Term
| Name the four basic components of an anesthetic machine: |
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Definition
1. a gas source
2. a pressure regulator
3. a flowmeter
4. a vaprizer
*breathing circuit is also attached to this machine |
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Term
| What are the 5 BASIC FUNCTIONS of an Anesthetic Machine and Breathing Circuit? |
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Definition
1. provide a source of oxygen for our patients
2. provide a means to support ventilation for our patients
3. provide a means of delivering inhalant anesthetics to our patients
4. provide a means to remove exhaled CO2 from our patients
5. Provide a means to remove inhalant anesthetics from our work environment |
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Term
| "SPDD" Model of an anesthetic machine and breathing circuit |
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Definition
-Supply (pipeline, cylinders, regulators)
-Processing (flowmeters, vaporizers)
-Delivery (breathing circuits, ventilators)
-Disposal (scavenging) |
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Term
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Definition
-cylinders: high pressure: 2200 psi
-two common sizes (E: 660 L (O2); H: 6,900 L (O2))
-E cylinders usually mounted to machines
-H cylinders on dollys or chained to wall
-banks of H cylinders for larger scale use |
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Term
| Color code for: Oxygen, nitrous oxide, nitrogen |
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Definition
-oxygen: US: green, intl: white
-Nitrous oxide: US and intl: blue
-Nitrogen: US and intl: Black |
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Term
| Physical states of oxygen and nitrous oxide: |
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Definition
-oxygen (gas)
-nitrous oxide: liquid + gas |
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Term
| How much is in a cylinder? (oxygen) |
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Definition
-gas under HIGH pressure
-pressure falls linearly as oxygen is used
-calculating remaining volume
-replace when less than 200 psig |
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Term
| How much is in a cylinder? (nitrous oxide) |
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Definition
-liquid under HIGH pressure
-pressure doesn't fall until all liquid is depleted (approx 75 %)
-replace when pressure starts to fall |
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Term
| Calculate volume in cylinder: |
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Definition
| -volume=(pressure on gauge (psig)/220 psig) X 660 L |
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Term
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Definition
-liquid oxygen tanks (BP of O2==148 C); one cubic foot of liquid O2 = 24,338 L O2 gas at 21C
-oxygen concentrators |
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Term
| Connecting gas sources to machine |
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Definition
-Hanger yolks=> E cylinders
-Pipeline systems=> quick connect, indexed connections |
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Term
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Definition
-Pin Index Safety System
-Diameter Index Safety System
** systems to prevent cross connection of cylinders, pipelines, and machines |
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Term
| Mounting cylinder to machine: |
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Definition
-remove plastic wrap, place washer on yoke
-"crack" valve
-use toe to help lift and stabilize cylinder
-align pins and gas outlet
-tighten securely |
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Term
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Definition
-reduce high VARIABLE pressure from cylinders to lower CONSTANT pressure tolerated by flow meteres
-cylinder regs: reduce pressure to 45 psig
-pipeline regulators: reduce pressure to 50 psig
-regulators are often not easily visible, and rarely cause machine malfunctions |
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Term
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Definition
-allow precise control of gas flow to the patient
-flow rates vary depending on design
-Read at the: top of the bobbin, middle of the ball |
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Term
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Definition
| convert volatile anesthetics from liquid phase to vapor phase |
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Term
| Vaporizers classification |
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Definition
1. precision vs. non-precision
2. regulation of output (variable-bypass, measured-flow)
3. method of vaporization (flow-over, bubble-through, injx)
4. localization (out-of -circuit vs. in-circuit)
5. compensation (temp, flow)
6. agent specificity (agent specific, multipurpose)
7. resistance (high/low resistance) |
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Term
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Definition
-most common type
-variable bypass
-out of circuit
-flow and temp compensation
-agent specific (vapor pressure)
-relatively complex and expensive
-require occasional maintenance
-output is controlled accurately by dial setting
-output not affected by patient's respiratory pattern
-can be used with any type of breathing circuit |
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Term
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Definition
-relatively uncommon now
-examples (ohio 8, stephens)
-in-circuit
-no flow or temp compensation
-not agent specific (safer with less volatile agents)
-simple, inexpensive
-minimal maintenance
-output not accurately controlled
-output is affected by patient's respiratory pattern and gas flow rates
-not effective with breathing systems that use high flow rates (e.g. non-rebreathing systems) |
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Term
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Definition
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Term
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Definition
-flow-over
-bubble-through
-injection |
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Term
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Definition
1. VIC-increased ventilation-> increased inspired anesthetic conc; increased O2 inflow-> decreased inspired anesthetic concentration
2. VOC-increased ventilation-> inspired anesthetic concentration; increase O2 inflow-> decreased inspired anesthetic concentration |
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Term
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Definition
-bypasses the vaporizer, and delivers a high flow rate of oxygen directly to the patient's breathing circuit (35-75 Ipm)
-used to RAPIDLY DECREASE the inhalant conc in the breathing circuit (WAKE UP button)
-potential for barotrauma in small patients, especially non-rebreathing circuits |
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Term
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Definition
-interface between and anesthetic machine and the patient breathing circuit
-blended anesthetic agent and carrier gas exit the machine at this point
-universal fitting to connect to various types of breathing circuits |
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Term
| Breathing Systems (Circuits) Provide a means to: |
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Definition
-to support ventilation
-to deliver O2 and inhalant to the patient
-to remove CO2 from the patient
-to remove waste inhalant from the work environment |
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Term
| Breathing systems (circuits) |
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Definition
-two main types based on design, method of CO2 removal:
