Datex-Ohmeda Aladin Cassette Vaporizer

The vaporizer system used in the Datex-Ohmeda ADU is unique, and the electronically controlled vaporizer is designed to deliver five different inhaled anesthetics, including halothane, isoflurane, enflurane, sevoflurane, and desflurane. The vaporizer consists of a permanent internal control unit housed within the ADU and an interchangeable Aladin agent cassette that contains anesthetic liquid. The Aladin agent cassettes are color coded for each anesthetic agent, and they are also magnetically coded so that the Datex-Ohmeda ADU can identify which anesthetic cassette has been inserted. The cassettes are filled using agent specific fillers.^{[54] [40]}

Although very different in external appearance, the functional anatomy of the Datex-Ohmeda S/5 ADU cassette vaporizer ( Fig. 9-19 ) is very similar to that of the Dräger vapor 19.1 or 20.n and the Datex-Ohmeda Tec 4, Tec 5, or Tec 7 vaporizers, because it is made of a bypass chamber and vaporizing chamber. A fixed restrictor is located in the bypass chamber, and flow-measurement units are located in the bypass chamber and in the outlet of the vaporizing chamber. The heart of the S/5 ADU cassette vaporizer is the electronically controlled flow control valve located in the vaporizing chamber outlet. This valve is controlled by a central processing unit (CPU). The CPU receives input from multiple sources, including the concentration control dial, a pressure sensor located inside the vaporizing chamber, a temperature sensor located inside the vaporizing chamber, a flow-measurement unit located in the bypass chamber, and a flow-measurement unit located in the outlet of the vaporizing chamber. The CPU also receives input from

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A fixed restrictor is located in the bypass chamber, and it causes the vaporizer inlet flow to split into two portions (see Fig. 9-19 ). One portion passes through the bypass chamber, and the other portion enters the inlet of the vaporizing chamber and passes through a one-way check valve. The one-way check valve protects against backflow of agent into the bypass chamber, and its presence is crucial when delivering desflurane if the room temperature is greater than the boiling point for desflurane (22.8°C).^[54] A precise amount of carrier gas flow and vapor flow passes through the flow control valve, which is regulated by the CPU. This flow then joins the bypass flow to the outlet of the vaporizer.^{[40] [54]}

Vaporization of desflurane presents a unique challenge, particularly when the room temperature is greater than the boiling point of desflurane (22.8°C). At higher temperatures, the pressure inside the sump increases, and the sump becomes pressurized. When the sump pressure exceeds the pressure in the bypass chamber, the one-way check valve located in the vaporizing chamber inlet shuts, preventing carrier gas from entering the vaporizing chamber. The carrier gas then passes straight through the bypass chamber. Under these conditions, the electronically controlled flow control valve meters in the appropriate flow of pure desflurane vapor.

When large quantities of anesthetic liquid are vaporized during high fresh gas flow rates and or high dial settings, the vaporizer cools because of the latent heat of vaporization. To offset this cooling effect, the S/5 ADU is equipped with a fan that forces warmed air from an agent-heating resistor across the cassette to raise its temperature when necessary.^[35] The fan is activated during two common clinical scenarios: desflurane induction and maintenance and sevoflurane induction.