Ultrasound guidance for regional block placement has become routine. Ultrasound helps to directly visualise anatomy, regional block needle, catheter and distribution of local anaesthetic around the nerve.1,2 Performing blocks with ultrasound requires extrapolation from a two-dimensional on-screen image to bimanual coordination in three dimensions. Needle advancement and/or local anaesthetic injection with inadequate visualisation can result in vascular, neural or visceral injury.3,4 Failure to visualise the needle tip remains a common problem even among experienced practitioners. To improve alignment of the needle and ultrasound visualisation of its tip, hyperechoic needles and needle guidance systems have been developed.5,6
Infiniti Plus (Fig. 1) is a needle guidance system developed to help clinicians perform ultrasound-guided nerve blocks. This system assists clinicians to align the block needle with the ultrasound beam. Previous studies indicate that other guidance systems improve needle visualisation, thus reducing the number of block attempts and needle manipulations, as well as shortening overall procedure times.6–8 However, the Infiniti Plus needle guidance system has yet to be evaluated for peripheral nerve blocks. We thus tested the primary hypothesis that femoral nerve catheter placements performed under ultrasound guidance would be quicker with the Infiniti Plus needle guidance system than with a conventional block needle (control group). Secondarily, we tested the hypotheses that use of Infiniti Plus would reduce the number of attempts required, increase block success rate and improve visibility of the needle.
With approval of the Cleveland Clinic Research Advisory Committee of Anesthesiology Institute (17 September 2013) and the Cleveland Clinic Institutional Review Board (no. 13-1299, 24 October 2013) and written consent, we enrolled adults having elective total knee arthroplasty (TKA) with a femoral nerve block and catheter. The trial was registered at ClinicalTrials.gov (NCT02080481) on 21 February 2014. Enrolment of patients was started on 18 March 2014. The authors confirm that all ongoing and related trials for this intervention were registered and reported to the Cleveland Clinic Institutional Review Board. Following completion of all required analysis and data collection, the study closed on 7 September 2015. We excluded patients who were pregnant, had preexisting neuropathy involving the surgical limb or had at least one of the following contraindications to the femoral nerve block: coagulopathy, infection at the needle insertion site or allergy to local anaesthetics.
Using a web-based system, patients were randomised 1 : 1 using permuted blocks with no stratification to ultrasound-guided insertion of a femoral nerve catheter using: Infiniti Plus needle guidance system, an Food and Drug Administration-approved device (Infiniti Plus; CIVCO Medical Solutions, Kalona, Iowa, USA); a conventional block needle (control group). The randomisation system was accessed shortly before blocks were performed.
All blocks were performed preoperatively by experienced attending anaesthesiologists who had performed at least 20 successful blocks with the Infiniti Plus needle guidance system. Premedication was administered at the discretion of the attending anaesthesiologist and standard monitors were used. The insertion point of the needle was standardised according to the location of the nerve and the ultrasound probe.
A linear array 6 to 13 MHz transducer (GE, Venue 40; GE Healthcare, Waukesha, Wisconsin, USA) was used in-plane, without nerve stimulation. The transducer was adjusted to achieve a short axis view of the femoral nerve. Afterwards, lidocaine 1% was injected subcutaneously. Using an in-plane technique, a 17-gauge, 10-cm long Tuohy needle (Teleflex, Arrow, Reading, Pennsylvania, USA) was advanced with direct visualisation to the desirable location. A 19-gauge Arrow nonstimulating catheter (Teleflex, Arrow, Reading, Pennsylvania, USA) was inserted through the Tuohy needle; 20 ml of 0.1% ropivacaine was then injected. Postoperatively, ropivacaine 0.1% was infused at the rate of 5 ml h−1 via the femoral catheter. Patients receive either general or neuraxial anaesthesia according to the anaesthesiologist's preference. Spinal anaesthesia was performed with bupivacaine 0.5%. General anaesthesia was induced with propofol or etomidate, fentanyl and rocuronium and thereafter maintained with sevoflurane or isoflurane. Postoperatively, all patients were given intravenous patient-controlled analgesia. Hydromorphone was the default drug, but fentanyl was substituted when patients were allergic to hydromorphone. Oral pain medications (comprising acetaminophen and hydrocodone or acetaminophen and oxycodone) were also given every 4 to 6 h, if required. Clinicians blinded to the block technique adjusted analgesia as necessary (including the local anaesthetic infusion) to maintain verbal response pain scores less than 4.
