Test 1- Week 1 Flashcards
Analgesia
Analgesia is a loss of sensitivity to pain
Nociception
Nociception is the neural process of encoding noxious stimuli Does not require consciousness
Tranquilization
Tranquilization is a state of behavioral change, wherein anxiety is relieved and the patient is relaxed, although aware of its surroundings
Sedation
Sedation is a state characterized by CNS depression accompanied by drowsiness. The patient is likely unaware of its surroundings
Compressed gas Oxygen
Absolutely necessary!
Delivering anesthetic gas in air (21% O2) would lead to hypoxemia due to hypoventilation and V/Q mismatch induced by anesthetics themselves
Remember your respiratory physiology!
30-35% O2 (FiO2=0.30-0.35) minimum acceptable for people and small animals
What is the metabolic requirement for oxygen?
5-10 mL/kg/min
Ex. 50-100 mL/min (0.05-0.1 L/min) in a 10 kg
dog
This would be the minimum O2 flow required
What colors are these correspond to green, blue, or yellow?
Oxygen = green
Nitrous oxide (N2O) = blue
Medical air = yellow
Tank safety
Tank safety
NEVER leave an unsecured tank sitting upright
E cylinders – rack, rolling cage
H cylinders – anchored to wall or in transport cart with chain
May explode if dropped or falls over Can become a projectile
TO AVOID FIRE (heat is created as gas expands):
Clean oils from hands and tank, open cylinder
valves slowly
Open and close valve briefly before attaching to machine to remove dust from connecting port
12
What is cylinder pressure in vs breathing system pressure?
Cylinder pressure usually in psi (pounds per square inch)
Breathing system pressure in cmH2O (centimeters water)
High and low pressure systems
High pressure (100-2200+ psi)
Gas cylinder, yokes, pressure gauges, regulators
Intermediate pressure (50 psi)
Central O2 supply, post-regulator, flush valve,
input to flowmeter, driving gas for ventilator
Low pressure (<15 psi)
Between flowmeter output and common gas outlet
Breathing system (= pressure in patients’ lungs)
Oxygen cylinders
E cylinder (MOST COMMON in small animal general practice)
Capacity = 660 L (memorize this number!)
H cylinder
Capacity = 6600 L
Both are filled to a pressure of 2200 psi
Pressure is proportional to volume P1V1 = P2V2 (Boyle’s law)
Therefore, you can figure out roughly how many liters are left in the tank if you know tank pressure
N2O cylinders
N2O exists in both a gaseous and liquid form in the tank
—– Gauge only reads gas pressure
Therefore, it is NOT POSSIBLE to calculate the amount of gas remaining based upon the pressure if liquid N2O remains
- you have to weight the tank in order to figure out much is left!
What are the safety systems in place to make sure that you don’t put the wrong tank on the wrong?
Color-coded tanks
Labelling
Diameter index safety system
Non-interchangeable gas-specific threaded connection system
Used universally by all equipment and cylinder manufacturers
Pin index safety system
Gas-specific pin patterns that only allow connections between the appropriate cylinder yokes and E tanks
Commonly found on yokes mounted to anesthesia machines, also some cylinder- specific regulators/flowmeters
Quick connectors
Manufacturer-specific
Facilitate rapid connecting and disconnecting of gas hoses
Useful for multipurpose work areas
Regulator
AKA pressure-reducing valve
Decreases tank pressure to a safe working pressure (approx. 50 psi) which is supplied to the flowmeter
Prevents pressure fluctuations as the tank empties
Flowmeter
Controls rate of gas flow through the vaporizer
L/min
Gas enters at bottom at 50 psi and exits at top at 15 psi
Tapered glass tube with moveable float
Narrow at the bottom, wider at top
Single- or double-taper Double taper for more
accuracy at lower gas flows
Calibrated for 760 mmHg and 20 C
Reduces gas pressure from 50 psi (intermediate) to 15 psi (low)
Where do you read the flow?
MIDDLE OF BALL
TOP OF BOBBIN
Are flowmeters gas specific or can they be used for any gas?
Gas-specific
Ex. O2 flowmeter NOT accurate if used for N2O
or medical air
If there are multiple flowmeters, O2 should be on the far right (downstream of all other gases) to prevent delivery of a hypoxic gas mixture
Quick flush
Delivers O2 from the intermediate pressure area of the machine (50 psi)
BYPASSES vaporizer
Contains NO anesthetic agent
Delivers gas at a rate between 35-75 L/min directly to the patient circuit
Appropriate use:
Quickly decrease anesthetic gas % in the circuit Emergency
Recovery
Remember this is pure O2 as it has bypassed the
vaporizer
Patient should be disconnected from the circuit temporarily before the O2 flush valve is utilized
Can result in dangerous increases in breathing circuit pressures
What is a possible complication of quick flush?
