Absorption and degradation of sevoflurane and isoflurane in a conventional anesthetic circuit.
Soda lime and Baralyme degrade sevoflurane, the rate of degradation being a direct function of temperature. We tested whether this degradation would impede the development of an anesthetizing concentration of sevoflurane (compared with isoflurane, a compound that is not degraded) in a circle-absorption system having an increased temperature consequent to (a) carbon dioxide production (200 mL/min) and absorption; and (b) a low inflow rate (70 mL/min). We also measured the temperatures reached in various parts of the absorption system when used in clinical practice, finding that peak temperatures usually reached 37 degrees - 46 degrees C when low inflow rates (500 mL/min) were applied. The tests in the model system demonstrated that soda lime and Baralyme absorbed both sevoflurane and isoflurane, and that both absorbants degraded sevoflurane but not isoflurane. Baralyme produced a fourfold greater degradation of sevoflurane vapor than did soda lime (0.66 mL/min compared with 0.17 mL/min). However, except for a slight delay at the start of anesthesia, neither absorption nor degradation should noticeably affect the requirement for anesthetic delivery in clinical practice, even in low-flow systems.
Liu
J
J
Department of Anesthesia, University of California, San Francisco 94143-0464.
Laster
M J
MJ
Eger
E I
EI
Taheri
S
S
D000042:Absorption; D000328:Adult; D000776:Anesthesiology / Q000295:instrumentation*; D001464:Barium; D017609:Barium Compounds; D001831:Body Temperature; D017610:Calcium Compounds; D002126:Calcium Hydroxide; D002675:Child, Preschool; D004987:Ethers; D006801:Humans; D007530:Isoflurane; D008738:Methyl Ethers; D008875:Middle Aged; D010087:Oxides; D011188:Potassium; D017680:Potassium Compounds; D000077149:Sevoflurane; D012972:Sodium Hydroxide
D017609:Barium Compounds; D017610:Calcium Compounds; D004987:Ethers; D008738:Methyl Ethers; D010087:Oxides; D017680:Potassium Compounds; D001464:Barium; D000077149:Sevoflurane; C068927:Baralyme; C004569:soda lime; D012972:Sodium Hydroxide; D007530:Isoflurane; D002126:Calcium Hydroxide; D011188:Potassium