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Year : 2023  |  Volume : 17  |  Issue : 1  |  Page : 18-22

Preprocedural ultrasonography as an adjunct to landmark technique for identification of epidural space in parturients for labor analgesia

Department of Anaesthesiology, Narayana Medical College Hospital, Nellore, Andhra Pradesh, India

Correspondence Address:
Shiny P Arumulla
Department of Anaesthesiology, Quarters 172 J Block Staff Quarters, Narayana Medical College, Nellore, Andhra Pradesh – 524 003
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/sja.sja_141_22

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Date of Submission13-Feb-2022
Date of Decision22-Feb-2022
Date of Acceptance09-Mar-2022
Date of Web Publication02-Jan-2023


Background: Pregnancy-induced softening of tissues and ligaments may increase the false-positive rates when identifying the epidural space in parturients by the landmark technique. To mitigate these problems, Ultrasonography (USG), which has now become the eye of anesthesiologists, can be used as a reliable tool to facilitate more accurate epidural needle placement in parturients. This study was conducted to know the efficacy of USG when compared to the traditional landmark method.
Methods: After the approval from the institutional ethics committee and CTRI registration, 62 parturients of ASA-2 requesting labor analgesia were randomized into 2 groups of 31 each: Group-L (conventional landmark technique) and Group-U (preprocedural USG done before epidural). In group-U, Tuohy's needle was introduced through the USG predetermined insertion point and epidural space was located using the LOR technique.
Results: USG increased the success rate of epidural at first attempt from 51.6% in group “L” to 87% in group “U.” Fewer needle attempts (P-value - 0.001) were required in group “U” as compared to group “L.” No accidental dural puncture in group-U, compared to 2 in group-L. Mean Depth of epidural space (cm) ultrasound depth (UD) = 3.89 ± 0.45 cm and needle depth (ND) = 4.05 ± 0.37 cm. Side effects profile in the ultrasound group was better.
Conclusion: Preprocedural ultrasonography is a simple safe,accurate tool with less number of attempts to determine the needle insertion site, decrease the incidence of accidental dural punctures, and assess epidural space depth in parturients.

Keywords: Epidural space, labor analgesia, preprocedural ultrasonography

How to cite this article:
Jayanth MN, Arumulla SP, Kesana P, Kandukuru KC, Basireddy HR, Peddi S. Preprocedural ultrasonography as an adjunct to landmark technique for identification of epidural space in parturients for labor analgesia. Saudi J Anaesth 2023;17:18-22

How to cite this URL:
Jayanth MN, Arumulla SP, Kesana P, Kandukuru KC, Basireddy HR, Peddi S. Preprocedural ultrasonography as an adjunct to landmark technique for identification of epidural space in parturients for labor analgesia. Saudi J Anaesth [serial online] 2023 [cited 2023 Mar 31];17:18-22. Available from:

  Introduction Top

It is on the shoulders of anesthesiologists to provide a safe and comfortable labor experience for the parturients requesting labor analgesia. Accurate epidural needle insertion has always been challenging in parturients due to the anatomical changes like presacral edema, exaggerated lumbar lordosis, and softened ligaments.[1] Furthermore, because of the venous engorgement, the risks of dural and vascular punctures are more common. This makes landmark-based epidural space identification difficult.[2] Ultrasonography (USG) helps in identifying the epidural space precisely and also measures the depth of space from the skin, which makes the procedure free of complications.[3],[4] Use of USG needs the expertise to identify the epidural space with accuracy failing which will lead to inadvertent dural punctures.[5],[6] Our aim is to determine the correlation between USG estimated depth versus landmark-based depth of epidural space in parturients and also to compare the number of attempts taken and incidence of dural punctures.

  Materials and Methods Top

This prospective randomized interventional study was conducted with due permission from the institutional ethics committee, CTRI approval (CTRI/2021/03/031846) and informed written consent from the participants between August 2021 to December 2021 in 62 full-term parturients. Those with ASA status more than 2, BMI greater than 35 kg/m2, spinal deformities, coagulation abnormalities, and any other contraindications to neuraxial blockade were excluded from this study. Simple randomization was followed with the closed envelope technique. 62 parturients were divided into 2 groups of Group-L and Group-U with 31 each.

