Is there enough evidence to recommend routine use of... : The Indian Anaesthetists Forum (2023)

In the epic story of Mahabharata, a character by name Sanjaya had the gift of seeing events at a distance (so called as ‘divya drishti’) right in front of him. He narrated all the actions happening in the climactic battle of Kurukshetra to his king Dhritarashtra. Similarly, while performing the central neuraxial blocks (CNBs), we all as anesthesiologists are playing the blind character of Dhritarashtra and ultrasound (US) can be casted in the role of Sanjaya. While the use of US has added objectivity to several interventions like vascular cannulation, peripheral nerve blocks, etc, its usefulness in providing the ‘divya drishti’ for CNBs is being explored.[^1,2] This includes two of the original articles which are published in this edition of the journal.[^3,4] This editorial aims to put up a general statement on the role of US in CNBs based upon the existing literature and the authors' perspective.

It is established beyond doubt that preprocedural US scanning can precisely identify the midline and level of intervertebral space (IVS), thereby determining the optimum level of needle insertion,[^3,5] which was by and large accurate in only about 50% of the patients under landmark guidance technique, with further lower accuracy in obese and obstetric patients.[⁵] We usually err to mark the space higher than intended, usually by one to two levels, thereby risking a spinal cord puncture.[³] While we agree that by determining the optimum level of blockade, US can unquestionably minimise higher IVS injections and thereby the risk of traumatic spinal cord injury, but the argument that arises is the usefulness of this technique in reducing the incidence of an outcome (spinal cord trauma) which itself is rarely reported.

Similarly, in recently published systematic reviews and meta-analysis, US has shown to accurately delineate the underlying relevant anatomy and hence increasing the first-time success rate.[^5,6] By determining the required needle trajectory, US helps in decreasing the number of needle passages and redirections. The projected benefits of this being lesser incidence of neurological complications like paresthesia, numbness, contact with facet joints and sudden back pain.[^1,7] However, in many of the randomised controlled trials (RCTs), the incidence of neurological complications did not achieve statistical significance between the groups.[^7,8] In addition, few of the systematic reviews and meta-analysis were underpowered and hence these results should be interpreted with caution. Moreover, the practice of landmark based neuraxial technique is as old as the inception of anesthesia and has long standing proven safety with insignificant rate of serious complications.

There is also conclusive data showing a close relationship between the depth of the epidural and intrathecal space estimated using US and the actual needle depth required for successful blockade.[⁹] The projected benefit being a reduction in the incidence of accidental dural puncture (ADP). However, the overall incidence of ADP reported in the literature using conventional technique is between 0.2 to 4%, and many of the studies did not find any significant difference in the rate of ADP between the two techniques.[^1,9] This is not to say that US has got no role in reducing the risk of complications. The subgroup analysis of available RCTs and meta-analysis suggest that the usefulness of US is more evident in specific population like the pediatric, geriatric, obstetric and in patients with variable anatomy (obese, kyphoscoliosis, previous spinal surgery) in whom the CNB is predicted to be difficult.[^5,6]

There is variable and insignificant data available on the role of US scanning in reducing the incidence of rare and long-term complications of CNB like post dural puncture headache, epidural hematoma, chronic headache and chronic backache. We understand that undertaking such studies with larger sample size to look at the rate of complications which are rarely seen is difficult to justify and perform. But probably this is where the real benefit of using the US is hiding as these complications determine the score of patients' comfort, satisfaction and overall outcome. Unless there is evidence emerging in near future to suggest that US does make a real difference in reducing the rate of these complications, it is hard to predict that application of this imaging technique will become a routine and widespread practice superseding the conventional landmark guided technique.

Similarly, there is varied data available on the procedural time using US. The duration of performing CNB is found to be highly variable with some studies showing longer duration with the use of US compared to landmark technique while others observed no clinically significant difference.[¹⁰] As the operator's experience plays a significant role on procedural time, we recommend using US for neuraxial scanning as a teaching and training tool for anesthesia residents and should be incorporated into postgraduates' curriculum. It is possible that the time saved with improved first pass success and reduced number of times the needle needs to be redirected balances the time taken for preprocedural US, but it remains to be seen what difference the use of US makes during rapid sequence spinal (RSS) anaesthesia for the most urgent scenarios like category-1 cesarean sections.

In spite of emerging evidence to show that US is a quick and noninvasive imaging tool which helps in improving both the efficacy and efficiency of performing the CNB, the role of modern Sanjaya remain debatable due to the lack of any real clinical benefit or improved patient outcome. Further RCTs are required to evaluate the role of US in RSS anaesthesia, incidence of ADP, thoracic epidurals, long-term neurological complications, real-time needling, among others.[^11,12] Hence, it remains to be seen what data will emerge in near future which would help us in deciding whether the use of this imaging technique will act as our ‘divya drishti’ or not while performing the CNBs.

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