Non-invasive ventilation with some gas mixtures, such as high flow oxygen or Heliox, can be problematic and/or require expensive equipment. The addition of a pressurised afferent reservoir to the Nippy 1 ventilator (B&D Electromedical) was studied to see if this would overcome these problems. The remote trigger of the Nippy 1 is essential to this design. A CPAP circuit was used to give a gas flow of at least 30 l/m; a 30 cm H2O safety valve was incorporated. A 3 l afferent reservoir (bag in bottle design) was added via a t-tube (Abstract P275 figure 1). The inner flexible bag was directly open to the CPAP circuit. The rigid outer casing had two ports, the first connected to the output from the Nippy 1 and the second connected to and exhaust valve controlled by the Nippy 1. A standard Nippy 1 breathing circuit conveyed the gas to the patient. As the patient breaths in the Nippy 1 is triggered and closes the two exhaust valves. The reservoir is pressurised by the ventilator providing a positive inspiratory pressure. In expiration both valves open enabling the patient to breathe out and the reservoir to refill. Pressure measurements at the mask showed that the system has an intrinsic PEEP of approximately 2.5 cm H2O; the trigger on the Nippy 1 was changed to a relative design to compensate. The circuit can be adjusted to deliver inspiratory pressures of up to 30 cm H2O. The pressure performance was unaltered when using Heliox, oxygen or air. The addition of a CPAP valve to the patient exhaust port could also be employed to raise the PEEP pressures as required. The development of this circuit may enable any gas to be used within the HDU/CCU setting without needing expensive equipment.
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