Breathing Systems PDF

6/20/24 Breathing Systems Ehrenwerth, Ch. 4 and Ch. 7 Miller, 9th ed., Ch. 22, P. 601 - 614 (Inhaled Anesthetics: Delivery Systems, Anesthetic Breathing Circuits section) Dorsch and Dorsch*** 1...

6/20/24 Breathing Systems Ehrenwerth, Ch. 4 and Ch. 7 Miller, 9th ed., Ch. 22, P. 601 - 614 (Inhaled Anesthetics: Delivery Systems, Anesthetic Breathing Circuits section) Dorsch and Dorsch*** 1 Definition Breathing system: 1. Receives gas mixture from the machine 2. Delivers gas to the patient 3. Removes CO2 4. Provides heating and humidification of the gas mixture 5. Allows spontaneous, assisted, or controlled respiration 6. Provides gas sampling, measures airway pressure, and monitors volume 2 1  6/20/24 Resistance ´ When gas passes through a tube, the pressure at the ETT Tube: the pressure at the beginning of the tube outlet will be lower than at the inlet will be higher than the pressure at the end of the tube ´ The drop in pressure is a measure of the resistance that If flow is coming from the machine through the must be overcome circle system and is being delivered to the patient: -the difference in pressure is the resistance that must be overcome [P2-P1] ´ Resistance varies with the volume of gas passing through -flow at the beginning is higher than the flow coming per unit of time into the patient. Q= Flow Overcoming differences in resistance: P2 [higher | ________________ P1 [lower|at P2= Higher pressure -as gas is turned up, the pressure increases in the circle system beginning of tube] ________________ end of tube] P1= Lower pressure -as gas is turned down, pressure decreases in the circle system R = Resistance -as other other connectors, ETT or length to the system is added = more resistance that the system has to overcome. ´ Flow types can change resistance ´ Laminar ´ Turbulent 3 Laminar Flow ´ Flow is smooth and orderly | same direction ´ Particles move parallel to the tube walls ´ Flow is fastest in the center where there is less friction Know that poiseuilles law is related to laminar flow ´ Poiseuille’s Law Won’t be asked to calculate, but be familiar with it 4 2  6/20/24 Laminar Flow Laminar flow| fastest in middle, edges are slower. Generalized turbulent flow| particles are bouncing against each Localized Turbulent Flow other & going across. Laminar Flow + Turbulent Flow| Anytime there’s a difference in diameter, or a bend/curve or a different connection there will be parallel/laminar flow that turns into turbulent flow and then back to laminar flow [Seen in D, E, F]. 5 Turbulent Flow ´ Flow lines are not parallel ´ ”Eddies”: composed of particles moving across or opposite the general direction of flow ´ Flow rate is same across diameter of tube Two types of tubulent flow: know difference between generalized and localized ´ Generalized [B from slide 5] ´ When the flow of gas through a tube exceeds the critical flow rate ´ Localized[C,D,E, F in image from slide 5] ´ Gas flow rate below the critical flow rate but encounters constrictions, curves, or valves ´ To minimize resistance, gas-conducting pathways should have minimal length, maximal internal diameter, and be without sharp curves or sudden changes in diameter -Ideal to have something that is short and straight, no curves, and wide 6 3  6/20/24 Significance of Resistance If adding more things for the pt to ´ Resistance imposes a strain with ventilatory modes initiate breaths through: where the pt must do part or all of the work -ETT = small straw so its harder for them to breath. Increased ´ Changes in resistance parallel changes in the work of resistance. breathing -As resistance increases = work of breathing increases. -everything we add to the circle -as resistance decreases =decrease work of breathing. system is increasing resistance. ´ ETT probably causes more resistance than breathing system -Because its one of the most narrowest things in the system ´ How much is too much resistance ´ No common agreement ´ Watch flow-volume loops -adding more things to the circle system increases resistance -we try to minimize resistance to make it easier for pt to breathe 7 Turbulent flow Will give description on the exam: -know which one is turbulent, localized, and laminar. 8 4  6/20/24 Compliance ´ Ratio of change in volume to change in pressure -how easily something expands, contract ´ Measures distensibility (mL/cm H2O) ´ Most distensible components Of the circle/breathing system: ´ Breathing tubes[corrugated tubing] ´ Reservoir -Peds: 0.5L bags -Adults: 3L ´ Helps determine Vt Corrugated Tubing 9 Rebreathing Low Flow Anesthesia -minimizing the amount of flow thats going -can be rebreathing of ANY inhaled anesthetics. into the system, and pt is rebreathing majority -does not just pertain to CO2. of gases ´ To inhale previously inspired gases from which CO2 may or may not have been removed ´ Rebreathing is influenced by ´ Fresh gas flow[high flow vs low flow] ´ Dead space ´ Breathing system design [Semi open, semi closed, closed system,completely open] 10 5  6/20/24 Fresh Gas Flow ´ Amount of rebreathing varies inversely with the total FGF ´ If the volume of FGF supplied per minute is equal to or Minute Volume greater than the pt minute volume, NO REBREATHING -amount of gas inhaled or exhaled