In group-L, the epidural space was identified by the conventional landmark-based technique. In group-U, the depth of epidural space (UD) was measured using machine built-in calipers. Mean number of attempts (needle reinsertion after taking out from skin), number of needle passes (needle redirections without taking out from skin), and number of accidental dural punctures were measured between the groups. In group-U, the correlation between the USG-guided estimated depth (UD) versus actual depth (ND) of epidural space was compared. The USG-guided procedure was performed by an anesthesiologist with 8 years of experience in USG-guided localization of epidural space.

After a thorough preanesthetic evaluation, all the investigations were checked and recorded. The parturient was transferred to the procedure room, IV line was secured with 20G cannula, and IV fluid was started. Standard monitors like pulse oximeter, NIBP, and ECG were connected and baseline vitals were noted, and the procedure was performed with parturient in sitting position.

In group-L, epidural procedure was performed by conventional landmark-based technique. In group-U, detailed preprocedural scan was done using 2–5 MHz curvilinear ultrasound probe of Philips-GE machine. Parasagittal view of L5–S1 space was identified by viewing the sacrum. From there by counting upwards, we identified L4-L5 space. After identifying the parasagittal paramedian view of L4-L5 space, the probe was rotated to obtain the transverse view of intervertebral space of L3-L4. In this view, epidural space was identified between ligamentum flavum and posterior dura mater. With the aid of the machine's built-in caliper, we measured the depth (UD) from skin to the epidural space [Figure 1]. At that moment, the transducer was kept steady, a vertical line was marked at the midpoint of the probe, and horizontally the edges were marked and later joined. The intersection of both the lines was considered as the needle insertion point [Figure 2]. Angle of the probe at which the best image of the posterior complex obtained was used as the angle at which the needle would be introduced. In the ultrasound group, the needle was introduced up to 0.5 mm behind the estimated epidural space and thereafter loss of resistance technique was used to identify the epidural space. After identifying the epidural space, the needle depth (ND) was marked on the needle at the skin level. The actual needle depth (ND) was measured using a ruler after removing the needle. This depth (ND) was compared with estimated depth of epidural space measured by USG (UD). A catheter was secured and labor analgesia was conducted.
Figure 1: Ultrasound view of epidural space

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Figure 2: Needle insertion point marking

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With the probe in transverse plane, ultrasound depth (UD) was measured and needle insertion point was marked.

Statistical analysis

SPSS version 27 was used for statistical analysis. For continuous data, descriptive statistics such as the mean and standard deviation were calculated, while for discrete data, percentages were generated. The Pearson correlation coefficient (r) and paired t-test were used to calculate the precision of measurement, i.e., the correlation and mean difference (with 95% confidence interval [CI]) between the ND and the UD, respectively. The concordance correlation coefficient was used to determine the accuracy. The UD was plotted against the ND to graphically display the data and regression analysis was performed to obtain the equation of the line of best fit.

  Results Top

After conducting a pilot study with 7 parturients in each group, the sample size was calculated with level of significance taken as 5% and power of study taken as 80%. The sample size required was 18 in each group. As the sample size was small, we have taken 31 parturients in each group.

All the patients were similar with respect to demographic profile for age, height, weight, and BMI. The average maternal age was 24.6 years, and the average height was 159 ± 7 cm. The mean prepregnancy BMI was 18–24 kg/m2, and the mean prepregnancy body weight was 50 ± 12 kg.

