Reversal of Neuromuscular Blockade

Audit of peripheral neuromuscular stimulators at the hospitals staffed by the Department of Anaesthesia and Perioperative Medicine at the University of Cape Town

Background: Inadequate monitoring of neuromuscular blockade (NMB) may result in worse patient outcomes, including airway compromise and postoperative pulmonary complications. Therefore, NMB monitor availability is a minimum requirement for perioperative care according to the South African Society of Anaesthesiologists’ (SASA) 2018 guidelines. The authors performed an audit of peripheral nerve stimulators (PNS) functionality and availability at their institution. Methods: The PNSs were attached to an electrical circuit with a skin equivalent resistance. The resultant current impulses generated using Train-of-Four (TOF) mode and Double Burst Stimulation (DBS) mode were recorded with a voltage scope meter. PNS availability was assessed in theatre and recovery areas. Results: Of the 65 PNS units assessed, 39 units were dysfunctional and 26 units fully functional. The most frequent fault found (30 units) related to faulty or absent PNS electrode cables. Eight functional PNS units with TOF ratio display capability were found. The working PNSs showed good inter-device peak voltage measurement correlation. Of the 59 areas identified where PNSs should be easily available, only 37 areas met the PNS availability criteria suggested in the SASA guidelines. Conclusion: This audit highlighted the need for more new generation PNSs with TOF-ratio-display-ability to align the institution with recommendations from SASA standards and the anaesthetic literature. It also highlighted the accuracy and consistency of delivered current bursts by the working PNS devices.

Current Status of Neuromuscular Reversal and Monitoring

Postoperative residual neuromuscular block has been recognized as a potential problem for decades, and it remains so today. Traditional pharmacologic antagonists (anticholinesterases) are ineffective in reversing profound and deep levels of neuromuscular block; at the opposite end of the recovery curve close to full recovery, anticholinesterases may induce paradoxical muscle weakness. The new selective relaxant-binding agent sugammadex can reverse any depth of block from aminosteroid (but not benzylisoquinolinium) relaxants; however, the effective dose to be administered should be chosen based on objective monitoring of the depth of neuromuscular block.

To guide appropriate perioperative management, neuromuscular function assessment with a peripheral nerve stimulator is mandatory. Although in many settings, subjective (visual and tactile) evaluation of muscle responses is used, such evaluation has had limited success in preventing the occurrence of residual paralysis. Clinical evaluations of return of muscle strength (head lift and grip strength) or respiratory parameters (tidal volume and vital capacity) are equally insensitive at detecting neuromuscular weakness. Objective measurement (a train-of-four ratio greater than 0.90) is the only method to determine appropriate timing of tracheal extubation and ensure normal muscle function and patient safety.

Peri-operative pulmonary dysfunction and protection

Pulmonary complications are a major cause of peri-operative morbidity and mortality, but have been researched less thoroughly than cardiac complications. It is important to try and predict which patients are at risk of peri-operative pulmonary complications and to intervene to reduce this risk. Anaesthetists are in a unique position to do this during the whole peri-operative period. Pre-operative training, smoking cessation and lung ventilation with tidal volumes of 6-8 ml.kg(-1) and low positive end-expiratory pressure probably reduce postoperative pulmonary complications.