in one minute. occurs -number of breaths in a minute x Vt= minute volume -Example: ´ As long as exhaled gas is vented -12 BPM x 500= 6L/min [as long as its leaving the scavenging the system] -Normal minute volume = 4-6 L/min -A closed system, where everything stays in and nothing is vented out. ´ If the volume of FGF supplied per minute is less than Rebreathing: -Low flows of O2 or air/O2 mixture going through the system the pt minute volume, then REBREATHING occurs - and minute volume is 6L/min and flow is at 2L/min [extremely ´ Some of the exhaled gases must be rebreathed to make low]—> the pt will rebreathe whatever comes out to make up the tidal/minute volume. up required volume 11 Dead Space Apparatus ´ Apparatus – volume in a breathing system occupied -anything distal [machine] to the y-piece= apparatus deadspace by gases that are rebreathed without change in -ETT, Facemask -Distal = towards the pt composition -inspiratory and expiratory limb= not apparatus deadspace ´ Decreased by having inspiratory and expiratory limb separation as close to patient as possible ´ Physiologic – anatomical and alveolar dead spaces "T · ´ Anatomical- conducting airways; adds H2O vapor ´ Alveolar- volume of alveoli ventilated but not perfused Apparatus Inspiratory/ Deadspace expiratory limbs 12 6  6/20/24 Effects of Rebreathing What is the difference between nonrebreathing and ´ No rebreathing – inspired gas composition is identical to the fresh rebreathing: gas delivered by the anesthesia machine -rebreathing: the pt is rebreathing everything but also ´ Rebreathing – inspired gas composition is part fresh gas and getting fresh gas at the same time rebreathed gas -nonrebreathing: just getting fresh gas Rebreathing Causes ´ Rebreathing reduces heat and moisture loss from the pt -way to conserve heat and moisture in the pt ´ Altered inspired gas tensions [AKA partial pressures] Altered Gas Tension: Induction: when you are preoxygenating Does turning on SEVO increase the flow? the pt -NO ´ Reduction in the inspired oxygen tension/PP -can see whats going in and out [inspired vs expired O2] -Flow is determined by fresh gas flow. ´ Inhaled anesthetic agents: Watch to see whats going in is also going back out -rebreathing and nonbreathing can alter the tension in -Sevo will affect partial pressure inspired oxygen. ´ Induction -if we turn down flow or disconnect in the system How is partial pressure different from flow? ´ Emergence -will not be going back to the machine bc the partial -Flow is volume ´ Carbon dioxide:Rebreathing increases CO2 pressure is decreased. -Nitrous, air, oxygen contribute to the volume. -Ex: Alveolar DS increases —>PP of arterial CO2 increases -can have small leak but machine is not alarm bc it’s being lost -Decreased ETCO2 BUT increased PaCO2 b/c not being blown off to outside the system. -Volatile gas affects partial pressure. -if in hypermetabolic state PP of CO2 could increase, esp if rebreathing CO2 in the system. -Volatile gas [sevo, des, iso] needs something to catch on [carrier -will be delivering 100% oxygen but whats going back is gas] to so it can get to the patient. 60%. Know that you have a leak in the system. -these dont contribute to volume but only partial pressure. 13 Breathing Circuit 14 7  6/20/24 Desirable Characteristics of A Breathing Circuit 1. Low resistance to gas flow 2. Minimal rebreathing 3. Removal of CO2 at rate of production 4. Rapid changes in delivered gas when required -We want to see these changes immediately [if we turn down sevo, want to see within minutes that its decreasing] 5. Warmed humidification of inspired gas 6. Safe disposal of waste gases -The scrubbers/CO2 canisters —> scavenging system -eliminates gases to reduce rebreathing 15 Semi-Closed: -Circle system | Tubing | Valves | reservoir bag Classifications of Circuits - Partial rebreathing depends on fresh gas flow, spontaneous breathing, APL valve open/closed/semi-open, exhaustion of CO2 canister, and amount of FGF To decrease pressure in the system: When reservoir bag is squeezed [APL Valve Fully Open] -some pressure goes to the patient -Open to the atmosphere -some pressure going out via the scavenging system ´ Open -EX: nasal cannula, or open drop ether When APL is all the way open: Partial rebreathing vs complete rebreathing: ´ No reservoir bag and no rebreathing -should not have any extra pressure in the system other than whatever the intrinsic -partial rebreathing: has a way to escape -no valves, no tubing pressure the pt has if you have the mask intact. ´ Semi-open-high fresh gas flows [higher than minute ventilation] -ex: minute ventilation is 4 L/m and FGF is 6L/min = semi open When APL is closed: ´ Reservoir bag but no rebreathing -cannot breath for the pt when wide open. -when closed a little, we can breath for the pt bc now the pressure in the system is ´ Semi-closed-typically used all the time increased to help support breathing. -Gas has a way to escape ´ Reservoir bag and partial rebreathing Closed system: -Whatever is coming in is circulating, staying, and the patient is rebreathing it. ´ Closed -Example 1: Pt has minute ventilation of 4L/min and FGF is 2 L/min = rebreathing is occurring. ´ Reservoir bag and complete rebreathing -Example 2: PT has minute ventilation of 4L and FGF is 5L/min but CO2 canister is -Gas doesnt have a way to escape ´Depends on FGF exhausted = rebreathing is possible’ -FGF is equal or less than minute ventilation = REBREATHING -rebreathing of inspired and expired gasses -if the CO2 scavenging system is working, the pt is not rebreathing CO2. *Closed system is always low flow. Will not ask about high flow rates in a closed system. *complete rebreathing: amount of rebreathing is dependent on FGF 16 -really low FGF= a lot of rebreathing -FGF equals MV = little bit of rebreathing. 