The canister (the absorber)

The Canister (The absorber) by Dr .Mohammad Abdeljawad

1. The Canister (The absorber) Dr.Mohammad Abdeljawad Anesthesia Specialist AL-Bashir Hospital 2020-08-28 1

2. 2020-08-28 2 Carbon Dioxide Absorber and the Absorbent Rebreathing alveolar gas conserves heat and humidity . the CO2 in exhaled gas must be eliminated to prevent hypercapnia . CO2 chemically combines with water to form carbonic acid. CO2 absorbents ( eg , soda lime or calcium hydroxide lime) contain hydroxide salts that are capable of neutralizing carbonic acid. Reaction end products include heat (the heat of neutralization), water, and calcium carbonate . CO2 absorbents is used to absorb the patient’s exhaled carbon dioxide . FGF requirements are low, making the circle system very efficient and causing minimal pollution.

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4. The Canister (The absorber) The absorbent granules (soda lime, baralyme, or amsorb ) are contained within one or two containers or cansters which fit snugly between a head and a base plate. They should have: . Transparent walls to allow clear inspection of the color of the indicator dye. . A baffle system to allow direction of flow and uniform dispersion of exhaled gases to minimize channelling. . dust trap at the bottom of the canister to collect alkaline dust and moisture . . A large size canister can be used with less frequent changing of the exhausted soda lime because the canisters are not part of the apparatus dead space as they are present on the expiratory limb of the circuit. 2020-08-28 4

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7. Types of Granules: 2020-08-28 7 Soda lime consists primarily of calcium hydroxide (80%), along with sodium hydroxide, water, and a small amount of potassium hydroxide. It has a pH of 13.5 and a moisture content of 14–19%.

8. 2020-08-28 8 Soda lime is an absorbent and is capable of absorbing up to 23 L of CO2 per 100 g of absorbent

9. Neutralization Reaction : Neutralization of C02 is done as a base neutralizing an acid. The base is the hydroxide and the acid is th carbonic acid. The following reactions occur: a) With Soda Lime: • At first, C02 (due to tissue metabolism) reacts with the water to form carbonic acid. Water is essential . for the reaction (reaction A). The source of the water is: - soda lime (14-19%) - exhaled gases - the chemical reaction. 2020-08-28 9

10. • Then, carbonic acid reacts with the hydroxides present in soda lime; At first with sodium and potassium hydroxide ( fast reaction, B ), Then with calcium hydroxide (slow reaction, C) The end results of the reactions are carbonates, water, and heat (i.e., an exothermic reaction). 2020-08-28 10

11. 2020-08-28 11 b) With Amsorb plus:

12. 2020-08-28 12 The water formed by neutralization of C02 is useful in: Humidification of the inspired gases. Dissipating some of the heat generated by the exothermic neutralization reaction. The heat of the reaction can be detected by the warmness of the canister containing the soda lime (the temperature in the center of a soda lime canister may exceed 60°C). Absence of this warmness indicates failure of the soda lime to neutralize C02

13. 2020-08-28 13 Indicator Dyes: • Chemical pH-sensitive dyes are added to the soda lime and the baralyme. When C02 is absorbed, the pH of the medium is changed; therefore, the color of the dye will change. • Ethyl violet is the most common indicator dye used by manufacturers. Its color is changed from white to violet when soda lime or baralyme are exhausted. • Although exhausted granules may revert to their original color if left (rested), they must not be reused because their absorptive capacity is not recovered. With amsorb plus, the color of indicator does not revert to its original color

14. 2020-08-28 14 Colour changes occur when the pH is less than 10.

15. 2020-08-28 15 Ethyl violet is a substituted triphenylmethane dye with a critical pH of 10.3.The dye changes from colorless to violet when the pH of the absorbent decreases as a surrogate indicator of exhaustion. When the absorbent is fresh, the pH exceeds the critical pH of the indicator dye, and it exists in its colorless form. However, as the absorbent becomes exhausted, the pH decreases below 10.3 and ethyl violet changes to its violet form because of alcohol dehydration. circumstances ethyl violet may not always be a reliable indicator of the functional status of the absorbent. For example, prolonged exposure of ethyl violet to fluorescent light can produce photodeactivation of this dye. When this occurs, the absorbent appears white even though it may have a reduced pH and its absorptive capacity has been exhausted.

