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Indian J Crit Care Med
Indian J Crit Care Med
IJCCM
Indian Journal of Critical Care Medicine : Peer-reviewed, Official Publication of Indian Society of Critical Care Medicine
0972-5229
1998-359X
Jaypee Brothers Medical Publishers

38994254
10.5005/jp-journals-10071-24751
Systematic Review
Acoustic Shadowing to Facilitate Ultrasound Guided Arterial Cannulation: A Systematic Review and Meta-analysis of Randomized Controlled Trials
Mishra Lipi 1https://orcid.org/0000-0002-3444-3841

Rath Chandra 235https://orcid.org/0000-0001-7584-1996

Wibrow Bradley 1https://orcid.org/0000-0002-7240-9679

Anstey Matthew 15https://orcid.org/0000-0001-7927-524X

Ho Kwok 45https://orcid.org/0000-0002-6705-6004

1 Intensive Care Unit, Sir Charles Gairdner Hospital, Nedlands, Western Australia
2 Neonatology, Perth Children's Hospital, Nedlands, Western Australia
3 Neonatology, King Edward memorial Hospital, Subiaco, Western Australia
4 Intensive Care Unit, Fiona Stanley Hospital, Murdoch, Western Australia
5 School of Medicine, University of Western Australia, Crawley, Western Australia
Lipi Mishra, Intensive Care Unit, Sir Charles Gairdner Hospital, Nedlands, Western Australia, Phone: +61 426771819, e-mail: he162306@health.wa.gov.au
7 2024
29 6 2024
28 7 677685
29 4 2024
26 5 2024
Copyright © 2024; The Author(s).
2024
https://creativecommons.org/licenses/by-nc/4.0/ © The Author(s). 2024 Open Access. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by-nc/4.0/), which permits unrestricted use, distribution, and non-commercial reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Abstract

Aim and background

Ultrasound-guided arterial catheterization is a frequently performed procedure. Additional techniques such as acoustic shadowing-assisted ultrasound may be useful in improving success rate. This systematic review aimed to assess the efficacy of acoustic shadowing assisted ultrasound for arterial catheterization.

Materials and methods

PubMed, Medline, EMBASE, Cochrane Library, EMCARE, and MedNar were searched in January 2024. Randomized controlled trials comparing the first attempt success rate of arterial catheterization using acoustic shadowing ultrasound vs unassisted ultrasound were included. Data were pooled for risk ratios (RRs) using the random-effects model. Subgroup analysis was conducted based on a single or double acoustic line. Sensitivity analysis was undertaken after excluding pediatric data. The certainty of evidence (COE) was assessed using the GRADE framework.

Results

Six randomized controlled trials (n = 777) were included. A meta-analysis found the first attempt success rate is significantly higher in the acoustic ultrasound group (n = 6, RR: 0.47, 95% CI: 0.34–0.66, p ≤ 0.00001). Hematoma formation was significantly less in the acoustic ultrasound group (n = 6, RR: 0.52, 95% CI: 0.34–0.80, p = 0.003). First attempt success was significantly higher in the single acoustic line ultrasound (USG) group compared to the unassisted ultrasound group (n = 3, RR: 0.41, 95% CI: 0.28–0.59, p ≤ 0.00001). Sensitivity analysis after excluding pediatric data was similar to the primary analysis (n = 5, RR: 0.50, 95% CI: 0.33–0.70, p ≤ 0.00001). Certainty of evidence was “Moderate” for the first attempt cannulation.

Conclusions

Acoustic shadowing-assisted ultrasound improved first-attempt arterial catheterization success rate and was associated with reduced hematoma formation.

How to cite this article

Mishra L, Rath C, Wibrow B, Anstey M, Ho K. Acoustic Shadowing to Facilitate Ultrasound Guided Arterial Cannulation: A Systematic Review and Meta-analysis of Randomized Controlled Trials. Indian J Crit Care Med 2024;28(7):677–685.

Keywords

Acoustic shadow
Arterial cannulation
Ultrasound
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pmcHighlights

Acoustic shadowing assisted USG during arterial cannulation may be associated with a significantly higher first-attempt success rate and less hematoma formation compared to unassisted USG.

