I. Anesthesia Breathing Circuit (cont.) Flashcards
(91 cards)
1
Q
A non-invasive & continuous means of estimating the percentage of Hgb saturated with oxygen in arterial blooda t the peripheral capillary level.
A
Pulse Oximetry
normal reading 94 -100%
measures SpO2 = estimated SaO2
2
Q
Benefits of Pulse Oximetry
A
- non-invasdive
- cheap
- compact & portable
- detects hypoxemia sooner than visual signs
- no contraindications
3
Q
Which CO2 absorbent is most commonly used today?
A
Soda Lime
4
Q
What are some drawbacks to soda lime?
A
- Contain strong bases
- At low flows of less than 2 L sevoflurane has been shown to produce Compound a (does not seem to harm humans)
- carbon monoxide is produced with all volatile anesthetics
CO is also produced with Baralyme
5
Q
When soda lime is used in conjunction with sevoflurane, what are two precautions that we should take?
A
- Avoid using FGF of less than 2 L
- Replace Canisters routinely
6
Q
What indicator dye is used to indicate the Soda Lime pH is decreasing (expiring)?
A
Ethyl Violet
Fluorescent lights may lead to photodeactivation
7
Q
Which two components of soda lime allow it to absorb carbon dioxide?
strong base activators
A
- Sodium Hydroxide (4%)
- Potassium Hydroxide (1%)
8
Q
What happens if a soda lime canister is desiccated but remains unchanged for an extended period of time (over the weekend)?
A
The ethyl violet will lose color and pellets will revert from purple back to white.
CO2 absorption is further decreased & CO production is increased⚠️
9
Q
When should the soda lime canister be replaced?
A
- When there is an increase in inspired CO2 (>2-3mmHg) = 😮💨 Rebreathing is occurring
- After color change 💜
- Lack of heat in the cansiter during anesthesia🥶
- Total time of use = 14 hours ⏰
10
Q
Factors affecting efficiency of canister absorption
A
- size of absorber canister
- Granules (rough texture allows for better absorption of CO2)
- Low FGF rates (↓ CO2 washout through scavenging = ↑CO2 Absorption = ↓ Life of Canister)
- Channeling **(Air passes preferentially through a channel = ↑Exhaustion & Absorption = ↓ Lifetime)
- Wall Effect (Loose packing allows exhaled gases & CO2 to bypass granules = ↓Absorption = ↑Lifetime)
Channeling & Wall effect both would cause ↑ inspired CO2 = replace can
11
Q
why is the size of the absorber canister relevant?
A
The size of the absorber canister must be large enough in order to accommodate the patients tidal volume entirely so the entire volume of carbon dioxide can be cleansed to prevent rebreathing.
12
Q
Which CO2 absorbant is functionally better compared to soda lime, and why is not used more widely?
A
Amsorb
More expensive & has half the absorption capacity as Soda Lime
13
Q
Which absorbant uses Calcium chloride (NOT a strong base), and what are its benefits?
A
Amsorb😁
- Non-hazardous & safe to handle/dispose
- Does NOT produce CO
- Does NOT produce Cmpd A
- Safe for use at low FGF rates
- Retains its dessicated color change
14
Q
What system was developed in order to collect and remove waste gases from the breathing circuit in order to avoid exposing personnel and atmosphere to trace anesthetic gases?
A
Scavenging System
15
Q
What is the NIOSH recommended exposure limit for halogenated agents (w/i 8 hr time frame)?
A
no more than 2ppm
If you can smell the gas, concentration = 5-300ppm
16
Q
What component was added to the scavenging system in order to catch and retain exhaled gases to accomodate the scavenging pipeline’s constant rate of suction (allowing for it to work optimally)
A
Reservoir Bag
17
Q
Which disposal system does not utilize a vacuum or negative pressure valves, but does still employ a positive pressure relief valve for safety
less common
A
Passive Disposal System
(waste gases proceed passively down corrugated tubing through the OR ventilation exhaust grill)
18
Q
What are the three components of the scavenging system?
A
- Gas-Collecting Assembly (APL & Relief Valves both connect to scavenger via tubing)
- ‼️Scavenging Interface (houses Positive & Negative Pressure Valves)
- Reservoir bag
Active systems require Reservoir Bags & Negative Pressure Relief Valves
19
Q
Which disposal system DOES employ suction at a constant rate IOT facilitate the removal of expired gases?
A
Active Disposal System
20
Q
The active disposal system employs the use of a reservoir bag, which provides what benefits?
