|Year : 2015 | Volume
| Issue : 4 | Page : 594-601
Hypobaric ropivacaine (0.1%) in spinal anesthesia with or without low-dose clonidine or fentanyl for anorectal surgery
Satish Dhasmana MD , Yadunath Vishwakarma, Vinita Singh, Mohammad Imran
Department of Anaesthesiology, King George's Medical University, Lucknow, Uttar Pradesh, India
|Date of Submission||01-Jul-2014|
|Date of Acceptance||29-Sep-2014|
|Date of Web Publication||29-Dec-2015|
Department of Anaesthesiology, King George's, Medical University, Lucknow, Uttar Pradesh, 226003
Source of Support: None, Conflict of Interest: None
Perineal and anorectal surgeries performed on an outpatient basis under spinal block lead to a shorter postoperative hospital stay. Spinal anesthesia has better cost efficacy and is very well accepted by patients. Ropivacaine is less toxic with rapid motor recovery. Clonidine provides dose-dependent analgesia. Intrathecal opioids decrease nociceptive afferent input without affecting dorsal root axons.
The aim of this study was to compare the onset, the level, and the duration of sensory and motor blockade occurring after the administration of low-dose hypobaric ropivacaine (0.1%) either alone or with clonidine or fentanyl as adjuvants in spinal anesthesia for anorectal surgeries in the jack-knife position.
A prospective, randomized, double-blind, comparative, case-control study. A total of 75 ASA grade I-III patients were randomized into three groups.
There was a significant difference in the heart rate among the three groups. The plain ropivacaine group had a significantly higher heart rate. The addition of fentanyl resulted in a stable heart rate, but with the addition of clonidine, there was a decrease in the heart rate from the baseline. Mean arterial pressure (MAP) in the ropivacaine group was significantly higher in comparison with the clonidine or the fentanyl groups. None of the patients in any of the groups had complete motor blockade (Bromage score ≥ 3) at any time. After 2 h, there was complete regression (Bromage score = 1) in all the patients in all the groups. The majority of cases, irrespective of their group, achieved a T10 level of sensory blockade. The time taken for two-segment regression of sensory block and the time required for the first analgesic dose was significantly higher (P < 0.001) in the clonidine group.
Hypobaric ropivacaine provides adequate surgical conditions for anorectal surgeries. Also, intrathecal clonidine with 0.1% hypobaric ropivacaine is a better adjuvant than fentanyl as it prolongs the duration and improves the quality of the sensory block and provides postoperative analgesia for longer periods.
Keywords: additives, anesthesia, anorectal surgery, clonidine, fentanyl, hypobaric ropivacaine, local anesthetic, spinal, surgery
|How to cite this article:|
Dhasmana S, Vishwakarma Y, Singh V, Imran M. Hypobaric ropivacaine (0.1%) in spinal anesthesia with or without low-dose clonidine or fentanyl for anorectal surgery. Ain-Shams J Anaesthesiol 2015;8:594-601
|How to cite this URL:|
Dhasmana S, Vishwakarma Y, Singh V, Imran M. Hypobaric ropivacaine (0.1%) in spinal anesthesia with or without low-dose clonidine or fentanyl for anorectal surgery. Ain-Shams J Anaesthesiol [serial online] 2015 [cited 2019 Jun 20];8:594-601. Available from: http://www.asja.eg.net/text.asp?2015/8/4/594/172747
| Introduction|| |
Now a days, 60-70% of elective surgeries in the developed world are being performed on an outpatient basis under peripheral or central neuraxial blocks  . With the introduction of new general anesthetics, spinal block for outpatient surgical procedures is now being challenged ,,, .
Patients who received conventional doses of anesthetic for spinal block had a longer recovery time and hospital stay than those who received general anesthesia; however, spinal anesthesia has fewer side effects, better cost-efficacy relationship, and is very well accepted by patient  . Conventional doses of local anesthetics used in spinal block may not be justified for outpatient usages; therefore, anesthesiologists need to familiarize themselves with techniques that present a rapid recovery profile. Here, the dose is more important than the concentration or the volume of the local anesthetic regarding the distribution of the spinal block, especially when the solution has the same density as the cerebrospinal fluid.