Introduction

Arterial line (AL) placement is a common procedure in intensive care units (ICUs), Emergency Departments, and operating rooms.1 Although AL placement is considered a safe technique, it is still associated with complications like bleeding, hematoma formation, arterial vasospasm, and injury of the adjacent nerve besides discomfort from skin puncture. Failed catheterization attempts may lead to vasospasm, intra, and extra-arterial hematoma, and further decrease the overall success rate. While uncommon, repeated attempts at cannulation can lead to severe complications such as permanent ischemic damage, sepsis, and the formation of pseudoaneurysms.2 In the cardiac Cath-lab setting, physicians constantly seek to attain lower puncture injury rates for better diagnostic angiography, intervention, or monitoring.3 The blind palpation technique is difficult in edematous, obese, and hypotensive patients which may lead to multiple failed-attempts. A recent Cochrane systematic review of 48 randomized controlled studies (RCTs) concluded that ultrasound (USG) guidance improves first attempt success rates, overall success rates, and time needed for a successful procedure.4 Another systematic review concluded that USG improves radial arterial cannulation success rate by 14–37% on the first attempt compared to the palpation method.5 Complications associated with USG-guided AL placement and aborted attempts are less frequent compared to palpation method.4,6,7 However, USG guided AL line placement is not without problems. New trainees who are not USG trained and lack hand eye coordination might find USG assistance not so useful. The changing USG position on the skin and the beam angle during the procedure might reduce the success rates in inexperienced hands. A systematic review found that USG guidance correlated with a higher rate of success on the first attempt when administered by a proficient operator compared to an inexperienced one.8 Investigators have used different USG modalities to improve the first attempt success rate. USG with developing line (acoustic shadow) by placing radiopaque objects on a USG probe is an easy technique to improve first attempt cannulation success rate. It can either be a single developing line (use of one radiopaque strip) or a double developing line (two radiopaque strips) and the artery on the USG screen is placed under (one strip) or in-between (two strips) the acoustic shadows so that arterial cannula can be introduced just below or in-between the radiopaque strips. While this technique utilizes USG guidance, it doesn't necessitate a highly skilled operator to pinpoint the puncture site. Consequently, it is theoretically suitable for both trainees and experienced clinicians. There are few recent publications available on this subject involving both inexperienced and experienced clinicians. Therefore, we undertook this systematic review to assess the effectiveness of acoustic shadow-assisted USG guidance in enhancing the success rate of first-attempt arterial cannulation.

Materials and Methods

This systematic review followed the guidelines outlined in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement.9 Additionally, it was registered on the international prospective register of systematic reviews (PROSPERO: CRD42022372361).

