The Science Journal of the American Association for Respiratory Care
BACKGROUND: Static pressure volume (PV) curves are essential for the implementation of lung protective strategies reported in the literature. The current ?gold standard? of using a calibration syringe for curve generation is problematic. An important limitation to more widespread use of static PV curves is related to the difficulty in their generation and their lack of reproducibility. We want to determine whether static PV curves comparable to those generated with a calibration syringe, could be produced without removing our patients from the ventilator.
METHOD: Using a mechanical lung model, inspiratory static PV curves were generated. A mechanics monitor (Novametrix Cosmo+) was attached inline with the circuit and interfaced to a laptop computer for data collection. Inspiratory PV curves were generated with a three-liter calibration syringe and compared to those generated using four commercially available ventilators (Bear 1000, Dräger Evita, Servo 900c, and Adult/Pediatric Star 2000). The ventilators were set to deliver 50ml VT, I:E of 1:3 and a rate of 40-60 bpm. A ball valve assembly was placed inline before the exhalation valve to allow for breaths to be stacked in the lung model.
Results: Cubic regression lines provided the best fit for the data obtained by each of the syringe and ventilator-based techniques and in each case the R-square was >95%. The 95% prediction interval was plotted for the syringe-generated breaths, and is illustrated in Figure 1. The curves generated by each of the ventilators fell within this prediction interval (see example Figure 2), indicating good approximation of the syringe method by each of the ventilators.
EXPERIENCE: While static pressure volume curves are a valuable clinical tool generation of these curves is sometimes very difficult in the clinical setting.
CONCLUSION: The curves generated via the ventilator method were essentially the same as the syringe curves and did not seem to be as operator dependent. Increments were less variable and curves were more easily repeated. In the clinical setting this method allows static PV measurements to be obtained while maintaining oxygen delivery and minimizing interruption of patient ventilation.
(See Original for Figures)