October 2002 / Volume 47 / Number 10 / Page 1173
Battery Duration of Portable Ventilators: Effects of Control Variable, Positive End-Expiratory Pressure, and Inspired Oxygen Concentration
INTRODUCTION: Portable ventilators require battery power during transport or when alternating current is unavailable. Manufacturers report battery duration at nominal ventilator settings. METHODS: We studied the effects of control variable (pressure control vs volume control), positive end-expiratory pressure (PEEP), and fraction of inspired oxygen (FIO2) on the battery duration of 8 portable ventilators: Achieva, HT50, iVent201, LTV1000, TBird Advanced Ventilator System (AVS), Avian, Uni-Vent 750, and Uni-Vent 754. Each ventilator was set to ventilate a test lung at a rate of 10 breaths/min, tidal volume of 750 mL, and inspiratory time of 1.5 s, with volume-controlled ventilation and then pressure-controlled ventilation (PCV), if available. FIO2 was set at 0.21 and then 1.0. PEEP was set at 0, 10, and then 20 cm H2O. Test lung compliance and resistance were set at 20 mL/cm H2O and 5 cm H2O/L/s, respectively. Five trials were performed with each portable ventilator, with each combination of settings. Time to low-battery alarm, battery-empty alarm, and failure to ventilate the test lung were recorded. Portable ventilator performance during the trials was determined by continuous recording of tidal volume. RESULTS: The battery duration of pneumatically driven portable ventilators is longer than that of electrically driven portable ventilators. The battery duration of pneumatically driven portable ventilators is minimally affected by ventilator settings. The battery duration of electrically driven portable ventilators is shortened by use of PCV, increasing PEEP, and increasing FIO2. Compared to zero PEEP, PEEP of 20 cm H2O reduced battery duration with HT50 (40%), LTV1000 (37%), TBird AVS (34%), and Achieva (15%). Compared to volume-controlled ventilation, PCV reduced battery duration with the LTV1000 (48%) and TBird AVS (18%). Compared to FIO2 of 1.0, FIO2 of 0.21 reduced battery duration with the Uni-Vent 754 (37%). Compared to FIO2 of 0.21, FIO2 of 1.0 reduced battery duration with the LTV1000 (17%) and TBird AVS (15%). The iVent201 was unable to deliver the set tidal volume with PCV and 20 cm H2O PEEP. Low-battery alarms functioned properly on all the ventilators. CONCLUSIONS: Battery duration differs greatly among the portable ventilators tested. Clinicians must be aware that portable ventilator battery duration is affected by control settings, lung impedance characteristics, and portable ventilator characteristics. Battery duration may be shorter than that reported in the operator's manual for each portable ventilator tested.
Key words: portable ventilators, mechanical respiration, transportation of patients, power sources, positive pressure ventilation.
[Respir Care 2002;47(10):1173–1183]
Portable ventilators require an internal power source (battery) for operation when alternating current (AC) power is unavailable. For home-care ventilation, battery power is essential for patient mobility and the resulting improved quality of life. During patient transport, battery power is essential for safe patient movement. Power for and control of ventilator operation can be accomplished by the gas source (pneumatic), a battery (electric), or both. Classification of portable ventilators requires definition of input power (electric, pneumatic, or both) and driving system (pneumatic, piston, turbine, or fluidics). Each type of control and driving system has advantages and disadvantages depending on the application (home, hospital, transport). Most new-generation portable ventilators are microprocessor-controlled and possess internal drive systems, both of which require a continuous source of electricity.
Pneumatically powered portable ventilators require a high-pressure (30-60 psi) gas source from either an external compressor or a compressed gas cylinder. Electrically powered portable ventilators generate gas pressure and flow by a piston, turbine, or internal compressor. The duration of operation of any portable ventilator depends on the power source (pneumatic and/or electric), driving system (pneumatic and/or electric), relative load (impedance to gas flow and minute ventilation requirement), capacity and type of battery used, and ventilator settings. Pneumatically powered ventilators have relatively high gas consumption and low electricity consumption, so their duration of operation may be affected more by the availability of compressed gas than by battery duration. Electrically powered and controlled ventilators may have lower gas consumption but usually require more electricity, so their duration of operation depends on battery duration.
Typically, manufacturers of portable ventilators report the battery duration at nominal ventilator settings and load (compliance and resistance) conditions. We evaluated the effects of control variable (volume-controlled ventilation [VCV] vs pressure-controlled ventilation [PCV]), positive end-expiratory pressure (PEEP), and fraction of inspired oxygen (FIO2) on the battery duration of 8 commercially available portable ventilators.