16. 2020-08-28 16 The Rate of CO2 Absorbent Exhaustion The rate at which soda lime becomes exhausted depends on: • The capacity of the canister. • The fresh gas flow rate. • The rate of C02 production i.e., the rate of tissue metabolism Sign of exhaustion: 1- Changes in color of the absorbent granules, due to changes in the color of the indicator dye. The absorbent should be replaced when 50-70%of the granules have changed in color .

17. 2020-08-28 17 2-Raise in end-tidal C02 by capnography. 3-Clincal signs of C02 accumulation (hypercapnia) as tachycardia, hypertension, flushed skin, sweating, and increased wound oozing Recantly. an anesthetic-gas monitor is applied to the anesthetic gases. If C02 is found in the inhaled gas, .this is the time at which the soda lime must be changed. Absorbent exhaustion typically occurs first where exhaled gas enters the absorber and along the canister’s smooth inner walls.

18. 2020-08-28 18 The lower the FGF used, the more rapidly soda lime granules are consumed. This is because most of the exhaled gases pass through the absorber with very little being discarded through the APL valve. For a 70–80 kg patient with a tidal volume of 500 mL , respiratory rate of 12 breaths/min and CO2 production of 250 mL /min, using an FGF of 1 L/min, the soda lime will be exhausted after 5–7 hours of use. For the same patient but using an FGF of 3 L/min, the soda lime will be exhausted after 6–8 hours of use. In a completely closed system, a standard 450-gram canister becomes inefficient after approximately 2 ‘h

19. 2020-08-28 19 The Efficiency of CO2 Absorption : 1- The Size of Absorbent Granules : • The size of soda lime, baralyme, or amsorb granules is expressed as the mesh size. ~ mesh size (the mesh number) corresponds to the number of holes per square inch of a screen. i.e., a 4 mesh sieve has 4 openings per inch (4 strands per linear inch), and 8 mesh sieve has 8 openings per linear inch . ( the higher the mesh number, the smaller the particles are ) • The optimal size of granules is from 4-8 mesh i.e., the diameter of the granules ranges from 1/4 to 1/8 inch because: Larger sized granules are avoided as this decreases the surface area for C02 absorption. Smaller sized granules are avoided because this increases the resistance to breathing .

20. 2020-08-28 20 2-The Volume of the Inter-Granular Space : • To ensure complete C02 absorption, the air space between the granules (i.e., the inter-granular space) when the canister is tightly packed should be equal to or exceed the tidal volume of the patient. . If the patient's tidal volume exceeds the inter-granular space, C02 accumulation will occur. • The intergranular space is roughly equal to 50% of the canister's capacity. So. To ensure complete absorption, a patient’s tidal volume should not exceed the air space between absorbent granules, which is roughly equal to 50% of the absorber’s capacity

21. 2020-08-28 21 3- Channelling: • It is the easy passage of expired gases through areas of loosely packed granules (unfilled areas with granules). This will cause incomplete C02 absorption because most of the granules are bypassed. • Channelling is decreased by: Tight packing of the canister by absorbent granules. Holding the absorbent granules in space by screens and baffles in the canister, to help direction of the flow and uniform dispersion of exhaled gases through the canister. which directs gas flow through the center. Mounting the canister vertically

22. 2020-08-28 22 Absorbent granules can absorb and later release medically active amounts of volatile anesthetic. This property can be responsible for modest delays of induction or emergence. The drier the soda lime, the more likely it will absorb and degrade volatile anesthetics.

