Effect of Ventilatory Variability
on Occurrence of Central Apneas
RESPIRATORY CARE • MAY 2013 VOL 58 NO 5
Paul F. Nuccio, MS, RRT, FAARC
Brigham and Women’s Hospital
Boston, MA
Background
Definitions:
• PSV = Pressure Support Ventilation
• NAVA = Neurally Adjusted Ventilatory Assist
• Periodic breathing
What is the research question?
• Is there a difference in the occurrence of central apnea episodes between
patients ventilated with a constant-level PSV vs. NAVA?
Is this research question relevant?
• Central apnea may be associated with significant pathophysiologic
changes, including stroke, brainstem lesion, encephalitis, and congestive
heart failure.
Background
What is known about this subject?
• normal ventilation varies from breath to breath
• traditional mechanical ventilation may be monotonous
• close association between arousal from sleep and ventilatory effort
Background literature
Anesthesiology 2010;112(3):670-681.
• NAVA resulted in more complexity of airflow and breathing pattern
compared with PPV
Anesthesiology 2009;110(2):342-350.
• Variability of pressure support improves lung function
Any concerns about COI?
• None. Dr. Delisle has disclosed a relationship with Fisher & Paykel.
Methods
What is the study design?
• Prospective, comparative, crossover study
Inclusion criteria
• Invasive mechanical ventilation
• Normal consciousness
• Absence of sedatives and opiates for > 24 hours
• PSV with FiO2 <0.60 and PEEP of 5cmH2O (SpO2 >90%)
Exclusion criteria
• Presence of a central nervous system disorder
• Glasgow Coma Scale score <11
• Hemodynamic instability
• Renal and/or hepatic insufficiency
• Ongoing sepsis
• History of esophageal varices or gastroesophageal bleeding (past 30 days)
• History of GI symptoms such as vomiting
Methods
What is the control group?
• With a crossover study, every patient serves as his or her own control.
Is the sample size appropriate?
• There were a total of 14 patients in the study.
• Very difficult to draw conclusions from such a small sample size.
What are the threats to validity of the design?
• Small sample size
• Compare apples to apples?
Was the statistical analysis appropriate?
• Statistical software utilized for analysis
• Comparisons made using general linear model for repeated measures
• Wilcoxon test for paired samples
Any ethical concerns?
• The ethics committee of the hospital approved the study, and the subjects
or their surrogates gave their informed consent.
• Potential ethics concerns if one therapy appears to provide more benefit.
Study Protocol
Delisle, S. et al. Respir Care 2013;58:745-753
(c) 2012 by Daedalus Enterprises, Inc.
Polysomnography tracings with neurally adjusted ventilatory assist (NAVA) and pressure
support ventilation (PSV) in a representative subject.
Delisle, S. et al. Respir Care 2013;58:745-753
(c) 2012 by Daedalus Enterprises, Inc.
Results
What are the main results?
Study population
• See table 1
Breathing pattern
• See table 2
Apneas
• See table 3
Variability of ventilation
• See table 4
Table 1 - Subjects
Delisle, S. et al. Respir Care 2013;58:745-753
(c) 2012 by Daedalus Enterprises, Inc.
Table 2 - VT, Breathing Frequency, Apneas per Hour, and PETCO2 While Awake
and Asleep.
Delisle, S. et al. Respir Care 2013;58:745-753
(c) 2012 by Daedalus Enterprises, Inc.
Table 3 - Oscillatory Behavior of VT, Breathing Frequency, V̇E, and PETCO2 During Sleep
Stages 2 and 3–4 During PSV in the 10 Patients With Central Apneas.
Delisle, S. et al. Respir Care 2013;58:745-753
(c) 2012 by Daedalus Enterprises, Inc.
Table 4 - VT, f-flow, and EAdi Peak Variability in the 10 Patients With
Central Apneas.
Delisle, S. et al. Respir Care 2013;58:745-753
(c) 2012 by Daedalus Enterprises, Inc.
Fig 3 - Variability during pressure support ventilation (PSV).
Delisle, S. et al. Respir Care 2013;58:745-753
(c) 2012 by Daedalus Enterprises, Inc.
Fig 4 - Variability during neurally adjusted ventilatory assist (NAVA).
Delisle, S. et al. Respir Care 2013;58:745-753
(c) 2012 by Daedalus Enterprises, Inc.
Discussion
What do these finding mean?
• Interesting & provocative study that lacks
clear clinical outcomes benefit
How should these findings impact practice?
• Unlikely to have a significant impact on
practice
How do these findings relate to previous
findings from other studies?
• Similar to other studies
Discussion
What are the study limitations/concerns?
• Single center study
• Small sample size
• Possible influence of sedation
• Single level of both NAVA and PSV
• Potential risk of using NG tubes
What additional work is needed in this area?
• Study findings of physiological effect of NAVA
must be confirmed by further clinical studies.
Editorial
… by Kathy S Myers Moss MEd RRT-ACCS
University of Missouri
“I commend the authors on their use of a prospective, randomized,
controlled trial, the gold standard of experimental research methods. In
addition, the research design integrated a crossover method with
attention to minimizing residual effects. The statistically significant effect
on tidal volume variation is especially noteworthy given the small sample
size of 14.’’
“Until well designed studies provide evidence suggesting reduced
morbidity, mortality, stay, number of ventilator days, or other desirable
clinical outcomes, clinical managers are unlikely to invest in the required
software and hardware upgrades necessary to implement NAVA.”
Conclusions
What are the authors’ conclusions?
• NAVA was associated with increased ventilatory variability compared to constant
level PSV. With NAVA absence of overassistance 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.
How do you think this should affect practice?
• Since NAVA is exclusively an option for one ventilator, widespread use of this
technology will continue to be limited. More widespread adoption of this
technology will require physiologic outcomes improvements, outcomes such as
decreased number of ventilator days, and fewer complications of mechanical
ventilation.
What is the take-home message?
• Further clinical investigations are needed to evaluate the impact of NAVA on
weaning time and patient outcomes.