| JOURNAL HOME | CME HOME | THIS MONTH | PAST ISSUES | ETOC | COLLECTIONS |
| AUTHORS | REVIEWERS | EDITORIAL BOARD | FEEDBACK | RSS | HELP |
| ||||||||||||||
| ||||||||||||||
|
|
|
|
||||||||||||
|
||||||||||||||
Address correspondence and reprint requests to Jie Zhang, Department of Anesthesiology, The First Affiliated Hospital of ZhengZhou University, No. 1 East-JianShe Road, ZhengZhou 450052, China. Address e-mail to joannyzh{at}hotmail.com.
Abstract
BACKGROUND: We evaluated sevoflurane requirements during combined general-epidural anesthesia with different concentration of ropivacaine.
METHODS: Fifty-six patients were randomly divided into three groups to epidurally receive saline, 0.2% ropivacaine or 1% ropivacaine. Sevoflurane concentration was adjusted to maintain certain anesthesia depth. BIS values and end-tidal sevoflurane concentrations were recorded at time points of pre-intubation and 5 min, 10 min, 15 min, 20 min, 25 min, 30 min after intubation.
RESULTS: End-tidal sevoflurane was significantly lower in the group receiving higher concentration of sevoflurane.
CONCLUSIONS: Epidural anesthesia can decrease sevoflurane requirements to a larger extent when a higher concentration of ropivacaine was applied.
A combined epidural-general anesthesia technique has been widely used in major abdominal and thoracic surgery. Hodgson et al. (1) demonstrated that epidural anesthesia with lidocaine markedly reduced the minimum alveolar concentration (MAC) of sevoflurane. Additionally, the quality of epidural blockade also varies depending on concentrations of local anesthetic used, which may consequently affect general anesthetic requirements (2,3). In the present study, we evaluated the sevoflurane requirements to keep bispectral index (BIS) at 45–55 in the absence of surgical stimulation during epidural blockade using different concentrations of ropivacaine.
METHODS
After institutional ethics committee approval and written informed consent, 60 patients, ASA I or II, 22- to 60-yr-old, undergoing abdominal surgery were recruited into the study. Exclusion criteria included a history of substance abuse, major back problems, coagulation abnormality, liver or kidney dysfunction, allergy to either sevoflurane or ropivacaine, or neurological disorders.
All patients received no premedication and fasted for at least 8 h. On arrival at the operating room lactated Ringer's solution was infused IV at a rate of 10 mL · kg–1 · h–1. Room temperature was adjusted to 22°C–25°C. Patients were randomized into 1 of 3 groups to receive epidural saline (Group S), 0.2% (Group R0.2), or 1% (Group R1) ropivacaine. After epidural catheterization, a bolus of 10 mL followed by continuous infusion at a rate of 6 mL/h was administered using a microinfusion pump. Cephalad limit of sensory block to cold sensation was determined by an alcohol-soaked swab bilaterally 15 min after bolus injection. Patients who had an asymmetric blockade of more than two dermatomes were excluded, as well as those whose upper level of blockade was higher than T3. General anesthesia was induced with 5% sevoflurane and 67% nitrous oxide (N2O) in oxygen, 0.15 mg/kg vecuronium, and 2 µg/kg fentanyl followed by tracheal intubation. N2O was discontinued and anesthesia was maintained with sevoflurane in a mixture of 67% air and oxygen. BIS was monitored during anesthesia and the inspired sevoflurane concentration was adjusted to keep the BIS value between 45 and 55. After tracheal intubation, the inspired sevoflurane concentration was first set at 2.0% according to the reported ED95 of sevoflurane (2.07%) (4) and adjusted based on a change in BIS by an increment of 0.2%. All patients presenting for the study were monitored with electrocardiography, noninvasive arterial blood pressure, pulse oximetry, and pharyngeal temperature. End-tidal concentrations of carbon dioxide and sevoflurane were measured. Ephedrine (10 mg) was administered when mean arterial blood pressure was lower than 60 mm Hg. Atropine (0.3–0.5 mg) was administered when heart rate was lower than 50 bpm. The lungs were mechanically ventilated and tidal volume was adjusted to keep end-tidal carbon dioxide between 35 and 40 mm Hg. Anesthetic procedures were performed by an anesthesiologist who was blinded to the study.
Datasets of BIS value and end-tidal sevoflurane concentration were recorded at the following time points: pre-intubation, 5, 10, 15, 20, 25, and 30 min after intubation. A second anesthesiologist who was also blinded to the study was responsible for recording data. Surgery did not commence until all the procedures were completed.
