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CRNA Scope of Practice
- •Professional functions, privileges, and responsibilities
- •Performed in collaboration with authorized professional healthcare providers
- •“Supervision” and “medical direction”
- •Practice rights determined by state regulatory agency
Is discharging a patient from post anesthesia care area and providing post anesthesia follow up evaluation and care part of CRNA Scope of Practice?
What is the difference between practice guidelines position statements and standards?
- Practice guidelines= provider behavior and critical decision-making
- Position statements represent emerging trends
- Standards: assist w/guidance & support for patient safety
- -define, justify, improve, & document quality of care
- -public demands accountability from health care providers
- -professional organizations must educate the public
- -AANA practice committee
Who developed CRNA Standards of practice & what does this represent?
- •AANA- develop educational standards and technique
- •Represents behaviors that must be exercised by the nurse anesthetist in similar circumstances
CRNA standards of practice
- •Rules or minimum requirements for clinical practice
- •Accepted principles of patient care
- •Used to evaluate CRNA care
- –Provide a framework for evaluation of practice
- –Describe accountability to the public
- –Establish expected level of patient care
- •Ensures quality of the individual and institutional risk
What are the classifications of CRNA standards?
- 1. Regulatory- based on government mandate
- 2. Voluntary- developed by healthcare practitioners
- 3. Involuntary- defined by professional liability carriers
What are the types of CRNA standards?
1. Process-particular behavior or mechanism by which a specific task as performed
2. Outcome- mechanism to identify exemplary performance and best practice
What are CRNA practice guidelines?
- •Assist CRNA’s to understand the indications for and methods to perform clinical procedures
- •Basic clinical management options
- •Assist instruction of student anesthetist
- •Measure and improve one’s practice
- •Used in malpractice litigation
What are position statements?
- •Documents that recommend clinical practice or reflect emerging trends
- •Notify practitioners of conduct related to clinical practice
- •Refer to a specific practice that is accepted and commonplace within the anesthesia profession
- •Reflects care that is reasonable and prudent
History of Nitrous Oxide
- •First gas recognized to have anesthetic powers
- •Isolated in 1772 by Joseph Priestly
- •Sir Humphry Davy= “laughing gas”
- •Weak anesthetic
- •Danger of hypoxia
- *inert, colorless, odorless, & tasteless
History of Ether
- •First discovered by Raymudus Lullius
- •Ether means heavenly
- •Paracelsus noted its tendency for sleep
- •Brand name Anodyne
- •Early-mid 1800’s= “ether frolics”
- *Liquid at room temp and vaporizes easily. Can swallow or inhale. Can induce anesthesia w/out use of oxygen.
History of Choloroform
- •Colorless, volatile liquid with sweet smell and taste
- •Discovered 1831 by Dr. Samuel Guthrie
- •Chlorodyne- chloroform and morphine
- •Not flammable
- •Less respiratory irritant
- •Cardiovascular depressant
- *Faster acting and easier to use than ether
Describe the difference between levels of alcohol intoxication & anesthesia
- Dizzy & Delightful = amnesia & analgesia
- Drunk & Disorderly = uninhibited
- Dead Drunk = surgical anesthesia
- Dangerously deep = vital center depression
what are some non-drug methods for anesthesia?
- Nerve compression
- Blood letting
Name some drugs used in ancient and medival times for pain
- •Hyoscine (Mandrake=scopalomine)
- •Cocaine (coca leaves used by Inca's)
Describe the works of Hickman
- •1824-Henry Hill Hickman
- **Used Carbon dioxide**
- •Asphyxiating small animals
- •Performed surgery
- •Closest of all to surgical anesthesia
Describe the works of Raymundus Lullius
- First discovered Ether
- Brand name Anodyne
Describe the works of Dr. Crawford Long
- •First surgical anesthetic use of ether
- •1842-removed a cyst
- •Used in obstetrics
- •Did not publish results until 1848 (credit given to William Morton)
Describe the works of Dr. Horace Wells
- •Connecticut dentist
- •Promoted N2O as safer than Either
- •Public demonstration at MGH=unsuccessful
- •Became addicted to chloroform and committed suicide
What is chloroform
- Colorless, volatile liquid w/sweet smell & taste
- Discovered in 1831 by Dr. Samuel Guthrie (American)
What was chlorodyne?
- chloroform and morphine
- Used for cholera
- Not flammable
- CV depresant, more than ether
- Faster onset than ether but ether is safer
- Delayed onset and liver damage d/t toxic metabolites
- 1st death w/chloroform lead to controlling concentrations
Rapid and short acting barbiurate
- •Hexobarbital- first rapidly acting IV anesthetic
- (1903- 1st sedative barbiturate, barbital)
- John Lundy-balanced anesthesia: emphasized combining multiple anesthestic drugs & techniques to provide hypnosis, muscle relaxation, & analgesia
- Thiopental: derivative from pentobarbital
- 1962- Ketamine synthesized
- 1964- Etomidate
nWho was sister Mary Bernard?
