Unit 6: Equipment & Monitors Flashcards
What components are present in the high pressure system of the anesthesia machine? What is the gas pressure in this region?
-Hanger Yoke
-Yoke block with check valves
-Cylinder pressure gauge
-Cylinder pressure regulators
Gas Pressure = Cylinder Pressure
What components are in the intermediate pressure system of the anesthesia machine?
Begins at the pipeline and ends at the flowmeter valve
-pipeline inlets
-pressure gauges
-ventilator power inlet
-oxygen pressure failure system
-oxygen second stage regulator
-oxygen flush valve
-flowmeter valve
Gas Pressure = 50 psi (if using pipeline) and 45 psi (if using tank)
What components are present in the low pressure system of the anesthesia machine?
Begins at the flowmeter tubes and ends at the common gas inlet
-flowmeter tubes (Thorpe Tubes)
-vaporizers
-check valves (if present)
-common gas outlet
Gas Pressure = slightly above atmospheric pressure
What are the 5 tasks of oxygen in the anesthesia machine?
- O2 pressure failure alarm
- O2 pressure failure device (failsafe)
- O2 flowmeter
- O2 flush valve
- Ventilator drive gas (if pneumatic bellows)
What is the pin index safety system?
PISS prevents inadvertent misconnections of gas cylinders
-pin configuration on each hanger yoke assembly is different for each gas, making unintended connections of the wrong gas unlikely
**presence of more than one washer between the hanger yoke assembly and the stem of the tank may allow bypassing of the PISS
What is the diameter index safety system?
DISS prevents inadvertent misconnections of gas hoses
-each hose and connector are sized and threaded for each individual gas
What are the max pressures and volumes for cylinders that contain air, oxygen, and nitrous oxide?
Air: 625 L – 1900 psi
Oxygen: 660 L – 1900 psi
Nitrous Oxide: 1590 L – 745 psi
The bourdon pressure gauge on an O2 cylinder reads 500psi. If the flow rate is 4 L/min, how long will this cylinder provide oxygen to the pt?
What is the equation?
Step 1: How much O2 is in the cylinder?
[tank capacity (L) / full tank pressure (psi)] x [contents remaining (L) / gauge pressure (psi)]
Step 2: How long will it last?
contents remaining (L) / FGF rate (L/min)
Example:
660L / 1900psi = X/500 psi = 174 L
174L / 4L per min = 43.5
Is it ever safe to use an O2 cylinder in the MRI suite?
Never take a cylinder into the MRI scanner unless it is made of a non-magnetic material (i.e. aluminum)
An MRI safe cylinder will have two colors: most of the tank is silver, and only the top is the color that signifies the gas it contains
What are the 3 safety relief devices that prevent a cylinder from exploding when the ambient temp increases?
- A fusible plug made of Wood’s metal (melts at elevated temps)
- A frangible disk that ruptures pressure
- A valve that opens at elevated pressures
never expose a cylinder to temps higher than 130F (57*C)
Give an example of how the O2 pressure failure device (failsafe) might permit the delivery of a hypoxic mixture
The failsafe device responds to pressure (not flow) –> if there is a pipeline crossover, the pressure of the second gas will produce pressure to defeat the failsafe device
Give 4 examples of how the hypoxia prevention safety device (proportioning device) might allow the delivery of a hypoxic mixture
- Oxygen pipeline crossover
- Leaks distal to the flowmeter valves
- Administration of a third gas (helium)
- Defective mechanic or pneumatic components
What is the difference between the oxygen pressure failure device and the hypoxia prevention safety device?
Oxygen Pressure Failure Device = Fail-safe Device
-shuts off and/or proportionately reduces N2O flow if O2 pressure drops below 20psi
Hypoxia Prevention Safety Device = Proportioning Device
-prevents you from setting a hypoxic mixture with the flow control valves
-limits N2O flow to 3x O2 flow (N2O max = 75%)
Describe the structure and function of the flowmeters
Annular space = area between the indicator float and the side wall of the flow tube – narrowest at the base and widest at the top
-this “variable orifice” provides a constant gas pressure throughout a wide range of flow rates
-Laminar flow is dependent on gas viscosity (Poiseuille)
-Turbulent flow is dependent on gas density (Graham)
What is the safest flowmeter configuration on the anesthesia machine?
