Study characteristics

Methods

RCT

Participants

Number: 84 radial arteries

Number per intervention

1. Ultrasound: 43 radial arteries

2. Palpation: 41 radial arteries

Inclusion criteria

1. Critically ill condition

2. Age 1 month–15 years

3. Need for invasive monitoring and frequent blood sampling

Exclusion criteria

1. Absence of an amplitude of radial pulsation 

2. Skin erosions near the insertion site

3. Former cannulation

Surgery/setting: paediatric ICU

Baseline characteristics

Ultrasound

1. Mean age: 20 months

2. Mean weight: 9 kg

3. Sex ratio (male:female): 25:16

Palpation

1. Mean age: 32 months

2. Mean weight: 11 kg

3. Sex ratio (male:female): 31:12

Interventions

Randomisation: stratified block randomisation (blocks of 4, stratified by age < 1 year and > 1 year)

Intervention: ultrasound‐guided artery cannulation (short‐axis view). Artery was lined up with centre of transducer, needle inserted at centre of transducer in real‐time. Single‐ or double wall technique chosen depending on operator preference (Seldinger technique employed in both cases).

Control: palpation

Co‐intervention: standard 22‐ to 24‐gauge Jelco intravenous catheter (Smiths Medical International, Ashford, England) percutaneously punctured the radial artery

Experience of operator: attended course in ultrasound‐guided vascular access course; experience of > 10 cases in ultrasound‐guided or traditional palpation technique.

Outcomes

Primary endpoints

1. First‐attempt success rate

2. Total success rate (within 3 attempts; attempts quantified as number of needle tips completely withdrawn from the skin

Secondary endpoints

1. Time to successful cannulation (from initial needle penetration through skin to removal of needle and flash of arterial blood)

2. Incidence of complications (hand ischaemia, haemorrhage, thrombosis, hematoma)

Notes

No information was provided regarding funding and conflicts of interest.

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Unclear risk

RCT with stratified randomisation (children < 1 year and > 1 year). Method of randomisation and stratification not explained.

Allocation concealment (selection bias)

Unclear risk

Method of randomisation and stratification not explained.

Blinding of participants and personnel (performance bias)
All outcomes

High risk

The anaesthesiologist was aware of the allocated intervention before performing arterial catheterisation.

Blinding of outcome assessment (detection bias)
All outcomes

Low risk

Objective outcomes not affected by lack of blinding.

Incomplete outcome data (attrition bias)
All outcomes

Low risk

 No missing data.

Selective reporting (reporting bias)

Low risk

All outcomes were addressed.

Other bias

Unclear risk

Quote: "The operators included 7 fellows. The experience of each fellow may have affected the success rate of radial artery cannulation; however, we used a multiple logistic regression analysis, which included the operator to reduce operator bias."

Study characteristics

Methods

RCT

Participants

Number: 152 radial arteries

Number per intervention

1. Ultrasound: 72 radial arteries

2. Palpation: 80 radial arteries

Inclusion criteria

1. Age < 18 years

2. Planned radial arterial catheterisation 

Exclusion criteria

1. Not reported

Surgery/setting: not reported

Baseline characteristics

Ultrasound

1. Mean age: 99.1 (SD 69.3) months

2. Mean weight: 32.2 (SD 22.6) kg

3. Sex ratio (male:female): 36:36

Palpation

1. Mean age: 99.6 (SD 71.6) months

2. Mean weight: 31.3 (SD 22.6) kg

3. Sex ratio (male:female): 38:42

Interventions

Randomisation: participants were randomised to US guidance technique (intervention) or palpation (control) for radial artery cannulation.

Intervention: ultrasound‐guided technique: after localisation of the radial artery, using a portable US device (SonoSite 180plus, SonoSite, Bothell, WA, USA) the physician inserted an age appropriate‐sized catheter over a needle distal to the transducer and directed it according to the US image.

Control: palpation (continuous or intermittent) of arterial pulsation.