Ropivacaine is the first single enantiomer-specific compound that has a reduced risk of cardiotoxicity, neurotoxicity, and rapid recovery of motor function , . Postoperative pain relief is an important issue with ropivacaine. It has been used with many adjuvants for lower abdominal surgery, which have other side effects. Hence, our concern was of using a drug as an adjuvant with ropivacaine that provides better intraoperative hemodynamic conditions and prolonged postoperative analgesia with minimal side effects. Many studies on the use of hypobaric spinal anesthesia with bupivacaine in the jack-knife position for anorectal surgery have been undertaken in the past ,, . Clonidine is the best a2 adrenergic agonist that provides dose-dependent analgesia, and it has side effects of hypotension, bradycardia, and sedation. The action of clonidine is based on the attenuation of nociceptive input from Ad and C fibers and synergism with spinal local anesthetics. It is not associated with the side effects of spinal opioids such as respiratory depression and pruritus and has less potential for producing urinary retention. The addition of either oral or spinal clonidine to spinal local anesthetics increases sensory and motor block ,,,,, . Opioids were the first clinically used selective spinal analgesics after the discovery of opioid receptors in the spinal cord. Intrathecal opioids selectively decrease nociceptive afferent input from Ad and C fibers without affecting dorsal root axons or somatosensory-evoked potentials. Lipophilic opioids (fentanyl, sufentanil) have a more favorable clinical profile of fast onset (min), modest duration (1-4 h), and little risk of delayed respiratory depression. The recommended safe effective dose of spinal fentanyl is 10-25 mg  .
On reviewing the literature, till date no study was found on the use of hypobaric ropivacaine in anorectal surgery. Therefore, the present study was designed to assess the use of hypobaric ropivacaine with or without low-dose clonidine or low-dose fentanyl in this surgical setting.
| Materials and methods|| |
After getting approval from the Ethical Committee of the King George's Medical University, an informed consent was obtained from all the patients for this prospective, randomized, double-blind comparative study. Patients aged 18-60 years, belonging to ASA grades I-III, undergoing anorectal surgery were enrolled in the study. Patients having absolute or relative contraindication for central neuraxial block, patients with a history of hypersensitivity or adverse drug reaction to any of the study medications, patients with chronic pain syndrome, patients with a history of b-blocker, calcium channel blocker, analgesic, or opioid use, and patients with heart block were excluded from the study.
All patients were given premedication on the night before surgery with ranitidine (150 mg), metoclopramide (10 mg), and alprazolam (0.25 mg) orally. Patients were explained about the process of spinal anesthesia.
In the operating room, standard monitors including noninvasive blood pressure, pulse oximetry, and ECG were applied, and the baseline blood pressure, heart rate, and oxygen saturation were recorded. An 18-G intravenous line was secured and 500 ml of lactated Ringer's solution was given for preloading. About 4 mg of ondansetron was given intravenously to each patient before spinal anesthesia. Patients were randomized into one of the following groups using a computer-generated random number table.
Group I: Patients received intrathecal 5 ml hypobaric ropivacaine 0.1%.
Group II: Patients received intrathecal 5 ml hypobaric ropivacaine 0.1% with 5 mg clonidine as an adjuvant.
Group III: Patients received intrathecal 5 ml hypobaric ropivacaine 0.1% with 15 mg fentanyl as an adjuvant.
Patients were placed in the jack-knife position, and after taking all aseptic precautions, spinal anesthesia was administered at the L4-L5 level with a 25-G Quincke's spinal needle.
