Fixed performance device:
Ans: A. Venturi maskRef: Ajar Yadov, Short Textbook of Anesthesia, 1st edition. pg 37.Explanation:Oxygen delivery SystemsOxygen is given thru fixed and variable performance devices.Fixed performance devices deliver a flow of oxygen equal to or in excess of peak inspiratory flowVariable performance devices use the deadspace of the nasopharynx or face masks as a reservoir of oxygen. They cannot deliver high inspired concentrations of oxygen.The oxygen delivery systems are classified into High flow delivery & low flow delivery systemsHigh flow delivery systemsThese work on Venturi Principle which states that if a gas is passed through a narrow orifice at high pressure it creates shearing forces around the orifice which entrain room air in specific ratio.The inspiratory gas flow should be 3 - 4 times the minute volumeThese high flow system include venture mask which delivers accurate inspired oxygen (FI02) (Error is only 1-2%)Venturi Mask:These are 'Fixed performance' oxygen delivery devices, delivering accurate oxygen concentration.'Fixed performance' because the performance is not affected by changes in patient's tidal volume and respiratory rate.The venture mask are available in different colours:ColourFlow rate of O2 (Litre per min)Delivered O2(FiO2)Blue0224%White0428%Orange0631%Yellow0835%Red1040%Green1560%The maximum oxygen that can be delivered by venture mask is 60%.Low flow oxygen delivery systemsThese includeNasal cannulaSimple mask ('Mary Carterall mask)Oxygen tentsNon rebreathing maskRebreathing maskPoly maskThe advantage is that these are very cheap and can he used in wards, preoperative and postoperative rooms and these are better tolerated by patients as compared to high flow systems.The disadvantage is that the delivered oxygen (FiO2) accuracy cannot be predicted (Compared to venturi mask which delivers accurate concentration)These low flow systems are 'variable performance* devices, since their performance is affected by changes in patient's tidal volume and respiratory rate.Oxygen Mask: Very commonly used in wards. Also known as Mary carterall maskOxygen flow rate/minDelivered oxygen (FiO2>5-6 litres40%6-7 litres50%7-8 litres60% So maximum concentration of oxygen that can be delivered by oxygen mask is 60%Increasing rate beyond 8 litres will not increase the Fi02 to more than 60% Attaching reservoir bag can increase Fi02 to 80%Nasal Cannula: The tip of nasal cannula should lie in nasopharynxFlow rate (litre/min)FiO2124%228%-332%436%540%644%- So. Maximum oxygen w hich can he delivered by nasal cannula is 44%Non rebreathing masks: Can deliver upto 80% of oxygenRebreathing mask: When tightly lit. they can provide 100% oxygen
Venturi mask
Nasal cannula
Simple mask
Non rebreathing mask
Breathing Systems