Background Although obese patients benefit from neuraxial anesthesia, technical difficulties often discourage its use. The current randomized trial compared Accuro, a hand-held, battery-operated ultrasound (US) device, and conventional palpation for spinal anesthesia in obese patients undergoing orthopedic surgery. We hypothesized that Accuro would decrease the number of needle redirections.
Methods We enrolled 130 men and women with a body mass index ≥30 kg/m2, scheduled for lower limb surgery under spinal block. Patients were randomized either to the Control group (group C: spinal block after palpation of cutaneous landmarks) or to the Accuro group (group A: preprocedural US scan with Accuro to identify the needle insertion point). The procedural time, the number of skin passes and of needle redirections, the occurrence of failure and adverse events were recorded.
Results Ninety-nine patients completed the study. Patients in group Accuro showed a median (IQR) number of redirections of 3 (0–9) and a median (IQR) number of needle passes through the skin of 1 (1-2) versus 6 (1-16) and 1 (1-3), respectively, in group Control (p=0.008, p=0.019). The performance time was 558±232 s in group Accuro versus 348±255 s in group Control (p<0.001). There were no intergroup differences in terms of failed blocks and adverse events.
Conclusions The use of Accuro reduced the number of needle redirections and passes through the skin when performing spinal anesthesia, but required a longer procedural time.
Trial registration number ClinicalTrials.gov registry (NCT03075488).
- neuraxial blocks: spinal/epidural injection
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Ultrasound (US) guidance for neuraxial blocks results in fewer needle passes, insertions and skin punctures, especially when performed by expert operators, thereby improving the success rate on first attempt and patient comfort during the procedure.1 2 ,–5
Recently, a handheld, battery operated, three-dimensional US device has been introduced (Accuro, Rivanna Medical, Praesidia Medical Devices, via dei Lapidari 19, Bologna, Italy, figure 1)6–8 to localize the desired intervertebral space and the correct needle insertion point for lumbar neuraxial blocks. This system’s image guidance is designed to visualize bony landmarks, while providing an automatic interpretation of the neuraxial space’s location and depth as well as the optimal needle insertion point. To date, the use of Accuro has been confined to the obstetrical population or the performance of epidural blocks.9 10
The current randomized trial aimed to compare Accuro and conventional palpation for spinal anesthesia in obese patients undergoing lower limb orthopedic surgery. We hypothesized that Accuro would decrease the number of needle redirections.
This randomized, controlled trial was performed at the Rizzoli Orthopedic Institute in Bologna, Italy, after obtaining the Institutional Review Board (IRB) approval (17 March 2017; Approval Number: 0022252) and written informed consent from all subjects participating in the trial. The trial was registered prior to patient enrollment at clinicalTrials.gov.
One hundred and thirty patients undergoing spinal anesthesia for lower limb orthopedic surgery were included between the 31 of March 2017 and the 3 of April 2018. The study population encompassed the following inclusion criteria: men and women with body mass index (BMI) ≥30 kg/m5, aged between 18 and 75 years, with American Society of Anesthesiologists (ASA) physical status I–III, scheduled for lower limb surgery under spinal block and able to understand and sign the study’s written informed consent. We excluded pregnant women and patient with allergies to local anesthetics, contraindications to spinal block, spinal deformities or a history of spine surgery.
Using a computer-generated random sequence, patients were allocated to the Control group (group C: spinal block guided by palpation of cutaneous landmarks) or the Accuro group (group A: preprocedural US scan with Accuro).
After arrival in the anesthesia induction room, all patients were monitored and an intravenous access was established. All patients received sedation, according to the anesthesiologist’s preference. Spinal injection was then performed with the patient in lateral decubitus or sitting position at the L3-L4, L4-L5 or L5-S1 level. Each spinal block was performed by anesthesiologists skilled in both techniques with a 25 or 27G needle.
