Table of Contents  
ORIGINAL ARTICLE
Year : 2015  |  Volume : 8  |  Issue : 2  |  Page : 265-268

The minimal effective dose of spinal hyperbaric bupivacaine for successful reliable saddle block for minor perianal surgeries


Department of Anesthesia, University of Dammam, Al-Khobar, Saudi Arabia

Date of Submission08-Dec-2014
Date of Acceptance22-Mar-2015
Date of Web Publication8-May-2015

Correspondence Address:
Roshdi R Al-Metwalli
Department of Anesthesia, King Fahad Hospital, University of Dammam, PO Box 40081, Al-Khobar 31952
Saudi Arabia
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/1687-7934.156714

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  Abstract 

Objective
The aim of this study was to determine the minimal effective dose of spinal hyperbaric bupivacaine required to induce a reliable and satisfactory saddle block for perianal surgeries (using a modified Dixon's up-and-down method).
Materials and methods
A total of 24 adult patients scheduled for perianal surgeries were enrolled in this study. Dural puncture was performed using a standard midline approach in the sitting position at the L3-L4 intervertebral space, using a 25 G Whitacre needle with its orifice directed caudal. A small quantity (1.5 mg) of hyperbaric bupivacaine was injected. All patients remained in the sitting position for 10 min immediately before and after surgery; the block was tested using a long surgical toothless clamp and modified Bromage scale. A successful block was defined as one that was sufficient to proceed with the surgery without any supplementation. The dose of bupivacaine given to the next patient was guided by modified Dixon's up-and-down method using 0.5 mg as a step size. Patients' ability to position themselves, ambulation time, time of hospital discharge, patient and surgeon satisfaction, and any intraoperative or postoperative complication were recorded. The minimal effective dose of hyperbaric bupivacaine for successful saddle block for 50% (ED 50 ) of patients was determined by calculating the midpoint dose of all independent pairs of patients after at least seven crossover points.
Results
The ED 50 of hyperbaric bupivacaine for successful saddle block for perianal surgeries was 1.9 mg (95% confidence interval = 1.7-2.1 mg). There were zero motor blockade, early ambulation, short time to void, and early hospital discharge, as well as no complications and excellent patient and surgeon satisfaction.
Conclusion
The ED 50 of spinal hyperbaric bupivacaine for saddle block for perianal surgery is 1.9 mg (95% confidence interval = 1.7-2.1 mg). This block is reliable and has short duration, no complication, and excellent patient and surgeon satisfaction.

Keywords: hyperbaric bupivacaine, perianal surgery, saddle block


How to cite this article:
Al-Metwalli RR. The minimal effective dose of spinal hyperbaric bupivacaine for successful reliable saddle block for minor perianal surgeries. Ain-Shams J Anaesthesiol 2015;8:265-8

How to cite this URL:
Al-Metwalli RR. The minimal effective dose of spinal hyperbaric bupivacaine for successful reliable saddle block for minor perianal surgeries. Ain-Shams J Anaesthesiol [serial online] 2015 [cited 2017 Oct 22];8:265-8. Available from: http://www.asja.eg.net/text.asp?2015/8/2/265/156714


  Introduction Top


An optimal anesthetic technique would provide excellent operating conditions, rapid recovery, early discharge, no postoperative side effects, and high patient satisfaction, in addition to the high quality and low costs of the anesthetic services [1] . Selective spinal anesthesia - spinal block with minimal effective doses for a specific type of surgery - has become a very popular technique [2] for some orthopedic and gynecological surgeries [3],[4],[5],[6],[7],[8],[9] .

Saddle anesthesia is a selective spinal anesthesia that directs a small bolus of hyperbaric local anesthetic toward S4-S5 and coccygeal nerve roots [10] , and is commonly utilized for perianal surgeries [11],[12],[13],[14] . Hyperbaric bupivacaine has safely replaced hyperbaric lidocaine for saddle block [11],[12] .

Although saddle blocks at different low doses of hyperbaric bupivacaine (1.5-4 mg) have been used previously for minor perianal surgeries [11],[13],[14] , the optimal effective dose is yet to be determined. We performed a prospective up-down sequential allocation study to determine the minimal effective dose of hyperbaric bupivacaine required to induce a reliable and satisfactory saddle block for perianal surgeries (using a modified Dixon's up-and-down method). Our secondary outcome was to monitor the quality of the postoperative recovery and possible complications.