One milliliter of isobaric ropivacaine 0.5% was added to 4 ml of distilled water to make it hypobaric, with a concentration of 0.1% and a total volume of 5 ml, which was administered intrathecally. The volume remained constant even after adding the adjuvants. The intrathecal injection was prepared by an anesthesia technician who did not take part in the study.
The onset and the duration of analgesia, the peak sensory level, the time to reach the maximum sensory level, and associated motor blockade were noted in each patient. The heart rate, the noninvasive blood pressure (systolic, diastolic, and mean), and oxygen saturation were recorded every 3 min for the initial 20 min, then every 5 min for the rest of the surgery, and then every 15 min. Patients were assessed as per the following clinical parameters:
The surgeon's opinion about the quality of anesthesia was recorded on a four-point scale (0 = poor anesthesia; 1 = satisfactory anesthesia; 2 = good anesthesia; 3 = excellent anesthesia). Any complications that occurred during anesthesia were noted and treated promptly. Dexamethasone (4 mg intravenously) was given to patients complaining of nausea and tramadol (0.5 mg/kg intravenously) was given to patients complaining of shivering. Lactated Ringer's solution was used as the intravenous fluid throughout the surgery. Supplemental oxygen with a facemask at the rate of 5 l/min was given to each patient throughout the surgery.
- Sympathetic blockade: Hypotension was defined as systolic blood pressure of less than 90 mmHg or greater than 20% decrease in baseline values, and it was treated with bolus doses of 0.1 mg/kg of mephentermine. Tachycardia was defined as heart rate of greater than 100/min and bradycardia was defined as heart rate of less than 60/min. It was treated with atropine 0.01 mg/kg bolus.
- Sensory block was assessed bilaterally using pin-prick sensation in the midclavicular line every 5 min. The time to reach the highest level of sensory block and the time for regression of two segments in the maximum block height were noted.
- Motor blockade was assessed using the Bromage scale (0, the patient is able to move the hip, the knee, and the ankle; 1, the patient is unable to move the hip, but is able to move the knee and the ankle; 2, the patient is unable to move the hip and the knee, but is able to move the ankle; 3, the patient is unable to move the hip, the knee, and the ankle).
- The time for first analgesic requirement postoperatively or the time when the patient perceives pain for the first time after spinal anesthesia was noted using visual analogue scale.
Sample size estimation
The sample size was calculated keeping in view the time taken to achieve a T10 level of motor block. It was assumed that the proposed intervention would reduce the time taken to achieve the block by 2-5 min, that is, 2 ± 2 min as compared with conventional intervention. At 95% confidence level and 80% power, a minimum sample of 17 patients in each group was determined. However, to increase the power and the confidence level of the study, a sample size of 25 was targeted in each group.
Data were analyzed using the Statistical Package for Social Sciences (SPSS) version 15.0 (SPSS inc. Chicago, USA). Data were represented as mean ± SD and number and percentages. For continuous parametric data, intergroup comparisons were performed using analysis of variance followed by an independent samples 't'-test. Comparisons of changes in parametric data were evaluated using the paired 't'-test. Categorical comparisons were performed using the c2 -test. The confidence level of the study was set at 95%, and hence, a 'P' value less than 0.05 indicated a statistically significant difference.
| Results|| |
The three groups were comparable with respect to their age, sex, BMI, and ASA physical status [Table 1]. The three groups were also identical with respect to their baseline hemodynamic parameters, that is, heart rate, systolic blood pressure, diastolic blood pressure and MAP [Table 2].
