Anesthesia Equipment Flashcards
What does an anesthesia delivery system consist of
An anesthesia delivery system consists of the anesthesia workstation (anesthesia machine) and anesthetic breathing system (circuit)
What is the function of the Anesthesia Machine
Delivers known concentrations of inhaled anesthetics and medical gases to the patient, as well as removes of the patient’s carbon dioxide through a CO2 absorber or a scavenging system
Electrical and Pneumatic Power Sources
- On and off switch
- Inlet of hospital pipeline
- Oxygen, nitrous oxide, and medical air
- Inlet of compressed gas cylinders
- Power failure indicator
- Visual/audible alarms
- Reserve power system
Pressure Regulators
Reduce pipeline and cylinder pressures
Oxygen Fail Safe Device
Prevent delivery of hypoxic gas mixture in the event of low or failed O2 supply (when O2 supplies drops below 30 psi)
Proportionately decreased (or shuts off) flow of all gases
Oxygen analyzer required and supply failure alarm
O2 Flush Control (emergency O2 flush valve)
By passes the flow meters and vaporizers
“O2+“
35-85L/min through the circuit to flush out anesthetic gases
Activated by demand, designed to prevent accidental activation
Flow Meters
Low pressure and precisely controlled gas flow
An oxygen analyzer is still needed in order to confirm the correct delivery of oxygen
Flowmeter Sequence
The flow meter sequence matters
Oxygen should always be downstream to other gases and closest to the patient
Oxygen delivery is preserved in the event of a leak upstream
Common Gas Line
Fresh Gas outlet (fresh gas flow)
A mixture of medical gases and volatile anesthetics
Common gas outlet directs anesthetic mixture to be delivered to the patient
Breath Limb Components
Oxygen Analyzer
Inspiratory and Expiratory one-way valves
Large bore corrugated tubing
The adjustable pressure limiting valve (APL)
Expiratory gas sampling line and spirometer
CO2 Absorber
Reservoir Bag
Mechanical vent
Scavenger system
What side should the oxygen analyzer be on
inspiratory side
Mechanical Ventilator on the Anesthetic Machine
There is a bag/vent selector switch
Modern machines will have the same functions as the ICU vent
powered pneumatically or/and electrically
Bellows
Humidity (both passive and active)
Scavenging System
Collects and removes vented gas from OR
Active or passive
Vaporizers
- Volatile anesthetics are liquids at room temperature and atmospheric pressure.
- A vaporizer will convert a liquid to a vapor and will take place into a closed container known as a vaporizer
Precision and Accuracy of vaporizers
Must be precise and accurate and is just as important as the delivery of gases
A measured amount of volatile gas is dispensed into the fresh gas mixture
Flow Over Method of Vaporization
Gas flows over the liquid agent and becomes saturated
Vaporizers variable bypass
The gas flow passing through the vaporizer is split
The amount passing into the vaporizing chamber is “variable” (based on operator adjusting the settings), and the rest bypasses the vaporizing chamber
Agent Specific Vaporizer
Each vaporizer is constructed to a specific volatile agent
Receiving port will only fit the filling spout for its particular anesthetic
Vaporizer Classification
Agent-specific
Variable bypass (concentration calibrated)
Flow-over
Temperature-compensated
Out-of-circuit
Color Coded Vaporizers
the vaporizer, spout, and bottle will all be color coded
What is the color-coded vaporizer for Isoflurane
Purple
What is the color-coded vaporizer for Desflurane
Blue
What is the color-coded vaporizer for Sevoflurane
Yellow
Anesthesia Machine Safety Feature
Alarms
Analyzer alarms (oxygen concentration)
Disconnect/power failure/machine alarms
Low flow
Ventilator alarms
Anesthesia Machine Safety Feature
Oxygen Fail Safe Valve
Prevents hypoxic gas delivery
Anesthesia Machine Safety Feature
Oxygen Flowmeter
Control is often different from other gases
Oxygen Downstream
Anesthesia Machine Safety Feature
Cylinders
Built and tested to specified standards, color-coded
PISS connectors, safety pressure relief
Anesthesia Machine Safety Features
Vaporizer Safety Features
Flowmetercontrols for oxygen and nitrous are linked
Ratio must always be at LEAST 1:3 (oxygen:nitrous)
Prevents <25% oxygen delivery
Anesthesia Machine Safety Features
Minimum O2/N2O Controller
Flowmetercontrols for oxygen and nitrous are linked
Ratio must always be at LEAST 1:3 (oxygen:nitrous)
Prevents <25% oxygen delivery
Anesthesia Machine Safety Features
Machine Checks and Alarms
Daily pre-use machine check
Quick check between cases
Anesthesia Machine Safety Features
Back Pressure Check Valve
Prevents back pressure from PPV going into the machine
Anesthesia Machine - Circuits Components
Gas reservoir bag in circuit
Rebreathingof exhaled gases
Chemical neutralization of CO2
Unidirectional valves
Anesthesia Machine - Circuits Classified
Open
Semiopen
Semiclosed,
Closed
Most common anesthesia machine circuits
}Most common are Mapleson F, Bain, and circle system
Mapleson Circuit
Six different designs
Bain Circuit
Modification of Mapleson D System
Circle Circuit
Most popular system in Canada/US
Clsoed or semi closed circuits
Components of the Mapleson Circuit
FGF, reservoir tubing, facemask, reservoir bag, expiratory valve (to administer anesthetic)
Varying arrangements
Mapleson Circuit -Semiopen
No valves to direct gas flow
No CO2 neutralization
Because of no clear separation of inspired and expired gases, rebreathing occurs when inspiratory flow exceeds the fresh gas flow.