8  6/20/24 Components ´ A facemask, LMA, or ETT ´ A Y-piece with mask/tube connectors -elbow, accordion ´ Breathing tubing ´ Respiratory valves Accordion -thin disc valves ´ Reservoir bag ´ A fresh gas inflow site ´ A pop-off valve leading to scavenging -APL ´ Carbon dioxide absorption canister -Additional things that can be added: filters, humidifiers, PEEP valves, in-line oxygen analyzer. 17 Masks ´ Clear ´ Inflatable or inflated cuff ´ Pneumatic cushion that seals to face ´ Fits between the interpupillary line and in the groove between the mental process and the alveolar ridge ´ Prongs for attachment to rubber mask holder or head strap ´ Connect to the Y-piece or connector ´ 22 mm female connection 18 9  6/20/24 19 Connectors/Adapters ´ A fitting that joins together 2 or more components -ex: the elbow joins the humidifier to either the LMA, face mask, ETT ´ Benefits ´ Extends distance between patient and breathing system -Like when turning the HOB away from anesthesia and towards the surgeon ´ Change angle of connection ´ Allow more flexibility/less kinking ´ Disadvantages ´ Increased resistance ´ Increases dead space ´ Additional locations for disconnects 20 10  6/20/24 Connectors/Adaptors 21 Breathing Tubing ´ Large bore, corrugated, plastic, and expandable ´ 1 meter in length ´ Internal volume - 400-500 mL/m of length ´ Low resistance, somewhat distensible ´ Flow always turbulent due to corrugation -will not have LAMINAR flow ´ 2 may be connected Why are the inspiratory and expiratory not included in ´ Longer tubes don’t increase dead space deadspace? -bc of the unidirectional valves. ´ Dead space only from Y piece to patient d/t -As long as the unidirectional valves are opening and closing we unidirectional gas flow still have flow. ´ Pressure check circuits before use ´ 30 cm H2O -This is a calibration test. We do this as part of SAMTIDE to check for circuit leaks 22 11  6/20/24 1. If inspiratory valve is open, it’ll delivery gas through the Y-piece. 2. Bidirectional gas flow: this is where ETT for a dog there is mixing of inspirational and expirational gases. -This is part of DS, not gas exchange When inspiratory valve is open & delivering from the system: -the expiratory valve is closed [NEVER OPEN OR CLOSED AT THE SAME TIME] If inspiratory valve is stuck closed during inspiration 1. -dont have flow going forward. - in this case, the deadspace extends into the inspiratory limb b/c no flow moving through 2. the inspiratory valve. During expiration: - inspiratory valve is closed -so air is pushed forward into the open expiratory valve If expiratory valve is stuck closed during expiration: If asked where is deadspace -the expiratory limb now becomes on test click here deadspace [anything from the y-piece and distal] Inspiratory and expiratory limbs are NOT usually apart of DS, only become DS when valves DO NOT work 23 Unidirectional Valves ´ Direct respiratory gas flow in the correct direction ´ Disks with knife edges, rubber flaps, or sleeves ´ Low resistance and high competence -Meaning they move very easily without a lot of pressure ´ Must open widely w/ little pressure ´ Must close completely and rapidly w/ no backflow ´ Apparatus dead space 24 12  6/20/24 Unidirectional Valves ´ Inspiratory valve ´ Opens on inspiration, closes on exhalation ´ Prevents backflow of exhaled gas ´ Expiratory valve ´ Opens on exhalation and closes on inspiration ´ Prevents rebreathing 25 Unidirectional Valves ´ Proper valve placement and functioning prevents any part of the circle system from contributing to apparatus dead space ´ Apparatus dead space ´ Distal limb of the Y-connector ´ Tube/mask ´ Valves are located near CO2 absorber canister Not spontaneous breathing: casing, fresh gas inflow site, and the pop-off valve -APL valve is bypassed bc vent is turned on. -but can be anywhere in the inspiratory and expiratory limbs. 26 13  6/20/24 Unidirectional valves ´ Requirements ´ Arrows or directional words ´ Hydrophobic -Meaning it doesnt like water lol ´ Must open and close appropriately ´ Clear dome -should be able to see them ´ Must be placed between pt and reservoir bag 27 Unidirectional Valves 28 14  6/20/24 Breathing/Reservoir Bags Why do have reservoir bags? -when pt is breathing spontaneously this is the way we can add more pressure to help pt breath. -we can close the APL valve a little to increase the ´ Non-slippery rubber, plastic, or latex pressure. -when pressure is increased in the system, with ´ Ellipsoidal for 1 hand ventilation assist ventilation we can control the pressure going ´ 3L traditional for adults into the pt. ´ 0.5 - 6L Example 1: -Pt not breathing as deep. Can close the APL valve ´ Must have 22 mm female connector a little and giving extra pressure when squeezing on neck the bag. ´ Minimum pressure 30 cm H2O Example 2: -If we open the APL valve, and pt is breathing good ´ Max pressure 40 - 60 cm H2O (rubber rate with good tidal volume, the bag is still offering bags) some type of pressure but just not as much as with an APL valve ´ Plastic bags – 2x the distending pressure of rubber bags *can look at the mechanical gages to see how -So can get even larger than rubber bags much pressure. 