- •First nurse anesthetist in the US
- •St. Vincent Hospital, Erie, PA
Who was Alice Magaw?
- •Most famous nurse anesthetist of the 19th century
- •Worked at St. Mary’s Hospital-1889
- •“mother of anesthesia”
- •Trained physicians and nurses
Who was Agatha Hodgins?
- •1915- Established Lakeside Hospital School of Anesthesia
- •6 month training for only $50
- •Trained military prior to WW1 in France
- •Founded the NANA
- **AANA was originally NANA (national assoc. of nurse anesthetist)
What was Lakeside Hospital?
- Agatha Hodgkins started Lakeside Hospital School of Anesthesia
- Leaned how to use nitrous oxide/oxygen technique from Agatha Hodgins
- Accepted and trained nurses, dentists, and physicians (1915)
What was the OMNIBUS BUDGET RECONCILIATION ACT OF 1986
- •Concerned with changes in Part B of Medicare and CRNA billing
- •Essentially allowed CRNAs to bill directly for services beginning in 1989
- •This did not become permanent until 1991
- Payments developed for CRNA alone, MD alone, and CRNA/MD
What was the TEFRA act?
- •Tax Equity and Fiscal Responsibility Act (prevents fraud)
- •Anesthesiologists must meet 7 conditions before getting paid by Medicare
- •Anesthesiologists are reimbursed based on supervision or direction
- •Final ratio 4:1 for supervision
What are the 7 conditions as part of the TEFRA act?
- •Perform a preanesthesia evaluation
- •Prescribe the anesthesia plan
- •Personally participate in induction and emergence and other demanding procedures in the plan
- •Monitor the course of anesthesia administration at frequent intervals
- •Remain physically available for the immediate diagnosis/treatment of emergencies
- •Provide needed postanesthesia care
- •Refrain from personally performing an anesthesia procedure when purporting to be engaged in medical direction
What are the high pressure portions of the anesthesia machine?
- Cylinders and hanger yokes
- Cylinders’ primary pressure regulator
- Cylinder pressure gauge
- Check valve assembly
- gas inlets & outlets to final gas composition
What are the intermediate pressure portions of the anesthesia machine?
- Cylinder supply source (45 psig)
- Pipeline sources (50-55 psig)
- Oxygen pressure failure devices
- •O2 failure safety device
- •O2 supply failure alarms
- Oxygen flush valve
- Flow control valves
What are the low pressure portions of the anesthesia machine?
- Flow meter indicators and tubes
- Check valve (one way)
- Low flow pressure reducing regulator if present
- Common gas outlet
What is the scavenger system?
- collection and subsequent removal of waste anesthetic gases from the OR
- minimizes OR contamination by removing excess gas
- five components
What are the five components of the scavenger system?
- 1. gas-collecting assembly
- 2. Transfer means (tubing)
- 3. Scavenging interface (closed vs open)
- 4. gas-disposal assembly tubing
- 5. active or passive gas-disposed assembly
- (active =vacuum and passive = weight or pressure of the waste gas itself to produce flow through the system)
What is the pressure in the cylinder of air?
What is the pressure in the cylinder of nitrous?
stored as a liquid by a pressure of 51 atm or 745 PSI in both E and H tanks
What is the pressure in the cylinder of oxygen?
What is the color and volume of a cylinder or air? (E & H)
- Air is YELLOW
- Volume E: 625 L
- Volume H: 6550 L
What is the color and volume of a cylinder of nitrous? (E & H)
- Nitrous is BLUE
- Volume E: 1590 L
- Volume H: 15900 L
What is the color and volume of a cylinder of oxygen? (E & H)
- oxygen is GREEN
- Volume E: 660L
- volume H: 6900 L
What are the components of medical gas cylinders?
- Handle or Handwheel
- Pressure Relief Device
- Conical Depression
- Noninterchangeable Safety System
From the pipeline to the anesthesia machine the pressure goes from _________ to ______
50-55psig to 40-48psig
From the cylinder to the anesthesia machine, pressure goes from _______ to ________.
- ~2200psig (air and O2) to 40-48psig
- ~745psig (N2O) to 40-48psig
signs and symptoms of a venous air embolism
- 1. sudden decrease in ETCO2
- 2. increase in ETN2
- 3. hypotension (↓ CO)
- 4.tachycardia/cardiac dysrhythmias
- 5. mill wheel murmur
- *also see increased CVP
What causes a venous air embolism?
