2001 OPEN FORUM Abstracts
The Response of Adaptive Support Ventilation (ASV) to Varying Spontaneous Minute Ventilation at Different Compliance and Resistance in a Lung Model
R. Wayne Lawson,MS, RRT, David L. Vines, MHS, RRT, David C. Shelledy, PhD, RRT. The Universityof Texas Health Science Center at San Antonio, TX
BACKGROUND:ASV is a servo-controlled mode of ventilation offered on the Hamilton Galileo,(Hamilton Medical, Reno, Nevada) designed to deliver pressure-targeted tidalvolumes as a variable rate, to achieve a target inute volume while utilizingprotective lung strategies. The mode will adapt to changing patient demand,from full ventilatory support to total spontaneous breathing, as the patienttakes over a greater share of the work of breathing. The purpose of this studywas to evaluate the ability of ASB to achieve targeted minute volumes in theface of varying levels of patient spontaneous ventilation, and under differentconditions of compliance and resistance, using a two-compartment lung model(Michigan Instruments, Inc., Grand Rapids, MI) to simulate spontaneous breathing.
Methods: Thedriver lung, lung B was ventilated using minute ventilations of 5L (f=10 bpmVt=500ml f=15 bpm Vt=335 ml f=30 bpmVt=165ml); 7L (f=10 bpm Vt=700 ml f=15bpmVt= 470 ml f=30 bpm Vt=235 ml); 9L f=10 bpm Vt=900 ml f=15 bpm Vt=600 ml f=30bpm Vt=300 ml). The spontaneous lung, lung A, was ventilated using ASV, programedfor an ideal body weight of 70kg. For each experiemental condition, measurementswere made at a normal compliance (0.05 L/cm H2O and resistance (2.7 cm H2O/L/sec),decreased compliance (0.02 L/cm H2O, and increased resistance 17.6 cm H2O/L/sec).Alveolar ventilation was calculated using the following formula (minute ventilationminus respiratory rate times deadspace). An anatomic deadspace of 150 ml waschosen as a normal value for a 70kg patient.
Results: Acrossall conditions combined, there were no significant differences (p>.05) foractual minute volume and calculated alveolar ventilation when driver minutevolume was 5L/m (8.97±2.93 & 6.56 ±1.83), 7 L/m (8.60±2.62& 6.45 ±1.57), or 9 L/m (9.06±2.50 &6.90 ±1.75).Under all conditions combined, there were also no significant differences (p>.05)between actual minute volume and calculated alveolar ventilation when complianceand resistance were normal (9.64±3.51 & 7.27±2.27), decreasedcompliance (8.67±2.74 & 6.12±1.58), or increased resistance(8.31±0.99 & 6.48±0.77). Table 1 displays minue ventilationand calculated alveolar ventilation for each level of spontaneous ventilation,compliance and resistance.
|Drive Ve||Ve Actual||Va Calc||Ve Actual||Va Calc||Ve Actual||Va Calc|
CONCLUSION: ASV effectivelymaintained minute ventilation and alveolar ventilation under varying conditionsof spontaneous ventilatin, compliance and airway resistance.