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Clinical evaluation of a new closed loop ventilation mode: adaptive supportive ventilation (ASV)


ASV (Galileo, Hamilton Medical, Inc.) is a mode of mechanical ventilation (MV) with a closed loop algorithm to determine and adjust ventilator settings. ASV may adjust mandatory breath rate, I : E ratio, and inspiratory pressure of mandatory breaths. Target minute ventilation (VE) is determined by ideal body weight (IBW) and clinician selected Percent Vent (% Min Vol). Galileo assesses the pt by measuring dynamic compliance and expiratory time constant. With IBW and %Min Vol settings, optimal settings for rate, Ti, VT, and VE are determined. We compared MV with ASV to MV with physician determined vent settings during the initiation of MV.


Ninteen post-operative pts requiring MV were studied. Vent settings by physician were noted and each pt was placed on these settings or ASV randomly. IBW was determined from standardized tables and %MinVol was set to 100%. PEEP and FiO2 were determined by staff and held constant. ABG's and cardiopulmonary variables (f, VT, VE, TI, PIP, Paw HR, MAP, and VCO2) were measured and recorded after 30 min on each mode. Data compared using student's t-test.


19 pts (14 male) were studied. Initial `test breaths' during ASV were well tolerated. Mean IBW was 88.8 Kg. Mean age was 54.3 years. Table 1 reveals set and measured ventilator parameters for both study periods. PIP and VT were lower during ASV. Respiratory rate was higher during ASV. VE, TI, and Paw were unchanged between study periods. Mean values for PEEP and FiO2, were 7.3 and 0.48, respectively. Table 2 reveals ABG measurements, CO2 production, and VD/VT ratio. There were no clinically relevant differences in ABG's or VCO2 between study periods. VD/VT was lower during ASV. No pt suffered any adverse events from derangments in ventilation or acid-base balance. One pt with ARDS receiving 17 cmH2O PEEP was hypoxemic during ASV (PaO2 57.2). Table 3 reveals heart rate and mean arterial pressure during each study period. There were no clinical changes to any measured vital sign between the two study periods.


Upon initiation of mechanical ventilation, the precise VE requirement of the pt may not be known. Clinicians use rough estimates and clinical experience to determine VE, respiratory rate, VT and Ti. Determination of vent settings made by the machine have been suggested (Intern Care Med 1996, 22:199). Our results suggest that ASV as startup mode of ventilation is acceptable and comparable to physician determined ventilator settings. Gas exchange during ASV is equivalent to physician determined ventilation. VT during ASV is more consistent with `lung protective' strategy (7.8 ml/kg) than was conventional VT (9.7 ml/kg). Mechanical ventilation with ASV is more efficient as evidenced by lower VD/VT and may be safer as a result of lower VT and PIP.

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Campbell, R., Sinamban, R., Johannigman, J. et al. Clinical evaluation of a new closed loop ventilation mode: adaptive supportive ventilation (ASV). Crit Care 3 (Suppl 1), P038 (2000).

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