Arterial cannulation is a common invasive procedure performed in operating rooms and intensive care units. Several different arteries can be cannulated, but the radial artery is most commonly used due to its superficial course, dual blood supply of the hand, and low risk of complications.1 Complications from arterial cannulation include edema, hematoma, thrombosis, infection, and nerve injury.2,3 In addition, multiple unsuccessful attempts at radial arterial cannulation can lead to arterial spasm and patient discomfort.
Many but not all studies have shown that ultrasound guidance results in a greater first-pass success rate of radial arterial cannulation in comparison to palpation (51%–95% vs 34%–57.5%).1,4–9 Although the use of ultrasound increases the success rates of radial arterial cannulation, the increase, albeit statistically significant, has been modest. Two studies that involved trainees reported the lowest ultrasound success rates of 53% and 62%.5,8 We thought that modifying the ultrasound technique could further increase the success rate.
Dynamic needle tip positioning is a modified ultrasound technique that was first shown to result in greater peripheral venous catheterization success rate when compared to the long-axis in-plane view in a phantom model.10 Use of this method for radial arterial cannulation was described in a case report by Goh et al.11 The dynamic needle tip positioning method combines the advantages of the short-axis out-of-plane and the long-axis in-plane ultrasound techniques (see Supplemental Digital Content, Video, http://links.lww.com/AA/B844). The short-axis ultrasound technique has the advantage of facilitating visualization of relevant structures, such as variant vascular anatomy, nerves, and veins during cannulation.4 The long-axis technique can provide clear visualization of the position of the needle as it approaches and enters the arterial lumen and thus increases the success rate of threading of a catheter. We hypothesized that a similar ultrasound technique would result in a significant increase in first-pass success rate during radial arterial catheterization.
This study was approved by the University of Iowa Institutional Review Board and was registered at www.clinicaltrials.gov (number: NCT02557828; principal investigator: R.K.K.; date of registration: September 22, 2015). This study is a parallel randomized controlled trial with an allocation ratio of 1:1. The transcript adheres to the CONSORT guidelines. There were no protocol changes after trial commencement. Each patient provided written informed consent.
Patients undergoing an elective surgical procedure that required the use of invasive arterial pressure monitoring, as determined by the attending anesthesiologist, were eligible for inclusion in this study. Patients were excluded if they were <18 years old or >90 years old, incarcerated, pregnant, in shock, non-English speaking, required radial forearm flap harvest, had a positive modified Allen test, or had radial artery cannulation in the previous 30 days. All eligible patients were approached on the morning of surgery in the preoperative room.
A total of 275 patients provided written informed consent, 15 were excluded prior to randomization, and the remaining 260 patients were randomized and included in the final analysis. The reasons for postconsent exclusion included lack of availability of research team to collect data (n = 6), anesthesia faculty deciding not to insert an arterial line (n = 7), or anesthesia faculty preference to use ultrasound in particular patients (n = 2; Figure 1).
Prior to study initiation, the department biostatistician created 2 groups of randomization assignments. The assignments were computer generated, with randomly selected block sizes using nQuery Advisor 7.0 (Statistical Solutions Ltd, Cork, Ireland) and then placed in sealed envelopes. One group was for faculty and the other for resident operators. Enrolled patients were randomized into either the dynamic needle tip positioning technique or the palpation group. The operators (anesthesia residents, fellows, and faculty) placing the arterial catheters were required to have placed at least 10 radial arterial catheters using each technique prior to participation in the study. Thus, residents who joined clinical anesthesia in July while the study was in process were not included. Each operator was limited to participating in 20 total cannulations in the study. The operators provided verbal consent to participate in the study.
The operator was allowed to independently choose which radial artery they would use for cannulation. Radial arterial cannulation was performed either before or after induction of general anesthesia based on the preference of the faculty anesthesiologist. The patient’s arm was slightly abducted from the body, and the wrist was positioned in a slightly extended position by placing a towel roll under the wrist. The wrist was then stabilized by taping it to the armboard. The research team used an ultrasound machine (NanoMaxx; SonoSite Inc, Bothell, WA) and probe (L25N/13–6; SonoSite Inc) to obtain an image of the radial artery at the estimated point of needle puncture. The operators were blinded to this image acquisition and any measurements. The arterial diameter was then measured using the caliper tool on the ultrasound machine. Thereafter, the technique to be used for cannulation was determined when the research team member opened an opaque randomization envelope containing a piece of paper with either ultrasound or palpation printed on it.