A
- Allows time for vacuum system to work
- If vacuum set too low = bag will overly distended and back pressure exits through PPV
- If vacuum set to high = bag will be fully collapsed, and negative pressure relief valve pops off
21
Q
What are the 3 main complications that can occur with scavenging systems?
- **FGF entering circuit must = ____ **
- Waste gas should only enter the scavenging system during ____
3.____ cause the the bag to compress
A
- FGF exiting the circuit
(backflow → barotrauma)
Action: Adjust vacuum rate/PPV Malfunction - Exhalation
(ventilator valve malfunction allowing FGF into bag during inspiration – valve should close only allowing FGF to patient)
Action: Switch to Ambu Bag & New Machine - Excess negative pressure
(Negative Pressure Valve malfunction – not allowing ambient air to enter bag preventing it from collapse & negative backpressure to patient)
Action: Turn down vacuum/disconnect NPV from collection tubing to get through case and have machine serviced
22
Q
______ were developed to automate the squeezing of the reservoir bag, to free up the anesthetist’s hands to do other tasks.
A
Ventilators
23
Q
On Vent mode ____ replaces the reservoir bag in the breathing system
A
Bellows or Piston Cylinder
APL valve has no function on mechanical vent mode
24
Q
List the components of the ventilator:
SIDEBASCH
A
- Driving gas Supply — ventilator power supply (O2 or air)
- Injector — allows ambient air to mix with drive gas
- Controls — pneumatic and/or electronic
- Alarms — loss of power is required
-
Safety-relief valve — limits driving gas pressure (pop-off valve; expiratory phase)
6.Bellows assembly — ascending vs. descending - Exhaust valve — closes during inspiration
- Spill valve — vents excess gas into the scavenger (inspiratory phase)
- Ventilator Hose connection — 22mm male fitting
25
what serves as a pressure limiting valve for the bellows, unrelated to the patient.
Ventilator Spill Valve
26
Describe the two ventilator systems used to deliver gas to patients.
1. **Single Circuit System** - Piston
*(Pressure is generated mechanically (i.e., electric motor) via respiratory gases - very accurate)*
2. **Double Circuit System**- Bellows
*(Pressure generated pneumatically by drive gas which is then compresses bellow to deliver respiratory gases)*
27
While the Piston ventilator historically has been more accurate, delivering precise tidal volume, what are the benefits of a bellows system?
- **Precision** now rivals piston models
- Driven by gases, not electronically, so **fewer parts that may malfunction**
| Bellows are more common due to reliability
28
In a bellows system, what may indicate a leak?
FiO2 change
| leak could lead to barotrauma
29
What are the two variations of bellows?
**Standing** and **Hanging**
30
Describe the Standing Bellows:
- *Ascending bellows* ____ during expiration
- ____ when a disconnect occurs (i.e, will not rise if leak exists = **Safety Feature**
- Adds ____ PEEP (even when set to zero)
- Rise
- Collapse
- 3 cmH20
31
Describe Hanging bellows:
- ____ *bellows*
- Continues to ____ in the event of a disconnect (especially if weighted) = *makes it difficult to recognize a leak → Barotrauma*⚠️
- Must have another ____, such as ____ .
- **OBSOLETE**
- *descending*
- Fill by gravity
- source of alarm
- CO2
32
Inspiratory Phase Steps (bellows)
1. Driving gas (air or O2) enters bellows housing
2. Pressure exerts on bellows
3. Bellows compresses
4. Breathing gas forced into breathing system
33
Expiratory Phase Steps (Bellows)
1. Pressure in Bellows chamber reaches ZERO
2. *Ventilator Relief Valve* opens
3. Exhaled gases passes *through CO2 absorber and into Bellows*
4. Bellows re-exands as breathing system gases (*air, O2, Vaporizers*) flow into it
5.Once Bellows fully expands, excess driving gas is vented through the *spill valve* to the *scavenging system*
34
The precision of the Piston system makes it a good candiate for what department?