At subsequent time intervals till 20 min observation, a significant difference in the heart rate of different groups was observed. At all these time intervals, group I had higher heart rate values as compared with groups II and III. The difference between groups I and III was also statistically significant at 0 min and then from 4 min till 20-min intervals. The difference between groups I and II was statistically significant from 2 min till 20-min intervals. Group III had a significantly higher mean value compared with group II at 0- and 20-min intervals [Table 3] and [Table 4].
|Table 3 Comparison of the heart rate among groups at different time intervals|
Click here to view
|Table 4 Between-group comparison of the heart rate at different time intervals|
Click here to view
In all the groups except group II, the heart rate as compared with the baseline showed a decrease at 0 min, which was also statistically significant. However, in group II, there was a reduction at 0 min itself. In all the groups, values were lower as compared with the baseline at all time intervals [Table 5].
|Table 5 Within-group changes in the heart rate (as compared with baseline) at different intervals (paired 't'-test)|
Click here to view
At subsequent time intervals, a significant difference in the MAP of different groups was observed. At all these time intervals, group I had a higher value as compared with groups II and III. Between groups I and II, a statistically significant difference was observed from 0 to 25 min: group I showed higher values as compared with group II at all time intervals except at 20 min, and the difference between the two groups was also statistically significant at 0 min and then from 6 min till 10-min intervals. In all the groups, the MAP was less than baseline values at all the time intervals [Table 6] [Table 7] [Table 8].
|Table 6 Comparison of mean arterial pressure among the groups at different time intervals|
Click here to view
|Table 7 Between-group comparison of mean arterial pressure at different time intervals|
Click here to view
|Table 8 Within-group changes in mean arterial pressure (as compared with baseline) at different intervals (paired 't'-test)|
Click here to view
The majority of the cases in all the groups achieved Bromage score 2 after 5 min and maintained a score of 2 immediately after surgery, showing no significant difference among the groups. Except two (8%) cases in group II and one (4%) case in group III, all the cases showed regression to Bromage score 1 at the 2-h postsurgery evaluation. Statistically, there was no significant difference among the groups (P > 0.05) [Table 9].
The majority of the cases, irrespective of their group, achieved a T10 level of sensory blockade, and thus, the median value was T10 in all the three groups. Sensory blockade above the T10 level was achieved in six (24%) cases each of groups I and III and three (12%) cases of group II. However, statistically, there was no significant difference among the groups with respect to the level of sensory blockade achieved (P = 0.742) [Table 10]).
As compared with group II, both groups I and III took significantly lesser time for two-segment regression of the block and the first analgesic dose, whereas compared with group III, group I took significantly lesser time for two-segment regression of the block and the first analgesic dose (P < 0.001).
A total of four (16%) patients in group III, two (8%) in group I, and 12 (48%) in group II reported bradycardia, shivering, and pruritus, respectively, with the difference being statistically significant for bradycardia and pruritus only. No other complication was observed in any patient [Table 11]). For the majority of the cases in all the groups, the surgeon's satisfaction rating was excellent (9-10). Although the proportion of cases with a higher satisfaction rating was higher in group II (84%) as compared with groups I (64%) and III (60%), yet the difference was not statistically significant (P = 0.144).
| Discussion|| |
With an increasing trend towards daycare surgery, ensuring patient satisfaction along with cost effectiveness is of prime importance. Up till now, spinal anesthesia had little importance in daycare surgeries due to the prolonged motor blockade and side effects, especially when using long-acting local anesthetics  . Attention to the technique, reduction of the dose, and addition of fentanyl to lidocaine result in effective spinal anesthesia with rapid recovery and a lower incidence of significant side effects or complications  . To compete with modern ambulatory general anesthesia, knowledge of special spinal anesthetic techniques is essential. Newer spinal anesthetic techniques for common ambulatory procedures highlight the success of combining subclinical doses of local anesthetics and intrathecal adjuncts  .
As anorectal surgeries are among the most common surgeries that are performed on an outpatient basis, we chose to conduct our study on such patients. Small doses of lidocaine (~40 mg) and bupivacaine (~7.5 mg) are found to be appropriate for ambulatory surgery. A minimum dose of 4-5 mg of 0.5% hyperbaric bupivacaine is required for anorectal surgeries  . This dose is also useful in providing selective sensory blockade with a reduced incidence of postoperative urinary retention in patients undergoing anorectal surgeries  .
