We appreciate Dr. Gal’s interest in our work. 1
In our study, inspiratory flow was more affected by residual paralysis than expiratory flow. We agree that it is unlikely that persistent inspiratory flow impairment was evoked by residual blockade of inspiratory respiratory muscles, which are believed to be least affected by curarization. 2
Rather, pharyngeal muscle dysfunction shown to persist after recovery of thumb muscles from partial neuromuscular blockade is likely responsible. 3
However, to our knowledge the dose-response relationship or recovery profile of neuromuscular blocking agents at pharyngeal muscles has not yet been studied. In fact, it is unclear whether relaxation of a particular airway abductor muscle is responsible for persistent extrathoracic airway obstruction. Furthermore, there are no data on the time course of the suggested upper airway obstruction over the respiratory cycle. Therefore, Dr. Gal’s hypothesis, that persistent inspiratory flow limitation during partial paralysis is due to variable extrathoracic obstruction as the result of weakened airway muscle activity during inspiration, is yet to be confirmed.
We cannot (and did not intend to) pinpoint to which degree the effects of relaxation on pulmonary function are evoked by diminution of respiratory strength and/or upper airway obstruction. Irrespective of responsible mechanisms, our data show that respiratory function can still be seriously impaired despite recommended neuromuscular function test results suggesting adequate neuromuscular recovery.
We agree with Dr. Gal that sensitivity to detect residual paralysis by forced vital capacity measurements is low. Our data suggest that measurements of forced inspiratory flow and assessment of the ability of normal swallow may be more sensitive. 1
In turn, however, our data also indicate that a marked forced vital capacity decrease may occur even with minimal neuromuscular blockade, suggesting impaired muscle strength. 4
As respiratory muscle weakness can result in an ineffective cough with inability to clear secretions from the airways, 5
we consider forced vital capacity recovery relevant for preventing pulmonary complications.
Matthias Eikermann, M.D.*
Harald Groeben, M.D.
Jürgen Peters, M.D.
1. Eikermann M, Groeben H, Hüsing J, Peters J: Accelerometry of adductor pollicis muscle predicts recovery of respiratory function from neuromuscular blockade. A nesthesiology 2003; 98: 1333–7
2. Saunders NA, Rigg JR, Pengelly LD, Campbell EJ: Effect of curare on maximum static PV relationships of the respiratory system. J Appl Physiol 1978; 44: 589–95
3. Sundman E, Witt H, Olson R, Ekberg O, Kuylenstierna R, Erikson L: The incidence and mechanisms of pharyngeal and upper esophageal dysfunction in partially paralyzed humans. A nesthesiology 2000; 92: 977–84
4. Gal TJ, Goldberg SK: Relationship between respiratory muscle strength and vital capacity during partial curarization in awake subjects. A nesthesiology 1981; 54: 141–7
5. Arora NS, Gal TJ: Cough dynamics during progressive expiratory muscle weakness in healthy curarized subjects. J Appl Physiol 1981; 51: 494–8
© 2004 American Society of Anesthesiologists, Inc.