Mapleson Circuit Optimal Fresh Gas Flow
Difficult to determine optimal FGF
Amount of rebreathing depends on FGF
Best way is to monitor EtCO2
- In order to prevent rebreathing of exhaled gases a fresh gas flow of 2-3 times the patient minute ventilation is recommended
Mapleson F (Jackson-Rees)
- Modification of the Mapleson D
- Has a pressure limiting overflow valve on the reservoir bag
- Used for pediatric anesthesia or transport because of minimal dead space and resistance
Mapleson F (Jackson-Rees) Disadvantages
Requires high FGF to prevent rebreathing
Potential for high airway pressure, barotrauma (if valve is occluded)
No humidification system
Pollution of atmosphere with anesthetic gas (can be hooked to scavenging system
Bain Circuit
Modification of Mapleson D
Coaxial version
Still has no CO2 neutralization, or valves to direct flow
Bain Circuit Advantages
FGF is warmed by exhaled gases
Moisture (from partial rebreathing)
Easy scavenging of waste gases from overflow valve
Bain Circuit Disadvantages
Disconnect or kinking of inner FGF tubing
Requires high FGF
What is the most common type of circuit
Circle Circuit
Circle circuits semiopen, semiclosed, or closed
- Depends on amount of FGF
- Rebreathingof exhaled gases
- Conservation of moisture and heat
- Decreased pollution of exhaled anesthetic gas
Circle Circuits Disadvantages
Increased airway resistance in system
Bulky, not portable
Higher risk of problems/malfunction
Circle Circuits Components
Insp/Exp unidirectional valves
Insp/Exp corrugated tubing
APL valve, reservoir bag
CO2 Absorbent
Bag/Vent selector switch, ventilator
Closed Circle Circuit
Total rebreathing of exhaled gases
Closed Circle Circuit Advantages
Max warming and humidification of inhaled gases
Less pollution of atmospheric exhaled gases
Economical
Closed Circle Circuit Disadvantages
Can not make rapid changes to delivered concentration of anesthetics or O2
Unpredictable concentrations of anesthetic and O2
Non-Invasive Types of monitoring
Electrocardiography (ECG)
Blood Pressure Cuff
PulseOximetry
Capnography
BispectralIndex (BIS Monitor)
Temperature Monitoring
Neuromuscular Twitch (NMT Monitor)
Invasive Types of Monitoring
Central Venous Pressure (CVP)
Pulmonary Artery Pressure (PAP)
Blood Pressure (Arterial Line)
Minimum Alveolar Concentration (MAC)
ECG
Heart rate, rhythm, waveforms
3-lead, 5-lead, 12-lead
Blood Pressure Monitoring
Automatic cuff, appropriately-sized
Systolic/Diastolic
BIS Monitoring
Level of consciousness (EEG activity)
Usually aim for 40-60 for healthy patient and routine anesthesia
Temperature Monitoring
Can be “invasive” (oral or nasal temp probes)
Normal for temp to drop after induction
Cold patients can have a lot of other difficulties
NMT Monitoring
Train of Four
Measures patient’s level of paralysis
Normal capnography
Shows the changes in CO2 throughout breath cycle
Decrease EtCO2 Levels
Hyperventilation
Decrease in metabolic rate
Decrease in body temp
Increasing EtCO2 Levels
Hypoventilation
Increased metabolic rate
Rapid rise in body temp- May be MH
Rebreathing
Malfunction of CO2 absorber (or needs to be changed)
Insufficient inspiratory flow, or expiratory time
Partial rebreathing circuits
Expiratory valve failure
Airway Obstruction
Obstruction in breathing circuit
Upper airway obstruction (foreign body?)
