Ultrasound versus C-arm fluoroscopic-guided subarachnoid block in patients with predicted difficulty for subarachnoid block posted for infraumbilical surgeries: A prospective randomized controlled study

Abstract

Background:

Subarachnoid block (SAB) is a preferred anesthetic technique for infraumbilical surgeries. However, in obese patients, landmark identification for SAB can be difficult, increasing the risk of procedural failure and complications. This study is determined to compare the efficacy of ultrasound (USG)-guided, C-arm fluoroscopy-guided, and anatomical landmark-guided SAB in obese patients.

Methods:

Sixty patients of 18–80 years with BMI ≥30 kg/m² of American Society of Anaesthesiologist Physical Status (ASA PS) II–III scheduled for infraumbilical surgeries were randomized into three equal groups: Group A, Group B, and Group C for USG-guided, C-arm-guided, and Landmark-guided SAB, respectively. Each received 0.5% hyperbaric bupivacaine intrathecally using a 25-G Quincke’s needle. Total time taken for the procedure, number of spinal needle insertion attempts, patient satisfaction score, success rate, and complications in each group were recorded.

Results:

All groups were comparable demographically. Group B had the significantly highest total time taken for the procedure, 380.4 ± 46.2 seconds, compared to Group A, 273.6 ± 7.5 seconds, and Group C, 165.7 ± 23.2 seconds. The number of spinal needle insertion attempts was lowest in Groups A and B, with higher patient satisfaction scores. Complications occurred only in Group C.

Conclusion:

Imaging modalities-guided SAB in obese patients took a prolonged procedure time but had fewer spinal needle insertion attempts and better patient satisfaction than the landmark-guided SAB. Between the imaging modalities, USG-guided SAB was faster, required fewer needle insertions, and gave better patient satisfaction than C-arm guided SAB.

Introduction

Subarachnoid block (SAB) is a well-established and widely utilized regional anesthesia technique, particularly for infraumbilical surgeries.[1] SAB, due to its rapid onset and reliable efficacy, remains the gold standard in such scenarios. The technique involves the injection of local anesthetic into the subarachnoid space, leading to blockage of nerve impulses at the spinal cord level.[2]

Conventional landmark-guided SAB in obese patients increases the likelihood of multiple attempts, failed blocks, procedural delays, and complications such as post-dural puncture headache (PDPH), nerve injuries, or inadvertent epidural placement.[3] To address these challenges, imaging-guided approaches to SAB, such as C-arm fluoroscopy and ultrasound (USG), have been introduced, offering greater precision in needle placement and improving success rates in patients with predicted difficulty in SAB.[4] Ultrasound allows for real-time visualization of spinal structures and identification of the midline without radiation exposure, making it an attractive option for guiding neuraxial procedures.[5] Despite its advantages, ultrasound-guided SAB requires advanced operator training and expertise to interpret spinal Sono anatomy accurately.[6] In patients with severe obesity, obtaining clear ultrasound images may still be challenging; thus, comparing ultrasound guidance with other modalities such as C-arm fluoroscopy is essential.

C-arm fluoroscopy is a real-time X-ray imaging technique that can be utilized in guiding SAB, providing precise needle navigation and accurate entry into the subarachnoid space. It is useful for patients with obesity or compromised landmarks, offering consistent visualization, particularly where traditional methods fail; however, it has limitations such as the need for specialized equipment, exposure to ionizing radiation to both patients and operator during the procedure, along with higher procedural costs and logistical challenges.[7] This study aims to compare the efficacy of C-arm fluoroscopy-guided, ultrasound-guided, and landmark-guided SAB in patients with predicted procedural difficulty posted for infraumbilical surgeries.

Materials and Methods

This prospective open-label randomized controlled study was conducted over 1 year following ethical committee approval (EC No. 63/2023-24) and registration with the Clinical Trial Registry of India (CTRI/2024/03/064430) on March 19, 2024. All the standards of the Declaration of Helsinki had been followed in the trial. Computer-generated random number tables were used for randomization to enroll an equal number of patients in three groups, and group allocation was concealed using an opaque sealed envelope technique.

The sample size was calculated based on the studies conducted by Elsharkawy et al.[8] and Omodu et al.[7] considering an alpha error of 0.05, a confidence interval of 95%, and a power of 80% using total time taken for the procedure as a primary variable. We calculated a minimum sample size of 18.5, and after considering some dropouts, a sample size of 20 patients in each group was considered for the study. Sixty obese patients aged between 18 and 80 years of BMI ≥30 kg/m², classified as American Society of Anaesthesiologists (ASA) physical status II–III,[9] scheduled for infraumbilical elective surgeries, were included after obtaining written informed consent. Patients were excluded if they refused spinal anesthesia, were on thromboprophylaxis, or had allergies to local anesthetics, local infections, coagulopathies, raised intracranial pressure, or pregnancy. According to group allocation, patients received SAB under USG guidance in Group A, under C-arm guidance in Group B, and using the Landmark-guided technique in Group C. All patients received intravenous (IV) 0.5% hyperbaric bupivacaine at a dose of 0.3 mg/kg intrathecally using a 25 Gauge 90 mm Quincke’s spinal needle. To achieve adequate expertise, ultrasound-guided SAB and C-arm fluoroscopy-guided SAB were performed on 50 normal patients 25, 25 each, respectively, posted for infraumbilical surgeries before the start of the study. All subarachnoid blocks were administered by the same expert anesthesiologist.