1. rebreathing-rebreath exhaled gases, chemically removes CO2, patients >5-7 kgs
2. non-rebreathing-exhaled gases removed from patient, high gas flow rates remove CO2, patients <5-7 kg |
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Term
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Definition
-def: inhale gases that have been recently exhaled
-Its OK to rebreath oxygen and inhalant anesthetics
-its NOT OK to rebreath CO2!!!-rebreathing CO2 results in hypercapnia-> respiratory acidosis; bad!! |
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Term
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Definition
| -rebreath O2 and inhalants (reduce cost, environmentally friendly); decrease heat/moisture loss; larger volume, buffers from barotrauma; any type of vaporizer; wider range of flow rates; greater familiarity |
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Term
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Definition
| -greater resistance to breathing (one-way valves, CO2 absorbent); absorbent must be changed regularly; more places for leads to develop (gaskets, connections) |
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Term
| Oxygen flow rates for circle system: |
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Definition
-flowmeter controls rate of anesthetic delivery-> higher flows initially, lower flows for maintenance (increase flows whenever conc. change needed)
-"wash-in" anesthetic based on-> time constant=volume/flow rate |
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Term
| Time constant: Rule of Thumb |
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Definition
| -it takes 3 time constants to result in a 95% change in conc within a system |
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Term
| Maintenance Flow Rates for Circle System: Closed |
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Definition
-flow rate=metabolic need (4-11 mls/kg/min)
-most economical
-change happens slowly
-higher vaporizer settings
-close attention to volume in circuit, O2 delivery to patient
-airway gas monitoring helpful |
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Term
| Maintenance flow rates for a circle system: semi-closed |
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Definition
-flow rate > metabolic need
-flow rate < minute ventilation
-22-44 mls/min/kg
->300 mls/min minimum
-more rapid changes in anesthetic concentration
-economical
-some waste (scavenging) |
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Term
| What flow rates are needed? |
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Definition
-varies over the course of procedure
-at induction and recovery: wash-in, wash-out
-"overpressure" plays a role |
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Term
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Definition
-two factors-> gas flow rate, volume (7 liters for normal circle system)
-time constant=volume/flow rate
-3 time constants required to reach 95% of inspired concentration: disregarding uptake and distribution by patient
-speed "wash-in" or "washout" by either: increased flow, decreased volume |
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Term
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Definition
-1 time constant=63% wash-in
-2 time constants=86% wash-in
-3 time constants=95% wash-in
-4 time constants=98% wash-in |
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Term
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Definition
-delivery of much higher than needed partial pressure of inhalant-> compensates for lower flow, compensates for patient uptake
-speeds the rate of rise of the alveolar conc
-the lower the flow you are using, the more overpressure you need |
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Term
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Definition
-semi-closed-> small animal-> induction 1-3 l/min; maintenance 0.5-1 l/min
-semi-closed-> LA-> induction 10 l/min; maintenance 5 l/m
-temporarily increase flows when change concentration |
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Term
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Definition
-sodalime
-basic reacton: CO2 + H2O+CaOH-> CaCO3 +H20+energy(heat); CaOH-> soft, crushable; CaCO3-> hard (limestome)
-contains indicator dye (white-> blue or violet): color change reverses with time, lack of use; some newer absorbents may have permanent color change
-must be changed after approx 8 hours use (depends on canister size, patient size, fresh gas flows) |
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Term
| Non-rebreathing systems: pros |
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Definition
-simple, inexpensive, durable
-only moving part: APL valve
-dec resistance, dec work of breathing
-lightweight/less bulk
-easy to position
-rapid change in anesthetic plane |
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Term
| Non-rebreathing systems: con |
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Definition
-high fresh gas flows used for CO2 elimination ($$$$, increased pollution)
-incr loss of heat, moisture
-low volumes + lack of distensibility + high flows-> Increased risk (barotrauma)
-must use precision vaporizers |
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Term
| Components and types of non-rebreathing systems |
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Definition
-hose to connect to common gas outled
-ET tube adapter
-length of flexible tubing
-optional parts: reservoir bag, pressure gauge, pressure relief valve; APL valve |
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Term
| Fresh gas flows with non-breathing systems |
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Definition
-oxygen flow prevents rebrething of CO2
-same flow rates used throughout anesthtesia
-recommended flow rate is 100-200 ml/kg/min (5 kg cat: 200 X 5 =1 L/min) |
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Term
| Basic machine checklist prior to use: |
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Definition
-connect and check O2 supply
-check vaporizer fill levels
-check CO2 absorbent
-leak check breathing system=> close APL valve, occlude patient connection, pressurize to 30 cm H20, should hold for >10 sec; what do you do if it leaks?
-connect and check scavenging system |
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Term
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Definition
-provide reservoir of gas from which patient can breath (peak inspiratory flow> fresh gas flow)
-3-6 X patient's tidal volume
-sizes: -cats, toy breed dogs: 0.5 L
-medium to large dogs: 1-3 L
-large animals: 5-30 L |
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Term
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Definition
-mechanical reservoir bags (always attach to same place as the breathing bag on a breathing circuit
-Ascending or descending
-volume limited, pressure limited, or both
-anesthesia ventilators are simple, easy to use |
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Term
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Definition
-"adjustable pressure-limiting"
-interface between breathing circuit and scavenging system
-controls "fill" of breathing circuit
-close to provide positive pressure ventilation
-inadvertently leaving in closed position is FATAL! |
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Term
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Definition
-evacuates waste gas to outside environ
-active vs. passive
-often simple, inexpensive
-active systems must have negative pressure relief
-absolute must!!! |
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Term
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Definition
-simple, inexpensive
-portable (useful when moving machines from room to room)
-only absorbs halogenated hydrocarbons (not NO)
-must be changed routinely |
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