Pediatrics
35
Advantages of the Rotary Piston Single Circuit Ventilator
- Precise Vt delivery (Esp. good for peds/small pts or those with poor lung compliance
- Less O2/Air used (not used to compress a bellows, only used for patient delivery)
- No intrinsic PEEP (compared to ascending bellows)
- Quiet
36
Disadvantages to the Single Circuit Ventilator - Rotary Piston System
- Leak in piston diaphragm can lead to hypoventilation
- Possible entrainment of room air as piston returns to filled position
- Mechanical failures
37
List all Ventilation Parameters
1. Tidal volume (Vt) *(amount inspired)*
2. Respiratory rate (RR) = *Breaths/min*
3. Minute ventilation *(VE) = Vt RR*
4. I:E ratio → *Ratio of inspiration to expiration (time)*
5. Inspiratory flow rate → *Set vs. predetermined*
6. Positive End-Expiratory Pressure (PEEP): *helps prevent atalectasis*
7. Pinsp *(peak inspiratory pressure)*
8. Pplat (plateau pressure): *pressure at end expiration *
9. Inspiratory Pause:* Increases filling time*
10. Pmax: *max working pressure* *(sometimes called P-Limit; if surpassed, activates audible alarm)*
38
List the phases of Mechanical Ventilation
| with regard to MV waveform
1. Inspiratory Tiggering (Expiratory → Inspiratory)
2. Pressurization (rapid rise in pressure: air enters lungs)
3. Inspiratory Plateau Level
4. Cycling Phase (Inspiratory → Expiratory)
5. Baseline or set PEEP level
39
What activates the Inspiratory Trigger phase
1. Set MV Rate
2. Spontaneous Breath by Pt
40
What 3 variables can determine the maximal allowed pressure that occurs concurrently with the conclusion of inspiration and start of expiration (i.e., the start of Cycling Phase).
1. Preset Time Limit (of inspiration)
2. Preset Max Inspiratory Pressure
3. Preset Tidal Volume
41
Pressure generated by the ventilator to overcome BOTH airway resistance AND alveolar resistance
Peak inspiratory pressure (Pinsp)
| An indication of dynamic compliance
42
Pressure measured during an inspiratory pause (no flow)
Indication of ____ compliance or stiffness
- Plateau pressure (Pplat)
- static
*Static = No flow/movement*
43
An increase in BOTH Pinsp & Pplat indicates:
1. ↑ Tidal Volume
2. ↓ Pulmonary Compliance
| pulmonary edema, MR recovery, PIP will also ↑
44
What does increase in Pins **WITHOUT** change in Pplat indicate?
↑ Airway Resistance
| Bronchospasm, Kink OETT, Poiseulle's Law
*TV is able to ↑ but Pplat is unable due to restriction/resistance*
45
Positive circuit pressure at the end of the expiratory phase of ventilation
PEEP
46
What functions does PEEP provide?
- Increases FRC by recruiting partially closed alveoli
- Reduces and/or prevents atelectasis
- Additive to intrinsic PEEP (Auto-peep) of ventilator
*(Commonly set to 4-6cmH2O)*
- May be integrated into the ventilator or may be an add-on device (i.e. for AMBU bag)
47
Ratio of inspiration time vs. expiration time
I:E Ratio
*- Default usually 1:2 (mimics normal breathing)
- Can be altered to allow more time for inspiration or expiration, depending on patient needs*
48
Assume we set the RR to 10 and set the I:E to 1:2. What is our inspiratory time and expiratory time?
1. 60sec/10RR = 6 sec/cycle
2. 1:2 ratio= **2 sec Inspiration & 4 sec Expiration**
49
What happens to PIP if we decrease the I:E from 1:2 to 1:1?
- Our inspiration time would increase
- This allows the set tidal volume to be inspired over longer period = less pressure is experience during inspiration
**↓I:E = ↑Inspiration Time = ↓PIP**
*1:2 → 1:1 = ↓I:E*
50
What happens to PIP if we increase the I:E ratio from 1:1 to 1:2?
**↑I:E = ↓Inspiration Time = ↑PIP**
*1:1→1:2 = ↑I:E*
| Same volume must be delivered over shorter period of time
51
What type of patient benefits from ↑PIP
*(↓ inspiration time & ↑ Expiration time)*
COPD
| have difficulty exhaling and "air trap"
52
What are the two categories of ventilation modes?
1. Volume Control
2. Pressure Control
53
What are the two volume control ventilation modes?
1. Volume Control Ventilation (VCV)
2. Synchronized Intermittent Madoatory Ventilation (SIMV-VC)
54
What are the four pressure control ventilation modes?
1. Continous Mandatory Ventilation (PCV)
2. Synchronized Intermittent Mandatory Ventilation (SIMV-PC)
3. Pressure Control with Volume Guarantee (SIMV-PC-VG)
4. Pressure Support Ventilation (PSV)
55
*Time Cycled & Volume Controlled* ventilation mode
**Volume Controlled Ventilation Mode (VCV)**
- Constant volume regardless of lung dynamics
- Pressure Varies with patient compliance/resistanct
- Volume is subject to preset pressure limit ???