Co‐intervention: after induction of general anaesthesia and endotracheal intubation, cannulation was performed according to the randomised method. After skin disinfection at the insertion site, the wrist was extended and the hand and forearm were taped. Skin puncture marked the start, and successful cannulation was the endpoint of the procedure. Failure of either technique and use of a cross‐over technique were determined by the consultant anaesthesiologist assigned to the case.

Experience of operator: paediatric subspecialty trainee anaesthesiologists who had completed a minimum of 3 years' training in anaesthesia, or consultant paediatric anaesthesiologists. No operator had performed > 10 US‐guided arterial cannulations before the study.

Outcomes

Primary endpoints

1. Time to successful cannulation by the first operator at the first site of arterial puncture

   1. Start time: time of initial skin puncture at the first site

   2. End time: time first operator successfully aspirated blood from the distal end of the inserted cannula

Secondary endpoints

1. Number of attempts at arterial cannulation (each attempt defined as reinsertion following withdrawal)

2. Number of cannulas required for successful catheter insertion

3. Need for additional assistance from another anaesthesiologist

4. Cross‐over between techniques or rescue after the first operator was deemed to have failed with the assigned technique

5. Number of sites attempted

Notes

Supported by departmental funds. Study authors disclosed no potential conflicts of interest.

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Low risk

Assignment by a computer‐generated random number sequence.

Allocation concealment (selection bias)

Unclear risk

No details were mentioned.

Blinding of participants and personnel (performance bias)
All outcomes

High risk

All participants underwent induction of general anaesthesia (low risk of bias). The anaesthesiologist was aware of the allocated intervention before performing arterial catheterisation (high risk of bias).

Blinding of outcome assessment (detection bias)
All outcomes

Low risk

Endpoint of procedure was aspiration of blood from the distal end of the inserted cannula (unequivocal endpoint).

Incomplete outcome data (attrition bias)
All outcomes

Low risk

There were no missing data.

Selective reporting (reporting bias)

High risk

All planned outcomes were reported, but the results were not stratified according to the age groups to which participants were originally randomised (< 2 years, 2–5 years, > 5 years).

Other bias

Unclear risk

Study did not define what constituted lack of success in terms of time or number of attempts.

Study characteristics

Methods

RCT

Participants

Number: 118 radial arteries

Number per intervention

1. Ultrasound: 59 radial arteries

2. Palpation: 59 radial arteries

Inclusion criteria

1. Infants and small children

2. Weight 3–20 kg

Exclusion criteria

1. Skin erosions or haematomas at or near the insertion site

2. Visible recent catheterisation scars

3. Prominent differences in arterial pressure between left and right arms

Surgery/setting: elective cardiac surgery for congenital heart disease

Baseline characteristics:

1. Median age: 18.4 months (range 7–28)

2. Median weight: 8.1 kg (range 6.04–10.48)

3. Sex ratio: not reported

Interventions

Randomisation: right and left radial arteries were randomly assigned to cannulation by the ultrasound‐guided technique (ultrasound group) or the usual palpation technique (palpation group) via the envelope method. The ultrasound‐guided group included 28 right and 31 left radial arteries, whereas the palpation‐guided group included 31 right and 28 left radial arteries.

Intervention: US usage (SonoSite, Bothell, WA, USA) with a 2‐ to 7‐MHz linear array transducer in real time using short axis.

Control: palpation using the pulsation of the radial artery.

Co‐intervention: non‐invasive electrocardiogram, pulse oximetry and blood pressure monitoring. After induction of general anaesthesia, cannulation was attempted with standard 24‐G JELCO cannulas (Smith's Medical, Dublin, OH, USA). A pillow was placed under the wrist to keep the arm slightly extended. The insertion site was disinfected, and no local anaesthetic was used.

Experience of operator: trainees in anaesthesiology with > 3 years of clinical training and familiar with the ultrasound‐guided technique for central venous catheterisation in adults and children.