The effective dose of hypobaric ropivacaine combined with sufentanil 5 mg providing 95% success in spinal anesthesia for traumatic femoral neck surgery in the elderly is 9 mg. Doses exceeding this may increase the incidence of hypotension  . Hypobaric ropivacaine is an effective and easy technique that allows the production of short-duration one‐sided spinal anesthesia  .
Low-dose ropivacaine (4 mg) is similar to lidocaine (25 mg) in promoting adequate anesthesia for outpatient anorectal surgeries in the jack-knife position; 3 ml (4.5 mg) of hypobaric 0.15% bupivacaine or 3 ml (18 mg) of hypobaric 0.6% lidocaine produce an adequate sensory level for surgery with no motor blockade  . In our study, 5 ml of 0.1% ropivacaine resulted in a prolonged duration of analgesia without any motor blockade in the jack-knife position for anorectal surgeries.
Various agents such as opioids, clonidine, ketamine, neostigmine, and midazolam have been used as adjuvants to bupivacaine for spinal analgesia. Although opioids are most commonly used, they have certain disadvantages such as delayed respiratory depression, pruritus, and postoperative nausea and vomiting. Intrathecal clonidine has been proven to be a potent analgesic, free of at least some of the opioid-related side effects  . It has been shown to produce analgesia without producing significant respiratory depression after systemic, epidural, or spinal administration  .
Intrathecal opioids added to low-dose local anesthetics produce a synergistic effect without increasing the level of sympathetic blockade or the duration of motor blockade, but it is not recommended as an adjunct due to prolongation of the recovery time. The minimum effective dose of intrathecal fentanyl that in combination with low-dose intrathecal bupivacaine (5 mg) would provide adequate surgical conditions without prolonging recovery is 12.5 mg, which provides better surgical anesthesia and increased reliability of block than an intrathecal dose of 7.5 or 10 mg  . Therefore, we used 15 mg of fentanyl in our study.
Higher doses of clonidine from 75 to 150 mg given intrathecally have been associated with significant adverse effects such as bradycardia along with considerable prolongation of motor and sensory blockade. Addition of clonidine 15 and 30 mg to bupivacaine prolongs the time to the first analgesic requirement and decreases postoperative pain with minimal risk of hypotension  .
We used an extremely low dose of 5 mg clonidine as an adjunct to hypobaric ropivacaine in our study and we did not see complete motor blockade in any of the patients suggesting the differential blockade produced by the ropivacaine. Although patients had a Bromage score of either 1 or 2 in all the groups after administration of spinal anesthesia, no technical difficulties were reported during the surgical procedure. After 2 h, there was complete regression (Bromage score = 1) in all patients in all the groups. This suggests that the quality of the differential blockade produced by ropivacaine (sensory > motor) is sufficient for producing adequate surgical conditions with no significant motor blockade.
The majority of the cases, irrespective of their group, achieved a T10 level of sensory blockade. This suggests that 5 ml of hypobaric (ropivacaine 0.1%) drug is adequate in producing a sensory level of T10 required for anorectal procedures. Addition of clonidine prolongs bupivacaine spinal block , . However, marked hemodynamic changes and sedation may limit the usefulness of intrathecal clonidine. Although clonidine prolonged sensory analgesia, there was also an undesirable prolongation of motor block postoperatively. Clonidine had no effect on the onset time and the spread or the intensity of spinal anesthesia. The higher dose of clonidine (150 mg) significantly prolonged the duration of sensory blockade by 50 min and the duration of motor block by 40 min, whereas 75 mg had no significant effect. In addition, there was a significant and long-lasting reduction in the heart rate and the MAP in both the clonidine groups  . Unfavorably, postoperative demand of analgesics was not reduced by spinal injection of clonidine. However, 5 mg clonidine as an adjuvant to hypobaric intrathecal ropivacaine did not cause any significant hemodynamic changes and sedation without any motor blockade in our study.
