The Indian Anaesthetists’ Forum

: 2020  |  Volume : 21  |  Issue : 1  |  Page : 10--15

A comparative study of ultrasound-guided caudal block versus anatomical landmark-based caudal block in pediatric surgical cases

Nethra H Nanjundaswamy, Saraswathi Nagappa, Raghavendra Biligiri Shridhara, Sandya Kalappa 
 Department of Anaesthesiology, Bangalore Medical College and Research Institute, Bengaluru, Karnataka, India

Correspondence Address:
Dr. Nethra H Nanjundaswamy
#SF4, VV Apartments, Contour Road, Padmanabhanagar, Bengaluru - 560 070, Karnataka


Background: Caudal block is a popular regional anesthesia technique in pediatrics for anesthesia and perioperative analgesia. Conventional landmark-based technique is a simple technique with good success rate but associated with complications such as dural puncture and venous injection. Ultrasound-guided caudal block is known to improve the success rate and reduce the complications noted with the landmark technique. We aimed to compare the success rates of caudal block in landmark- and ultrasound-guided techniques. Methods: One hundred and twenty-four children under 10 years admitted for infraumbilical surgeries were randomly allocated to Group L and Group U caudal block was administered based on landmarks in Group L and by using ultrasound in Group U. In both the groups, observations noted were success of caudal block, visibility and palpability of sacral cornu; identification of hiatus; first attempt success; number of attempts; block performance time; and complications. In Group U, ultrasound visualization of sacral hiatus, needle, and distension of sacral canal with injection was also noted. Results: Success rates were 81.8% and 92.1% in Group L and Group U, respectively (P = 0.045). Complications noted in Group L were blood tap (23.8%), subcutaneous swelling (15.2%), dural puncture (1.5%), and rectal perforation (1.5%). In Group U, only blood tap (3%) was the complication noted. Block performance was faster in Group L than Group U. There was no significant difference in the first attempt success rate and number of attempts. Conclusion: Ultrasound-guided caudal block improves the success rate, reduces complications, and ensures safety.

How to cite this article:
Nanjundaswamy NH, Nagappa S, Shridhara RB, Kalappa S. A comparative study of ultrasound-guided caudal block versus anatomical landmark-based caudal block in pediatric surgical cases.Indian Anaesth Forum 2020;21:10-15

How to cite this URL:
Nanjundaswamy NH, Nagappa S, Shridhara RB, Kalappa S. A comparative study of ultrasound-guided caudal block versus anatomical landmark-based caudal block in pediatric surgical cases. Indian Anaesth Forum [serial online] 2020 [cited 2020 Aug 14 ];21:10-15
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Full Text


Caudal block is the commonly performed regional procedure in children for anesthesia and perioperative analgesia. It is routinely performed under general anesthesia by palpation of landmarks over sacral bone. The anatomical variations in sacral size, shape, and width of sacral hiatus pose challenges for landmark technique. The success rate of caudal block with anatomical technique is 75% and depends on correct placement of needle in sacral canal.[1],[2] Wrong placement of needle can lead to complications such as dural puncture, presacral, intravascular, or subcutaneous (SC) injection. Needle in caudal space can be confirmed with fluoroscopy or ultrasound imaging.[3] Ultrasound is preferred over fluoroscopy for its absence of radiation risk and noninvasiveness.

Modern ultrasound machines are user-friendly, portable, and affordable. Regular use of ultrasound has contributed in better understanding of the sonoanatomy for regional blocks. Ultrasound imaging scores over fluoroscopy, peripheral nerve stimulator and nerve mapping for its real-time imaging, visibility of needle trajectory, depth, injection site, and spread of drugs. Ultrasound-assisted regional blocks are known to reduce the number of attempts and improve patient comfort.[4],[5],[6]

Ultrasound is routinely used for peripheral nerve blocks, caudal, central neuraxial, and field blocks in adults. Its use in pediatric blocks is limited. Conventional technique is popular as the landmarks are palpable with ease, convenience, and has good success rates. In ultrasound, sacral hiatus and caudal epidural space are easily visualized due to nonossification of sacral bone.[4],[5] Studies report varying success rates with the use of ultrasound for caudal blocks in pediatric anesthesia.[5],[6] There is a lack of evidence for the need of ultrasound in pediatric caudal blocks.[5],[7],[8] Hence, we aimed to study the success rate and complications of ultrasound-guided and landmark techniques in pediatric caudal blocks performed in our institution.


