Breathing Circuits – Flashcards
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Breathing Circuits
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Environment created by anesthetist Fresh gas flow from common gas outlet Inspiratory side goes to patient Expiratory side returns exhaled gases Several different breathing circuits
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Anesthesia Machine Designed to Prevent
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Hypoxia (O2 pressure, N2O 3:1) Hypercarbia (absorber) Barotrauma (regulators, O2 flush) Foreign matter to airway (filters, check valve) Anesthetic overdose Vaporizer (baffles, interlock) Machine built for optimizing ventilation Know what is normal for patient Deliver the safest ventilation
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Fresh gas flow or inspired mixture
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The gases from the flowmeters The anesthetic agent from the vaporizer Should be dry relatively clean mixture
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Dead space
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Anatomic due to conducting airways Physiologic due to mismatch in V/Q Mechanical due to breathing circuit
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Alveolar gas or exhaled mixture
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Oxygen left over after metabolism Nitrous oxide not taken up by body Air mixture left over Any contaminants not taken up by body (carbon monoxide, ex.) Agent not taken up by body What is added from the alveoli Carbon dioxide Water vapor Gases from the body (methane, acetone, N2)
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Breathing Circuit and Rebreathing
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Should not allow rebreathing of CO2 Should allow rebreathing of Oxygen not metabolized Nitrous oxide or air Anesthetic agent Design revolves around delivering what is physiologic & 'normal' for patient
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Functions of Breathing
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Gas exchange Cellular respiration aerobic metabolism anaerobic metabolism effects of anesthesia on cell metabolism
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Control of breathing
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central respiratory center peripheral chemoreceptors lung receptors (beta2) effects of anesthesia
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Chemical Regulation of Respiration
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Maintains proper levels of O2 & CO2 Located in brain stem Medulla oblongata Pons
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Voluntary Control of Breathing
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Cerebral cortex controls Abolished once patient deeply sedated or anesthetized past Stage II Compare eye reflexes to laryngeal reflexes If you rub eyelash and no response, through stage II and should have weakened laryngeal reflexes, can give NMBA now.
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Effects of Anesthesia on Breathing
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Inhalation agents lower tidal volumes/increase resp. rate Narcotics lower respiratory rates/increase tidal volume Deep sedation can lead to apnea Muscle relaxation leads to apnea "High" spinal or epidural paralyzes diaphragm & intercostals and lead to apnea
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Limbic System Stimulation
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Anticipation of activity Emotional anxiety Increases rate and depth of ventilation
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Temperature
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Increased temperature increases respiratory rate Decreased temperature decreases respiratory rate Controlled ventilation recommended for febrile patient Controlled ventilation recommended for cold patient
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Pain
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Sudden severe pain causes apnea Prolonged somatic pain increases respiratory rate ( like with contractions in labor) Visceral pain decreases respiratory rate (like with deep abdominal pain) Listen and react to respiratory clues about depth
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Stretching the Anal Sphincter
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Stimulates respiration Consider intubating these cases Frequent episode laryngospasm Watch the surgeon and have patient deep
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Airway Irritation
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Mechanical irritation Airways, LMA's, larynoscopes, ETT's Chemical irritation Inhalation agents (SEVO LEAST) Take patient through Stage II gently or IV induction
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Blood Pressure
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Sudden rise in blood pressure decreases respiration Sudden drop in blood pressure increases respiration Small effect you may not appreciate unless patient breathing spontaneously
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Responses to O2, CO2 & pH
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Since responses impaired, anesthetist must take over ventilation low ph/high co2 = increase rr high ph/low co2 = decrease rr high o2 = decrease o2 flow
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Pressure Changes in Respiration
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Alveolar pressure changes 758 - 762 mmHg Pleural cavity pressure always subatmospheric Normally no communication with 760 mmHg Pneumothorax caused from trauma from outside or from inside alveolar from ventilation Diaphragm Skeletal muscle Innervated from phrenic nerve C 3-4-5
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Minimum Oxygen Requirements
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Diffusing capacity for hemoglobin Volume of a gas that diffused through membrane each minute for a pressure difference of 1 mmHg Normally 21 ml/min/mmHg (O2 into hgb) Mean oxygen pressure difference = 11 mmHg (b/w alveoli and hgb) 21 ml/min/mmHg x 11 mmHg = 230 ml/min (Min. O2 requirements) Explains why we breathe such low TV