Addition of clonidine 15 and 30 mg to bupivacaine prolonged the time to the first analgesic requirement and decreased postoperative pain with minimal risk of hypotension  . It has been shown to produce analgesia without producing significant respiratory depression after systemic, epidural, or spinal administration  . As mentioned in above studies, in our study, intrathecal clonidine also prolonged the duration of sensory block. In the majority of the cases, irrespective of their groups, they achieved a T10 level of sensory blockade. The highest sensory level achieved with an equal volume of drug was higher in the clonidine and the fentanyl groups, but a T10 level was achieved in all three groups; thereafter, surgery could be performed in all groups comfortably. Thus, there was no significant difference among the groups with respect to the level of sensory blockade achieved. There was significant prolongation of the duration of analgesia without any significant difference in the incidence of complications/adverse effects. Adding clonidine or fentanyl to hypobaric ropivacaine provided early onset of sensory block, adequate sedation, and prolonged postoperative analgesia.
| Conclusion|| |
Hypobaric ropivacaine provides adequate surgical conditions for anorectal surgeries. Also, intrathecal clonidine with 0.1% hypobaric ropivacaine is better than fentanyl as an adjuvant because it prolongs the quality and the duration of the sensory block produced, providing postoperative analgesia for longer periods, resulting in better patient satisfaction and postoperative recovery and a reduced need for postoperative rescue analgesics without compromising surgical conditions.
| Acknowledgements|| |
Conflicts of interest
| References|| |
Dahl V, Raeder J. Regional anaesthesia in ambulatory surgery. Curr Opin Anaesthesiol 2003; 16:471-476.
Vaghadia H, McLeod DH, Mitchell GW, Merrick PM, Chilvers CR. Small-dose hypobaric lidocaine-fentanyl spinal anesthesia for short duration outpatient laparoscopy. I. A randomized comparison with conventional dose hyperbaric lidocaine. Anesth Analg 1997; 84:59-64.
Pavlin DJ, Rapp SE, Polissar NL, Malmgren JA, Koerschgen M, Keyes H. Factors affecting discharge time in adult outpatients. Anesth Analg 1998; 87:816-826.
Vaghadia H. Spinal anaesthesia for outpatients: controversies and new techniques. Can J Anaesth 1998; 45:R64-R75.
Vaghadia H, Viskari D, Mitchell GW, Berrill A Selective spinal anesthesia for outpatient laparoscopy. I: characteristics of three hypobaric solutions. Can J Anaesth 2001; 48:256-260.
Yamashita A, Matsumoto M, Matsumoto S, Itoh M, Kawai K, Sakabe T. A comparison of the neurotoxic effects on the spinal cord of tetracaine, lidocaine, bupivacaine, and ropivacaine administered intrathecally in rabbits. Anesth Analg 2003; 97:512-519, table of contents.
McNamee DA, Convery PN, Milligan KR. Total knee replacement: a comparison of ropivacaine and bupivacaine in combined femoral and sciatic block. Acta Anaesthesiol Scand 2001; 45:477-481.
Maroof M, Khan RM, Siddique M, Tariq M. Hypobaric spinal anaesthesia with bupivacaine (0.1%) gives selective sensory block for ano-rectal surgery. Can J Anaesth 1995; 42:691-694.
Ariyama J, Hayashida M, Sugimoto Y, Imanishi H, To-Oyma Y, Kitamura A. Spread of spinal anesthesia in patients having perianal surgery in the jackknife position: effects of baricity of 0.5% bupivacaine and positioning during and after induction of spinal anesthesia. J Clin Anesth 2009; 21:408-413.
Imbelloni LE, Gouveia MA, Vieira EM, Cordeiro JA. Selective sensory spinal anaesthesia with hypobaric lidocaine for anorectal surgery. Acta Anaesthesiol Scand 2008; 52:1327-1330.
Berstock DA. Haemorrhoidectomy without tears. Ann R Coll Surg Engl 1979; 61:51-54.