In group C, the anesthesiologist palpated traditional cutaneous landmarks, that is, the intercristal line, the interspinous line, and the space between the two selected spinous processes after sterile field preparation and before needle insertion. Patients in group A received instead a preprocedural scan using the Accuro device after sterile field preparation and draping of the probe. The desired interspace was identified using the counting-up method. The midline was identified with the dashed indicator (figure 2a) sliding the probe laterally until the indicator turned orange (figure 2b). After the triangular shadow of the spinous process was identified, the probe was moved longitudinally along the midline untill the image of the vertebral body together with the articular porcesses was obtained and the spinous process disappeared (figures 3 and 4). The angle of the US beam with the skin was noticed. Finally, the entry point was identified at the intersection of the four cutaneous indentation marks using the sterile Accuro Locator by gently pressing the latter against the skin (figure 5).
In both groups, an observer reported the performance time (from opening of sterile gloves to the start of the local anesthetic injection), the number of skin passes (defined as each needle introduction through the skin) and the number of redirections (defined as a needle advancement preceded by a withdrawal of 1 cm or more), the occurrence of failure (defined as the need for general anesthesia to complete surgery), and any adverse event.
On the first postoperative day, all patients were questioned about the comfort during the procedure using a four-point scale (1=intolerable; 2=painful; 3=unpleasant; 4=comfortable). In addition, the patients were asked about possible residual pain at the needle insertion site as measured with a numerical rating scale (NRS), with 0=no pain to 10=worst pain. Any other side effect or adverse event was recorded.
The study primary outcome is the number of needle redirections necessary to perform a spinal injection. Previous literature reported a mean number of needle redirections of 3.3 (SD 3.1) during spinal anesthesia performed with cutaneous landmark palpation.11 With an alpha error of 0.05, a beta error of 0.20, 38 patients were required per group to demonstrate a 60% reduction in the number of needle redirections with Accuro. We therefore planned to enroll 45 patients per group accounting for drop outs. After enrollment of the first 90 patients, we noticed a higher rate of drop outs than expected (28/90 patients, drop out rate 31%). After protocol amendment and IRB approval, we therefore enrolled an additional 40 patients after taking appropriate corrective actions (training more anesthesiologists to use Accuro). We therefore enrolled a total of 130 patients with 99 subjects completing the study protocol (final drop-out rate 24%).
Data were analyzed with SPSS V.17.0 software for Windows and R V.184.108.40.206 Deviations from the normality assumption were detected for the number of redirections, the number of skin passes and the procedural time using the Shapiro-Wilk test. Dicotomous variables were analyzed with the exact test of Fischer and results presented as frequencies and percentages. The effect of the group (Accuro/Control) on the procedural time was evaluated fitting a linear model after applying a log transformation of the dependent variable and setting gender, age and BMI as covariates. A generalized linear model (glm) was used to test the effect of the group on the number of needle redirections and the number of skin passes using the same set of covariates. A quasi-poisson link function and the sandwich variance estimator were specified in the glm model to take into account the overdispersion typical of count data and non-constant residual variance, respectively. Results with a p≤0.05 are considered significant.
Patients in group Accuro required a median (25–75 IQR) number of redirections of 3 (0–9) versus 6 (1-16) in group control (p=0.008 (Cohen’s d effect size 0.49) independently of the covariates gender, age and BMI). Patients in group Accuro showed a median (IQR) number of needle passes through the skin of 1.0 (1–2) versus 1 (1-3) in group control (p=0.019 (Cohen’s d effect size 0.32) independently of gender, age and BMI).
The performance time was longer in group Accuro: a mean (SD) of 558±232 s was necessary in group Accuro versus 348±255 s in group Control (p<0.001 independently of the covariates gender, age, BMI).
All patients received the spinal block with the lateral decubitus position except for 13 patients (5 patients in group Accuro vs 8 patients in group Control, p=0.441). A 25G needle was used in 77 patients (38 in group Accuro and 39 group Control), while a 27G needle was used in 22 patients (11 in group Accuro and 11 in group Control). The number of failed blocks requiring general anesthesia to complete surgery was also comparable between groups: 0/47 in group Accuro versus 2/52 in group Control (p=0.520), independently of covariates. The number of adverse events in group Accuro was 3/47: one patient reported a paresthesia in the lower limb during spinal, one patient experienced a bloody tap through the spinal block needle, and one patient had a headache at the 24-hour visit (not diagnosed as postdural puncture headache because of lack of clinical characteristics). The number of adverse events in group control was 4/52: one patient displayed multiple ecchymosis in the lumbar zone where spinal puncture was performed and three patients experienced a bloody tap. No difference was found between the two groups (p=0.799).
