THE BREATHING CIRCUIT – Flashcards
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How does gas get from machine to breathing circuit?
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Common Gas Outlet (Fresh Gas Outlet)
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What is the purpose of the Expiratory Reserve bag? What happens when it is squeezed and patient is connected to breathing circuit?
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It acts as a reservoir for gas (holds CO2 laden gas). Squeezing bag pushes exp gas thru CO2 absorber and back to inspiratory low (degree of gas return depends on how APL is calibrated). If APL is open then most of the expired gas is vented to scavenging system.
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Name the purpose of the expiratory valve/port
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The valve promotes uni-directional flow and prevents DEADSPACE. Expired gas vented to atmosphere.
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Name the three classifications of breathing systems
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OPEN - no rebreathing. Ex. open drop ether Semi-open/closed - Partial rebreathing. Ex. semi-open there is no rebreathing w/circle at HIGH Fresh Gas Flows. Ex. semi-closed, partial rebreathing at low FGF (Semi)CLOSED- Total rebreathing. Ex. is circle valve w/APL closed at low FGF
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What type of system is the Bain breathing System
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Modified Mapleson D Semi-Open Non-rebreathing and NO UNI-DIRECTIONAL VALVES Uses HIGH FGF for CO2 removal (70ml/kg for controlled ventilation and 100-300ml/kg for spontaneous ventilation) FGF enters at END of circuit for MAPLESON D EXP FGF==+==========PATIENT BAG BAIN APL Valve EXP==+============PATIENT BAG FGF CO2 removal dep on FGF, MV, and Breathing pattern
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Advantages of a BAIN SYSTEM Disadvantages of a BAIN SYSTEM
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ADV Lightweight Easily sterilized & Scavenged Exhaled gas in corrugated limb give heat/humidity to inhaled gas! DISADV Unrecognized disconnection or kinking of inner hose (ENTIRE SYSTEM BECOMES DEADSPACE!!!!!!) Pollution and increased cost of agents and gases r/t INCREASED FLOW RATE LOSS OF HEAT from patient r/t high flow Difficult changeover from circle to Bain
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PETHICK TEST
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Test of Bain system inner tube patency Assures patency of inner tube (occlusion means entire corrugated limb becomes deadspace) IF bag COLLAPSES = INTACT IF bag DOES NOT = INNER HOSE PROBLEM
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Describe properties of Open Breathing System (blow by)
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Anesthetics are blown directly across face No direct connection between machine and patient No valves, reservoir bag, or CO2 absorbers NO DEADSPACE Ex. Blow by or mask held over face
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Purpose/Function of Circle Breathing system (Most popular system in US at 99% use) What determines DIRECTION of flow? What determines if system will be closed, semi-closed, or semi-open?
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-Cleanses CO2 chemically via absorber -Allows rebreathing of all other exhaled gases -Gas flows via insp and exp limbs UNIDIRECTIONAL VALVES determine direction of flow Flow rate determines system classification
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Attributes of CLOSED CIRCLE SYSTEM What is Fresh Gas Flow for this system?
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FGF equal to pt uptake Complete rebreathing after CO2 absorbed and APL Closed FGF = 300-500mls Conserves anesthetic gases Conserves heat and moisture
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Attributes of SEMI-CLOSED SYSTEM What is FGF for this system?
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SOME rebreathing occurs, therefore CO2 absorbers are in play. APL at intermediate value. FGF = 3-6L
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Attributes of SEMI-OPEN SYSTEM FGF for this system?
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NO REBREATHING OCCURS FGF = >6L and APL fully open CO2 absorber NOT in play w/this mode. Scavenger vents all CO2
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Advantages of Circle System
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Constant inspired concentrations Conserves resp. HEAT and HUMIDITY Used in all ages Used in closed system w/low flow. Low Resistance (less than ETT but more than NRB circuit)
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Disadvantages of Circle System
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Increased DEADSPACE Unidirectional VALVE MALFUNCTION (creates more deadspace) CO2 Absorber may exhaust
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What function does the APL valve serve when the ventilator is on?
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None. APL is bypassed when ventilator mode is on. Bag will not fill. All ventilated gases have outlet to scavenging system
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Describe the Co-axial breathing system
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King system (technically circular) Insp/Exp limbs are connected FGF delivered via inner tube and EXPIRED gases exit via corrugated outer tube. Check BOTH ENDS of breathing hose for lapses in integrity (creates deadspace
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What pieces of the circuit pose the highest resistance to spont. breathing?
