A new generation of Large Animal ventilators

Abstract

Most commercial large animal ventilators rely on the bag-in-the-box principle system where compressed gas is the driving power to drive a volume of gas into the lungs via a large animal circle system. A new generation of ventilators use special electrical motors and arrangements to force a volume of gas into the lungs. Two examples are the Tafonius (Vetronics Services) which is on the market and the Horsevent which has been developed as an University funded project (University of Veterinary Medicine Vienna). Tafonius uses a rigid piston in a cylinder with a rolling diaphragm. The piston is driven by an electronically controlled linear actuator. Airway pressure is measured at the Y-piece of the breathing circuit. This set-up allows precise control of pressures during spontaneous ventilation with or without continuous positive airway pressure and intermittent positive pressure ventilation (pressure and volume controlled mode) with maximum peak inspiratory and end-expiratory pressures of 80cm H2O and 50cm H2O respectively. In the Horsevent a linear motor operated in a forcecontrolled mode drives a standing concertina type of bellow. The ventilator which has no pressure sensor can be used in a spontaneous breathing mode with or without continuous positive airway pressure as well as in pressure controlled intermittent positive pressure ventilation with maximum peak inspiratory and end-expiratory pressures of 60cm H2O and 30cm H2O respectively. Manual operation of the concertina via the linear motor is possible at any time. Both ventilator designs carry substantial advantages over their bag-in-the box counterparts. Instead of costly compressed gas they need only electrical power and they function in an almost silent way. Both ventilators can also be used during spontaneous ventilation thereby avoiding disconnection or switching to an additional breathing bag. Both have direct microprocessor control of gas movement with ability to generate almost any desired pattern during inspiration and expiration and a large range of end-expiratory pressures. These features allow the implementation of modern ventilatory strategies including lung expansion maneuvers.