Mapelson Circuits in Anaesthesia (Breathing System)

Mapelson Circuits -included additional components to avoid the listed complications of an open drop system -additional components include: breathing tubes, fresh gas inlets, pressure-relief valves, breathing bags -relative location of the components create differing performance traits on the circuit systems identified by Mapleson classification Components of Mapelson Circuits breathing tubes fresh gas inlets pressure relief valve resevoir bag Performance Characteristics of Mapelson Circuits General Mapleson classification A Mapleson classification B Mapleson classification C Mapleson classification D Mapleson classification E Mapleson classification F Disadvantages of mapleson circuits Breathing Tubes -corrugated breathing tubes connect the components of the mapleson circuit to the patient -made of rubber (reusable) and plastic (disposable) -large diameter tubes allow for low resistance of airflow -large diameter tubes may be a potential resevior for anesthetic gases to reside -volume of most mapleson breathing tubes should be at least as great as the patient's tidal volume to minimize FGF requirements -high compliance large breathing tubes increase the difference between the volume of gas delivered by ventilator and recieved by pt factors involved : gas compression and breathing tube expansion effects: positive pressure ventilation Fresh Gas Inlet -continuous flow system -anesthetic gases and carrier gases from the anesthetic machine continuously enter the circuit via the fresh gas inlet -mapleson performace has differing charecteristics depending on the relative position of the fresh gas inlet Pressure Relief Valve -pressure rises as the anesthetic gases enter the breathing circuit greater than the combined uptake from patient and circuit -pressure relief valve allows gases to exit the circuit avoiding pressure buildup -pressure relief valve directs exiting gases to either the operating room or preferably scaveging system -spontaenous ventilation: pressure relief valve should be completely open -assist/controlled ventilation pressure relief valve may have partial closure to create positive pressure ventilation Resevoir Bag -resevoir of anesthetic gases and assist in generating of positive pressure ventilation -special design to increase compliance of the resevior bag with increasing volume -increased compliance with increased volume attempts to protect the patients lungs from unintentional closure of PRV three distinct phases of filling the resevior bag: phase I: normal filling of the 3L resevior bag phase II: rapid rise to peak filling of resevoir bag phase III: plateau or slight decrease in pressure with further volume filling of resevoir bag Performance Characteristics of Mapelson Circuits General -mapleson circuits are: lightweight, inexpensive, simple, and do not require unidirectional valves -elimination of C02 rebreathing is dependant on fresh gas flow -lack of unidirectional valve and C02 absorber requires the venting of C02 through a pressure relief valve before inspiration -to ensure adequate venting of C02 through the pressure relief valve to prevent rebreathing:generally high fresh gas flows are needed Mapleson classification A: (Magill attachment) -spontAneous ventilation: fresh gas flow requirement equals minute ventilation ( approx 80 ml/kg/min) -controlled ventilation: fresh gas flow requirement very high and difficult to predict therefore not a good choice for controlled ventilation Mapleson classification B: -spontaneous ventilation: 2x's minute ventilation -controlled ventilation: 2- 2 1/2 minute ventilation Mapleson classification C (Water;s to-and-fro) -spontaneous ventilation: 2x's minute ventilation -controlled ventilation: 2- 2 1/2 minute ventilation Mapleson classification D (Bain circuit) -spontaneous ventilation: 2-3x's minute ventilation -controlled ventilation: 1-2x's minute ventilation Mapleson classification E (Ayre's T-piece) -spontaneous ventilation: 2-3x's minute ventilation -controlled ventilation: 3x's minute ventilation Mapleson classification F (Jackson-Rees' modification) -spontaneous ventilation 2-3x's minute ventilation -controlled ventilation 2x's minute ventilation for spontaneous ventilation: A>D>C>B ( All Dogs Can Bite) for controlled ventilation: D>B>C>A ( Dead Bodies Cant Argue) Disadvantages of Mapleson Circuits: (due to high fresh gas flow requirements in order to prevent rebreathing of C02) -waste of anesthetic gases -pollution of the operating room environment -loss or patient heat and humidity