|Year : 2012 | Volume
| Issue : 2 | Page : 74-78
The analgesic efficacy of ultrasound-guided modified rectus sheath block compared with wound infiltration in reduction of postoperative morphine consumption in women undergoing open hysterectomy or myomectomy: A randomized controlled trial 14/09/2012 trial
Mukesh Kumar Shah, Sandeep S Kulkarni, Wendy Fun
Department of Women's Anaesthesia, K K Women's and Children's Hospital, Singapore
|Date of Web Publication||17-Dec-2012|
Sandeep S Kulkarni
Department of Women's Anaesthesia, K K Women's and Children's Hospital, 100 Bukit Timah Road, Singapore-229899
Source of Support: None, Conflict of Interest: None
Introduction: As ultrasound allows more accurate placement of local anesthetic (LA), ultrasound-guided modified rectus sheath block (MRSB) was compared with wound infiltration (WI) in women having open hysterectomy or myomectomy for fibroids via a Pfannenstiel incision under general anesthesia.
Materials and Methods: Forty-two American Society of Anesthesiologists Class ASA I,II and III patients were recruited into two groups in a randomized patient-blinded controlled trial excluding those with coagulopathy, infection, or LA allergy. At the end of surgery, in the study group (Group U), an MRSB, under ultrasound guidance, was administered with 20 ml 0.25% levobupivacaine through a single skin puncture in the midline, 2 cm below the umbilicus, on either side of the midline, above the posterior sheath. In the control group (Group W), WI with 20 ml 0.5% levobupivacaine was done by the surgeon. The primary outcome measure was the amount of morphine consumed in the first 24 h after the surgery in the ward. Statistical analysis was performed with SPSS v.14.0.
Results: Morphine consumption in the intraoperative and recovery periods was 10 mg and 0.0 mg, respectively, in both groups. In both the groups, pain measured by visual analog scale correct (VAS) (both at rest and on movement), morphine consumption (12.0 mg [18.0 mg] vs. 12.0 mg [23.0 mg], median interquartile range [IQR], p = 0.950), and the number of oral analgesic doses administered during the study period were comparable. However, number of patients who were "extremely satisfied" compared to "satisfied" with the analgesia were more in the Group U than in Group W (15/6 vs. 4/17, P-0.001). Sedation, nausea and vomiting, and antiemetic doses given were minimal and comparable in both groups.
Conclusion: Ultrasound-guided MRSB does not show any significant difference in the 24 h morphine consumption as compared to WI.
Keywords: General anesthesia, rectus sheath block, ultrasound, wound infiltration, 24 h patient-controlled intravenous morphine
|How to cite this article:|
Shah MK, Kulkarni SS, Fun W. The analgesic efficacy of ultrasound-guided modified rectus sheath block compared with wound infiltration in reduction of postoperative morphine consumption in women undergoing open hysterectomy or myomectomy: A randomized controlled trial 14/09/2012 trial. J Obstet Anaesth Crit Care 2012;2:74-8
|How to cite this URL:|
Shah MK, Kulkarni SS, Fun W. The analgesic efficacy of ultrasound-guided modified rectus sheath block compared with wound infiltration in reduction of postoperative morphine consumption in women undergoing open hysterectomy or myomectomy: A randomized controlled trial 14/09/2012 trial. J Obstet Anaesth Crit Care [serial online] 2012 [cited 2020 Jul 11];2:74-8. Available from: http://www.joacc.com/text.asp?2012/2/2/74/104731
| Introduction|| |
Both open myomectomy and hysterectomy may be associated with severe acute postoperative pain. Currently, patient-controlled intravenous analgesia (PCIA) with morphine is used in our center. However, it may be associated with potentially serious side effects such as cardiovascular and respiratory depression and others such as nausea, vomiting, sedation, pruritus, and urinary retention. Use of local anesthetic (LA) blocks is believed to reduce postoperative morphine consumption and its attendant side effects. The modified rectus sheath block (MRSB) is a fairly easy and reliable procedure when performed using ultrasound guidance. RSB blocks the sensory nerves that innervate the anterior abdominal wall and hence somatic pain associated with incision of skin, subcutaneous tissue, and sometimes rectus muscle and rectus sheath itself, but not visceral pain.  Ultrasound use guides accurate placement of needle, allows visualization of LA solution spread in the appropriate plane, and therefore provides precision and safety. , Wound infiltration (WI) with LA at the end of the surgery is also a popular technique to provide postoperative analgesia. However, conventional WI is not uniform, and therefore unreliable, as some LA gets lost through the skin wound. We hypothesized that ultrasound-guided (US-guided) modified rectus sheath block (USMRSB) performed at the end of surgery would reduce ward postoperative morphine PCIA requirements and its accompanying side effects compared to conventional WI, following open hysterectomy or myomectomy for uterine fibroids under general anesthesia.