  Materials and methods Top


The study was approved by the Research and Ethics Committee of University of Dammam and started at King Fahad University Hospital on October 2013, as well as registered as NCT 02299167 at clinicaltrials.gov. Written informed consent was obtained. Patients with physical status I and II according to the American Society of Anesthesiologists, aged between 20 and 55 years, scheduled for outpatient elective perianal surgery in the lithotomy position (hemorrhoidectomy, fistulectomy), were prospectively enrolled in this study. Patients unwilling to participate, those with contraindications to regional anesthesia, morbid obesity, bleeding disorders, mental health problems or language barrier, those taking psychotropic or analgesic medication or with a known history of allergic reactions to amide local anesthetics were excluded from the study.

All patients were made to fast for over 6 h and were premedicated with 0.2 mg/kg oral diazepam 60 min before spinal anesthesia. In the operating room, an intravenous 18-20 G catheter was placed, and standard monitoring (ECG, heart rate, oxygen saturation, and noninvasive blood pressure) was started.

Under aseptic conditions, dural puncture was performed by staff-grade anesthesiologists, using a standard midline approach in the sitting position at the L3-L4 or L4-L5 intervertebral space, with a 25 G Whitacre needle with its orifice directed caudal. A predetermined small dose of hyperbaric bupivacaine (Marcaine Spinal Heavy; Astra Zeneca, Lund, Sweden), which was prepared in 1 ml tuberculin syringe, was injected. All patients remained in the sitting position for 10 min. Patients were asked if they perceived any change in motor power. If not, the patients were allowed to position themselves without aid for surgery in the lithotomy position. Immediately before surgery, the level of sensory block was tested using a long surgical toothless clamp gently applied radially, starting from the anal orifice, in different diagonal directions. Motor block was tested with the modified Bromage scale (0 = no motor block, 1 = able to flex ankle and bend knees, 2 = able to flex ankle, and 3 = full motor block) [15] . A successful block was defined as one that was sufficient to proceed with the surgery without any supplementation (intravenous analgesic, local anesthetic infiltration, or general anesthesia).

The dose of bupivacaine given to each patient was determined by the response of the previously tested patient using a modified Dixon's up-and-down method (using 0.5 mg as a step size) [16] . The first patient was tested at a dose 1.5 mg bupivacaine. If the patient responded with failed block, then the next patient received an increment of 0.5 mg bupivacaine; if the patient responded with successful block, then the next patient received a decrement of 0.5 mg bupivacaine. The research continued until we obtained seven crossover midpoints. The initial starting dose of 1.5 mg hyperbaric bupivacaine of the first patient was selected from the findings of Wassef et al. [13] , who demonstrated adequate anesthesia for short perianal surgery with the use of 1.5 mg spinal hyperbaric bupivacaine. Bupivacaine was prepared immediately before injection by an anesthesiologist blinded to the study methodology and was administered by a second blinded anesthesiologist. Block assessment and clinical follow-up of the patients was also performed by a third blinded anesthesiologist.

The following data were recorded: patient demographics; duration of anesthesia and surgery; and level of sensory and motor block immediately before surgery, at the end of surgery, and every 30 min until resolution of the block. Noninvasive blood pressure and heart rate were documented every 5 min in the operating room and postanesthesia care unit. Time to ambulation, first voiding time, and time to home discharge were also recorded. Patient and surgeon satisfactions were evaluated with a four-point score (0 = poor, 1 = good, 2 = very good, 3 = excellent). Patients were followed up through phone call to note down any possible postoperative complication (postdural puncture headache, transient neurologic symptoms, or backache) at day 1 postoperatively and 10 days later. The time of dural puncture was used as the primary starting point of assessment.

Statistical data analysis

We used descriptive statistics to calculate the mathematic mean (SD) of demographic, surgical, and other postoperative continuous data and to calculate the median (range) of sensory and motor block levels, as well as the degree of patient and surgeon satisfactions using MedCalc, version 12 (MedCalc Software bvba, Mariakerke, Belgium). The ED 50 % of spinal bupivacaine was estimated using a modified Dixon's up-and-down method [16] . According to this method the study should continue up and down until seven crossover midpoints were obtained, and in our study this was achieved after 24 patients were studied ([Figure 1]).
Figure 1: Bupivacaine dose– response data for each patient obtained with a modified Dixon's up-and-down method.