The mean UD was 3.89 ± 0.45 cm and mean ND was 4.05 ± 0.37 cm. The comparison of both the depths is depicted in the bar diagram [Figure 3] and scatter plot diagram [Figure 4].
Figure 3: Comparison of epidural depth measured by USG and LOR

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Figure 4: Scatter plot for correlation between ultrasound measured depth (UD) and actual needle length (ND)

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In between the UD and the ND, the Pearson correlation coefficient (r) was 0.85 (95% CI: 0.74–0.91, r2 = 71.4, P < 0.001) and concordance correlation coefficient was 0.79 (95% CI: 0.71–0.88). The line of best fit and the regression equation are shown graphically in this comparison of the UD and the ND [Figure 5].
Figure 5: Scatter plot and regression analysis of ultrasound depth (UD) versus needle depth (ND)

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In [Figure 5], the solid line is the regression analysis showing ultrasound depth (UD) versus needle depth (ND). The equation for the line of best fit is: ND = 0.98 (UD) +0.05. The dotted line is the line of identity.

The mean total number of attempts is less in the ultrasound group (1.13 ± 0.59) when compared with the landmark group (1.73 ± 0.89) with P value 0.001, which is strongly significant [Table 1].
Table 1: Summary of the results

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The epidural needle placement was done without reinsertions (first attempt success) in 87% of the patients in the ultrasound group and only 51.5% in the landmark group.

There was no need to redirect (first-pass success) the needle in 74% of the parturients in the ultrasound group when compared to 48.38% in the landmark group.

The mean of the total number of passes in the ultrasound group was 1.32 ± 0.58 and that in the landmark technique group was 1.87 ± 1.03 with P value 0.03, using 95% confidence interval. This is depicted using a bar diagram in [Figure 6].
Figure 6: Comparison between USG and LOR

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  Discussion: Top

Labor pain is considered one of the most severe pains that a woman would experience in her lifetime. The position of woman in any civilization is an index of advancement of that civilization and the position is gauzed best by the care given to her at birth of child. Central neuraxial analgesia has become the gold standard for obstetric pain alleviation. This method provides the mother greater satisfaction and participation during childbirth. Labor epidural analgesia alleviates the effects of pain such as the release of catecholamines and rise in blood pressure, which may compromise the uretoplacental blood flow, prevents hyperventilation and respiratory alkalosis in mother, and allows participation of mother in childbirth actively. USG in anesthesiology practice is a revolution in current practice. It aids in visualizing the structures, placement of needle and catheter precisely. USG for regional anesthesia like epidural analgesia will reduce the incidence of accidental dural punctures. Though the conventional landmark technique for neuraxial blockade has been practiced successfully, we find it challenging in the cases of altered spine anatomy, obesity, and pregnancy. Preprocedural USG helps in identifying the epidural space and estimating the depth of epidural space from skin and, thus, increases the success rate and reduces the incidence of accidental dural punctures.

Ki Jinn Chin et al.[5] in 2011 summarized that the USG-guided neuraxial blockade is a valuable tool for identifying intervertebral levels, estimating depth to the epidural space, and locating an acceptable interlaminar area for needle insertion, especially in patients who are likely to have technical difficulties due to deformed spinal architecture or poor surface anatomical landmarks (e.g., in obesity or post spinal surgery or scoliosis). Thus, in our study, we have selected parturients as our study group due to their unique spinal architecture to provide the mother with a painless and safe labor experience.

In our study, we compared two groups, i.e., Group-L (landmark technique) and Group-U (USG guided), in terms of number of attempts, number of needle first-pass success, and inadvertent dural punctures. Also, we compared the estimated epidural space depth (US) with actual depth (ND), in the group-U.

Arzola et al.[7] in 2007 found that the transverse view was good enough to show a near estimate of distance from skin to epidural space. They also stated that adding more views increases the time required to do the procedure. Thus, we used only the transverse view to measure the epidural space depth and mark the point of needle entry. The difference between UD and ND in our study was 0.16 cm, which was similar to their study. The reason for this difference is probably due to compression of the probe to overcome local edema in parturients.

Young[8] in 2009 conducted meta-analysis and systematic review of preprocedural USG spinal anesthesia in the obstetric population and found that first-pass success of needle reaching the epidural space was more in ultrasound group compared with landmark group. Similarly, in our study, we found that the first-pass success rate was 75% in the ultrasound group compared to 48% in the landmark approach.