Well known consequence of sitting position
Negative pressure gradient between RA and veins at operative site. Air enters RV leads to interference w/blood flow at PA, death d/t CV collapse and arterial hypoxemia.
what is the FIRST S/S you'll see for a venous air embolism?
mill wheel murmur on the doppler
What is the LAST things you'll see from a venous air embolism?
What is the most sensitive monitor for VAE?
- transesophageal echocardiography and doppler US
- (followed by expired nitrogen fraction, EtCO2, trancutaneous oxygen, & R sided heart catheterization)
What is the least sensitive monitor for VAE?
esophageal stethoscope measurements
What monitors do we use to assess for a venous air embolism?
- 1. arterial line
- 2. multilumen central line
- 3. doppler (over R side of heart)
- 4. esophageal stethoscope (old days-don’t need if doppler)
What do you do if you have a venous air embolism?
Two empty syringes in CVL so you can aspirate quickly. Also inform surgeon right away, so he can soak area w/pads of NS, get out of sitting, gently compress internal jugular veins and start aspirating
- Will have CVL, and will test it.
- Take 20cc of NS and flush into CVL as fast as possible, and hear it. That’s what you’ll hear if air entrained into pulmonary. Make sure doppler in correct position.
how does the APL valve work?
APL valve will trap more gas inside the breathing circuit, a spring inside the APL valve is compressed according to how much the user turns the APL valve. The degree of spring compression exerts a proportional force on a sealing diaphragm in the APL Valve. The pressure inside the breathing circuit must generate a force that exceeds the spring compression force for the APL valve to open.
What happens to the APL valve as pressure continues to build from the combination of fresh gas flow and manual compression of the breathing bag?
the opening pressure of the APL valve will be exceeded and excess gas will be vented to the scavenging system.
Can you ventilate the patient w/the APL valve completely open?
no, all the gas is vented. there is no gas buildup and the manual breathing bag stays fully deflated.
What is the APL valve? Does it work with the ventilator?
- adjustable pressure limiting valve: primary component of the circle system, overflow, or pop-off valve
- prevents barotrauma by limiting the pressure build up that can occur w/manual ventilation
- it does not work w/the ventilator
- *APL valve in breathing system is either closed or isolated during ventilator operation)
Should you keep the APL valve open during induction?
YES. Don't want patient to breathe against it. If falling asleep close slightly so you can fill the bag and help ventilate
What are the hazards of vaporizers?
- Misfilling (most have key fillers)
- Contamination (assess for weird smells)
- Tipping (most have transport valves so if tipped won't leak)
- Overfilling (could deliver 10x more)
- Simultaneous administration of inhaled anesthetics (interlockiing mechanism won't allow this to happen)
What should you do if the anesthesia machine accidently gets tipped?
Run flows for 20min (not to patient)
Who regulates the cylinders we use?
Department of Transportation (DOT) DOT is regulatory body which governs the use of the cylinder. (Require specific markings on each cylinder and are stamped.
- 1st # is DOT specification # (3AA specifies the type & material of the cylinder and 2265 is the service pressure of the cylinder)
- 2nd # cylinder serial # (12345)
- 3rd # identifying symbol of either the purchaser, user, or manufacturer
- 4th Manufacturer data: date of manufacture and the original test date. (Includes inspectors official mark, and + means the cylinder qualified for 110% filling)
- 5th # manufacturer's identifying symbol
- 6th Retest markings: the date of the firsthydrostatic retest. (includes retesters identifying symbol, + means the cylinder re-qualifiies for 110% filling, and * indicates the cylinder qualifies for 10yr retest interval
- 7th # in the neck is ring’s owner
Each cylinder must have a label on the slide. (bottom is old school) (full, used, empty). Now there is a plastic coating on it that shows it’s a brand new tank, check it if that’s gone w/regulator to see how much oxygen is left before putting it on anesthesia machine
What is a packing valve?
- Valve attached to the neck of the cylinder (cylinders are filled and discharged through it)
- Made of bronze or brass
- Should be removed only during testing or maintenance of the cylinder
- the port of the valve is where gas will exit the cylinder and go into the anesthesia machine
- Each valve contains a stem that closes the valve by sealing against the seat, when the valve is open the stem moves upward allowing gas to flow into the port
What is the purpose of pressure relief devices on cylinders?
vents the tank contents to the atmosphere if the pressure of the enclosed gas increases to a dangerous level
Most cylinder valves are __________
packing type. In these, the stem is sealed by Teflon, which will prevent leakage around the threads. Packing type is capable of withstanding very high pressures
What is a diaphragm valve?
- Diaphragm in this one the stem in this valve is separated from the seat. There is a flexible diaphragm that seals the opening from the internal parts. Turning raises or lowers this diaphragm
What are the advantages of the diaphragm valves?
