acting agents. The two most commonly used non-depolarizing NMBDs in the operating room are rocuronium and vecuronium. Both are intermediate-acting, steroidal NMBAs.

Vecuronium Vecuronium bromide, sold under the brand name Norcuron among others, is a medication used as part of general anesthesia to provide skeletal muscle relaxation during surgery or mechanical ventilation. It is also used to help with endotracheal ...

and rocuronium can be reversed by anticholinesterases (neostigmine) or

. If sufficient spontaneous recovery has not been achieved, neostigmine (or sugammadex) should be administered.

Depolarizing neuromuscular blocking agents

Succinylcholine is the only depolarizing NMBA available for clinical use. It produces a neuromuscular blockade that is the fastest in onset and has the shortest duration of all NMBDs. Due to these properties, succinylcholine is often used for rapid sequence induction and intubation. When a continuous infusion, repeated doses, or a large dose of succinylcholine (>4 mg/kg) is used, the risk of a Phase II block and prolonged paralysis is increased. This type of block occurs when the desensitizing phase sets in and the muscle is no longer responsive to acetylcholine and full neuromuscular blockade is achieved. TOF fade is indicative of phase II block that is likely to occur in patients who received succinylcholine and may resemble features of a nondepolarizing block. During phase II, reversal with neostigmine should not be attempted. Anticholinesterase agents can worsen paralysis in this setting. Prolonged paralysis after succinylcholine administration may be due to butyrylcholinesterase (pseudocholinesterase) deficiency and may require prolonged mechanical ventilation. Unlike non-depolarizing NMBDs, reversal with

should not be attempted and sugammadex will have no effect on recovery.

Adverse events from inadequate neuromuscular blockade reversal

Inadequate reversal of NMBAs is an important risk factor for anesthesia related complications. Even small degrees of residual paralysis are associated with weakness of upper airway muscles which may lead to

airway obstruction Airway obstruction is a blockage of respiration in the airway that hinders the free flow of air. It can be broadly classified into being either in the upper airway (UPA) or lower airway (LOA). Airway obstruction is a life-threatening condition ...

and increased risk of aspiration. The hypoxic ventilatory response (HRV) can also be severely depressed as well leading to

hypoxemia Hypoxemia is an abnormally low level of oxygen in the blood. More specifically, it is oxygen deficiency in arterial blood. Hypoxemia has many causes, and often causes hypoxia as the blood is not supplying enough oxygen to the tissues of the bod ...

and need for reintubation. Studies have shown that incomplete neuromuscular recovery is associated with an increased risk of pulmonary complications. A prospective observational study including patients who underwent

for noncardiac surgery reported that the "use of NMBAs was independently associated with an increase in postoperative pulmonary complications within 28 days of surgery."

Monitoring neuromuscular blockade

Peripheral nerve stimulation patterns and definitions

Train-of-four (TOF)

TOF stimulation consists of four successive supramaximal stimuli delivered at 2 Hz. After administration of a nondepolarizing NMBD, responses at this frequency progressively decrease in amplitude (referred to as "fade" or a decrease in the TOF ratio from a normal ratio of 1).

Train-of-four ratio (TOFR)

A TOF ratio (TOFR) is calculated by dividing the amplitude of the fourth response by the amplitude of the first response (requires an quantitative measure of the response to stimulation).

Train-of-four count (TOFC)

The TOF count (TOFC) is defined as the "number of detectable evoked responses, and it correlates with the degree of neuromuscular block, as follows: * TOFC = 1 : >95 percent of

nicotinic acetylcholine receptor Nicotinic acetylcholine receptors, or nAChRs, are receptor polypeptides that respond to the neurotransmitter acetylcholine. Nicotinic receptors also respond to drugs such as the agonist nicotine. They are found in the central and peripheral ner ...

s (nAChRs) blocked * TOFC = 2 : 85 to 90 percent of nAChRs blocked * TOFC = 3 : 80 to 85 percent of nAChRs blocked * TOFC = 4 : 70 to 75 percent of nAChRs blocked

Train-of-four ratio <0.9

Data suggests that a TOF ratio measured qualitatively with EMG, MMG, or AMG must reach the threshold value of >0.9 to assure recovery of neuromuscular function. TOF ratios <0.9 are associated with residual blockade and paralysis and have demonstrated an increased risk of aspiration.

Subjective monitoring

Subjective monitoring refers to the clinical evaluation of assessing the TOFC or degree of fade by using methods such as physically touching the patient and feeling movement or visibly observing a twitch in response to

neurostimulation Neurostimulation is the purposeful modulation of the nervous system's activity using invasive (e.g. microelectrodes) or non-invasive means (e.g. transcranial magnetic stimulation or transcranial electric stimulation, tES, such as tDCS or trans ...

provided by a peripheral nerve stimulator. If subjective monitoring is used, its limitations should be recognized: "clinicians tend to overestimate the TOFC when using subjective evaluation, especially at moderate levels of block. Likewise, the level of fade is difficult to detect subjectively, with most clinicians unable to detect fade when TOF ratios >0.4."

Objective/quantitative monitoring

Due to the difficulty detecting fade subjectively (TOF ratios between 0.4 and 0.9) when using peripheral nerve stimulators, clinicians are unable to reliably exclude residual neuromuscular blockade. TOF ratios >0.4 can be measured accurately and displayed numerically using quantitative neuromuscular monitoring. However, TOF ratios >4 can be measured accurately by using quantitative monitoring methods such as

(EMG), kinemyography (KMG),

phonomyography Phonomyography (PMG) (also known as acoustic myography, sound myography, vibromyography, and surface mechanomyogram) is a technique to measure the force of muscle contraction by recording the low frequency sounds created during muscular activity. ...

(PMG), and acceleromyography (AMG).

Reversal of NMBDs and methods to avoid residual neuromuscular blockade

•Using short-acting or intermediate-acting NBMDs whenever possible can decrease the risk of residual neuromuscular blockade when compared with long-acting NMBDs. •Use objective neuromuscular monitoring (acceleromyography, electromyography, kinemyography) if possible. Peripheral nerve stimulators may be more readily available and can be used as well. However, peripheral nerve stimulators can only subjectively determine the depth of block (train-of-four count) and cannot provide accurate information needed for the timing and dosing of reversal agents as well as ensure full recovery (TOF fade). •If spontaneous recovery has not reached a TOFC = 4, use sugammadex rather than neostigmine for reversal of steroidal NMBDs. •If sugammadex is unavailable, wait for spontaneous recovery to achieve a TOFC = 4 before administering neostigmine. •Extubate the trachea only after a TOFR ≥0.9 is achieved (if quantitative monitors are available) •If objective monitoring is not available, administer reversal agents (neostigmine) only when TOFC = 4. Wait at least 10 minutes after neostigmine is given to ensure enough time for the neuromuscular blockade to be fully reversed before tracheal extubation.

References

{{Anesthesia Anesthesia