Breathing System

Anesthesia CircuitsProf. Amir B.ChannaFFARCS, DA (Eng)King Khalid Univ.Hospital.Riyadh KSA.

Anesthesia Circuits Link machine to patient and supply anesthetic gases and volatile anesthetics Eliminate carbon dioxide Mapleson classification Many circuits in use Modified Mapleson still in use Know the current applications of modified Mapleson circuits

The basic functions of any breathing systems are to 1. maintain the delivery of oxygen and /or anesthetic gases (vapours) to the patient 2. remove CO2 excreted in alveolar gas

An Ideal Breathing System Be reliable, easy to use, fail safe Possess safety features to prevent patient morbidity (e.g pressure limitation, no cross infection, etc.) Impose no additional inspiratory or expiratory resistance or compliance that adversely effects breathing Provide an adequate peak inspiratory flow during spontaneous ventilation ( normally about 30 L/min but on ocassionsupto 60L / min, usually from a reserve volume of fresh gas)

An Ideal Breathing System contd. Impose no additional anatomical dead space in the form of apparatus dead space, this is the volume within the system that may contain exhaled alveolar gas, which will be rebreathed at the beginning of the subsequent inspiration Be adoptable for various sizes and types of patients and can be used for both SPONT. & CONTROLLED VENTILATION. Minimize wastage of gases and permit satisfactory scavenging during spontaneous and controlled ventilation Maintain temp. & humidity Permit easy use of monitoring

Breathing systems can be broadly subdivided into the following: Group 1; those that possess no reservior bag and no valve Group 2; those that have a single reservior bag and a single adjustable spill valve Group 3; those that in addition have 1 or more valves that control the direction of gas flow. This group can be further categorized into those with and those without CO2 abosorbers

Four Basic Circuits Open Semi-open Semi-closed Closed

Open Systems Insufflation blow anesthetic gas over face no direct contact no rebreathing of gases ventilation cannot be controlled unknown amount delivered

Open Systems Open drop anesthesia gauze covered wire mask(schimalbusch mask) anesthesia dripped inhaled air passes through gauze & picks up anesthetic

Open Systems (Cont’d) Open drop anesthesia (cont’d) concentration varies re-breathing may occur environmental pollution

Semi-open Systems Breathing system which entrains room air Self inflating resuscitator system

Semi-closed System Gas enters from machine part leaves via scavenger Circle system Bain system

Closed System Only enough gas enters to meet metabolic needs Scavenger is closed Closed circle system To-and-fro system

Types of Circuits Basic circle system Mapleson Classification

Closed System Anesthesia Technique not commonly used APL is closed and only enough O2 is added to meet metabolic needs Anesthetic added based on square root of time Conserves anesthetic gas an eliminates pollution

Disadvantage of MC MC required high FGF prevent rebreathing waste of ane.agent air pollution loss of pt.’heat & humidity

Mapleson Systems Factors influence carbon dioxide rebreathing the fresh gas inflow rate the minute ventilation the mode of ventilation (spontaneous or controlled), the tidal volume the respiratory rate the inspiratory to expiratory ratio the duration of the expiratory pause the peak inspiratory flow rate the volume of the reservoir tube the volume of the breathing bag ventilation by mask ventilation through an endotracheal tube the carbon dioxide sampling site.

Mapleson Systems Prevention of rebreathing, during spontaneous ventilation: A > DFE > CB. During controlled ventilation, DFE > BC > A A, B, and C systems are rarely used today

The Bain circuit a modification of the Mapleson D system spontaneous and controlled ventilation.

