Evaluation of efficacy of ultrasound guided erector spinae plane block and oblique subcostal transversus abdominis plane block for postoperative analgesia in laparoscopic cholecystectomy

Aim & Objective: Laparoscopic cholecystectomy (LC) is a commonly performed minimally invasive surgery. LC can cause moderate to severe postoperative pain due to small keyhole entries on the abdominal wall. The oblique subcostal transversus abdominis plane block (OSTAP) has been used for postoperative analgesia after LC but found not so effective. Our aim is to compare the effectiveness of erector spinae block with OSTAP block for postop analgesia after LC. Materials and Methods: This prospective, randomized study was conducted at a tertiary care hospital. Seventy patients, 18 to 65 years old posted for LC were divided into two equal groups of 35 each. Erector spinae plane block was performed in the ESP group and oblique subcostal transverses abdominis plane block was performed in the OSTAP group. Postoperative rescue analgesic consumption, time to 1st rescue analgesia, numerical rating score (NRS), and any complications in 1st 24 hrs between the groups were compared. Results: Postoperative rescue analgesic (paracetamol) consumption was 1.9± 0.85gm in ESP group and 2.84 ± 0.29gm in OSTAP group which was statistically significant. Time to 1st rescue analgesia request was 360.34±28.94 mins in ESP group and 280.51±45.66 mins in OSTAP group which was statistically significant. Although NRS scores at almost all time-points were lower in the ESP group compared to OSTAP block, the difference was significant in 1st 6 hrs. Conclusion: Ultrasound guided ESP block reduced postoperative rescue analgesic consumption and pain scores more effectively than OSTAP block after laparoscopic cholecystectomy surgery. © 2020 Published by Innovative Publication. This is an open access article under the CC BY-NC license (https://creativecommons.org/licenses/by-nc/4.0/)


Introduction
Laparoscopic cholecystectomy (LC) is the most common minimally invasive surgery in which intraoperative access is provided with small keyhole entries on abdominal wall. LC causes moderate to severe postoperative pain which has different components; incisional pain from the trocar site (somatic pain),and local visceral pain (deep abdominal pain). 1 Many patients ALSO suffer from shoulder pain which is due to subdiaphragmatic irritation, tramsmitted by phrenic nerve causing referred pain in C4 dermatome. Multimodal approaches with nonsteroidal anti-inflammatory drugs, dexamethasone, gabapentinoids, opioids, local anesthetic infiltration to port sites, epidural analgesia and transversus abdominis plane block (TAP) have been used to attenuate postoperative pain caused after LC. 2 Hebbard et al. 3 described the subcostal approach of TAP block for postoperative analgesia for upper abdominal surgeries. Many studies have reported that ultrasound guided oblique subcostal abdominis plane (OSTAP) blocks reduced postoperative pain scores and opioid consumption in the first 24 hrs after LC. 4,5 Although OSTAP block https://doi.org/10.18231/j.pjms.2020.028 2249-8176/© 2020 Innovative Publication, All rights reserved. provides analgesia for somatic pain, it is ineffective in reliving visceral pain. Forero et al 6 described the ultrasound guided ESP block which is a novel technique targeting the ventral rami, dorsal rami, and rami communicantes of the spinal nerves there by effective against both somatic and visceral pain. Also after injection of the local anesthetic agent, spread of drug extend cranially and caudally over several dermatomal levels producing widespread analgesia. Few studies have reported that ESP block provided analgesia after different abdominal, thoracic, breast and spinal surgeries. 7,8 The present study was aimed to evaluate the analgesic efficacies of ultrasound-guided ESP block and OSTAP block after laparoscopic cholecystectomy surgeries. Our primary endpoint was the comparison of the total rescue analgesia consumption at the postoperative 24th hour between the two groups. The secondary endpoints were time of 1 st rescue analgesia request, comparisons of NRS score at different time points, and complications in 1 st 24 hrs.

