QUALITATIVE vs QUANTITATIVE MONITORING

Monitoring of the neuromuscular function can guide the clinical management of neuromuscular blockade and help to minimize the incidence of residual neuromuscular blockade.

The neuromuscular assessment can be subjective or objective . Visual or tactile assessment of the twitch responses is encompassed as qualitative neuromuscular monitoring. The result is therefore subjective and dependent on the anesthetist. Low, but still clinically meaningful degrees of neuromuscular blockade can only be measured using a quantitative, objective, monitoring device. A residual neuromuscular block of TOFR > 0.4 cannot be reliably detected by tactile or visual sense even by an experienced anesthetist. Clinical tests, such as 5s head-lift, tidal volume, grip strenghth or 5 s leg lift do not guarantee complete resolution of neuromuscular block.

In 2018 a group of experts in the field of neuromuscular blockade monitoring issued a consensus statement in Anesthesia & Analgesia concluding that whenever a neuromuscular blocker is administered, neuromuscular function must be monitored by observing the evoked muscular response to peripheral nerve stimulation. Ideally stimulation of the ulnar nerve should be performed and the muscle response should be measured quantitatively at the adductor pollicis muscle or the hypothenar muscles.

QUANTITATIVE (OBJECTIVE) MONITORING

Quantitative assessment of the train-of-four fade by neuromuscular transmission monitoring is the only suitable method to identify low but clinically meaningful levels of residual neuromuscular block.

Mechanical techniques such as mechanomyography (MMG), acceleromyography (AMG), and kinemyography (KMG) are measuring twitch responses related to the muscle contraction, such as force, acceleration , or velocity. Historically, mechanomyography has been the gold standard for measurement of neuromuscular function due to it´s high accuracy. Today, there is no commercially available MMG device. From the commercial techniques mentioned above, acceleromyography has been the most commonly used technique in clinical settings.

Electromyography (EMG) is measuring the compound muscle action potential. Due to limited access to commercial devices this technique has been less common although it is considered as the new gold standard. In the recent time this has changed and there is now devices available. TetraGraph is one of them.

REFERENCES

Viby Mogensen J et al. Tactile and visual evaluation of the response to train-of-four  nerve stimulation. Anesthesiology 1985;63:440-3

Murphy GS et al. Residual neuromuscular blockade and critical respiratory events in the postanesthesia care unit. Anesth Analg 2008; 107:130-7