The Bain circuit Exhaled gases in the outer reservoir tubing add warmth to inspired fresh gases unrecognized disconnection or kinking of the inner fresh gas hose The fresh gas inflow rate necessary to prevent rebreathing is 2.5 times the minute ventilation

Modifictaion of ayres by Jackson-Rees'

Circle System Allows rebreathing of anesthetic gases lower FGF rates Less pollution Requires CO2 absorption Conserves heat and humidity

Advantages of Circle System Highly efficient Minimal dead space Conserves heat and moisture Minimal pollution Disadvantage - many places to leak

Components of the Circle System Fresh gas source Unidirectional valves Inspiratory & expiratory tubing Y-piece connector

Circle System Components APL valve Reservoir bag CO2 absorber

The Circle system Consists of Seven Components 1. Fresh gas inflow source 2. Inspiratory and expiratory unidirectional valve 3. Inspiratory and expiratory corrugated tubes 4. A Y-piece connector 5. Overflow or pop-off valve, referred to as the APL valve 6. A reservoir bag 7. A canister containing a carbon dioxide absorbent

Components of the Circle system APL, adjustable pressure limiting; B, reservoir bag; V, ventilator

Adv/DisAdv of the circle system

Definition of low-flow The suggestion of Simionescu as: Metabolic flow = 250ml/min Minimal flow = 250-500 ml/min Low flow = 500-1000 ml/min Medium flow = 1-2 L/min High flow = 2-4 L/min Super-high flow = >4 L/min

Adv/DisAdv for waters canister

CO2 Absorption Soda lime 94% calcium hydroxide 5% sodium hydroxide 1% potassium hydroxide silica to harden granules ethyl violet as an indicator

CO2 Absorption Baralime 80% calcium hydroxide 20% barium hydroxide ethyl violet as an indicator

CO2 Absorption pH is extremely high Granule size 4 to 8 mesh Water is required for chemical reactions to occur

Circle Breathing Systsemiopenem A circle system can be, semiclosed, or closed, depending on the amount of fresh gas inflow Semiopen system has no rebreathing and requires a very high flow of fresh gas Semiclosed system is associated with rebreathing of gases Closed system is one in which the inflow gas exactly matches that being consumed by the patient

Circle Breathing System Components of The circle system (1) a fresh gas inflow source (2) inspiratory and expiratory unidirectional valves (3) inspiratory and expiratory corrugated tubes (4) a Y-piece connector (5) an overflow or pop-off valve, referred to as the APL valve (6) a reservoir bag (7) a canister containing a carbon dioxide absorbent

Circle Breathing System Rules to prevent rebreathing of carbon dioxide in a traditional circle system Unidirectional valves must be located between the patient and the reservoir bag on the inspiratory and expiratory limbs of the circuit. The fresh gas inflow cannot enter the circuit between the expiratory valve and the patient. The overflow (pop-off) valve cannot be located between the patient and the inspiratory valve.

Circle Breathing System Advantages stability of inspired gas concentrations, conservation of respiratory moisture and heat, prevention of operating room pollution Disadvantage complex design

ABSORPTION Lack of toxicity with common anesthetics, low resistance to airflow, low cost, ease of handling, and efficiency 3 formulations soda lime Baralyme calcium hydroxide lime (Amsorb)

ABSORPTION Soda lime (most commonly used ) 80% calcium hydroxide, 15% water, 4% sodium hydroxide, and 1% potassium hydroxide (an activator) silica The equations 1) CO2 + H2 O ⇔ H2 CO3 2) H2 CO3 + 2NaOH (KOH) ⇔ Na2 CO3 (K2 CO3 ) + 2H2 O + Heat 3) Na2 CO3 (K2 CO3 ) + Ca(OH)2 ⇔ CaCO3 + 2NaOH (KOH)

ABSORPTION Baralyme 20% barium hydroxide and 80% calcium hydroxide Calcium hydroxide lime lack of sodium and potassium hydroxides carbon monoxide and the nephrotoxic substance known as compound A

ABSORPTION Absorptive Capacity soda lime is 26 L of carbon dioxide per 100 g of absorbent calcium hydroxide lime has been reported at 10.2 L per 100 g of absorbent size of the absorptive granules surface area air flow resistance