Outcomes

Primary study endpoints

1. Rate of successful cannulation on first attempt

2. Success rate after 3 attempts

Secondary study endpoints

1. Time to identification of the artery

2. Overall number of cannulation attempts

3. Incidence of complications

Notes

No information was provided regarding funding. Dr Sawa received royalties from The Reagents from the University of California. The remaining study authors disclosed that they had no potential conflicts of interest.

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Low risk

Quote: "The right and left radial arteries were randomly assigned to cannulation by the ultrasound‐guided technique (ultrasound group) versus the usual palpation technique (palpation group), using the envelope method."

Allocation concealment (selection bias)

Low risk

Quote: "The right and left radial arteries were randomly assigned to cannulation by the ultrasound‐guided technique (ultrasound group) versus the usual palpation technique (palpation group), using the envelope method."

Blinding of participants and personnel (performance bias)
All outcomes

High risk

All participants underwent induction of general anaesthesia before arterial line cannulation (low risk of bias). The anaesthesiologist was aware of the allocated intervention before performing arterial catheterisation (high risk of bias).

Blinding of outcome assessment (detection bias)
All outcomes

Low risk

Quote: "The procedure was classified as successful when the artery was cannulated and an arterial waveform was recorded."

Incomplete outcome data (attrition bias)
All outcomes

Low risk

Data available for all randomised participants.

Selective reporting (reporting bias)

Low risk

All outcomes were reported.

Other bias

Low risk

We identified no other sources of bias.

Study characteristics

Methods

RCT

Participants

Number: 74 radial arteries

Number per intervention

1. Ultrasound: 37 radial arteries

2. Palpation: 37 radial arteries

Inclusion criteria

1. Age < 12 months

2. Scheduled cardiac surgery

Exclusion criteria:

1. Signs of skin infection or a recent wound at or near the puncture site

2. Diagnosed abnormal peripheral circulation of the hand

3. Diagnosed vascular abnormality or radial arterial variation

4. Problem at the radial or ulnar artery sites

5. Haemodynamic instability 

Surgery/setting: cardiac surgeries for congenital heart disease

Baseline characteristics

Ultrasound

1. Mean age: 1.7 (SD 2.7) months

2. Mean weight: 4.8 (SD 1.9) kg

3. Sex ratio (male:female): 18:19

Palpation

1. Mean age: 3.5 (SD 3.5) months

2. Mean weight: 5.7 (SD 2.1) kg

3. Sex ratio (male:female): 24:13

Interventions

Randomisation: participants were assigned randomly to either a palpation‐guided group or an ultrasound‐guided group using computer‐generated numbers found in sealed envelopes.

Intervention: a linear ultrasound transducer in the short‐axis view was used in the US group. The least depth‐of‐field setting was 1.5 cm, and a 24‐gauge angiocatheter was inserted. The needle was advanced until a bright white dot of the needle tip was observed. The needle was then advanced, targeting the radial artery using an anterior or posterior puncture technique.

Control: palpation of the radial arterial pulse

Co‐intervention: general anaesthesia with inhaled sevoflurane, intravenous midazolam (0.15 to 0.3 mg/kg) and rocuronium (0.6 to 0.9 mg/kg)

Experience of operator: all ultrasound recordings and arterial catheterisations were performed by one of two anaesthesiologists (> 2 years of experience in paediatric cardiac anaesthesia and > 50 cases of ultrasound‐guided radial arterial catheterisation in paediatric patients).

Outcomes

Primary endpoints

1.  First‐pass success

2.  Success within 10 minutes

3. Total number of attempts

4. Total procedural time for successful catheterisation 

Secondary endpoints

1. Complications during the procedures (e.g. haematoma formation, arterial spasm or ischaemic signs) 

Notes

Supported by institutional resources. Study authors disclosed no potential conflicts of interest.

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Low risk

Quote: "Patients were assigned randomly to either a palpation‐guided group or an ultrasound‐guided group using computer‐generated numbers found in sealed envelopes."

