I. Anesthesia Breathing Circuit (cont.) Flashcards
A non-invasive & continuous means of estimating the percentage of Hgb saturated with oxygen in arterial blooda t the peripheral capillary level.
Pulse Oximetry
normal reading 94 -100%
measures SpO2 = estimated SaO2
Benefits of Pulse Oximetry
- non-invasdive
- cheap
- compact & portable
- detects hypoxemia sooner than visual signs
- no contraindications
Which CO2 absorbent is most commonly used today?
Soda Lime
What are some drawbacks to soda lime?
- 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
When soda lime is used in conjunction with sevoflurane, what are two precautions that we should take?
- Avoid using FGF of less than 2 L
- Replace Canisters routinely
What indicator dye is used to indicate the Soda Lime pH is decreasing (expiring)?
Ethyl Violet
Fluorescent lights may lead to photodeactivation
Which two components of soda lime allow it to absorb carbon dioxide?
strong base activators
- Sodium Hydroxide (4%)
- Potassium Hydroxide (1%)
What happens if a soda lime canister is desiccated but remains unchanged for an extended period of time (over the weekend)?
The ethyl violet will lose color and pellets will revert from purple back to white.
CO2 absorption is further decreased & CO production is increased⚠️
When should the soda lime canister be replaced?
- 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 ⏰
Factors affecting efficiency of canister absorption
- 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
why is the size of the absorber canister relevant?
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.
Which CO2 absorbant is functionally better compared to soda lime, and why is not used more widely?
Amsorb
More expensive & has half the absorption capacity as Soda Lime
Which absorbant uses Calcium chloride (NOT a strong base), and what are its benefits?
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
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?
Scavenging System
What is the NIOSH recommended exposure limit for halogenated agents (w/i 8 hr time frame)?
no more than 2ppm
If you can smell the gas, concentration = 5-300ppm
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)
Reservoir Bag
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
Passive Disposal System
(waste gases proceed passively down corrugated tubing through the OR ventilation exhaust grill)
What are the three components of the scavenging system?
- 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
Which disposal system DOES employ suction at a constant rate IOT facilitate the removal of expired gases?
Active Disposal System
The active disposal system employs the use of a reservoir bag, which provides what benefits?
- 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
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
- 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
______ were developed to automate the squeezing of the reservoir bag, to free up the anesthetist’s hands to do other tasks.
Ventilators
On Vent mode ____ replaces the reservoir bag in the breathing system
Bellows or Piston Cylinder
APL valve has no function on mechanical vent mode
List the components of the ventilator:
SIDEBASCH
- 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
what serves as a pressure limiting valve for the bellows, unrelated to the patient.
Ventilator Spill Valve
Describe the two ventilator systems used to deliver gas to patients.
-
Single Circuit System - Piston
(Pressure is generated mechanically (i.e., electric motor) via respiratory gases - very accurate) -
Double Circuit System- Bellows
(Pressure generated pneumatically by drive gas which is then compresses bellow to deliver respiratory gases)
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
In a bellows system, what may indicate a leak?
FiO2 change
leak could lead to barotrauma
What are the two variations of bellows?
Standing and Hanging
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
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
Inspiratory Phase Steps (bellows)
- Driving gas (air or O2) enters bellows housing
- Pressure exerts on bellows
- Bellows compresses
- Breathing gas forced into breathing system
Expiratory Phase Steps (Bellows)
- Pressure in Bellows chamber reaches ZERO
- Ventilator Relief Valve opens
- Exhaled gases passes through CO2 absorber and into Bellows
- 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
The precision of the Piston system makes it a good candiate for what department?
Pediatrics
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
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