The Science Journal of the American Association for Respiratory Care

1995 OPEN FORUM Abstracts

Infant Ventilator Performance Varies With Lung Condition And Cycling Frequency

Dennis R. Bing, Kendra M. Smith, Stephen J. Boros, Mark C. Mammel. Infant Pulmonary Research Center, Children's Health Care, St. Paul, MN

In a previous study, we demonstrated poor performance of conventional infant ventilators at rapid cycling frequencies (Pediatrics 1984; 74:487). Does the new generation of neonatal ventilators exhibit similar limitations? This study compares tidal (Vt) and minute (Ve) volume delivery of 8 current neonatal ventilators under 4 simulated pulmonary conditions using a Biotek VT-2 test lung. We monitored pressures at the proximal airway (Paw) and within the "lung" (PL), and Vt delivery to the lung with a PeDS^{TM} analyzer. We tested the Bear Cub, VIP Bird, Drager Babylog, Infrasonics 500, Newport Breeze and Wave, Sechrist 100-V, and Siemens 300 ventilators under various conditions of compliance (Crs, ml/cmH_2O) and resistance (Raw, cmH_2O/L/sec) at set rates of 25, 50, 75, 100, 125, and 150 per minute. We also studied two methods of management: 1) constant peak inspiratory_pressure with 25/5 PIP/ PEEP and I:E ratio of 1:3, 2) constant Vt delivery of 10 ml, PIP variable, rate adjusted with Te. Mean data for all ventilators:

Constant PIP Constant Vt

Rate Vt, mls Ve, mls mn Paw Ve, mls

HMD 25 19 4867 277

Crs=1, Raw=200 15071028 191393

HMD< 1000 gm25 18 4778 260

Crs=1, Raw=400 1505 690 261180

BPD 25 24 5917 269

Crs=3, Raw=400 1504 640 301269

Normal25 5515066 314

Crs=3, Raw=50150 16243371368

Ventilators in this study performed similarly, but with greater scatter at each rate than those tested in 1984. As before, high cycling rates caused either loss in delivered Vt or increased Paw to maintain Vt. Inspired PL fell and end- expiratory PL increased dramatically. This effect was less pronounced in the new ventilators.

Conclusions: Conventional neonatal ventilators' performance still decreases at high cycling frequency. At rapid rates, tidal volume delivery is adversely affected and expiratory gas trapping is likely. These effects are most pronounced in lung conditions with long respiratory time constants.


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