Tolerability of the procedure was comparable between the two groups (p=0.284) as well as NRS for pain in the lumbar region at the 24-hour visit (p=0.726) (table 2).
The present study shows that the use of Accuro for preprocedural US scans of the spine significantly reduces the number of needle redirections through the skin when performing spinal anesthesia, compared with the traditional landmark palpation technique in an obese population with a BMI ≥30 undergoing orthopedic surgical procedures. Nevertheless, the use of Accuro requires a longer performance time when compared with the traditional palpatory technique: the time necessary for applying the sterile cover on the handheld US device may account for this. The paucity of adverse events did not allow us to find a significant reduction in the complication rate in our population. While the number of redirections was almost halved with the use of Accuro (48% reduction, Cohen’s d effect size 0.49), the difference in number of needle insertions, although statistically significant, might be too small to be regarded as clinically relevant.
Differently from standard ultrasonography, Accuro is a handheld, battery operated US device. It includes a touchscreen display that provides an automatic interpretation of the neuraxial space location and depth, and enables to target the correct needle insertion point. It offers immediate comprehension of the anatomical structures and easy location of the needle’s entry point. In our clinical experience, Accuro makes the prescan of the lumbar anatomy easier even to those who are not skilled in US-guided neuraxial blocks. The study presents some limitations. First of all, we had a high rate of drop outs in the first 90 patients: our surgical activity is scattered across 10 different operating rooms 13 hours a day with a total of 28 attending anesthesiologists who are hand-on providers with a 1:1 ratio between anesthesiologists and number of operating rooms. However, only three anesthesiologists were involved in the present research project and oversaw all the study’s phases (enrollment, performing of spinal block, follow-up, and data collection). Most patients were enrolled on the day before the planned procedure, according to ethical committee standards, but then underwent surgery at a time when the investigator in charge could not attend the operation. Patients who dropped out were therefore not lost during the procedure or at follow-up. We then took corrective actions, such as including more attending anesthesiologists in the research project, and amended the protocol to reach the correct sample size. The number of patients who completed all the steps of the study complied with the initial power calculation. Another study limitation is that we did not specify a maximum time or number of attempts to define failure of the procedure in the two groups, which accounts for the high dispersion of our data. Third, the group allocation was not masked, except to the investigator who followed up the patient 24 hours after spinal injection. Despite these limitations, to our knowledge, the present study represents the first description of the use of the Accuro device in an obese orthopedic population.
In conclusion, in the current randomized controlled trial, Accuro helped reducing the number of needle redirections to perform a subarachnoid block in a population of obese patients undergoing lower limbs orthopedic surgery when compared with the conventional cutaneous landmark palpation-based approach, although almost taking twice as much procedural time.
Thanks to Praesidia s.r.l. for their support with images and donation of disposable materials to the IRCCS Istituto Ortopedico Rizzoli.
Contributors DG: planning, conduct, reporting, conception and design, acquisition of data, redaction of the manuscript. MT: conception and design, acquisition of data. SG: data analysis and interpretation of data. AL: conception and design, acquisition of data. LA: acquisition of data, redaction of the paper. LT: acquisition of data. AB: data analysis and interpretation of data. SB: planning, conduct, reporting, conception and design, final revision of the manuscript.
Funding Self-funded by Istituto Ortopedico Rizzoli Bologna, Italy. The Accuro device was temporarily borrowed while the disposable materials (skin marker and sterile cover for the probe) were donated to the IRCCS Istituto Ortopedico Rizzoli only for the period of the study by Praesidia Medical Devices (via dei Lapidari, 19 Bologna, Italy).
Competing interests None declared.
Patient consent for publication Not required.
Provenance and peer review Not commissioned; externally peer reviewed.