Introduction
ICU-ventilators are designed for use at normobaric conditions. Under certain circumstances patients need mechanical ventilation during hyperbaric oxygen therapy. The aim of the investigation was to analyse the function of four different ICU-ventilators [EVITA-4, Microvent, Oxylog 2000 HBO (Drägerwerk AG, Germany) and Servo ventilator 900 C (Siemens-Elema, Sweden] under 5 (normobaric, 1.3, 1.6, 1.9 and 2.8 ATA, EVITA-4 and Oxylog 2000 HBO) or 6 (additionally 6 ATA, Servo ventilator 900 C and Microvent) different atmospheric pressure conditions, regarding the difference of present and effectively applied volume and pressure from those set at the control panel.
Methods
We tested the following ventilator modes: volume (VCV) and pressure controlled ventilation (PCV, EVITA-4 and Servo ventilator 900 C only), the electromechanical lung simulator LS 1500 (Drägerwerk AG, Germany) consisting of a motor driven bellow.
During VCV tidal volume was set at (VT) = 750 ml, respiratory rate (f) = 15/min, I:E ratio = 1:2, positive endexpiratory pressure (PEEP) = 0 cmH2O. During PCV (f) = 10/min inspiratory pressure (Pinsp) was set in order to achieve a Vt of 750 ml keeping all others ventilator parameters constant. The VT applied by the ventilator was measured as the linear displacement of the bellows at each ambient pressure. (Paw) was measured inside of the bellows.
Results
During VCV applied Vt of the ventilator decreases significantly with increasing ambient pressure while PCV with constant Pinsp and PEEP Vt was stable at each depth.
Conclusions
Under hyperbaric conditions PCV should be preferred due to the stability of VT applied. If PCV is not available, VT needs to be adjusted during VCV depending on the actual ambient pressure.
Acknowledgement
We thank Drägerwerk AG, Germany for kindly providing us the lung simulator LS 1500.
