Use of spectral entropy monitoring in reducing the quantity of sevoflurane as sole inhalational anesthetic and in decreasing the need for antihypertensive drugs in total knee replacement surgery.
BACKGROUND
The use of spectral entropy for monitoring the depth of anesthesia or level of hypnosis in surgery or painful procedures can reduce the consumption of drugs and shorten the recovery time of total intravenous anesthesia such as by propofol. The aim of this study was to investigate: (1) the consumption of sevoflurane as the sole anesthetic; and (2) hemodynamic stability in orthopedic surgery with tourniquet inflation under the guidance of spectral entropy, in contrast with the conventional method.


METHODS
Sixty-five patients, ASA I or II, scheduled to undergo total knee replacement were enrolled and randomized into an entropy-guided group or a conventionally-monitored group. In the conventional group, the depth of anesthesia was judged by the clinical experience of the anesthesia provider based on the hemodynamic response. In the entropy group, state entropy (SE) and response entropy (RE) were kept within the range of 35-45 and an adequate gradient of 5-10 intraoperatively. The overall consumption of sevoflurane (mL) was monitored by the GE Datex-Ohemda S/5 Anesthetic Delivery Unit System. The physiologic changes during five major events in sequence in total knee replacement surgery, i.e., intubation, tourniquet inflation, skin incision, deflation and extubation, were observed closely over the first 5 minutes after each individual event. Within the first 5 minutes of each event, antihypertensive drugs were prohibited. The rest of the time, changes were recorded at 5-minute intervals and the use of rescue medication was allowed in case of need. We compared the heart rate, mean arterial pressure, SE, RE, sevoflurane concentration and rescue drugs in both groups.


RESULTS
The sevoflurane consumption was significantly lower in the entropy group than in the conventional group (27.79 +/- 7.4 mL vs. 31.42 +/- 6.9 mL; p < 0.05). During the first 5 minutes of each major event, there were no significant differences in hemodynamics between the two groups. In the ensuing time, entropy-guided anesthesia was associated with significantly less frequent need of antihypertensive drugs (0.94 vs. 1.48 times; p = 0.043), especially in the 45-60 minutes after tourniquet inflation (p = 0.012).


CONCLUSIONS
Using spectral entropy monitoring for guiding the depth of sevoflurane anesthesia in total knee replacement surgery can reduce its consumption and the frequency of use of antihypertensive drugs.
Wu
Shao-Chun
SC
Department of Anesthesiology, Chang Gung Memorial Hospital-Kaohsiung Medical Center, Chang-Gung University College of Medicine, Kaohsiung, Taiwan.
Wang
Peng-Chih
PC
Liao
Wen-Tzu
WT
Shih
Tsung-Hsiao
TH
Chang
Kow-Aung
KA
Lin
Kun-Chen
KC
Chou
An-Kuo
AK
D000368:Aged; D018685:Anesthetics, Inhalation / Q000008:administration & dosage*; D000959:Antihypertensive Agents / Q000008:administration & dosage*; D019645:Arthroplasty, Replacement, Knee; D019277:Entropy; D006439:Hemodynamics; D006801:Humans; D008738:Methyl Ethers / Q000008:administration & dosage*; D016343:Monitoring, Intraoperative / Q000379:methods*; D000077149:Sevoflurane
D018685:Anesthetics, Inhalation; D000959:Antihypertensive Agents; D008738:Methyl Ethers; D000077149:Sevoflurane