Data Sources and Searches

Three reviewers autonomously conducted searches across electronic databases such as PubMed, EMBASE, EMCARE, MEDLINE, The Cochrane Library, and Google Scholar. The search encompassed records from their inception up to January 2024. Additionally, grey literature searches were performed on the “Opengrey” and “Mednar” databases. In March 2024, we conducted searches on ClinicalTrials.gov (www.ClinicalTrials.gov) and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) Search Portal to identify ongoing or unpublished trials. PubMed was searched using the following broad keywords: (“acoust”[All Fields] OR “acoustical”[All Fields] OR “acoustically”[All Fields] OR “acoustics”[MeSH Terms] OR “acoustics”[All Fields] OR “acoustic”[All Fields]) AND (“shadow”[All Fields] OR “shadow s”[All Fields] OR “shadowed”[All Fields] OR “shadowing technique, histology”[MeSH Terms] OR (“shadowing”[All Fields] AND “technique”[All Fields] AND “histology”[All Fields]) OR “histology shadowing technique”[All Fields] OR “shadowing”[All Fields] OR “shadows”[All Fields])) OR ((“develop”[All Fields] OR “develope” [All Fields] OR “developed”[All Fields] OR “developer”[All Fields] OR “developer s”[All Fields] OR “developers”[All Fields] OR “developing”[All Fields] OR “developments”[All Fields] OR “develops”[All Fields] OR “growth and development”[MeSH Subheading] OR (“growth”[All Fields] AND “development”[All Fields]) OR “growth and development”[All Fields] OR “development”[All Fields]) AND “line”[All Fields])) AND (“diagnostic imaging”[MeSH Subheading] OR (“diagnostic”[All Fields] AND “imaging”[All Fields]) OR “diagnostic imaging”[All Fields] OR “ultrasound”[All Fields] OR “ultrasonography”[MeSH Terms] OR “ultrasonography”[All Fields] OR “ultrasonics”[MeSH Terms] OR “ultrasonics”[All Fields] OR “ultrasounds”[All Fields] OR “ultrasound s”[All Fields]) AND ((“arterialization”[All Fields] OR “arterializations”[All Fields] OR “arterialize”[All Fields] OR “arterialized”[All Fields] OR “arterializing”[All Fields] OR “arterially”[All Fields] OR “arterials”[All Fields] OR “arterie”[All Fields] OR “arteries”[MeSH Terms] OR “arteries”[All Fields] OR “arterial”[All Fields] OR “arteris”[All Fields] OR “artery”[All Fields] OR “arterious”[All Fields] OR “artery s”[All Fields] OR “arterys”[All Fields]) AND (“cannulate”[All Fields] OR “cannulated”[All Fields] OR “cannulating”[All Fields] OR “cannulator”[All Fields] OR “cannulators”[All Fields] OR “cannulisation”[All Fields] OR “cannulization”[All Fields] OR “cannulized”[All Fields] OR “catheterization”[MeSH Terms] OR “catheterization”[All Fields] OR “cannulation”[All Fields] OR “cannulations”[All Fields]). Consistent terminologies were utilized across all database searches. Furthermore, reference lists of relevant articles were manually screened. No language or period limitations were imposed.

Study Selection and Outcomes

Randomized controlled trials (RCTs) (both parallel and crossover) and quasi-randomized trials that met the following criteria were included: (1) Adults or children of either gender who required arterial line for diagnostic or therapeutic purposes (2) USG was used to cannulate any artery by any of the Seldinger techniques (3) Unassisted USG (without acoustic shadowing) and acoustic shadow assisted USG were compared. Cohort, case-control studies, and case series were excluded.

Primary outcome of interest: First-attempt success rate of arterial cannulation (Both single and double developing lines).

Secondary outcome of interest: (1) Hematoma formation (2) Second attempt success rate of arterial cannulation (3) Time, in minutes, needed for a successful procedure, (4) Any other adverse events.

Data Extraction and Quality Assessment

Two authors autonomously evaluated titles and abstracts to identify full-text articles suitable for inclusion in the review. Full-text articles of potentially eligible studies underwent meticulous examination by two reviewers to confirm eligibility. Data extraction was performed using a standardized form. The occurrence of various clinical outcomes of interest in both groups (ultrasound guidance unassisted vs. ultrasound guidance with acoustic shadow assistance) was documented. For binary outcomes, recorded risk ratios (RRs) with 95% confidence intervals (CIs) were noted if provided by the authors. The quality assessment of randomized controlled trials (RCTs) was conducted using the Cochrane risk-of-bias-2 tool by two independent reviewers.10 The certainty of evidence (COE) was assessed using the GRADE methodology and categorized as high, moderate, low, or very low.11 In case of discrepancies, reviewers engaged in discussions to achieve a consensus.

Data Synthesis

Meta-analysis was conducted utilizing Review Manager V.5.4 (Cochrane Collaboration, Nordic Cochrane Center, Copenhagen, Denmark). Reported RRs from included studies were pooled using the inverse-variance method (Cochrane Handbook section 10.3.3). Subgroup analysis was performed based on studies that had reported the first attempt success rate for acoustic shadow-assisted USG with either a single developing line or double developing lines. A sensitivity analysis was conducted by excluding studies that had included pediatric populations. One study has provided data on both single and double acoustic lines, in that case double acoustic line data was used for the primary outcome analysis and single acoustic line data was used for subgroup analysis. Due to anticipated heterogeneity, a random-effects model (DerSimonian and Laird) was employed for meta-analysis. Raw numbers were utilized to calculate RRs if the included study manuscripts did not provide this information. Pooled effect size estimates for dichotomous outcomes were presented as pooled RRs with 95% CIs. We analyzed continuous data as mean differences (MD) with the same scale, and as standardized mean differences (SMDs) with different scales, with 95% CIs. For studies where meta-analysis was not feasible, a qualitative synthesis was conducted. Statistical heterogeneity was evaluated by visually inspecting forest plots and quantified using the I2 statistic. The interpretation of I² results adhered to established guidelines: 0–40% indicated heterogeneity might not be significant; 30–60% suggested moderate heterogeneity; 50–90% indicated substantial heterogeneity; and 75–100% suggested considerable heterogeneity (Cochrane Handbook).12 Given the inclusion of only a small number of studies, substantial uncertainty existed in the value of I²; therefore, the p-value from the Chi-square test was also considered.