O2 flowmeter should always be furthest to the RIGHT
-a leak will allow O2 to escape the low-pressure system which could result in the delivery of a hypoxic mixture
-O2 should be closest to the manifold outlet (right side) because if a leak occurs in any other flowmeter, it won’t reduce the FiO2
How do you calculate the FiO2 set at the flowmeter?
FiO2 = (Air flow rate x 21) + (Oxygen flow rate x 100) / Total flow rate
Ex: air at 1 L/min and O2 at 3 L/min
(1 x 21) + (3 x 100) / 4 = 80.25 (80%)
How do you determine the total tidal volume that will be delivered to the patient?
Vt total = Vt set on ventilator + FGF during inspiration
Step 1: Convert FGF from L/min to mL/min
- 4 L/min = 4000 mL/min
Step 2: Multiply FGF by I:E ratio
- 4000 mL/min x (1/3) = 1300 mL/min
Step 3: Calculate tidal volume per breath
- 1300 mL / 10 breaths per min = 133 mL
Step 4: Add volume set on ventilator to FGF during inspiration
- 500 + 133 = 633 mL tidal volume
- (4000 x 1/3) / 10 = 133 mL + 500 mL = 633 mL
When using a ventilator that couples fresh gas flow to tidal volume, what increases and decreases the tidal volumes delivered?
Tidal Volume Increases with:
- decreased RR
- increased I:E ratio (1:2 to 1:1)
- increased FGF
- increased bellows height
Tidal Volume Decreases with:
- increased RR
- decreased I:E ratio
- decreased FGF
- decreased bellows height
**when using a ventilator that couples FGF to tidal volume – making nearly any change on the vent settings will ultimately impact the Vt delivered to the pt
What is the vaporizer splitting ratio?
Modern variable bypass vaporizers split fresh gas into 2 parts:
- Some fresh gas enters the vaporizing chamber and becomes 100% saturated w/ a volatile agent
- The rest of the gas bypasses the vaporizing chamber and doesn’t pick up any volatile agent
-before leaving the vaporizer, these two fractions mix, and this determines the final anesthetic concentration exiting the vaporizer
What is the pumping effect?
Pumping effect can increase vaporizer output
-anything that causes gas that has already left the vaporizer to re-enter the vaporizing chamber can cause the pumping effect
-generally due to positive pressure ventilation or the use of the O2 flush valve
*modern anesthesia machine design mitigates this risk
Describe the variable bypass vaporizer. What are examples?
-Splitting Ratio = variable bypass (vaporizer splits fresh gas)
-Method of Vaporization = flow over
-Temp Compensation = automatic
-Calibration = agent specific
-Position = out of circuit
-Elevation Compensation = yes
Ex: Datex-Ohmeda Tec 4, 5, 7AU – Aladin – Drager Vapor 19, 2000
Describe the injector-type vaporizer. What are examples?
Desflurane
-Splitting Ratio = dual circuit (fresh gas is not split)
-Method of Vaporization = gas/vapor blender (heat creates vapor that is injected into the fresh gas)
-Temp Compensation = electronically heated to 39*C
-Calibration = agent specific
-Position = out of circuit
-Elevation Compensation = no
Ex: Datex-Ohmeda Tec 6 – Drager D-Vapor
What does the oxygen analyzer measure, and where is it located?
Monitors oxygen concentration (not pressure)
-the only device downstream of the flowmeters that can detect a hypoxic mixture
What 2 things must you do in the event of an oxygen supply line crossover?
- Turn ON the oxygen cylinder
- Disconnect the pipeline oxygen supply **KEY STEP
Pressing the oxygen flush valve exposes the breathing circuit to ___ O2 flow and ___ O2 pressure
Oxygen Flow = 25-75 L/min
Oxygen Pressure = 50 psi (pipeline pressure)
What are the two risks of pressing the O2 flush valve?
