Condensation
The change of state from a gas to a liquid
Vaporization
The change of state from a liquid to a gas
Vapor pressure
the pressure caused by the collisions of particles in a vapor with the walls of a container above a liquid
When is vapor pressure exerted?
When the amount of particles leaving the liquid equals the amount of particles entering the liquid (dynamic equilibrium)
What is vapor pressure dependent upon?
Temperature, vapor pressure of the liquid, and partial pressure of the vapor above the liquid.
NOT ambient pressure!
Atmospheric pressur
the pressure exerted by atoms and molecules in the atmosphere surrounding Earth, resulting from collisions of these particles with objects
Volatility
a measure of how readily a substance vaporizes
Volatility is directly correlated with what?
The vapor pressure of the liquid.
At a given temperature, a substance with a higher vapor pressure vaporizes _______________ than a substance with a lower vapor pressure?
More readily
Sublimation
A change directly from the solid to the gaseous state without becoming liquid
Example of sublimation
dry ice (solid carbon dioxide)
Atmospheric pressure boiling point (normal boiling point)
Temperature at which a liquids vapor pressure is equal to the surrounding atmospheric pressure
The higher the vapor pressure (des), the higher the volatility, and the ____________ the normal boiling point of the liquid.
Lower
How does elevation affect atmospheric pressure and boiling point?
As elevation increases, atmospheric pressure and boiling point decrease
Synopsis of above
As temperature increases, more particles have enough energy to escape to the gas phase. This increases the vapor pressure. When the vapor pressure equals atmospheric pressure, the liquid boils.
Two classifications of vaporizers?
Variable bypass and injector
Variable bypass
flow over, automatic temp compensation, compensates for elevation changes, ADU Microprocessor controls output monitoring. Calibarated for CONCENTRATION and are agent specific. OUT OF BREATHING CIRCUIT (TE6 also out of the breathing circuit).
Injector
gas-vapor blender, heated to 39 C, does not compensate for elevation
Two vaporizers specific for desflurane?
GE-Datex-Ohmeda Tech 6 and Drager D-Vapor
Splitting ratio
-ratio of fresh gas flow that passes through the vaporization chamber, compared to the gas that does not
the splitting ratio is unique to each vaporizer
Said another way:
Gas entering vaporizer chamber DIVIDED by FGF.
Note: In variable bypass vaporizer th
Can any vaporizer be used for any anesthetic agent?
No. Vaporizers function differently depending on the physical characteristics of the volatile agents.
Temperature compensation of vaporizers?
As the vaporizer cools, more gas is directed into the vaporizing chamber to maintain the same concentration of anesthetic
Safety systems for filling the anesthetic vaporizer chamber?
Key system (notches) and funnel system.
Anesthetic colors:
Red: halothane
Blue: desflurane
Purple: isoflurane
Orange: enflurane
Yellow: sevoflurane
Tec 6 Vaporizer
Anesthetic agent is heated to 39 C, held at 1500 mmHg (approx. 2 atm)
Desflurane near boiling point at room temperature
(660 mmHg)
Anesthetic chamber can be filled while the machine is running.
What extremes can affect accuracy of modern vaporizers?
High or low FGF, temperature, back pressure from breathing circuit or vent
What primarily affects depth of anesthesia?
Partial pressure NOT concentration of anesthetic agent/ MAC actually refers to the partial pressure created by the concentration
Back pressure?
Back pressure can effect gauges and cause more FGF to enter the vaporizer chambers= higher volatile anesthetic concentration
Vaporizers not affected by altitude
Fluotec Mark II, Dragger, Aladin
Flowmeters at altitude
Decreased barometric pressure, causes lower gas density, possible for hypoxemic mixture
Effects of altitude
Less potent anesthetics, standard flow meters read lower than actual flows, lower boiling point for anesthetic agents, and increased risk for explosions from static electricity.
MAC
Mean alveolar concentration: the concentration of the vapor (measured as a partial pressure) that prevents the reaction to a standard surgical stimulus in 50% of subjects
MAC (concentration or partial pressure?)
