Equipment for inhalation anaesthesia for children

Automatic ventilation with the Ayre's T-piece. A modification of the Nuffield Series 200 ventilator for neonatal and paediatric use

A simple modification to an existing adult ventilator has been designed to permit mechanical ventilation of neonates and small children with the Ayre's T-piece circuit. The Nuffield Anaesthesia Ventilator Series 200 has been modified by replacing the piston in the patient valve with a fixed leak. This arrangement avoids the problems of critical adjustment commonly encountered with other methods of converting adult ventilators to paediatric use, and allows the ventilator controls to be used normally. The ventilator has been assessed according to the proposed International Standards Organization specifications for the evaluation of the performance of lung ventilators, and the results are described in detail. The modified ventilator is shown to perform as a time-cycled pressure generator capable of delivering tidal volumes between 10 and 300 ml at frequencies from 10 to 85/minute. It is therefore ideally suited to neonatal and paediatric use.

A new humidifier

A new heated water-bath humidifier operates on a new basic principle which overcomes the practical disadvantages of existing systems. A heated hose is used to control a temperature drop along the whole length of the delivery line instead of raising the temperature of the gases in the delivery line as in previous systems. Therefore the tank does not have to fully saturate the gases and a simple, totally cleanable design is possible. A temperature sensor at the delivery point controls the hose heater, constituting a rapid response, low thermal inertia system and delivery temperature is displayed on the unit. Compensation for varying gas flows and ambient temperature changes is inherent and the unit is suitable for neonatal/paediatric and adult use without special adjustment. The tank has a separate reservoir chamber which feeds an evaporation chamber via a cleanable float valve, conferring many advantages including clearly visible water levels, easy filling without breaking the circuit and constant compression volume. Full fail-safe alarm systems are incorporated.