29 Bag Function Reservoir: When flow is turned up: -reservoir bag fills up ´ Reservoir for anesthetic gases or O2 -if its not going to the pt, it’ll go to the bag. Or both ´ A means of manual ventilation ´ Assistance with spontaneous ventilation -Close the APL valve and give a squeeze ´ Visual/tactile monitor of ventilation ´ Estimation of volume of ventilation -if bag quivering pt breathing rapid shallow breaths -if bag completely deflates pt taking large breaths ´ Protection from excessive positive pressure -some of the positive pressure can also go into the bag and distend more instead of staying in the pts lungs 30 15  6/20/24 Gas Inflow Site ´ Fresh gas inlet ´ Gases are delivered from the common gas outlet to the circuit ´ Located near the inspiratory unidirectional valve or CO2 absorbent canister housing in circle systems ´ Preferred location – between CO2 absorbent and inspiratory valve -Makes sense if between CO2 absorbent and inspiratory valve, after expiration it gets scrubbed, fresh gas can pick up whatever volatile gas thats left, pick it up, travel towards the inspiratory limb, travel to the pt 31 Adjustable Pressure-Limiting Valve (APL) AKA: ´ Pop-off valve ´ Permits gas to leave the circuit -Open= gas can leave -Closed= gas can’t leave ´ Dome valve loaded by a spring and screw cap ´ User-adjustable ´ Controls pressure in breathing system ´ Tightened screw cap,= more gas pressure is required to open it ´ Releases gases to scavenging system 32 16  6/20/24 APL requirements ´ Clockwise motion, increases pressure ´ Opposite motion, decreases pressure ´ 1-2 clockwise turns from fully open to fully closed ´ An arrow must indicate direction to close valve This is the knob we see on the machine -The needle valve: allows vented gas to go through to the scavenging system. Think of this as inspiratory/ -Check Valve: still have a check value. Think of it expiratory disk as the inspiratory and expiratory disk which allows gas/flow to come from the breathing circuit. -depending on how open or closed, it goes through the scavenging system 33 APL Use -This is still talking about the APL but we aren’t manually opening or closing the valve. -During spontaneous inspiration, the APL valve is open. -When we inspire, the check valve gets closed shut. What the disk is doing [not the twisting & turning] -when we expire, the check valve gets pushed open Type of During Inspiration During Expiration which lets air to go to the scavenger system. Ventilation Spontaneous Closed Open Respiration Partially closed: CPAP Assisted/Manual Partially open Partially Open Ventilation Excess diverted ^gas Mechanical Bypassed Bypassed Ventilation what should you be doing with APL valve with ventilator on? -doesnt matter what APL valve is doing because its being bypassed 34 17  6/20/24 Absorber Canister ´ Canisters ´ Transparent sides ´ Single or 2 in a series (stacked) ´ Remove wrap before use -If wrap stays on it wont filter, will alarm high pressure ´ Absorbent ´ Housing - incorporates valves that closes when the canister is removed to prevent gas loss -Can change in the middle of case if needed ´ Side/center tube – returns the gas to the pt 35 Canisters -Were introduced in 1924, so around 100 years 36 18  ⭐ 6/20/24 Absorbent Chemical Reaction -Dont need to know the chemical equation, but know absorbent is a chemical reaction -Will have an exothermic -Sodium hydroxide, potassium hydroxide, calcium hydroxide, reaction that combines CO2 lithium hydroxide: interact with CO2 thats passing through to with/ calcium hydroxide to form form an exothermic reaction which leads to exhausting the calcium carbonate absorbent -when the exorbant turns into carbonates thats when we have the color change -White: normally -Purple: exhausted -newer absorbents have less than 2% sodium hydroxide or potassium hydroxide, or dont have it at all because it was causing interactions that were toxic 37 Absorbents ´ Soda lime ´ Calcium hydroxide (~80%) ´ Sodium hydroxide and potassium hydroxide (~5%) ´ Water (~15%) ´ Small amounts of silica and clay -To keep it from hardening and drying out ´ Exhausted when all hydroxides become carbonates ´ Can absorb 19% of its weight in CO2 ´ 100 g can absorb approximately 26 L CO2 38 19  6/20/24 Absorbents ´ Calcium hydroxide lime AKA Amsorb ´ Calcium hydroxide (70%) ´ Calcium chloride (0.7%) ´ Calcium sulfate (0.7%) ´ Polyvinylpyrrolidone (0.7%) ´ Water (14.5%) What are the problems with Na/K hydroxide? —> Doesn’t have Na hydroxide or K hydroxide because it causes : ´ Compound A :in the presence of SEVO. So the Na/K hyrodxide are removed **in mice ´ CO :in the presence of DES with K hydroxide ´ Destruction of inhaled gases 39 Types of Absorbents ´ Lithium hydroxide ´ Reacts with CO 2 to form carbonate ´ More CO 2 absorption