Allocation concealment (selection bias)

Low risk

Quote: "The sealed envelope was opened by a physician just after induction of general anaesthesia."

Blinding of participants and personnel (performance bias)
All outcomes

High risk

All participants underwent induction of general anaesthesia prior to arterial catheterisation (low risk of bias). The anaesthesiologist was aware of the allocated intervention before performing arterial catheterisation (high risk of bias).

Blinding of outcome assessment (detection bias)
All outcomes

Low risk

Successful arterial cannulation is the endpoint of the procedure for both techniques (unequivocal endpoint).

Incomplete outcome data (attrition bias)
All outcomes

Low risk

No missing data.

Selective reporting (reporting bias)

Low risk

 An investigator recorded all procedures on video for analysis.

Other bias

Unclear risk

Participant age and height were significantly different between the 2 groups. The investigators set a time limit of 10 minutes.

Study characteristics

Methods

RCT

Participants

Number: 40 femoral arteries

Number per intervention

1. Ultrasound: 20 femoral arteries

2. Palpation: 20 femoral arteries

Inclusion criteria

1. Neonatal age

2. ASA score 3–4

3. Scheduled congenital heart surgery

Exclusion criteria

1.  Parents' refusal to participate in study

2.  Undetectable femoral arterial pulse 

3.  Haemodynamic instability

4.  Allergy to US gel 

5.  Emergency surgery 

Surgery/setting: paediatric cardiac surgery.

Baseline characteristics

Ultrasound

1. Mean age: 21 days

2. Mean weight: 3.5 Kg

3. Sex ratio (male:female): 14:6

4. Mean length: 51.4 cm

Palpation

1. Mean age: 18.3 days

2. Mean weight: 3.4 kg

3. Sex ratio (male: female): 14:6

4. Mean length: 51.2 cm

Interventions

Randomisation: participants were randomized using the envelope method to the US group or the palpation group.

Intervention: linear probe (5–12 MHz, Esaote, MyLab Six, the Netherlands) was used in the US group. After the transducer was placed in a sterile sheath, the femoral artery and vein were identified (short axis view). A 20 G needle was used to puncture the artery (out‐of‐plane technique). After adequate arterial flow was ensured, the guidewire (0.43 mm size and 200 mm length) was placed in the lumen of the vessel. The cannula was placed through the guidewire using the Seldinger technique, and the guidewire was removed.

Control: after palpation of the femoral artery, a 20‐G needle was used for arterial puncture. A guidewire (0.43 mm size and 200 mm length) was inserted in the lumen of the vessel. The catheter was sent over the guidewire using the Seldinger technique and the guidewire was removed.

Co‐intervention: induction of anaesthesia using 0.1 mg/kg midazolam, 2 mcg/kg fentanyl, 2–3 mg/kg propofol, and 0.6 mg/kg rocuronium. After orotracheal intubation, a pad under the pelvis in supine position was placed and the legs were positioned in 30‐degree abduction, and the knees were bent. Before the procedure, in both groups, the anterior‐posterior diameter of the femoral artery was measured at 1–2 cm distal of the ligament by using linear US probe in an out‐of‐plane technique. A 22‐G catheter was used for all cannulation.

Experience of operator: > 3 years' experience in paediatric cardiac anaesthesia and > 5 years' experience and certification of US use.

Outcomes

1. Time to successful cannulation (from skin puncture to blood aspiration; limited to 15 minutes)

2. Number of attempts (skin puncture considered an attempt; needle redirection not considered an additional attempt) 

3. Success on first attempt

4. Success rate (total successful cannulation after multiple attempts)

5. Number of cannulas used

6. Complications (haematoma, pseudoaneurysm, accidental vein puncture) 

7. Total cost of the procedure

Notes

The author received no financial support for the research, authorship or publication of the article.

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Low risk

Envelope method.

Allocation concealment (selection bias)

Low risk

Quote: "Assignments were contained in prepared opaque envelopes that were opened just before cannulation."

