Neuromuscular block may not hamper facemask airway success

By Eleanor McDermid, Senior medwireNews Reporter

It may not be necessary to wait to establish good facemask ventilation before administering neuromuscular block, a study suggests.

Researchers found that rocuronium did not interfere with ventilation in patients with normal upper airway anatomy, while succinylcholine significantly improved it.

In an editorial accompanying the study in Anesthesiology, Michael Richardson (Vanderbilt University School of Medicine, Nashville, Tennessee, USA) and Ronald Litman (University of Pennsylvania, Philadelphia, USA) say that the findings will encourage those who wish to abandon "ventilate before paralyze."

They say that this traditional, "perhaps dogmatic," approach is based partly on fears that early muscle paralysis could cause problems in the event of difficult mask ventilation, in particular by blocking return to spontaneous ventilation as a rescue strategy in very severe cases.

"We too advocate rejecting dogma, but we have not rejected the 'ventilate before paralyze' approach completely," write Richardson and Litman. "We cannot find evidence to support its wholesale abandonment, and it continues to be useful to us."

Shiroh Isono (Chiba University, Japan) and colleagues report that administration of rocuronium did not significantly alter total, oral, and nasal tidal volumes in 14 patients with established facemask ventilation and neutral head and lower jaw positions.

By contrast, administration of succinylcholine to 17 patients significantly improved total tidal volume, measured at 60 seconds after treatment, by about a third, from 4.2 to 5.4 mL/kg. This was mostly because of increased oral ventilation, which rose 64%, from 1.4 to 2.3 mL/kg, but increased nasal ventilation also contributed, rising by a significant 15%, from 2.7 to 3.1 mL/kg.

Endoscopic examination of oral ventilation revealed "abrupt and significant" dilation of the space at the isthmus of the fauces on administration of succinylcholine. This narrowed during observation, but at 60 seconds (the point of tidal volume measurement) it remained dilated relative to at baseline.

"In most cases, anesthesiologists use one hand alone for holding a mask," comment Isono et al. "The hand often closes the bite and oral airway route. Even with the anesthesia full facemask, the mask ventilation is performed predominantly or exclusively through the nasal airway route without an oral airway in place or active bite opening with the two hands."

They say: "Our results suggest use of both airway routes for maximizing ventilation in patients receiving muscle relaxants under general anesthesia, preferably with using an oral airway and/or two hands specifically in obese patients and patients with severe obstructive sleep apnea."

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