Correspondence Address:
Debesh Bhoi
Room No. 5012, Department of Anesthesiology, All India Institute of Medical Sciences, New Delhi – 110 029
India

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Sir,

Central neuraxial blocks are traditionally performed by identifying intervertebral spaces by palpation of surface anatomic landmarks. Often, there are unanticipated difficulties that result in multiple attempts at needle placement and failed blocks. The use of real-time ultrasound imaging of the spine to guide needle placement has been found to decrease errors in identifying the correct vertebral level and decrease the number of attempts at needle pass.[1] The conventional method of scanning the spine and the neuraxial structures involves the placement of an ultrasound probe, scanning from lateral to medial in three paramedian sagittal planes to identify the transverse process, the articular processes, the laminae, the spinous process, and the underlying structures.[2] Various probe manipulations are required to correctly identify the interspinous space where the needle has to be placed and advanced to reach the neuraxial structures. This is technically challenging and often time-consuming for anesthesia practitioners and trainees who are not well trained in the use of ultrasound. Moreover, real-time ultrasound needle guidance requires two operators. Therefore, many still rely on the surface landmarks combined with the loss of resistance or the free flow of cerebrospinal fluid techniques for performing central neuraxial blocks.

In the lumbar region, anatomically, the horizontal level of the transverse process corresponds to the level of the intervertebral space through which epidural and subarachnoid spaces are accessed. Based on this anatomical concept, we placed a low-frequency probe (2–5 MHz) just above the iliac crest in parasagittal orientation [Figure 1]a. The acoustic shadow created by the transverse process (trident sign)[2] was identified. [Figure 1]b Skin marking was done corresponding to one of the transverse process shadows. The depth of the transverse process from the skin was measured. A horizontal line was drawn toward the midline, and the intersecting point was marked. Then, the needle insertion was performed by directing a slight cephalad. [Figure 1]c,[Figure 1]d,[Figure 1]e,[Figure 1]f,[Figure 1]g. After a successful attempt, the depth of the neuraxis was also noted.{Figure 1}

Using this approach, we performed a neuraxial block successfully in six patients in the same line (mean age 33.6 years and weight 65.8 kg) who were scheduled for gynecological surgeries [Table 1]. Written informed consent was taken from all patients. Neuraxial block was performed in a single attempt in all, with a mean difference in the depth of neuraxis from skin (SN) to skin to transverse process depth (ST) of 3.86 mm.{Table 1}

The transverse process being the lateral-most structure of the arch makes it easily identifiable by ultrasound.[2] The depth of the transverse process from the skin derived from the ultrasound image can guide the operator to anticipate the depth of the epidural and intrathecal spaces from the skin. This helps in ruling out false loss of resistance which may often be encountered in the subcutaneous plane. This technique may be useful in conditions such as obesity where it is difficult to palpate the iliac crest or spine and at the same time difficult to obtain high-quality images by conventional scanning to differentiate the structures of the vertebral arch.

The caudad angulation of the spinous process and the resulting need for steep cephalad angulation of the needle during insertion may limit the use of this technique at thoracic levels.[3] It also may not help in scoliosis and other vertebral anomalies as there is a lack of correlation of intervertebral space with the inter-transverse line.[4] However, the use of this simple sonogram aid may help anesthesiologists perform lumbar neuraxial blocks in a shorter time and lesser number of attempts with minimal technical expertise in ultrasound.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/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.

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Nil.

Conflicts of interest

There are no conflicts of interest.

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