We studied the cardiorespiratory effects of altering ventilator-set inspiratory flowrate (Vvent) during pressure support ventilation (PSV) in 15 patients using the IRISA microprocessor-controlled ventilator.
Methods
All patients were being ventilated at PSVmax (ie, PSV level adjusted to provide tidal volume [VT] = 10-12 mL/kg and f≤ 20 breaths/min) following a mean (SD) duration of ventilatory support of 16.1 (7) days. Patients were initially ventilated with the maximum Vvent for 1 hour. During this hour, tidal volume, inspiratory time (T₁), minute ventilation (VE), respiratory frequency (f), oxygen consumption (Vo₂), heart rate, and mean arterial blood pressure were monitored continuously. Additionally, at the end of the 1-hour period, arterial blood gas analysis and expired-gas collection for calculation of dead-space-to-tidal-volume ratio were performed. Patients then were ventilated at the lowest Vvent that would maintain PSVmax, and measurements were repeated. A third, midrange Vvent was then used, and measurements were repeated after 1 hour.
Results
A variable response to alterations in Vvent was observed. Four patients exhibited a lower f, longer T₁, and larger V₁ at the highest Vvent; four at the lowest Vvent; and seven patients at the midrange Vvent. Patients with the highest VE preferred the highest Vvent and decreasing Vvent in this population resulted in tachypnea and dysynchrony. When Vvent was increased in the group preferring the lowest Vvent, T₁ and V₁ fell while f increased. No clinically important changes were seen in pulse rate or mean arterial blood pressure in any patient during the Vvent manipulation.
Conclusion
Variable Vvent during PSV allows titration of ventilator output to patient demand, improves patient-ventilator synchrony, and should be incorporated into current PSV systems.
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References
1.
MacIntyreNR. Respiratory function during pressure support ventilation. Chest1986;89:677–683.
2.
KacmarekRM. The role of pressure support ventilation in reducing work of breathing. Respir Care1988;33:99–120.
BrochardL, HarfA, LorinoH, LemaireF.Inspiratory pressure support prevents diaphragmatic fatigue during weaning from mechanical ventilation. Am Rev Respir Dis1989;139:513–521.
5.
BrochardL, PluskwaF, LemaireF.Improved efficiency of spontaneous breathing with inspiratory pressure support. Am Rev Respir Dis1987;136:411–415.
6.
FiastroJF, HabibMP, QuanSF. Pressure support compensation for inspiratory work due to endotracheal tubes and demand continuous positive airway pressure. Chest1988;93:499–505.
7.
HurstJM, BransonRD, DavisKJr, BarretteRR. Cardiopulmonary effects of pressure support ventilation. Arch Surg1989;124:1067–1070.
8.
TokiokaH, SaitoS, KosakaF.Effects of pressure support ventilation on breathing patterns and respiratory work. Intensive Care Med1989;15:491–494.
9.
GibneyRTN, WilsonJRS, PontopiddanH.Comparison of work of breathing on high gas flow and demand valve continuous positive airway pressure systems. Chest1982;82:692–695.
VialeJP, AnnatG, BertrandO.Additional inspiratory work in intubated patients breathing with continuous positive airway pressure systems. Anesthesiology1985;63:536–539.
12.
CappsJS, RitzR, PiersonDJ. An evaluation in four ventilators of characteristics that affect the work of breathing. Respir Care1987;32:1017–1024.
13.
BeydonL, ChasseM, HarfA, LemaireF.Inspiratory work of breathing during spontaneous ventilation using demand valves and continuous flow systems. Am Rev Respir Dis1988;138:300–304.
14.
DownsJB. Mechanical ventilatory support. Part II. Curr Rev Respir Ther1981;3:82–88.
15.
MariniJJ, CappsJS, CulverBH. The inspiratory work of breathing during assisted mechanical ventilation. Chest1985;87:612–618.
16.
MariniJJ, SmithTC, LambVJ. External work output and force generation during synchronized intermittent mechanical ventilation. Am Rev Respir Dis1988;138:1169–1179.
17.
MariniJJ. Mechanical ventilation: Taking the work out of breathing. Respir Care1986;31:695–702.
18.
CzervinskeMP, ShreveJ, LesterKB, TeagueWG. Effects of working pressure on respiratory pattern and airway pressure during pressure support ventilation in infants with chronic lung disease (abstract). Respir Care1988;33:930.
19.
DurhamR, TrevinoMD, RogalMG, WaltersPR, BormanKR. Effects of gas flow characteristics during pressure support ventilation (abstract). Crit Care Med1989;17:S26.
20.
IottiG, BraschiA, RodiG, ChiarandaM.Mechanical effects of pressurization rate changes during pressure support ventilation (abstract). Intensive Care Med1988;14(Suppl 1):326.
21.
HoL, MacIntyreNR. Pressure-supported breaths: Ventilatory effects of breath initiation and breath termination design characteristics (abstract). Crit Care Med1989;17:S26.
22.
MessadiAA, Ben-AyedM, BrochardL, IottiG, HarfA, LemaireF.Comparison of the efficacy of two waveforms of inspiratory pressure support: Slow versus fast pressure wave (abstract). Am Rev Respir Dis1990;141:A519.