- Parameter settings set by operator *(TV, Rate, I:E Ratio, PEEP, Inspiratory Pause, etc.)*
56
# Ventilation Mode
- Set Tidal Volume
- Set RR
- Flow is constant
**Volume Control Ventilation (VCV or VC-CMV)**
- PIP Varies (kept low as possible: **<35cmH20**)
- I:E default = 1:2
- PEEP may be added
*Common Settings:
- Vt: 5-7 ml/kg
- RR: 6-12 (titrate to EtCO2)
- PEEP: 4-6 cmH2O → If trouble oxygenating or using small Vt)*
57
Which ventilation mode do most older anesthesia machines use as the default?
VCV (VC-CMV)
58
Which categorical ventilation mode delivers a constant pressure regardless of lung compliance/reistance (i.e., tidal volumes will vary based on patient lung compliance and resistance).
Pressure Controlled Ventilation Modes
59
# Ventilation Mode
Controls Inspiratory Pressure (Pinsp), PEEP, & RR
**Pressure Control Ventilation (PCV or PC-CMV)**
- Pressures are maintained in case of a leak
- *Tidal Volumes * and *Minute Ventilation* *(Ve)* vary with changes in patient effort, compliance, and airway resistance*
- The flow generated varies *(Highest at first IOT set PIP & lower later during inspiration IOT maintain set pressure)*
60
Which ventilation mode often results in a higher Vt with a lower PIP?
PCV
*This may be useful in laparoscopic procedures, allowing higher tidal volumes at lower PIP*
| *Compared to VCV*
61
Pressures should be set reasonably in order to avoid what two extremes?
1. Atalectasis
2. Barotrauma
62
# Ventilation Mode
Two Settings in One:
- Pressure support (Deliver pressure-supported breaths initiated by pt IOT reach set Vt)
- Will trigger mandatory breaths if the patient becomes apneic or has low Ve
**Synchronized Intermittent Madatory Ventilation** (SIMV-PSV, SIMV-VC, SIMV-PC)
- Intermittent *synchronized* delivered breaths are modified usings settings such as:
*- Trigger Window
- Sensitivity*
63
# term
*will not deliver breath during exhalation (avoids breath-stacking & bucking)*
synchronized
64
# Ventilation mode
- The ventilator dynamically adjusts the PIP while staying within the set maximal pressure IOT achieve the desired Vt, breath by breath
- For each mandatory breath, the Vt is achieved with the lowest pressure necessary
**SIMV-PC-VG
**"Volume Guarantee"
- Smartest Mode
- If the complianec or resistance changes, it automatically adjusts Pinsp (over a few breaths) to restore set Vt
65
# Ventilation Mode
- Every detected inspiratory effort is pressure supported
-
**Pressure Support Ventilation (PSVPro)**
- Number, Timing, Duration of *pressure-supported* breaths **determined by patient**
- Pro = *Protect* (If no breaths are detected, 10-30 sec, backup mode is initiated)
| often used with LMA or during emergence
66
What factors determine Vt during PSVPro
**Pressure difference** b/w:
*-PEEP
- Psupport
- Lung Mechanics
- Pt breathing effort*
67
what backup mode kicks in if patient becomes apneic while using PSVPro
**SIMV-PC + PSV**
Returns to last used ventilation mode
68
# Optimal Ventilation Goal
Vt
*smaller* 6-8 mL/kg
-improves respiratory function and reduces the incidence of post-op pulmonary complications
69
# Optimal Ventilation Goal
PEEP
4-6 cmH20
prevention of atelectasis
70
# Optimal Ventilation Goal
I:E Ratio
- Obesity/Restrictive lung disease (ILD/PF/ALS):
**↓I:E = ↑Insp Time/↓Exp Time = ↓PIP**
(1:1 better than 1:2)
- Obstructive Lung Disease (COPD/Asthma):
**↑I:E = ↓Insp Time/↑Exp Time = ↑PIP**
(1:2 better than 1:1)
71
Diseases with limitation of airflow due to narrowed or blocked airways, making it *difficult to exhale effectively.*
Obstructive Lung Disease
*(COPD, Asthma)*
72
Dz whenlung tissue itself becomes stiff or loses its elasticity, reducing ability of lungs to expand fully, *effecting ability to inhale air.*
Restrictive Lung Disease
*(Pulmonary Fibrosis, Interstitial Lung Disease, NM Disorders: ALS)*
73
# Optimal Ventilation Goal
FiO2
lowest possible IOT maintain SpO2 > 97%
74
# Optimal Ventilation Goal
PaCO2
35-45
(EtCO2 32-35 under GA)
| normocapnea
75
# Optimal Ventilation Goal
Adequate ventilation with lowest possible _______.
