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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 26, No 1, January/February 2015
AFRICA
43
age, gender, history of hypertension, hyperlipidaemia, diabetes
mellitus, chronic obstructive pulmonary disease, coronary artery
disease, current smoking status and pre-operative vein diameters
between patients who were operated with and without the U-vein
compressor.
There were no significant differences in the pre-operative
diameters of the veins at the 0-, 4-, 8- and 12-cm points in the
groups. Postoperative vein diameters in the patients where U-vein
compressors were used were significantly greater at all points,
compared with patients where it was not used (
p
<
0.001). Also,
postoperative flow velocities were significantly higher in patients
where U-vein compressors were used (
p
<
0.001) (Table 2).
In patients where the U-vein compressor was used,
pre-operative mean transverse diameters (range 1.60–1.95 mm)
at the 0-, 4-, 8- and 12-cm points were increased at least 75%
postoperatively (range 2.80–3.90 mm). Flow measurements were
between 326 and 670 ml/min.
Discussion
Endogenous AVF, first described in 1966, remains the optimal
vascular access for chronic dialysis.
2
The RCAVF has remained
the access for maintenance haemodialysis because of its low
incidence of complications and high long-term patency rate.
An AVF within the anatomical snuffbox (triangular deepening
on the radial, dorsal aspect of the hand) has a high incidence
of early failure and requires a longer maturation time. The
proximal elbow fistula predisposes to ischaemic complications
and can lead to congestive heart failure as a result of increasing
flow through a chronic fistula that is made too large. The distal
radial–cephalic anastomosis just above the wrist is still the best
site for an internal AVF. This provides a relatively long, straight
cephalic vein for catheter insertion. It also leaves more proximal
sites for future use should the RCAVF fail.
The fistula is allowed to mature for six to eight weeks prior
to puncture. Occasionally longer periods of maturation are
required to allow sufficient arterialisation of the vein, but if
little venous distention is present at six weeks, either revision or
an alternate access site is usually required. Having the patient
perform repetative hand exercises such as squeezing a ball or a
similar-sized compressable object may facilitate development of
the outflow vein.
A failure-to-mature AVF is caused by intrinsically poor native
vessels or by post-surgical derangements. Poor native vessels
relate to the use of a suboptimal artery or vein to create the AVF.
It has been noted that arteries less than 1.5 to 2 mm and veins
less than 2 to 2.5 mm in diameter are associated with poor AVF
maturation.
3-6
Silva
et al
. used a minimum of 2.5-mm vein size as
predictable for fistula success.
1
In our technique, veins between
1.5 and 2 mm were associated with good AVF maturation by
intra-operative use of a U-vein compressor.
Larger veins mean larger flow. However, such a simplistic
view does not take into account arterial factors and normal
pulsatile blood flow. Furthermore, venous compliance after
fistula creation needs to be considered. In the study by Lauvao
et al
., eight patients with the smallest diameter between 1.5 and
2 mm on Doppler ultrasonograhy went on to develop mature
fistulae, and three did not.
7
Their experience shows that vein size
is the major predictor for a succesfull fistula.
In our study, pre-operative mean transverse diameters (range
1.60–1.95 mm) at the 0-, 4-, 8- and 12-cm points were increased
at least 75% postoperatively (range 2.80–3.90 mm) and flow
measurements were between 326 and 670 ml/min. The risk of
failure was zero in the group where U-vein compressors were
used, but the wrist radiocephalic arterio-venous fistula failed in
six in the other group.
A well-functioning vascular access for haemodialysis plays
a key role in the quality of life and clinical outcome of dialysis
patients. Johnson
et al
. reported that a high intra-operative flow
volume defined as 320 ml/min or greater was associated with a
lower number of surgical revisions and longer access survival
regardless of gender, race and the presence of diabetes.
8
The
same authors reported that an intra-operative flow rate of less
than 170 ml/min was correlated with a 56% risk for AVF failure
within 50 days of construction.
8
A recent study including a
cohort of 109 patients undergoing vascular access surgery for
first-time haemodialysis showed that an intra-operative flow rate
greater than 200 ml/min was associated with better mid-term
outcomes in terms of requirement for revision and early patency
rate.
9
Fistula maturation is defined by the determination of both
vascular surgeon and nephrologist that an access is patent
and ready for cannulation based on adequency of blood flow
through the fistula and adequency of vein dilatation in the 10-cm
Table 2. Comparison of pre- and postoperative diameters and
postoperative flow velocity between patients where the U-vein
compressor was not used and those where it was used
Patients
(U-vein
compressor
not used)
(
n
=
20)
Patients
(U-vein
compressor
used)
(
n
=
20)
p
-value
0 cm pre-operative
1.77
±
0.11 1.79
±
0.12 0.709
0 cm postoperative
2.45
±
0.25 3.27
±
0.42
<
0.001
4 cm pre-operative
1.78
±
0.11 1.79
±
0.11 0.832
4 cm postoperative
2.45
±
0.25 3.27
±
0.40
<
0.001
8 cm pre-operative
1.78
±
0.11 1.81
±
0.10 0.282
8 cm postoperative
2.47
±
0.26 3.33
±
0.38
<
0.001
12 cm pre-operative
1.79
±
0.11 1.83
±
0.10 0.307
12 cm postoperative
2.46
±
0.26 3.33
±
0.36
<
0.001
Flow velocity (postoperative) 197.15
±
53.52 371.75
±
93.98
<
0.001
Table 1. Comparison of patients where U-vein compressors
were not used and those where they were used
Variable
Patients
(U-vein
compressor
not used)
(
n
=
20)
Patients
(U-vein
compressor
used)
(
n
=
20)
p
-value*
Age (years)
55.8
±
7.52 57.9
±
8.12 0.41
Male,
n
(%)
12 (60)
10 (50)
0.53
Hypertension,
n
(%)
7 (35)
8 (40)
0.74
Hyperlipidaemia,
n
(%)
9 (45)
7 (35)
0.52
Chronic obstructive pulmonary
disease,
n
(%)
5 (25)
6 (30)
0.72
Coronary artery disease,
n
(%)
7 (35)
6 (30)
0.74
Diabetes mellitus,
n
(%)
5 (25)
6 (30)
0.72
Current smoker,
n
(%)
5 (25)
6 (30)
0.72
Pre-operative vein diameter
1.77
±
0.11 1.79
±
0.12 0.71