Kinked or occluded ETT
Bronchospasm
Muscle Relaxants
- NMBA wearing off
- Patient is triggering breaths again
Esophageal ETT
-May not see ANY CO2, or may only see small, transient waves
1.0 MAC
Concentration of anesthetic required to suppress movement in 50% of patients in response to pain
Measured as the end-tidal concentration of anesthetic gas
0.8-1.2 MAC
MAC Variation
Varies with each person
Age
Medications or Illicit drug use
Ventilation Monitors
- Capnography
- Spirometry
- Volume, and flow waveforms
- Oxygen Analyzer
- FIO2 and EtO2
- Airway Pressures
- Low/High Alarms
- PEEP
- Volume
- Low/High Alarms
Mapleson A
Mapleson D
Mapleson B
Mapleson E
Mapleson C
Mapleson F
Flowrate of the quick flush
35-75L/min
Should the patient be hooked up to the circuit when using the quick flush?
NO- results in dangerous pressure in the breathing circuit which could result in pneumothorax
Anesthetic Vaporizers
Change liquid anesthetic into vapor
Deliver selected % of vapor to the fresh gas outlet
Quick Flush
Delivers intermediate pressure O2 bypassing the vaporizer
Use for the quick flush
Quickly decrease gas percentage in circuit
Emergency or recovery
Modern vaporizer compensations
Temp: Between 15-35C
Achieved using efficient heat conducting materials
Flow rate- 0.5-10 L/min
Back pressure- associated with positive pressure ventilation and flush valve
Variable Bypass System
Delivers a specific concentration by flowing fresh gas over a reservoir of liquid anesthetic and mixing it from carrier gas
What do you do if vaporizers are filled with the wrong anesthetic?
Drain and run 1L/min O2 until dry
Common Gas Outlet
Where gas exits the vaporizer, connected by a hose to the fresh gas inlet
Universal for rebreathing and non-rebreating units
Rebreathing system advantages
- Lower fresh gas flow rate
- Saves money
- Decreases pollution
- Patient breathes warm humidified air
Non-rebreathing tube types
- Mapleson D
- Mapleson F
- Bain
Rebreathing system disadvantages
- More components and potential for leaks
- Increased resistance for smaller patients
Position of the pop-off valve
ALWAYS OPEN
Unless checking for leaks or administering positive pressure ventilation
If the pop off valve is closed Increases pressure in breathing system, Results in possible cardiopulmonary injury
Breathing system pressure gauge
SHOULD ALWAYS BE ZERO
Except: performing leak checks or providing positive pressure ventilation
Colour change in soda lime
White- fresh
Violet- exhausted
Components of the Rebreathing system
- Fresh gas and O2 flush
- Unidirectional valves (inspiratory and expiratory)
- Breathing hoses
- CO2 absorber
- Adjustable pressure limiting valve aka pop-off valve
- Reservoir bag
Signs of exhaustion
- Increase in tidal CO2
- Increased ventilation, HR/BP (then drop) if light enough
- Rebreathing capnograph
- Respiratory acidosis
- Red mucous membranes due to carbon monoxide production/inhalation
Calculation for reservoir bag size
Tidal volume = 10-20mL/kg x 6
Round UP if between sizes
Reservoir bag function
Observe ventilation, inspiratory reserve, administer manual positive pressure ventilation
Non-rebreathing system components
- Fresh gas
- Non-rebreathing tubes
- APL (mapleson D) or open/close (mapleson F) valve
- Reservoir bag
Non-rebreathing Advantages
- Very light with minimal dead space
- Minimal resistance to ventilation
Non-rebreathing Disadvantages
- High Gas flow rate
- More expensive to run larger patients
- Increased environmental pollution
- Gas cold and dry
Non-rebreathing Oxygen flow rates
2-3x tidal volume in most cases
200-300mL/kg/min O2
Benefits of intubation
- Reduced anatomical deadspace
- Maintain inhalant anesthesia with minimal environmental contamination (with properly inflated cuff)
What type of tube provides the least air resistance
Larger radium and shorter length (Poiseuille’s law)
Hwo can carbon dioxide be removed from the anesthesia system
- Carbon dioxide can be removed either by washout (delivered gas flow greater than 5 L/min from the anesthesia machine) or by chemical neutralization.
Flowmeter Pressure
- Anything prior to the flow meters is called the high pressure side and after is the low pressure side.