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Tidal Volume
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500ml or 7ml/kg IBW 70% of TV reaches alveoli 30% does not-anatomic dead space Respiratory rate = 12 breaths per minute
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After exhaling considerable amt of gas in lung
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Forceful exhalation = expiratory reserve volume Residual volume left over
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Functional residual capacity
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ERV 1,200 + RV 1,200 = 2,400 ml FRC Stays in lungs at end expiration Why we need so little volume with each breath Each breath brings in 350 ml and out 350 ml At end-expiration we still have FRC-2,400ml Amt of alveolar air replace with each breath is 1/7 of the total Many breaths required to totally exchange alveolar gas Even after 16 breaths, some of original alveolar air remains
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Minute Ventilation
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Respiratory rate x tidal volume 12 x 500 ml = 6,000 ml or 6 L Lower than normal = hypoventilation Patient disease Anesthetist must compensate
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Alveolar Ventilation
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Total volume of new gas entering each minute AV = RR x (TV - dead space) Dead space = 150ml for 70kg male 4,200 = 12 x (500 - 150) Should keep CO2 at normal levels If you want hyperventilation increase RR or TV Alveolar gas consists Fresh gas - metabolized gas Carbon dioxide Water vapor
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Importance of Hemoglobin
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Oxygen solubility low Needs transport protein in adequate concentration (albumin) Ensure patient hemoglobin adequate Perfusion important to deliver hemoglobin Keep blood pressure within 20% of normal
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Gas Exchange and Ventilation
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Ventilation not necessary for oxygenation Ventilation necessary for removal CO2 High solubility (of CO2) necessitates removal Quantity produced dictates minute ventilation Cardiopulmonary bypass (Iow CO2 produced, decreased minute ventilation needed) ECMO only exceptions Spontaneous breathing keeps PCO2 - 40mmHg in Absence of disease High altitude and Pharmacologic intervention
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Carbon Dioxide Production
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Resting adult produces .008 gm molecules/min At STP: 1 mole = 22.4 liters If 1 mole = 22.4, how much does .008 mole =? 180 ml @ 0 degrees C 1/22.4=0.08/x Solve for x 0 C = 273 K 37 C = 273 + 37 = 310 K Charles Law
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Breathing Circuit Function
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Function is to provide final conduit for the delivery of anesthetic gases link a patient to anesthesia machine where respiratory exchange takes place You create the respiratory environment for the patient
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Ideal Breathing Circuit
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Ventilates efficiently Easily controls depth of anesthesia Conserves Heat & humidity Contributes no resistance to flow Doesn't cause pollution of OR Easy to use Inexpensive
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Open (Insufflation)
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blowing of anesthetic gases across patient's face avoids direct contact between patient's airway and breathing circuit valuable during pediatric anesthesia no rebreathing of exhaled gases if high flows are used (>10 L/min) ventilation cannot be controlled
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Open-drop anesthesia
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not used in modern medicine except developing countries highly volatile anesthetic (ether or halothane) Schimmelbusch mask Why do think the metal mask would get cold? => heat of vaporization!!! air is carrier gas; supplemental oxygen can be used rebreathing can be significant => only way to get rid of CO2 is to take mask off
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Disadvantages of Open Circuits
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poor control of inspired gas concentration and depth of anesthesia inability to assist or control ventilation no conservation of exhaled heat or humidity pollution of OR with large volumes of waste gases
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Draw-over anesthesia
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nonrebreathing circuits that use ambient air as carrier gas can use supplemental O2 inspired vapor and O2 concentrations are predictable and controllable allow IPPV and passive scavenging allow CPAP and PEEP low resistance vaporizers never use N2O may have low O2 saturation with room air advantage: simple and portable disadvantages: depth of TV not well known due to no rebreathing bag; awkward to use for ENT/head surgery due to components located near patient's head
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Semi-Open (Mapleson systems)
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solve problems of insufflation/draw-over by adding components breathing tubes, fresh gas inlets, adjustable pressure-limiting valves (APL's), reservoir bags location of components is basis of Mapleson classification high FGF's prevent rebreathing of CO2 can use with scavenger system breathing tubes fresh gas inlet APL valve reservoir bag (breathing bag) performance characteristics lightweight, inexpensive and simple some rebreathing occurs (flow controls amount) allow quick change in anesthetic concentration due to high FGF
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Best Mapleson for Spont Vent and Controlled
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Mapleson A best for spontaneous ventilation Mapleson D best for controlled ventilation Bain circuit is modification of D fresh gas inlet tubing inside breathing tube Spontaneous ventilation (A, D, F, E ) Controlled ventilation (D, F, E, B, C )
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Advantages of Mapleson system