ABSORPTION Indicators Ethyl violet :pH indicator added to soda lime and Baralyme from colorless to violet when the pH of the absorbent decreases as a result of carbon dioxide absorption Fluorescent lights can deactivate the dye

ABSORPTION Sevoflurane interaction with carbon dioxide absorbents Compound A fluoromethyl-2,2-difluoro-1-(trifluoromethyl)vinyl ether Factors low-flow or closed-circuit concentrations of sevoflurane higher absorbent temperatures fresh absorbent Baralyme dehydration increases the concentration of compound A, and soda lime dehydration decreases the concentration of compound A

ABSORPTION Desiccated soda lime and Baralyme carbon monoxide after disuse of an absorber for at least 2 days, especially over a weekend

ABSORPTION Several factors appear to increase the production of CO and carboxyhemoglobin: Anesthetic agents (desflurane ≥ enflurane > isoflurane ≥ halothane = sevoflurane) The absorbent dryness (completely dry absorbent produces more carbon monoxide than hydrated absorbent) The type of absorbent (at a given water content, Baralyme produces more carbon monoxide than does soda lime)

ABSORPTION Several factors appear to increase the production of CO and carboxyhemoglobin: The temperature (a higher temperature increases carbon monoxide production) The anesthetic concentration (more carbon monoxide is produced from higher anesthetic concentrations) Low fresh gas flow rates Reduced animal size per 100 g of absorbent

ABSORPTION Interventions have been suggested to reduce the incidence of carbon monoxide exposure Educating anesthesia personnel regarding the cause of carbon monoxide production Turning off the anesthesia machine at the conclusion of the last case of the day to eliminate fresh gas flow, which dries the absorbent Changing carbon dioxide absorbent if fresh gas was found flowing during the morning machine check

ABSORPTION Interventions have been suggested to reduce the incidence of carbon monoxide exposure Rehydrating desiccated absorbent by adding water to the absorbent Changing the chemical composition of soda lime (e.g., Dragersorb 800 plus, Sofnolime, Spherasorb) to reduce or eliminate potassium hydroxide Using absorbent materials such as calcium hydroxide lime that are free of sodium and potassium hydroxides

CO2 Absorber Incompatibility Trichlorethylene dichloroacetylene neurotoxin Phosgene pulmonary irritant Sevoflurane degrades in absorber

The Scavenger System Releases excess pressure from the system Prevents operating room pollution Gases leave through APL May put too much negative pressure on the system

SCAVENGING SYSTEMS The collection and the subsequent removal of vented gases from the operating room Components (1) the gas-collecting assembly (2) the transfer means (3) the scavenging interface (4) the gas-disposal assembly tubing (5) an active or passive gas-disposal assembly

With air or O2 +N2O a National Institute for Occupational Safety and Health.

Fluoride Nephrotoxicty F- is nephrotoxic F- is a byproduct of metabolism in liver and kidney Fluoride nephrotoxicity [F-] = 50 mol/l F- opposes ADH leading to polyuria methoxyflurane 2.5 MAC-hours (no longer used) enflurane 9.6 MAC-hours Methoxy > enfl > sevo >>> iso >des Results in potentially permanent renal injury Less of a problem with modern anesthetics

Toxins – Sevoflurane and Compound A Sevoflurane reacts with soda lime used in anesthetic circuit to form “compound A” fluoromethyl-2-2-difluoro-1-(trifluoromethyl) vinyl ether Some reports of fires and explosions Compound A is renal toxin Large amounts are produced at low gas flow rates Recommended 2 L / min flow rate Little evidence of harm unless Low flows Long exposure Some evidence for changes in markers of damage but not clinically significant

Anesthetics and CO All anesthetic agents react with soda lime to produce CO CO is toxic and binds to Hgb in preference to oxygen Des > enfl >>> iso > sevo >halo Risk Factors Dryness of soda lime Temperature of soda lime Fi(agent) Barylime produces more than soda lime Barylime removed from market In general, not clinically significant No deaths reported Do you want your anesthetic first Monday morning?