23. 2020-08-28 23 Disadvantages of C02 Absorbents: (The Interaction between the C02 Absorbent and Inhalational Anesthetics) The heat (60°C) and strong alkalinity of soda lime and baralyme can decompose volatile anesthetics producing toxic by-products. Factors that Increase the Level of Toxic By-Products: 1- Low fresh gas flow (FGF)rates less than 1 L/min (especially with haloalkane toxicity). 2- The dryness of the absorbent (especially with carbon monoxide toxicity). 3- Increased C02 absorbent temperature. 4- High anesthetic concentrations. 5- Increased C02 production by the patients. 6- The use of baralyme more than soda lime. 7- Prolonged time of exposure

24. 2020-08-28 24 Mechanism of Production of Toxic By-Products: There are two types of toxic products produced: a) Haloalkane: (with halothane and sevoflurane). • In animals (as rats), halothane and sevoflurane react with soda lime and baralyme producing toxic haloalkane compounds. - Halothane is decomposed to haloalkane 2-bromo-2-chloro-1,1-difluoro ethane (BCDFE)compound. - Sevoflurane is decomposed to fluoromethyl-2,2-difluoro-l-(tri-fluoro-methyl) vinyl ether which is known as " compound A" or "Olefin". Both compounds are metabolized in the liver to cysteine conjugates which are metabolized in the kidney by a (3-lyaseenzyme giving nephrotoxins that cause proximal tubular necrosis .

25. 2020-08-28 25 • In Humans, the P-lyase activity is only 10%that in the kidney of rats, and so, the levels of haloalkane in humans are very low, and no halothane or sevoflurane nephrotoxicity is seen in humans . For sevoflurane, some studies are still controversial; therefore, Factors that increase the production of compound A are : a. increasing temperature b. high sevoflurane concentrations c. use of barylime rather than soda lime d. low FGF e. newer designs of soda lime, being non-caustic (no KOH and only very low levels of NaOH), claim less or no production of compound A. For substance A production, barylime is worse than soda lime and Amsorb is the safest

26. 2020-08-28 26 Food and Drug Administration (FDA)recommends: 1- Avoiding the use of sevoflurane in patients with renal dysfunction especially at low fresh gas flow rates< 1 L/min. 2- Exposure to sevoflurane should not exceed 2 MAC-hour (i.e., exposure for one MAC for 2 hours) at< 1-2 L/min. Compound A has been shown to produce nephrotoxicity in animals but has never been associated with ill effects in humans .

27. 2020-08-28 27 b) Cardon Monoxide with (desflurane, enflurane or isoflurane). Desflurane, enflurane, and isoflurane (not halothane or sevoflurane with sevoflurane , it occurs at a higher temperature .) react with soda lime and baralyme producing carbon monoxide (CO) toxicity. This is more with the volatile anesthetics in the order desflurane, enflurane and then isoflurane. The incidence increases with Monday's first case because the absorbent becomes dry by accidentally leaving continuous gas flow through an anesthetic machine over the weekend. Carbon monoxide is a colorless, odorless, non-irritating gas that is easily absorbed through the lungs.

28. 2020-08-28 28 Carbon monoxide causes hypoxia because hemoglobin (Hb) has 220 times greater affinity for carbon monoxide than for O2.;therefore, carbon monoxide displaces 02 from hemoglobin forming carboxyhemoglobin (CO-Hb) which may reach> 30%.This: decreases the ability of Hb to carry 02. shifts the 02-Hb dissociation curve to the left causing increased Hb affinity to 02 which in turn decreases 02 release to the tissues. Carbon monoxide binds more tightly to fetal hemoglobin than adult hemoglobin, making infants particularly vulnerable to its effects; therefore, more care is taken in pregnant females.

29. 2020-08-28 29 Children because of their higher metabolic rate and oxygen consumption, are also very susceptible to carbon monoxide toxicity. Carbon monoxide also disrupts oxidative metabolism, increases nitric oxide concentrations, causes brain lipid peroxidation, generates oxygen free radicals, and produces other metabolic changes that may result in neurological and cardiac toxicity.

30. 2020-08-28 30 Several factors increase the production of CO and resultant increased carboxyhemoglobin levels, including the following : • The inhaled anesthetic used (for a given MAC multiple, the magnitude of CO production from greatest to least is desflurane ≥ enflurane > isoflurane >> halothane = sevoflurane), • The dryness of the absorbent • The type of absorbent • The temperature (increased temperature increases CO production) • The anesthetic concentration (more CO is produced with higher anesthetic concentrations)187 • Low fresh gas flow rates • Reduced experimental animal (patient) size per 100 g of absorbent

31. 2020-08-28 31 clinical picture of carbon monoxide toxicity: 1-Central nervous symptoms: Acute: headache, nausea, vomiting, irritability, dizziness, visual/ motor disturbances and decreased consciousness. Delayed: may occur 3-21 days later in 67% of patients in the form of cognitive deficits, personality changes, and dementia, incontinence and gait disturbances. 2- Cardiovascular symptoms: tachyarrhythmias, angina especially in patients with coronary artery disease. Cherry-red lips may be present in some patients. 3- Death : occurs if CO-Hb reaches 67%.