All patients were instructed to keep fasting according to recent nil per os guidelines[10] and premedicated with tablet alprazolam 0.25 mg and tablet ranitidine 150 mg the night before the surgery. On the arrival of the patient in the operating theater, all ASA standard monitors, which include electrocardiogram (ECG), noninvasive blood pressure (NIBP), pulse oximetry (SpO2), and temperature, were attached. An 18-gauge intravenous (IV) cannula was secured under aseptic precautions, and the patient was preloaded with Ringer’s lactate at the rate of 10–15 mL/kg. In Group A patient, USG-guided SAB was performed, keeping him in a sitting position using a low-frequency (2–5 MHz) curvilinear ultrasound (Sonosite Fujifilm M-Turbo) transducer placed vertically at the sacrum to obtain a parasagittal view with slight medial tilt. The transducer was moved cephalad to identify the desired intervertebral space, either L3-L4 or L4-L5 [Figure 1]. The desired intervertebral space was marked, and after skin topicalization with 2% lidocaine, the spinal needle was inserted in plane to the transducer. The needle tip was adjusted in real time until it was pointed between two laminae. The direction of the needle shaft was adjusted to direct the needle trajectory until the dura was penetrated and free flow of cerebrospinal fluid (CSF) was seen. Intravenous (IV) bupivacaine 0.5% hyperbaric at a dose of 0.3 mg/kg was injected into the subarachnoid space. In Group B patients, C-arm fluoroscopy-guided SAB was performed by first identifying the desired intervertebral space with an anterior-posterior view of the lumbar spine on the C-arm view. 25 25-gauge 90 mm long Quincke’s spinal needle was placed parallel to the intervertebral space without puncturing the skin with the C-arm ring being positioned perpendicularly where the image intensifier end was placed at the ventral side of the patient and the X-ray tube at the dorsal end of the patient with the C-arm ring axis at 100 degrees to identify the desired intervertebral space as shown in. That desired space was marked, and then the C-arm position was changed with the C-arm ring axis placed transversely at the level of the iliac crest. After skin topicalization with 2% lidocaine, a spinal needle was inserted under guidance of transverse view of C-arm [Figure 2], and the direction of the needle shaft was adjusted under real-time C-arm guidance till it penetrated the dura with free flow of CSF coming out, followed by intrathecal IV hyperbaric bupivacaine injection.

Figure 1.

Ultrasound view in parasagittal plane using curvilinear transducer at L3-L4 level. LF, Ligamentum flavum; VB, Vertebral body

Figure 2.

C-arm image showing transverse view of the lumbar spine with spinal needle at L4-L5 intervertebral space. *, Spinal needle

In Group C patients, landmark-guided SAB was performed after palpation of the spinous processes of the lumbar vertebrae, parallel to the iliac crest. A horizontal imaginary line passing over the top of both iliac crests, known as Tuffier’s line, corresponding to the L4-L5 intervertebral space, was used as a guide to identify the intervertebral space.[11] After proper skin topicalization, a spinal needle was inserted till a free flow of CSF came out, and intrathecal IV hyperbaric bupivacaine injection was given.

All the patients were immediately placed in the supine position after giving SAB. Hemodynamic parameters, such as heart rate (HR), systolic blood pressure (SBP), diastolic pressure (DBP), mean arterial pressure (MAP), respiratory rate (RR), and SpO2, were monitored throughout the surgery. After completion of surgery, patients were shifted to the PACU.

All outcome variables were recorded by a separate anesthesiologist. The primary outcome variable was the total time taken for the procedure, which was defined as the time taken to identify the landmarks by each technique up to the free flow of CSF from the spinal needle. The starting point of landmark identification began with the placement of a USG transducer on the skin in Group A, the first C-arm image acquisition in Group B, and the start of surface palpation in Group C. Secondary outcomes included the number of spinal needle insertion attempts, patient satisfaction scores, success rate, and complications. The number of spinal needle insertion attempts was defined as the number of any separate skin puncture by a spinal needle.