We recorded demographic and morphometric characteristics, including height, weight, age, sex, American Society of Anesthesiologists physical status, self-declared ethnicity and procedure type. The primary anaesthetic management strategy was also recorded.
Block time was defined as the time elapsed from beginning the block procedure (after prepping and draping) until the catheter was successfully inserted. The number of attempts was recorded, with an attempt considered as pulling block needle back to skin and redirecting it. The block procedure was digitally recorded starting from first needle visualisation on the ultrasound screen and was saved on the ultrasound machine hard disk for later evaluation by a blinded independent investigator to assess the percentage of time the needle tip was visualised. Opioid use, converted to morphine sulphate equivalents, was recorded intraoperatively and during the first 24 postoperative hours. Blocks were considered to have failed when postoperative reinsertion was clinically required.
All postoperative measurements were evaluated by investigators who were blinded to both the randomisation and other treatment administered. Pain scores after surgery were measured using a verbal response scale (VRS). VRS is a scale from 0 to 10 where 0 signifies no pain and 10 signifies worst pain ever experienced. For all assessments, the localisation of pain was documented and pain scores from the front and the back of the knee collected separately. The VRS were recorded every 30 min in the recovery area for the first 2 h, then approximately every 4 h thereafter while awake for 24 h.
The acute pain service, which was blinded to treatment, was notified when extra boluses of local anaesthetics were required or when blocks failed. If determined necessary by the acute pain service, sciatic nerve blocks were inserted to supplement the femoral nerve catheter to treat posterior knee pain. When available, the VRS scale was used to determine pain with motion during physical therapy. Patient satisfaction with their pain treatment was evaluated after 24 h using 0 to 100 scales, and the Myles quality of recovery (QoR) questionnaire was used to formally evaluate postoperative status using a 0 to 150 point scale.9
We used a modified intention-to-treat approach, including all randomised patients who received a femoral nerve catheter in the analyses. We assessed group balance on baseline and demographic characteristics using absolute standardised difference (ASD), defined as the absolute difference in means or proportions divided by the pooled SD. Variables with ASD exceeding 0.2 were considered imbalanced. Some variables had sparse counts in categories, so we collapsed the following variables into two categories for the analyses: race (Caucasian versus noncaucasian), procedure type (primary TKA versus other procedures) and intraoperative management strategy (general anaesthesia versus other). Primary and secondary analyses adjusted for any imbalanced variables associated with the primary outcome based on univariable tests (i.e. t-test).
We estimated the effect of Infiniti Plus on time spent performing an ultrasound-guided femoral nerve catheterisation using a multivariable linear regression model. Time spent was log transformed because it appeared to be log normal. Thus, treatment groups were compared on the ratio of geometric mean time to perform the nerve catheterisation.
We estimated the effect of Infiniti Plus on odds of a failed block using a multivariable logistic regression model. The vast majority of patients only required one block attempt, so we collapsed number of block attempts into two categories for the analysis: one attempt and more than one attempt. We estimated the odds of more than one block attempt using a multivariable logistic regression model. Finally, we compared groups on the mean percentage of time with perfect needle visibility using a multivariable linear regression model.
We summarised additional measurements, including number of extra boluses of local anaesthetic, number of rescue sciatic blocks, pain scores, pain associated with motion, patient satisfaction rating and postoperative Myles QoR questionnaire using appropriate descriptive statistics.
We used a α of 0.05 for both the primary and secondary analyses, using a significance criterion of 0.05 in the primary analysis and 0.0167 for each secondary analysis to control for multiple comparisons (i.e. Bonferroni correction, 0.05/3). We used SAS Version 9.3 (Carey, North Carolina, USA) for all analyses.
Sample size and power
With 67 patients in each randomised group, we had 90% power at the 0.05 significance level to detect a 30% or greater reduction in mean time spent performing the ultrasound-guided femoral nerve catheterisation using Infiniti Plus compared with a conventional needle, as specified a priori. We assumed a conservative coefficient of variation (CV = mean/SD) of 0.70, and that the time spent performing blocks was log normally distributed.