- Gases are regulated to a typical operating pressure of 50 PSI
- Back pressure compensated (Thorpe tube) type flow meters will then allow mixing of these gases in very accurate amounts.
- All flow meters are calibrated to their specific gas.
- Elongated or ‘I’ shaped flow indicators (rotameters) should be read at the upper edge —-ball shaped indicators must be read at the equator (as always).
Flow Meters and Speific Gases
- All flow meters are calibrated to their specific gas, because
- Because few gases have the same density and viscosity, flowmeters are not interchangeable with other gases.
Nitrous Oxide Tanks
- Pressure gauges on nitrous oxide tanks do not serve as contents gauges like oxygen.
- They are measuring only the vapour pressure of the gas above the liquid/gas interface.
- N2O is stored as a liquid under about 750 PSI.
- As the liquid phase changes to a gas, it creates a vapour pressure.
- Therefore pressure gauges will read ‘full’ until all the liquid is converted and only the gas remains.
Vapoorizers and Temperature Compensated
- Some variable by-pass vaporizers have a temperature sensitive device that will increase the fraction of gas in the bypass circuit as the temperature falls thus ensuring a constant concentration of anesthetic vapour despite falling temperature.
Desflurance and Temperature Compensation
- Desflurane has a vapor pressure near 1 atm atm (664 mm Hg) at 20 C, nd for this reason , a desflurane vaporizer is electrically heated to 23C to 25C and pressurized with a backpressure regulator to 1500 mm Hg to create an environment in which the anesthetic has relatively lower, but predictable volatility.
Circle Anesthesia System During Spontanesou and Positive Pressure Ventilation
- During spontaneous ventilation, excess pressure may build during the last part of exhalation, and be allowed to vent at the pt. APL.
- During positive pressure ventilation, excess pressure may build at the end of inspiration and be allowed to vent at the ventilator APL. (Pressure relief, depending on mode.)
Advantages of the Circle System Anesthesia
- Low flow rates are needed from the fresh gas outlet (economy)
- Warming and humidification are achieved from the reaction sin the CO2 absorber
- Reduced chance of overflow and therefore reduced pollution of theatre
Transcutaneous Nerve Stimulation
- Small hand-held electric devices are used to introduce a low voltage electrical stimulation to peripheral nerves.
- The muscles’ reaction to these artificial stimulations can be interpreted by the clinician to quantify muscle block.
- Supra-maximal stimulation (above that which is needed for muscle contraction) of a facial nerve or the ulnar nerve will yield a muscle twitch in a nerve that is not blocked.
- A blocked nerve/muscle will not move.
Transcutaneous Nerve Stimulation Modes
- Single twitch—can identify if a non-depolarizing agent was used.
- Train of Four—can indicate degree of block.
- Tetany—can help identify correct dose of anticholinesterase etc. (post tetanic fasciculation).
Train of Four Monitoring
- When the last of the four responses in ‘Train of Four’ is absent, this correlates to about a 70% muscle blockade.
- The last two absent, correlates to a 80% blockade.
- The last three absent correlates to a 90% blockade
- If no response is seen there is a complete block.
- 90% is seen as adequate in most cases.
Tetany
- can help identify correct dose of anticholinesterase etc. (post tetanic fasciculation).
- Three or more twitches present during emergence indicates little risk of problems with reversal agent.
PETCO2 and Alveolar Gas
- Very small Vt may cause increased PACO2 but a ↓PETCO2.
- This may hinder its usefulness in weaning
- Weaning patient seldom hyperventilate is a patient has their fear/anxiety/pain under control
- Small Vt may increase PACO2 but decrease PetCO2 by just shuffling deadspace volume
- Leak around ETT, unchanged PACO2 but ↓PETCO2
- Leak in sampling system, unchanged PACO2 but ↓PETCO2.
Increased PETCO2
- Malignant Hyperthermia (medical emergency)
- Decreased Alveolar Ventilation (VA)
- Hypoventilation Decreased minute ventilation (VE)
- Increased CO2 production: shivering, pain, fever
- Seizures, sepsis, rebreathing, admin of HCO3
- Exhausted carbon dioxide scrubber
Increase in V/Q -Ventilation in Excess of Perfusion
- Decrease PACO2
- Examples
- Pulmonary embolism
- Decreased CO
- Hypovolemia
- Severe hypotension
- Cardiac arrest
Decreased PETCO2
- ↑ VA —-well above metabolic need
- Very low Vt, approaching dead-space volume
- Low perfusion / ↓ cardiac output / arrest
- Pulmonary emboli
- ↓ CO2 production eg. Hypothermia
- Accidental disconnection or extubation