Peak pressures
76
General Hazards of Anesthesia Ventilators:
- Barotrauma/Volutrauma
- Negative Pressure during expiration
- Alarm Failure
- Hypoventilation
- Hyperventilation
- Hyperoxia
- Hypoxia
- Hypercapnia
- Hypocapnia
- Inhalation of foreign substance
- Inadvertent exposure to remnant VA (MH)
- Fires & Explosions
77
Common problems with anesthesia ventilators
1. **Ventilator & FGF coupling - Older machines**:
- *FGF → ↑Vt, Ve & PIP* due to *coupling*⚠️
- Newer machines *uncoupled* BUT **NEVER** USE O2 FLUSH DURING INSPIRATION‼️
2. **Excessive Positive Pressure**:
- ↑ Risk of pulmonary barotrauma⚠️
- hemodynamic compromise⚠️
3. **Vt discrepancies**
- caused by circuit or lung compliance, ventilator-fresh gas coupling, leaks in system
- Piston vs Bellows
78
What are the two categories of alarms?
1. Pressure Alarms
2. Volume Alarms
79
Pressure alarm examples:
1. Low PIP/High PIP
2. High PEEP
3. Sustained High Airway Pressure
4. Negative Pressure (subatmospheric)
80
Volume Alarm Examples:
1. Low Vt/High Vt
2. Low Ve/High Ve
3. "Cannot Drive Bellows"
4. Possible Disconnect Alarm
81
All current gas machines have ____ monitoring built into the breathing circuit.
VPO (Volume, Pressure, O2)
*most have agent monitoring as well. Some have spirometry & capnometry*
82
Why is the Apnea/Disconnect Detection alarm significant?
How does it work?
- It tells us the patient is not being ventilated
- Chemical monitoring (EtCO2)
- Mechanical monitoring (failure to reach Inspiratory Peak Pressure or failure to sense return of Vt on spirometer)
- Visual monitoring
- Auditory monitoring
83
The oxygen analyzer is located where?
Immediately before the inspiratory limb of the circle system just before reaching the patient
84
What is a mandatory safety feature and is the last line of defense to prevent hypoxic mixture delivery?
O2 analyzer
**only instrument that actually measures the concentration of O2 being delivered to patient**
| must be calibrated regularly
85
What are the two types of O2 analyzers?
1. Fuel Cell 🔋
2. Paramagnetic 🧲
86
How is *Delivered Volume* calculated?
DV = Set Volume + FGF - Compliance Loss
87
In order to calculate the *Delivered Volume*, we must first calculate the *FGF*. How is this done?
**PART I**
1. (60/RR) = *breath cycle*
2. Using I:E, determine *Inspiratory Duration*
**Part II**
1. (Total mL FGF/60 sec) = *FGF/sec*
**Part III**
1.**(FGF/sec x Inspiratory Duration) + Set Vt** = *Delivered Flow*
**Part IV (if *Compliance Loss* exists)**
1. *Delivered Flow* - *Compliance Loss* = *Total Delivered Flow*
88
How to calculate FiO2 using mL:
- Air = 210 mL per 1000L = 21%
- O2 = 1000mL per 1000mL =100%
Part I (Air):
(mL x total liters delivered)
Part II (O2):
(mL x total liters delivered)
Part III:
(Total mL Air + Total mL O2)/Total Liters delivered
| **Can also use % counterparts instead of mL**
89
Simple way of calculating FiO2 with percentages
Air @ 4 L/min
O2 @ 3 L/min
Air: 20% x 4 = 80
O2: 100% x 3 = 300
380/7L = 54.3% FiO2
*use 21% O2 for more accuracy
384/7 = 54.9%*
90
during inspiration, the ventilator spill valve is ____.
closed
This allows the driving gas to be delivered to the patient and not exit the system.
91
during expiration, the ____ opens once the PP (used to fill bellows) exceeds limit, thereby venting excess gas to the scavenging system.
ventilator spill valve