In total, 134 patients were enrolled, with 67 randomised to each group. One additional patient was enrolled in the trial, but did not receive a femoral nerve block and was thus excluded from analysis in the CONsolidated Standards of Reporting Trials (CONSORT) flowchart (Fig. 2). Patients’ baseline characteristics are presented in Table 1. According to our a priori definition of imbalance (i.e. ASD > 0.20), patients assigned to the Infiniti Plus group were more likely to be men, less likely to be white, less likely to have a primary TKA and more likely to have general anaesthesia than spinal anaesthesia. However, only intraoperative management strategy was associated with time to perform block and was adjusted for in the analyses.
The median (interquartile range Q1 to Q3) time to complete successful femoral nerve catheter placement was 118 s (100 to150) in the Infiniti Plus group versus 177 s (130 to 236) in the control group (Table 2). The estimated ratio of geometric means for Infiniti Plus versus control was 0.68 [95% confidence interval (CI): 0.61, 0.76], P < 0.001. The Infiniti Plus system thus significantly reduced the time required for ultrasound-guided femoral nerve catheter placement.
We observed block failure in 7% of Infiniti Plus patients and 4% of control patients. Infiniti Plus had no significant effect on the odds of block failure, with an estimated odds ratio of 1.55 [(98.3% CI: 0.25 to 9.6), P = 0.56]. Only 1% of Infiniti Plus patients and 5% of conventional patients required more than one block attempt, for an estimated odds of 0.13 [(98.3% CI: 0.01 to 1.78), P = 0.06].
Needle visibility data were missing in two Infiniti Plus patients for technical reasons. The needle tip was visible 59 ± 28% (mean ± SD) of the time in patients assigned to Infiniti Plus that was similar to the 55 ± 24% visibility in control patients. Infiniti Plus had no significant effect on the mean percentage of needle tip visibility; with an estimated mean increase of 4.6% [(98.3% CI: −7.7 to 14.6), P = 0.74].
Table 3 summarises the number of extra boluses of local anaesthetic, number of rescue sciatic blocks, pain scores, pain associated with motion, patient satisfaction rating and postoperative Myles QoR questionnaire for Infiniti Plus and control patients.
We found that the use of the Infiniti Plus needle guide reduced the time required to correctly place femoral nerve catheters by 32%, which corresponded to a mean decrease of 1 min. Our result is consistent with previous studies of the Infiniti Plus system which were conducted in porcine or phantom models.10–12 The only other clinical study compared breast biopsies guided by the system with a freehand approach, and also demonstrated a reduction in procedure time.13
Avoiding unnecessary block attempts may reduce the risk of block complications which are, however, rare.14 Interestingly, using the Infiniti Plus needle guide did not improve block success rate. However, this outcome is hard to interpret as the success rate in our study in control patients with ultrasound guidance alone was 96% and the study was not powered to detect a 4% improvement in block success rate. Furthermore, in our study anaesthesiologists with extensive experience performed all blocks and femoral nerve block is considered a basic technique, which will have a low incidence of block failure regardless of the needle guidance used.15
Despite the fact that Infiniti Plus guidance reduced the time required for femoral nerve catheter insertion, the fraction of time that the needle tip was visible was similar with each approach. The question, then, is how the Infiniti Plus system sped insertion. One possible explanation is that the mechanical guide kept the needle on track, even when the needle itself was not visible. An appropriate needle direction, combined with good visualisation of critical anatomic structures, may thus have been sufficient. Another confounding factor may be that the time calculated in this study includes the time for catheter insertion. Without the needle guidance you need a third hand to introduce the catheter, but with the needle guidance, the needle is stable inside the system and usually does not need a third hand to insert the catheter, which may decrease the time.
Previous mechanical needle guide systems have seen limited clinical use largely because they restricted needle redirection, therefore requiring complete withdrawal and reinsertion of the needle when the initial direction proved unsuitable.11 The Infiniti Plus system differs in keeping the needle aligned with the ultrasound beam, yet allowing clinicians to freely redirect the needle if necessary.