Institutional ethical committee clearance was obtained. For this prospective observational study, we included 124 male children aged under 10 years, ASA Physical Status 1 and 2, and admitted for infraumbilical surgeries. Children with coagulation abnormalities, local infection, systemic infections, and allergy to study drugs were excluded from the study. The primary objective was to compare the success of ultrasound-guided versus landmark-guided caudal block in pediatric cases. The secondary objectives were to compare the block performance duration, first attempt success rate, and complications.

Written informed consent was obtained from parents. In this single-blind study, patients were randomly allocated to Group U or Group L by computer-generated random numbers. All the patients were administered general anesthesia with controlled ventilation with supraglottic airway device or endotracheal tube. Intravenous (IV) thiopentone 5 mg/kg, fentanyl 2 mcg/kg, and atracurium 0.5 mg/kg was administered to facilitate placement of I gel/endotracheal tube. Anesthesia was maintained with sevoflurane 2% in 50:50 air-oxygen mixture and intermittent doses of muscle relaxants.

Patients were placed in the left lateral position with hips flexed to 90°. In landmark technique, bilateral posterior superior iliac spine, sacral cornua, and hiatus were identified by palpation. 22G or 20G (Angiocath) needle was introduced at 60°–90° angle at the apex of the hiatus and observed for “pop” or “loss of resistance.” After the “pop” was felt, the needle was realinged by 20°–30° to the skin and pushed 2–3 mm inside the hiatus. Needle placement was confirmed by “swoosh” test.[3],[4],[9] Injection ropivacaine 0.2% was administered as per the Armitage regime. Visibility of landmark, palpability of sacral cornu, identification of hiatus, number of attempts, result of Swoosh test, visual observation of bulge, and duration for the procedure were noted.

In ultrasound technique, SonoSite M-turbo® with high frequency linear array probe (6–13 MHz) with 38 mm footprint was used.[7],[10] Preprocedural scanning of the sacral and coccyx was done. The probe was placed transversely over coccyx and moved cranially to identify sacral cornu which appears “frog eye sign” and hyperechoic sacroccygeal ligament as “the hump” on imaging[6],[7],[10] [Figure 1]. At this point, the probe was turned longitudinally and observed for sacrococcygeal ligament, sacral canal, and sacral vertebrae [Figure 2]. Needle was inserted under vision in longitudinal plane. The needle trajectory was observed throughout the procedure. Placement of needle was confirmed by observing the distension of the sacral canal in transverse and longitudinal views [Figure 3]. Injection ropivacaine 0.2% was administered as per the Armitage regime. Visualization of sacral cornu, needle tip, and bulging of SC with injection was observed.{Figure 1}{Figure 2}{Figure 3}

All study cases were observed for complications – dural puncture, blood taps, SC bulge, rectal perforation, and drug-related adverse effects. Hemodynamics – heart rate and mean arterial pressure were recorded throughout the surgery. All patients were administered IV paracetamol before extubation.

The primary outcome measure was success rate of block. The secondary outcome measures were block performance time, first puncture success rates, and complication rate. Successful block was defined as the absence of increase in the heart rate and blood pressure with surgical site incision. Block time was defined as the period between the insertion of the needle and termination of local anesthetic administration. First puncture success rate was defined as reaching the sacral canal or hiatus with single-needle orientation on the first puncture without any withdrawal from the skin.

Statistical analysis

Assuming the success rate of 75% with anatomical landmarks technique, to detect a difference of 20% success rate between two groups, to attain a power of 80% at alpha error of 0.05, we needed 56 patients in each group. However, we recruited 124 children for the study, considering dropouts from the study. Statistical analysis was performed with IBM SPSS version 21.0 software (IBM Corp.released 2015.IBM SPSS Statistics for Windows, Version 23.0; Armonk, NY). Mean and standard deviation was calculated for age, weight, and block performance duration; independent Student's t-test was used. Frequency and percentages were used for descriptive parameters. Chi-square test was used to compare parameters.


In the study of 124 male patients, posted for infraumbilical surgeries were enrolled. Patient characteristics were comparable. Mean age was 33.9 months and mean weight was 10.75 K. The primary and secondary outcome measures are mentioned in [Table 1]. Observations in ultrasound-guided technique and landmark-guided blocks are listed in [Table 2] and [Table 3]. Significant difference (P < 0.05) was observed in success rates and block performance duration. Ultrasound-guided block had higher success rate with less complications. Landmark-guided block was performed in lesser duration than ultrasound-guided blocks. Blood taps, SC swelling, and dural and rectal punctures were present in landmark-guided technique. There was no significant difference between the number of attempts and first-attempt success rates. Swoosh test was 100% sensitive, positive predictive value was 87.1%; specificity of 33.33% and negative predictive value of 100%. Diagnostic accuracy of swoosh was 87.88%.{Table 1}{Table 2}{Table 3}

Hemodynamics was well controlled throughout the study in both the groups. Significant reduction (P < 0.001) in the heart rate from the baseline values were noted in both groups. Mean values of reduction in heart rate was 18.54% in landmark group and 14.64% in ultrasound group. Mean arterial pressures reduced by 15.26% in landmark and 13.7% in ultrasound groups, respectively. 12 patients (18.2%) in landmark group and 4 patients (6.3%) had increase in heart rate and blood pressure for surgical incision and was considered as failed caudal blocks. IV fentanyl and skin site infiltration were used for analgesia in failed caudal cases.


