Correlation between the %MinVol setting and work of breathing during adaptive support ventilation in patients with respiratory failure.
BACKGROUND
Adaptive support ventilation (ASV) is a new mode of mechanical ventilation that seeks an optimal breathing pattern based on the minimum work of breathing (WOB) principle. The operator's manual for the ventilators that provide ASV recommends that the %MinVol setting be started at 100% (the 100%MinVol setting), but it is unclear whether that setting reduces WOB in patients with respiratory failure.


METHODS
We studied 22 hemodynamically stable patients with respiratory failure who were on pressure-support ventilation. We switched the ventilation mode to ASV and started at the 100%MinVol setting. We then increased the %MinVol setting by 10% every 5 min until 1-3 mandatory breaths per min appeared, and called that setting the ASV target point. We then tested 2 additional %MinVol settings: 20% below the ASV target point (target-point-20%), and 20% above the ASV target point (target-point+20%). We tested each %MinVol setting for 10 min. At the end of each 10-min period we measured respiratory variables, pressure-time product (PTP), and airway occlusion pressure at 0.1 s after the onset of inspiratory flow (P(0.1)).


RESULTS
In 18 patients (82%), at the 100%MinVol setting, the actual minute volume (V(E)) was greater than the target V(E). At the ASV target point the mean +/- SD %MinVol setting was 165 +/- 54% and was associated with a 40% decrease in PTP and P(0.1), but V(E) did not change. At target-point+20%, V(E) increased slightly, primarily due to a small increase in tidal volume, and PTP and P(0.1) further decreased. At target-point-20%, PTP and P(0.1) were similar to those at the 100%MinVol setting. At the ASV target point the 6 patients with chronic obstructive pulmonary disease had a lower mean %MinVol setting (125 +/- 23%) than the 16 patients who did not have chronic obstructive pulmonary disease (180 +/- 55%).


CONCLUSIONS
The 100%MinVol setting was frequently not associated with lower WOB in patients with respiratory failure. The %MinVol setting that significantly reduced WOB could be detected by increasing the %MinVol setting until a few mandatory breaths began to appear, and was on average 165% of the MinVol setting.
Wu
Chin-Pyng
CP
Division of Chest Medicine, Department of Internal Medicine, Tri-Service General Hospital, Taipei, Taiwan.
Lin
Hen-I
HI
Perng
Wann-Chern
WC
Yang
Shih-Hsing
SH
Chen
Chien-Wen
CW
Huang
Yuh-Chin T
YC
Huang
Kun-Lun
KL
D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D007362:Intensive Care Units; D008297:Male; D008875:Middle Aged; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology / Q000628:therapy; D012121:Respiration, Artificial / Q000379:methods*; D012129:Respiratory Function Tests; D012131:Respiratory Insufficiency / Q000503:physiopathology / Q000628:therapy*; D014939:Work of Breathing / Q000502:physiology*