Success was defined as successful dural puncture followed by free flow of CSF. “Failure” was defined as failure of localization of the subarachnoid space with lumbar puncture in five needle insertion attempts. The patient satisfaction score with the block procedure was rated by the patient immediately after completion of SAB administration on a 5-point Likert scale (5 = very satisfied, 4 = satisfied, 3 = neutral, 2 = dissatisfied, 1 = very dissatisfied). All the patients were followed in the postoperative period to look for complications like back pain, PDPH, retention of urine, nausea, and vomiting.

Statistical analysis

All randomized patients were included in the analysis, and none of the patients was lost to follow-up [Figure 3]. The data collected from study participants were entered into a Microsoft Excel sheet, and statistical analysis was done by using Statistical Package for the Social Sciences (SPSS) software, version 25, IBM Inc., Chicago, USA. Normality of data distribution was confirmed by the Shapiro–Wilk Test. One-way ANOVA test with Tukey post hoc correction was applied for continuous variables and Chi-square or Yates’s correction tests for categorical variables, considering P < 0.05 as statistically significant.

Figure 3.

CONSORT flow diagram

Results

All three groups were comparable in terms of demographic profile and patient characteristics, as shown in Table 1. The mean value of total time taken for the procedure in Group B was 380.4 ± 46.2 seconds, which was higher compared to Group A (273.6 ± 7.5 seconds) and Group C (165.7 ± 23.2 seconds). Statistical analysis revealed a significant difference in total time taken for the procedure among the three groups (P < 0.001). Pairwise analysis among the groups is shown in Table 2.

Table 1.

Distribution of demographic variables among groups

Variables	Group-A (USG) (n=20)	Group-B (C-arm) (n=20)	Group-C (LM) (n=20)
Age (year)	41.4 (15.58)	43.05 (17.15)	35.3 (11.62)
Gender (Male/Female)	9/11	10/10	8/12
BMI (kg/m2)	34.99 (2.53)	35.33 (1.84)	35.44 (2.57)
ASA Physical Status
II	19	16	17
III	1	4	3
Duration of Anesthesia (minutes)	136 (33.38)	126.33 (45.35)	148.12 (41.96)

n=number, ASA=American Society of Anaesthesiologists, BMI=body mass index. Group A, USG-guided SAB; Group B, C-arm-guided SAB; Group C, LM, Landmark-guided SAB. Data expressed as mean (standard deviation) and frequency

Table 2.

Comparison of total time taken for the procedure (Seconds)

Comparison groups	Mean difference	95% confidence interval for mean difference		P
		Upper Limit	Lower Limit
Group-A (USG) vs Group-B (C-arm)	106.8	129.75	83.85	<0.001*
Group-A (USG) vs Group-C (LM)	−107.9	−84.95	−130.85	<0.001*
Group-B (C-arm) vs Group-C (LM)	−214.7	−191.75	−237.65	<0.001*

Group A, USG-guided SAB; Group B, C-arm-guided SAB; Group C, LM, Landmark-guided SAB. The test applied was one-way ANOVA with Tukey post hoc correction. *Highly significant (P<0.001)

The total number of spinal needle insertion attempts was categorized as ≤2 attempts and ≥3 attempts. Seventeen patients in Group A, 16 patients in Group B, and 12 patients in Group C received SAB in ≤2 attempts. 40% of patients (8 out of 20 patients) in Group C required ≥3 attempts, which was more compared to Group A and Group B [Table 3]. The Chi-square analysis revealed a highly significant difference among the three groups in the number of attempts required for successful SAB placement in obese patients (P < 0.001) [Table 3]. Groups A and B were comparable in terms of needle insertion attempts. Single attempt success was higher in patients receiving SAB under USG and C-arm guidance.

Table 3.

Comparison of spinal needle insertion attempts

Variables	Group-A (USG) (n=20)		Group-B (C-arm) (n=20)		Group-C (LM) (n=20)		P
	f	%	f	%	f	%	All
							A vs B	A vs C	B vs C
Spinal needle insertion attempts
≤2 attempts (1/2)	17 (15/2)	85	16 (10/6)	80	10 (2/8)	60	0.029*
≥3 attempts (3/4/5)	3 (1/2/0)	15	4 (3/1/0)	20	10 (3/5/2)	40	0.677	0.018*	0.047*

n, number; f, frequency; %, percentage; Group A, USG-guided SAB; Group B, C-arm-guided SAB; Group C, LM, Landmark-guided SAB. Data expressed as frequency and percentage were analyzed by a Chi-square test with Yates’s correction. *Significant (P<0.05)

The patients of Group A and Group B had significantly higher patient satisfaction scores compared to Group C (P < 0.001) [Figure 4]. All three groups had achieved a 100% success rate with no failure recorded. None of the patients in Groups A and B reported any complication related to SAB, while in Group C, 2 patients had PDPH. The hemodynamic parameters were noted in all the patients, and their differences were not statistically significant at any time points of the study (P > 0.05).