% concentration is appropriate but partial pressure (mmHg) of the inhaled anesthetic is most important physiologically
Vapor pressure of sevoflurane
170 mmHg - yellow
Vapor pressure of enflurane
170 mmHg (actually 172) - orange
Vapor pressure of isoflurane
240 mmHg - purple
Vapor pressure of halothane
240 mmHg (actually 244) - red
Vapor pressure of desflurane
670 mmHg (actually 669) - blue
Partial pressure of oxygen
760 mmHg
If Isoflurane is added to a flask of oxygen, what is the % Oxygen and % Isoflurane in the flask above the liquid?
The vapor pressure of Iso is 239 mmHg. The partial pressure of Oxygen after the Iso is added is (760-239 mmHg)= 521 mmHg
%O2= 521/760= 68.6%
%ISO= 239/760= 31.4%
If sevoflurane is added to isoflurane vaporizer, will the delivered concentration be higher or lower than the dial setting?
LOWER: lower vapor pressure agents placed in vaporizer designed for a HIGHER vapor pressure agent, results in lower concentrations of agent delivered to patient than indicated by the dial setting.
If Halothane is added to an Enflurane Vaporizer, will the delivered concentration be higher or lower than the dial setting?
The delivered concentration will be higher than the dial setting because halothane (244) has a higher vapor pressure than enflurane (172).
1 atm= ? mmHg= ? psi= ?kPa= ?Pa
1atm = 760 mmHg= 14.7 psi= 101 kPa= 101,325 Pascals
What kind of gauge measures cylinder pressures?
Bourdon gauge
When the Bourdon gauge pressure reads zero, what is the pressure in the cylinder?
The pressure in the cylinder is the same as atmospheric. (Gauge pressures measure the pressure relative to atmospheric pressure.)
What is critical temperature?
The temperature above which a gas cannot be liquefied, regardless of the pressure applied.
Critical temperature of N2O?
39.5 C (can be compressed and stored at room temp)
What explains why a compressed gas cylinder cools (and condensation forms) after opening the valve?
Joule-Thompson effect: a compressed gas is allowed to escape freely into space, the process is adiabatic, and cooling occurs. "COOL JOULE
High pressure system components
Beginning and end? Pressures?
1.) Hanger yoke
2.) Yoke block w/ check valves
3.) Cylinder pressure gauges
4.) Cylinder pressure regulators
***starts at the cylinder and ends at the pressure regulators (50-2000psi)
Intermediate pressure system
Beginning and end? Pressures?
1.) Pipeline inlets
2.) Pressure gauges
3.) O2 pressure failure device
4.) O2 second stage regulator and FLUSH VALVE
5.) Ventilator power inlet/ O2 flowmeter VALVES (needle)
***starts at pipelines and ends at the flowmeter valves (45-50 psi)
Low pressure system
Beginning and end? Pressures?
1.) Flowmeter tubes
2.) Vaporizers
3.) Check valve
4.) Common gas outlet
***starts at flowmeter tube and ends at the common gas outlet (> 14.7 psi)
5 Tasks of O2
O2 pressure failure ALARM
O2 pressure failure DEVICE (fail-safe)
O2 flowmeters
O2 flush valve
Ventilator driving gas
O2 pressure failsafe device functions off ____________? When will it alarm and why?
Pressure. Less than 28-30 psi because O2 tank is empty, pipeline pressure drops, or O2 hose becomes disconnected
Hypoxia prevention safety device (proportioning system) functions off __________________ of gaseous agents? When will it alarm and why?
Percentages. Prevents you from setting a hypoxic mixture, limits N2O to approximately 3x the O2 flow. Alarms when N2O is increased > 75%. (Ensures FIO2 is at least 23-35%)
When proportioning devices cant prevent a hypoxic mixture?
1. oxygen pipeline crossover
2. leaks distal to the flowmeter valves
3. administration of a third gas
4. defective mechanic or pneumatic components
Oxygen analyzer
Resides on the inspiratory limb, can detect pipeline crossover and leaks in breathing circuit
What is the first device to detect an oxygen pipeline crossover?
A. Failsafe device
B. Proportioning device
C. Oxygen analyzer
D. Pulse oximeter
C.
