Effect of pressure rise time on tidal volume and gas exchange during pressure control ventilation

Jeong, Byung O; Koh, Youn Suck; Shim, Tae Sun; Lee, Sang Do; Kim, Woo Sung; Kim, Dong Soon; Kim, Won Dong; Lim, Chae Man

Abstract

BACKGROUND
Pressure rise time (PRT) is the time in which the ventilator aclieves the set airway pressure in pressure-targeted modes, such as pressure control ventilation (PCV). With varying PRT, in principle, the peak inspiratory flow rate of the ventilator also varies. And if PRT is set to a shorter duration, the effective duration of target pressure level would be prolonged. which in turn would increase inspiratory tidal volume(Vti) and mean airway pressure(Pmean). We also postulated that the increase in Vti with shortening of PRT may relate inversely to the patients' basal airway resistance.
METHODS
In 13paralyzed patients on PCV(pressure control 18±9.5cm H2, FIO2 0.6±0.3, PEEP 5±3cm H2O, f20/min, I : E, 1 : 2) with Servo 300(Siemens-Elema, Solna, Sweden)from various causes of respiratory failure, PRT of 10%, 5% and 0% were randomly applied. At 30min of each PRT trial, peak inspiratory flow (PIF, L/sec), Vti(ml), Pmean(cm H2O) and ABGA were determined.
RESULTS
At PRT 10, 5% and 0%, PIF were 01.69±0.13, 0.77±0.19, 0.83±0.22, respectively(p<0.001). Vti were 425±94, 439±101, 456±106, respectively(p<0.001), and Pmean were 11.2±3.7, 12.0±3.7, 12.5±3.8, respectively(p<0.001). pH were 7.40±0.08, 7.40 ±0.92, 7.41±0.96, respectively (p=0.004) ; PaCO2 (mm Hg) were 47.4±15.8, 47.2±15.7, 44.6±16.2, respectively (p=0.004) ; PAO2 - PaO2 (mm Hg) were 220±98, 224±95, 227±94, respectively(p=0.004) ; and Vd/Vt as determined by (PaCO2 - P CO2/PaCO2 were 0.67±0.07, 0.67±0.08, 0.66 ±0.08, respectively(p=0.007). The correlation between airway resistance and change of Vti from PRT 10% to 0% were r=-0.243(0.498).
CONCLUSION
Shortening of pressure rise time during PCV was associated with associated with increased tidal volume, increased mean airway pressure and lower PaCO2.