| Materials and Methods|| |
After obtaining Local Research Ethics Committee approval and written informed consent, 42 women, aged between 30 and 60, of ASA physical status I, II, and III, weighing more than 50 kg, undergoing open hysterectomy or myomectomy for uterine fibroids via a Pfannenstiel incision under general anesthesia, were included in the study. They were randomized preoperatively, using a computer-generated random number table to receive either an USMRSB (study group U) or WI (control group W). Group allocation was done by a sealed opaque envelope technique containing the randomly selected number, the envelope of which was opened by another investigator who had no subsequent involvement in the study. Selection then to either group was done depending upon the selected number being odd or even. Exclusion criteria included a history of coagulation disorders, consumption of anticoagulants such as warfarin, aspirin more than 100 mg/day or clopidogrel, local abdominal wall infection or LA allergy.
Sample size was computed to detect a 25% difference in the mean 24 h postoperative morphine consumption, as a clinically significant end-point. Based on previous institutional data, 30 patients (15 pairs) were required to have an 80% power of detecting a 25% decrease in the mean 24 h postoperative morphine consumption at a 0.05 significance level (a 0.05, β 0.2).
Using these calculations, we decided to randomize 21 patients into each group (total 42) to account for protocol breaches and dropouts.
On arrival in the operating room, physiological monitoring with pulse oximetry, continuous electrocardiogram (ECG), and noninvasive blood pressure measurement was commenced. Anesthesia was induced with IV fentanyl, 1.5-2.0 mcg/kg and IV propofol, 1.5-2.0 mg/kg and tracheal intubation was facilitated with IV rocuronium, 0.6 mg/kg. Patients' lungs were ventilated with oxygen in air (F I O 2 0.4), maintaining E T CO 2 at 35-40 mmHg. Anesthesia was maintained at minimum alveolar concentration MAC 1.0 desflurane. Intraoperative analgesia was provided by IV morphine, 0.1-0.2 mg/kg and supplementary postoperative analgesia by rectal paracetamol, 1,300 mg (about 20-25 mg/kg). To prevent postoperative nausea and vomiting, all patients received IV dexamethasone, 4 mg after induction of anesthesia and IV ondansetron, 4 mg was given 15 min before the end of surgery.
At the end of surgery, patients in group U (n = 21) received MRSB under strict aseptic precautions, by one of three skilled investigators, using a L 38 linear broadband probe (7-13 MHz) connected to a Titan ultrasound system (SonoSite, Inc., Bothell, WA 98021, USA). The probe was placed horizontally over the rectus sheath below the umbilicus on either side of the midline. Upon visualization of the abdominal wall layers, an 8-cm long sono-opaque 22 G Pajunk block needle attached by a flexible tubing to a 0.25% levobupivacaine-filled syringe was introduced in the midline 2 cm below the umbilicus and directed laterally through the rectus sheath till its tip was positioned between the rectus muscle belly and the posterior sheath. After negative blood aspiration, a 2-ml test dose was injected to confirm correct needle placement followed by a slow injection of total dose of
18 ml. A correct placement of the needle is evident by the distension of the space by the injected LA solution. Another 20 ml was deposited similarly on the opposite side. Group W (n = 21) received conventional WI (by the surgeon) at the end of surgery with 20 ml 0.5% levobupivacaine. The patients and the nursing staff providing postoperative care were blinded to group allocation. Residual neuromuscular blockade was reversed with IV neostigmine, 2.5 mg and IV atropine, 0.9 mg. The trachea was extubated following adequate reversal of neuromuscular block. After extubation, patients were brought to the recovery room, their pain was monitored and morphine was given by the recovery room clinician in 1 mg incremental doses or self-administered through PCIA on demand till patients were relieved of their pain.