- Advantages of these valves:
- 1. can be fully opened w/ 1/2 or ¾ of a turn (packing valve need 3-4 good twists to open them completely)
- 2. the seat doesn’t turn (therefore less likely to leak)
- 3. no stem leaking can occur because of this diaphragm.
- These reasons are why diaphragm is generally preferred when pressure is relatively low and when no leaks can be allowed such as for flammable gases.
What are the pressure relief devices on the cylinders?
- 1. Rupture disc- nonreclosing device with a disc held against an orifice
- 2. Fusible plug- thermally operated, nonreclosing pressure-relief device
- 3. Pressure relief valve- spring- loaded device
Describe how the rupture disc acts as a pressure relief device on the cylinder.
1.When predetermined pressure is reached, the disc will rupture allowing contents of cylinder to be discharged. This protects against excess pressure as a result of high temperatures or overfilling of a tank.
Describe how the fusible plug acts as a pressure relief device on the cylinder
If temperature or pressure increase, these discs will rupture and you will loose contents of the tank. Made of metal alloy (WOODS metal) ***Boards question!***will melt at elevated temps usually around 212 F.
Describe the spring loaded device and how it acts as a pressure relief device on the cylinder
Designed to reclose and prevent discharge of all the cylinder contents after normal pressure of contents is restored. * only one that will close itself again! (pressure high, will let a little gas out and then when pressure normal it will reclose and will still have some gas left in tank (ex: oxygen))
What is the purpose of the pressure relief devices?
Each valve is fitted w/pressure relief device w/purpose of venting tanks contents to atmosphere if pressure of closed gas increases to a dangerous level. Important to see when changing oxygen tanks ove, if you put the pin into the pressure relief valve, the contents will spill out and empty your tank.
What is the difference between the conical depression and the pressure relief valve?
The conical depression is the little indentation that hold the oxygen or nitrous tank onto the back of the machine The hanger yoke goes into this part. Conical depression and pressure relief device are different, need to know which is which so you don’t hit wrong one. Don’t want to puncture pressure relief device and spill all the contents of the cylinder.
The hanger yoke has 3 functions. What are they?
- Has 3 functions:
- 1.Orients the cylinder
- 2.Provides a gas tight seal
- 3.Ensures unidirectional flow (O2 into machine, not the reverse going from the machine to cylinder)
What are the parts of the hanger yoke?
- 1. Body is principle framework and supporting structure.
- 2. The retaining screw is what tightens the cylinder into the yoke. That is done through the conical depression.
- 3. The gas inlet (where gas enters the machine) has the index pins (remember from safety (2,5 and 3,5 of nitrous and oxygen)-pins on yolk, holes on tank
- 4. There is also a washer that helps form a seal between the cylinder and the yoke.
- 5. There is a filter to remove dirt from the gas in the cylinder (very important for anesthesia machine don’t want dust, etc.)
- 6. Next is a check valve assembly, ensures a unidirectional flow of gas through the yoke, this check valve not only allows gas from cylinder to enter the machines but prevents gas from exiting the machine when there is no cylinder in the yoke. If you are using just pipeline, it wouldn’t allow oxygen from pipeline to exit through this yoke into the atmosphere. This check valve also prevents the transfer from one cylinder to the next, (two oxygen tanks, won’t go from high pressure tank to low pressure tank, it prevents that)
What is the Pin Index Safety System? What is oxygen and what is N2O?
- used to prevent mix up of gases
- Oxygen: 2 & 5
- N2O: 3 & 5
- *multiple washers will make the pins obselete so you could still have an error
TRUE or FALSE You must have a pressure indicator for the hanger yolk system
TRUE. Can use the same pressure indicator for 2 tanks of gas, this will display on the front of your anesthesia machine, the cylinder gas pressure
What is the critical temperature of Oxygen?
What is the critical temperature of Nitrous Oxide?
What is the critical temperature of Air?
What is the critical temperature of Nitrogen?
What does the critical temperature means?
- temperature at which a liquid becomes a gas
- When hospitals use a large amount of oxygen, it is less expensive and more convenient to use liquid. To prevent the liquid from evaporating, must be kept at or below its critical temperature
In a full tank you have 660 L of O2, with pressure of 2000 PSIG. Your tank has a pressure of 500 PSIG when you crack tank. How many L do you have?
- 660L = xL
- 2000psig 500psig
X=165L left in oxygen tank, now need to figure out what to put flows at to have as much time as possible. Say you’ll run at 2L/min, then divide by 2.