Figure 4.

Comparison of patient satisfaction score

Discussion

In our study, the total time taken for the procedure was highest in C-arm-guided SAB placement, followed by USG-guided and Landmark-guided SAB administration. Similar to our study result, one study conducted by Lim et al.[12] also observed that the USG-guided technique took a longer time in placing SAB compared to the landmark technique in patients scheduled for elective orthopedic surgeries. In contrast to our study, Chong et al.[13] conducted a randomized controlled trial comparing real-time ultrasound-guided SAB with landmark palpation-guided SAB. They observed that the total time taken for SAB was longer in the landmark-guided traditional technique than the USG-guided technique, but this difference was statistically not significant. The disparity in the results may be attributed to the fact that, in our study, the total time taken for the procedure included both the time required to identify the desired intervertebral space and the time taken to perform the SAB, whereas in the research done by Chong et al.,[13] only the SAB placement time was considered, excluding the time spent on landmark identification. One of the key factors contributing to this prolonged procedure time in C-arm and USG-guided SAB placement was the additional time spent on visualizing the relevant spinal structures and identification of the space requiring equipment positioning, adjustment, and handling. Image acquisition, probe manipulation in the case of USG, and optimal positioning under fluoroscopy in the case of C-arm guidance may add to the overall time taken for block administration, unlike the landmark-guided technique, which relies solely on anatomical landmark palpation and can be initiated immediately after patient positioning.

The total number of spinal needle insertion attempts was significantly less in the C-arm-guided technique and least in the USG-guided technique, though they were comparable after statistical analysis of the records obtained. These findings strongly support the use of imaging modality-guided SAB in obese patients; these methods significantly reduce the number of needle insertion attempts and thus minimize patient discomfort.

Obesity can obscure the palpation of anatomical landmarks due to excessive soft tissue, resulting in difficulty in identifying the desired intervertebral space. In such patients, reliance on traditional landmarks often can lead to multiple spinal needle insertion attempts, prolonged procedure time, failed blocks, and complications that ultimately lead to patient discomfort. To address these challenges, imaging modalities such as C-arm fluoroscopy and ultrasound have been introduced, offering greater precision in needle placement and improving success rates in patients with difficult spinal anatomy. Several recent studies have demonstrated the utility of ultrasound in challenging spinal anatomies.[14,15,16] They had demonstrated that ultrasound imaging improves accuracy and reduces failure rates in SAB placement in high-BMI patients. Nomura et al.[17] confirmed increased first-pass success rates using ultrasound-assisted lumbar puncture in a randomized trial. Additionally, Balki et al.[18] validated the transverse plane approach to identify lumbar interspaces with high accuracy using ultrasound.

Most patients who received USG and C-arm-guided SAB reported high satisfaction, whereas 50% of patients who received Landmark-guided SAB experienced neutral to poor satisfaction. Other studies also support that patient satisfaction improves with the use of ultrasonography in neuraxial block placement.[12] Previous data on patient satisfaction with C-arm fluoroscopy for SAB administration were lacking. This study highlighted significantly higher patient satisfaction with C-arm guidance for SAB placement in obese patients scheduled for infraumbilical surgeries. In our study, all patients successfully received SAB despite varying numbers of needle insertion attempts and procedure times. There was no difference in success rates among the three groups. Elsharkawy et al.[8] conducted a randomized controlled trial comparing Landmark-guided and USG-guided techniques for spinal anesthesia in obese patients, also observing no significant difference in success rates between the two methods. We had fortunately been able to achieve successful SAB placements in all obese patients using standard-sized needles. The standard spinal needles may sometimes be inadequate for obese patients due to the increased tissue depth.[19] In such patients, it is advisable to use longer spinal needles specifically designed to ensure adequate reach to the target structures.

Limitations

We did not analyze the time spent separately on identifying the intervertebral space and placing the SAB. Additionally, the small sample size limits the generalizability of our results. Future studies should examine the relation between the intervertebral space identified by the landmark technique and both imaging techniques. Currently, there are no universally accepted predictors that can accurately forecast difficult spinal anatomy. Future research ought to develop standardized clinical, radiological, or anthropometric predictors to identify patients at risk for difficult spinal access reliably.

Conclusion

Although imaging modalities guiding SAB in obese patients take longer for the procedure, they offer better patient satisfaction with fewer needle insertion attempts compared to landmark-guided SAB. Among the imaging methods, USG-guided SAB takes less time, with a similar number of needle attempts and improved patient satisfaction compared to C-arm-guided SAB.

Ethical statement

The study was approved by Institutional ethical committee with approval no. 63/2023-24 dated on 22/08/2023. This study has been registered in Clinical Trial Registry India (CTRI) with Reg. no. CTRI/2024/03/064430 on 19-03-2024. The Declaration of Helsinki has been complied with in this trial.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.