Low flow anesthesia allows for economy of volatile anesthetics, makes possible heating and humidification of gases and reduces environmental pollution
Sodalime contains 94% Calcium hydroxide, 5% Sodium hydroxide and also Potassium hydroxide, Silica and dying agent
CO2 + 2NaOH –> Na2CO3 + water + heat
Na2CO3 + Ca(OH)2 –> 2NaOH + CaCO3
..this sequence gets back Sodium hydroxide
1 Kg of Sodalime can absorb >120 L of CO2
Carbon monoxide which is a byproduct of protein metabolism can accumulate in the system, but levels are <4%
If there is intoxication by alcohol or poisoning by Carbon monoxide or severe diabetic ketosis, alcohol or CO or acetone from the expired gases, will recirculate and accumulate inside the system; so low flow anesthesia is contraindicated in such states
Prolonged anesthesia with sevoflurane may generate Compound A inside the system, which can cause acute tubular necrosis in rats at concentrations around 250 ppm, a dose that is nearly 200 times seen in clinical practice. So any proteinuria, glycosuria or enzymuria which does develop in such a context has not been shown to have any clinical significance, even in patients with pre-existing renal disease
Reference: Al-Shaikh B, Stacey S. Essentials of Anaesthetic Equipment, 2nd edn. Edinburgh: Churchill Livingstone, 2002; pp. 74–9 . Nunn G. Low-flow anaesthesia. Contin Educ Anaesth Crit Care Pain 2008; 8: 1–4.