Materials and Methods
This is a single blinded, prospective, randomized controlled study conducted at a tertiary care hospital after approval of institutional ethical committee between Sept 2018 and Sept 2019. All patients gave written informed consent for inclusion into this study.Patients aged 18-65 years with an American Society of Anesthesiologists (ASA) physical status classes of I and II who were scheduled to undergo elective LC were included in this study. Patients who refused enrolment, known allergy to regional anesthesia, those with bleeding diathesis, presence of severe kidney disease, BMI>30kg/m 2 and infection at the site of needle puncture were excluded from the study. Randomization was performed according to computer-generated random number tables, and allocation to treatment group was done using the sealed opaque envelope technique. According to randomization, patients were divided into two groups to receive either ultrasound guided ESP block or OSTAP block.
General anesthesia was administered to all patients in both groups. Standard monitoring procedures included pulse oximetry, electrocardiography, bispectral index and noninvasive arterial pressure. Ringers lactate (15ml/kg) started after putting a 20 G iv cannula. All patients were premedicated with intravenous (i.v.) midazolam 0.04 mg/kg and fentanyl 2mcg/kg. Induction was performed using propofol 2-3 mg/kg and vecuronium bromide 0.01 mg/kg and maintained with 0.6 minimum alveolar concentration sevoflurane with target BIS 40-60. Pneumoperitoneum was evacuated in all patients at the end of surgery and blocks were performed by the same anaesthesiologist. For all blocks, a GE Logiq F TM (General Electric Healthcare, Little Chalfont, United Kingdom) ultrasound with a high frequency (6-15 MHz) 38mm L6-12 linear probe and a Stimuplex (R) A 50mm (B Braun HNS 11-12218, Stockert GmbH, Botzinger Strabe72, D-79111 Freiburg, Germany) were used. 20 ml of bupivacaine 0.375% was administered to each side in each block. Then patients were extubated and transferred to the postoperative recovery room. Recovery room and ward follow up was performed by anaesthesiologist who were blinded to the group.

Erector spinae plane block
Patients were placed on their left side so that their right side was superior. The linear ultrasound transducer was placed in a longitudinal parasagittal orientation 2.5-3 cm lateral to the T9 spinous process. The erector spinae muscles were identified superficial to the tip of the T9 transverse process. A 21G 10-cm needle (B.Braun) was inserted using an out of plane approach. The tip of the needle was placed into the fascial plane on the deep (anterior) aspect of the erector spinae muscle. The location of the needle tip was confirmed by visible fluid spread lifting the erector spinae muscle off the bony shadow of the transverse process on ultrasonographic imaging. A volume of 20 mL of bupivacaine 0.375% was injected. Due to reports that ESP blocks visceral pain especially that of peritoneal distention, and as at least one trocar is placed in the midline, the same procedure was repeated for the opposite side.

Oblique subcostal transversus abdominis plane block
Blocks were performed in the supine position using a high frequency linear transducer with the in plane technique. The transducer was placed immediately below the costal margin on the oblique plane. The rectus abdominis, transverse abdominis, and internal oblique and external oblique muscles were identified. A 21G 10-cm needle (B.Braun) was inserted using an in plane approach from medially to laterally. 20 ml of bupivacaine 0.375% was injected between the fascia immediately above the rectus abdominis muscle.
Postoperative pain was evaluated using the numerical rating score (NRS). The NRS is a segmented numeric version of the Visual Analog Scale (VAS) in which a respondent selects a whole number (0-10) that best reflects the intensity of his/her pain. It is considered a one dimensional measure of pain intensity in adults. The 11point numeric scale ranges from 0 representing no pain to 10 representing extreme pain. Changes in NRS at rest and on movement were recorded at different time intervals. During the 1 st 24 hr postoperative period, Paracetamol 1gm was given if Numeric Rating Scale score (NRS)>4. Total consumption of paracetamol in 1 st 24 hrs and time to 1 st rescue analgesia was measured in both groups.
NRS pain scores was recorded at the 1st, 3rd, 6th, 9th, 12th, 15 th , 18th, 21st and 24th hr both at rest and when coughing. Shoulder pain during the first 24 h and presence of postoperative nausea and vomiting were noted.
The severity of nausea was assessed by patients on a 4point scale (none, mild, moderate, and severe). Sample size was calculated based on a pilot study with 10 patients in each group.20% reduction in consumption of rescue analgesia in postoperative 24 hr was considered to be clinically significant. The mean Paracetamol consumption in ESP block group was 2.08± 0.9 gm and 2.9± 0.64gm in OSTAP block group. Our study hypothesis was that, there was significant difference in rescue analgesia consumption in 1 st 24 hr postoperatively as ESP block produces lower NRS score compared to OSTAP block.
Using power of 0.90 and significance level of 0.05. minimum sample size was calculated to be 28 patients for two groups each. Considering the possibility of dropouts, we decided to include 35 patients for each group.
Statistical Package for the Social Sciences version 16.0 statistical package program (SPSS Inc., Chicago, IL, USA) was applied for statistical analysis. Descriptive statistics were expressed as mean ± standard deviation. For univariate analysis of means between the groups a 2 sample, independent t-test assuming equal variances were used. For data without normal distribution, Mann-Whitney U test was used. Ratios were compared using Chi square test and Categorical variables were compared using Fisher's exact test. Continuous variable was tested for normality via the Shapiro-Wilk test. P < 0.05 was considered statistically significant.

