Clinical Trial Details
— Status: Completed
Administrative data
| NCT number |
NCT03535311 |
| Other study ID # |
18/WA/0117 |
| Secondary ID |
236837 |
| Status |
Completed |
| Phase |
|
| First received |
|
| Last updated |
|
| Start date |
May 21, 2018 |
| Est. completion date |
December 31, 2021 |
Study information
| Verified date |
March 2022 |
| Source |
Cardiff and Vale University Health Board |
| Contact |
n/a |
| Is FDA regulated |
No |
| Health authority |
|
| Study type |
Observational
|
Clinical Trial Summary
Insertion Length of Umbilical Catheters
Umbilical catheters, inserted through the umbilical artery and vein of newborn babies at
birth, are crucial in neonatal care of sick babies. They allow delivery of medication and
fluids and to provide access for blood sampling and blood pressure monitoring. Incorrect
positioning of the catheter tip due to under- or over-insertion length can lead to
significant complications in newborn infants. Currently, several methods are used to estimate
insertion length of umbilical catheters based on one of two beliefs; that the insertion
length of the umbilical catheter is proportional to either the infant's birth weight or an
external length measurement.
Several research studies have identified that existing methods often result in incorrect
positioning of umbilical catheters, with studies showing a variable range of proportions of
umbilical lines being correctly or incorrectly placed.
In particular, formulas for predicting umbilical venous catheter (UVC) length have been shown
to be particularly unreliable.
The investigators propose a new observational study which uses a novel but easy-to-measure
external length measurement, the sternal notch (upper end of breast-bone) to umbilicus (upper
margin of belly-button) length, along with other clinical information to develop a more
reliable formula for estimating the insertion length of umbilical venous and arterial
catheters to an appropriate length.
Our study population will include newborn babies admitted to the neonatal unit requiring
umbilical venous (UVC) and/or arterial catheterisation (UAC) over a two-year period.
Demographic information will be recorded for each child and once position has been confirmed,
the new external length will be measured. New formulae for estimating required insertion
length will be developed using statistical (regression) analysis.
Description:
Introduction
Umbilical catheters, both arterial (UAC) and venous (UVC), are an integral part of neonatal
care to provide access for blood sampling and blood pressure monitoring, and to allow for the
delivery of intravenous medication and fluids. It is important to ensure the correct position
of the catheter tip on first attempt to minimise additional handling, further radiological
exposure and risk of hospital-acquired infection. Other complications of malposition of the
catheters include injury of surrounding structures, false passages, bleeding, and injury to
other organs including the heart, the liver, and nerves. In one study, the most common
complication with umbilical venous catheters was incorrect position.
The British Association of Perinatal Medicine (BAPM) advise that the ideal placement of a UVC
should be at the thoracic 8-9 (T8-9) vertebrae (backbone) outside of the heart shadow, with
those being placed below T10 being at high risk of extravasation injury. The UAC should lie
in a high position above the level of the diaphragm in the descending aorta and below the
subclavian artery. This correlates to being positioned between the upper border of T6 and the
lower border of T10 with T8 being the ideal position. Currently, the recommended method to
confirm the position of umbilical catheters is by radiological imaging in the form of
antero-posterior chest and abdominal x-rays.
Prior to insertion of umbilical catheters, it is routine practice to calculate the estimated
length required for suitable placement. Currently, there are several methods for calculating
length which are primarily based on one of two measurements; birth weight or an external
length measurement. In 1966, Dunn identified in a post-mortem study of 50 newborn babies that
the length of the catheter required correlated to external length measurements such as total
body length and shoulder to umbilicus length. This study introduced a series of scatter
graphs to estimate the length of UACs and UVCs in the clinical setting using these external
length measurements. However, the external length proposed by the study, the
shoulder-umbilical length, was not based on fixed anatomical landmarks, leading to potential
errors. More importantly, the target placement for the UVC was in the heart chamber, which is
now an unacceptable position. In addition, these catheters were often performed in an
emergency setting with limited access to the graphs. Some of the external measurements were
potentially affected by increased flexor tone of newborn infants and variation in methods
used leading to inconsistencies, particularly with shoulder to umbilicus length.
In view of limitations of external length measurements, Shukla et al identified a formula
using body weight to calculate the required length of catheter for insertion.
Retrospectively, their study involved 43 neonates with a UAC and 10 neonates with a UVC in
suitable positions. They generated mathematical formulae based on birth weight and length of
UVC and UAC; UAC length in centimetres was = (3 x birthweight in kg + 9) divided by 2 + 1 and
UVC length in centimetres was ½ x UAC insertion length +1cm. Prospectively, they implemented
their formulae to calculate the required length of insertion of 26 UACs and 16 UVCs of which
all were in acceptable positions. However, there was no explanation in the paper as to how
the final formula was derived, as this was different from the original statistical analysis.
The authors also correctly cautioned about using this formula in babies who are small- or
large-for-dates, as the formula would over- or under-estimate the length in such cases.
However, this formula is widely used currently, leading to erroneous results.
