Gilbert 1995.

Methods	Prospectively randomized controlled trial (RCT) Randomization method: no details in the text
Participants	76 consecutive, consenting adult patients with preexisting obesity or coagulopathy requiring central venous access. Obesity was defined as weight greater than 130% of ideal body weight for height and body mass index greater than 28. Coagulopathy was defined as a platelet count less than 50,000 thrombocytes/mm3 or an increase of greater than 30% above maximum laboratory control value for 1 or more of the following variables: prothrombin time; partial thromboplastin time; activated clotting time; or template bleeding time Inclusion and exclusion criteria clearly defined in the text Treatment and control groups adequately described at entry. A minimum of 4 admission details were described. 6 admission details was described (sex, weight, height, BMI, age, anatomical distinctiveness) Participants awake and anaesthetized    Operators: number: no details   Experience: junior house staff, who were relatively inexperienced in using either technique, performed all cannulations under the direct supervision of attending faculty. They were instructed in ultrasound device use by listening to a prepared 5‐minute audiotape depicting arterial and venous signals. Years of postgraduate training and experience in control or ultrasonic techniques were similar among junior house staff for both groups of participants. The average operator was in the third postgraduate year and had greater familiarity with use of the control technique than the ultrasound technique
Interventions	Technique: LM: high/central approach, initially performing venipuncture with a 22‐gauge finder needle vs US: SmartNeedle   LM Unclear whether direct or indirect puncture Technique standardized: unclear Head up (anti‐Trendelenburg); down (Trendelenburg)/flat; head rotation no details; only positioning was similar for all participants Seldinger technique: catheter over needle, no details Vessel and side: IJV no details US Direct puncture Technique standardized: unclear Head up (anti‐Trendelenburg); down (Trendelenburg)/flat; head rotation no details; only positioning was similar in all participants Seldinger technique Vessel and side: IJV no details
Outcomes	Overall success rate (N, %) Failure rate (N, %) Number of attempts until success (N, SD) Complication rate: total, arterial puncture, haematoma formation (N, %) Carotid artery puncture was defined as inadvertent placement of any size needle or catheter into a neck vessel that yielded bright red or pulsatile blood Haematoma formation was defined as the appearance of visible neck swelling at the site of cannulation (or attempted cannulation) and distortion of existing anatomical landmarks within 1 hour of study Time to successful cannulation (seconds): Time for cannulation was recorded with a finder (control) or cannulation (ultrasound) needle, beginning with the initial skin puncture and ending with successful placement of a Seldinger wire, or until a given technique failed Success with attempt number 1 (N, %) Success rate after cross‐over (N, %)
Notes	Cross‐over landmark‐guided puncture and ultrasound‐guided puncture 3 cannulation attempts were allowed with the initial randomized technique before cross‐over to 3 attempts with the alternative technique. The study was discontinued if more than 6 total attempts were required LM: cross‐over after failure of the initial technique 17 LM → 12 (70.6%) success with Doppler US: cross‐over after failure of the initial technique 5 Do → 2 (40%) successes with LM
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Randomization method: no details (B)
Allocation concealment (selection bias)	Unclear risk	Randomization method: no details (B)
Blinding (performance bias and detection bias) All outcomes	Unclear risk	Subject blinded: Unclear__X__ Physician blinded: No__X__ Outcome assessor blinded: Unclear__X__
Incomplete outcome data (attrition bias) All outcomes	Low risk	Outcomes of participants who withdrew or were excluded after allocation were EITHER detailed separately OR included in an intention‐to‐treat analysis OR the text stated no withdrawals
Selective reporting (reporting bias)	Low risk	No
Other bias	Low risk	Participant selection: Yes _X_ Withdrawals: No _X_ Postrandomization exclusion: No _X_ Intention‐to‐treat analysis: Yes _X_
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Subject blinded: Unclear__X__ Physician blinded: No__X__
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Outcome assessor blinded: Unclear__X__
Treatment and control groups were adequately described at entry.	Low risk	Yes