2007 OPEN FORUM Abstracts
A DIFFERNCE OF A PRESSURE WAVE FORM IN GRAPHIC DISPLAY OF SOME VENTILATORS
Background: Current generation ventilators have graphic displays to assist in the clinical evaluation and management of patients. Clinicians frequently use pressure, volume and flow scalar waveforms. During pressure-targeted ventilation, the pressure versus time waveform is used. The displayed pressure is usually measured at either the patient Y, the inspiratory pressure transducer or at the expiratory pressure transducer. We evaluated the pressure versus time waveform on five current generation ventilators.
Method: Each ventilator was connected to the Michigan Instruments Training Test Lung (TTL) with the standard circuit. Pressure was measured at three points (inspiratory limb at the ventilator outlet, patient Y piece and at the expiratory limb at the ventilator inlet) using a pressure transducer (PF-300). Ventilator settings: Mode: CPAP with PSV; PEEP 5 cm H2O; PSV 15 cm H2O. TTL settings: Resistors: # 5 and # 20; Compliance 20 and 50 mL/cm H2O). Spontaneous breathing was simulated using the TTL as previously described by various authors. Ventilators evaluated: Puritan Bennett 840, Drager Evita XL, Maquet Servo-i, Viasys Avea and Hamilton Galileo.
Results: The pressure waveforms on the PB 840 and Drager Evita XL appear to be the average inspiratory pressure and average expiratory pressure. The pressure waveform on the Servo-i, appears to display expiratory pressure at the time of inspiration and then display inspiratory pressure at the time of expiration. On the Viasys Avea, the pressure waveform displays inspiratory pressure at the time of inspiration, and the expiratory pressure at the time of expiration. On the Hamilton Galileo, the pressure is measured at the patient Y piece.
Conclusions: There are many kinds of ventilators in Japanese hospitals. It is important to know the characteristics of each ventilator. We were able to confirm that there were four different types of pressure waveforms. When evaluating compliance and airway resistance of a patient, and when evaluating pressure waveforms, it is important to understand that pressure waveforms are different on different ventilators.