capacity ´ Used in submarines and spacecrafts -doesnt interact with anesthetic agents - it doesnt have Na+ hydroxide and K hydroxide -very expensive -can cause burns to the skin, eyes, and lungs 40 20  6/20/24 Absorbents ´ Litholyme ´ Lithium chloride catalyst, no reaction with inhaled anesthetic agents ´ No activators/strong bases ´ Does not form compound A and CO ´ No regeneration ´ pH indicators do not become colorless| Does not revert back. -Regeneration: the soda lime has color change and then reverts back ´ Lower exothermic reactivity, reduced risk of fire, and reduced economic/environmental impact 41 Absorbents ´ Spira-Lith ´ Anhydrous LiOH powder within a nongranular partially hydrated polymer sheet ´ Larger surface area for reaction ´ No activators/strong bases -no K/Na hydroxide ´ Reduced temperature production ´ Longer duration of use ´ Cost-effective ´ No color indicator - dont know when it’s exhausted, so really have to monitor ETCO2, -baseline will increase on capnograph 42 21  6/20/24 Dont have to know this chart 43 Absorbent Indicators White —> ´ Ethyl violet is the most common dye ´ Ethyl orange,->cresyl yellow ´ Carbonate formation ´ pH becomes less alkaline ´ White to blue violet ´ Undergoes color change around pH of 10.3 ´ Fresh absorbent is colorless, pH > 10.3 ´ Exhausted absorbent is purple, pH < 10.3 ´ Bleaching -If exposed to bright fluorescent light can have bleaching/fading ´ Reliability ´ Regeneration ´ Color fading ´ Capnometry -Desiccation: Dried out absorbent -Left on flows which can dry out absorbent. -Absorbents have water in them which is used for the exothermic reaction. -Dried out can lead to compound A & heat formation in the canister. -cannot visualize it. 44 22  6/20/24 Mesh Size *refers to granular size ´ Maximize absorption and minimize resistance ´ 4 – 8 mesh size ´ Rough, irregular surface ´ Half volume of cannister is gas ´ Excess liquid water within canister, decreases surface area and efficiency of CO2 absorption -if granules get wet, they wont work anymore. 45 Channeling ´ Small passage ways allowing gas to flow through low- resistance areas ´ Decreases functional absorptive capacity ´ Minimized by ´ Circular baffles:Round circular tube that goes through the canister ´ Placement for vertical flow ´ Permanent mounting ´ Prepackaged cylinders ´ Avoiding overly tight packing 46 23  6/20/24 Channeling Channeling: E: Channeling -instead of gas funneling through evenly/uniformed and then gettting exhausted. -it creates a path of low resistant to be exhausted. Not uniform. 47 Absorbent and Anesthetic Agents Reactions ´ Compound A formation ´ Decomposition of sevoflurane Turns into this: ´ 2-fluoromethyl-2,2-difluoro-1-(trifluoromethyl) vinyl ether Na hydroxide ´ Dry absorbent [dessicated] ´ Carboxyhemoglobin levels -if COhb increasing > 35%, will see a dip in pulse Ox. But IR gas monitors dont pick up ´ Pulse ox or IR gas monitors COhb levels. ´ ’Monday, 1st case’ -CO-OXIMETRY PICKS UP CO. -Leaving flows up ´ Highest levels ´ Desflurane ≥ enflurane > isoflurane > halothane > sevoflurane ´ Increased temperatures ´ Increased concentrations of anesthetic gases ´ Low FGF rates ´ sStrong base absorbents Desflurance + dry absorbent + Na or K hydroxide = CO 49 Absorbent Heat Production ´ Exothermic reactions, leading to fires and explosions NA or K hydroxide ´ Desiccated strong base absorbents interact with sevoflurane ´ Baralyme, anhydrous LiOH ´ Absorbers exceed 200 degrees Celsius (392 degrees Fahrenheit) and higher w/ fire in some breathing circuits Causes: ´ Buildup of high temperatures, flammable degradation products (formaldehyde, methanol, and formic acid), and oxygen or nitrous rich gases w/in the absorber all provide basis for combustion ´ Avoid sevoflurane use with desiccated strong base absorbents 50 25  6/20/24 APSF Recommendations ´ ALL gas flows turned off after each case To prevent desiccation ´ Vaporizers turned off when not in use ´ Absorbent changed regularly ´ Change when color change indicates exhaustion ´ Change all absorbent ´ 2 canister system – change both, not 1 ´ Change absorbent when uncertain about the state of hydration ´ If using compact canisters, change more frequently -Referring to if you are filling canisters, so doesn’t really happen nowadays Stoped here [6/20] 51 -not used a lot in current practice. Mapleson Circuits -has no CO2 absorber. 52 26  6/20/24 Components Of Mapleson circuit ´ Reservoir bag -not all have this ´ Corrugated tubing -not all have this ´ APL valve ´ Fresh gas inlet ´ Patient connection 53 What is Missing? Of Mapleson circuit ´ CO2 absorber Missing unidirectional valves: -allows for a lot of mixing fresh gas flow, alveolar gas, ´ Unidirectional valves deadspace gas -depending on where the APL valve is the gas can be ´ Separate inspiratory and expiratory limbs vented out either on inspiration or expiration based on amount of FGF. -can be losing a lot of gasses breathing in or expiring last just depending on the set up. ´ Also called, carbon dioxide washout circuits or flow- controlled breathing systems Big overall: which ones are efficient in spontaneous vs controlled respiration? -wont see Mapleson A and B in practice. -not really asked on boards. -no clear separation between inspired and expired gasses so the FGF determines how much rebreathing can occur. -Gas gets vented to the APL or to the atmosphere. Best to see if ETCO2 is vented out appropriately: -monitor ETCO2 via sampling line or we wont know about rebreathing since we dont have the CO2 absorber. 