Buckenmaier CC III, Nielsen KC, Pietrobon R, Klein SM, Martin AH, Greengrass RA, Steele SM Small-dose intrathecal lidocaine versus ropivacaine for anorectal surgery in an ambulatory setting. Anesth Analg 2002; 95:1253-1257, table of contents.
Coloma M, Duffy LL, White PF, Kendall Tongier W, Huber PJ Jr. Dexamethasone facilitates discharge after outpatient anorectal surgery. Anesth Analg 2001; 92:85-88.
Davis BR, Kopacz DJ. Spinal 2-chloroprocaine: the effect of added clonidine. Anesth Analg 2005; 100:559-565.
De Kock M, Gautier P, Fanard L, Hody JL, Lavand'homme P. Intrathecal ropivacaine and clonidine for ambulatory knee arthroscopy: a dose-response study. Anesthesiology 2001; 94:574-578.
De Santiago J, Santos-Yglesias J, Girón J, Jiménez A, Errando CL. Low-dose hypobaric spinal anesthesia for anorectal surgery in jackknife position: levobupivacaine-fentanyl compared to lidocaine-fentanyl. Rev Esp Anestesiol Reanim 2010; 57:565-570.
Zoremba M, Wulf H. Spinal anaesthesia in day case surgery - old technique - new trends. Anasthesiol Intensivmed Notfallmed Schmerzther 2010; 45:176-180.
Urmey WF. Spinal anaesthesia for outpatient surgery. Best Pract Res Clin Anaesthesiol 2003; 17:335-346.
Salinas FV, Liu SS. Spinal anaesthesia: local anaesthetics and adjuncts in the ambulatory setting. Best Pract Res Clin Anaesthesiol 2002; 16: 195-210.
Gudaityte J, Marchertiene I, Pavalkis D, Saladzinskas Z, Tamelis A, Tokeris I. Minimal effective dose of spinal hyperbaric bupivacaine for adult anorectal surgery: a double-blind, randomized study. Medicina (Kaunas) 2005; 41:675-684.
Park SY, Park JC, Park SH. Is it useful and safe to maintain the sitting position during only one minute before position change to the jack-knife position? Korean J Pain 2010; 23:190-197.
Lilot M, Meuret P, Bouvet L, Caruso L, Dabouz R, Deléat-Besson R, et al
. Hypobaric spinal anesthesia with ropivacaine plus sufentanil for traumatic femoral neck surgery in the elderly: a dose-response study. Anesth Analg 2013; 117:259-264.
Brichant S, Dereeper E, Guntz E, Vandenbroeck V, Sosnowski M. Spinal anaesthesia with hypobaric ropivacaine for ambulatory knee arthroscopy: 8AP6-7. Eur J Anaesthesiol 2008; 25:120.
Imbelloni LE, Gouveia MA, Cordeiro JA. Hypobaric 0.15% bupivacaine versus hypobaric 0.6% lidocaine for posterior spinal anesthesia in outpatient anorectal surgery. Rev Bras Anestesiol 2010; 60:113-120, 64-68.
Eisenach JC, De Kock M, Klimscha W. alpha(2)-adrenergic agonists for regional anesthesia. A clinical review of clonidine (1984-1995). Anesthesiology 1996; 85:655-674.
Basker S, Singh G, Jacob R. Clonidine in paediatrics - a review. Indian J Anaesth 2009; 53:270-280.
Goel S, Bhardwaj N, Grover VK. Intrathecal fentanyl added to intrathecal bupivacaine for day case surgery: a randomized study. Eur J Anaesthesiol 2003; 20:294-297.
Dobrydnjov I, Axelsson K, Thörn SE, Matthiesen P, Klockhoff H, Holmström B, Gupta A. Clonidine combined with small-dose bupivacaine during spinal anesthesia for inguinal herniorrhaphy: a randomized double-blinded study. Anesth Analg 2003; 96:1496-1503, table of contents.
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9], [Table 10], [Table 11]