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  Results Top


All recruited patients completed the study to make a total of 24 patients. Only 12 patients (50%) had successful blockades and completed their surgeries without any supplement. Patients' demographic data are shown in [Table 1]. Dose-response data for each patient obtained with the up-and-down method are shown in [Figure 1]. The minimal effective dose of spinal hyperbaric bupivacaine for perianal surgery in 50% (ED 50 ) of patients was 1.9 mg [95% confidence interval (CI) = 1.7-2.1 mg). The block characteristics for patients with successful blockade showed a significantly restricted sensory block (median maximum = S4 and no motor block, Bromage = 0). All patients were able to move and did not require aided positioning preoperatively or postoperatively. Almost all patients as well as all surgeons expressed complete overall satisfaction. None of the patients developed postdural puncture headache, urinary retention, or backache ([Table 2]).
Table 1 Demographic and surgical data

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Table 2 Block characteristics and PACU variables for patients with successful blockade

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  Discussion Top


Our study showed that the minimal effective dose of hyperbaric bupivacaine to induce successful saddle block for perianal surgeries in 50% (ED 50 ) of patients was 1.9 mg (95% CI = 1.7-2.1 mg). The block was restricted to the most caudal spinal nerve roots (S4-coccygeal) supplying the perianal area. Lack of motor and sensory blockade of the lower limbs allowed early ambulation, voiding, and hospital discharge. Moreover, all patients were able to position themselves unaided preoperatively and postoperatively. The block was also associated with no complication, as well as excellent patient and surgeon satisfaction.

Our study was the first to calculate the ED 50 of hyperbaric bupivacaine for perianal surgeries using a modified Dixon's up-and-down method. Although our initial dose (1.5 mg) was based on the results of Wassef et al. [13] , none of our patients who received 1.5 mg had successful block. This was in agreement with the results of Carron et al. [10] , who also reported 100% saddle block failure using 1.5 mg hyperbaric bupivacaine. This could be explained by the use of different methodology and different drug concentration and could open the door for further dose-response studies, using different methodology and different methods of estimation.

In our present study, patients with successful block showed zero motor blockade, with early ambulation (96.82 ± 15.07 min), no complication, and early home discharge (108.27 ± 19.22 min). These were comparable to the results of all previous studies that used low doses (1.5-3 mg) of spinal hyperbaric bupivacaine for perianal surgeries [11],[13],[14] .

Irrespective of the period of sitting (2-60 min), upward spread of local anesthetic through the cerebrospinal fluid occurs (analgesia levels increases several segments) when the patient is repositioned from the sitting to the supine position. The greater the time of sitting the lesser the amount of local anesthetic available for upward spread; this is presumably due to binding of local anesthetic to tissue structures within the subarachnoid space [17],[18] . This could explain why our block was localized to the caudal spinal nerve roots (S4-coccygeal) and did not spread up after changing to the lithotomy position, as the amount remaining (after 10 min sitting) of the small dose of bupivacaine injected was not enough to induce significant upward spread after changing position.

One limitation of our study was the inability to record the onset of anesthesia at S4 dermatome. This was because we did not have the horseshoe-shaped chair, as well as because some of our patients were female, and testing sensation in perianal area in this position is very shameful socially and religiously. Thus, we relied on previous studies of the same methodology, which recoded 4-10 min as an onset for S4 dermatome sensory block [11],[13],[14] . Moreover, none of our patients had a block level below S4 immediately after change to lithotomy position.


  Conclusion Top


The minimal effective dose of spinal hyperbaric bupivacaine for saddle block for perianal surgery in 50% (ED 50 ) of patients is 1.9 mg (95% CI = 1.7-2.1 mg). This block is reliable and has short duration, no complications, and excellent patient and surgeon satisfaction, thus supporting the growing need for day-case surgery.


  Acknowledgements Top


The authors thank all members of the Department of Anesthesia in King Fahad Hospital, Al-Khobar, Saudi Arabia, with special thanks to Dr. A. Abdulfattah, Dr. A. Sidiqui, Dr. M. Tantawy, Dr. M. Shafi and Mr. A. Taha for their encouragement and help in the clinical work.

Clinicaltrial registration: The study registered as NCT 02299167 at clinicaltrials.gov.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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