Each patient was assessed by a blinded investigator in the ward at 0, 2, 4, 8, 12, and 24 h. The primary outcome was 24 h postoperative morphine consumption from the time patient reached the ward postoperatively (bolus dose, 1 mg; lockout interval, 5 min; and maximum dose, 10 mg/h). Secondary outcome measures were VAS pain score (0-10) at rest and with activity (movement in bed) at 0, 2, 4, 8, 12, and 24 h; number of oral analgesic (paracetamol, 1 g 6 h and/or mefenamic acid, 500 mg 8 h as per individual surgeon's preference) doses during the first 24 h on patient's demand; worst nausea severity (0 = none, 1 = mild, 2 = moderate, and 3 = severe), vomiting frequency, number of antiemetic (IV ondansetron, 4 mg) doses, and worst sedation level (1 = wide awake, 2 = minimally sedated, appropriate response to conversation, 3 = asleep, rousable by tactile stimulation, 4 = deeply asleep, rousable only with significant physical stimulation, and 5 = unrousable) during the first 24 h; and patient satisfaction at 24 h on a four-point verbal rating scale (1 = extremely unsatisfied, 2 = unsatisfied, 3 = satisfied, and 4 = extremely satisfied).
Statistical analysis was performed with SPSS v.14.0. Parametric data were analyzed using Student's t-test (and presented as mean and 95% confidence Interval [CI]) and repeated measurements by repeated measures ANOVA, if normally distributed. Categorical data were analyzed using the Fisher's exact test. Nonparametric (or categorical) data and parametric data when not normally distributed were analyzed using Mann-Whitney U test (and presented as median and minimum-maximum or interquartile range [IQR]). A P value less than 0.05 was considered significant.
| Results|| |
A total of 42 patients were recruited, with 21 patients in each group, without any dropouts and protocol breaches. Patient characteristics were comparable between the two groups [Table 1]. Ultrasound images before and after USMRSB are shown in [Figure 1]. The data given in [Table 2] being categorical data and not normally distributed parametric data have been presented as median with minimum-maximum and IQRs. The median 24 h postoperative morphine PCIA consumption (and the median number of oral analgesic doses given) in the ward was similar. The minimum-maximum range of this 24 h postoperative morphine PCIA consumption, though clinically similar, was statistically different [Table 2]. None of the patients in either group made any PCIA demands during transport from the recovery room to the ward. VAS pain scores at rest and with activity at 0, 2, 4, 8, 12, and 24 h were similar [Figure 2] and [Figure 3] (p = 0.169 and 0.134, respectively, generated from graphs in SPSS). All patients were satisfied with their pain relief but there were more patients in group U who reported being very satisfied. Nausea and vomiting, antiemetic doses given, and sedation were comparable in both groups.
|Table 1: Characteristics of patients receiving ultrasound-guided modifi ed rectus sheath block or wound infi ltration|
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|Table 2: Analgesic consumption, pain satisfaction, and side effects of patients receiving ultrasound-guided modifi ed rectus sheath block or wound infi ltration|
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| Discussion|| |
Postoperative pain arises from the abdominal wall incision or abdominal viscera. Both USMRSB and WI, being distally applied, do not relieve visceral pain.  Postoperative pain following open hysterectomy or myomectomy, following either USMRSB or WI supplemented by rectal paracetamol, in patients on PCIA morphine was mild, judged by VAS pain scores at rest and on activity (0-4), ward 24 h PCIA morphine consumption (12 mg, i.e., 0.22 vs. 0.21 mg/kg, respectively), total (intraoperative + recovery + ward postoperative 24 h) morphine consumption (23 vs. 22 mg, i.e., 0.42 vs. 0.38 mg/kg, respectively) and number of oral analgesic doses (0) required. The visceral pain component at its worst did not appear to be prominent and the incisional pain component adequately relieved post-open hysterectomy or myomectomy in both groups indicating the efficacy of both USMRSB and WI. Also, USMRSB did not appear to be superior to WI.
Having a third comparison group with only rectal paracetamol but no abdominal wall nerve block would give us the ward 24 h PCIA morphine consumption in the absence of abdominal wall nerve block.
