DRAW-OVER VAPORISERS IN A NUTSHELL FOR EXAMS

🏺They are placed inside the breathing system and rely on a negative pressure downstream from the vaporiser to create the flow required to entrain the agent. This negative pressure is generated either by the patient’s own inspiration or by a self-inflating bag

🏺So they must have a very low resistance to flow to avoid additional resistance to the patient’s breathing. 

🏺Goldman vaporiser, the Oxford miniature vaporiser (OMV) and the Epstein MacIntosh vaporiser (EMV) etc are draw-over vaporisers. The triservice apparatus, used by the military, incorporates two OMVs

🏺 They are simpler, lightweight, smaller and less expensive. 

🏺 As it is not possible to calibrate for the large range of tidal volumes created by the patient/ self-inflating bag, they are inaccurate 

🏺So they are not generally used in hospitals, and are reserved for ‘in-the-field’ use, where portability is required. 

Reference: Al-Shaikh B, Stacey S. Essentials of Anaesthetic Equipment, 2nd edn. Edinburgh: Churchill Livingstone, 2002 . Davis PD, Kenny GNC. Basic Physics and Measurement in Anaesthesia, 5th edn. Oxford: Butterworth–Heinemann, 2003 .