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CON:
There is no question that vascular ultrasound
imaging can elucidate difficulties in obtaining central vascular access
and may even facilitate the process for difficult patients (Table 1).
However, its routine use is unnecessary, and not supported by available
data.
The incidence of complications and difficulties
during central venous cannulation (CVC), using surface landmarks as a
guide, varies from study to study, but is relatively low and probably
related to operator experience. The more commonly presented and studied
complications include pneumothorax, arterial puncture, prolonged procedural
time, and failure to obtain access (Table 2).1-8 In a systematic
review of 17 prospective studies using surface landmarks including 2085
internal jugular cannulations and 2428 subclavian cannuluations, the incidence
of carotid artery punctures and pneumothoraces ranged from 0-7% and from
0-4.5% respectively.9 The highest incidences were reported
when house officers or trainees performed the procedure during urgent
or emergent settings. In a large series (n=6245) of attempted CVCs the
incidence of carotid artery puncture was 0.9% (120 patients), and pneumothorax
was 0.5% (31 patients) .10 Of 1000 patients with known coagulopathy
undergoing transvenous liver biopsy there were only 7 unsuccessful attempts
(0.8%).11 In this high risk group there were only 10 hematomas
reported, and only one required surgical drainage.11 In this
case the hematoma was caused by venous bleeding in a patient with a goiter.
Other large series report a 95% success rate for internal jugular access
(n=2305) and a 74% success rate for external jugular (n=1086).12
The lower value for external jugular attempts was due to difficulty in
advancing the guide wire past the clavicle and not due to accessing the
external jugular vein. The incidence of requiring multiple needle sticks
or advances (> 2) has been reported to be as low as 5.1% (27/500).13
A number of studies have compared the
use of vascular ultrasound to surface landmarks to guide CVC.1-8
These studies report a greater percentage of successful cannulation, fewer
needle punctures, decreased time required for cannulation, and fewer carotid
artery punctures. However, two of these studies did not demonstrate a
significant difference between landmark and ultrasound in the incidence
of carotid artery puncture.2,3 Several showed no difference
in the time required to achieve cannulation,1,3 and one showed
no difference in the percent of patients cannulated on the first attempt.2
Several ultrasound studies report a significant
decrease in time required for cannulation of the vein.1-8 With
the exception of one study, the authors uniformly report the data as the
mean, range, and standard deviation. Consistently the standard deviation
is much larger reflecting a greater spread of data points. Since CVC was
uncomplicated in the majority of cases it is likely that the distribution
of data points (times) did not make a normal bell shaped curve and contains
significant outliers (ones with very prolonged time for cannulation).
These data would be better represented by a median value. If this were
done I suspect that the difference between the two techniques would have
been less. Furthermore, the reported time differences between landmark
and ultrasound only range from 4 to 140 seconds. The clinical significance
of these time differences is very small…..if they even exist at all.
Verghese et al reported the median values
for cannulation in infants. In this study, the median value for ultrasound
guided technique was 4.2 minutes compared to 14 minutes for landmark guided
technique.7 These data are significantly prolonged for both
study groups when compared to Alderson et al in their study of pediatric
patients.8 Verghese et al studied infants who were less than
1 year old compared to Alderson et al who studied children younger
than 6 years old.7,8 It is
likely that neonates and infants represent a high
risk population for difficult cannulation, and may benefit from ultrasound
guided imaging.
Cannulation time in these studies did
not include preparation time, but instead measured the time from the initial
needle entry into the skin to either aspiration of blood or cannulation
of the vein. This does not reflect the amount of time required to prepare
the ultrasound probe, and the time needed to visualize the vascular structures.
It is important to include these times since a finite period of time is
required to prepare the ultrasound device and the vascular structures
may be difficult to visualize is as many as 12% of cases.14
Inclusion of preparation time would likely result in ultrasound guided
procedures requiring more time than landmark guided CVCs.
Similarly, the number of needle sticks
or advances required for cannulation is presented as the mean value, which
may not be as accurate a reflector as the median value. On average the
difference in number of needle advances was between 1 and 2, which has
minimal clinical significance. These studies report a range of successful
cannulation on the first attempt from 26-54% with landmark guidance and
from 43-78% for ultrasound guided procedures.1-8 These data
are inferior to that reported by Dee Boyd et al in which CVC using landmark
guidance was successful on the first attempt in 95%, suggesting that operator
experience contributed more significantly than the guidance technique
used.1-8,13
It is interesting that the ultrasound
studies tended to report a higher failure rate for cannulation using landmark
guided procedures than previously reported series.11,12 Failure
to cannulate ranged from 4 to 50% with landmark guidance, and from 0 to
11% for ultrasound guided procedures.1-8 This likely represents
inadequate operator experience, and small numbers of patients studied.