How does the the FDA regulate cylinders?
enforces the purity of medical gases
How does the DOT regulate cylinders?
published requirements for the manufacturing, marking, labeling, filling, qualification, transportation, storage, maintenance, and disposition of medical gas cylinders and containers
How does OSHA regulate cylinders?
regulates matters affecting the safety and health of employees in all industries
How does the NFPA (national fire protection agency) regulate cylinders?
published a number of standards
What are the advantages of a closed circuit?
- relative stability of inspired gas concentrations
- conservation of respiratory moisture & heat
- prevention of OR pollution
- Economical- less gas used
- Less danger of barotrauma
What are the advantages of a circle system?
- Low fresh gas flows can be used w/the physiologic, economic, & enviornmental advantages of rebreathing
- PaCO2 depends only on ventilation, not fresh gas flow
- normocarbia can be achieved when a malignant hyperthermia syndrome develops
- the lengths of tubing can be varied so that the machine can be placed away from the patient to allow optimal surgical exposure
What are the disadvantages of the circle system?
- it is composed of many parts that can be arranged incorrectly or may malfunction.
- It has a large # of connections which can disconnect or leak
- Some components are difficult to clean
- System is bulky and not easy to move
- Minute volume must be limited to avoid profound hypercarbia
- Compliance of the system is high compared to other systems. Consistent ventilation may be more difficult
What are the disadvantages of a closed circuit?
- inability to alter quickly inspired concentrations
- danger of hypercarbia
- greater knowledge is required
- accumulation of undesirable gases in the system
- -metabolites of anesthetic agents
What are the advantages of the circle system over the mapleson?
the circle system adds components to avoid problems of the Mapleson system, including "high fresh gas flow required to prevent rebreathing of CO2 resulting in waste of anesthetic agent, pollution of the OR enviornement, & loss of patient heat/humidity."
What are the components of the circle system?
- Fresh gas inlet
- Inspiratory and expiratory unidirectional valves
- Inspiratory and expiratory corrugated tubes
- Y-piece connector
- Pop-off valve (APL)
- Reservoir bag
- Canister containing a CO2 absorbent
Explain the fresh gas inlet of the circle syste,
- Gas enters the circle system from the common gas outlet by the fresh gas delivery hose
- Placed between the absorber and inspiratory valve
What are the two unidirectional valves in the circle system and how do they work?
- consist of a disk resing horizontally on the annular valve seat.
- Forward flow displaces the disck & allows air flow through the valves. Reverse flow pushes the disk against the seat, preventing reflux.
- Inspiratory valve between absorber and patient Expiratory is between the patient and absorber.
The APL valve is part of the circle system. Where is it usually placed?
between the CO2 absorber and the expiratory valve, close to the reservoir bag. Positioning it before the absorber helps to conserve absorption capacity and minimize the venting of fresh gas
Describe the breathing tubes in the circle system
- Carry gases to and from the patient
- Each tube connects to a port on the absorber assembly at one end and the Y piece at the other
- Length of tube doesn’t affect the amount of dead space or rebreathing
- Longer tubes are available
- (corrugated tubes)
Describe the role of the reservoir bag in the circle system
Allows accumulation of gas during exhalation so a reservoir is available for the next inspiration. This permits rebreathing, allows more economical use of gases, and prevents air dilution
Provides means whereby ventilation may be assisted or controlled
Serves visual and tactile observation as a monitor of patient’s spontaneous respiration
Protects the pt from excessive pressure in the breathing circuit
Describe the three types of CO2 absorbents
Soda lime- 80% calcium hydroxide, 15% water, 4% sodium hydroxide, 1% potassium hydroxide, small amt of silica
Baralyme- 20% barium hydroxide and 80% calcium hydroxide
Calcium hydroxide lime- calcium hydroxide and calcium chloride. 2 setting agents= calcium sulfate and polyvinylpyrrolidine
What is essential to have in the CO2 absorbent for reactions to take place?
WATER! Water content of granules is ESSENTIAL since the reactions will only take place in the presence of water. THEY CAN’T DRY OUT!
Why do we use granules in the CO2 absorbent?
- Smaller granules= more surface area available
- for absorption
- --But Air flow will increase resistance
- Granular size of sodium lime and baralyme- between 4 and 8 mesh
- (Mesh= # of openings per linear inch in a
- sieve through which granular particles can pass)
- * because this is the size at which absorption and low air flow resistance are optimized
Absorptive capacity=26L of CO2/100g absorbent
What is the absorptive capacity of soda lime?
- 26L of CO2/100gm of absorbent
- (Ca hydroxide lime absorbs much less, only 10.2L/100gm)
- *Loose packing and channeling can also decrease absorption.
How can you tell its time to change your CO2 absorbent?
- Ethyl violet- pH indicator added
- Changes from colorless to violet
- Not always reliable indicator
- Fluorescent lights can deactivate the dye
What are the CLINICAL signs that you need to change your CO2 absorbent?
