Principles of the Anesthesia Machine Part 2 Flashcards
An anesthetist is running 6L/min Air, 3L/min N2O, and 1L/min O2. What is the FiO2?
22.6%
An anesthetist is running 3L/min of air and 0.5L/min of oxygen. What is the patient’s FiO2?
32.3%
What is vapor pressure?
the pressure a vapor exerts above the liquid in a closed container
What is latent heat of vaporization?
when the liquid evaporates it loses heat (gets cold)
What is the vaporizer dial?
It determines the concentration of the agent that is delivered to patient
An anesthetist is delivering straight Air and 6% Desflurane to a patient. What is the patient’s FiO2?
19.74%
An anesthetist is delivering 1L/min O2, 1L/min N2O, and 2% Sevoflurane. What is the FiO2?
49%
What is variable bypass?
some of the FGF gases bypass the vaporizer
What volatile agents have variable bypass?
Isoflurane and Sevoflurane
What volatile agent doesn’t have variable bypass? What happens instead?
Desflurane; a percentage of Des joins the FGF gases
What is special about Desfluranes vaporizer?
It is pressurized and heated; Des has a high vapor pressure and would lose heat and it’s ability to vaporize without this special vaporizer
What are the volatile agent safety features?
1-color
2-safety interlock system (one on at a time)
3- keyed filler adapter (only can put it in correct vaporizer)
How does the machine control pressure in vent mode?
The ventilator has its own APL valve, relieves pressure at the end of expiration
What could a leak in the bellows of the ventilator lead to (2)?
1- higher than expected PIP
2- Higher than expected FiO2
Would you prefer your ventilator to have descending (hanging) bellows or ascending (standing) bellows? Why?
Ascending bellows because you can better diagnose a leak in the bellow. (No gravity to help open it up)
What is compliance?
The ability of a container to expand when pressure is added to it. (old balloon [high] vs. new balloon[low])
What are the units of pulmonary compliance?
mL/cmH2O
What is the equation for pulmonary compliance?
change in volume (mL)/change in pressure (cmH2O)
What is pulmonary elastic recoil (elasticity)?
the ability of a container to return to the original volume after the pressure has been released
Fill in the blank:
High compliance means _____ elasticity.
low
What type of patients would have high compliance?
COPD patients, smokers (easy inhale, hard exhale)
What type of patients would have low compliance?
acute respiratory distress syndrome (hard inhale, easy exhale)
A patient’s pulmonary compliance is 20mL/cmH2O. They are being ventilated with positive pressure ventilation (PPV) on a ventilator with 30cm/H2O pressure. What is the patient’s tidal volume?
600mL
A patient on a ventilator is receiving a tidal volume of 600 mL. The inspiratory pressure waveform is shown. What is the patient’s dynamic lung compliance in mL/cmH2O?
30mL/cmH2O
What are the 5 common ventilator settings?
1- Tidal volume (Vt) 2- Respiratory Rate (RR) 3- Inspiratory:Expiratory Ratio (I:E) 4- Peak Inspiratory Pressure (PIP) 5- Positive End Expiratory Pressure (PEEP)
What is a normal Vt?
5-10L/min
What is a normal RR for vent mode?
8-12
What is a normal I:E?
1:2 (smokers/COPD= 1:2.5)
What is a normal PIP?
35-40cm/H2O for ETT
What is a normal PEEP?
~5cm/H2O (if used)
Why use PEEP?
To keep a small volume in the lungs after expiration to keep alveoli open and prevent atelectasis.
What is CPAP?
Continuous positive airway pressure; constant PEEP
When do you (anesthesia) use CPAP?
preoxygenation for obese patients
What are the common uses for CPAP?
1-sleep apnea
2-patients intubated for long periods of time
3-intubated patients getting lung surgery
4-preoxygenation for obese patients
A patient is being ventilated with a ventilator in the operating room. The respiratory rate is 10, and the I:E ratio is 1:2. How long is each inspiration/expiration for this patient?
2sec inspiration; 4sec expiration
A patient is being ventilated with a ventilator in the operating room. The respiratory rate is 6, and the I:E ratio is 1:4. How long is each inspiration/expiration for this patient?
Each breath is 10. 2, 8 respectively
A patient is being ventilated with a ventilator in the operating room. The respiratory rate is 3, and the I:E ratio is 1:3. How long is each inspiration/expiration for this patient?
Each breath is 20. 5, 15 respectively
A patient is being ventilated with positive pressure ventilation on the ventilator. Their respiratory rate is 8 and their minute ventilation reads 3.2L. What is their tidal volume?
400mL
A 35 year old, 85kg male patient is undergoing a laparoscopic hiatal hernia repair in the operating room. They are being mechanically ventilated. The fresh gas flow and ventilator settings are as follows:
RR= 10, I:E Ratio= 1:2, FGF= 2L/min air and 1L/min O2
How much FGF is entering the circuit during each inspiration?
100mL
A patient is receiving mechanical ventilation with the following parameters:
RR= 10, Vt= 300mL, I:E Ratio= 1:2
What is the inspiratory flow rate in L/min?
9L/min
A patient is receiving mechanical ventilation with the following parameters:
RR: 4, Vt= 600mL, I:E Ratio= 1:2
What is the expiratory flow rate in L/min?