Blinding of participants and personnel (performance bias)
All outcomes

High risk

All participants underwent induction of general anaesthesia prior to arterial catheterisation (low risk of bias). The anaesthesiologist was aware of the allocated intervention before performing arterial catheterisation (high risk of bias).

Blinding of outcome assessment (detection bias)
All outcomes

Low risk

Aspiration of blood from the inserted cannula was the endpoint of the procedure in both techniques (unequivocal endpoint).

Incomplete outcome data (attrition bias)
All outcomes

Low risk

Low risk of attrition bias because only 3 children were removed after randomisation (because of the presence of hematoma at the site of operation due to previous interventions).

Selective reporting (reporting bias)

Low risk

All outcomes were addressed.

Other bias

Low risk

We identified no other sources of bias.

Study characteristics

Methods

RCT

Participants

Number: 30 radial arteries

Number per intervention

1. Ultrasound: 15 radial arteries

2. Palpation: 15 radial arteries

Inclusion criteria

1. Small children

Exclusion criteria

1. Not reported

Surgery/setting: major neurosurgery

Baseline characteristics

1. Age: 6 months–9 years; median age 28 months; mean age 40 (SD 33) months

   1. Ultrasound group: mean 40.3 (SD 34.9) months

   2. Palpation group: mean 39.6 (SD 32.5) months

2. Mean weight: not reported

3. Sex ratio: not reported

Interventions

Randomisation: coin toss

Intervention: the radial artery was first localised by ultrasound in its short cross‐section. The cannula was advanced toward the vessel at an angle of 45 degrees. When the cannula appeared to be within the vessel, the transducer was removed and catheterisation was accomplished.

Control

1. Palpation technique: the position and course of the artery were identified, the skin was repeatedly disinfected, and the cannula was inserted distally to the fingertip and was directed according to continued palpation.

2. Cross‐over to the other technique: after 3 failed cannulation attempts, the initial approach was changed to the alternative method

Co‐Intervention: a normovolaemic status was achieved using crystalloids given the night before the procedure. A linear transducer connected to an ultrasound system (Sonos 5000; Hewlett‐Packard, Andover, MA, USA) was used with a focal length positioned 1.8 cm to identify the radial artery. The cross‐sectional area of the artery was measured at the head of the radius with and without dorsiflexion of the hand by about 45 degrees. The transducer or the physician's fingertip was applied to the skin, and the radial artery was identified as the pulsating vessel. Following further local disinfection, the vessel was approached with standard 24‐G cannulas (Becton Dickinson, Helsinborg, Sweden) via 1 of the 2 techniques.

Expertise of operator: experienced personnel (> 20 paediatric arterial catheterisations)

Outcomes

1. Cross‐sectional area of the radial artery with or without dorsiflexion

2. Cannulation success rates with palpation and ultrasound techniques

3. Cannulation success rate on first attempt

4. Time for successful insertion of the catheter between palpation and ultrasound techniques (interval between skin puncture and successful intra‐arterial advancement of the catheter)

5. Total number of attempts at arterial cannulation with palpation and ultrasound techniques

6. Total number of technique switches

7. Rate of complications for palpation and ultrasound techniques

Notes

No information was provided regarding funding, and no conflicts of interest were declared.

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Low risk

Quote: "The technique to be used for radial artery puncture and insertion of the catheter was selected by tossing a coin: heads for ultrasound guidance and tails for palpation."

Allocation concealment (selection bias)

Unclear risk

No information.

Blinding of participants and personnel (performance bias)
All outcomes

High risk

All participants underwent induction of general anaesthesia prior to arterial catheterisation (low risk of bias). The anaesthesiologist was aware of the allocated intervention before performing arterial catheterisation (high risk of bias).

Blinding of outcome assessment (detection bias)
All outcomes

Low risk

Quote: "When the cannula appeared to be within the vessel, the transducer was removed and catheterization was accomplished."

Incomplete outcome data (attrition bias)
All outcomes

Low risk

No participants withdrawn.