32. 2020-08-28 32 • Detection of carbon monoxide toxicity is very difficult intraoperatively due to the following reasons: 1- Although the patient is hypoxic, cyanosis is not obvious because CO-Hb has a cherry red color, which is visible in the skin, mucous membranes and nail beds. 2 - The clinical picture of CO toxicity is masked by the anesthesia 3 - Certain mass spectrometers and infrared anesthetic detectors (but not all) may give warnings of "mixed agent or the wrong agent", when isoflurane or desflurane degrades to carbon monoxide. Appearance of these warnings should trigger a practitioner to consider carbon monoxide formation and change the C02 absorbent.

33. 2020-08-28 33 4 - Pulse oximetry cannot detect the hypoxia of CO poisoning because CO-Hb and Oxy-Hb absorb light at the same wavelength (660 nm); therefore, the pulse oximeter will give a false high reading because the CO-Hb is interpreted as Oxy-Hb. Routine blood gas analysis does not recognize the presence of abnormal hemoglobins. However, CO-Hb level can be detected by co-oximetry (multi-vavelength oximetry) in vitro by testing a blood sample. Arterial blood sampling is not necessary since arterial and venous CO-Hb levels correlate well.

34. 2020-08-28 34 Treatment of CO toxicity Treatment of CO toxicity is limited. 1- Oxygenation by 100% 02 at atmospheric pressure or by using hyperbaric 02. 02 therapy shortens the elimination half-time of carbon monoxide by competing at the binding sites for hemoglobin. It decreases the half-life of CO-Hb from 4-6 hours while breathing room air to 40-60 minutes when breathing 100%oxygen. It is administered until carboxy -Hb levels <10%. 2- Supportive treatment such as cardiovascular stabilization

35. 2020-08-28 35 Absorbent Heat Production. One extremely rare but potentially life-threatening complication related to carbon dioxide absorbent is the development extreme exothermic reactions that lead to fires and explosions within the breathing system. Specifically, this seems to occur as a result of interactions between desiccated strong-base absorbents (particularly Baralyme ) and the inhaled anesthetic sevoflurane.

36. 2020-08-28 36 Other substances can accumulate such as methane, acetone, ethanol and hydrogen . However, they do not generally become clinically significant.

37. 2020-08-28 37 Patient Safety Foundation provides guidance to reduce the risk adverse interactions , The recommendations include the following : • Turning off all gas flow when the machine is not in use • Changing the absorbent regularly • Changing the absorbent whenever the color change indicates exhaustion • Changing all absorbent, not just one canister in a two canister system • Changing the absorbent when uncertain about the state of hydration, such as if the fresh gas flow has been left on for an extensive of indeterminate period of time • If used, changing compact canisters more frequently Finally, educating anesthesia personnel regarding these hazards and their preventive measures will also reduce the likelihood of an adverse event.

38. 2020-08-28 38 Soda lime is corrosive. Protective clothing, gloves and eye/face protection can be used . Opening the canister assembly abolished the integrity of the breathing circuit, so ventilation had to be accomplished via other means if the absorbent had to be changed during the course of anesthesia and apnea could not be tolerated. Increasingly, workstation design allows the canister to be replaced during anesthesia without interfering with breathing system continuity, sometimes referred to as a bypass feature

39. 2020-08-28 39 If one could design an ideal carbon dioxide absorbent, its characteristics would include : a lack of reactivity with common anesthetics, an absence of toxicity, low resistance to airflow, minimal dust production, Small cost, ease of handling, high efficiency carbon dioxide absorption. There should also exist a reliable method of assessing for absorbent depletion the container that houses the absorbent should be easy to remove and replace Should impose minimal risk of causing breathing system leaks or obstruction.

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