However, our results were not similar to the study conducted by Arzola et al.[9] in 2015 who found no significant difference between ultrasound and landmark groups. This is probably because, in their study, they incorporated only the cases with an easily palpable spine.

Evans et al.[10] in 2019 conducted a study on the comparison of USG-guided and conventional landmark techniques for lumbar punctures in inexperienced residents. Their study showed that with untrained physicians, using US guidance to aid in lumbar punctures did not increase the procedural success rate over standard landmark procedures. Although employing USG for procedural guidance reduced the number of attempts, it had no effect on postprocedural pain or the time it took to get CSF. In order to eliminate this bias, we, in our study, had included anesthesiologist who had 6 years of experience in labor epidural and 2 years exclusively in USG-guided epidural procedures.

In our study, we observed that first attempt success rate was higher in ultrasound group (87%) when compared with landmark group (51.6%). The mean number of attempts were significantly less in ultrasound group. Our first-pass success rate was significantly high in ultrasound group (74%) compared with landmark group (48%). We also observed that needle distance (ND) and estimated epidural distance by USG (UD) were comparable and the difference between them was found to be 0.16 cm. From our study, we found that the preprocedural USG of epidural space was beneficial when compared to the landmark technique.

Limitations of our study are that the anesthesiologist was not blinded, as the skin marking will be seen in the ultrasound group. We did not measure the time taken by anesthesiologist to identify epidural space as it is not an emergency procedure. A larger sample size should be studied in order to confirm the utility of preprocedural USG for labor epidural analgesia.

  Conclusion Top

We conclude that preprocedural USG is very useful adjunct in identifying the depth of epidural space, point of needle entry, and reducing the number of attempts when performed by an experienced anesthesiologist.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patients have given their consent for their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Gomar C, Fernandez C. Epidural analgesia-anaesthesia in obstetrics. Eur J Anaesthesiol 2000;17:542-58.  Back to cited text no. 1
Aspden RM. The theory of bre-reinforced composite materials applied to changes in the mechanical properties of the cervix during pregnancy. J Theor Biol 1988;130:213-21.  Back to cited text no. 2
National Institute for Health and Care Excellence. Ultrasound guided catheterisation of the epidural space. Interventional procedures guidance [IPG249] Published: 23 January 2008.  Back to cited text no. 3
Bhatia K, Kochhar P, Clegg I, Maguire S. The availability and use of ultrasound in UK obstetric anaesthesia. Int J Obstet Anesth 2016;25:91-2.  Back to cited text no. 4
Chin KJ, Karmakar MK, Peng P. Ultrasonography of the adult thoracic and lumbar spine for central neuraxial blockade. Anesthesiology 2011;114:1459–85.  Back to cited text no. 5
Balki M. Locating the epidural space in obstetric patients—ultrasound a useful tool: continuing professional development. Can J Anaesth 2010;57:1111–26.  Back to cited text no. 6
Arzola C, Davies S. Ultrasound using the transverse approach to the lumbar spine provides reliable landmarks for labor epidurals. Anesth Analg 2007;104:1188-92.  Back to cited text no. 7
Young B. Conventional landmark palpation vs. preprocedural ultrasound for neuraxial analgesia and anaesthesia in obstetrics - A systematic review and meta-analysis with trial sequential analyses. Eur J Anaesthesiol 2021;38(Suppl 2):S73-86.  Back to cited text no. 8
Arzola C, Mikhael R, Margarido C. Spinal ultrasound versus palpation for epidural catheter insertion in labour: A randomised controlled trial. Eur J Anaesthesiol 2015;32:499-505.  Back to cited text no. 9
Evans DP, Tozer J, Joyce M, Vitto MJ. Comparison of ultrasound-guided and landmark-based lumbar punctures in inexperienced resident physicians. J Ultrasound Med 2019;38:613-20.  Back to cited text no. 10


  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]

  [Table 1]


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