Possible complication = PNEUMOTHORAX
Small circuit, high pressure, small patient
Anesthetic vaporizers
Change liquid anesthetic into vapour
Deliver selected % of anesthetic vapour to
the fresh (common) gas outlet
“Volumes percent”
Inhalants
Vapor = Gaseous state of substance that is liquid at ambient temp and pressure
Halothane, Isoflurane, Sevoflurane, Desflurane Gas = exists in gaseous state at ambient T
and P
N2O, Xenon
Vapor pressure
Vapor pressure = Pressure exerted by vapor molecules when liquid and vapor phases are in equilibrium
Depends on temperature
Increases with increasing temperature
Inversely related to boiling point
saturated vapor pressure
Vapors have a maximum administration percentage = saturated vapor pressure- most amount of anesthestic that can be in vapor gas
Vapor pressure/Barometric pressure
Ex. Iso 32%
Vaporizers needed to reduce this to clinically useful doses
Anesthetic vaporizers
Modern vaporizers are:
Agent-specific
Concentration-calibrated
Variable-bypass
Flow-over
Out-of-circuit
High resistance
Compensated for temperature, flow, and back- pressure
variable-bypass
A specific concentration is created by variable-bypass system, where fresh gas flows over a reservoir of liquid anesthetic and mixes with carrier gas
out-of- circuit (VOC)
All modern vaporizers are out-of- circuit (VOC)
Carrier gas is from flowmeter
Anesthetic % is known = precision vaporizer
VAPOR IS NOT IN THE PT CIRCUIT
VIC vaporizers – Non-precision
In the past, vaporizers were in the circuit (VIC) – non-precision
Glass jar containing wicking material
Increase surface area for vaporization Ensures saturation with anesthetic gas
Variable bypass
Carrier gas is patient’s expired gases Cannot produce a known anesthetic %
Not temperature compensated
Not currently recommended
Precision vs non-precision
Modern vaporizers compensate for:
Temperature between 15-35 C.
Flow rate between 0.5 and 10 L/min
Back pressure associated with positive pressure ventilation and use of flush valve
Vaporizers
Require no external power (except desflurane)
Routine maintenance is required and must be performed by a qualified technician
Mounted on a “back bar” on the machine
Cannot be tipped – must be emptied before transporting
Filled with wrong agent? What would happen?
What would happen?
Depends on vapour pressure and potency of each agent
Iso in sevo vaporizer could produce a lethal concentration (higher vapour pressure AND higher potency)
Drain and run 1 L/min O2 until completely dry
Vaporizer tipped
What would happen?
Vaporizer tipped
What would happen?
Anesthetic may enter the bypass channel and deliver a high concentration
Run 1 L/min O2 through machine with vaporizer off
Re-breating System
i.e. Circle/Y-piece
- Re-breating System
Universal “F”
- Non-rebreathing System
i.e. Mapleson D
The Re-breathing System
One-way (circular) gas flow
Inspiratory and expiratory breathing limbs
CO2 absorber prevents rebreathing of excessive CO2
Patient re-breathes inhalant and O2 via inspiratory limb
The Re-Breathing System Advantages Vs disadvantages
Advantages
Lower fresh gas flow rate
Saves $$$
Decreases environmental pollution
Patient breaths warm, humidified gases (re-breathes)
Disadvantages
More components more potential for leaks ↑resistance for smaller patients (< 3-10 kg)
[anesthetic gas] changes SLOWLY
Due to lower O2 flow rate (more on that in the inhalant lecture!)
How do rebreathining systems work?
One-way or Unidirectional Valves
Inspiratory
Expiratory
Oxygen Flush Valve:
Oxygen Flush Valve:
Bypasses vaporizer!
DILUTES gases in breathing system and reservoir bag Delivers oxygen directly to the breathing system 35-75 L/minof100%oxygen
CAUTION:
Avoid activation with patient attached to system NEVER NEVER NEVER w/non-rebreathing system!
Fresh Gas Inlet:
Fresh Gas Inlet:
fresh gas (not breathed)
= Hose that provides breathing system with:
oxygen +/- inhalant
MUST check this connection when changing breathing systems
It is SHARED btw re-breathing and non-rebreath
Adjustable Pressure-Limiting (APL) Valve:
Adjustable Pressure-Limiting (APL) Valve:
Aka pop-off valve
Limits pressure buildup in breathing system
OPEN ALWAYS unless:
Pre-use machine check (MUST OPEN when done!)
Must close to administer positive pressure ventilation Manual or controlled
Closed APL valve ↑ pressure in breathing system cardiopulmonary injury
Can result in patient DEATH!
