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Methods to detect soda lime exhaustion?


Soda lime is chargeable for the elimination of carbon dioxide (CO2) in rebreathing circuits. When exhausted, CO2 accumulates within the circuit and is rebreathed by the affected person, inflicting respiratory acidosis that may be dangerous.

Key factors: strategies to know when to vary soda lime:

  • Elevated impressed CO2 (detected by capnography)
  • Coloration change
  • Lack of warmth within the canister
  • Medical indicators
  • Hardness of granules
  • Time in perform

Measuring impressed CO2

Measuring impressed CO2 is the most dependable methodology to detect absorbent exhaustion. This may be carried out with a capnograph. A typical waveform obtained throughout CO2 reinspiration brought on by soda lime exhaustion is illustrated in Determine 1. Throughout inspiration, the affected person breathes CO2: the curve doesn’t return to 0 throughout inspiration. The form of the hint is regular, and the end-tidal CO2 worth is elevated.

Determine 1: Typical capnograph waveform obtained when soda lime is exhausted (yellow), in comparison with a traditional waveform (gray). Throughout inspiration, the curve doesn’t return to 0, however the form of the waveform is regular. Finish-tidal CO2 worth is elevated.

Indicator colour change

When CO2 reacts with soda lime, warmth and water are fashioned, and pH adjustments. The latter causes the indicator contained in soda lime to vary colour (usually from white to pink), indicating that the absorbent is close to the purpose of exhaustion.

Absorbent ought to be modified when 2/3 of the canister has modified colour. Remember the fact that the colour could revert again to its pre-exhaustion colour when not in use. Upon reuse, the indicator colour will quickly return to it’s exhausted state. Subsequently, a rested canister may give a false sense of safety. Because of this, inspection of the absorbent colour ought to be made throughout or simply after anesthesia. 

Moreover, if the absorbent just isn’t packed correctly within the canister, channeling can happen: the airflow passes by way of a channel within the soda lime, exposing solely a small a part of the absorbent to CO2. As absorbent alongside the channel turns into exhausted rapidly, the affected person rebreathes CO2. The remainder of the soda lime stays white, giving a false sense of safety. Determine 2 illustrates these patterns of absorption.

Subsequently, indicator colour change is beneficial however just isn’t dependable.

Determine 2: Sample of CO2 absorption within the canister. Purple circles characterize exhausted soda lime; white circles characterize recent soda lime.

  • A) Unused canister, or look of the canister after a while unused: all granules are white.
  • B) After restricted use: absorption of CO2 has occurred primarily on the inlet and to a lesser extent alongside the perimeters.
  • C) After intensive use: the canister seems practically fully purple as granules on the facet are exhausted.
  • D) Exhausted soda lime: CO2 is filtering by way of the canister; the one granules which can be nonetheless able to absorbing CO2 are within the distal third.
  • E) Channeling impact: air passes by way of the soda lime preferentially by way of a channel. Soda lime, on this channel, is rapidly exhausted, and the affected person breathes COalthough the canister stays white if the channel just isn’t alongside the wall.

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Different indicators

As said above, throughout CO2 absorption, warmth and water are fashioned. Subsequently, throughout anesthesia, the canister ought to be barely heat to the contact and water droplets ought to be seen on its wall. The quantity of warmth and water vapor is proportional to the quantity of absorbed CO2. If a excessive oxygen stream is used (100 ml/kg/min), CO2 just isn’t eradicated from the circuit by the soda lime. On this state of affairs, the canister might stay chilly. Nevertheless, if the canister stays chilly with an applicable oxygen stream (20 ml/kg/min on a normal rebreathing circuit), it’s crucial to test for different indicators of soda lime exhaustion.

When a affected person breathes CO2, medical indicators could embrace: elevated respiratory fee, elevated amplitude of respiratory motion, improve sympathetic tone (elevated coronary heart fee and blood stress), vasodilation, and purple mucous membrane. A blood fuel evaluation will reveal a respiratory acidosis. With out a capnograph, if these medical indicators are seen, it is very important contemplate soda lime exhaustion within the record of differential analysis.

The facet of the granules can be used as an indicator. Granules ought to fragment simply. If this isn’t the case, it means that soda lime could also be exhausted. It’s notably necessary when altering soda lime. If the hardness of the soda lime is completely different in comparison with regular, it could recommend it’s already exhausted.

With out a capnograph, even when the colour of the soda lime doesn’t change, it is strongly recommended to vary the absorbent after a given period of time. For the standard anesthesia machine, Dispomed recommends altering the soda lime after 14 hours of use. Nevertheless, remember the fact that soda lime could also be exhausted sooner than in 14 hours and that you’ll have to vary it extra typically than each 14 hours.

Lastly, if there’s mud within the canister or if the canister is cracked or not crammed, soda lime ought to be modified.


Soda lime is a key aspect in a rebreathing circuit. As with most anesthesia gear, inappropriate use might be dangerous, and even deadly, for the affected person. Capnography is the one manner to verify the soda lime is useful. The opposite strategies solely recommend that the soda lime must be modified, however they aren’t dependable. It’s subsequently crucial to think about all these strategies when utilizing soda lime.

Lastly, it’s best to vary soda lime earlier than the affected person conjures up CO2.  Altering soda lime throughout anesthesia requires altering the circuit, delaying the procedures, and exposing the affected person to anesthesia for an extended time. The time wanted to do all of this is not going to be devoted to monitoring the affected person, which can improve anesthesia threat. Moreover, as most indicators seem when soda lime is already exhausted, the affected person would already suffers from the results of rebreathing CO2.

Dr. Truchetti Geoffrey, DMV, MSc, DES, DACVAA

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