Nevertheless, ultrasound imaging assistance for thoracic epidural catheters is not a missing topic in current research. Evidence-based knowledge has been acquired in the decade since the seminal study by Grau et al3 on ultrasound imaging of the thoracic epidural space as compared to magnetic resonance imaging and continues to be acquired. Investigators in addition to our group have contributed with knowledge-based studies developing this line of research as it was previously done for lumbar neuraxial anesthesia. First came the descriptive studies on sonoanatomy of the thoracic spine, then identification of thoracic levels mirroring the recurrent topic of inaccuracy in determining lumbar spine levels, and then clinical studies of feasibility.4 While the first study published on efficacy, trying to elucidate the clinical utility of ultrasound assistance as compared to palpation, demonstrated no major differences,5 a few more will follow coming from our own group and from others by reviewing current trial registries.
Both imaging techniques, fluoroscopy and ultrasound, may be suitable for clinical practice. The main limitation of ultrasound assistance is related to the “blind” nature during the actual needle insertion. The fluoroscopy advantage of directing the needle through the interlaminar space when difficulty is encountered will prevail unless real-time ultrasound guidance evolves. Nevertheless, ultrasound definitely represents a more portable resource to be deployed in cases when avoidance of radiation is desirable or there is a documented allergic reaction to contrast dye. Although the comparison between ultrasound- and fluoroscopic-guided epidural steroid injection showed no difference in the lumbar spine, it remains to be investigated in the thoracic spine. Furthermore, alternative methods to confirm the correct catheter location rather than an epidurogram can be utilized when using ultrasound, such as transcatheter electrical stimulation and epidural waveform analysis.
In recent years, bedside ultrasonography has been growing steadily and has greatly improved both quality and safety in common technical procedures in anesthesia practice. In addition, it has played a leading role as a point-of-care diagnostic strategy in perioperative decision making. Advancing evidence in ultrasound imaging will certainly clarify its role in thoracic epidural catheter placement as a meaningful clinical tool or merely a complementary alternative.