The Science Journal of the American Association for Respiratory Care

1998 OPEN FORUM Abstracts

ASSIST CONTROL VENTILATION DECREASES BREATHING EFFORT IN AN ANIMAL MODEL OF RESPIRATORY DISTRESS SYNDROME.

Patricia A. Meyers RRT, EM Bendel-Stenzel MD, DR Bing RRT, JE Connett PhD, MC Mammel MD. Infant Pulmonary Research Center, Children's Hospital-St. Paul, Minnesota and Depts. Of Pediatrics and Biostatistics, University of Minnesota, Minneapolis, MN.

Introduction: Synchronous mechanical ventilation is now readily available for small infants. Does a fully synchronized patient- triggered mode of ventilation reduce breathing effort and provide adequate gas exchange in an animal model of RDS? We compared A/C to IMV and SIMV in a spontaneously breathing, surfactant depleted newborn piglet.

Method: Ten piglets (1.9±0.4 kg) were sedated, but not paralyzed, and ventilated using a targeted tidal volume of 15cc/kg (Drager Babylog(r)). We induced lung injury, defined as PaO2 < 100 torr at FiO2 1.0 and lung compliance reduction by >30%, with repeated saline lavage. We randomized the piglets to sequential 30 minute periods of either IMV>SIMV>A/C, or A/C>SIMV>IMV. Respiratory rate (RR) and minute ventilation (Ve) were determined as 1 minute moving averages. For each breath we measured tidal volume (Vt), mean airway pressure (MAP), and esophageal pressure-time-rate index (PE*RR). PE*RR, an estimate of patient breathing effort, is defined as the area below baseline of the esophageal pressure- time curve x RR (Novametrix VenTrak(r)). A continuous intra-arterial monitor (Diametrics Paratrend7(r)) recorded blood gases every 30 seconds; we calculated a/A with period means. We assessed Vt variability using the coefficient of variation (V of Vt, SD/ mean x 100). Data were analyzed using paired t-tests with Bonferroni correction; Wilcoxon rank-sum test for nonparametric data.

Results: Breathing effort, estimated by PE[cdot]RR, was significantly lower with A/C than either SIMV or IMV. Statistically significant differences in A/C vs IMV and SIMV included lower RR and increased Ve and MAP. No differences in a/A were seen. Vt was always less variable during A/C.

Mode a/A Ve MAP RR

IMV 0.10±0.01 0.82±0.08 7.7±0.2 144±15

SIMV 0.14±0.03 0.81±0.08 7.4±0.2 144±10

A/C 0.14±0.03 1.07±0.11* 11.1±0.9* 85±9*

Mode PE[cdot]RR V of Vt

IMV 57.8±16.0 80±12%

SIMV 52.3±13.7 94±11%

A/C 15.7±?* 9±1%*

*p < 0.05 A/C vs IMV, SIMV.

Conclusion: In spontaneously breathing animals, fully-synchronized A/C ventilation produced the highest Ve and the most consistent Vt, with the lowest breathing effort as estimated by PE[cdot]RR.

The 44th International Respiratory Congress Abstracts-On-Disk®, November 7 - 10, 1998, Atlanta, Georgia.

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