Comparison of proximal versus distal approach for ultrasound-guided obturator nerve block for prevention of adductor spasm in patients undergoing transurethral resection of urinary bladder tumors

Abstract

Background and Aims:

Adductor muscle spasm occurs when the obturator nerve is directly stimulated by the electrical current transmitted by the resectoscope. Ultrasound-guided ONB is regarded as the optimal technique and is classified as the proximal and distal approach based on the anatomical location of the obturator nerve.

Material and Methods:

This study included 90 adult patients of ASA grades I–III and aged more than 18 years undergoing transurethral resection of bladder tumors under spinal anesthesia. Patients were randomized into two groups: group P received ultrasound-guided obturator nerve block (ONB) by proximal approach, and group D received ultrasound-guided ONB by distal approach. Adductor muscle power after the block, block performance time, complications, and adductor jerks during surgery were compared. A P value of < 0.05 was considered statistically significant.

Results:

Adductor jerks during the surgery were absent in 85.7% of patients in group P and 78.0% of patients in group D. The mean block performance time in group P was 4.33 ± 0.38 minutes, and in group D was 4.00 ± 0.34 minutes. Vascular puncture during the block was observed in nine patients in group P and two patients in group D.

Conclusion:

The success rate in terms of the absence of adductor spasm during surgery was higher in proximal than in distal ultrasound-guided ONB. However, the proximal technique requires more time to perform the block than the distal technique, as it is technically challenging and carries a risk of vascular puncture.

Introduction

Urinary bladder cancer is considered the fourth most common malignancy. Most of the patients presenting with bladder cancer present only with involvement and not invasion of the urothelium or lamina propria.[1] In such patients, transurethral resection of bladder tumors (TURBT) is considered a gold standard for the evaluation and management of bladder cancer.

TURBT can be performed under either spinal or general anesthesia.[2] The advantages of performing TURBT under spinal anesthesia as compared to general anesthesia are reduced recovery time and delirium in patients, early identification of TURP syndrome, better postoperative analgesia and recovery (especially in elderly patients due to cardiac and pulmonary abnormalities), and avoidance of polypharmacy. The obturator nerve arises from the anterior rami of the second, third, and fourth lumbar nerves and passes over fibers of the psoas major muscle and lies deep in the obturator canal, from which it exits and divides into anterior and posterior branches. During its course in the pelvic cavity, it passes close to the inferolateral surface of the bladder neck and lateral prostatic urethra.[3] It is situated directly adjacent to the lateral wall of the bladder during TURBT when the irrigation fluid used in this procedure fills the bladder. Any electrical stimulation caused by tumor resection involving the bladder may induce sudden adductor muscle contraction. Although spinal anesthesia blocks the nerve’s motor branch, the sensory branch is spared. Vigorous adductor muscle spasms can be seen due to this stimulation, which is called as obturator reflex, and it generally causes involuntary movement of the legs (leg jerking). As a result, some serious complications such as bladder perforation, vascular injury, extravesical dissemination of cancer cells, uncontrollable bladder hemorrhage, incomplete resection, and obturator muscle hematomas can happen.[1,2,3]

There are several mechanisms to prevent the obturator reflex, such as general anesthesia with muscle relaxant, the use of laser resectors, reducing the intensity of the current of the resectoscope, changing the site of the inactive electrode, use of saline irrigation, superficial resection with low current, and cutting with a bipolar resectoscope. Spinal anesthesia with selective obturator nerve block (ONB) is considered an appropriate and safe option for elderly patients.

The technique of ONB was first introduced by Labat and Mayo in 1922 and has been used for the management of various conditions.[3] US-guided ONB has been regarded as the optimal technique as it is safe, cost-effective, and provides a real-time image of the injection needle.[4] In clinical practice, the techniques are classified into distal and proximal approaches, which are based on the anatomical location of the obturator nerve.

In the proximal approach, a single injection of LA is deposited in the interfascial plane between the pectineus and obturator externus muscle. This requires various manipulations, including tilting the ultrasound transducer,[5,6,7] using an out-of-plane technique,[5,6] or inserting a needle at small needle–ultrasound beam angles.[6,7,8] In the distal approach, the anterior and posterior divisions of the obturator nerve are blocked separately by two injections of local anesthetic directed toward the interfascial plane.[9,10]

This study aimed to compare the success rates of the proximal and distal approaches.

Material and Methods

This prospective interventional randomized comparative study was conducted for 18 months in the Department of Anesthesia and Intensive Care, after approval from the hospital ethics committee (IEC/VMMC/SJH/THESIS/2020-11/CC-62) and CTRI Registration (CTRI/2022/01/039492). Written informed consent was obtained from all 90 patients.