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Low resistance to breathing made them popular in pediatrics Less work of breathing Simple, portable Easy to assemble Minimal moving parts Some retention heat & humidity
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Disadvantages of Mapleson
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Most advantages overshadowed by need for high flow rates Costs Dry & cold airway OR pollution Difficult to change from spontaneous to controlled ventilation Has led to many 'modifications' of Mapleson systems for modern use
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Additional Components (not in Mapleson, for semi-closed)
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CO2 absorber canisters Unidirectional valves Inspiratory check valve Expiratory check valve reduces need for high FGF OR pollution reduced by using scavenger system mandatory oxygen analyzer, airway pressure gauge, respiratory volume monitor
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Semi-closed (Circle System)
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Most commonly used Adults and pediatrics More complex but more efficient than Mapleson Prevents rebreathing of CO2 Allows use of low flows
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Unidirectional Valves
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gas vented through APL valve or rebreathed after passing through CO2 absorber to prevent rebreathing: valve must be between patient and rebreathing bag on both inspir/expir limbs FGF cannot enter circuit between expir. valve and patient APL cannot be located between patient and inspir. valve
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Valve ASTM Requirements
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Flow direction shall be permanently marked Functioning of valves should be visible Resistance of dry & moist valves shall not exceed a pressure drop of 0.15 kPa (1.5cmH2O) at 1L/second flow (60L/min-test flowrate for adults) Opening pressure of moist valve should not exceed 0.15 kPa (1.5cmH2O) Reverse flow shall not exceed 60mL/min at any pressure differential to 0.5 kPa (5cmH2O) Determined to be clinically acceptable & detectable with currently available volume monitors Valve shall not become dislocated with a reversed pressure differential of 5 kPa (50cmH2O) Maximum pressure in bag mode of circle system
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Testing for Valve Resistance
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Discs are light-weight, made of mica (ceramic) Conditioned with heated & humidified gas flow Until condensate on valve dome or disc visible (will wear down disc). Test rig introduces a 1.0L/second flow of gas Turn flow off and allows valve to close Adjusts flow of gas to 1.0L/second Measures the pressure drop across the disc Shall not exceed 1.5 cmH2O (0.15 kPa) Limits the work of breathing for spontaneous respiration
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Reported Problems with Unidirectional Valves
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Malfunction of either valve may allow rebreathing of CO2, resulting in hypercapnia Faulty valve can lead to increased PIP's or increased ETCO2 with elevated baseline on waveform Increased resistance
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Increased Work of Breathing
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Spontaneous ventilation depends on low resistance of light-weight mica discs Should be no more than 1.5 cmH2O Increased resistance occurs with Excessive moisture build-up Electrostatic build-up Heavier than normal disc Taped or glued back together Replacement with anything other than manufacturer disc Patient may c/o 'not being able to breathe'
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Incompetent Expiratory Valve
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Capnograph shows 'elevated baseline' Baseline should always return to zero if you have no re-breathing Re-breathing occurring on expiratory limb of waveform Anatomic dead space exhaled at baseline Also look at inspired CO2 numeric - FiCO2
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Incompetent Inspiratory Valve
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Capnograph shows abnormal 'beta angle' Normal beta angle approximately 90° Re-breathing occurring during inspiration Shows on inspiratory side of waveform Shaded area represents approximately 180° beta
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Prevent problems with check valves
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Check that valves are present If too wet, carefully dry and replace If you drop it & break it, ask for replacement! Don't leave any foreign matter in dome cup Watch movement while checking ventilator function FDA Checkout 12.1: Check for proper action of the unidirectional valves Watch valves during case Be alert to high pressure alarm-switch to bag mode Recommendation to put circuit on machine (not ports) at end of day to allow evaporation of condensate
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Tubes of Breathing Circuit
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attached to ports that are connected to unidirectional valves made of disposable plastic or rubber of various lengths usually 1 meter in length and has large bore to decrease resistance to gas flow corrugations present to permit flexibility without kinking internal volume approx. 400-500ml per meter (.3 meter = 1 foot) Depends on single or double lumen Gas flow usually turbulent due to corrugations & angles Always test circuit before using by determining oxygen flow required to maintain 30 cm H2O pressure in circuit Length of tubing does not affect mechanical dead space ...it is just empty space Longer tube...longer diffusion time
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Breathing Circuit Dead Space
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Dead space is space in circuit occupied by gases that are rebreathed without any change in composition Part of TV that doesn't undergo alveolar ventilation Dead space begins at Y piece and extends to any adaptors distal to Y piece (distal limb of Y piece and any ETT or mask between it and patient's airway) Any increase in dead space should be accompanied by an increase in TV if alveolar ventilation is to remain unchanged (not usually clinically significant) Always put extension tubings at inspiratory & expiratory check valves NOT at end of breathing circuit