- ↑pp of EtCO2; may also have ↑ inspired CO2
- ↑ (& later a ↓) in HR and BP
- Resp. acidosis
- S&S of SNS activation (flushed appearance, CV irregularities, sweating)
- ↑bleeding at surgical site
- color of indicator at end of case
If the absorber is dessicated, what can you do?
You can rehydrate but adding water, always ensure that fresh gas flows are turned off at the end of the day! if you find they are still on when you come in the morning, change the canister even if the indicator hasn't turned violet
How do we change a canister
- Protective wear for skin/eyes
- Check color and/or date of last change
- remove plastic wrap
- new canister on bottom and old canister on top (if it's a new canister system)
- check for leaks
Explain the fail safe valve
- "oxygen failures cutoff valve"
- located downstream from the nitrous oxide supply source. Serves as an interface between the oxygen and N2O supply sources.
- This valve shuts off, or proportionally decreases, the supply of N2O (and other gases) if the oxygen supply pressure decreases
- A high priority alarm is actuated when a decreasing oxygen supply pressure reaches a predetermined threshold (ex: 30psig)
Describe the second stage reducing device
- Upstream of N2O and O2 flow valves
- Reduce pressures to 26 psig for N2O and 14 psig for O2
Eliminates fluctuations in pressure supplied to flow indicator
Flow will remain constant
Describe the low-pressure alarms
- Signals operator when pressure is lost in O2 circuitry
- Dragers- sound alarm at 30-37 psig
- Datex- whistles at 28 psig
- Medium priority alarm
- **Dependent on pressure not flow, there are limitations and don’t offer protection of hypoxic mixture.
- Helps prevent hypoxia from disconnection of oxygen hose or depleted oxygen cylinder.
- If nitrous or oxygen are crossed over, still has pressure so not going to know they are switched!
What are the 5 pathways of oxygen
- Proceeds to the fresh gas flowmeter
- Powers the O2 flush
- Activates fail-safe mechanisms
- Activates O2 low-pressure alarms
- Compresses the bellows of mechanical ventilators
Describe the O2/N2O ratio controller
Safety feature. Designed to maintain a fresh gas of 25% oxygen +/- 3%. Ratio of N2O to O2 is never more than 3:1. Limits so you don’t deliver hypoxic flow.
If you forget to turn on Oxygen, you CAN’T turn on N2O.
Say you have 4L of N2O and 2L of oxygen and you turn it down. You have N2O at 4L and you put Oxygen at 1L, it will wean the N2O down so you can only give 3L.
Name some circumstances in which a hypoxic mixture could be delivered to the patient
- wrong supply gas in oxygen pipeline or cylinder
- defective pneumatics or mechanics
- leaks downstream of flow control valves
- inert gas administration (3rd gas like helium-system won't sense it)
What is the correct order of flow meters?
substantial hazards, flow meters located down stream from all safety devices except O2 analyzer. Even though gross damage to glass flow tubes is apparent, may be crack or chip you don’t see resulting in inaccurate flows.
In this diagram, in A & B, N2O is located in downstream position, oxygen is leaking out and not diluting out N2O, could have hypoxic mixure. Want Oxygen to be closest to patient.
What are the components of soda lime?
- 80% calcium hydroxide, 15% water, 4% sodium
- hydroxide, 1% potassium hydroxide, small
- amt of silica
What are the components of baralyme?
20% barium hydroxide and 80% calcium hydroxide
What causes risk of Compound A?
- Sevoflurane produces degradation products= compound A
- Results from low flow or closed circuit
- Baralyme vs soda lime (Baralyme causes it more than Soda lime)
- Higher concentrations of sevo
- Higher absorbent temperatures
- Fresh absorbent
What causes increased CO
- Desiccated soda lime and baralyme= degrade inhaled anesthetics to CO
- Produces carboxyhemoglobin concentrations reaching 30% or more
- Higher levels of CO more likely to be caused after (came in on Monday morning, saw Oxygen is going) soda lime is dried out, need to switch canister
**Low fresh gas flow rates can also increase CO production
Which inhaled anesthetics increase production of CO
for a given MAC multiple, the magnitude of CO production is greatest from Desflurane ≥Enflurane≥Isoflurane≥Halothane = sevoflurane
What causes more production of CO, Baralyme or Soda lime?
At a given water content, Baralyme produces more CO than soda lime
Does temperature effect CO production?
YES! a higher temperature increases CO production
Does anesthetic concentration effect CO production?
YES! More CO is produced from higher anesthetic concentrations
What is the second stage regulator?
- Upstream of N2O and O2 flow valves
- Reduce pressures to 26 psig for N2O and 14 psig for O2
- Eliminates fluctuations in pressure supplied to flow indicator
- Flow will remain constant
What is the latent heat of vaporization?
