Anesthesia Machines and Breathing Systems Flashcards
what are the 5 basic functions on the anesthesia machine?
- provide a source of oxygen
- provide a means to support ventilation
- provide a means of delivering inhalant anesthetics
- provide a means of removing exhaled CO2
- provide a means to remove inhalant anesthetics from our work environment
describe the components of/the flow of gas through the anesthesia machine and breathing system
- oxygen source
- flowmeter and vaporizer
- breathing circuit
- scavenging system (gets rid of inhalant and expired gases)
describe the different sources of oxygen and when they can be used
- cylinders
-2 common sizes: E 660L, H 6,900L
-high pressure: E 1900psi, H 2200psi
-E cylinders usually mounted to machines
-H cylinders on dollies or chained to wall
-only gas in the tank at room temp, NO liquid! - oxygen bank
- liquid oxygen:
-1 cubic foot of liquid O2 = 24,080L O2 gas at 21 degrees celsius or 70 degrees fahrenheit
-good for places that need a lot of oxygen (heavy anesthetic load)
-but not great for when have to move patient (not mobile source, will need an oxygen tank) - oxygen concentrators
-don’t need tanks; filters room air and concentrates O2 (not entirely 100% O2 but close), flow good enough to also run ventilators
-maintenance: change filter when needed
how do you tell how much O2 is in a cylinder?
- pressure falls linearly as O2 is used
-pressure proportional to the amount of oxygen in the cylinder - calculate remaining O2 by:
volume (L) = pressure on gauge(psig)/1900(psig) x 660L
-also need to know the rate of O2 delivered to determine how long tank will last (L/min) - replace when less than 200 psig
describe cylinder safety
- cylinders are potential missiles!!
-prevent them from falling over please
-never store vertically without being chained!! if no chains, better to lay them down so they won’t fall and missile - handle cautiously
-store safely: away from heat and fire - no oils or grease: silicone lubricants only
how do you mount a cylinder to the anesthesia machine?
- remove plastic wrap, place washer on yoke
- crack the valve
- use foot to help lift and stabilize the cylinder
- align pins and gas outlet
- tighten securely
describe pressure regulators
from high variable pressure to lower constant pressure
-cylinder regulators: reduce to 45 psi
-pipeline regulators: to 50-55 psi; higher to save oxygen tanks! the higher pressure will go into the tank first/selectively so tank lasts longer
to reduce high pressure coming from oxygen source to lower pressure that won’t explode patient’s lungs
close oxygen tank when connected to pipeline to preserve pressure in O2 tank for use
describe flowmeters
- allow precise control of gas flow to patient
- flow rates vary depending on design
- knobs have different feel so don’t confuse different gases
- read at the:
-top of the bobbin
-middle of the ball
describe vaporizers
- convert volatile anesthetics from liquid phase to vapor phase
- classification:
-precision (deliver a specific amount) versus non-precision
-regulation of output: variable bypass (bypass vaporizer chamber of oxygen) or measured flow
-method of vaporization: flow-over, bubble-through, injection
-localization: out of circuit (upstream of rebreathing system) or in circuit
-compensation: temperature or flow
-agent specificity: agent specific of multi purpose
-resistance: high or low
(see picture for what red to focus on)
describe the oxygen flush valve
- oxygen bypasses the vaporizer
- delivers a high flow rate (35-75L/min)
- used to RAPIDLY DECREASE the inhalant concentration in the breathing circuit
-a wake up button!! - potential for barotrauma in small patients
- DO NOT use with non-rebreathing circuits (no need to flush bc as soon as you turn it off the patient gets 0%)
describe the common gas outlet
- interface between machine and breathing circuit
- blended agent and carrier gas exit the machine at this point
- universal fitting to connect various types of breathing circuits
-this is where you attach breathing or non-rebreathing system
-if not connected, inhalant go to room, patient die bc no breathe and all doctors pass out bc breathing inhalant anesthetic
what is the function of breathing systems?
provide a means to:
1. support ventilation
2. deliver O2 and inhalant to patient
3. remove CO2 from patient
4. remove waste inhalant from work environment
describe the 2 types of breathing circuits
- rebreathing/circle: like a toyota; it’ll get you from point A to point B, just takes a little longer
-rebreathe exhaled gases
-chemically remove CO2
-adult and pediatric circuits - non-rebreathing: like a ferrari, turn it on and will cross distance much quicker but cost you more
-exhaled gases removed from the patient
-high gas flow rates remove CO2
-for patients <3-5kg that may not be able to force air all the way through the whole rebreathing system
describe the pros and cons of a rebreathing system
pros:
1. rebreathe O2 and inhalants
-reduce cost
-environmentally friendly
- decreased heat and moisture loss
- larger volume provides buffers from barotrauma
cons:
1. greater resistance to breathing: takes more work to move all the air to take a breath (consider patient size)
-one way valves
-CO2 absorbent
- absorbent (granules) must be changed regularly
-will turn purple when used but if exposed to room temp will turn back to white
-check if can crumble: if can, still good, if not, change! - more places for leaks to develop
-gaskets
-connections
describe flow rate of rebreathing systems
- based on metabolic need, 10-20ml/kg/min
- economical, but change happens slowly
-need higher vaporizer settings
-some waste into scavenging system - flowmeter controls rate of anesthetic delivery:
-high flow at beginning:
–wash-in: time constant (vol/flow rate)
-higher time constant means it takes more time to deliver your desired anesthetic concentration, so push higher at the beginning to expose them to more anesthetic quicker, then dial it back for maintenance
-lower flow for maintenance
-it takes 3 time constants to result in a 95% change in concentration within the system!!