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Common (Fresh) Gas Outlet
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only one outlet that supplies gas to the circuit adds new gas of fixed and known composition has antidisconnect device used to prevent detachment of hose usually latex-free oxygen flush valve provides O2 to common gas outlet
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Fresh Gas Inlet
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gases (anesthetics with oxygen/air/nitrous) from the machine continuously enter the circuit through this inlet placed between absorber and inspiratory valve connected with flexible rubber tubing (delivery hose)
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Reservoir bag (breathing bag)
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attached to bag mount 3 functions reservoir for anesthetic gases from which patient can inspire provide visual/tactile means of existence and of volume of ventilation serve as means for manual ventilation usually elliptical in shape nonslippery plastic or latex rubber sizes from 0.5 to 6L 3 L bag is usually sufficient for most adults ****think of breathing bag as patient's lungs
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Adjustable Pressure-Limiting Valve (APL)
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pressure relief or pop-off valve fully open during spontaneous vent. but must be partially closed during manual/assisted vent. (until desired inspiratory press. is achieved) this allows reservoir bag to fill valve will open after bag has become distended during expiration if valve open too much, bag won't fill; if closed too much, rise in pressure could result in barotrauma (pneumothorax) usually requires fine adjustments on modern machines, APL valves can never be completely closed; upper limit is 70-80 cm H2O
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Pressure Gauge (manometer)
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always used to measure circuit pressure between expir./inspir. valves usually reflects airway pressure if measured close to patient's airway ASTM standard requires measurement in kPa or cm H2O rise in pressure may signal worsening pulmonary compliance; increase in TV; obstruction in circuit, tracheal tube or airway drop in pressure may indicate improvement in compliance; decrease in TV; or leak in circuit do not give pressure above 20 cmH20 because it will open up esophageal sphincter
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Spirometers (respirometers)
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used to measure exhaled TV in circuit (usually near exhalation valve) newer machines measure inspiratory TV near inspiratory valve flow of gas across vanes within spirometer causes their rotation which is measured electronically changes in exhaled TV may represent changes in vent settings; circuit leaks; disconnections; or vent malfunction prone to errors caused by inertia, friction, and water condensation
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Disadvantages of circle system
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greater size less portable increased complexity, resulting in higher risk of disconnect or malfunction increased resistance, difficulty of predicting inspired gas concentrations during low FGF's
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Resuscitation Breathing Systems
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AMBU bags or bag-valve-mask units used for emergency ventilation due to simplicity, portability, ability to deliver almost 100% FiO2 contains a nonrebreathing valve (unlike a Mapleson or circle system) source of high FGF connected to inlet nipple patient valve opens during inspiration to allow gas from bag to patient rebreathing is prevented by venting exhaled gas to atmosphere through exhalation ports 3 sizes : adult, child and infant adult-TV over 600ml infant-TV 20-50 ml components self-expanding bag, bag refill valve, and nonrebreathing valve bag is inflated in resting state intake valve in bag allows PPV because it closes during compression bag is refilled by flow through fresh gas inlet has check valve in case FGF is excessive ***may connect a PEEP valve to expiratory port
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Functional Analysis of Ambu Bags
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minute volume is determined by TV x RR determined by performance of the resuscitator and the operator volume varies with size of user's hand (using 2 hands will increase TV) ASTM standard: capable of delivering at least 40% oxygen when connected to source supplying not more than 15 L/min delivered O2 concentration is limited by size of reservoir and O2 flow
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Disadvantages of Ambu Bags
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require high FGF to achieve high FiO2 max. achievable TV's are less than those achieved with a system that uses a 3-L bag most adult AMBU's have max. TV of 1000ml moisture in valves can cause them to stick considerable loss of heat and humidity bag feels different from other breathing bags valve is heavy and may cause ETT to be displaced downward may harbor bacteria-dispose of bags when appear contaminated
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FRESH GAS DECOUPLING
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modern ventilators compensate delivered TV for the FGF with traditional ventilators, delivered TV is sum of volume delivered from vent and FGF during inspiratory phase (ex. Narkomeds) so, TV may change if FGF changes if FGF increases, TV increases (significant in pediatrics) if FGF decreases, TV decreases (increases ETCO2)
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Drager Julian, Narkomed 600, Fabius GS use fresh gas decoupling
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fresh gas is not added to delivered TV ensures that set and delivered TV's are = bag inflates during inspiration and deflates during expiration as contents empty into absorber and move toward patient if a disconnect occurs, breathing bag rapidly deflates