DISS
Diameter index safety system: used to decrease inadvertent misconnections of gas pipelines
PISS
Pin index safety system: used to decrease inadvertent misconnection of gas cylinders
E cylinder of N2O? PISS configuration?
1600L/745 psi.
PISS: 3-5.
E cylinder of O2? PISS configuration?
660L/2,000 psi
PISS: 2-5.
E cylinder of air? PISS configuration?
630L/2,000 psi
PISS: 1-5.
Cylinder safety
Protect the valve, upright position and secured, if no replacement cylinder USE A YOKE PLUG to prevent leaks, remove plastic cover, do not oil, use only one washer, tested q 5 years, q 10 with special permit (5 pointed star)
Which agency transports cylinders?
Department of Transportation
Which agency sets expectations for what is needed for the anesthesia workstation?
What is the standard?
Components?
American Society of Testing and Materials (ASTM)
ASTM F1850
30 min backup battery, pressure in breathing circuit is limited to 125 cm/H2O, electrical supply chord must be nondetachable, O2 flush valve at 35-75L/min and does not pass vaporizers, checkout c
OSHA (Occupational Safety and Health Administration) ppm guidelines
No more than 25ppm of N2O, 2ppm of halogenated agents, or 0.5 ppm if halogenated agent is combined with N2O
CO2 absorber equation?
CO2 + H2O = H2CO3 (carbonic acid)
H2CO3 + NaOH (sodium hydroxide) = Na2CO3 (sodium carbonate) + H20 heat (energy)
Na2CO3 + Ca(OH)2 (calcium hydroxide) = CaCO3 (calcium carbonate) + NaOH
At what pH does the granules change color?
10.3
Water content on granules of CO2 absorber?
How to prevent channeling of gases through the CO2 absorber?
15 % (high fresh gas flow dries out CO2 absorber faster: turns purple/blue)
Pack granules in a uniform way to eliminate areas of lower resistance (equal resistance over and through all granules is desired) = 4-8 method (4-8 mesh granules are used which ar
Two problems with the CO2 absorber?
Exhaustion and desiccation.
What is a 4-8 mesh strainer for soda lime?
BEST option for CO2 absorption, produces even distribution of gases! (4-8 openings per inch)
Average CO2 production of an anesthetized adult?
12-18 L/HR
Disadvantage of hanging bellows (descending bellows)?
If the patient becomes disconnected from the circuit, gravity will still pull the bellows down (imitating the patient expiring)
With ascending bellows, if the patient becomes disconnected, the bellows will not rise- very obvious the patient is disconnecte
Advantages of piston driven bellows?
Disadvantages?
Quiet, no PEEP, precise volumes, requires power source (no driving gas- ideal in pipeline failure) and fewer compliance losses.
No visual representation, harder to hear, cannot accommodate non-rebreathing systems.
Machines without gas decoupling?
10 breaths per minute, 500 ml per breath, I:E ratio 1-2.... Minute ventilation=5L/minute
Old machines without decoupling.... FGF are not accounted for!
FGF at 3L/min (with I:E ratio 1-2) 1L is added to inspiration and 2 L are expired.
Minimizing exposure for OR staff
Minimizing pollution
Good mask seal, maintaining scavenger, refilling vaporizer container appropriately, packing oral airway if cuff leak is present, disposal of gases through the scavenger system, use low FGF, turning off anesthetic gas before suctioning patient, do not turn
Most important part of the scavenging system??
Two types?
Interface
1.) OPEN(all modern systems)- if suction fails, waste enters the atmosphere/ OR. NO POSITIVE OR NEGATIVE VALES NEEDED; MUST HAVE SUCTION (therefore it cannot be "passive"). TOO LITTLE SUCTION? THEN O.R personnel GETS SLEEPY. TOO MUCH SUCTION? No
Common sources of low pressure in breathing circuit
1. Disconnect at Y-piece
2. Defective CO2 canister
3. CO2 absorbent granules if they have recently been changed?...
4. Malfunctioning bag/vent switch?
5. Incompetent ventilator spill valve (Vt goes to scavenger and not pt)
6. Leaks in the breathing circui
Best action if you are unable to ventilate due to low pressure?