At most, failure rate of CVC should not exceed 5% in unselected patients.11,12
While ultrasound imaging is not routinely
necessary, there is a definite niche for these devices. Complicated patients
(Table 1) may require significantly greater effort to perform CVC.
For these patients, especially with a previous history of difficult CVC,
an ultrasound device is likely to be beneficial.
Another niche for ultrasound imaging is for teaching.
The newer technology may help teach us to better perform CVC using the
older technology landmark. Learning the effects of head rotation, valvsalva,
Trendelenberg, and/or external compression on vessel position and caliber
will improve the success rate with any technique. With the head in neutral
position or 30 degrees rotation, the internal jugular was anterior and
lateral to the carotid artery in 183/200 (92%) of patients.15
In 5 patients (2.5%) no internal jugular vein was visualized suggesting
the increased likelihood that the vessel was thrombosed. All had had previous
procedures or the internal jugular vein. Six patients (3%) had a small
internal jugular vein (< 0.5 cm) which did not enlarge with valvsalva
or Trendelenberg position suggesting scarring of the surrounding tissue
or the vein itself. Again, all six of these patients had previous procedures.
Finally, in 2 patients (1%) the IJ was significantly lateral to the CA,
and in 4 patients (2%) the IJ was more medial and overlapped the carotid
artery more than would have been suspected. These data may explain why
difficulties accessing the internal jugular occurs in approximately 5%
of patients. They also demonstrate that previous central venous procedures
increase the difficulty in obtaining future access at the same site.
Other studies showed variations in the
relationship of the internal jugular and the carotid artery with changes
in head position.14,16 When the head is rotated to the contralateral
side, at least 50% of the cases show overalapping of the carotid artery
and internal jugular vein by > 50%. In 6.4% the internal jugular vein
was significantly lateral and did not overlap at all. Sulek et al reported
minimal overlap when the head was in neutral position or rotated to 40
degrees to the contralateral side.16 However, with greater
head rotation (>40 degrees) the internal jugular vein tended to lie
over the carotid artery. This occurred more frequently on the left side.
These data help to explain the difficulties
encountered in attempted central venous access in a small number of patients.
The data also remind us that significant head rotation (>40 degrees)
and/or extension will not only alter the relative position of the major
vascular branches but also increase the chance of compressing the vein.
In the studies comparing ultrasound to landmark,
the approach to internal jugular cannulation proceeded from the apex of
the middle cervical triangle (formed by the anterior and posterior bellies
of the sternocleidomastoid (SCM) muscle.1-8 It is possible
that a greater success may be achieved with another approach such as the
anterior approach in which the needle entry is anterior to the anterior
SCM muscle and directed laterally. Using this approach, rotation of the
head is minimized and vascular relations and caliber are left unchanged.
There is a finite cost for the use of
ultrasound imaging. Current ultrasound machines range from several thousand
to greater than 100 thousand dollars which may not include the costs of
the transducer, technical maintenance, and costs (time and/or money) necessary
to train operators to become proficient at using ultrasound. There is
also the need for assistance during the ultrasound guided procedure to
either help pass the probe in a sterile manner or for assistance in imaging
the vascular structures if the operator is inexperienced. To date, there
is no data showing cost savings over a large series of patients when using
the ultrasound device.
Routine use of ultrasound technology may
create an unwanted dependency on this technology. If this were the case
then the ultrasound machine and probe would need to be readily available
twenty-four hours per day. Our efforts would be better directed at educating
ourselves and our students at being proficient using landmark guided techniques.
Although its routine use is not necessary, ultrasound technology would
be a useful part of our armamentarium for these difficult cases.
Conclusion: As discussed above,
the significance of any clinical benefits of routine Uultrasound imaging
have not been demonstrated. Furthermore, given the time to prepare the
ultrasound equipment, the total procedural time may be longer when compared
to landmark guided CVC. Finally, there is still a finite failure and complication
rate with the ultrasound device, which may not be different than that
reported by experienced technicians using landmark guidance for CVC. While
ultrasound may help facilitate CVC in difficult cases, its routine use
is not justified.
Table 1: List of complications during
central venous cannulation
Multiple sticks
Arterial punctures
Hematomas
Pneumothorax
Brachial Plexus injury
Failure to Cannulate
Table 2: List of risk factors predicting
difficulty in obtaining central venous access.
Previous central venous catheter at same site
Radiation
Clavicular injury
Previous sternotomy
Coagulopathy
Venous thrombosis at site
Restless Patient
Morbidly obese
Infant/child
Lack of experience
Scarred Vessel
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Andrew D. Maslow, MD
Rhode Island Hospital
Providence, RI
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