- Energy for vaporization
- When a molecule is converted from a liquid to the gaseous phase, energy is consumed because the molecules of a liquid tend to cohere
- The amount of energy that is consumed by a given liquid as it is converted to a vapor = the latent heat of vaporization.
- The number of calories required to change 1 g of liquid into a vapor without a temperature change
- Thermal energy for vaporization must come from the liquid itself or an external heat source.
What is thermal conductivity?
- Measure of the speed with which heat flows through a substance
- The higher the thermal conductivity, the better the substance conducts heat.
- Vaporizers are constructed of metals that have relatively high thermal conductivity so they maintain a uniform internal temperature.
What is the specific heat of a substance?
- Number of calories required to increase the temp of 1 g of a substance by 1° C
- Specific heat value of an anesthetic is important because it tells us how much heat must be applied to maintain vapor pressure
- Also determines how the manufacturer selects vaporizer component materials → a high specific heat minimizes temperature changes associated with vaporization.
What is the Vapor pressure of Sevoflurane?
What is the Vapor pressure of Isoflurane?
What is the vapor pressure of Desflurane
What helps with humidity in the breathing circuit? (What are some means of adding humidification to the Anesthesia breathing circuit?)
- Low flows
- Heat & moisture exchanges (HME)
- Active: (Heated humidifiers)
- Flow-over, heated water bath
- Heated-wire circuits (With or without wick)
What happens when you put the flow of oxygen too high or too low?
- TOO HIGH:
- Valve sticks
- TOO LOW:
- not enough carrier to deliver the anesthetic & your patient could become hypoxic!
- At low flow rates, insufficient turbulence is generated in the vaporizing chamber to advance the vapor molecules upwardly
What is the side effect/complications of the supine position?
- 1. almost no perfusion gradient exists in the arterial tree between the heart and either the cerebral or lower extremity vessels
- 2. Venous return is increased
- 3. Increase preload, HR, and myocardial contractility
- 4. CO and BP transiently increased
- 1. FRC and TLC significantly reduced
- 2. Increased perfusion of dependent (posterior lung segments)
What are the side effects/complications of Trendelenburg?
- 1. Decreased FRC r/t the ° of tilt
- 2. Movement of the ETT
- 3. Increased risk of aspiration
What are the side effects/complications of prone position
- 1. CO decreased
- 2. Extreme flexion of the hips can occlude femoral vessels and decrease venous return & increase the risk of compartment syndrome
- 3. Increased venous pooling
- 4. Compression of the abdomen may decrease preload
- 1. Compression of abdomen & thorax ↓ total lung compliance and ↑WOB
2. Proper positioning can retain nearly normal pulmonary compliance
What are some complications of the prone position?
- 1. eye injury
- 2. breast injury
- 3. neck injury
- 4. facial edema
- 5. VAE
- 6. Neuro injury (brachial plexus, spinal cord, & thoracic outlet syndrome)
What are some SE and complications of the sitting position?
- 1. Hypotension
- 2. CO, SV decreases while HR and SVR increase to maintain a steady MAP
- 3. Cerebral blood flow decreases w/high head elevation
- 4. Renal blood flow decreases
- 1. FRC and forced VC are within normal parameters.
What are some SE and complications of the lithotomy position?
- 1. Nerve injury
- a. peroneal nerve
- b. femoral & obturator nerve
- c. sciatic nerve
- d. saphenous nerve
- 2. Back pain
- 3. compartment syndrome
What are some complications w/the lateral position?
- 1. hypotension w/flexion or use of kidney rest
- 2. Decreased ventilation & increased perfusion of dependent lungs = V/Q mismatch
- 2. injury to brachial plexus, ulnar, and peroneal nerves
- 4. damage to dependent eye
What causes ulnar nerve problems?
- Compression between medial epicondyle of humerus; pronated arms; arm hangs over edge
- RESULT: "Claw hand" or numb pinky
What causes brachial plexus injury?
- excessive abduction >90°, improper shoulder/wrist braces, sternum spreading, stretch of neck by extreme rotation
- injury may occur if arm falls off the armboard, hyperextended & abducted at level of the shoulder
- RESULT: weakness, inability to flex
What causes injury to the radial nerve?
- arm slips off of the table, pressure on bar of either screen, pressure on edge of bed
- RESULT: wrist drop, weak thumb, numbness of dorsal surface
What causes damage to the medial nerve?
- IV damages antecubital fossa
- RESULT: inability to oppose thumb
What causes damage to the femoral nerve?
- Excessive angulation at thigh or retractor compressing pelvic brim
- RESULT: Loss of hip flex or knee extension, numbness of superior thigh
What causes damage to the common peroneal nerve?