Ventilate pt with Ambu-bag and O2 tank.
What kind of vaporizers are approved to administer Desflurane? (2 kinds)
1. Ge Datex Ohmeda Tec-6
2. Drager-D
What are the anesthesia tanks made out of?
What are the vaporizers made out of?
Most anesthesia gas tanks are made out METAL (unless MRI Safe than aluminum)
Vaporizers are made out of COPPER. Copper has a high thermal conductivity and helps to stabilize the temperature in of the volatile anesthetics
What are the first 3 steps you take in the event your machine alarms LOW PRESSURE?
1. Turn 02 tank on FULLY
2. Disconnect pipeline pressure
3. Consider low gas flows AND Manual ventilation
(The first 3 steps for suspected PIPELINE CROSS OVER are exactly the same
as long as
02 rises as expected... {if not ambu bag them})
The power just went out...what features on your gas machine are still going to work?
1. Your flowmeters
2. The scavenging
3. The vaporizers**
4. The Manual and SPONTANEOUS assisted ventilation
What leads to
reduced vaporizer output
on the variable bypass vaporizer? (2 things. Hint: related to flow rates)
Flows >15L/min or <2Lmin (extremes in FGF's) Other things that effect Vaporizer output? = TEMP & BACK PRESSURE FROM BREATHING CIRCUIT
You forgot to fill your vaporizer before the case started (whoops). Your using Desflurane with a FGF of 10L/min and you have 2mL left and 1 hr left in the case. Do you have enough des to finish the case?
Yes. Just enough. You need 1.8mL
(Check me on this on the apex variable bypass vaporizer overview page).
For this know your MACS of your gases:
Des-6% (FYI Vapor pressure: 660 mmhg)
Sevo-2% (FYI Vapor pressureL 157 mmgh)
Iso-1.15 (FYI Vapor Pressure (238
About how many mL on average can a variable bypass vaporizer hold?
200-300mL
All modern vaporizers will increase agent concentration when you turn clockwise OR counter clockwise?
Dial turned
counter-clock wise
=increase agent concentration
Your using a semi-closed system...you begin notice your inspired CO2 on the monitor reaching more than 1 -3mm Hg. There is nothing wrong with CO2 absorber. What do you do?
The patient is rebreathing too much. The fresh gas flow should be increased 5-8L/min (theoretically converting patient to a semi open system)
You have an increase in your INSPIRED AND EXPIRED Co2 on the capnograph but no changes in ETCO2 morphology....what the deal? What do you need to investigate?
See page 252 Nagel figure 16.35. This is incompetent EXPIRATORY valve. How do you fix this?- take it out and dry it etc....WHAT IF YOU CANT FIX IT???? Convert CONVERT TO SEMI OPEN SYSTEM!
You have an increase in your INSPIRED AND EXPIRED Co2 on the capnograph with a prolong inspiratory downstroke? What this?
Incompetent INSPIRATORY VALVE. 252 nagel fig 16.34. How do you fix this?- take it out and dry it etc....WHAT IF YOU CANT FIX IT???? Convert CONVERT TO SEMI OPEN SYSTEM!
How can you avoid
hypercarbia
in the event you are faced with increased dead space? (Increased dead space from a say a longer breathing circuit)
Increase your MINUTE VENTILATION
Alveolar ventilation = min ventilation - deadspace
(Va=Ve-Vd)
What are two reasons that the non breathing systems (Maplesons/Bain) have such lower resistance?
1) all of these systems lack unidirectional valves
2) CO2 absorber is NOT USED here. Rather exhaled CO2 goes to a reservoir bag
What are the safety concerns with the Bain Breathing system? And how to you mitigate those concerns?
The Bain (aka modified maple sons D) breathing system can KINK in the INNER TUBING (the inside is where FGF is delivered) you should check this by performing the Pethick test.
The pethick tests checks the integrity of the inner tube. If you check and rese
Name the RXN's that take place in the CO2 absorber. 1, 2, and 3.
