title: Effect of ventilatory variability on occurrence of central apneas.
abstract: OBJECTIVE
  To compare the influence of 2 ventilation strategies on the occurrence of central apneas.
  
  
  METHODS
  This was a prospective, comparative, crossover study with 14 unsedated subjects undergoing weaning from mechanical ventilation in the medical ICU of Hôpital du Sacré-Cœur, Montréal, Québec, Canada. The subjects were ventilated alternately in neurally adjusted ventilatory assist (NAVA) and pressure support ventilation (PSV) modes. Inspiratory flow/time and pressure/time waveforms and diaphragmatic electrical activity were used to detect central apneas. Ventilatory variability and breathing pattern were evaluated in both modes. Breathing patterns just before central apneas, and associations between apneas and sleep patterns (electroencephalogram) were studied.
  
  
  RESULTS
  Switching from PSV to NAVA did not change mean minute ventilation, tidal volume, or breathing frequency. However, tidal volume variability, defined as the coefficient of variability (standard error/mean), was significantly greater with NAVA than with PSV (17.2 ± 8 vs 10.3 ± 4, P = .045). NAVA induced a greater decrease in central apneas, compared to PSV (to 0 with NAVA vs 10.5 ± 11 with PSV, P = .005). Central apneas during PSV were detected only during non-rapid-eye-movement sleep.
  
  
  CONCLUSIONS
  NAVA was associated with increased ventilatory variability, compared to constant-level PSV. With NAVA the absence of over-assistance during sleep coincided with absence of central apneas, suggesting that load capacity and/or neuromechanical coupling were improved by NAVA and that this improvement decreased or abolished central apneas.
authors.affiliation: Service des Soins Intensifs, Hôpital du Sacré-Cœur de Montréal, Montréal, Québec, Canada. sdelisle@hotmail.com
authors.forename: Stephane
authors.initials: S
authors.lastname: Delisle
authors.forename: Nicolas
authors.initials: N
authors.lastname: Terzi
authors.forename: Paul
authors.initials: P
authors.lastname: Ouellet
authors.forename: Patrick
authors.initials: P
authors.lastname: Bellemare
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Tétrault
authors.forename: Pierre
authors.initials: P
authors.lastname: Arsenault
mesh_terms: D000368:Aged; D018592:Cross-Over Studies; D004569:Electroencephalography; D005260:Female; D006801:Humans; D059725:Interactive Ventilatory Support / Q000009:adverse effects*; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration / Q000009:adverse effects*; D012123:Pulmonary Ventilation; D015656:Respiratory Mechanics; D056152:Respiratory Rate; D020182:Sleep Apnea, Central / Q000209:etiology* / Q000503:physiopathology; D012895:Sleep, REM / Q000502:physiology*; D013990:Tidal Volume; D015300:Ventilator Weaning