Transcript CIRCLE SYSTEM - Pheonix India

CIRCLE SYSTEM AND LOW
FLOW ANESTHESIA
PRESENTED BY-DR. POOJA
MODERATOR – DR.DARA SINGH
CIRCLE SYSTEM DEFINITION AND
COMPONENTS
Named so because gases flow in a circular pathway
through separate inspiratory and expiratory channels
Its primary components are1. Fresh gas inlet
2. Inspiratory and expiratory unidirectional valves
3. Inspiratory and expiratory corrugated tubes
4. Y-piece connector
5. APL valve
6. Reservoir bag
7. Canister containing CO2 absorbent
Other components included in circle system are Respiratory gas monitor sensor
 Airway pressure monitor sensor
 Respirometer
 PEEP valve
 Filters
 Heated humidifier
 Bag ventilator selector switch
FRESH GAS INLET
 connected to common gas outlet on anesthesia
machine by flexible tubing
 ASTM standards require that inlet port has an inside
diameter of atleast 4.0mm and fresh gas delivery
tube has an inside diameter of atleast 6.4mm
 On newer machines, direct connection between
machine outlet and breathing system so user does
not see a fresh gas hose.
UNIDIRECTIONAL VALVES(flutter, one-way, check,
directional, dome, flap, nonreturn, inspiratory, and expiratory)
 direction of intended
gas flow permanently
marked on the valve
housing or near its
associated port with
either a directional
arrow or with the
marking inspiration or
expiration so that it is
visible to the user
 Valves ensure that gas flows in
one direction only
 Gases enter at the bottom
raising the disc from its
seat.gas then passes under
dome and through breathing
system
 Reversing gas flow causes disc
to contact seat preventing
retrograde flow
One or both unidirectional
valves may become
incompetent
 A unidirectional valve may jam,
obstructing gas flow
BREATHING TUBES
 Each tube connects to a
port on the absorber at
one end and the Y-piece
at the other
 The dead space extends
from Y-piece to patient
 Length of tubes does not
affect the dead space
 Longer tubes allow the
anesthesia machine to
be located farther from
the patient's head
 The inspiratory port has a 22-
mm male connector
downstream of the inspiratory
unidirectional valve through
which gases pass toward the
patient during inspiration
 The expiratory port has a 22mm male connector upstream
of the unidirectional valve
through which gases pass
during exhalation
Y-PIECE
 Three-way tubular connector with two 22-mm
male ports for connection to the breathing tubes
and a 15-mm female patient connector for a
tracheal tube or supraglottic airway device
 Patient connection port usually has a coaxial 22mm male fitting to allow direct connection between
Y-piece and face mask
APL VALVE
 During spontaneous breathing, the valve is left
fully open and gas flows through the valve during
exhalation
 When manually assisted or controlled
ventilation is used, the APL valve should be
closed enough that the desired inspiratory
pressure can be achieved
 When this pressure is reached, the valve opens
and excess gas is vented to the scavenging system
during inspiration
RESERVOIR BAG
 The bag is usually
attached to a 22-mm
male bag port (bag
mount or extension)
 It may also be placed at
the end of length of
corrugated tubing or a
metal tube leading from
the bag mount .
CANISTERS( CO2–ABSORBENT CONTAINERS,
CHAMBERS, UNITS, CARTRIDGES)
 Transparent side wall
 Screen at bottom which holds absorbent
 There may be 2 canisters in series or 1 single
canister
SIZE
 Small canisters are used more frequently
 Frequent changes help to provide fresh
absorbent
 Internal volume of the breathing system is
reduced
CANISTER
 First absorption occurs at the inlet and along
canister sides. As this absorpion is exhausted, CO2
absorption occurs further downstream
 No difference whether gases enter at the top or
bottom
 Spaces at the top and bottom of
absorber for incoming gases to
disperse before passing through
the absorbent or for outgoing
gases to collect before passing on
through the circle
 Canister is attached to housing
that incorporates valves that will
close the entrance and exit from
the canister when the canister is
removed.
Allows breathing system
continuity to be maintained
when the canister is changed.
COMPOSITION OF ABSORBENTS
HIGH ALKALI ABSORBENTS
 Soda lime – KoH -1 % ,NaOH- 4%, H2O-15% Ca(OH)2-80%
and silica
 Keiselguhr is used as hardening agent
 When desiccated, form CO with anesthetics
 Sevoflurane - Compound A is formed.