The primary objective was to compare the success rate of the proximal versus distal approach of ultrasound-guided ONB as determined by the absence of adductor muscle jerks during surgery in patients undergoing transurethral resection of lateral wall bladder tumor under spinal anesthesia. The secondary objectives were to compare the proximal versus distal approach of ultrasound-guided ONB for adductor muscle power after the block, block performance time, and complications.

Adult patients who fulfilled the criterion of the American Society of Anesthesiologists (ASA) grades I–III of age more than 18 years undergoing unilateral transurethral resection of lateral bladder wall tumor under spinal anesthesia were included. Patients with pre-existing obturator nerve injury, adductor muscle weakness, local anesthetic allergy; infection at the site of injection; abnormal coagulation studies; and patients who refused to provide consent were excluded.

The patients were divided into two groups by randomization:

Group P: Patients received ultrasound-guided ONB by the proximal approach.

Group D: Patients received ultrasound-guided ONB by the distal approach.

Sample size: The study by Nida Farooq Shah et al.[11] observed that the success rate of distal nerve block was 76.7%. Taking these values as a reference and assuming a difference of 20% between proximal nerve block and distal block, the minimum required sample size with 80% power of study and 5% level of significance is 42 patients in each study group. Considering the 5% attrition factor, the final sample was taken as 45 in each group.

Block randomization with a sealed envelope system was done. In this, 10 randomly generated treatment allocations were prepared within sealed opaque envelopes assigning A and B in five envelopes each, where A represented the proximal nerve block and B represented the distal nerve block. Once a patient consented to enter the trial, an envelope was opened and the patient was offered the allocated group. In this technique, patients were randomized in a series of blocks of ten, and single blinding was done.

The patient was taken to the block room and positioned supine. Standard monitors for non-invasive blood pressure, electrocardiography, and pulse oximetry (SpO₂) were attached. Basal heart rate, BP (systolic, diastolic, and mean), and SpO₂ were noted.

An intravenous line was established with an 18-G cannula, and 0.5 microgram/kg of intravenous fentanyl was administered to each patient. The ONB was performed with the patient in the supine position and the thigh slightly abducted and externally rotated. A linear transverse high-frequency probe (8–18-MHz M Turbo Sonosite) was used for both proximal and distal approaches of ultrasound-guided ONB.

In the proximal group, the linear transducer probe was placed on the medial aspect of the inguinal crease and was tilted 40–50 degrees cranially until a hyperechoic structure deep and lateral to the muscle pectineus was visualized (inferior margin of the superior pubic ramus). The intermuscular fascia deep to the pectineus muscle, separating it from the obturator externus muscle, was identified.[5,6,7] Using a 24-G needle, local infiltration of 2 mL of 2% lignocaine was done 1 cm away from the lateral edge of the transducer. A 22-G, 80-mm Sonoplex needle was inserted in this fascia under ultrasound guidance in an in-plane direction, from lateral to medial, and 10 mL of 0.5% ropivacaine was injected after negative aspiration. The local anesthetic solution spread was monitored under real-time visualization [Figure 1].

Figure 1.

Proximal approach: (a) Ultrasonographic view; (b) Labelled structures; (c) Spread of local anesthetics

In the distal group, the ultrasound transducer was placed along the inguinal crease, and the femoral vessels were identified. Tracing the ultrasound probe medially, the pectineus, adductor longus, adductor brevis, and adductor magnus muscles were identified by the classic Y shape.[9,10] Using a 24-G needle, local infiltration was done using 2 mL of 2% lignocaine 1 cm away from the lateral edge of the transducer. A 22-G, 80-mm Sonoplex needle was inserted from lateral to medial in an in-plane approach to place the tip at a hyperechoic structure of the fascial interface between the adductor longus and adductor brevis muscles. After negative aspiration, 5 mL of 0.5% ropivacaine was injected. Then, the needle was withdrawn and reinserted to be positioned at the fascial plane between the adductor brevis and adductor magnus muscles, and 5 mL of 0.5% ropivacaine was injected after negative aspiration. All the blocks were performed by a single experienced anesthesiologist [Figure 2].

Figure 2.

Distal approach: (a) Red arrow shows local anesthetic spread between the adductor longus and adductor brevis; (b) Red arrow shows local anesthetic spread between the adductor brevis and adductor magnus

Block performance time was noted as the time taken from the start of ultrasonography to the needle removal. Complications while performing the block, such as vascular puncture and hematoma, were noted.