Toxicities – Nitrous Oxide Hematologic: N2O antagonizes B12 metabolism inhibition of methionine-synthetase Decreased DNA production RBC production depressed post a 2 h N2O exposure ca. 12 later Leukocyte production depressed if > 12 h exposure Megoloblastic anemia Marked depression if exposure longer than 24 hours

Toxicities – Nitrous Oxide Neurologic Long term exposure to N2O (vets, dentists and assistants) is hypothesized to result in neurologic disease similar to B12 deficiency Evidence only shows an association Increased risk of spontaneous abortion in dental/vetrinarian and OR personel (RR 1.3) Teratogenic in rats (prolonged exposure of weeks)

Other Toxicity Issues Reproduction Increased miscarriage rate in pregnant patients given GA Related to underlying medical condition responsible for need for surgery Low birth rate Getting and staying pregnant (veterinary and dental workers less for OR personnel) Teratogenicity No evidence that the halogenated agents N2O is suspect risk but not proven in human studies Carcinogenicity OR, dental and vet personnel have increased rates of cancer (1.3-1.9 increase in rate in dental workers) But studies have been negative for AA as cause

Components of a scavenging system. APL valve, adjustable pressure limiting valve

Each of the two open scavenging interfaces requires an active disposal system. An open canister provides reservoir capacity. Gas enters the system at the top of the canister and travels through a narrow inner tube to the canister base. Gases are stored in the reservoir between breaths. Relief of positive and negative pressure is provided by holes in the top of the canister. A and B, The open interface shown in A differs somewhat from the one shown in B. The operator can regulate the vacuum by adjusting the vacuum control valve shown in B. APL, adjustable pressure limiting valve

Closed scavenging interfaces. Interface used with a passive disposal system (left). Interface used with an active system (right)

Wall terminal Unit compared with pipeline of air supply

Diagrammatic representation of a passive scavenging system

Allergic Side Effects of Anaesthetic gases & Vapours Increased incidence of spontaneous abortion Vitamin B12 inactivation by nitrous oxide with neurological sequelae Increased incidence of female births Reduce fertility in females exposed to nitrous oxide Increased incidence of minor congenital abnormalities Increased incidence of leukaemia and lymphoma in exposed females

Expressed, vol/vol, imp.p.m., i.e. 100% of a single gas is 1 000 000 p.p.m. NB: 1% of a single gas = 1 0, 000 p.p.m. Remember Daltons Law of Partial Pressures

Causes & Control Of Pollution The frequency with which gases and vapours are used The anaesthetic technique ( insufflation, gas induction, closed circuit, total intravenous, regional blockade, etc.) Good working practices (minimal spillage, switching gases off immediately after use, no excess flows, etc. ) Leakage from anaesthetic equipment and joints

Causes & Control Of Pollution contd. Efficiency of the air conditioning system (15 changes per hour is regarded as the minimum for good practice), and the area in which it is installed; it is often not placed in such places as obstetric and delivery rooms The size and layout of the anaesthetic room, operating room, or recovery room The effectiveness of the scavenging system

The principle sources of pollution by anesthetic gases and vapours include: Discharge of anesthetic gases from ventilators Expired gas vented from the spill valve of anesthetic breathing systems Leaks from equipment, e.g. from an ill-fitting face mask Gas exhaled by the patient after anesthesia. This may occur in the operating theatre, corridors and recovery room Spillage during filling the vaporizer Thus; reduce use of anesthetic gases and vapors Maintain air conditioning Take care in filling vaporizers

Active system-home built interface

Easy Fil™ No Spill Press toovercomespring Auto Fill ? No

Which is filling as we watch? Desflurane Tec6 Semi-Automatic Fill (no patent pending)

VaporizersLow resistance vaporizers

Vaporizers should be arranged in the order

The Tec 6 Desflurane Vaporizer

A gas-specific pin-index system

Gas-specific connectors are used on large (G and H) cylinders

Conventional manual breathing circuit.