Use of ultrasound for performance of regional block and cannulation has gained popularity around the world. The newer machines with higher resolution offer a safe and convenient alternative to conventional landmark techniques. Ultrasound- and landmark-guided techniques of regional block are commonly practiced in adults. In pediatric anesthesia, caudal block is the commonly followed method for providing perioperative analgesia. Landmark-guided caudal block is a convenient, easy, and a simple technique, which can be performed with a little training. In pediatric age, the landmarks are easily identified, hence anatomical techniques are popular.[5],[10] Success rates with landmark technique are high, but are associated with complications such as nerve damage, dural puncture, and vascular injections.

Ultrasound-guided blocks rose to popularity due to visualization of nerves and structures in regional block. However, ultrasound blocks do not assure 100% success but reduce complications and failures as compared to landmark techniques.[2],[10],[11],[12] There is not much data and evidence in support of ultrasound use for caudal block in pediatrics. The ultrasound use is particularly beneficial in patients with obesity, sacral agenesis, and anomalous spine.[10],[13]

The success rate in our study is 92.1% with ultrasound and 81.8% with landmark techniques. Ahiskalioglu et al.[2] recorded higher success rates in both ultrasound technique (97%) and conventional landmark technique (93%). Riaz et al.[14] and Wang et al.[15] reported success rate with ultrasound technique as 92.8% and 95.7%, respectively. Our results of caudal success match with that of Riaz et al.[14] and Ahiskalioglu et al.[2]

Success of caudal with landmark technique depends on the identification of hiatus.[16] In our study, visibility and palpability of sacral cornu were graded as easy in 86.4% of cases. Although sacral hiatus was identified by palpation in 92.4%, caudal success was recorded as 81.8%. The reason could be narrow canal (<3 mm) which poses difficulty for placement of needle in canal injection technique in spite of easy landmarks.[16] In study by Wang et al.,[15] the success was higher (95.7%) in conventional landmark-based sacral canal injection than ultrasound-guided sacral hiatus injection technique (92.8%). We experienced difficulty in identification of hiatus in 7.6% of cases. Abukawa et al.[1] recorded the absence of hiatus in 4% of cases. The reasons for nonpalpability may be due to anatomical variations in sacral bone, sacral agenesis, and narrow canal.[3],[16]

Placement of needle in the sacral canal is commonly confirmed with swoosh test which depends on the audible turbulence created due to injection of saline through the needle. Hence, the sensitivity and specificity depend on the observer, site of needle placement, auscultation site, and gauge of the needle.[9],[17] In our study, sensitivity was 100% and specificity of 33.3%. Eastwood et al.[18] found sensitivity of 94% but low specificity (20%). In our study, false-positive results were 8, hence the specificity was low. False-positive results were high probably due to more number of neonates and infants, in whom 22G needle was used. Narrower the needle, higher the turbulence, hence contribute to false-positive results. Similarly, broader needle offers less resistance for injection, thus record false negatives.[9],[17],[18] In our study, true negatives were 4; therefore, negative predictive value was 100%. The diagnostic accuracy of swoosh test in our study is 87.8%. Our results contradict the findings of Orgme et al.,[17] who recorded 91% sensitivity, 100% specificity, and positive predictive value of 100%. By optimizing the needle size and use of Doppler sonography, false negatives can be minimized.[19] Swoosh test remains a reliable test in landmark-based caudal block. Roberts et al.[12] recorded 96.5% sensitivity and positive predictive value of 100% for ultrasound in detecting correct needle placement. Raghunathan et al.[9] had similar conclusion, where in ultrasound, with likelihood ratio of 2.8, was accurate than swoosh test. Hence, visualization of canal distension under ultrasound is considered more reliable than swoosh test alone.