Results

Figure 1 presents a PRISMA flowchart depicting the screening and selection results. Initially, 792 articles were identified through the search, from which 6 studies met the selection criteria and were included.13–18 All 6 studies were incorporated into the meta-analysis, with a total sample size of 777, ranging from 77 to 237 individuals per study. All 6 studies were parallel RCTs. Five out of the 6 studies were conducted on adults undergoing elective surgical procedures while one was conducted on pediatric population undergoing elective surgical procedure.13–18 Patients underwent radial artery catheterization in all the 6 studies. Inexperienced physicians performed the procedure in 2 of the studies while experienced physicians inserted the cannulas in the other 4 studies.13,14,16–18 Four out of the 6 trials used metal-containing strands from the X-ray detectable gauge to create acoustic shadow, while the other two trials used sutures.13–18 Table 1 presents the characteristics of all the included studies. Among the included studies, five exhibited a low risk of bias, while one had some concerns. The risk of bias assessment graph and summary are depicted in Figure 2.

Table 1 Study characteristics

Study ID; Design; Sample size	Inclusion criteria	Proceduralist, artery	Acoustic shadowing procedure	Results	Procedure related adverse effects	Conclusion	
Siddaramaiah 2023_India; RCT;120 (c 60, DDL 60)	>18 years, undergoing major surgeries
where an arterial line was required	Experienced clinicians, RA	Metal containing strands from surgical gauze were positioned parallel to one another on the USG probe.
The probe was positioned so that the RA was located between these shadows in short axis view.	The success rate at the first attempt in the control (DNTP) and DDL groups was 66.7 and 71.7% respectively. The median cannulation attempt was 1 both the groups. The overall success rate among the C and DDL group was 98.3%, and 96.7%, respectively.
(p = 0.789). The median time for RA cannulation in the C and DDL group was 71.0 (50.0–170) s and 108.0 (58.0–181.0) respectively.	Hematoma 0/60 in C and 0/60 in DDL group. Spasm 1/60 in C group and 1/60 in DDL group. Hematoma and spasm 0/60 in C group compared to 1/60 in DDL group.	RA cannulation by DNTP, as well as acoustic shadowing techniques performed by experienced clinician's in
hemodynamically stable adult patients are equally advantageous.	
Zou 2022_China; RCT; 237 (C 80, SDL 78, DDL 79)	Patient undergoing bariatric surgery, Age: 18–70 years, BMI > 30	Trained anesthesia residents, RA	The metal-containing strand taken from X-ray-detectable gauze was bound to the middle of the USG probe and positioned perpendicularly to the long axis. In the SDL group, one strand was set, whereas 2 parallel
strands (2 mm interval) were placed in the DDL group	First attempt success rate: SDL: 90%, DDL: 91% and C: 71%. (p = 0.003 and 0.001 when compared with SDL and DDL)
Time to a successful first attempt: 54, 40 and 63 seconds for SDL, DDL and C respectively (p = 0.004 and < 0.001 when compared with SDL and DDL)
Two attempt success rates: 96, 97 and 86% for SLD, DDL and C respectively (p = 0.003 and 0.001 when compared with SDL and DDL).
No difference between SDL and DDL group in terms of success or time.	Overall complications (Vasospasm and hematoma): 10%, 9% and 29% for SDL, DDL and C respectively (p < 0.003 and 0.001when compared with SDL and DDL). Each of these complications were significantly lower in the SDL and DDL group compared to C. Hematoma 21, 7 and 5% for C, DDL and SDL respectively.	SDL and DDL improve first attempt success rate and reduce complication rates in obese patients.	
Dong 2022_China; RC; 101 (DDL 51, C 50)	Patients undergoing an elective surgical procedure	Post graduate students who had not performed artery puncture or received relevant training previously, RA	The metal-containing strand of the X-ray detectable surgical gauze is separated and placed on the USG probe to make it perpendicular to the long axis of the USG probe. The USG coupler and sterile 3 M membrane were applied over the USG probe to secure the USG probe and the metal-containing strand	First attempt success rate: DDL: 74.51% and C: 52%. (p = 0.019).