Selective reporting (reporting bias)

Low risk

All outcomes were addressed.

Other bias

Low risk

We identified no other sources of bias.

Study characteristics

Methods

RCT

Participants

Number: 106 femoral arteries

Number per intervention

1. Ultrasound: 53 femoral arteries

2. Palpation: 53 femoral arteries

Inclusion criteria

1. Age < 12 years

2. ASA score 3 or 4

3. Scheduled cardiac surgery

Exclusion criteria

1. Emergency surgery

2. Haemodynamic instability

3. Allergy to the ultrasound gel

Surgery/setting: cardiac surgeries

Baseline characteristics

Ultrasound

1. Mean age: 37.9 months

2. Mean weight: 12.4 kg

3. Sex ratio (male:female): 33:20

Palpation

1. Mean age: 30.6 months

2. Mean weight: 10.6 kg

3. Sex ratio (male:female): 29:24

Interventions

Randomisation: participants were randomly assigned by randomised block design to femoral arterial catheterisation by the pulse palpation technique (palpation group) or femoral arterial catheterisation using ultrasound guidance (ultrasound group). Results of randomisation were concealed in sealed opaque envelopes and opened after participants' consent. Each operator was randomly assigned procedures in blocks of, where each block was composed of 2 ultrasound‐guided and 2 palpation techniques arranged randomly. Each participating operator was required to complete 2 blocks. In both groups, the first site of insertion was the left femoral artery. 

Intervention: the transducer was covered by a sterile sheath. The inguinal area was scanned immediately distal to the inguinal ligament and the femoral artery was identified. Using a short axis and an out‐of‐plane technique, and after visualisation of the artery, a metallic cannula was introduced and redirected until adequate arterial flow was obtained. The guidewire was introduced, and the catheter was slid over the guidewire.

Control: palpation technique. A metallic cannula was inserted, and after adequate blood flow a guidewire was inserted followed by the catheter.

Co‐intervention: after induction of anaesthesia, all participants were positioned supine with their legs in neutral position with a pad under the pelvis. In both the groups, the size of the cannula was 24/22 gauge for children weighing < 10 kg and 22 gauge for those weighing 10–40 kg. The study period was limited to 10 minutes.

Expertise of operator: clinical anaesthesia year 2 or 3 resident with minimal experience in paediatric femoral artery cannulation (no residents had previously performed either US‐guided or palpation‐guided femoral artery cannulation in paediatric patients > 5 times). 

Outcomes

Primary endpoint:

1.  Time taken for attempted cannulation by the resident at the first site of arterial puncture

Secondary endpoints

1. Number of attempts at arterial cannulation

2. Number of successful cannulations on first attempt

3. Success rate

4. Number of cannulae required for successful cannula insertion

Notes

The study was supported by the Department of Anesthesiology. No conflicts of interest.

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Low risk

Quote: "Patients were randomly assigned by randomised block design to one of the two groups. Results of randomization were concealed in sealed opaque envelopes and opened after patients’ consent".

Allocation concealment (selection bias)

Low risk

Quote: "To ensure balance between operators in each study procedure, each operator was randomly assigned procedures in blocks of four. Each block was composed of two ultrasound‐guided and two palpation techniques were arranged randomly. Once an operator participates, he or she was required to complete two blocks (i.e., each operator performed four ultrasound‐guided techniques and four palpation techniques)".

Blinding of participants and personnel (performance bias)
All outcomes

High risk

The anaesthesiologist was aware of the allocated intervention before performing arterial catheterisation.

Blinding of outcome assessment (detection bias)
All outcomes

Low risk

Quote: "Time to arterial cannulation is the primary outcome measured from the time of initial skin puncture until proper placement of the catheter that was confirmed by an arterial waveform seen on the monitor."

Incomplete outcome data (attrition bias)
All outcomes

Low risk

2 children excluded because the residents were unavailable to perform the procedures. However, no missing data for the remaining participants.