The wrist was then prepped with Chloraprep 2% (Becton Dickinson, Franklin Lakes, NJ) and sterile technique including sterile gloves, towels, and ultrasound probe covers were used. The specified technique was then used to place the radial artery catheter using a 20-gauge intravenous catheter (Jelco; Smith Medical International Ltd, Rossendale, UK).
The timer was started at the beginning of ultrasound scanning, or palpation of the patient’s prepped wrist, for dynamic needle tip positioning and palpation techniques, respectively. For each technique used, the timer was stopped when an arterial waveform appeared on the monitor. If after 5 minutes the selected radial artery was not cannulated, the study was stopped and the operators were free to use any method for cannulation. The cannulation time was then recorded as 300 seconds. First-pass success was defined as successfully obtaining an arterial waveform after one pass through the skin with the needle.
The data that were collected included first-pass success of radial arterial line placement (yes/no), number of catheters used, number of skin perforations, time to achieve successful cannulation (seconds), systolic blood pressure before and after radial artery puncture, diastolic blood pressure before and after radial artery puncture, and heart rate before and after puncture. Patient information that was obtained from the medical record included age, height, weight, body mass index, sex, and history of peripheral vascular disease (PVD). PVD was defined as presence of aortic or carotid disease, vascular claudication, prior revascularization procedure, or prior diagnosis of PVD in the medical record.
Dynamic Needle Tip Positioning Technique
For the dynamic needle tip positioning technique, a short-axis out-of-plane view of the radial artery was obtained and then the needle and catheter were advanced through the skin at a 30° to 40° angle until the hyperechoic needle tip was seen on the ultrasound image. The ultrasound probe was then moved proximally along the arm and away from the needle insertion point until the needle tip disappeared from the ultrasound image. The needle and catheter were then advanced a few millimeters until the needle tip was seen again on the ultrasound image (Figures 2–4). This stepwise process was repeated several times until the needle tip was visualized in the lumen of the radial artery. At this point, the angle of approach was decreased and the same process continued, keeping the needle tip in the center of the arterial lumen. The needle and catheter were both advanced stepwise for at least 1 cm inside the arterial lumen. The catheter was then threaded off the needle and then the transducer tubing attached (see Supplemental Digital Content, Video, http://links.lww.com/AA/B844). If the operator advanced through the posterior vessel wall, they were allowed to withdraw and advance again. The operator was not allowed to use a wire for cannulation (Figures 2–4).
For the palpation method, the operator palpated the radial arterial pulse with their nondominant hand. The needle and catheter were advanced toward the radial artery at a 15° to 30° angle until a flash back of blood was observed in the needle hub. Once blood appeared in the hub, the needle angle was decreased slightly and the catheter was advanced about 0.5 cm. If blood continued to flow into the hub, the catheter was advanced into the artery. The operator was also allowed to use a wire or the through-and-through technique to cannulate the artery.
Statistical analysis was conducted on an intention to treat analysis. We assessed the effect of the cannulation technique on the first pass, overall success rate, and number of attempts using χ2 test or Fisher exact test. Two-sample independent test or Mann-Whitney U test, if appropriate, was used to assess the effect of cannulation method on the cannulation time.
Standardized differences as effect sizes in patient baseline characteristics were calculated using the stdiff macro in SAS (SAS Institute, Inc, Cary, NC). Variables including PVD, sex, precannulation blood pressure, radial artery diameter, and operator experience (faculty/fellow versus resident) were predetermined from the previous study.5 Time to successful arterial cannulation was illustrated by the Kaplan-Meier curve (Figure 5). A 2-tailed value of P < .05 was considered statistically significant. SPSS 23.0 (SPSS Inc, Chicago, IL) was used for statistical analysis.