Adductor muscle power was assessed after 15 minutes using the following grading.[12]

• 0: No observable adductor muscle contraction

• 1: Unable to adduct the hip joint with gravity elimination

• 2: Able to adduct the hip joint through a full range of motion with gravity elimination

• 3: Able to adduct the hip joint against gravity

• 4: Able to adduct the hip joint against moderate resistance

• 5: Able to adduct the hip joint against maximal resistance.

Grade 2 or less was considered a successful block; grades more than 2 were excluded from further study.

After a successful block, the patient was shifted to the operation theatre, and spinal anesthesia was given using a 25-G Quincke’s spinal needle at the L3-4 or L4-5 interspace in the lateral position. After confirming the presence of free-flow and clear cerebrospinal fluid in the syringe, 2.2 mL of 0.5% hyperbaric bupivacaine with 10 mcg fentanyl was administered. The patient was laid supine, and after confirming the sensory blockade at the T-10 level, surgery was started. The patient was continuously monitored throughout the surgery using standard monitoring. The success rate was determined by the absence of adductor jerk/spasm during the surgery. Jerk/spasm was graded as:[7]

• 0: No adductor muscle contraction

• 1: Slight adductor muscle contraction, but surgery can be continued

• 2: Severe adductor muscle contraction, surgery discontinued, and general anesthesia given. Intraoperatively, if any jerks were observed and led to discontinuation of surgery, then general anesthesia with a muscle relaxant was given.

Statistical analysis

Categorical variables were presented in numbers and percentages (%), and continuous variables were presented as mean ± SD and median. Normality of data was tested by the Kolmogorov-Smirnov test. When the normality tests were rejected, non-parametric tests were used.

Statistical tests were applied as follows-

1. Quantitative variables were compared using an unpaired t-test/Mann-Whitney test (when the datasets were not normally distributed) between the two groups.

2. Qualitative variables were compared using the Chi-square test/Fisher’s exact test.

A P value of < 0.05 was considered statistically significant.

The data were entered in an MS EXCEL spreadsheet, and analysis was done using Statistical Package for Social Sciences (SPSS) version 21.0.

Results

Both groups were comparable in terms of patient profile and ASA status [Table 1].

Table 1.

Data Interpretation

Parameters	Group		P
	P (n=45)	D (n=45)
Age (years)	55.42±6.36	57.09±15.13	0.288
Gender			0.438
Male	37 (82.2%)	34 (75.6%)
Female	8 (17.8%)	11 (24.4%)
Height (cm)	163.73±4.68	163.58±5.70	0.528
Weight (kg)	61.96±4.99	61.76±6.36	0.935
BMI (kg/m²)	23.17±2.23	23.02±1.29	0.100
ASA			0.387
I	25 (55.6%)	29 (64.4%)
II	20 (44.4%)	15 (33.3%)
III	0 (0.0%)	1 (2.2%)
Block Performance Time***	4.33±0.38	4.00±0.34	<0.001
Complications: Vascular Puncture (Yes)***	9 (20.0%)	2 (4.4%)	0.024
Adductor Muscle Power After the Block			0.722
Grade 1	20 (44.4%)	24 (53.3%)
Grade 2	22 (48.9%)	17 (37.8%)
Grade 3	2 (4.4%)	2 (4.4%)
Grade 4	1 (2.2%)	2 (4.4%)
Adductor Jerks During Surgery***	n=42	n=41	<0.001
None	36 (85.7%)	32 (78.0%)
Yes Grade 1	0 (0.0%)	4 (9.8%)
Yes Grade 2	0 (0.0%)	5 (12.2%)
Yes Grade 3	3 (7.1%)	0 (0.0%)
Yes Grade 4	3 (7.1%)	0 (0.0%)

The adductor muscle power was assessed after the block. Grade 2 or less was considered a successful block. Three patients in group P and four patients in group D had muscle power more than grade 2 and were excluded from the further study. The success rate as determined by the absence of adductor jerks during the surgery was 85.7% in group P, which was significantly higher compared to 78.0% in group D (P value < 0.001). Six patients out of 42 patients in group P and nine patients out of 41 in group D experienced adductor jerks during the surgery. These 15 patients who experienced adductor jerks during the surgery were administered general anesthesia with muscle relaxant. A statistically significant difference was seen in the block performance time (in minutes) between groups P and D with P value < 0.001. The mean block performance time was 4.33 ± 0.38 minutes in group P and 4.00 ± 0.34 minutes in group D. Vascular puncture during performing the block was observed in nine patients in group P and only two patients in group D (P value = 0.024).