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second approach is fresh gas compensation
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Aestiva and S/5 ADU volume and flow sensors allow ventilator to adjust delivered TV so it matches set TV despite FGF
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Closed System
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extremely low flow anesthesia and completely closed circuit (less than 500ml) maintenance of constant anesthetic state by addition of gases and inhalation agent at same rate that body stores or eliminates them (do calculations for MV and CO2 production) once stable level is established using high flows, APL is closed completely and FGF rate is reduced to levels equal to patient's metabolic need induction is difficult hypoxia or recall if nitrous is administered (b/c low flows) unpredictability of dosage of anesthesia for each patient induction may be prolonged when using low flows once adequate depth is established, there is little need for agent or nitrous oxide as they are rebreathed (O2 needs replenished due to its metabolism) open circuit every 1-3 hours and run at higher flows for 5-10 min to washout nitrogen eliminate harmful substances/metabolic gases not used frequently due to empirical calculations and fear of morbidity and mortality
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CO2 Absorbers
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Difference in circle system from Mapleson (in Mapleson, increase FGF to blow off/dilute CO2) Inclusion of absorber canisters beneficial Not necessary to use high flowrate More economical to recycle mixed gases Retention of heat and humidity Patient will be warmer Airways better humidified Location between bag/APL or vent & fresh gas inlet sends mixed gases via canisters where carbon dioxide absorbed
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Granules Chemically Neutralize CO2
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Chemical reaction between acid & base Weak acid reacts with strong base Products are weak base & byproducts CO2 + H2O H2CO3 Carbonic acid neutralized by base Sodium hydroxide Potassium hydroxide Calcium hydroxide Products: carbonates, water & heat
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Water
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H2O composed of 2 H atoms & 1 O atom When water dissociates or separates it forms H+ and OH-. This process is known as ionization The hydrogen ion, H+, has a positive charge because it lost an electron The hydroxide ion, OH-, has a negative charge due to its gaining an electron When another substance that ionizes is added, acids and bases are formed An acid is created when excess hydrogen ions are present A base is formed due to extra hydronium/hydroxide ions To determine if a substance is acidic or basic, the pH should be determined.
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Acids
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Substances produce H+ in aqueous solution Proton donor Add hydrogen ions to a solvent Strong acids dissociate 100% in water Every molecule breaks apart pH very low (0 - 3) Stomach-hydrochloric acid, car battery-sulfuric acid Weak acids dissociates at lower % Not every molecule breaks apart pH closer to 7 (3 -6) Citric acid in lemons, acetic acid in vinegar
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Bases or Alkali
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Substance produces OH- in aqueous solution Able to accept an H+ (proton acceptor) Strong base dissociates 100% in water Every molecule breaks apart High pH (10 -14) Na, K & Ca hydroxides reactive & caustic to skin Weak base dissociates to lesser degree Not every molecule breaks apart pH closer to 7 (8 - 10) Baking soda Minerals react w/ acid to form water & salt Oxides, hydroxides & carbonates of metals
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Neutralization Reaction
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Acid + Base => H2O + Salt Always exothermic (produces heat) 57.7 kj per mole H+ Granules (metal hydroxides) are the base Carbon dioxide + water is carbonic acid Products are heat and water Adds "heat and humidity" Chemically absorbs carbon dioxide
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Water ON & IN Granules
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Required for chemical reaction Patient's carbon dioxide Water in granules Carbonic acid is acid for base to absorb Prevents agent absorption into granule If dry, pores open & more agent absorbed Percent water depends on formula USP requires 14-19% Baralyme (octahydrate) performs worse than Soda sorb when dry
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Requirements for CO2 Absorbers
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Should not be toxic itself or when mixed with inhalation agents All agents have been shown to degrade to some degree by absorbent granules Low resistance to airflow 100% efficiency All of the carbon dioxide that enters the absorber canister should be absorbed
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CARBON DIOXIDE ABSORPTION
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CO2 absorption makes rebreathing of exhalations possible conserves agent and gases while preventing respiratory acidosis/hypercarbia rebreathing gas conserves heat & humidity CO2 must be eliminated to prevent hypercapnia Gas flows determine amount of rebreathing in circle system (increased FGF = decreased rebreath and vice versa) FGF's 0.3-0.5 L/min provide near-total rebreathing with full reliance on CO2 absorption FGF's greater than 4-5 L/min have little reliance on absorbent
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CO2 Absorbents Equation
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CO2 chemically combines with H2O to form carbonic acid CO2 absorbents contain hydroxide salts that neutralize carbonic acid end products include heat, water, and calcium carbonate CO2 + H2O = H2CO3 H2CO3 + 2NaOH =Na2CO3 + 2H2O + heat (fast) Na2CO3 + Ca(OH)2 = CaCO3 + 2NaOH (slow) note: water and sodium hydroxide are regenerated
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Dessication
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is the physical break down of the granules, this can lead to increased agent absorption and CO poision.
