Denys 1993.

Methods	"… sequential protocol was used in this study. Since we have a similar number of procedures each week, the ultrasound device was used one week and the landmark technique was used the next week. This was continued until we had 302 patients in each group. Thereafter, the ultrasound technique was used exclusively in an additional 626 patients. There was no provision for crossover in this study design. Because many patients had more than one procedure, it was possible that the same patient was cannulated using a different technique on separate occasions"
Participants	"… evaluated an ultrasound‐guided method in 302 patients undergoing internal jugular venous cannulation and compared the results with 302 patients in whom an external landmark‐guided technique was used. Ultrasound was used exclusively in an additional 626 patients. Patients undergoing internal jugular venous cannulation as part of a cardiac catheterization or placement of a central venous line (N =1,230) were studied" Inclusion and exclusion criteria not clearly defined in the text Treatment and control groups not adequately described at study entry 2 admission details described (sex, age) Participants awake Operators: number: 29. 15 operators performed fewer than 20 procedures (range, 1 to 19), and 14 operators performed more than 20 (range, 20 to 288) Experience: All cannulations were performed by operators with extensive experience in landmark‐guided internal jugular vein access, including attending cardiologists and cardiology fellows
Interventions	Technique: LM: no details, finder needle used vs US: ultrasound with 7.5‐MHz resolution (SiteRite scanner) with needle guide probe wrapped in a sterile plastic bag ((short axis) see typical image in the article) LM Unclear whether direct or indirect puncture Technique standardized: unclear Head up (anti‐Trendelenburg); down (Trendelenburg)/flat; head rotation no details Seldinger technique Vessel and side: IJV no details US Direct puncture Technique standardized: unclear Head up (anti‐Trendelenburg); down (Trendelenburg)/flat; head rotation no details Seldinger technique Vessel and side: IJV, RIJV 96.4% (N = 894), LIJV 3.6% (N = 34) because IJV absent or very small
Outcomes	Overall success rate (N, %) Failure rate (N, %) Number of attempts until success (N, SD) Complication rate: total, arterial puncture, local bleeding, haematoma formation, cardiac complications, malpositioned catheter tips, rate of catheter‐related infection, mortality, rate of other complications (thrombosis, embolism, haematomediastinum and hydromediastinum, haematothorax and hydrothorax, pneumothorax, subcutaneous emphysema, nerve injury) (N, %) Time to successful cannulation (seconds): time between penetration of the skin and aspiration of venous blood into the syringe. When multiple sticks were required, only the time when the needle was on the skin or was advanced was taken into account Success with attempt number 1, 2  (N, %)
Notes	No cross‐over landmark‐guided puncture or ultrasound‐guided puncture
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	High risk	Sequential protocol was used in this study
Allocation concealment (selection bias)	High risk	Sequential protocol was used in this study
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	Yes
Other bias	Unclear risk	Participant selection: No _X_ Withdrawals: Unclear _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.	Unclear risk	No