Discussion

A successful ONB obliviates the requirement of general anesthesia, and resection of lateral wall bladder tumors can be successfully done under subarachnoid block. Ultrasound-guided ONB can be divided into proximal and distal according to the anatomical course of the nerve. In the proximal approach, local anesthetic is deposited in the interfascial plane between the pectineus and obturator externus muscle. In the distal approach, the anterior and posterior divisions of the obturator nerve are blocked separately by two injections of local anesthetic.[8,9] The anterior division is blocked by depositing local anesthetic between the adductor longus and adductor magnus muscles, and posterior is blocked by depositing local anesthetics between the adductor magnus and adductor brevis.

The ultrasound-guided proximal ONB has not been studied extensively in the literature. Different approaches have been proposed in the literature; these require various manipulations, including tilting the ultrasound transducer,[5,6,7] using an out-of-plane technique,[5,6] position of the patient, or inserting a needle at small needle–ultrasound beam angles.[6,7,8,9]

Taha[6] conducted a case series on 60 patients who were scheduled to undergo hamstring anterior cruciate ligament reconstruction to evaluate the efficacy of ultrasound-guided proximal ONB. In our study, we used Taha’s approach, but needling was done using an in-plane technique with a lateral-to-medial approach.

Han et al.[13] conducted a study on 50 patients undergoing transurethral bladder tumor resection and divided them into two groups. One group received ultrasound-guided proximal ONB (proximal group), and the other group received ultrasound-guided distal ONB (distal group). They reported that one patient in the proximal group and two patients in the distal group had to be administered general anesthesia intraoperatively due to severe adductor spasm. Two vascular punctures were reported in the proximal approach as compared to one in the distal group, which was not statistically significant. They reported that the duration of block procedure was lower in the proximal group (8.5 ± 1.7 min) than in the distal group (8.9 ± 2.2 min). In comparison to the above study, six patients in the proximal group and nine patients in the distal group experienced adductor spasm in our study and had to be administered general anesthesia (P = <0.001). The success rate of the above study was not mentioned by the authors. Several studies have reported that ultrasound-guided ONB is associated with success rates of 88%–100%.[6,14,15,16,17,18] The success rate in our study was 85.7% in group P and 78.0% in group D, which corresponds to the literature.

Taha[6] observed a success rate of 85.7% in ultrasound-guided proximal nerve block. Our success rate is comparable to the study conducted by Taha,[6] but we used an in-plane technique of needle insertion and visualized the whole length of the needle. In our study, the mean block performance time was 4.33 ± 0.38 minutes in group P and 4.00 ± 0.34 minutes in group D. Taha[6] observed a median block onset time of 4 minutes (95% CI: 3–5 minutes) while performing the proximal ONB, which is similar to our study.

In a clinical observational study of 18 male patients undergoing TURP surgery by Thallaj and Rabah,[18] the average time taken for proximal ONB was 4.3 min (SD: ±0.8 min). Shah et al.[11] observed a mean block performance time of 2.10 ± 0.51 min for performing a distal ONB. The mean block performance time for performing proximal and distal ONB in our study corresponds to the mean block performance time mentioned in various studies in the literature. The longer time taken for proximal nerve block could be because the authors faced difficulty in needle visualization while performing the block due to the cranial tilt of the probe.

Vascular puncture during the block in our study was observed in nine patients in group P and in only two patients in group D, which is similar to the study by Han et al.[13] Vascular puncture during proximal nerve block could be attributed to the deeper location of the obturator nerve and increased vascularity of the pelvic area. Thus, the authors would strongly recommend using Doppler imaging to reduce vascular puncture, and probably an out-of-plane technique could be employed to avoid vascular puncture.

Shah et al.[11] observed a success rate of 90% for ONB using ultrasound with nerve stimulation-assisted technique as compared to 76.7% for ONB under ultrasound guidance only, which is parallel to our study, as the success rate of group D in our study was 78.0%. The higher success rate in the other group may be because of the use of the nerve stimulation technique with ultrasound guidance by Shah et al.[11] The authors would recommend that further studies be done to ascertain if the success rate increases by using nerve stimulation technique with ultrasound guidance for proximal ONB.

We recommend multicentered studies with a larger sample size to further assess the safety and success rate of the proximal and distal ONB. There is a steep learning curve to perform the proximal ONB as it is a relatively difficult block to perform because of the deeper location of the anatomical structures.

Conclusions

The success rate in terms of the absence of adductor jerks during surgery was higher in the proximal ultrasound-guided ONB technique than in the distal technique. However, the proximal technique requires more time to perform the block than the distal technique, as it is technically challenging and carries a risk of vascular puncture as attributed to the deeper location of the anatomical structures.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.