Efficiency of Face Mask Ventilation before and after Neuromuscular Blockade : A Randomised Control Trial

A very important aspectof inducing a patient under general anaesthesia is securing an airway forintraoperative ventilation. Expert airway management is an essential skill inanaesthetic practice for allowing oxygenation, ventilation and anaesthetic gasdelivery.[1] Tracheal intubation remains the most common approach to airwaymanagement.

The general sequence ofinduction of anaesthesia is administration of an analgesic and IV anaestheticagent after which facemask ventilation is tested and lastly a neuromuscular blockingagent is administered. Because of possible development of airway catastrophes,muscle relaxants have long been recommended to be administered after confirmingadequate face mask ventilation, without any scientific validation of thisprincipal.

The rationale fordelaying administration of muscle relaxant is the belief that if face maskventilation in an anaesthetised non-paralysed patient is ineffective, thepatient can be reversed and an alternative airway management can be considered.Life threatening hypoxemia can therefore, theoretically, be averted.[2]

In 2008, Calder and Yentis argued against thepractice of checking facemask ventilation. They questioned the validity andsafety of this practice. The argument against the practice was that ifneuromuscular blocking agent is delayed on the pretext of assessing facemaskventilation, the anaesthetist has already lightened the plane of anaesthesiafor the said patient and caused difficult ventilation. [4]

If facemask ventilationis difficult or impossible in an anaesthetised non-paralysed patient there aretwo courses of action that may be followed. First course could be to withholdall anaesthetic agents and allow the plane of anaesthesia to become superficialcausing the spontaneous return of respiration. The second approach is toadminister a neuromuscular blocking agent (Suxamethonium or rocuronium) tofacilitate intubation and ventilate the patient, but, if even intubation fails,patient can be reversed and spontaneous respiration awaited. Both approachesseem logical as long as spontaneous respiration is achieved before severehypoxemia develops. The limitation here, however, is that the pre-existinganatomic problems which were causing difficult facemask ventilation in thefirst place have been worsened with administration of anaesthetic agents whichled to collapse of the upper airways. Therefore, the chances of achievingspontaneous respiration in an apnoeic, anaesthetised patient before severe hypoxemiadevelops is minute. [4]

At this crossroads the rationale of the practice of delayedadministration of neuromuscular blocking agent becomes questionable.

  Investigatorshave reported either no effect or improvements in mask ventilation difficultyscores and exhaled volumes after neuromuscular blocking drugs have beenadministered.

This study uses cis-atracuriumas the non-depolarising neuromuscular blocking agent. It is four to five times as potent as atracurium and does not causehistamine release. It provides intubating conditions in a dose of 0.10 -0.15mg/kg within 2 minutes and results in blockade of intermediate duration.