Moderate to severe pain (e.g., VAS pain score > 30 mm) is required in pain studies to achieve adequate sensitivity because it may not be possible to detect any difference if there is little or no pain.  An unpublished study in our department in 40 patients undergoing non-gynecological surgery did not show US-guided transversus abdominis plane (USTAP) block to be superior to WI for ward postoperative pain as ward pain VAS was mild and ward 24 h morphine PCIA consumption was less than 10 mg. However, another unpublished but presented study in 39 patients undergoing major gynecological surgery showed USTAP block to be superior to WI, as ward postoperative pain was moderate at rest and severe on activity. Ward 24 h PCIA morphine consumption was 16 ± 2.4 mg compared to 33 ± 4.5 mg, P < 0.025, i.e., more than a 50% reduction in morphine requirement was observed. Pain VAS at rest (23.5 ± 3.8 cm/h), and more so on activity (62.7 ± 8.6 cm/h), was less than control (44.7 ± 4.6 cm/h and 99.5 ± 12.5 cm/h, respectively), though these were secondary outcomes. USTAP block, which blocks the L1 nerve in addition, may be superior to USMRSB for major gynecological surgery but this has yet to be studied.
Yentis et al.  in 1999 compared in abdominal gynecological surgery combined supra- and infraumbilical bilateral rectus sheath block plus bilateral ilioinguinal block for midline incision vs. infraumbilical bilateral rectus sheath block plus bilateral ilioinguinal block plus bilateral deep subcutaneous LA infiltration above the inguinal ligament for transverse incision using the scratch method. The authors found this additional combination of ilioinguinal block and deep subcutaneous LA infiltration was required to block the skin and subcutaneous tissue of the lateral parts of the transverse incision. Authors used a higher total volume of LA: 60 ml 0.25% bupivacaine with adrenaline 1:400,000 and rectal diclofenac suppository. The study showed that median (IQR) 48 h morphine consumption (including
0.15 mg/kg given intraoperatively) for 16 patients in the transverse incision group was 0.47 (0.35-0.64) mg/kg. This was relatively lower over 24 h than the ward 24 h consumption in our study. This could be due to different study populations, possibly different surgery mix, and possible contribution from additional L1 nerve block, use of adrenaline and use of rectal diclofenac. The anterior cutaneous branch of the iliohypogastric nerve (L 1 ) supplies the skin of the abdomen above the pubis, and the inguinal portion of the ilioinguinal nerve (L 1 ) serves the inguinal region. 
The volume and concentration of LA solution used for USMRSB in our study are comparable to those in the literature, e.g., 20 ml 0.5%-20 ml 0.25% bupivacaine on each side (40 ml of 0.25% bupivacaine). The average weight of the patients in our study was 56 kg. We did not want to exceed the maximum recommended dose for bupivacaine of 2 mg/kg; hence, we used 100 mg of bupivacaine in our study. If we would have used 10 ml of 0.5% bupivacaine for the U group, it would have been too insufficient volume for the block to work effectively. Using 40 ml of 0.25% bupivacaine into the wound infiltration in the W group would not have been practical. Hence, the total dose of bupivacaine used in the entire study was the same.
There were no patients with complications from USMRSB or WI. Side effects of morphine, namely nausea, vomiting, and sedation, were minimal, mild and similar between the two groups. Our observation is in line with the Cochrane database review. 
All patients were satisfied, related to good analgesia with minimal side effects, but more patients receiving USMRSB reported being very satisfied. This may be due to their being able to move the trunk without causing pain, but this was not tested. Abdominal wall sensation was not tested as this could compromise wound sterility after bandage removal. Patients might also become unblinded as a result. Other studies claim the surgical rectus sheath block appears to provide effective postoperative analgesia for patients undergoing major gynecological surgery and also the pain scores being less while walking as compared to wound infiltration of LA. 
Carney et al.  in their study involving the use of transversus abdominis plane (TAP) block for providing analgesia for total abdominal hysterectomy via a transverse lower abdominal incision demonstrated its effectiveness. They had used 0.75% Ropivacaine as a LA for TAP block. Also they had performed it before the surgical incision. In their study, 24 h mean morphine consumption in the TAP block group was 21.1 ± 12.7 mg. These morphine requirements are quite comparable with the morphine requirements in our study.
There is some evidence to suggest that the use of ultrasound guidance is a safe and effective means to facilitate correct placement and adequate spread of LA for truncal blocks; hence, we chose to perform the MRSB using ultrasound guidance. 
In conclusion, USMRSB, when compared to conventional WI, following open hysterectomy or myomectomy for uterine fibroids under general anesthesia did not result in lower ward 24 h postoperative morphine patient-controlled intravenous analgesic consumption or VAS pain scores, though patients were more satisfied.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2]