Selective reporting (reporting bias)

Low risk

All outcomes were addressed.

Other bias

Unclear risk

Investigators set time limit of 10 minutes.

Study characteristics

Methods

RCT

Participants

Number: 40 radial arteries

Number per intervention

1. Ultrasound: 20 radial arteries

2. Palpation: 20 radial arteries

Inclusion criteria

1. Age < 24 months

2. Elective surgical procedure with indication for indwelling arterial catheterisation

Exclusion criteria

1. Refusal of consent from parents or attending anaesthesiologist

2. Anticipated circulatory instability after anaesthesia induction 

Surgery/setting: not reported

Baseline characteristics

Ultrasound

1. Mean age: not reported

2. Mean weight: 6.14 kg (95% CI 4.9–7.4)

3. Sex ratio (male:female): not reported

Palpation

1. Mean age: not reported

2. Mean weight: 5.5 kg (95% CI 4.1–6.9)

3. Sex ratio (male:female): not reported

Interventions

Randomisation: participants were randomised to US guidance technique (intervention) or palpation (control) for radial artery cannulation.

Intervention: SonoSite M‐Turbo (SonoSite, Bothell, WA, USA) SLAX "hockey stick" ultrasound probe.

Control: palpation

Co‐Intervention: cross‐over with another technique was allowed after 3 failed attempts.

Experience of operator: all catheterisations were performed by anaesthesiology fellows who underwent practice with customised age‐specific forearm and femoral phantoms. 

Outcomes

Primary endpoints

1. Time to successful cannulation within 3 attempts

   1. Start time: when the palpating finger touches the participant's skin to feel for the arterial pulse (palpation method), or when the gel is applied to the skin (ultrasound) at the first intended cannulation site

   2. End time: when the arterial cannula was successfully placed

Secondary endpoints

1. Number of attempts at arterial cannulation 

2. Success rate

3. Number of attempted sites

4. Number of cannulas required for successful catheter insertion

5. Estimated cost of the procedure

6. Need for assistance from another anaesthesiologist

7. Cross‐over between techniques or rescue after the first operator was deemed to have failed with the assigned technique

Notes

Supported by departmental funds. Study authors disclosed no potential conflicts of interest.

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Low risk

Computer‐generated random number sequence.

Allocation concealment (selection bias)

Unclear risk

No information.

Blinding of participants and personnel (performance bias)
All outcomes

High risk

All participants underwent induction of general anaesthesia prior to arterial catheterisation (low risk of bias). The anaesthesiologist was aware of the allocated intervention before performing arterial catheterisation (high risk of bias).

Blinding of outcome assessment (detection bias)
All outcomes

Low risk

Successful arterial cannulation was the endpoint of the procedure for both techniques (unequivocal endpoint).

Incomplete outcome data (attrition bias)
All outcomes

Low risk

No missing data.

Selective reporting (reporting bias)

Low risk

All planned outcomes were reported.

Other bias

Low risk

We identified no other sources of bias.

Study characteristics

Methods

RCT

Participants

Number: 104 radial arteries

Number per intervention

1. Ultrasound: 52 radial arteries

2. Doppler: 52 radial arteries

Inclusion criteria

• Children

• Weight 3–12 kg

Exclusion criteria

1. Signs of skin infection or a wound near the puncture site

2. Abnormal circulation of the hand

3. Arterial puncture within previous month

4. Need for emergency surgery

Surgery/setting

Ultrasound

1. Cardiac: 36 (69%)

2. Non‐cardiac: 16 (31%)

Doppler

1. Cardiac: 39 (75%)

2. Non‐cardiac: 13 (25%)

Baseline characteristics

Ultrasound

1. Median age: 6.0 (range 2.0–9.0) months

2. Mean weight: 7.0 (SD 2.4) kg

3. Sex ratio: not mentioned

Doppler

1. Median age: 5.0 (range 2.0–9.0) months

2. Mean weight: 6.7 (SD 0.4) kg

3. Sex ratio: not mentioned

Interventions

Randomisation: randomised block design with opaque envelopes that were opened just before cannulation. Each operator was randomly assigned procedures in blocks of 4. Each block had a random arrangement of 2 US‐guided and 2 Doppler‐guided techniques. Participating operators had to complete 2 or 3 blocks.