54 27  6/20/24 Mapleson A (Magill’s system) FGF enters toward the reservoir bag —> then goes to point of least resistance: ´ FGF enters near reservoir bag -fills bag -corrugated tubing ´ Opposite of the pt -pop-off or APL valve -Patient ´ APL is near pt ´ Best efficiency of all systems for spontaneous FOCUS ON where the FGF is and where the APL is. -Which set up has APL valve near the patient. ventilation, worst during controlled ventilation ______________________________________________ -Which one is efficient or inefficient for spontaneous breathing vs controlled breathing. ´ To prevent rebreathing, FGF must be greater than or equal to minute volume to prevent rebreathing during spontaneous ventilation ´ Rebreathing during controlled ventilation occurs -this is why controlled ventilation is not good bc its wasteful. unless minute ventilation is very high, more than Need to crack up the FGF to 20L/min 20L/min -MV > 20L/min = no rebreathing -FGF 3-5x MV to have no rebreathing -MV < 20L/min = rebreathing 55 Spontaneous ventilation End-Expiration: -FGF is flowing. Mapleson A (Magill’s system) -A lot of the dead space gas and alveolar gas gets vented -Blue=FGF out to the pop off valve -Orange = DS -FGF has to be very high to help vent this off. -Red = Alveolar gas Inhalation: -Getting little bit of this mixture [deadspace + alveolar gas] and then will get some the FGF alveolar B deadspace gas is vented out Controlled Ventilation: End-Expiration -see less DS gas & a lot more alveolar gas. -this is at end-expiration. alveolagasy Fresh is vented Inspiration: out -to have flows up, need to be at 20L/min. This is wasteful bc as it’s it breaths being breathed out alot is vented out to the pop off valve. Alveolar gas. -as pt takes breath in, they are getting alvolar gas, little DS gas, but not too much of the FGF gas bc it gets vented out via the APL valve before it gets to the mask/pt. -higher flows = more pressure in the system -intrinsic pressure is created in the system. -Horrible for control ventilation -with high flow of 20L/min = a lot of pressure in the -Great for spontaneous ventilation system. So the easiest place for this pressure to go through -know where the FGF is relative to the APL valve. is the first valve or the APL valve [vented out to the -FGF is by the reservoir bag while the APL valve is right before the pt mask atmosphere] -this is wasteful! 56 28  6/20/24 Mapleson B ´ APL and FGF near pt ´ Reservoir bag at the end of the system -Bc FGF is right next to the APL, as soon as the pt breaths out & ´ Much of FGF is vented through APL during exhalation as soon as the FGF comes in, it flows through the APL valve, ´ Inefficient making this more inefficient. To work appropriately: ´ FGF should be 2x minute volume during spontaneous Which set up is obsecelete? and controlled ventilation to prevent rebreathing -Mapleson B ´ Obsolete 57 Mapleson B Fresh flow gas Alveolar vented gasisa L - -have a mixture of gas in the reservoir bag and have FGF coming in -DS, alveolar gas, and then have FGF that comes in. - Follows path of least resistance. -Path: -Since it nests the APL valve, alveolar gas and FGF is vented out toward the APL alve. -Pt still gets some FGF but not a lot = obscelete. 58 29  6/20/24 Mapleson C ´ Identical to Mapleson B except corrugated tubing omitted -looks like AMBU bag - based on the expiratory pause. ´ Almost as efficient as Mapleson A With spontaneous ventilation -depends on how long the pt is expiring and how long the pause is in between. ´ FGF 2x minute volume -if expiratory pause is longer than it becomes less efficient. -Want it to be minimal expiratory pause. ´ Used for emergency resuscitation -for spontaneous ventilation, this is intrinsic. 59 Mapleson C -FGF goes in. Not losing as much when it’s vented to the APL valve compared to Mapleson B. -It’s based on the expiratory pause [is its better or worse] 60 30  6/20/24 *will see most Mapleson A -has another set up called the LACK setup which has coaxial tube [wont be on the test] Mapleson D ´ 3 way T- piece: pt connection, fresh gas inlet, and - corrugated tubing ´ Reservoir at the end, APL near reservoir, and fresh gas inlet near pt ´ PEEP valves may be added Picture B: -to add some support/pressure -almost like inspiratory and expiratory limb. ´ Most efficient system for controlled ventilation ________________________________________________________ -Fresh gas inlet allows gas to flow in towards the pt ´ FGF 2 – 2.5x minute ventilation more so. -allows mixture of DS gas and alveolar gas towards ´ Bain modification the APL valve. ´ FGF coaxial inside tubing Picture A Picture B Bain Circuit Drawback -disconnection are not know it bc its inside the corrugated tubing -kinking of the inner hose 61 Mapleson D Spontaneous: Assisted ventilation : -APL valve is open. -Partially closed APL -FGF come in + alveolar gas [pt gets a both] -if we are increasing the pressure in the system [d/ -some alveolar gas gets vented out via pop off t partially closed