Time to a successful first attempt: 10.43 ± 2.38 and 14.78 ± 8.02 seconds for DDL and C respectively (p = 0.012)	Hematoma: 15.7% and 24% in DDL and C respectively (p = 0.295)	Using acoustic shadowing-facilitated USG guided arterial catheterization. Standardized
teaching of residents can help students master the skills
more quickly and increase the first-attempt success rate.	
Quan 2014_China; RCT; 163 (SDL 81, C 82)	Patients
undergoing liver surgery or splenic resection
under GA.	Experienced anesthesiologists, who had
previously cannulated 450 arteries and used the USG-
guided technique for approximately 200 procedures, RA	A suture was tied on the midpoint of the ultrasound probe
(a developing line) and perpendicular to the long axis as a guide. (Compared with long axis plane technique)	First attempt success rate: SDL: 88.9% and C: 73.2%. (p = 0.015).
Two attempt success rates: 96.3 and 95.1% for SLD and C respectively (p = 1.0)
Time to a successful cannulation (mean (SD): 29.7 (17.20) and 26.2 (9.8) seconds for SDL and C respectively.	No thrombosis, edema, or vasospasm in either group.
Hematoma: 14.8% and 18.3% in SDL and C respectively (p = 0.674)	The modified short axis out of plane technique may improve the success rate of cannula insertion
into the radial artery on the first attempt	
Quan 2019 (A)_China; RCT; 79 (DDL 39, C 40)	Children age range, 4–24 months; weight
range, 4–10 kg undergoing elective surgical procedure	Attendants who had performed more
than 50 USG guided punctures, radial artery	The metal-containing strand taken from X-ray–detectable
surgical gauze was bound parallelly (interval: 2 mm) to the
USG probe and positioned perpendicular to the long axis of the probe. An ultrasonic couplant and sterile 3M membrane were applied over the USG probe to fix the DDL.	First attempt success rate: DDL: 90% and C: 60%. (p = 0.002).
Time to a successful cannulation (median (IQR): 24 (15, 41) and 40 (23, 56) seconds for DDL and C respectively) (p = 0.012)	Bleeding at the puncture site: 10 vs 30% in the DDL and C group respectively (p = 0.029)
Hematoma: 8 and 18% in DDL and C respectively (p = 0.19)	Acoustic shadowing via the use of DDL
significantly improved the success rate of radial artery puncture in young children, compared with that achieved with the use of traditional USG
guidance.	
Quan 2019 (B)_China; RCT; 77 (SDL 39, C 38)	Adults 18–60 years schedule to undergo
elective hepatectomy or splenectomy with GA	USG trained interns, RA	A suture was tied on the midpoint of the ultrasound probe
(a developing line) and perpendicular to the long axis as a guide.	First attempt success rate: SDL: 71.79%, C: 34.21% (proportion difference: –0.3408 (95% CI, –0.5483 to –0.1334), p = 0.0025)
Cannula insertion failure rates were SDL: 5.13% and C: 18.42% (proportion difference: 0.1329 (95% CI, −0.0084 to 0.2743), p = 0.0866)
Time to successful cannulation:
No significant between-group difference (mean difference: –4.90 s (95% CI, −11.85–2.04 s), p = 0.1637)	Vasospasm: No significant between-group difference was observed (proportion difference: –0.0963 (95% CI, −0.3316 to 0.1391), p = 0.4361] Hematoma: No difference (proportion difference: –0.0963% (95% CI, –0.1391–0.3316), p = 0.4361)
No instances of thrombosis, occlusion, or aneurysm occurred in this study	Use of USG with developing line significantly improved the success rate of radial artery puncture performed by interns.	
BMI, body mass index; C, control; DDL, double developing line; DNTP, dynamic needle tip positioning; GA, general anesthesia; IQR, inter quartile range; RA, radial artery; RCT, randomized controlled trial; SDL, single developing line; SD, standard deviation; USG, ultrasonography