Barotrauma: pressing during inspiration
Awareness: gas from flush valve doesn’t pass through the vaporizers, excessive use adds gas to the breathing circuit that doesn’t contain a volatile diluting the partial pressure of the agent
Describe the function of the ventilator spill valve in relation to using the O2 flush valve
Inspiration:
1. drive gas compresses bellows
2. drive gas closes spill valve
3. fresh gas from the ventilator goes to the pt
Expiration:
1. expired gas refills the bellows
2. bellows fill completely
3. when circuit pressure >2-4 cmH2O expired gas is directed through the spill valve to the scavenger
What is volume controlled ventilation?
Delivers a preset tidal volume over a predetermined time
-tidal volume is fixed so the inspiratory pressure will vary as the patient’s compliance changes
-inspiratory flow is held constant during inspiration
Fixed: tidal volume, inspiratory flow rate, inspiratory time
Variable: peak inspiratory pressure
What is pressure control ventilation?
Delivers a preset inspiratory pressure over a redetermined time
-pressure and time are fixed so tidal volume and inspiratory flow will be variable and dependent of the pt’s lung mechanics
-if airway resistance rises or lung compliance decreases, then tidal volume will suffer
Fixed: peak inspiratory pressure and inspiratory time
Variable: tidal volume and inspiratory flow
What conditions can alter the tidal volume delivered to the patient during pressure control ventilation?
Tidal Volume Decreases With:
-decreased compliance (pneumoperitoneum or Trendelenburg position)
-increased resistance (bronchospasm or kinked ETT)
Tidal Volume Increases With:
-increased compliance (release of pneumoperitoneum or going from trendelenburg to supine)
-decreased resistance (bronchodilator therapy or removing airway secretions
What is the best action to take when the soda lime becomes exhausted in the middle of a surgical procedure?
If you can’t replace the CO2 absorbent –> increase the fresh gas flow to convert the circle system into a semi-open configuration
What is desiccation and how does it apply to soda lime?
-Water is required to facilitate the reaction of CO2 with Co2 absorbent – the granules are hydrated to 13-20% by weight
-Desiccation = when the absorbent is devoid of water
In the presence of halogenated anesthetics, desiccated soda lime increases the production of carbon monoxide (Des > Iso»»Sevo) and compound A in presence of Sevo
*carbon monoxide can cause carboxyhemoglobinemia
*compound A may cause renal dysfunction
What are the 7 ways to monitor for disconnection of the breathing circuit?
Via pressure, volume, ETCO2, and your own vigilance
- Precordial stethoscope
- Visual inspection of chest rise
- Capnography
- Respiratory volume monitors
- Low expired volume alarm
- Low peak pressure alarm
- Failure of bellows to rise with an ascending bellows
What are the OSHA recommendations regarding inhalation anesthetic exposure for health care workers in the OR?
Halogenated agents alone <2 ppm
Nitrous Oxide alone <25 ppm
Halogenated agents + Nitrous Oxide <0.5 ppm and 25 ppm respectively
What are the four types of breathing circuits? List examples of each
Open: non-rebreathing, no reservoir
-insufflation, simple face mask, nasal canula, open drop
Semi-Open: non-rebreathing, has a reservoir
-mapleson circuit (FGF dependent on design) and circle system (FGF > minute ventilation)
Semi-Closed: partial rebreathing, has a reservoir
-circle system (FGF < minute ventilation)
Closed: complete rebreathing, has a reservoir
-circle system (very low FGF and APL closed)
What are the 4 phases of the normal capnograph?
Phase I (A-B): exhalation of anatomic dead space
Phase II (B-C): exhalation of anatomic dead space + alveolar gas
Phase III (C-D): exhalation of alveolar gas
Phase IV (D-E): inspiration of fresh gas that does not contain CO2
What is the cause of the following abnormal CO2 waveforms?
How do you determine the appropriate distance to thread a central line or PA catheter?
- You must know the distance from the site of entry to the vena cava junction
- You must know the distance from the vena cava junction to where the catheter’s tip should be placed
- Add these two numbers to determine this distance from the insertion site to the tip of the catheter
What are the 3 waves and 2 descents on the CVP waveform? What does each signify?
A wave = right atrial contraction
C wave = tricuspid valve elevation into right atrium
X descent = downward movement of contracting right ventricle
V wave = right atrium passive filling
Y descent = right atrium empties through open tricuspid valve
How does the waveform change as the PA catheter is guided into position? What are the normal pressures at each step?
What are the different types of EEG waveforms?
