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.