Maintaining sevoflurane anesthesia during low-flow anesthesia using a single vaporizer setting change after overpressure induction.
OBJECTIVE
A sevoflurane vaporizer dial setting of 1.9% was previously found to maintain the end-expired sevoflurane concentration (Et(sevo)) at 1.3% during maintenance of anesthesia for procedures up to one hour with an O(2) FGF of 1 L/min. We examined whether applying these parameters could simplify low-flow sevoflurane anesthesia after overpressure induction using two slightly different techniques.


METHODS
Prospective clinical study.


METHODS
Large teaching hospital.


METHODS
Sixteen patients receiving general anesthesia for a variety of peripheral procedures.


METHODS
Anesthesia was induced with overpressure with sevoflurane (8%) in an 8 L. min(-1) O(2)/N(2)O mixture (30%/70%). After a laryngeal mask airway (LMA) was placed, fresh gas flow (FGF) was lowered to 1 L. min(-1) using O(2) and N(2)O (FiO(2) 30%) with patients breathing spontaneously. In group I patients (n = 8), the vaporizer dial was set at 1.9% at the same time the FGF was lowered. In group II patients (n = 8), the vaporizer was turned off until Et(sevo) had decreased to 1.3%, after which the dial was set at 1.9%. The course of Et(sevo) in the two groups was examined.


RESULTS
In group I, Et(sevo) after 3 min was 4.88 +/- 1. 12%. Et(sevo) decreased slowly after reduction of FGF to 1.83 +/- 0. 19%, 1.59 +/- 0.18%, and 1.52 +/- 0.19% at 10, 20, and 30 min, respectively. In group II, Et(sevo) after 3 min was 4.34 +/- 0.84%, and decreased more rapidly after reduction of FGF to 1 L. min(-1) than in group I. Et(sevo) was 1.40 +/- 0.09%, 1.40 +/- 0.11%, and 1. 38 +/- 0.13% at 10, 20, and 30 min, respectively.


CONCLUSIONS
After high-flow overpressure induction with sevoflurane, a single change in vaporizer setting (to 1.9%) and FGF (to 1 L. min(-1)) suffices for the Et(sevo) to approach the predicted Et(sevo) (1.3%) within 10-15 min; thereafter the Et(sevo) remains nearly constant. As expected, the predicted Et(sevo) is attained slightly faster when the vaporizer is temporarily turned off. Clinically applying previously derived pharmacokinetic parameters simplifies low-flow sevoflurane anesthesia after overpressure induction.
Hendrickx
J F
JF
Departments of Anesthesiology, Onze Lieve Vrouwziekenhuis, Aalst, Belgium.
Vandeput
D M
DM
De Geyndt
A M
AM
De Ridder
K P
KP
Haenen
J S
JS
Deloof
T
T
De Wolf
A M
AM
D000328:Adult; D000769:Anesthesia, Inhalation / Q000295:instrumentation; D000776:Anesthesiology / Q000295:instrumentation*; D018685:Anesthetics, Inhalation; D005260:Female; D006801:Humans; D008297:Male; D008738:Methyl Ethers; D008875:Middle Aged; D009330:Nebulizers and Vaporizers; D000077149:Sevoflurane
D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D000077149:Sevoflurane