1998 OPEN FORUM Abstracts
SYNCHRONIZED PARTIAL LIQUID VENTILATION IMPROVES GAS EXCHANGE AND DECREASES BREATHING EFFORT.
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: Does mode of assisted ventilation affect breathing effort and gas exchange during partial liquid ventilation (PLV) in an animal model of neonatal RDS? We compared IMV, SIMV, and A/C modes during PLV with perflubron (Liquivent(r), Alliance Pharmaceuticals) in surfactant depleted, spontaneously breathing newborn piglets.
Method: Ten piglets (1.19±0.04 kg) were sedated, but not paralyzed, and ventilated using a volume target 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, during PLV. 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[cdot]RR). PE*RR, an estimate of nonventilator 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 SIMV during PLV (A/C vs IMV, p=0.06). a/A was significantly better with A/C than either IMV or SIMV. Ve and MAP increased during A/C. RR was significantly less in AC vs SIMV, and trended lower in A/C vs IMV (p=0.07). Vt was always more consistent during A/C.
Mode a/A Ve MAP RR
IMV 0.27±0.11 0.78±0.11 6.8±0.3 112±16
SIMV 0.26±0.02 0.75±0.13 6.7±0.3 114±16
A/C 0.35±0.03* 0.98±0.13* 10.7±0.7* 77±10**
Mode PE[cdot]RR V of Vt
IMV 49.7±13 54±10%
SIMV 46.8±10.9 72±12%
A/C 13.7±5.1** 11±2%*
*p < 0.05 A/C vs IMV, SIMV; **p < 0.05 A/C vs SIMV.
Conclusion: In spontaneously breathing animals, fully-synchronized PLV using A/C mode required the least breathing effort, increased Ve and a/A at the lowest RR and least variable Vt. These data suggest physiologic benefit from A/C during PLV in nonparalyzed subject.
The 44th International Respiratory Congress Abstracts-On-Disk®, November 7 - 10, 1998, Atlanta, Georgia.