Conventional mechanical ventilation. (Representing Dräger Narkomed AV2+)

ANESTHETIC CIRCUITS Deliver oxygen and anesthetic gases to the patient Eliminate carbon dioxide adequate inflow of fresh gas carbon dioxide absorbent Semiclosed rebreathing circuits and the circle system.

Inspiratory (A) and expiratory (B) phases of gas flow in a traditional circle system with an ascending bellows anesthesia ventilator. The bellows physically separates the driving-gas circuit from the patient's gas circuit. The driving-gas circuit is located outside the bellows, and the patient's gas circuit is inside the bellows. During the inspiratory phase (A), the driving gas enters the bellows chamber, causing the pressure within it to increase. This causes the ventilator's relief valve to close, preventing anesthetic gas from escaping into the scavenging system, and the bellows to compress, delivering the anesthetic gas within the bellows to the patient's lungs. During the expiratory phase (B), the driving gas exits the bellows chamber. The pressure within the bellows chamber and the pilot line declines to zero, causing the mushroom portion of the ventilator's relief valve to open. Gas exhaled by the patient fills the bellows before any scavenging occurs because a weighted ball is incorporated into the base of the ventilator's relief valve. Scavenging happens only during the expiratory phase, because the ventilator's relief valve is open only during expiration

Inspiratory (A) and expiratory (B) phases of gas flow in a Dräger-type circle system with a piston ventilator and fresh gas decoupling. NPR valve, negative-pressure relief valve.

Open System No reservoir No rebreathing

Semi-open System Has reservoir No rebreathing

Semi-closed System Has reservoir partial rebreathing

Closed System Has reservoir Complete rebreathing

Mapleson Breathing Circuits Early pioneers developed their own delivery systems Mapleson classified types of breathing devices

Mapleson Breathing Circuits(Cont’d) Mapleson circuits fall into which type of system? See Morgan p. 26, Table 3-1

Mapleson A FGI near bag Breathing tubing Expiratory valve near mask Volume of breathing tube should be as great as the tidal volume

Mapleson A Spontaneous ventilation High FGF flushes tubing between breaths

Mapleson A (Cont’d) Using “pop-off” enables controlled ventilation but also causes CO2 rebreathing Current use?

Mapleson B Similar to A with FGI near expiratory valve System fills with FGF inhaled by patient

Mapleson B (Cont’d) Exhaled gas forced out through expiratory valve Current use?

Mapleson C Similar to Mapleson B Shorter breathing tubing less dead space Current use?

Mapleson D Long breathing tube FGI near mask Exhalation valve at distal end of breathing tubing Current use?

Bain Breathing Circuit Modified Mapleson D Tube within a tube FGF tube within larger tube Mounts on anesthesia machine APL valve Connects to scavenger

Bain System Advantages compact, easy to handle warming of inspired gases partial rebreathing improves humidification APL controls system pressure ability of scavenging

Bain System Flow Rates Spontaneous ventilation 200-300 ml/kg/min Controlled ventilation infants <10kg 2 l/m 10 - 50 kg 3.5 l/m > 60 kg 70 ml/kg/min

Bain System Depends on fresh gas flow to flush out CO2 Spontaneous ventilation 200 - 300 ml / kg / min Controlled ventilation 70 ml / kg / min

Mapleson E Exhalation tube is reservoir no bag FGI near mask Current use?

Mapleson F FGI near mask Breathing tubing/bag Expiratory valve at end of bag Current use?

Nitrous oxide and oxygen proportioning flowmeters

Oxygen released by the quick-flush valve should not pass through the vaporizer

Anesthesia machine breathing circuit

Circuits (Breathering Systems) ,[object Object]

Waters to and fro system ,[object Object]

Spontaneous Ventilation Controlled Ventilation

Breathing System

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