Sample Size Calculation
A sample size calculation was based on our previous study that showed a first-pass success rate of 40% with palpation and 53% with standard ultrasound.5 To compare 40% first-attempt success rate in the palpation group versus 60% rate in the dynamic needle tip positioning group with 90% power and 0.05 two-sided type I error rate, we needed to enroll 130 patients per group. Note that, this assumption corresponds to a 50% relative increase in success rate (relative risk of 1.5). We randomized only 260 patients because we did not expect patient drop off, and there was no follow-up needed in the study.
The study was conducted at the University of Iowa Hospitals and Clinics main operating rooms between May and December 2015 and was stopped after adequate enrollment of patients. Of the 260 randomized patients, there were 3 protocol violations: one was due to the use of a different catheter, one operator refused to use the palpation technique after randomization, and another used a wire to guide the catheter into the vessel lumen while using the dynamic needle tip positioning technique. These 3 patients were treated as failed attempts in the intention to treat analysis.
There were 132 patients in the dynamic needle tip positioning group and 128 patients in the palpation group. There were no apparent differences in any of the baseline characteristics that we evaluated between the 2 groups (Table 1). The faculty group was composed of 9 fellows and faculty, and the resident group had 32 residents. Among those 41 operators, 21 operators performed <5 cannulations, 13 performed 5 to 9 cannulations, and 7 operators performed 10 or more cannulations. The first-pass success rates were 109 of 132 (83%) in the dynamic needle tip positioning group, and 62 of 128 (48%) in the palpation group (P < .001; relative risk was 2.5; 95% confidence interval, 1.7–3.6). The overall 5-minute success rate was 118 of 132 (89%) in the dynamic needle tip positioning group and 83 of 128 (65%) in the palpation group (P < .001; relative risk was 2.4; 95% confidence interval, 1.2–1.6; Table 2).
The dynamic needle tip positioning group had a median cannulation time of 81.5 seconds, and the palpation technique had a median cannulation time of 76 seconds (P = .7) The observed interquartile range (IQR) was slightly narrower for the dynamic needle tip positioning technique group (61–122 vs 48–175).
A secondary analysis of the first-pass success rates in the dynamic needle tip positioning technique when broken down by residency class revealed success rates of 81%, 82.9%, 80%, and 86.2% in the clinical anesthesia (CA)-1, CA-2, CA-3, and fellow/faculty groups, respectively. The palpation group had first-pass success rates of 38.7%, 51.6%, 40%, and 66.7%. There was no significant difference between the operator groups for dynamic needle tip positioning or palpation (P = .9 and .09), respectively (Table 2).
The current study confirms that the use of the dynamic needle tip positioning ultrasound technique is more effective than palpation for radial artery cannulation. A similar result was also found to be true within subgroups of operators with different experience levels. This result is in concordance with other randomized controlled studies comparing ultrasound and palpation for radial arterial line placement.5,6,8
Notably, it appears that use of the dynamic needle tip positioning technique resulted in a much greater first-pass success rate especially compared to previous studies that used the standard short-axis ultrasound technique with trainees. We observed a first-pass success rate of 82% in the resident group compared to success rates between 78% and 53% in other studies involving trainees.5,8,12 Notably, the study involving trainees, which reported a success rate of 78%, used 10 minutes to define failure and did not report a first-pass success rate.12 There were other studies that had higher success rates than our study, but the operators were faculty members with vast experience in arterial catheter placement, and in the study by Zaremski et al,13 the Seldinger technique was used.6,7 In contrast, in the current study, the experience of operators ranged from residents with less than a year of clinical anesthesia experience to experienced faculty. The relative risk favored the dynamic needle tip advancement technique throughout different operator experience groups, but larger studies are needed to assess for a treatment effect between the subgroups. We feel that this result is more representative of the experience ranges in most academic center operating rooms where residents and faculty are involved in arterial cannulation. The current study showed a relative risk of 2.5 favoring the dynamic needle tip positioning technique. In contrast, the systematic reviews comparing ultrasound versus palpation for radial arterial cannulation reported relative risks between 1.47 and 1.71 in adults.1,4,14,15 The study by Gu et al16 instead reported a first-attempt failure reduction with ultrasound relative risk 0.68.