APL] when we squeeze on valve. inspiration, the DS and alveolar gas can get -DS might or might not get vented out depending vented out via the pop off valve on FGF. -Depends on how much FGF goes to the -might stay in the reservoir bag & delivered reservoir bag. to the pt when squeezed -Since FGF is towards the the pt end, a lot will go towards the pt. 62 31  6/20/24 Mapleson E (Ayre’s T-Piece) ´ Corrugated tubing attached to the T-piece forms reservoir ´ No reservoir bag/No APL Used in spontaneously breathing pts to deliver O2 ´ _____________________________________________ -might see in peds rotation, for transport. -For transport: Mapleson E, or D but E mainly. -has decreased resistance in the system bc of no APL valve. -this is why it’s preferred in PEDS. Since we dont want any increased pressure in this population. 63 Mapleson E (Ayre’s T-Piece) Spontaneous: -limb is open to the atmosphere. -great for spontaneous breathing. Controlled: -can only do controlled by pinching of the end of the tubing. -will need to pinch, which allows FGF to inflate the lungs, then release the pinch to allow to expire the gases then repeat. -Closely watch pressures and for chest rise and fall to prevent increases in pressure. -no way to give extra help without timing it appropriately. Bc we cant read it and say how much pressure is being given. 64 32  6/20/24 Mapleson F (Jackson Rees) ´ Jackson-Rees modification (of Mapleson E) ´ Reservoir bag added -has a hole at the end of it. Has some assistant for breath. ´ 2 - 2.5x minute ventilation -FGF needs to be 2-2.5 x Vm ´ Excessive pressure less likely to develop ´ No APL valve -To increase pressure, pinch off the hole in the reservoir bag. -Use: Pt transport, preoxygenation. -Reservoir bag: -helps assist with monitoring of respiration -can give breaths -can pinch of the hole to increase pressure on the breath. 65 Mapleson F (Jackson Rees) -DS gas still goes to the reservoir bag and then goes to the atmosphere via the hole -PT is getting mostly alveolar gas and FGF. 66 33  6/20/24 Mapleson Efficiency Know where the APL valve is & where the FGF is. ´ Improved rebreathing efficiency is d/t location of the pop-off valve relative to FGF ´ BC systems – significant amounts of fresh gas is vented through pop-off at end expiration ´ DEF systems FGF drives exhaled alveolar gas away from pt Best spontaneous ventilation: ´ Spontaneous ventilation -A Worst spontaneous ventilation: ´ Mapleson A is greater than Maplesons DFE, which are -C,B greater than Maplesons CB Best at controlled ventilation: ´ Controlled ventilation D,F,E ´ Maplesons DFE are greater than Maplesons BC, which are greater than Mapleson A Worse at controlled ventilation: -A 67 Advantages of Maplesons ´ Simple, inexpensive, and lightweight ´ Changes in FGF composition result in rapid changes in the circuit -increase and decrease = will see changes very rapidly. ´ Low resistance to gas flow -corrugated tubing is wide. Increased resistance on the outer edges [turbulent] ´ No toxic products d/t lack of CO2 absorbent -dont have to worry about compund A, CO bc we dont have the absorbent ´ No degradation w/ VAs 68 34  6/20/24 Mapleson D Disadvantages of Maplesons ´ Require high FGF ´ Conservation of heat and humidity less efficient -Also r/t to the CO2 absorbent where humidification & heat can be conserved. ´ Scavenging challenging -when APL valve is closer to the pt end, scavenging is challenging bc it’s more wasteful bc a lot of the ´ Except Mapleson D gas is vented out. ´ Not suitable for patients with MH ´ May not be possible to increase FGF to remove excess CO 2 -MH: ETCO2 climb 69 Ventilator off or bypassed: Spontaneous inspiration The Circle System -APL valve open Inspiration: -reservoir bag goes in. Whatever mixture is the bag [Alveolar gas, SEVO, DES] travels: ´ Spontaneous inspiration -bypasses pressure gauge -CO2 absorber ´ Allows circular, unidirectional flow -Inspiratory valve -picking up some FGF -valve is open -Pt lungs -lungs expand -Gas sampling port -on exhalation, this will give the ETCO2 readout. 70 35  6/20/24 The Circle System FGF inflow cannot be here -if expiratory valve is closed, ´ Spontaneous expiration the flow has no where to go and it’ll go into the pts lung. Spontaneous Ventilation: Exhalation -expiratory valve open, inspiratory valve is closed [no flow - here now] -gas follows path of least resistance so it goes to the expiratory valve. -FGF makes a U-turn/goes backwards since the inspiratory valve is closed and FGF goes to the CO2 absorber -Exhaled breath from the patient goes to the expiratory valve then expiratory sensors. -Exhaled breath meets up with FGF [thats leaving from CO2 absorber] 7 -Reservoir Bag -On exhalation, if bag expands too much & pressure increases too much then some will go out to be vented via APL valve cannot be here the APL valve. -bc during inspiration gas M -Needs to be located here so it can would some gas would just be reverse the flow during expiration. vented out and some to the -allows bag to have flow to be filled pt. up. 71 Circle System Function ´ Extent of rebreathing and conservation of exhaled gases, depends on FGF ´ Higher FGF = less rebreathing and greater waste gas -we dont need high flows in circle systems [depending on the type] ´ Rules to prevent rebreathing ´ Unidirectional valve must be located between the pt and the reservoir bag on both the inspiratory and expiratory limbs ´ The fresh gas inflow cannot enter the circuit between the expiratory valve and the pt ´ APL valve cannot be located between the pt and the inspiratory valve 72 36  6/20/24 Circle System Function Semi-closed ´ Contemporary systems ´ Partial rebreathing occurs but some waste flow is vented through APL or waste gas valve of ventilator ´ Ex: low-flow anesthesia *what we typically do ´ FGF is less than minute ventilation ´ 50% of expired gas is rebreathed after CO 2 removal -to make up the minute volume, part of the gas has to be rebreathed. 