Results
Seventy patients scheduled to undergo LC were evaluated for inclusion in this study. Two patients for coagulopathy, two for infection at block site, two for CRF, one for BMI>25kg/m 2 were excluded from the study. (Figure 1) 64 patients were included for randomisation. Two patients in each group were again excluded as LC was converted to open cholecystectomy.60 patients completed the study. Average age, male to female ratio, ASA scores, average surgical time, block performing time and body mass index were similar in all groups. (Table 1) Mean paracetamol consumption in 1 st 24 hrs postoperatively was 1.9± 0.85 gm in ESP group and 2.84± 0.29gm in OSTAP block which was statistically significant.(p<0.05) Time to 1 st rescue analgesia was 360.34±28.94min in ESP group and 280.51±45.66 min in OSTAP block which was statistically significant. (p<0.05) In ESP group 12 patients required rescue analgesia in 1 st 12 hrs compared to 25 in OSTAP group which was statistically significant ( Table 2).
In 1 st 6hrs NRS score both at rest and on coughing was lower in ESP group than OSTAP group which was statistically significant(p<0.05). After 6 hrs NRS score was comparable in both groups. (Tables 3 and 4) No patient had right shoulder pain in either group. There was no statistical difference in complications in both groups. 4 patients in ESP group and 6 patients in OSTAP group had nausea and vomiting which was not statistically significant. 2 patients in both group developed sedation.(table5)