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Insp/Exp valves (MOST RESISTANCE) APL valve
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When inspecting valves what are the three checks that must be done?
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Check for: 1. Presence 2. Function 3. Integrity
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What does the ASTM require of valve housings?
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DIRECTION must be marked on limb or valve housing with insp/exp or arrow marking direction of intended flow. Must be fitted w/22mm male connector
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What happens if Insp. limb malfunctions? if Exp. limb malfunctions?
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The limb where the malfunction occurs becomes deadspace (Insp. limb malfunction = exhaled gases follows path of least resist. expelling CO2 laden gas back down inspiratory limb)
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What do you do in the event of an exp. limb outlet occlusion?
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Disconnect patient Ambu If exhalation valve fails result may be volu/baro trauma and tension pneumo if problem is not corrected
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What is normal circle system pressure gauge reading?
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20cmH2O PIP >than 20cm H2O risks overcoming esoph sphincter pressure and insufflating stomach PIP measured on machine AND at circle system (physical gauge)
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APL Valve Which direction tightens/loosens APL
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Releases gas to scavenger/atmosphere Provides PRESSURE CONTROL in breathing system RIGHT TURN - tightens APL therefore fills bag LEFT TURN - loosesn APL therefore vents to scavenger
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Your breathing system is set to 300-500ml/min. Is rebreathing occuring? How is CO2 removed?
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Near total rebreathing is occurring at this flow. FULL RELIANCE on CO2 absorber
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Your breathing system is set to between 6-8L/min. Is rebreathing occurring? How is CO2 removed here?
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Rebreathing is NOT occurring at this flow. Almost NO reliance on CO2 absorber. CO2 flows past open pop-off valve to scavenger carried by high flow.
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What is the MAJOR component of Soda-lyme (Sodasorb) absorbent? What is H2O Content?
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Calcium Hydroxide 80% H2O content is 10-20% (range depends on manufacturer) Absorbent historically contained potassium/sodium hydroxide but associated w/nephrotoxic compound A and CO
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Describe the Reaction occurring in CO2 absorber
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CO2 + H2O(in granules) --> H2CO3 (carbonic acid) Carbonic acid dissociates to--> H+ and HCO3 HCO3--> H and CO3(-2) THEN NaOH dissociates to Na+ and OH- Ca(OH)2 dissociates to Ca2+ and 2OH- Sodium and Calcium ions combine w/carbonate ions to form END PRODUCTS sodium carbonate and calcium carbonate 2NaOH + 2H2CO2 + Ca(OH)2 ==> CaCO3 +Na2CO3 + 4H2O (4H2O is CORROSIVE-DO NOT TOUCH!)
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If you touch the CO2 canister during anesthesia delivery and ventilation will the canister be warm or cool and why?
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Warm r/t exothermic reaction (can reach 45-50 C) 13,700 kcal per 22.2 L of CO2 absorbed
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What are the THREE phases of reaction in the CO2 absorbent?
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GASEOUS - CO2 given off by patient LIQUID - Thin film of H2O in hydroxides which surround granules SOLID - Undissolved Na, Ca, K, inert silicate and diatomaceous earth (Sodasorb) or undissolved barium, Ca, K, (Baralyme)
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What granule sizes are used in CO2 absorbers? What are the most important factors for absorbent granules?
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4-8 mesh 4 mesh is a granule that passes thru screen w/4wires per linear inch 8 mesh is granule that passes thru screen w/8wires per linear inch FACTORS: 1. SIZE, 2. POROSITY, 3. NATURE of SURFACE Pitted pores and different size granules INCREASES SURFACE AREA. Variable size DECREASES CHANNELING PHENOM.
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Airspace occupies how much of the canister volume? What is the optimal moisture content for Soda lime?
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48-55% of canister volume. Void space vs. Pore space should be about 50/50 (as per notes) 10-22% moisture content (p.38 slide 3) Moisture is IMPERATIVE b/c w/o it reaction WILL NOT OCCUR!
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What is the relationship between pt tidal volume and absorber efficiency?
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GREATEST efficiency when void space is GREATER/EQUAL to pt TV. take home point = DO NOT PACK GRANULES! Also, avoid dust r/t chemical burn and bronchospasm potential
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100 grams of Sodalyme absorbs _____L CO2?
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26 (Board Question) 500 gram canister absorbs 130L CO2
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What is ave CO2 production is _____ml/min
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200ml/min (12-18L/hr) 500 gram canister lasts about 10 hrs
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Describe the CHANNELING(wall) EFFECT
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Occurs in a loosely pack canister where airflow may occur along sides of canister. The loosely packed areas will wear out faster. Area near exp. valve will also wear out first. Leave 1/2 inch at top of canister
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What are dust fines implicated in?