73 Circle System Function Semi-open ´ Non-rebreathing systems ´ Higher FGF with minimal rebreathing and more venting of waste gas ´ Ex: post-op and ICU vents, scuba gear 74 37  6/20/24 Circle System Function Closed **dont really do this anymore ´ Rate of oxygen inflow exactly matches metabolic demand ´ Rebreathing is complete -what was going into the system, pt was rebreathing ´ No waste gas is vented ´ VAs are added to circuit in liquid form in precise amounts or through the vaporizer ´ Ex: Low- and minimal-flow anesthesia ´ Impractical for use – rarely done Low flow rebreathing is complete & no -bc we can now use semi-closed and still use low flow with partial rebreathing with CO2 absorbed. waste gas is vented out. -rate of oxygen inflow is going to match the metabolic demand for the patient. 75 Advantages/Disadvantages of Low-Flow Anesthesia Advantages Disadvantages ´ Decreased use of VAs ´ Difficulty in rapidly -dont need to over pressurize adjusting anesthetic ´ Improved temperature Improved humidity/temp depth -inspiration: any flow is not humidified. and humidity control -Expiration has water vapor. ´ Possibility of ´ Reduced accumulating environmental pollution unwanted exhaled gases ( ex: CO, acetone, methane) -acetone and methane are byproduct of VA when in contact with certain drugs. ´ VA degradation by- -Not really seen in practice. products (ex: CO, compound A) 76 38  6/20/24 Advantages/Disadvantages of Circle System Advantages Disadvantages ´ Low FGF can be used ´ Complex design ´ Elimination of CO2 ´ CO or compound A -not common d/t changes in absorbent ´ Relatively stable ´ May compromise Vt inspired gas during controlled concentration ventilation -lost in corrugated tubing. Does not happen alot. ´ Conservation of ´ ASA Closed Claims moisture/heat/gases Project #1. ´ Prevention of OR ´ Misconnections/ pollution disconnections -gas isn’t just out to the -ETT not secured tight. atmosphere. -disconnection at Y-piece. -some is still vented via -inspiratory/expiratory limb not on tight. scavenging system -WALK BACK YOUR CONNECTIONS 77 Self-Inflating Manual Resuscitators [AMBU Bag] POST) ´ Components BE. ´ Self-expanding Bag ´ T-shaped non-rebreathing Valve ´ Bag Inlet Valve ´ Pop-off valve ´ Excess oxygen venting valve ´ Oxygen reservoir 78 39  6/20/24 -has extra oxygen which can be delivered to pt Expiratory port Ventilates to atmosphere 79 Self-Inflating Manual Resuscitators ´ Uses ´ Hand ventilation in the absence of an oxygen or air source ´ Pt transport ´ CPR ´ Emergency back-up -ALWAYS have one in set up. 80 40  6/20/24 Self-Inflating Manual Resuscitators ´ Hazards ´ Barotrauma or gastric insufflation -gastric insufflation is very common d/t incorrect head position. ´ Significant variation of tidal volume, PIP, and PEEP -hard to get consistent Vt. ´ Nonrebreathing valves generate resistance -when pt has ROSV, it’ll be hard to breath against a non rebreathing valve. 81 Bacterial Filters ´ Routine use to prevent contamination or infection by airborne diseases ´ M. Tuberculosis ´ COVID ´ PUI [person under investigation] ´ Effective preventing contamination anesthesia machine from airborne diseases ´ Placed on expiratory limb 82 41  6/20/24 Bacterial Filters Cont 2 different types ´ Small-pore compact matrix ´ High airflow resistance [as air goes through it, it’ll increase the resistance] ´ Pleated to create a larger surface area -To pick up more of the pathogen. ´ A less dense, larger pore size arrangement ´ Less resistance ´ Smaller surface area ´ Permanent electrical polarity -designed to enhance Vander Val forces that hold organism within the matrix. 83 Bacterial Filters Cont ´ Hydrophobic Filters ´ Prevents water penetration ´ Increased resistance ´ Decreased efficiency ´ Combination (filter + HME) ´ Placed at the Y-piece ´ Inspiratory and expiratory barrier -if any of the filters get wet from excess expiration or whatever [sputum, blood, vomit], can get accumulation of condensation in circuit—> increases resistance -can get condensation in sampling line too. - air or oxygen doesnt travel well through a wet surface. -Tx: just dump it out, get a new defen [housing unit that catches the condensation as it’s being sampled out. -dont need to a new circle system. 84 42  6/20/24 Bacterial Filters ´ Complications Nebulized aerosols: -can be attached to the circle system or can ´ Obstruction get aerosol +20-30 ml syring and give squirts ´ Sputum, edema fluid, nebulized aerosols, or malpositioning ´ Leakage ´ Housing of a gas line filter 85 Anesthesia Patient Safety Foundation: 86 43