Discussion
In the current study Paracetamol consumption was significantly lower in the ESP group at 24 hr postoperatively compared to OSTAP group. Time to 1 st rescue analgesia was prolonged in ESP group compared to OSTAP block which was statistically significant. Moreover, the NRS scores at rest and after coughing were significantly lower in the ESP group compared to OSTAP block. Larger no of patients in OSTAP block group required rescue analgesia compared to ESP group. There was no significant difference between the groups in postoperative complications. Acute pain following LC has different components: incisional pain from the trocar site, local visceral pain, parietal pain, and referred shoulder pain. Bisgaard et al. 9 reported that parietal pain due to a skin incision contributed more to laparoscopic pain than did other components. Recent studies evaluated the effect of OSTAP block for post-operative analgesia after LC. 4,5,10 Few studies have reported that TAP/OSTAP block provided analgesia for somatic pain and parietal pain of almost the entire anterior abdomen and effectively reduced postoperative pain. 11 Oksar et al. 12 compared the effects of intercostal-iliac TAP block, OSTAP block, and intravenous multimodal analgesia after LC, and they found that OSTAP block was more effective than the other methods in reducing postoperative pain scores. Similarly, Basaran et al. 13 reported that OSTAP block successfully reduced postoperative pain and improved respiratory function after LC. In a recent study, ultrasound guided OSTAP block was shown to provide effective analgesia in the entire anterior abdominal wall; however, TAP block was less effective over the lateral abdominal wall and there was almost no analgesic efficacy at the posterior abdominal wall. The authorsreported that OSTAP block gradually weakened from the anterior to the posterior of the abdominal wall. Ramkiran et al. 14 compared the effectiveness of a rectus sheath block-OSTAP block combination, OSTAP block alone, and conventional port site infiltration in alleviating postoperative pain after LC. They reported that pain scores were significantly lower in the combination group at the second postoperative hour. In addition, opioid consumption in the postoperative 24 h was significantly lower in the combination group. Despite the reported successful outcomes of previous studies, the patchy pattern of sensory block over the lateral and posterior abdominal walls may cause discomfort in some patients after LC treated with OSTAP block. Visceral pain that occurs due to tissue trauma during gall bladder resection is generally accepted as the most predominant component after LC. Although OSTAP block can affect somatic and parietal components of postoperative pain after LC; however, the lack of a       15 Tulgar et al. 16 described multimodal analgesia protocols in three patients who had endoscopic retrograde cholan-giopanc reatography, followed by LC. They performed ultrasound guided ESP block at the level of T8 with 10 ml of 0.5% bupivacaine 5 mL of 2% idocaine and 5 mL of isotonic saline following anesthesia induction. They reported that the NRS scores of the patients were under 3/10 in an ambulatory surgical setting. In a recent study, Tulgar et al. 17 evaluated the effect of ultrasound guided ESP block on postoperative pain scores and analgesic consumption after LC in a randomized controlled trial. In their study, they reported that they increased the bupivacaine concentration to 0.375% due to block failure and insufficient sensorial block. Aksu et al. 18  Altiparmac et al 19 in their study concluded that ultrasound guided ESP block reduced the postoperative opioid consumption, pain scores, and intraoperative fentanyl requirements of patients more effectively than OSTAP block after LC surgery.
The ideal concentration of local anesthesia for ESP block in thoracic and abdominal surgeries was yet to be determined. In a study by Kashani et al, 3.6 ml of local anaesthetic per vertebral level was reported to be adequate in ESP block. 20 However, spread of local anesthesia at different thoracic or lumbar vertebral levels may differ. So local anesthesia volume and concentration may vary according to patients' age and type of surgery to be performed. 21 Few studies have reported that, 20 ml of local anesthesia applied at T4 has been shown to spread caudal and cephalad for three to seven vertebral levels. 22 Though ideal concentration of local anesthetic for ESP block has yet to be decided, we in our study used 20 mL 0.375% bupivacaine. The most important reason for this difference is that ESP blocks facilitate greater dermatomal spread of local anesthetic agent in the fascial plane than does OSTAP block. The subcostal approach of TAP produces sensory blockade between the T6-T10 dermatomes. Therefore, OSTAP block provides analgesia especially for upper abdominal surgeries.
Vidal et al in a cadaveric study opined that ESP block produced epidural, neural foraminal, and intercostal spread of local anesthetic agent. 23 This more extensive spread of local anesthetic agent might have covered a larger dermatomal area than the OSTAP block. Also when ESP block was performed at a lower thoracic level, the local anesthetic was shown to spread anteriorly and enter the thoracic paravertebral space which may be the reason for producing wie spread analgesia.Thoracic epidural analgesia, thoracic paravertebral block, and quadratus lumborum block are the alternative approaches that can block both somatic and visceral pain. However, these approaches are not only difficult and time consuming but they can produce potential complications. Thoracic epidural analgesia was shown to be associated with longer hospital stay when compared with conventional analgesia. 24 Similarly, ultrasound guided thoracic paravertebral block can produce complication like pneumothorax. 25 But ultrasound guided ESP block can be performed simply and quickly with easily identified ultrasound landmarks which can provide the same benefits with less risk when compared with the alternative block techniques. 26 Limitation of our study was that, no data was collected to assess the success of both blocks. So we may have missed some block failure.

Conclusion
Ultrasound guided ESP block performed at the end of LC decreased consumption of analgesic in first 24 h and delayed the time of 1 st analgesia request when compared to OSTAP block. But the volume and concentration of local anesthesia is still not clear which will provide adequate analgesia. So further studies are required to determine the ideal volume and concentration to produce quality analgesia in ESP block.

Source of Funding
None.

Conflict of Interest
None.

Acknowledgement
We are very thankful for the statistician for helping us in analysing the records.