LOW ALKALI ABSORBENTS
 Barylime- barium hydroxide-20%,Ca(OH)2-80%
ALKALI FREE ABSORBENTS
 Calcium hydroxide ,CaCl2 with other agents like CaSO4 and
polyvinylpyrolidine , inc porosity and hardness
 No CO , compound A formation
 Indicator changes color on drying
 CO2 absorption capacity is less
 CO2 absorption employs general principle of base
neutralizing acid
 Acid is carbonic acid formed by reaction of CO2 with
water.
CO2+H2O=H2CO3
H2CO3+2NaOH=NaCO3+2H2O+Heat
Na2CO3+Ca(OH)2=CaCO3+2NaOH
 An indicator is added to absorbent to signify whether
its ability to absorb CO2 has exhausted
 Its an acid or base whose colour depends on pH
SIZE AND SHAPE
 Pellets or small granules provide greater surface area
 Size is measured by mesh number-no of openings per
linear inch in a sieve through which granular particles
can pass
 4-mesh strainer has four openings per square inch , 8
mesh has eight openings per square inch
 Mostly 4-8 mesh size is used
HARDNESS
 Some granules fragment easily, producing dust
 Excessive powder produces channeling, resistance to
flow
 small amounts of a hardening agent are added
 Coating of granules is done with film
PRODUCTS OF RXN B/W ABSORBENT AND
ANESTHETIC AGENT
HALOALKENE FORMATION
Compound A – vinyl ether
 Sevoflurane decomposes to produce compound A
 More so when prolonged anesthesia
 Dry absorbent
 lower fresh gas flows
 Higher temperature
 Higher concentration of sevoflurane
 Absorbets containing KOH or NaOH
Carbon Monoxide Highest levels are seen with desflurane followed by
enflurane and isoflurane
 When absorbent is dry
 High temperature
 Absorbents with KOH or NaOH
 Small patient size
 High fresh gas flow
PREVENTION
- All fresh gas flow should be turned off after each
case.
- Vaporizers should be turned off .anesthetic system
flushed with fresh gas
- Absorbent should be changed regularly
- Practice of supplying O2 through circle system
should be discouraged when not receiving GA
- Temperature should be monitored
-Integrity of absorbent packaging should be tested
 Excessive heat and fires-more so with dessicated
Baralyme and sevoflurane
 Sodalime results in less elevated temperature
WHEN TO CHANGE
 Appearance of CO2 in inspired gas
 Indicator colour change-a phenomenon of
regeneration is noticed. Exhausted colour show
reversal on rest but absorption capacity will be low
and colour will reappear after brief exposure to CO2
 Heat in canister
RESPIRATORY GAS MONITOR SENSOR
 Oxygen analyzer-ASA standards require use of O2
analyzer on breathing circuits with alarms
-to detect hypoxic mixture inspiration
-to detect leaks and disconnections
-to detect hypoventilation
PARAMAGNETIC and ELECTROCHEMICAL O2
Analyzers-when a gas containing O2 is passed
through magnetic field,gas will expand and contract
causing a pressure wave proportional to O2 partial
pressure
 In electrochemical , sensor contains a cathode and
anode surrounded by electrolyte. Gel is held in place
by membrane permeable to O2
 O2 diffuses through membrane to cathode where it
is reduced causing current to flow . The rate of O2
entering membrane is proportional to partial
pressure of O2
 Display is usually in percent O2
 CO2 monitors –diverting and non diverting
 Diverting type uses a pump to aspirate gas from sampling
site to the sensor through a sampling tube
 Sampling flow rate less than 150ml/min should not be
used
 During low flow techniques flow should be returned to
circuit
 Based on infrared technology-gases with 2 or more
dissimilar atoms have specific absorpion spectra. Since
amount of infrared light absorbed is proportional to
concentration of absorbing molecules its conc. Is
determined by comparing with known standard
ADVANTAGES AND DISADVANTAGES
 Low flow can be used with its advantages
 Useful for malignant hyperthermia
DISADVANTAGES
 Chances of disconnections and leaks
 Bulky
 Difficult to clean
 Toxic product formation
CIRCLE SYSTEM TEST
To check the integrity of circle system spanning from
common gas outlet to Y-piece
Leak test and Flow testClosing pop-off valve, occluding y-piece, pressurizing the
circuit to 30cm of H2O with oxygen flush valve.Value on
pressure gauge will remain fixed for atleast 10sec.
