Effect of Ventilatory Variability on Occurrence of Central Apneas RESPIRATORY CARE • MAY 2013 VOL 58 NO 5

Effect of Ventilatory Variability on Occurrence of Central ApneasRESPIRATORY CARE • MAY 2013 VOL 58 NO 5

Paul F. Nuccio, MS, RRT, FAARCBrigham and Women’s Hospital

Boston, MA

BackgroundDefinitions:• 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.

BackgroundWhat 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 literatureAnesthesiology 2010;112(3):670-681.• NAVA resulted in more complexity of airflow and breathing pattern

compared with PPVAnesthesiology 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.

MethodsWhat 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

MethodsWhat 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 samplesAny 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 1Breathing pattern• See table 2Apneas• See table 3Variability 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.

DiscussionWhat do these finding mean? • Interesting & provocative study that lacks

clear clinical outcomes benefitHow should these findings impact practice?• Unlikely to have a significant impact on

practiceHow do these findings relate to previous

findings from other studies?• Similar to other studies

DiscussionWhat 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 tubesWhat 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.”

ConclusionsWhat 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.