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Exhaustion
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This is when less CO2 is being absorbed and the absorbent is almost worn out by all the chemical reactions, when the carbonates outweigh the hydroxides. Will see increased FiCO2, ETCO2 and white to purple.
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Soda Lime
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Soda Lime most common absorbent can absorb 23-26 L per 100g of absorbent hardeners (silica and kieselguhr) added minimize formation of dust/harder to break down water content (15%) calcium hydroxide is main ingredient (80%) sodium hydroxide and potassium hydroxide (5%) size 4 to 8 mesh exhausted when all hydroxides have become carbonates freshness determined by feel, taste and appearance half of volume of canister is gas regeneration or peaking seen with soda lime soda lime appears to be reactivated with rest color will revert back to white but absorptive capacity will be low and purple color will reappear quickly after brief exposure to CO2 ***there is no true regeneration of activity occurring (just a dye reaction).
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Baralyme
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similar to soda lime activator is barium hydroxide (20%) calcium hydroxide (80%) small amount of water present no hardeners needed (less likely to produce dust) slightly less efficient than soda lime but less likely to dry out if stored under poor conditions also contains an indicator for color change may undergo some false regeneration size 4 to 8 mesh
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Indicators
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acid or base whose color depends on pH as carbonate is formed from hydroxide, pH becomes less alkaline and granules change color (becomes ACIDIC) from white to violet/blue added to absorbent to indicate when exhaustion has occurred does not affect absorption ethyl violet is most common due to vivid color change undergoes deactivation in high intensity light (tinted cover) due to regeneration, may not be able to rely on color change solely for granule exhaustion ***use of capnometry to detect rising inspired CO2 is most important
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High COHgb in Swine Study
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48 hour drying time @ 10 LPM H2O: from 12% to 3% Reservoir bag removed 3 pigs died due to 80% COHgb after 20 minutes 24 hour drying time @ 10 LPM Bag removed: H2O dec. and inc. temp and inc. CO CO peaked at 8,800 to 13,600 ppm Baralyme (73%) Sodalime (53%) Bag removed @ 5 LPM: Not dry enough to produce CO2 Bag ON: Not dry enough to produce CO
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High COHgb in Swine Study Conclusions
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Oxygen @ 10 LPM for 24 hours (with bag OFF) can lead to CO poisoning with Desflurane in pigs Oxygen @ 10 LPM for 24 hours (with bag ON) insufficient to dry granules Oxygen @ 5 LPM for 24-48 hours (with bag ON) insufficient to dry granules If you walk in and see 5-10 LPM flowing with no bag what should you assume? If you walk in and see 5-10 LPM flowing with bag ON what should you assume? Would you change canisters?
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When to Change the Canisters
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1990 FDA/CDC recommended Q 24 hours Few departments complied due to $ Most follow manufacturer recommendation Change when they become exhausted Color change means exhaustion No indication when dessication occurs NO indication if flow left on Aline patients COHgb Vigilance to turning OFF flows Technicians help ensure flows OFF At end of case At end of day Change every 30 days now Cannot use with flammable anesthetics
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Consult WR Grace
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H2O content stable for one month after plastic wrapping removed Chemical reaction product = H2O If no flows run without patient on circuit, H2O should remain stable Vigilance to flows with techs and staff OK to leave on machine for 1 month Change if we suspect flows left ON
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Halothane + Soda Lime
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Metabolite forms BCDFE 2 bromo, 2 chloro, 1, 1 difluoethane Specific nephrotoxin in rats No nephrotoxicity in humans Metabolite found in human urine after Halothane
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Degradation of Sevoflurane
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CH4 + O2 → CH3OH → CH2O → HCOOH → CO2 Methane → Methanol → Formaldehyde → Formic acid → Carbon Dioxide Products of this pathway (methanol, formaldehyde, formate or formic acid) Each of the compounds are quite toxic in relatively low concentrations. Compound A Fluoromethyl-2-,2-diflouro-1-triflouromethyl vinyl ether Nephrotoxic in rats Proximal tubule lesions Controversial renal effect in humans Increase levels for 1-2 hours Level plateaus, then declines HIGHEST DURING LOW FLOW (less than 1L)
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Compound A
