Randomized Controlled Trial of Ultrasound versus Palpation
Method for Arterial Cannulation in Infants Less Than 24
Months of Age
Tracy YS Tan1, Jens AK Petersen2, Xiuyan Zhao3 and Katherine L Taylor4*
1Department of Anesthesia, Kandang Kerbau Hospital, Singapore City, Singapore
2Department of Anaesthesia, Aarhus University Hospital, Aarhus, Denmark
3Department of Biostatistics, Hospital for Sick Children, Toronto, Canada
4Department of Anesthesia, Hospital for Sick Children, Toronto, Canada
K L Taylor, Department of Anesthesia, Hospital for Sick Children, 555 University Avenue , Toronto, Canada,M5G 1X8, Tel: 1 416
813 7445; Fax: 416 813 7543; E-mail:
Received: February 19, 2015; Accepted: April 15, 2015, Published: April 15, 2015,
Citation: Tan TYS, Petersen JAK, Zhao X, Taylor KL (2015) Randomized Controlled Trial of Ultrasound versus Palpation Method for
Arterial Cannulation in Infants Less Than 24 Months of Age. SOJ Anesthesiol Pain Manag, 2(2): 1-3.
Introduction: Ultrasound guided peripheral arterial
cannulation may increase success as the small diameter vessel
can be visualized. Fewer attempts at arterial cannulation may
reduce local vessel damage. However even the current small
ultrasound probes provide additional bulk in a small area and
palpation method may be preferred.
Aim: To determine if ultrasound guided peripheral arterial
catheter insertion results in fewer attempts, shorter time to
cannulation and cost savings compared to palpation method
in children <2 years of age.
Methods: Patients ≤ 24 months scheduled for elective
surgical procedures where arterial cannulation was planned
were eligible for recruitment. Forty patients were randomized
to receive either Ultrasound Assisted (US) or palpation method.
The primary endpoint was time to successful cannulation
between two groups using intention to treat analysis. After 3
failed attempts, providers could switch to alternative method.
Secondary endpoints were number of attempted sites, number
of attempts and cost of equipment.
Results: Average weight of patients was 6.14 kg (95% CI
4.9-7.4 kg) for the US group and 5.5 kg (95% CI 4.1-6.9) for the
palpation group. There was no age difference between groups.
The initial randomized method was successful in 33/ 40
patients (17/ 20 Ultrasound and 16/ 20 Palpation method).
Crossover to the other method resulted in an additional 4
ultrasound successes and 3 palpation successes. There was no
difference in technique for rates of initial randomized method
of success or time to successful insertion. Cost savings in
disposable equipment were demonstrated.
Conclusions: For infants and small children, ultrasound
and palpation methods for arterial cannulation are similar
with respect to time to secure arterial access.
Keywords: Infant; Vascular Access device; Palpation;
Ultrasound; Costs and Cost Analysis; Time
Arterial cannulation is a commonly performed invasive
procedure in the operating room and intensive care unit.
Traditionally, the artery is located by palpating the pulse of the
patient. The catheter may not pass smoothly into the artery
despite apparent blood return on initial puncture; resultant
hematoma or arterial spasm hinders subsequent attempts.
Furthermore, the pulse may be weak or absent in patients with
hypotension, edema, obesity or local thrombosis due to previous
arterial cannulation in the same location. The radial artery in
children has a cross-sectional area of 1-4.2mm,  i.e. an inner
diameter of 0.5-1.2mm . Arterial catheter insertion can be
challenging in the best of hands.
While ultrasound (US) is being used with increasing frequency
for central venous access, fewer clinicians are familiar with USguided
arterial cannulation. In adults, US was found to improve
successful arterial cannulation at first attempt, thus decreasing
the time to establish an arterial cannulation . Schwemmer
reported similar results in a small study in children (n=30,
mean age 40 months) . However, Ganesh et al.  reported
no significant effect of US guidance compared with the palpation
technique in a larger study of older children (n=152, mean age
Arterial cannulation in small children is difficult, with smaller
arterial diameter and greater subcutaneous fat. The bulk of
current US probes may hinder arterial catheter insertion. Our
null hypothesis is that US does not facilitate arterial cannulation
in small children compared with the palpation method.
Materials and Methods
This trial was registered with www.clinical trials.
gov protocol # 1000030723. After Research Ethics Board
approval and parental informed consent, children <24 months
undergoing elective surgical procedures where indwelling arterial catheterization was indicated were randomized into
Palpation Method (PM) (standard practice) or US (group US)
(www.randomizer.org). Arterial cannulation was performed
after induction of anesthesia. If not accomplished by the initial
randomization method after three attempts, the anesthesiology
fellow was able to change to the other technique (Figure 1).
Patients were excluded for the following reasons: refusal of
consent from parents or attending anesthesiologist, anticipated
circulatory instability after anesthesia induction such as those
with pulmonary hypertension (defined as estimated pulmonary
arterial pressure ≥66% of systemic blood pressure) or severe
heart failure were also excluded. The patients were recruited
over 6 months. The primary endpoint was time to successful
cannulation using the primary randomization method. Secondary
endpoints were number of attempted sites, number of attempts
by practitioner and estimated cost of the procedure. An “attempt”
was defined as a forward movement of the needle with the intent
of hitting the artery. ‘Time to successful cannulation’ began
when the palpating finger touches the patient’s skin to feel for
the arterial pulse (Palpation Method- PM) or the gel is applied
to the skin (Group US) at the first intended cannulation site and
completed when the arterial cannula was successfully placed.