Evidently, these were both small studies and subsequently there have been multiple studies
evaluating these two methods in the clinical setting in larger populations. In 2010, Verheij
et al compared both the Dunn and Shukla methods in 153 patients in a single-centre
prospective cross-sectional study in the Netherlands. The authors reported that the existing
two methods often led to high positions of umbilical catheters, particularly UVCs. The Shukla
method has more high-positioned UVCs (75% compared to 57% with the Dunn method, p<0.05) and
the Dunn method has more highly placed UACs (34% compared to 13% in Shukla group, p<0.05).
Furthermore, in both groups, with UVCs there was poor accuracy with correct positioning (24%
in Shukla group and 41% in Dunn group, p<0.05) to reach a correct position which was more
accurate with UAC placement (up to 87% correctly placed in Shukla group and 63% in Dunn
group, p<0.05).
A randomised control trial by Kieran et al in 2016 also compared the Dunn and Shukla methods
in a tertiary neonatal unit in Ireland. The neonates were randomised and stratified according
to weight with the outcome assessor blinded. There was no significant difference between
correctly sited UVCs between the two methods however the overall rate of correct placement
was low (28% in Dunn group compared to 31% in Shukla group, p value 0.826). The Shukla group
was more reliable in UAC insertion with 91% in a correct position compared to 50% of the Dunn
group (p< 0.001) which was consistent with the study by Verheij et al.
With particular reference to UVC insertion length, the Shukla formula was found to have a
higher rate of over-insertion as previously mentioned. Verheij et al proposed a revised
Shukla formula by removing the additional 1cm from the original formula; (3 x birthweight BW
in kg + 9)/2 cm. This study of 185 neonates compared this revised formula to the original and
found higher rates of correct placement their revised formula (43% compared to 26%, p<0.05).
The rate of over-insertion improved with their revised formula (54% versus 73% in Shukla
group, p<0.01) with no difference in under-insertion. However, this study was not randomised
and their revised formula still resulted in 56% of UVCs being incorrectly positioned on
x-rays. This formula was later compared with the Dunn and original Shukla methods for UVC
insertion by Mutlu et al. They found that of 91 successfully inserted UVCs, only 56% were
inappropriately positioned and there was no statistical difference between the three groups,
highlighting the poor methods which exist for UVC length estimation.
Although insertion rates for UACs are often more successful than for UVCs, both Dunn and
Shukla only studied low numbers of very low birth weight (VLBW) infants and there has been
consistent over-insertion of UACs with the Shukla formula. In view of this, Wright et al
proposed a new formula (UAC length in cm = 4 x birth weight in kg + 7) for the insertion of
UACs. When compared with the Dunn method in all gestations, 83% UACs were correctly sited
with the Wright formula compared to 61% with the Dunn method (p=0.007). This was
statistically significant in the term group but not the preterm infant group. 90% were
correctly inserted in the preterm group with the Wright formula.
However, when Lean et al compared 11 different formulae for UAC insertion length, they found
a lower predicted success rates (57.3%) with birth weight related formulae like the Wright
formula compared to external length measurement formulae. In this study, the formulae chosen
depended on the clinician inserting the catheter and calculations were predominantly
theoretical to compare the result with a predefined length required for acceptable placement.
All methods proposed so far are based on a fundamental assumption: that internal lengths of
vessels are proportional to an external body measurement. Many formulas have used birthweight
as an easily accessible measurement to estimate internal length. However, this assumption is
inherently flawed, especially when looking at weight and length proportions of newborn
infants at various gestations. Centile charts plotting birthweight and length seem to be
proportional at lower gestations, but become clearly disproportionate closer to term (when
the fetus gains majority of its birthweight). Thus, formulas which were prepared using a
mixture of preterm and term infants would result in estimated lengths which are likely to be
too long for preterm infants and too short for term infants. In addition, infants who are
born small or large for a particular gestation would face similar problems as well. As
birthweight does not seem to be proportional to length, it is unlikely to be the ideal
external measurement for estimating internal length.
On the other hand, an external length measurement is more likely to be closely correlated
with internal (vessel) length as it does not suffer from the above problems. Dunn's formula
used this principle to create the nomogram. However, the external measurement he proposed was
not based on fixed anatomical landmarks. This has probably contributed significantly to the
malposition of catheter tips in the above studies.
From the current literature, it is evident that umbilical catheters, both arterial and
venous, are often incorrectly positioned when using existing methods for calculating required
length for correct placement. There is a wide range of different success rates with
positioning of these umbilical catheters with lower rates for UVC length estimation. The
investigators propose that a new formula, based on an external length measurement between two
fixed, easily accessible anatomical landmarks, and adjusted for gestation, is urgently needed
to improve accuracy of placement of umbilical catheter.
The investigators propose a study which uses a novel external length measurement, the sternal
notch to umbilicus length, to develop a new formula for the insertion of UVCs and UACs. This
measurement is less affected by the normal newborn flexor tone or weight centile size
differences at different gestations. Using this measurement, The investigators propose to use
regression analysis to develop novel formulae based on its relationship with length of UACs
and UVCs respectively.