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Laryngospams Bronchospasm Machine failure Inert silicate and Keiselgurh added to increase hardness and decrease friability (REDUCES DUST!)
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Does the resp. filter go on the Y-piece, expiratory limb, or inspiratory limb?
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Expiratory limb OR Y-Piece.
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Describe REGENERATION
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Absorbent turns white after "rest period" Absorbent IS NOT OK TO USE if regeneration occurs! ASSESS at end of each case and CHANGE CANISTER IF WARRANTED!
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COMPOUND A
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Decomp product of SEVO (vinyl ether breakdown product) Produces renal injury at 25-50ppm, which is achievable in clinical practice. SEVO NOT REC at FGF less than 1-2L/min or more than 2MAC hrs! and AVOID sevo in pts w/renal failure ABSORBER DRYNESS INCREASES COMP-A Change absorber routinely (every monday morning) NEVER re-hydrate granules
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CO
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Only in compounds w/presence of machines that utilize absorbents w/K or Na hydroxide -If granules are hydrated there is no problem HIGH FGF increase removal of CO, HOWEVER, they also desiccate absorbent more rapidly and increase risk of CO formation.
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PREVENTING CO FORMATION
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Turn off gas flow at end of each case Turn vaporizers OFF when not in use Flush circuit 1 minute at END of each case and before START of next case Regular absorbent change ( every monday morning ) ==>consideration for CO, comp A, and fire reduction!
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Current CO and Comp A
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PROBLEM FIXED r.t ALKALI FREE absorbents and Calcium Hydroxide composition
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SCAVENGING SYSTEM What is its purpose?
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Removes breathing circuit and ventilator gases AANA recs published in 92 and OSHA/ANSI has reqs as well.
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If you can smell an agent what does this tell you about your work area?
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It is massively contaminated 100% of a gas is 1,000,000 ppm 1% is 10,000 ppm
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Standard ppm for: Halogenated agent w/100% O2 Halogenated agent w/N2O N2O in scavenged room, unscavenged OR, dentist's office
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HALOGENATED AGENT w/100% 02-less than 2ppm in 8 hr time HALOGENATED AGENT w/N2O-Less than 0.5ppm in 8 hr time N2O in unscavenged room is upto 7,000ppm 25ppm in 8hrs weighted time sample or 50ppm in dentist office
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Scavenging system components
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Gas collection assembly - capture gas at emission site Transfer means - convey gas to interface INTERFACE- provides + pressure or - pressure relief and may provide reservoir capacity (MOST COMPLEX PART). May be OPEN or CLOSED Disposal tubing - conducts gas from interface to disposal assembly Disposal assembly - conveys gas to discharge point (usually roof of hospital) May be ACTIVE or PASSIVE
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INTERFACE
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Most complex part Has POS and NEG pressure relief to prevent pressure increases/decreases in scavenging system from reaching the breathing circuit AKA - balancing valve IF hose gets kinked==>vent releases gas to environment IF neg pressure builds up==>air pulled from environment rather than breathing circuit
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PASSIVE vs. ACTIVE
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All OPEN interface systems must be ACTIVE (vacuum) CLOSED (bag) interface systems may be ACTIVE (vacuum) or PASSIVE (venting w/each breath)
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Scavenging flow meter
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Ball must remain between lines At this point flow is approx 25L/min!
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OPEN SYSTEM
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Relies on pressure relief ports for +/- pressure relief.
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CLOSED SYSTEM
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if suction breaks/machine sitting on transfer means/gas disposal assembly EXCESSIVE SUCTION builds up, GAS VENTED TO OR via POS pressure relief. There is a neg-pressure relief valve on the interface to draw room air and prevent emptying of gas from patient circuit
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GAS MONITORING
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Dosimeter - measure N2O Ionizing Leak Detector-Electron capture detector, good for detecting low concentrations of halogenated agent Thermocamera - Infrared camera, Sensitive to 100ppm or more. Used mainly during construction. Grab sampling (instantaneous) - single shot or periodic sampling
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Ways to improve waste gas scavenging
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GOOD MASK FIT or intubate! turn off anesthetic and dump circuit reservoir bag into scavenger system before suctioning or extubation Give O2 for as long as possible during end of case. Avoid vaporizer spills Use low flows Cuffed ETTs Regular machine checks