Our study was conducted in a single centre with a large caseload by experienced anaesthesiologists. The observed statistically significant 1-min reduction in block time is of marginal clinical importance; however, differences might be greater for less experienced clinicians or for infrequent users. Our study was restricted to insertion of femoral nerve catheters, which are among the most common peripheral nerve blocks performed. The femoral nerve is relatively superficial and it would be well worth determining whether the Infiniti Plus needle guide provides comparable benefit for blocks that require deeper needle insertion. The Infiniti Plus system costs approximately $8 extra for each nerve block in the United States and 1 min gained may not justify widespread use in relatively easy nerve blocks. However, when used in deeper and complicated blocks and in the hands of inexperienced clinicians, relatively more time may be saved and an increase in success rate may justify the extra cost.
In summary, the Infiniti Plus needle guide reduced the time required for placement of femoral nerve catheters by 1 min on average but did not reduce the number of attempts, increase the block success rate or improve visibility of the needle. Although speculative, the Infiniti Plus needle guide system may prove more helpful for deeper blocks or for use by less experienced clinicians.
Acknowledgements relating to this article
Assistance with the study: none.
Financial support and sponsorship: supported by CIVCO Medical Solutions. The sponsor was not involved in study design, data analysis or manuscript preparation. None of the authors has a personal financial interest related to this research.
Received from Department of Outcomes Research, Qualitative Health Sciences and General Anesthesiology and Anesthesiology Institute, Cleveland Clinic, Cleveland, Ohio. http://www.duplichecker.com was used for plagiarism check.
Conflict of interests: none.
Presentation: the report was previously presented, in part, at the 40th Annual Regional Anesthesiology and Acute Pain Medicine Meeting 14 to 16 May 2015, Caesars Palace Hotel, Las Vegas, Nevada.
1. Yuan JM, Yang XH, Fu SK, et al. Ultrasound guidance for brachial plexus block decreases the incidence of complete hemi-diaphragmatic paresis or vascular punctures and improves success rate of brachial plexus nerve block compared with peripheral nerve stimulator in adults. Chin Med J (Engl)
2. McCartney CJ, Lin L, Shastri U. Evidence basis for the use of ultrasound for upper-extremity blocks. Reg Anesth Pain Med
3. Neal JM, Brull R, Chan VW, et al. The ASRA evidence-based medicine assessment of ultrasound-guided regional anesthesia and pain medicine: executive summary. Reg Anesth Pain Med
4. Nadeau MJ, Lévesque S, Dion N. Ultrasound-guided regional anesthesia for upper limb surgery. Can J Anaesth
5. Guo S, Schwab A, McLeod G, et al. Echogenic regional anaesthesia needles: a comparison study in Thiel cadavers. Ultrasound Med Biol
6. Deam RK, Kluger R, Barrington MJ, et al. Investigation of a new echogenic needle for use with ultrasound peripheral nerve blocks. Anaesth Intensive Care
7. McVicar J, Niazi AU, Murgatroyd H, et al. Novice performance of ultrasound-guided needling skills: effect of a needle guidance system. Reg Anesth Pain Med
8. Tielens LK, Damen RB, Lerou JG, et al. Ultrasound-guided needle handling using a guidance positioning system in a phantom. Anaesthesia
9. Stark PA, Myles PS, Burke JA. Development and psychometric evaluation of a postoperative quality of recovery score: the QoR-15. Anesthesiology
10. Ball RD, Scouras NE, Orebaugh S, et al. Randomized, prospective, observational simulation study comparing residents’ needle-guided vs free-hand ultrasound techniques for central venous catheter access. Br J Anaesth
11. Gupta RK, Lane J, Allen B, et al. Improving needle visualization by novice residents during an in-plane ultrasound nerve block simulation using an in-plane multiangle needle guide. Pain Med
12. Whittaker S, Lethbridge G, Kim C, et al. An ultrasound needle insertion guide in a porcine phantom model. Anaesthesia
13. Shabana W, Kielar A, Vermani V, et al. Accuracy of sonographically guided biopsy using a freehand versus needle-guided technique: computed tomographic correlation study. J Ultrasound Med
14. Chin KJ, Perlas A, Chan VW, et al. Needle visualization in ultrasound-guided regional anesthesia: challenges and solutions. Reg Anesth Pain Med
15. Szucs S, Morau D, Iohom G. Femoral nerve blockade. Med Ultrason