- compression head of fibula & metal bar, this happens a lot in lithotomy position
- RESULT: foot drop
What causes damage to the sciatic nerve?
- Too much leg rotation or knee extension
- RESULT: foot drop, weak lower leg
What causes damage to the obturator?
- Damage during difficult forceps delivery or excessive flexion of thigh to groin
- RESULT: inability to adduct leg; loss of sensation to medial thigh
What causes compartment syndrome?
results from hemorrhage into a closed space following a vascular puncture or prolonged venous outflow obstruction, particularly when associated w/hypotension. In severe cases, this may lead to muscle necrosis, myoglobinuria, & renal damage unless the pressure within the compartment is relieved by surgical decompression (Fasciotomy)
What three positions can cause compartment syndrome?
- 1. Extreme flexion of the hips in prone position can occlude femoral vessels and decrease venous return & increase the risk of compartment syndrome
- 2. Lithotomy position *biggest factor per Morgan
- 3. Lateral position
How do we prevent compartment syndrome?
maintain perfusion pressure and avoid external compression
What is wrist drop?
- Injury to radial nerve results in wrist drop
- Inability to extend metacarpal joints and pharyngeal joints.
- Weakness in abduction of the thumb
- Decreased sensation in the middle, ring, and first finger
Describe pulmonary perfusion in the lateral position
Dependent lung is under ventilated because it is compressed by abdominal contents and weight of mediastinum. Because of gravity the dependent lung receives more blood flow, this causes a V/Q mismatch and can result in hypoxemia.
Absorbents work via _______ process.
CHEMICAL. don't need to know the process, just need to know it's chemical not physical
In the absorbent canister, the granules should be filled allowing ___% to be airspace or ____x TV
50% airspace or 2x TV (don't want to have them overpacked)
What happens if the absorbent canister is too loosely packed or packed with too large of particles?
- Increased incidence of channeling.
- A preferential passage of gas through the canister via path of least resistance, leads to less absorption of CO2
- *Want to balance area of absorbent and resistance to airflow (resistance to patient breathing), smaller particles = more surface area for absorption BUT causes more airflow resistance
What are some safety features of vaporizers?
- Temperature compensated
- Works independently of atmospheric pressure
- Vaporizers are color coded and have keyed filler systems
- Desflurane vaporizer is different
- Can't turn on more than one volatile at a time (except N2O)
- Transport valve that protects against tipping
Describe the temperature compensating device (safety feature of vaporizer)
Increased temp = increased VP and more delivered anesthetic to patient so there is a bi-metallic strip that will move to the RIGHT with INCREASED temperature so less gas will flow through the vaporizer and more will flow straight into the bypass chamber
Vaporizers work independently of atmospheric pressure, how is this a safety measure?
- when ambient pressure is lower at higher altitudes it results in a higher partial pressure of gas (Ex: VP is 100 then at sea level pp is 100/760 but at higher altitudes the pp is 100/550, so it equals a higher pressure)
- * When not independent of atm. pressure, there was an equation and you would change the dialed setting
How does the desflurane vaporizer work?
It's VP is near atmospheric so you need a pressurized vaporizer and it needs to be heated beacuse the MAC of Desflurane is high so you give high concentrations and these high concentrations cause cooling from latent heat of vaporization
Which is the only vaporizer that alarms when the volume of the agent is getting low?
What happens if you put the wrong anesthetic agent in the wrong vaporizer?
It will change the concentration of the volatile agent you are trying to give (Think of VP of the gas that should be in the vaporizer vs the one you put it)
If a gas with a higher VP is put into a vaporizer that normally contains a gas with a lower VP, what will happen?
- HIGHER concentration of gas is delivered to the patient than what is dialed
- (EX: Halothane VP 241 and put into Sevo vaporizer, sevo's VP is 170, get a higher delivered concentration than what is dialed)
What happens if you put Sevo (VP of 170) into the Iso vaporizer (VP 238)?
Lowered delivered concentration than what is dialed
What are the National Institute of Occ. Safety and Health recommendations for non-scavenged inhalation gases and nitrous waste levels that are acceptable of ether agents ALONE? (Halogenated alone and N2O alone)
- Halogenated alone: 2 (TWA)
- N2O alone: 25 (TWA)
- TWA= time weighted average
What are the National Institute of Occ. Safety and Health recommendations for non-scavenged inhalation gases and nitrous waste levels that are acceptable of ether agents combined? (Halogenated and N2O)
- Halogenated agent = 0.5 TWA
- N2O = 25
- (TWA = time weight average)
What are the National Institute of Occ. Safety and Health recommendations for non-scavenged inhalation gases and nitrous waste levels that are acceptable in Dental facilities (N2O alone)?
- N2O = 50 TWA
- (time weighted average)