Fig. 1 Flowchart for study selection

Fig. 2 Risk of bias and applicability concerns summary

Pooling of RRs from 6 studies found first attempt arterial cannulation success rate to be significantly better with the use of acoustic shadow compared to unassisted USG (RR of failed first attempt: 0.47, 95% CI: 0.34–0.66, p ≤ 0.00001) (Fig. 3). However, there was no significant difference in the second attempt success rate between acoustic shadow and unassisted USG when RRs of 3 studies were pooled (RR: 0.44, 95% CI: 0.19–1.03, p = 0.06) (Fig. 4). Pooling of RRs from 3 studies that have reported comparison of a single acoustic shadow line with unassisted USG also found a significantly better first attempt success rate with acoustic shadow USG (OR: 0.41, 95% CI: 0.28–0.59, p ≤ 0.00001) (Fig. 5). Hematoma formation was significantly less common with the use of acoustic USG compared to unassisted USG when RRs from 6 studies were pooled (RR: 0.52, 95% CI: 0.34–0.80, p = 0.003) (Fig. 6). Result of the sensitivity analysis after excluding pediatrics data was similar to the primary analysis (n = 5, RR: 0.50, 95% CI: 0.36–0.70, p ≤ 0.00001). Pooled SMD from 6 studies did not show a significantly less time to canulation with acoustic-assisted USG (Mean difference: –0.26, 95% CI: –0.72–0.20, p = 0.27) (Fig. 7).

Fig. 3 Forest plot showing first attempt arterial cannulation success rate to be significantly better with the use of acoustic shadow compared to unassisted USG

CI, confidence interval; IV, inverse variance; USG, ultrasound

Fig. 4 Forest plot showing no significant difference in second attempt success rate between acoustic shadow and unassisted USG

CI, confidence interval; IV, inverse variance; USG, ultrasound

Fig. 5 Forest plot showing first attempt arterial cannulation success rate to be significantly better with the use of single acoustic shadow compared to unassisted USG

CI, confidence interval; IV, inverse variance; USG, ultrasound

Fig. 6 Forest plot showing significantly less hematoma formation in the acoustic USG group compared to unassisted USG

CI, confidence interval; IV, inverse variance; USG, ultrasound

Fig. 7 Forest plot did not show a significantly less time to canulation with acoustic assisted USG compared to unassisted USG

CI, confidence interval; IV, inverse variance; USG, ultrasound

Heterogeneity (I2) was 33% for first attempt success rate (p = 0.19), 0% for single acoustic shadow (p = 0.74), 15% for hematoma formation (p = 0.32), and 3% for second attempt success (p = 0.36). Time to arterial cannulation was highly heterogeneous (I2 = 89%, p ≤ 0.00001).

Assessment of publication bias was not feasible due to the limited number of studies (<10) included in the meta-analysis. The certainty of evidence was “Moderate” for the outcomes of first attempt success for all studies, the first attempt success including only single line acoustic shadow USG, and hematoma formation. The certainty of evidence for the second attempt success was “Low” and for time to cannulation was “Very low” (Table 2).