Sample size was estimated by a power analysis based on the variability observed in a preliminary study (sd 0.2%). A minimal sample of 16 patients in each group would give a power of 80% and an 
level of 0.05 for detecting a difference in end-tidal sevoflurane of 0.35%. Data are expressed as mean ± sd unless otherwise stated. Demographic data were compared among groups using one-way ANOVA and upper dermatomal levels were compared between the two ropivacaine groups using Mann–Whitney rank-sum test. For comparison of BIS value and end-tidal sevoflurane concentration among groups, repeated measures ANOVA and post hoc comparisons (Fisher's L. sd test) were used. Linear regression analysis was used to investigate the relationship between end-tidal sevoflurane concentration and time after intubation in all three groups. P values of <0.05 were considered statistically significant.
RESULTS
Fifty-six patients completed the study, 18 in Group S, 19 in Group R0.2, and 19 in Group R1. All patients had been maintained at a body temperature of near 37°C during the study. There were no significant differences in demographic data among the groups. However, patients in Group R1 had a higher upper dermatomal level than those in Group R0.2 (Table 1). BIS values at all time points were similar among the three groups (Fig. 1). The end-tidal sevoflurane concentration in Group R1 was significantly lower than that in Group R0.2 and Group S (P < 0.01). Group R0.2 also had a significantly lower end-tidal sevoflurane concentration than Group S (P < 0.01) (Table 2) at all time points after tracheal intubation. The end-tidal sevoflurane concentration was inversely related to time after intubation. No patient received ephedrine or atropine to maintain hemodynamics during the study period (Table 3).
|
|
|
|
DISCUSSION
A BIS value about 50 is considered to be an indication of an adequate hypnotic effect for surgical procedures (5). In the present study, BIS was used as an index for adequate anesthesia and was maintained between 45 and 55. To eliminate the influence of other drugs, we used no premedication and N2O was discontinued right after tracheal intubation.
This study demonstrated that epidural ropivacaine reduced sevoflurane requirements and the effect was ropivacaine concentration-dependent. This sparing effect may have been due to a supraspinal effect that suppressed the level of consciousness indicated in one study (1). As demonstrated by Ishiyama et al. (6), when a fixed concentration of inhaled sevoflurane was administered, epidural ropivacaine decreased BIS during general anesthesia. Hodgson et al. (1,7) and Shono et al. (8) reported that epidural anesthesia reduced requirements for volatile anesthetics during general anesthesia. These investigations used lidocaine for epidural blockade and applied noxious stimuli such as transcutaneous electrical stimulation. No previous study evaluated sevoflurane requirements during epidural anesthesia. During general anesthesia we noted a trend of decrease in sevoflurane requirements with or without epidural blockade. No noxious stimulus was applied during our study to maintain a fairly stable environment for the patients in order to observe the changing end-tidal sevoflurane concentrations in the specific time periods.
We demonstrated that sevoflurane requirements were significantly less in the group using high concentration (1%) ropivacaine than in the low concentration (0.2%) group. This could have resulted from the difference in intensity of the sensory blockade due to the difference in dosage and concentration of local anesthetics (2,3). The two ropivacaine groups had significantly different upper levels for sensory block to cold. We speculate that the higher the upper dermatomal level, the more spinal afferent fibers are blocked, thus creating a more intense suppression of consciousness. Another possible mechanism may be the systemic general anesthetic effects of absorbed epidural ropivacaine. It is reported that IV lidocaine would cause a reduction in MAC of halothane in a dose-dependent mode (9). Conversely, Casati et al. (10) reported that epidural bupivacaine and fentanyl induced a sparing effect of isoflurane and the sparing effect was similar between the higher and lower concentrations of bupivacaine. These results differ from those of our study and may have been due to the co-administration of epidural fentanyl.
In summary, we report epidural ropivacaine causes a reduction in sevoflurane requirements in a dose-dependent fashion.
Footnotes
Accepted for publication December 22, 2006.
REFERENCES
This article has been cited by other articles:
|
|
 |
|
  M. Senturk, B. Gucyetmez, T. Ozkan-Seyhan, M. Karadeniz, S. Dincer, D. Akpir, T. Sengul, and T. Denkel Comparison of the effects of thoracic and lumbar epidural anaesthesia on induction and maintenance doses of propofol during total i.v. anaesthesia Br. J. Anaesth., August 1, 2008; 101(2): 255 - 260. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
