Evaluation of Asynchrony Index (ASI) During Noninvasive Ventilation With Portable Ventilators (PV)

Introduction: NIV is beneficial for many forms of ventilatory failure. NIV benefits may be realized in austere environments and during transport by use of a PV with NIV capabilities. We evaluated the ASI of 4 PVs set to provide NIV with varying Leak (Lk), Pressure Support (PS), and physiologic conditions.


Methods: Four PVs (Sparrow Robust, Inovytec; 731 EMV+, Zoll; T1, Hamilton; V60, Philips) were set to deliver NIV to an ASL5000 simulator (Ingmar) at 192 conditions based on physiology (normal (C=60, R=5) and COPD (C=70, Ri=20, Re=35), inspiratory effort (Insp) (Low=-3, Norm=-7, High=-15), Lk, and PS (5 and 10) at a rate of 15, Ti 1.0, and PEEP of 5. Each PV used default settings for trigger, rise time, and exp cycle. Lk conditions were characterized by Lk flow at P of 5 and 15 cmH2O: Lk0=no additional Lk, Lk1=constant Lk (14.4, 27.9), L3=Lk during inspiration only >7.5 via water column ( < 1,17.0), and L2=both L1+L3 (14.6, e14.6/i46.11). Each PV used a recommended circuit, and data/waveforms were collected for 2 min after 30 sec stabilization. ASI was determined by analysis of waveforms of 25 breaths at each condition by 2 raters. Five AS types were defined: Missed Trigger (MT) = no breath delivery during Ti, Delayed Trigger (DT) = breath initiated > 300ms following start of effort (SOE), Auto Trigger (AT)= any breath initiated prior to SOE + breaths initiated during Ti without visible evidence of trigger, Premature Cycle (PC) and Delayed Cycle (DC) = vent cycle off > 300ms prior to or following end of Insp effort, respectively. ASI for each PV was compared for all conditions and specific to conditions related to physiology, Insp effort, Lk setting, and PSV level.


Results: Conditions with 0% ASI for each PV were: V60 68 (35%), T1 64 (33%), 731 44 (23%), Sparrow 20 (10%). The ASI for all 192 conditions [ASI (COPD ASI, NORM ASI)] for each PV was: T1 37% (64%, 11%); V60 39% (65%, 13%); 731 68% (79%, 58%); Sparrow 69%, (88%, 49%). The most common ASI type for each PV was: V60 DT (24%), T1 DT (24%), 731 AT (34%), Sparrow MT (44%). COPD, low effort, and Lk2 conditions had the highest ASI; PS had minimal effect on ASI.


Conclusions: NIV performance varies greatly among PVs. T1 and V60 had the lowest ASI. The 731 and Sparrow had high ASI, and their NIV use should be limited with COPD, low Insp effort, and high Lk.