Table 2 Grade analysis

	Certainty assessment	No. of patients	Effect		
Outcomes	No. of studies	Study design	Risk of bias	Inconsistency	Indirectness	Imprecision	Other considerations	Acoustic shadow ultrasound	Unassisted ultrasound	Relative (95% CI)	Certainty	
First attempt success	6	Randomised trials	Not seriousa	Not serious	Not serious	Not serious	Publication bias strongly suspectedb	61/349 (17.5%)	130/350 (37.1%)	RR 0.47 (0.34–0.66)	⨁⨁⨁◯ Moderate	
Second attempt success	3	Randomised trials	Not seriousa	Not serious	Not serious	Seriousc	Publication bias strongly suspectedb	8/220 (3.6%)	20/222 (9.0%)	RR 0.44 (0.19–1.03)	⨁⨁◯◯ Low	
Single developing line first attempt success	3	Randomised trials	Not seriousa	Not serious	Not serious	Not serious	Publication bias strongly suspectedb	28/198 (14.1%)	70/200 (35.0%)	RR 0.41 (0.28–0.59)	⨁⨁⨁◯ Moderate	
Haematoma formation	6	Randomised trials	Not seriousa	Not serious	Not serious	Not serious	Publication bias strongly suspectedb	33/349 (9.5%)	66/350 (18.9%)	RR 0.52 (0.34–0.80)	⨁⨁⨁◯ Moderate	
Time to cannulation	6	Randomised trials	Not serious	Very seriousd	Not serious	Very seriousc	Publication bias strongly suspectedb			not estimable	⨁◯◯◯ Very low	
CI, confidence interval; RR, risk ratio. aSelection and performance bias; bPublication bias could not be assessed since there are less than 10 studies; cWide confidence intervals; dHigh statistical heterogeneity

Discussion

This systematic review, encompassing 6 randomized controlled trials (n = 777), concluded that acoustic shadowing-assisted USG guidance during arterial cannulation is linked to a significantly higher first-attempt success rate and reduced incidence of hematoma formation compared to unassisted ultrasound guidance.

Multiple punctures and use of multiple arterial catheters involve cost.19,20 The use of USG to cannulate arteries has certainly improved the first attempt success with a reported rate of around 76 and 70% in experienced and inexperienced hands respectively.4 Different methods like dynamic needle tip positioning, long axis view in-plane approach, bevel orientation, and Nitroglycerin have been used to improve first attempt success rate and to reduce complications.21 The use of acoustic shadow to improve success rate is an easy technique and may be useful in the hands of both experts and novices.

Successful arterial cannulation comprises two crucial steps: accurately identifying the puncture point and assessing the depth of the puncture. Acoustic shadow-assisted USG guidance aids in pinpointing the puncture point accurately, while 2D USG guidance assists in determining the depth, thus complementing each other in the process. It is important to have a guiding line or two guiding lines to ascertain the puncture point, which can be done by either using acoustic shadow or in some USG machines using M mode.22 However, the M mode can only draw a single line corresponding to the center of the USG probe and not 2 lines. Is the use of 2 lines more accurate than 1 line in determining the point of puncture? The answer is still unclear. One of the included studies has compared first-attempt success rates between single and double-developing lines and did not find any significant difference.16 In addition, pooling RRs from studies that have reported first-attempt success rates using single or double acoustic lines were no different. However, this needs to be tested in a setting where inexperienced physicians are undertaking this procedure.

Preparation of the USG probe to produce an acoustic line is cumbersome, takes time, and might compromise asepsis integrity. Future USG probes can be designed to have either one or two central M mode line along with probe markings to facilitate cannula insertion.

Our systematic review possesses several strengths, particularly its robust methodology incorporating risk of bias assessment and sensitivity analyses. To the best of our knowledge, this represents the inaugural systematic review with meta-analysis on this subject. Nonetheless, our review also presents several limitations. The pool of studies and participants was constrained. A publication bias assessment couldn't be conducted due to the scant number of studies. The studies included in our review encompassed diverse patient cohorts, and the USG operators exhibited varying levels of experience, potentially introducing notable heterogeneity. Additionally, achieving blinding of clinicians to the study intervention was unattainable in all included trials, possibly leading to performance bias.

Conclusions

Acoustic shadowing assisted USG during arterial cannulation is associated with a significantly higher first-attempt success rate and less hematoma formation compared to unassisted USG. Future RCTs should be conducted in various clinical settings like ICUs and emergency departments on patients with compromised hemodynamics. Studies should also endeavor to report success rates by experienced and inexperienced clinicians using single or double acoustic shadow.

Orcid

Lipi Mishra https://orcid.org/0000-0002-3444-3841

Chandra Rath https://orcid.org/0000-0001-7584-1996

Bradley Wibrow https://orcid.org/0000-0002-7240-9679

Matthew Anstey https://orcid.org/0000-0001-7927-524X

Kwok Ho https://orcid.org/0000-0002-6705-6004

Source of support: Nil

Conflict of interest: None
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