What are the final products of these rxns?
1.C02+H20
<>
H2CO3
2.H2CO3+NaOH
<>
Na2CO3+H20+Energy
3. Na2CO3+ Ca(OH)2
->
CaCO3 (reduction) + NaOH
How can you reduce "Channeling" in the CO2 absorber?
SHAKE when in changing.
This "channeling" occurs as there will be lower resistance on the inside edge of the canister therefore outside edge will exhaust quicker. So be sure to SHAKE canister when you change it out to tightly pack those 4-8 mesh size ball
What is the actual function and purpose of the "interface" in the scavenging system?
This is the most important component to the scavenger as it PROTECTS THE PATIENT from a build up of positive and negative PRESSURE.
The scavenger must only remove an amount that is EQUAL to FGF MINUS vol of gas lost due to patient oxygen consumption (02 c
In event of emergency -what gas machine checks are ESSENTIAL?
1.Suction
2.Back up means of ventilation (Ambu bag)
3. High pressure leak test of breathing circuit before placing mask on patient
If you have a leak in the low pressure system...what are your concerns for the patient? (2 major ones)
1. Hypoxic Mixture
2. Patient awareness
What monitors will detect a patient discontent?
-ETCO2 (carbon dioxide)
-Respirometer (monitors exhaled VOLUME)
-Airway pressure monitor (senses low pressure)
How many minutes will it take to achieve 1 unit of exchange (63%) in a 12L system at 2L/min of FGF?
6 min for 63%
Remember some is still flowing out of the "sink" that's why its 6 min
1 unit of exchange (63%)
2 unit (85%)
3 units (95%)
what is your Fio2 if you have Air set to 3L/min and 02 set to 4L/min?
66%
What determines LAMINAR flow?
What determines Turbulent flow?
VISCOSITY (Poiseillus Law)
DENSITY (Grahams Law)
This is important when you think about why a very low dense gas like helium is used to promote laminar flow in asthmatics (Heloix)
1cmH20 is how many mmHg?
What is 760mmHg in PSI?
14.7PSI
In what two scenarios would the vaporizer output be INCREASED with DES?
1.Hyperbaric chamber
&
2. Low Altitudes (=higher pressure & requires Lower dial setting)
What are the actual components that are going INTO the bellows? (2 things)
SUM of vT during EXHILARATION PLUS flowmeter flow
(Remember-this gas is considered "outside" of the breathing circuit)
The 02 analyzer on your patient monitor is all of a sudden reading abnormally HIGH? Whats the likely cause? (Note your using a machine that uses 02 as its drive gas)
Leak" in the bellows.
If AIR was the driving gas you would see a DECREASE in the 02 analyzer.
In PCV mode your
pressure
is
set
to deliver it to the patient over a preset time of course... However-this patient has a decreased compliance/airway resistance and is causing the Tidal Volumes (vT) to decrease because of it. How do you overcome this to en
Higher Inspiratory Flows!!
With Consideration to lung compliance, which mode of ventilation (VCV or PCV) would be beneficial for a COPD patient?
COPD= low compliance (high compliance would be emphysema)
The best mode between the two for low compliance is PCV.
PCV is useful in "low compliance states".
Think..if you blasted a stuff lung with a bunch of PRESET VOLUME you would cause volutrauma becaus
How do you perform a high leak test
Close the APL valve pressurize assessment of 30 cm of water and observe airway resistance pressure is it constant?
What works when the anesthesia machine is turned off
Pressure gauges
Monitors
O2 FLUSH VALVE
What works when the anesthesia machine is turned on
...
Vaporizers are good conductors of thermal energy
The metals that are made in the vaporizer are made with high thermal conductivity messengers that there is a conduit of heat so heat required for vaporization is constantly restored from the environment in the rate of vaporization in the volatile anesthet
What determines the depth of anesthesia
The partial pressure of the vapor or volatile a anesthetic in the brain NOTTTTTTTTT the concentration
Can to use a piston with a non rebreathing system??
Nuppppe.
�Cannot accommodate non-re-breathing systems
What two factors increase the risk of compound a production
desiccated soda lime and sevo