Breathing System Pressure Gauge:
Breathing System Pressure Gauge:
Measures pressure in the breathing system
Should be ZERO (0)!
Exceptions:
unless performing leak checks (pre-use check) providing positive pressure ventilation (IPPV)
Carbon Dioxide Absorber:
Soda lime most commonly used today
Absorber assembly has canister to hold soda lime, 2 ports for connecting breathing tubes, fresh gas inlet, +/- unidirectional valve mount and bag mount
What is soda lime?
Calcium hydroxide with small amount of sodium hydroxide
and color indicator
Indicator = ethyl violet (fresh white; exhausted purple)
Carbon Dioxide Absorber (continued…) Monitor time (limited)
Heat reaction and color change when active
When filling:
Do not pack tightly, avoid dust of broken particles
Check gaskets & seals as a source of leaks (esp if dust particles present)
Signs of Exhaustion
Increase end tidal CO2
If at a light enough plane of general anesthesia: Increased ventilation
Increase in HR & BP initially (then decrease)
Rebreathing (seen on ETCO2)
Respiratory acidosis
Red mucous membranes (carbon monoxide production and inhalation)
Reservoir Bag:
Functions
Observe ventilation, inspiratory reserve, administer manual positive pressure ventilation
Calculation of bag size:
Formula = tidal volume (10-20 mL/kg) x 6 Round UP if in between sizes
Example:
10 kg canine patient x 10-20 mL/kg x 6
= 600mLround up to 1L bag
Oxygen Flow Rates:
Oxygen Flow Rates:
MANY different flow rates may be used with this type
of system
Typically in small animals
Induction & Recovery = (HIGH)50-100 mL/kg/min O2
Maintenance =(SEMI-CLOSED)20-50 mL/kg/min O2
Typically in large animals
Induction & Recovery = 20-50 mL/kg/min O2
Maintenance = (LOW)10-20 mL/kg/min O2
The Non-rebreathing System
Components:
Fresh gas
Nonrebreathing tubes
APL (Mapleson D) OR open/close (Mapleson F) valve Reservoir bag
Missing components:
Soda lime canister
Unidirectional valves
O2 flush button (NEVER USE WITH THIS SYSTEM!)
Advantages and Disadvantages of Non-rebreathing system
Advantages
Very light, with minimal dead space or resistance to
ventilation (good for patients < 3-10 kg; 5kg @ RUSVM) Fewer components = fewer potential for leaks
[anesthetic gas] changes rapidly (high gas flow)
Disadvantages
High gas flow rates
$$$ to run in larger patients
↑ environmental pollution
No rebreathing = gases not as warm or humidified
The Non-rebreathing System
Oxygen Flow Rates:
Oxygen Flow Rates:
HIGH when compared to rebreathing systems
*O2 flow is mechanism for eliminating CO2 !*
Must be a least 2-3 x tidal volume in most cases
200-300 mL/kg/min O2
What monitor would help determine if rebreathing CO2 via O2 flow rate too low?
Endotracheal Tubes and Intubation
Indications:
Indications:
Maintain patent airway
Protect airway from foreign material
Blood, regurgitation
Provide intermittent positive pressure ventilation
(IPPV)
Apply tracheal or bronchial suction
Administer oxygen
Deliver inhalant anesthesia
Benefits of Intubation:
Reduced anatomical dead space
IF correct size and position of tube
Dead space = air WITHOUT gas exchange
Maintain inhalant anesthesia with minimal environmental contamination
Properly inflated cuff
Routes of Intubation:
Oral
Nasal
External Pharyngotomy
Tracheostomy
What is the most common type of ET tube?
Murphy
Laryngoscope:
Laryngoscope:
Makes intubation safer and easier!
Allows visualization of airway
Light source
Apply light pressure to base of tongue, just rostral to epiglottis
Apply gentle pressure ventrally, this tilts larynx, opens glottis, & frees soft palate from epiglottis (if it was entraped)
Do NOT apply significant pressure directly on epiglottis! Risk = fracture of hyoid apparatus
Scavenging Waste Gases
PASSIVE SYSTEMS:
Non-recirculating room ventilation system
Charcoal absorption (F air canisters)* Does NOT scavenge nitrous oxide
Piping direct to atmosphere (i.e. via window)
ACTIVE Scavenging systems
Piped vacuum (white drop and tubing)*
SCAVENGING GASES: CHARCOAL ABSORPTION
ADVANTAGES:
- Absorbs hydrocarbons
- Does not release to ozone
• Portable
DISADVANTAGES:
- Does not adsorb N2O
- Absorbs hydrocarbons only!
- Flow- limited
- Added Resistance
- Weigh before use
- record number of grams
- Discard when 50 grams + or 8-12 h of use
thus, FINITE USE
