Reliability of measured tidal volume in mechanically ventilated young pigs with normal lungs

Objective: This study examined whether volumes can be accurately measured at the expiratory valve of a conventional ventilator using pressure support ventilation and positive end expiratory pressure with software compensation for circuit compliance available in the Servo i ventilator. Design and setting: Comparison of two methods for measuring tidal volume in an animal laboratory. Subjects: Twenty healthy, intubated, sedated, spontaneously breathing pigs. Interventions: Volume was measured in ten neonatal-sized and ten pediatric-sized pigs ventilated with the Servo i' ventilator using pressure support ventilation and positive end expiratory pressure with and without circuit compliance compensation. We compared volume measured at the airway opening by pneumotachography to volume measured at the expiratory valve of a conventional ventilator. Measurements and results: The use of circuit compliance compensation significantly improved the agreement between the two volume methods in neonatal-sized piglets (concordance correlation coefficient: with circuit compliance compensation, 0.97; without, 0.87, p=0.002). In pediatric-sized pigs there was improvement in agreement between the two measurement methods due to circuit compliance compensation (concordance correlation coefficient with circuit compliance compensation, 0.97; without, 0.88, p=0.027). With circuit compliance compensation off there was positive bias: mean difference (bias) 2.97 +/- 0.12 in neonatal-sized and 3.75 +/- 0.38 in pediatric-sized pigs. Conclusions: Our results show that volume can be accurately measured at the expiratory valve of a conventional ventilator in neonatal- and pediatric-sized animals.