Impaired upper airway integrity by residual neuromuscular blockade: increased airway collapsibility and blunted genioglossus muscle activity in response to negative pharyngeal pressure.
BACKGROUND
Residual neuromuscular blockade increases the risk to develop postoperative complications. The authors hypothesized that minimal neuromuscular blockade (train-of-four [TOF] ratio 0.5-1) increases upper airway collapsibility and impairs upper airway dilator muscle compensatory responses to negative pharyngeal pressure challenges.


METHODS
Epiglottic and nasal mask pressures, genioglossus electromyogram, respiratory timing, and changes in lung volume were measured in awake healthy volunteers (n = 15) before, during (TOF = 0.5 and 0.8 [steady state]), and after recovery of TOF to unity from rocuronium-induced partial neuromuscular blockade. Passive upper airway closing pressure (negative pressure drops, random order, range +2 to -30 cm H2O) and pressure threshold for flow limitation were determined.


RESULTS
Upper airway closing pressure increased (was less negative) significantly from baseline by 54 +/- 4.4% (means +/- SEM), 37 +/- 4.2%, and 16 +/- 4.1% at TOF ratios of 0.5, 0.8, and 1.0, respectively (P < 0.01 vs. baseline for any level). Phasic genioglossus activity almost quadrupled in response to negative (-20 cm H2O) pharyngeal pressure at baseline, and this increase was significantly impaired by 57 +/- 44% and 32 +/- 6% at TOF ratios of 0.5 and 0.8, respectively (P < 0.01 vs. baseline). End-expiratory lung volume, respiratory rate, and tidal volume did not change.


CONCLUSIONS
Minimal neuromuscular blockade markedly increases upper airway closing pressure, partly by impairing the genioglossus muscle compensatory response. Increased airway collapsibility despite unaffected values for resting ventilation may predispose patients to postoperative respiratory complications, particularly during airway challenges.
Herbstreit
Frank
F
Oberarzt, Klinik für Anästhesiologie und Intensivmedizin, Universität Duisburg-Essen and Universitätsklinikum Essen, Essen, Germany. frank.herbstreit@uk-essen.de
Peters
Jürgen
J
Eikermann
Matthias
M
D000328:Adult; D000399:Air Pressure; D002245:Carbon Dioxide / Q000097:blood; D004576:Electromyography; D006801:Humans; D008297:Male; D019148:Neuromuscular Blockade / Q000009:adverse effects*; D009469:Neuromuscular Junction / Q000187:drug effects / Q000502:physiology; D010100:Oxygen / Q000097:blood; D010614:Pharynx / Q000502:physiology*; D010991:Plethysmography; D015656:Respiratory Mechanics / Q000502:physiology; D012132:Respiratory Muscles / Q000503:physiopathology*; D012137:Respiratory System / Q000503:physiopathology*; D012140:Respiratory Tract Diseases / Q000139:chemically induced* / Q000503:physiopathology*; D009435:Synaptic Transmission / Q000187:drug effects; D013990:Tidal Volume / Q000502:physiology
D002245:Carbon Dioxide; D010100:Oxygen