Intervention: US (HD 11 XE; Andover, MA, USA) via a linear transducer (L15‐7io) was utilised to measure 3 times the diameter of the radial artery in the short axis view without dorsiflexion of the wrist. The field was then prepped and draped. A 24 G catheter (Jelco, Smith Medical International Ltd, Rossendale, UK) was advanced at a 15‐ to 30‐ degree angle until the tip of the needle was seen on the image and the artery collapsed and re‐expanded, or until blood appeared in the hub. The metal stylet was removed, and a wire was inserted through the catheter and was advanced into the artery via the Seldinger technique. If no flash of blood was seen after the stylet was removed, the cannula was withdrawn until blood flow was observed. The catheter was then replaced with a 22 G catheter (Cook Medical Inc., Bloomington, IN, USA) over a guidewire.

Control: Doppler‐assisted technique: the radial artery was located when the area of maximum flow (sound) was found with the Doppler probe (915 BL Doppler Ultrasound, 9 MHz, 1/4‐inch diameter, skinny pencil style; Parks, Las Vegas, NV, USA). The technique of cannulation was similar to the US group but using the Doppler‐assisted technique.

Co‐intervention: after anaesthetic induction, the participant's hand was secured on an armboard in a neutral position without a wrist roll.

Experience of the operator: clinical anaesthesia year 2 or 3 resident or cardiac anaesthesia fellow with minimal experience in US‐guided or Doppler‐assisted radial artery cannulation in paediatric patients (< 5 times).

Outcomes

1. First‐attempt success rate (%)

2. Success within 10 minutes (%)

3. Number of attempts (stratified as 1, 2, 3 or more)

4. Adverse events (haematoma and ischaemia)

Notes

Supported by departmental funds. Study authors disclosed no potential conflicts of interest.

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Low risk

Quote: "Participants were assigned by randomised block design to the Doppler‐assisted technique group or the US‐guided technique group. To ensure balance between operators for each study procedure, each operator was randomly assigned procedures in blocks of 4. Each block had a random arrangement of 2 US‐guided and 2 Doppler‐guided techniques. Once an operator participated, he or she was required to complete 2 to 3 blocks."

Allocation concealment (selection bias)

Low risk

Quote: "Assignments were contained in prepared opaque envelopes that were opened just before cannulation."

Blinding of participants and personnel (performance bias)
All outcomes

High risk

All participants underwent induction of general anaesthesia prior to arterial catheterisation (low risk of bias). The anaesthesiologist was aware of the allocated intervention before performing arterial catheterisation (high risk of bias).

Blinding of outcome assessment (detection bias)
All outcomes

Low risk

An arterial waveform is seen on the monitor after the catheter is connected to a transducer (unequivocal endpoint).

Incomplete outcome data (attrition bias)
All outcomes

Low risk

Quote: "Two cases were counted as failures according to the intention‐to‐treat principle: (1) an unintentional femoral arterial cannulation while the faculty was trying the femoral venous cannulation before the radial arterial cannulation was attempted, which was allocated to the US‐guided technique, and (2) unavailability of the operator to perform the procedure once the participant had been randomised to the Doppler‐assisted group."

Selective reporting (reporting bias)

Low risk

All outcomes were addressed.

Other bias

Unclear risk

Possible effect of confounding variable. Quote: "Further investigation is warranted if any haemodynamic manipulation (i.e. volume load or vasopressor administration) could enlarge the size of a radial artery and thus improve the success rate of cannulation."

The trial was prematurely terminated. Quote: "After the first 50% of patients' enrolment (104 patients), the departmental research committee decided to terminate the study because of low accrual."