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Sevoflurane reacts with CO2 granules to produce compound A lethal at 130-340 ppm; renal injury at 25-50 ppm nephrotoxic in rats; NO HUMAN CASES REPORTED blood levels increase for 1-2 hrs after administration, plateau then decline recommend using higher FGF's with Sevo (2-5 L/min) to flush absorber of toxic compounds ***product insert does not recommend sevoflurane at total FGF's of less than 1L/min for more than 2 Mac-hours -higher FGF dilute and decrease risk of Comp A and renal injury
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Trichloroethylene (Trilene)
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Used in 1970s for analgesia for trigeminal neuralgia and dentistry In alkali and heat, it degrades into toxins Dichloroacetylene (cranial nerve lesions, encephalitis) Phosgene -COCl2 (pulmonary edema & ARDS) CO (phosgene + water product) If patient had in past 24-36 hours, do not use breathing circuit with CO2 absorber Use regional if possible and/or Mapleson system
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Trichloromethane (Chloroform)
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Phosgene formation Toxicity arise from inhalation Reacts with water, forms hydrochloric acid Symptoms appear 2-24 hours later Pulmonary edema, pneumonia, abscess, death Break down product of chloroform .1% ethanol acts as preservative Carbon monoxide formed from reaction
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Fires with Sevoflurane
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Rare (4 in 1 year) fires in Baralyme Baralyme dessicated One airway fire in St. Louis One explosion of expiratory valve through ceiling tile at CHMC induction room Details of others unknown Baralyme taken OFF market Recommendations issued
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Recommendations from Abbott
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Replace canisters if possibly desiccated Walk into room and flowmeters ON Walk into room and vent still cycling Turn OFF flows and machine at end of day Turn OFF vaporizers when not in use Check for proper plastic packaging when replacing canisters Periodically monitor temperature How are we supposed to do this? Replace canisters routinely (every 30 days or less)
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New Absorbents
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strong bases (NaOH, KOH) implicated in CO and compound A eliminating these activators produces absorbent that has similar physical characteristics and CO2 absorption efficiency (controversial) as compared with soda lime Amsorb is now widely available...CHMC lithium hydroxide is also effective but not available goal is to maintain efficiency while lessening production of byproducts Dragersorb 800 and Medisorb are used now (contain less NaOH and no KOH)
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Absorber Toxicity
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resistance of filled canisters is low inhaled dust is caustic and is an irritant may lead to bronchospasm, laryngospasm and pneumonia trap for water and dust that prevents passage of dust toward patient is incorporated beneath the lower canister (empty as needed) FDA recommends: when circuit is pressurized, release pressure through APL valve and not through elbow near patient's face (in case of dust) handle absorbents gently avoid fragmentation and dust formation (always wear gloves)
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Low Resistance to Airflow in Absorbers
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Inside canister, there are granules and... Empty space for gases to flow through Tightly packed granules adds resistance Specifically sized to minimize resistance Compromise between resistance and absorptive capabilities of granules Mesh size screens control size of granules
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USP Mesh Standards
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'85% 4 to 8 mesh' '7% oversized' '7% undersized'
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Air Space in Canister
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Goal is 65% of canister as airspace Best compromise between Maximum absorptive capacity Minimal resistance to airflow Size of absorber must match patient TV Estimate with 50% of total capacity Precise at 65% of total capacity Similar to Mapleson length of tubing
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Match TV to Absorber Capacity
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If absorber capacity = 1400 ml Airspace is 50-65% of 1400 Airspace = 700 - 910 ml Appropriate for patient up to 90 Kg Assuming 10 ml/kg for TV What happens if airspace was 350 ml? ---up to about 45kg, so only can be used on small pt. TV should NOT exceed airspace
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Wall Effect
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More resistance inner diameter of canister Less resistance near wall due to more air space distribution Gas flows here preferentially
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Channeling
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Gas flows in characteristic pattern through absorber..path of least resistance Top center Down the sides To the bottom When we change, we'll get rid of top canister and let bottom canister go to top (b/c top wears out first and then bottom).