Wang et al.[15] visualized the distension of the sacral canal and bulging of sacrococcygeal ligament on caudal injection. In a study by Roberts et al.,[12] distension on injection and displacement of dural sac was taken as confirmation for successful needle placement. In our study too, we noted expansion of sacral canal with caudal injection in all cases of ultrasound block. Distension of canal and bulging of sacrococcygeal ligament were also noted in both transverse and longitudinal view. Needle tip was better visualized in longitudinal view, whereas bulging of sacrococcegeal membrane, distension of canal was better in transverse view. In a study by Ahiskalioglu et al.,[2] needle was visualized in transverse plane in 60% of patients and distension was recorded in 92.8%. Visualization of whole length of needle and expansion of canal with injectate in both planes offer confirmation.[20]

Although canal expansion was observed in 100% cases, success of caudal block was 92.1%. The difference in success may be due to bloody taps (3%), redirection of needle and loss of potency of drug due to blood in caudal space.[21] Furthermore, one case of ultrasound block was excluded from the study due to repeated bloody taps. Roh et al.[22] in their study of caudal blocks with ultrasound observed that in 26%, the needle can be either deviated to right or left after placement and determine the extent of spread of local anesthetic. This can add to failure rate.

Riaz et al.[14] noted longer time for performance of block with ultrasound. Wang et al.[15] recorded shorter time for anatomical block. In our study too, landmark technique was performed in shorter time (5.9 min) than with ultrasound technique (7.71 min). Ahiskalioglu et al.[2] did not find significant difference between ultrasound-guided block and anatomical block; however, they recorded shorter time in both groups compared to our study. In our study, blocks were performed by faculty and residents with experience in anesthesia of at least 3 years. The longer time to perform block observed in our study may be due to visualization in both transverse and longitudinal view, the optimization of ultrasound locating the needle and visualization of distension of canal during injection.

In this study, first-attempt success is 60.6% of patients in landmark group and 54% in ultrasound group. There was no statistical difference in number of attempts and first-attempt success rates between groups. First attempt success with landmark technique matches with Wang et al.[15] This may be due to familiarity with conventional sacral canal technique. Ahiskalioglu et al.[2] and Wang et al.[15] recorded higher first puncture success (92.8%) in ultrasound-guided hiatus group. The difference observed with our study may be due to nonvisualization of needle tip in horizontal and longitudinal view, poor window due to ossification of sacrum, and expertise of ultrasound usage.

The incidence of blood tap (23.8%) was higher in landmark group. Ahiskalioglu et al.[2] (12%), Roberts et al.[12] (10.6%), and Wang et al.[15] (18.6%) observed similar, higher vascular punctures compared to ultrasound-guided block. The higher rate of vascular punctures are caused by needle injury to sacral venous plexus which may extend till S4 vertebrae.[5],[6],[21] Vascular punctures may not be completely prevented in ultrasound.[23],[24] We had 3% vascular punctures. Ahiskalioglu et al.[2] recorded 1.4% and Wang et al. noted 5.7% of bloody punctures with ultrasound. Blood vessels are visualized only if Doppler flow mode is used to rule out vascular injection.[19],[20] Hence, color Doppler imaging might prevent vascular injections and reduce the failure rate.

SC bulge (15.2%), dural puncture (1.5%), and rectal perforation (1.5%) were noted only in landmark technique. No such complications were seen in ultrasound group. The possible explanation could be due to the distal site of needle entry in ultrasound-guided caudal blocks as compared to hiatal entry in landmark technique.[21],[23] Therefore, complications such as inadvertent venous puncture, dural injuries, and rectal injuries may be prevented by use of ultrasound.[25]

Limitations of our study

We did not study the consumption of inhalational agents, recovery score, and postoperative analgesia. All cases received paracetamol 15 mg/kg IV as a protocol of multimodal analgesia in our hospital; hence postoperative analgesia requirement was not studied. We were concerned with technique of caudal and its success which was assessed with intraoperative changes in heart rate and mean arterial pressures. Ultrasound-guided blocks were performed by Faculty and residents in anesthesiology. This might have influenced the results and duration taken to perform the block. It would be ideal to record data from one or two experienced anesthesiologists in ultrasound-guided block. We did not assess the end of dura or shift of dural sac with injection. We did not assess the extent of spread of local anesthetic within the epidural space. The study was not a double-blind one.


Safety is the concern in pediatric anesthesia practice. Landmark-guided caudal blocks are time tested, simple, and easy to perform technique with good success rates. Ultrasound-guided blocks are the emerging, safe, and reliable techniques in practice of regional blocks in pediatrics. Ultrasound-guided block has higher success rate and less complications. Both techniques are reliable in providing analgesia. Landmark technique is convenient in centers where ultrasound is not available. Ultrasound use for regional blocks is the future and maybe preferred in pediatric cases to ensure safety with blocks.


The authors would like to thank Faculty and residents, Department of Anaesthesiology, Bangalore Medical College and Research Institute.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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