Residual neuromuscular blockade

Residual neuromuscular blockade

Residual neuromuscular blockade can be defined by inadequate neuromuscular recovery as measured  by objective neuromuscular monitoring. It is also referred to as residual paralysis, residual  curarisation, and residual neuromuscular block. More specifically, recent opinion suggests a definition  of inadequate train of four recovery of less than 0.9 (TOF <0 .9="" p="">

On a practical level, the concept of adequate neuromuscular recovery is intended as the return to a  basline muscular function, particularly the ability to breathe normally, maintain a patent airway, and  retain protective airway reflexes.

 INCIDENCE

current estimates are that around 40% of post-operative patients (who have been paralised)

arrive in PACU with TOF <0 .9="" 12="" and="" p="" tof="" with="">

ADVERSE EFFECTS OF RESIDUAL NEUROMUSCULAR BLOCKADE

The following tables detail the implications of residual neuromuscular blockade (these are more

illustrative than exhaustive)

Table 1: Physiological changes

Impaired muscle tone and Coordination	Upper airway pharyngeal and oesophageal muscles	Increased risk of aspiration Increased risk of airway obstruction
	Laryngeal muscles	Increased risk of aspiration Impaired phonation Impaired cough
	Respiratory muscles	Impaired ventilation and oxygenation
	Impaired function of other muscles throughout                the body

Table 2: Clinical implications

Symptoms and signs of  muscle weakness	Difficulty breathing         Generalised weakness  Difficulty speaking           Visual disturbances         Patient distress
Immediate critical respiratory events  in PACU	Post-operative  hypoxaemia                Upper   airway   obstruction
Later respiratory events	Prolonged ventilator weaning                Post-operative  pulmonary complications    (eg. atelectasis, pneumonia)

INVESTIGATIONS

 Clinical criteria for evaluating adequacy of muscle function include: assessment of a patient’s ability to maintain adequate head lift, jaw clench, grip strength, and tidal volume. These are unreliable predictors of neuromuscular recovery. For example, it is possible to maintain a 5 second head lift with  TOF <0 .52.="" addition="" are="" for="" function.="" in="" many="" not="" of="" p="" respiratory="" specific="" tests="" these="">

Train-of-four neuromuscular monitoring is commonly conducted with a subjective measurement, either  as a simple train of four count (TOFC) or train of four ratio (TOF). The latter refers to when there is  already a TOFC of 4, and subsequent assessment is made for fade in T4 compared to T1.

Double Burst Stimulation (DBS) is another method of neuromuscular monitoring, but is also

commonly measured in a subjective manner..

Objective measurement of neuromuscular monitoring is the only way of accurately assessing residual  neuromuscular blockade. In general, it is conducted via quantitative measurement of the strength of  contraction of a peripheral muscle (eg. adductor pollicis muscle in thumb) in response to peripheral  nerve stimulation (eg. ulnar nerve at wrist) produced by 2 stimulating electrodes. Each measurement  technique measures the force of contraction, either directly or by a factor that is proportional to force.

 Table 5: Common sites of peripheral nerve stimulation

Nerve:  Ulnar     nerve                   

Muscle:                Adductor             pollicis  

Action:  Thumb  adduction                           

Black:    1-2cm    proximal              to            wrist      crease  

Red:       2-3cm    proximal              to            black     

Nerve:  Facial    nerve                   

Muscle:                Orbicularis           oculi       and        Corrugator          supercilii                             

Action:  Twitching             of            eyelid    and        eyebrow                             

Black:    Just        anterior                to            tragus  

Red:       Lateral  to            outer     canthus                of            eye

Nerve:  Posterior tibial nerve    (sural    nerve)                 

Muscle:                Flexor   hallicus brevis                   

Action:  Plantar  flexion  of great                toe                        

Black:    Over posterior aspect of medial                malleolus, over posterior tibial   artery   

Red:       2-3cm    proximal to black             

REVERSAL  AGENT

It is good practice to always consider giving a reversal agent, unless there is objective neuromuscular  monitoring demonstrating a TOF >0.9 (giving neostigmine to fully recovered patients may decrease  upper airway muscle activity and tidal volume) . Adequate spontaneous recovery of train of four count should be established BEFORE giving reversal. When using anaesthetic techniques that do not potentiate neuromuscular blockers, eg. TIVA, a  minimum TOFC of 2 should be established. When using anaesthetic techniques that do potentiate        neuromuscular blockers, eg. inhalational volatiles, a TOFC of 4 should be established. This is to

ensure adequate antagonism by the reversal agent of the additional depth of neuromuscular blockade.

Table 5: Train of four count and physiological correlation              

Trainof  four count  %     neuromuscular blockade at muscle        

    4                                                      0–75%      

    3                                                      75%           

    2                                                      80%            

    1                                                      90%            

    0                                                      100%         

Reversal with subjective neuromuscular monitoring     

- TOFC 1 or zero = delay reversal

- TOFC 2 or 3 = give reversal

- TOFC 4 with fade = give reversal

- TOFC 4 with no perceived fade = give reversal, consider low dose (20 µg/kg) neostigmine

- TOFC 4 and >0.9 = withhold reversal

               

Reversal with objective neuromuscular monitoring       

- TOFC 0 or 1 = delay reversal

- TOFC 2 or 3 = give reversal

- TOFC 4 with < 0.4 = give reversal

- TOFC 4 with 0.4-0.9 = give reversal, consider low dose neostigmine

- TOFC 4 and >0.9 = withhold reversal

               

Reversal guidelines with clinical neuromuscular monitoring

- Only consider reversal when spontaneous muscle activity is present

- Remember that clinical tests of adequate reversal are unreliable indicators of neuromuscular

Blockade

TREATMENT OF RESIDUAL NEUROMUSCULAR BLOCKADE

1. ABC. Basic resuscitation is the foundation on which the following steps are to be considered:

support the patient’s airway, breathing, and circulation.

2. Rule out other potential causes. Is this really residual neuromuscular blockade? Check nerve

stimulator, use a different nerve-muscle combination.

3. Consider giving reversal. In some institutions, it is still not routine for reversal to be used,

largely due to concerns of cholinergic symptoms of nausea and bradycardia with  cholinesterase inhibition.

4. Wait. Have you given enough time for the reversal to have effect? Is the patient stable enough  to tolerate watchful waiting.

5. Consider giving additional reversal. Note however, that if there is already complete

inhibition of acetylcholinesterase, giving further neostigmine will not serve any useful

purpose.

6. Treat potentiating factors. Many factors prolong neuromuscular blockade, such as

inhalational agents, opioids, acidosis, hypothermia, hypercarbia, hypoxia.

7. Consider alternative methods of reversal (Sugammadex if available)