Residual Neuromuscular Block

The clinical implications of residual neuromuscular block are important.

TOF ratio to as low as 0.63, may cause difficulty breathing and swallowing, and decreases inspiratory force and peak expiratory flow rate.

TOF ratio to 0.85 is associated with general discomfort, malaise, ptosis and blurred vision.

Other more recent studies with volunteers have shown that TOF ratios of 0.6 to 0.7 are associated with decreased upper esophageal tone and a decrease in the coordination of the esophageal musculature during swallowing.
Fluoroscopic study of these individuals while swallowing demonstrated significant pharyngeal dysfunction resulting in misdirected swallowing, leading to a four to five-fold increase in the risk of aspiration.

A TOF recovery = 0.90 is required to return esophageal tone and pharyngeal coordination to baseline. Only with this degree of recovery do patients manifest normal swallowing, fully protect their airways, and resume normal respiratory function. It may require this more robust level of neuromuscular recovery to minimize the postoperative risk of aspiration and pneumonia

NMB drugs also interfere with hypoxic ventilatory control.

In vitro, while application of acetylcholine to the carotid body results in hyperventilation, application of anticholinergics eliminated the increase in neuronal activity of the carotid body sinus nerve that otherwise occurs with hypoxia. In awake volunteers who have received atracurium, vecuronium or pancuronium, with a train-of-four ratio of 0.70, the hypoxic ventilatory drive is reduced by 30%.

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