CIRCLE SYSTEM AND LOW FLOW ANESTHESIA

1. CIRCLE SYSTEM AND LOW FLOW ANESTHESIA Presented by-Dr. pooja Moderator – dr.darasingh

2. CIRCLE SYSTEM DEFINITION AND COMPONENTS Named so because gases flow in a circular pathway through separate inspiratory and expiratory channels Its primary components are- 1. 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

3. 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

4. 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.

5. 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

6. 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

7. 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

8. 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 22-mm male connector upstream of the unidirectional valve through which gases pass during exhalation

9. 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 22-mm male fitting to allow direct connection between Y-piece and face mask

11. 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

12. 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 .

13. 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

14. CANISTER

15. 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

17. 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.

18. 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

19. 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

20. 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

22. 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

23. 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

24. 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

25. 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

26. Excessive heat and fires-more so with dessicatedBaralyme and sevoflurane Sodalime results in less elevated temperature

27. 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

28. 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

29. 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

31. 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

34. 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

35. CIRCLE SYSTEM TEST To check the integrity of circle system spanning from common gas outlet to Y-piece Leak test and Flow test- Closing 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

36. 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.

37. 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.

38. 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

39. Based on fact that O2 consumption is equal to basal metabolic consumption under anesthesia Nitrous oxide consumption depends on alveolar-arterial pressure gradient. Requirement decreases when peripheral tissues are saturated Newer inhalation agents are minimally metabolized. They are mainly exhaled into the breathing system

40. 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

41. EQUIPMENT Standard anesthesia machine with flowmeters providing low flow. Vaporizers –in-circle vaporizers,calibrated vaporizers or liquid injection Monitors-continuous measurement of oxygen mandatory.

42. 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.

43. 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

44. 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)

45. CONTRAINDICATIONS Malignant hyperthermia Smoke or gas intoxication Uncompensated diabetes Acute alcohol intoxication Chronic alcoholism Gas volume deficiency Insufficient depth of anesthesia Insufficient dinitrogenation Sodalimeexhausion Failure of O2 monitor

46. 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

47. 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

48. THANK YOU