Real‐time ultrasound‐guided spinal anesthesia using the SonixGPS ultrasound guidance system: a feasibility study

Background Real‐time ultrasound‐guided neuraxial blockade remains a largely experimental technique. SonixGPS ® is a new needle tracking system that displays needle tip position on the ultrasound screen. We investigated if this novel technology might aid performance of real‐time ultrasound‐guided spinal anesthesia. Methods Twenty patients with body mass index < 35 kg/m 2 undergoing elective total joint arthroplasty under spinal anesthesia were recruited. Patients with previous back surgery and spinal abnormalities were excluded. Following a pre‐procedural ultrasound scan, a 17 G proprietary needle‐sensor assembly was inserted in‐plane to the transducer in four patients and out‐of‐plane in 16 patients. In both approaches, the trajectory of insertion was adjusted in real‐time until the needle tip lay just superficial to the ligamentum flavum‐dura mater complex. At this point, a 25 G 120 mm Whitacre spinal needle was inserted through the 17 G SonixGPS ® needle. Successful dural puncture was confirmed by backflow of cerebrospinal fluid from the spinal needle. Results An overall success rate of 14/20 (70%) was seen with two failures (50%) and four failures (25%) in the in‐plane and out‐of‐plane groups respectively. Dural puncture was successful on the first skin puncture in 71% of patients and in a single needle pass in 57% of patients. The median total procedure time was 16.4 and 11.1 min in the in‐plane and out‐of‐plane groups respectively. Conclusion The SonixGPS ® system simplifies real‐time ultrasound‐guided spinal anesthesia to a large extent, especially the out‐of‐plane approach. Nevertheless, it remains a complex multi‐step procedure that requires time, specialized equipment, and a working knowledge of spinal sonoanatomy.