Anesthesiology Research and Scholarship. Follow this and additional works at:

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1 University of New Mexico UNM Digital Repository Anesthesiology Research and Scholarship Anesthesiology Breathing Systems Janet Brierley Follow this and additional works at: Recommended Citation Brierley, Janet. "Breathing Systems." (2013). This Presentation is brought to you for free and open access by the Anesthesiology at UNM Digital Repository. It has been accepted for inclusion in Anesthesiology Research and Scholarship by an authorized administrator of UNM Digital Repository. For more information, please contact

2 BREATHING ATTACHEMENTS BREATHING SYSTEMS TERMINOLOGY Janet K Brierley MB.BS., FRCA Professor University of New Mexico Open Semiopen Semiclosed Closed OPEN SEMI-OPEN No seal on face Open-drop anesthesia for ether and chloroform e.g. Schimmelbusch mask napkin over face like baddies in movies Similar to open Some seal with face and some degree of rebreathing e.g. Ogston s inhaler SEMI-CLOSED CLOSED Rebreathing of alveolar gases is not intended but can happen with misuse e.g.mapleson A-F Total or partial rebreathing intended CO 2 absorption Some fresh gas flow necessary May operate with intentional spill May be totally closed Also called circle or to-and-fro 1

3 MAPLESON ATTACHMENTS Non-rebreathing systems Some have valves Semi-closed No CO 2 absorption A,B,C,D,E,F Instill irrational fear in residents MAPLESON ATTACHMENTS COMPONENTS FGF = fresh gas flow arriving in a tube Corrugated hose Mask of some kind or ET tube Reservoir bag* Expiratory valve Mapleson A (aka Magill) Efficient for spontaneous ventilation FGF < minute volume 3 phases in breathing cycle Unwieldy EXP valve gives resistance to expiration Coaxial version Lack Mapleson A with controlled ventilation Problems: have to keep EXP almost closed at end insp, excess FGF goes out of EXP at end insp, bag almost empty all exp gas goes into bag no exp pause Mapleson A Aide memoire Expiratory pause is key Dead space gas is fresh gas Efficient for SV (FGF < minute volume) Mapleson D Spontaneous ventilation Type of T-piece FGF plus exhaled gases mix in expiration Dead space gas is voided first, then alveolar gas Inspiration is mix of FGF plus mix left in tubing 2

4 Mapleson D Spontaneous ventilation Rebreathing occurs unless: FGF at least 2x minute volume expiratory pause is long enough for all exp gases to be flushed out also: vol of tubing + FGF must be big enough to supply V T Mapleson D Controlled ventilation Bit better than with SV Lose fresh gas when squeezing bag Lose fresh gas and dead space gas during exp pause Have to have FGF > minute volume Have to have exp pause (difficult) Mapleson D Controlled ventilation Overall good with valve near machine (less unwieldy with scavenging) Long hose convenient for head and neck surgery Overall good economy with controlled ventilation Coaxial version is Bain - humid, warm, scavenging easier Mapleson B and C Inefficient: SV needs 2 x minute volume controlled needs 2.5 min vol Version of C called Waters To and Fro incorporates CO 2 absorber (makes it a closed system) C with the short tail, better than B for SV B with the long tail, better than C for CV Summary Risk of Rebreathing For spontaneous A Dog Can Bite A is best, D is okay, C & B are awful For controlled ventilation Dog Bites Can Ache D is best, B is okay (use for transport to ICU post op) C not too good and A is awful A System for Children Q.Why do they need something special? A. Resistance to expiration from EXP Solution: Ayre s T-piece: key part of the Mapleson E system 3

5 Mapleson E System Requirements Diameter of reservoir limb? Too big vs too small Volume of reservoir limb? Minimum length vs very long tubing Optimum FGF? If volume = V T, then 2.5 x minute vol Mapleson E Drawbacks How can we tell if child is breathing? How can we ventilate the child? Need large FGF same whether SV or controlled Solutions to Problems Machine Components Whisp of cotton wool? Add bag - Jackson-Rees modification called Mapleson F Original bag open ended - of course Scavenging is a problem Bags we have incorporate a VALVE! Aaargh! Gas inlets (pipeline and cylinders) Pressure regulators Oxygen pressure failure devices Flow control valves and flowmeters Vaporizers Fresh gas outlet Machine High pressure system >50psi Intermediate pressure system 37-55psi Low pressure system >atmospheric but <30psi High Pressure System Cylinders Connected on the hanger-yoke assembly Pin index system for safety Each has a filter Each has a check valve to prevent retrograde flow Pressure measured by Bourdon pressure gauge 4

6 High Pressure System Cylinders Pressure in cylinder varies with temperature and content This results in changing supply pressure Pressure regulator reduces cylinder gas pressure to <50 psi Two-stage pressure regulators further prevent fluctuations in flow of gas Oxygen Liquid oxygen is delivered to large tank Stored at -183 o C Critical temp is -119 o C Tank is vacuum insulated Evaporated gas has to be heated before delivery Nitrous oxide N 2 O stored in banks of cylinders Critical temperature is 36.5 so it is really a vapour! Pipeline pressure of oxygen, nitrous oxide and air is between 45 and 55 psi Pipeline gas pressures do not need to be reduced in the anesthetic machine Pipeline Supply Pipeline connection is noninterchangeable quick connect Inlet has check valve to prevent backflow of machine gas into hospital pipes Bourdon tube pressure gauge on pipeline side of check valve Pipeline pressures should be 45-55psi Flowmeters ( rotameters ) A ball or float indicator in a tapered tube Smallest diameter is at bottom Flow control valve opened, more gas in. Indicator pushed up tube by gas pressure Higher the indicator, wider the annular gap between it and wall of tube Gas passes around indicator Indicators Flow is read at centre of a ball indicator It should spin freely to show that it isn t stuck in the tube Flow is read at the top of all other indicators 5

7 Gas Flow in Flowmeter Rate of flow depends on Pressure drop across the indicator Constant for all positions in the tube Size of annular opening Gas properties O 2 Pressure Failure Devices O 2 failure alarm Oxygen failure safety valve Oxygen Ratio Monitor Ensures a minimum flow of oxygen in the presence of nitrous oxide Prevents administration of <25% oxygen in the presence of Nitrous oxide Other stuff The oxygen flush valve: O 2 at high pressure (50psi) and flow l/min - potentially dangerous - straight into breathing system. The ventilator driving gas: taken off the intermediate pressure system: Pressure must be 40-60psi Vaporizer Low Pressure System Components Back pressure safety devices Common gas outlet Low Pressure System Back pressure safety devices Pressurizing valve Unidirectional valve Pressure relief valve 6

8 And that s as much as anyone can take. The End! 7