The successful cannulation of an artery requires the completion of 2 separate steps: entering the vessel and subsequent catheter advancement.17 A possible reason for the failure in cannulation with the standard short-axis technique may be failure in catheter advancement. Due to the small size of the artery, the needle tip may be placed only partly into the vessel lumen, or in the vessel wall, or all the way through the posterior arterial wall.9,17 In a study comparing short-axis versus long-axis ultrasonography for arterial catheter placement, Berk et al9 showed significantly higher posterior wall damage and hematoma with the short-axis technique. The dynamic needle tip positioning technique has the advantage of easy arterial puncture while decreasing the risk of subsequent unsuccessful cannula advancement. Sequential advancement under ultrasound tracking helps to confirm that the needle and cannula are both completely in the vessel lumen before advancing the cannula.
Eisen et al18 showed that female sex and low systolic blood pressure were both patient characteristics associated with increased failure rates during arterial line placement. Female sex is associated with smaller arterial size compared to matched men.19 It has been postulated that the smaller arterial size is related to the increased failure rate of arterial cannulation in females. In addition, our previous study showed that smaller radial artery diameter and operator inexperience are significant factors associated with arterial cannulation failure.5 In our current study, there was no difference in the baseline characteristics between the groups.
One concern about the use of ultrasound is that it may take longer than the palpation method. However, median cannulation times in this study did not differ between the dynamic needle tip positioning and palpation groups (Table 2). This shows that even when including the scanning time, the use of ultrasound does not make the procedure of arterial cannulation longer. Moreover, the IQR (25%–75%) of the dynamic needle tip positioning successes was 61 seconds compared to 127 seconds for the palpation successes (Table 2). Figure 5 also shows that the ultrasound cannulation times were not longer but most successful cannulation times were between a shorter period compared to palpation. Although IQR was not a variable that was evaluated, the smaller IQR may signify that the dynamic needle tip positioning technique had more consistent procedural times, which is likely the more clinically relevant variable, as it could predict anesthesia ready times.
In this study, we used the dynamic needle tip positioning technique, which is similar to the dynamic needle tip positioning technique that has been described for placement of peripheral intravenous catheters, and the “follow the tip” technique described for radial artery cannulation.10,11 A similar technique was used in a study by Hansen et al.6 In that study, the needle and ultrasound probe were sequentially advanced until arterial puncture was made and then the cannula was blindly advanced into the artery. In contrast, in our study, we continued advancement of the needle and catheter as a unit under ultrasound guidance for about 1 cm in the vessel lumen. This additional manipulation assured that the cannula would advance into the lumen while decreasing complications such as posterior wall puncture.
A limitation of this study is that it was conducted in an environment with clinicians experienced with the use of the dynamic needle tip positioning ultrasound technique for vascular access. After our previous study, the dynamic needle tip positioning ultrasound technique has become standard for vascular access in our department. Therefore, the results of this study may be different if this technique was introduced in an ultrasound naive culture. Another limitation is the assessment of adverse events. Although we hypothesize that the dynamic needle tip positioning technique will reduce the risk of posterior arterial wall puncture, and other complications, we did not evaluate these outcomes in this study and further studies would be needed to prove this hypothesis. In our previous study, there was no difference in adverse effects, including hematoma, nerve injury, or ischemia, between ultrasound and palpation.5
In conclusion, our study demonstrated an improvement in radial artery cannulation success rate with a novel ultrasound technique when compared with palpation. The first-pass success rate was also greater than that of other studies involving trainees where the standard short-axis ultrasound technique was used. We believe that with continuing improvement of ultrasound-guided vascular techniques and availability of ultrasound machines, ultrasound-guided vascular access should become standard.
We thank Bradley J. Hindman, Professor and Vice Chair, Department of Anesthesia, University of Iowa Hospitals and Clinics, Iowa City, IA, for the preparation of this manuscript.
Name: Roy K. Kiberenge, MD.
Contribution: This author helped design the study, conduct the study, and prepare the manuscript.
Name: Kenichi Ueda, MD.
Contribution: This author helped design the study, conduct the study, and analyze the data.
Name: Brett Rosauer, BS.
Contribution: This author helped conduct the study and collect the data.
This manuscript was handled by: Richard C. Prielipp, MD.
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