A pocket-sized ultrasound device for spinal anesthesia guidance accurately predicts Tuohy needle depth to epidural space. In addition, using the epidural insertion point identified by the hand-held device was associated with high first-pass success and minimal needle redirections.
“This preliminary feasibility study in laboring parturients showed that the hand-held ultrasound [device] accurately predicted Tuohy needle depth at loss of resistance within the standard of error of the traditional ultrasound device,” said Katherine Seligman, MD, chief of obstetric anesthesia at the University of New Mexico School of Medicine, in Albuquerque. “It was also very closely associated with the traditional ultrasound device’s estimated depth, and may be of utility in laboring parturients.”
As Dr. Seligman reported, although ultrasound guidance for neuraxial blocks is gaining popularity, lack of clinician expertise and availability of equipment have limited more widespread adoption.
“We wanted to investigate this novel hand-held ultrasound device in laboring parturients to see how accurately its pattern recognition software identifies lumbar spine bony landmarks and to see its accuracy in calculating depth to epidural space,” she said.
Study on Parturients
At Stanford University Medical Center, where the study was conducted, Dr. Seligman and her colleagues enrolled a total of 47 women (age, 32.3±5.6 years). Using the Accuro hand-held device (Rivanna Medical), which is battery operated and about the size of a smartphone, the researchers identified, marked and measured the L2/3, L3/4, L4/5 interspaces and respective depths to epidural space. The researchers then used a traditional curvilinear probe on a GE Logiq S8 ultrasound system to make the same measurements.
An epiduralist who was blinded to measured ultrasound depths used the hand-held device–identified L3/4 interspace insertion point without palpation for the first epidural placement attempt. The accuracy of the hand-held and traditional ultrasound measurements were then compared with Tuohy needle depth at loss of resistance during epidural insertion. The investigators also recorded the number of Tuohy needle passes, redirects and the interspaces attempted.
As Dr. Seligman reported at the 2017 annual Spring meeting of the American Society of Regional Anesthesia and Pain Medicine (abstract 3809), the mean difference between the hand-held ultrasound and Tuohy needle depth at loss of resistance was –0.61 cm (95% CI, –1.75 to 0.52). The mean difference between the hand-held ultrasound and traditional curvilinear probe ultrasound device was –0.29 cm (95% CI, –1.08 to 0.50).
“The hand-held ultrasound, on average, was about 0.6 cm shallower than the actual depth to loss of resistance and about 0.3 cm shallower than the estimates from the GE console ultrasound device,” Dr. Seligman said.
The hand-held device–identified insertion point resulted in successful epidural placement at first attempt in 87% of patients, and 78% of these required no redirects, Dr. Seligman added. Furthermore, the hand-held ultrasound accurately identified L3/4 interspacing in 94% of patients.
Although the hand-held ultrasound device appears to be useful to guide epidural insertion, future investigation is needed to examine its utility in an obese population, the investigators noted. According to Dr. Seligman, 32% of the patients in the study had a body mass index over 30 kg/m2, but the average BMI was 28.8 kg/m2.
“ Additional studies are required to see how this device can be used in more obese patients where you can’t feel spinous processes, which could make lumbar neuraxial analgesia more difficult,” Dr. Seligman concluded.