3.6 L/min
What is the Valsalva Maneuver?
forced exhalation against a closed glottis
What are the three results of a Valsalva Maneuver?
- increased intrathoracic pressure
- decreased venous return
- decreased arterial blood pressure
How can a patient do their own valsalva maneuver?
bearing down or blowing through a straw
What is a valsalva maneuver for?
it is a vagal response to terminate a tachyarrhythmia known as supraventricular tachycardia (SVT)
Under general anesthesia we can deliver a valsalva maneuver by?
- close APL valve
- deliver positive pressure via bag
- hold pressure for several seconds at 30-40cm/H2O
Why would we do a valsalva maneuver (3)?
1- treat atelectasis
2- lung leak (lung surgery)
3- dura leak (neurosurgery)
What is volume control ventilation?
We set the Vt that the machine will deliver no matter what pressure (assuming no Pressure limit is set)
Let’s say that an anesthetist sets a tidal volume of 900mL for me, and it generated a peak inspiratory pressure (PIP) of 28cm/H2O. What would you expect to happen to the peak inspiratory pressure if I were 300lbs heavier, had my abdomen insufflated with CO2 for a laparoscopic surgery, and/or was placed in the Trendelenburg position?
It would still deliver 900mL, but the PIP would INCREASE
Suppose an anesthetist ventilated their previous patient with 700mL tidal volumes. The next patient is 2-years old. On this 2 year old, the anesthetist turns on the ventilator without remembering to lower the tidal volume. What’s gonna happen?
It would still deliver 700mL, and the kids lungs would “blow up”
What is pressure control ventilation?
we set the Pinspired (pressure inspired)
What is the advantage of pressure control ventilation?
You will never exceed the pressure set
What are the disadvantages of pressure control ventilation?
1- don’t know immediately the Vt that will be given
2- Vt will change as things in surgery change (trendelenburg; laparoscopic)
An anesthetist is using volume control when ventilating a patient. Vent settings are as follows:
RR= 8, Vt= 700mL, PIP= 30cm/H2O
If the anesthetist increases the respiratory rate to 12, what will happen to the patients Vt and PIP?
Tidal volume (Vt)? Unchanged
Peak Inspiratory Pressure (PIP)? Increase, same volume must go in over a shorter period of time; vent must push faster/harder
An anesthetist is using pressure control when ventilating a patient. Vent settings are as follows:
RR= 8, Vt= 550mL, PIP= 25cm/H2O
If the anesthetist increases the respiratory rate to 12, what will happen to the patients Vt and PIP?
Tidal volume (Vt)?
Decrease, bc the ventilator has to push it in faster/harder, the PIP is reached sooner; the lungs have less time to expand
Peak Inspiratory Pressure (PIP)?
Unchanged
An anesthetist is using volume control when ventilating a patient. Vent settings are as follows:
PIP= 25cm/H2O ,Vt= 550,I:E= 1:2
If the I:E ratio is changed to 1:3, what will happen to the patient’s Vt and PIP?
Tidal volume (Vt)? Unchanged Peak Inspiratory Pressure (PIP)? Increase, shorter time to deliver the Vt
An anesthetist is using pressure control when ventilating a patient. Vent settings are as follows:
PIP= 25cm/H2O ,Vt= 550,I:E= 1:2
If the I:E ratio is changed to 1:1, what will happen to the patient’s Vt and PIP?
Tidal volume (Vt)? Increase; inspiratory time is longer and more volume is able to get in Peak Inspiratory Pressure (PIP)? Unchanged
Spirometer
in front of expiratory valve
measures patients exhaled Vt
measures concentrations of gases used
Oxygen analyzer
reveals FiO2
Fail safe valve
prevent OD of nitrous oxide
if wall supply of oxygen fails(< 25psi)
Check valve
prevents back flow (to the flowmeters and vaporizers) of positive pressure ventilation
Auxiliary oxygen flowmeter
for MAC cases
oxygen comes from this
False Negative example
pulseless electrical activity of the heart
What is the low oxygen alarm triggered by?
low FiO2
What are possible triggers for the high circuit pressure alarm?
kinked ett
weight against diaphragm
light anesthesia (bronchospasm)
What triggers the sustained airway pressure alarm?
APL valve closed
scavenging hose blocked
What triggers a low circuit pressure alarm?
large circuit leak
What is critical temp of FGF gases?
the temperature it must be kept below in order to stay liquified
Suppose a gas has a low critical temperature
Will it be easier or harder to liquefy that gas?
Harder
What is the critical temperature for oxygen?
-119 C
What is the critical temperature for nitrous oxide?
36.5 C
What is the critical temperature for air?
-140.6 C
What is the pressure and volume of a full tank of oxygen?
2000psi
660L
An E cylinder has 1500psi and the anesthetist is delivering oxygen at 2L/min. How long can oxygen be delivered to the patient?
247.5 minutes
What is the pressure and volume of a full nitrous oxide tank?
750psi
1590L
At what volume does the pressure start to drop for a nitrous oxide tank?
<400L
What is the tank color for nitrogen and carbon dioxide?
nitrogen= black
carbon dioxide= gray
DISS
diameter index safety system
prevents incorrect connection from wall to machine
PISS
pin index safety system
prevents incorrect connection from the E cylinder to the machine
