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*Klinik für Anästhesiologie und Intensivmedizin, Universitätsklinikum Essen; Klinik für Anästhesiologie, Technische Universität München; Klinik für Anästhesiologie und Operative Intensivmedizin, Kreiskliniken Reutlingen; and Institut für Medizinische Informatik, Biometrie und Epidemiologie, Germany
Address correspondence and reprint requests to Matthias Eikermann, MD, Visiting Assistant Professor of Medicine, Division of Sleep Medicine, Sleep Disorders Program, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115. Address e-mail to meikermann{at}rics.bwh.harvard.edu.
Anesthetics, and even minimal residual neuromuscular blockade, may lead to upper airway obstruction (UAO). In this study we assessed by spirometry in patients with a train-of-four (TOF) ratio >0.9 the incidence of UAO (i.e., the ratio of maximal expiratory flow and maximal inspiratory flow at 50% of vital capacity [MEF50/MIF50] >1) and determined if UAO is induced by neuromuscular blockade (defined by a forced vital capacity [FVC] fade, i.e., a decrease in values of FVC from the first to the second consecutive spirometric maneuver of 
10%). Patients received propofol and opioids for anesthesia. Spirometry was performed by a series of 3 repetitive spirometric maneuvers: the first before induction (under midazolam premedication), the second after tracheal extubation (TOF ratio: 0.9 or more), and the third 30 min later. Immediately after tracheal extubation and 30 min later, 48 and 6 of 130 patients, respectively, were not able to perform spirometry appropriately because of sedation. The incidence of UAO increased significantly (P < 0.01) from 82 of 130 patients (63%) at preinduction baseline to 70 of 82 patients (85%) after extubation, and subsequently decreased within 30 min to values observed at baseline (80 of 124 patients, 65%). The mean maximal expiratory flow and maximal inspiratory flow at 50% of vital capacity ratio after tracheal extubation was significantly increased from baseline (by 20%; 1.39 ± 1.01 versus 1.73 ± 1.02; P < 0.01), and subsequently decreased significantly to values observed at baseline (1.49 ± 0.93). A statistically significant FVC fade was not present, and a FVC fade of 10% was observed in only 2 patients after extubation. Thus, recovery of the TOF ratio to 0.9 predicts with high probability an absence of neuromuscular blocking drug-induced UAO, but outliers, i.e., persistent effects of neuromuscular blockade on upper airway integrity despite recovery of the TOF ratio, may still occur.
This article has been cited by other articles:
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  M. Eikermann, F. M. Vogt, F. Herbstreit, M. Vahid-Dastgerdi, M. O. Zenge, C. Ochterbeck, A. de Greiff, and J. Peters The Predisposition to Inspiratory Upper Airway Collapse during Partial Neuromuscular Blockade Am. J. Respir. Crit. Care Med., January 1, 2007; 175(1): 9 - 15. [Abstract] [Full Text] [PDF]
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