Flow test check integrity of unidirectional valve .By
removing Y-piece and breathing through 2 tubes
individually. The valves should move
appropriately.operator should be able to inhale not
exhale through inspiratory limb and vice-versa.
Alternately by using breathing bag and ventilator
LOW FLOW ANESTHESIA
 Inhalation technique in which circle system with
absorbent is used with a fresh gas inflow of less than
patient,s alveolar minute volume
- less the 1 or 1.5 l/min
- 3L or less
-0.5-2l/min
-0.5-1l/min
 Inhalation technique via a rebreathing system in which
rebreathing fraction amounts to atleast 50% i.e.atleast
50% of exhaled gas volume is led back to patient after
CO2 absorption.
 Closed system anesthesia is a low flow anesthesia in
which fresh gas flow equals uptake of anesthetic
gases and oxygen by the patient ,system and gas
sampling.
 No gas is vented through APL valve.
FLOW TECHNIQUE NOMENCLATURE
 High flow- >1l/min
 Low flow anesthesia-1l/min
 Minimal flow anesthesia-500ml/min
 Basal metabolic-250ml/min
 Uptake-140-180ml/min
 Based on fact that O2 consumption is equal to basal
metabolic consumption under anesthesia
 Nitrous oxide consumption depends on alveolararterial pressure gradient. Requirement decreases
when peripheral tissues are saturated
 Newer inhalation agents are minimally metabolized.
They are mainly exhaled into the breathing system
Requirements can be calculated by VO2=10 x Kg3/4
 N2O=o.7x0.47x%N2Ox Q
 Inhalation agents=G(b/G)x C(A-V)xQ
EQUIPMENT
 Standard anesthesia machine with flowmeters
providing low flow.
 Vaporizers –in-circle vaporizers,calibrated
vaporizers or liquid injection
 Monitors-continuous measurement of oxygen
mandatory.
TECHNIQUE
 Induction
-Intavenous induction
-By injection of liquid anesthetic in expiratory limb but
takes prolonged time to establish concentration
-By using high flow initially to allow denitrogenation,
establish anesthetic agent concentration. After gas
exchange low fresh gas flow are used.
MAINTENANCE
 Nitrous oxide, oxygen flows and vaporizer settings
should be adjusted to maintain a satisfactory oxygen
concentration and desired level of anesthesia.
 Constant circuit volume is achieved by-constant reservoir
bag size(increasing FGF if bag size decreases, decreasing
FGF if bag size increases)
 Ventilator with ascending bellows-FGF is adjusted so
that bellows is below the top of its housing at the end of
exhalation
 Ventilator with descending bellows-bellows just reaches
the bottom of its housing at the end of exhalation
High flows should be used for 1-2min atleast once an
hour to eliminate gases such as nitrogen and carbon
monoxide that have accumulated in system.
EMERGENCE-anesthetic administration is stopped
toward end of operation and circuit is maintained
with enough oxygen flow to maintain end tidal
volume of the reservoir bag(coasting)
CONTRAINDICATIONS
 Malignant hyperthermia
 Smoke or gas intoxication
 Uncompensated diabetes
 Acute alcohol intoxication
 Chronic alcoholism
 Gas volume deficiency
 Insufficient depth of anesthesia
 Insufficient dinitrogenation
 Sodalime exhausion
 Failure of O2 monitor
ADVANTAGES
 Economy
 Reduced operating room pollution
 Reduced environmental pollution
 Estimation of anesthetic agent uptake and oxygen
consumption
 Buffered changes in inspired concentration
 Heat and humidity conservation
 Less danger of barotrauma
DISADVANTAGES
 More attention required
 Inability to alter inspired concentration quickly
 Danger of hypercarbia
 Accumulation of undesirable gases in the system-
CO, compound A, acetone, methane,hydrogen,
argon,nitrogen acrylic monomer when joint
prosthesis is cemented
 Faster absorbent exhaustion
 Uncertainty about inspired concentration
 THANK YOU