If fellows were unable to cannulate withint 3 attempts, staff
anesthesiologists were permitted to attempt insertion.
All anesthesiology fellows in the department were invited to
participate in the study. To facilitate learning US-assisted arterial
cannulation, each of them underwent practice with customized
age-specific forearm and femoral phantoms using Sonosite
M-Turbo (Sonosite,Wash,USA) SLAX “hockey stick” probe until
self-reported comfort with the technique before actual patient
recruitment was commenced. Each fellow could use an axial or
longitudinal approach and each received a new piece of ‘skin’ for
each practice session with the phantom to avoid following the
defined ‘track’ of previous attempts (Figure 2). Cannulation was
observed and time recorded by the same observer (TT) for all the
recruited patients using the same stopwatch.
Descriptive statistics (means and standard deviation for
continuous data and proportions for categorical data) were used
to summarize the characteristics of the study population. Chi
squared or Fisher exact test were used for categorical data. The
time to arterial cannulation in this age group was not known a
priori therefore no power calculations were possible.
Fifty patients were approached with 40 obtaining both
parental and treating anesthesiologist’s consent. Average weight
of patients was 6.14 kg (95% CI 4.9-7.4 kg) for the US group and
5.5 (95% CI 4.1-6.9) for the palpation group. There was no age
difference between groups. Cannulation of the artery within 3
attempts was successful in 85% (17/20) of the ultrasound group
and 80% (16/20) of the palpation group (chi squared p=0.67).
Mean ultrasound guided arterial cannulation within the first
three attempts was shorter (7.8 minutes) than the palpation
Figure 1: Study Procedure.
Figure 2: The training model: A new piece of “skin” is applied after each
After three attempts, unsuccessful cannulation in the primary
randomization method was allowed to switch to the alternate
method if desired. All patients eventually received an arterial
line. Of note in 25/ 40 patients required 4 or more attempts. In
the palpation group, 13 had more than 4 attempts, with 4/13
obtaining success using ultrasound. In the ultrasound group 12
patients had more than 4 attempts with 3 obtaining success. The
first attempts were performed amongst 7 fellows in pediatric
anesthesia with 6 staff operating as the ‘rescue’ proceduralist.
In both groups, 9/20 patients had successful cannulation after
attempting at 2 or more sites. There was no difference in method of
cannulation between fellows operators p=0.26 or staff operators
p=0.31, no difference in time to success p=0.76 and no difference
according to patient surgical condition p=0.27. For the entire
sample including crossovers, there was no difference for mean
time to success (Ultrasound 10.5 minutes palpation 11.7 minutes
p=0.73). Minor disposable cost savings were demonstrated in the
US group (Table 1).
Table 1: Disposable cost comparison in CAD
Randomized to PM group
Randomized to US group
Total number of cannulas
Total cost for cannulas
Total number of chlorhexidine sticks
Total cost of chlorhexidine sticks
We demonstrated cost savings to our hospital but no
significant time or operator determined difference in ultrasound
versus palpation method. There are mixed results from ultrasound
arterial cannulation in the literature, with reduced time to
success in adults  and in older children by Consultant level
proceduralists . Our population is younger and coincides with
the peak time for difficulty with cannulation, due to the adiposity
in subcutaneous tissues. The fellows studied were considered
inexperienced in both techniques as arterial cannulation is small
children is infrequent and usually performed at specialized
children’s hospitals. Success with ultrasound in small children
has been demonstrated for peripheral venous cannulation .
The classical palpation technique teaches dorsiflexion of
the wrist to stabilize the vessel although ultrasound imaging
has demonstrated that in this position the cross sectional area
of the vessel is reduced and therefore reduces the likelihood
of successful cannulation. We allowed the staff inserting the
cannulas to use their preferred wrist positioning and preferred
insertion technique (transfixing vessel, wire introduction after
successful “flashback” of blood ) and timed the completed event
as the time when the cannula was completely in the artery. This is
a more accurate reflection of “real world practice”. We encounter
proceduralists of differing experience in our university affiliated
teaching hospital and felt that identification of a superior
technique for arterial cannulation in small infants in real world
conditions is clinically valuable. The first order proceduralists
were fellows training in pediatric anesthesia.
Ganesh et al.  found no significant improvement in
arterial cannulation by personnel inexperienced in ultrasound
technique cannulating older children. Our trainees practiced on their individual phantoms until they reported comfort with the
technique prior to demonstrating on patients and have most
experience with ultrasound guided central line insertion in
adults prior to working in our hospital. They have had limited
pediatric arterial cannulation practice prior to their fellowship
and therefore no dominant preferred technique.
In conclusion, we find no difference in time to successful
cannulation with either technique and no operator defined
characteristics determining greater likelihood of success. We
demonstrated some cost savings of disposable equipment.
Ultrasound capital costs are not included in this calculation as
we believe many centers providing care for small infants who
require intraoperative invasive arterial monitoring would have
access to such equipment.
The study pertaining to this manuscript has satisfied the
Hospital for Sick Children Research Ethics Board guidelines (REB
Centre of Image-Guided Innovation and Therapeutic
Intervention, Hospital for Sick Children
The study was funded by departmental resources. There are
no disclosures to report.
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