Arterial cannulation in one of the frequently performed procedure under anaesthesia in cases with expected massive blood loss, large hemodynamic changes and frequent blood gas sampling in perioperative period (1). Radial artery is preferred over other arteries as the hand has dual arterial supply from radial and ulnar artery (2).

Ultrasound (US) can be used for guiding arterial cannulation in difficult cases. US guided radial artery cannulation has shown to have a higher first attempt success rate compared to palpation method (3–6). Two approaches have been used for US guided arterial cannulation: short axis out-of-plane (SAX-OOP) and long axis in-plane (LAIP) approach. In SAX-OOP approach, US image of the shaft or the tip of the cannula will appear as hyperechoic dot; whereas in LAIP approach whole path of needle including the tip can be visualized. LAIP technique has been shown to be better than palpatory method of arterial cannulation (5). Moreover, previous randomized controlled trials (RCT) comparing these two US guided techniques demonstrated higher first attempt success rate with LAIP technique for radial artery cannulation (7,8).

However, in order to overcome the problems of SAX-OOP approach, recently a modified short axis technique using dynamic needle tip positioning (DNTP) was introduced. It has shown to have higher first attempt success rate and lesser posterior arterial wall puncture compared to palpation method (5) and SAX-OOP method (6).

A previous study comparing DNTP with LAIP demonstrated higher first attempt success rate with DNTP technique in adult patients for cardiac surgery. However, cannulating the radial artery in elderly population is difficult due to age related vascular changes and tortuosity of the vessels (9) and no studies have compared these two techniques in elderly patients.

Therefore, we planned to conduct a study to compare the US guided DNTP versus LAIP technique in elderly patients. We hypothesise DNTP technique has higher first attempt success rate in elderly compared to LAIP technique for radial artery cannulation.

Methodology

Aims and Objectives

Aim – To compare ultrasound guided dynamic needle tip positioning and longitudinal axis in-plane technique of radial artery cannulation

Study setting and design:

After ethics committee approval and informed written consent from the participants, this randomised controlled trial will be conducted in the Department of Anaesthesiology Pain Medicine and Critical Care. The protocol will be registered in the clinical trial registry of India (www.ctri.nic.in).

Primary objective – First attempt success rate between the two techniques

Secondary objectives –

1. No of attempts and redirections

2. Time to successful cannulation

3. Posterior wall puncture

4. Hematoma formation

Inclusion criterion

1.     Patients undergoing general anaesthesia and requiring arterial cannulation

2.     ASA status I, II or III

3.     Age 65 years or older

Exclusion criterion

1.     Patient’s refusal to participate

2.     Hemodynamically unstable

3.     Allen’s test positive

4.     Hematoma or local site infection

5.     Known peripheral vascular disease or Raynaud’s phenomenon

Randomization

180 patients will be recruited and randomised using computer generated serial number technique into two groups

Group A – DNTP group

Group B – LAIP technique

Methods

After institutional ethics committee approval, the patients will be recruited based on inclusion and exclusion criterion. The patients will be randomly allocated to two groups. ASA standard monitors including ECG, noninvasive blood pressure and saturation probe will be attached after shifting the patients to the operation theatre (OT). The anaesthesiologist will select the right or left radial artery depending on the surgery site, location of blood pressure cuff and his/her preference. Allen’s test will be performed to confirm the patency of superficial and deep palmar arches. The wrist will be placed on a soft roll to achieve a mild dorsiflexion. The diameter of radial artery will be measured at the level of radial styloid process. The depth of radial artery will also be measured. We will be using a vascular transducer with small footprint (8–13 MHz) and a two‑dimensional SonoSite Edge2 ultrasound machine (SonoSite Inc. Bothell, WA). Depending on the randomisation group, further procedure will be carried out.

Intervention in group A – After identifying the artery in a SAX view a 20 G arterial cannula will be inserted in an out-of-plane (OOP) approach keeping the artery in the centre of the screen. The needle will be advanced in the midline till a hyperechoic dot will be visible in the centre of the screen. Then only the probe will be moved proximally without moving the needle till the hyperechoic dot just disappears. Next, keeping the probe fixed at that place, needle will then be advanced towards the radial artery till hyperechoic dot reappears. Once the needle punctures the radial artery, the probe will be moved further proximally leaving the needle tip in the centre of the radial artery. After confirmation that sufficient length of the needle tip remains in the radial artery, the outer catheter will be pushed to the end, and the stylet will be removed.

Intervention in group B – After identifying the artery in the LAX a 20G arterial cannula will be inserted keeping the longitudinal section of artery in view. The needle will be advanced in an in-plane (IP) approach visualising the whole path of the needle including the needle tip till the radial artery will be punctured. Once the radial artery is punctured the outer catheter will be pushed to the end and the stylet will be removed.

An attempt will be defined as the needle penetration from the skin. The time to cannulation will be taken from needle puncturing the skin to appearance of an arterial waveform on the monitor. This will be counted as the successful attempt. The procedure will be declared failed if the anaesthesiologist fails to cannulate the artery even after 5 attempts. The cannulation time of the successful attempt will be recorded. Hematoma will be defined by localised swelling on the puncture site.

The successful cannulation in both the groups will be recorded once the arterial waveform is obtained on the monitor. All the cannulations will be performed by consultant anaesthesiologists who performed at least more than 50 US guided radial artery cannulations by each of the techniques (5).