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Efficiency, Break Point, and Exhaustion
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100% efficient if 100% of carbon dioxide absorbed in the canister Amount of time 'time efficiency' Breakpoint - inspired CO2 = .1% Exhaustion - inspired CO2 = .5% Rebreathing - if inspired CO2 goes higher
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Efficiency Varies with Hardness
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Porous granules absorb more Hard granules absorb less 100% hard rock absorbs nothing O% hard sponge absorbs everything Compromise between absorption and dust Additives to decrease dust Silica added to dec. dust-clogs the granules Kieselguhr (diatomaceous earth) hardens
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How to Measure Hardness
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Start with 50 gram sample Subject to 45 psi pressure for 1 minute or Put in pan with steel ball bearings Agitate granules and ball bearings Put what remains into 10 mesh screen Agitate again and weigh what remains Remains must weigh 40 grams Sift through 8 mesh screen 75-80% of granules should remain
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Variables that Affect Efficiency
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Packing of canister Channeling If airspace = patient TV Granules'characteristics Hardness Size Water content Flowrate used through granules If exceed pt minute ventilation, residence time low Absorption capacity reduced Ideal flowrate = minute ventilation or less
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Void Space in Canister
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Efficiency decreases when empty space fills up with products of reaction As carbonates and water are produced, they have to be somewhere They fill up interstitial (void) space As void space dec., less airspace to accommodate patient's tidal volume Lose 60cc/hour per 1000 cc Sodasorb (may see CO2 rebreath before large color change, may need to increase TV to compensate for lost space) TV >or equal to available void space = inefficiency
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Exhaustion
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breakpoint is defined as time at which the first trace of unabsorbed CO2 is detected in inspiratory port of the absorber approx 0.1% exhaustion is the time at which the CO2 level at the inspiratory port reaches 0.5%
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Replace Canisters When:
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when inspired CO2 is > 3-5 mmHg when ETCO2 is increased when 50-75% color is changed when temperature of canister is cool (not reliable)
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Bases Caustic to Skin
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Sodalime more caustic to Baralyme Led many departments to use Baralyme Along with high water content in product Dust implicated in patient injury Facial burns Bronchospasm Irritation to mucous membrane Direction of gas flow dec. dust expulsion Able to drain out via absorber drain Prevention of foreign matter to airway
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Use Redundancy in Monitoring
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Rely on monitors that measure CO2 Look at expiratory number...chart it Keep your eye on inspiratory number If rebreathing occurs, look at canisters If dye added, granules should be purple Change canisters when necesssary Don't forget clinical signs Hyperpnea...deep breathes Hypertension - esp. with long laproscopic procedure.
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Absorber
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granules of absorbent are contained within 1-2 canisters that fit snugly between a head and base plate this is called an absorber usually double canisters because they permit more CO2 absorption, less frequent absorbent changes, and lower resistance absorber includes 2 ports for connection of breathing tubes, fresh gas inlet, inspiratory and expiratory unidirectional valves, an APL valve and bag mount
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Canisters
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hold absorbent side walls are transparent with fresh absorbent in each canister, CO2 is absorbed mostly in upstream chamber then as that becomes exhausted, it enters downstream chamber disposable canisters available
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Housing (canister support)
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head and base usually made of metal gaskets at top and bottom fit against canisters can raise base of housing so canisters seal against gaskets lowering base creates gap between canister and gasket (a leak) absorbers have actuated cam to raise and lower base there are spaces at top and bottom of absorber for incoming gases to disperse before passing through absorbent or for outgoing gases to collect before passing on through circle (this promotes even distribution of flow)
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Baffles
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annular rings that serve to direct gas flow toward central part of canister placed at top and bottom of absorber increase path of travel for gases along sides and help compensate for wall effect (or else sides would get worn out first)
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Side Tube
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external to canisters conducts gases either to or from bottom of absorber main flow of gases passing through absorber will be opposite to gases passing through side tube
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Exhaustion of Absorbent
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means 'drying out' clinical signs increased ETCO2; increased FiCO2 increased HR and BP hyperventilation respiratory acidosis arrythmia SNS activation color of granules at end of case ***capnography and indicator color change are primary indications of exhaustion if inspired CO2 is more than 3-5 mm Hg, FGF should be increased to 5-8 L/min this converts system to semi-open where rebreathing of exhaled gases is minimized
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only 2 reasons for increase in inspired CO2:
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absorbent granules are exhausted unidirectional valves are faulty
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Replacement
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do not change old-style canisters or loose fill in middle of case (may delay ventilation if you can't get canister to seal) may change canister in newer machines without interrupting ventilation if granules do become exhausted, and it's not safe to change in middle of case, change FGF to 1-2 times MV this will ensure inspired CO2 is reduced to acceptable levels replace granules after end of case wear gloves in Drager Narkomed, lower base of absorber housing with cam remove canisters discard upper canister and move lower canister to upper position insert new canister in lower position always date and time canister canister position is reversed when you are finished!!
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Replacement Recommendations by Company
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Sodasorb manufacturer recommends changing the absorbent if left in machine for > 48 hrs. Drager recommends their absorbent in Fabius GS be changed if machine has been idle for 48 hrs. or at least every Monday morning 2 reasons for these cautious guidelines: gas flows may be left on overnight or all weekend which dries out granules (they do not regenerate) ethyl violet indicator may be inactivated by intense light ***University Anesthesia Techs change soda lime when 75% exhausted OR 30 days from date
