StenTec™ Gauge explanation
August 2010
S.R.Ash
HemoCleanse, Inc.
Lafayette, Indiana
The StenTec™ Guage provides a method to determine the static Intra-access Pressure Ratio (PIA)
within a fistula or graft. PIA is the ratio of pressure in the fistula or graft to the systemic arterial
pressure. The StenTec measures the peak systolic pressure within the fistula or graft by the length
that the blood-air interface progresses into the tubing of the fistula needle, after the needle is inserted
“dry” into the fistula or graft and before the cap is removed. The peak systolic pressure is then
graphically compared to the systolic arterial blood pressure of the patient (BPS), to determine P IA.
For best accuracy, the StenTec Gauges should be matched to the internal volume of the fistula needle
tubing (2.3-2.6 ml for 12 inch tubing and 3.6 ml for 16 inch tubing) and the approximate elevation of
your city (0-1000, 1000-3000 and 3000-6000 feet above sea level). The tubing internal volume is
written on the package which contains the fistula needle.
Values of PIA that indicate upstream or midstream stenosis of a fistula or graft are provided in
K/DOQI Guidelines of 2000. These values are based on mean arterial pressures of fistulas and grafts
compared to mean systemic arterial pressure. However, the same ratios should be obtained using
systolic pressure ratios in the StenTec Gauge, and the systolic pressure ratio has been shown to
accompany graft or fistula stenosis1, 2. The table below includes K/DOQI (2000) recommendations
for interpreting PIA Ratios3:
Access Type
Normalized
PIA
Normal
Graft
Graft
Native
Native
Arterial
Ratio
Venous
Ratio
Arterial
Ratio
Venous
Ratio
0.35-0.74
0.15-0.49
0.13-0.43
0.08-0.34
>0.75
>0.5
>0.43 or
>0.35
>0.75 and
<0.5
>0.43 and
<0.35
Stenosis
Venous outlet
Intra-access
To use the StenTec Gauge, do the following:
1) Place fistula needle “dry” and capped into the fistula or graft and tape in place as usual.
2) Note the systolic blood pressure of the patient.
3) Lay the clear plastic Gauge over the fistula needle and tubing, with the left end of the clear
tubing at the “0” point of the graph, and the fistula needle tubing under the line that most
closely indicates the systolic blood pressure (BPS) of the patient.
4) Note the highest point of progress of the air-fluid interface into the tubing, and compare it
to the slanted lines to determine the PIA Ratio.
5) Repeat for the other fistula needle.
6) The red lines for PIA values of 0.5 or more indicate a high probability of outflow stenosis of a
fistula. PIA values of 0.75 or more indicate a high probability of outflow stenosis of a graft
(as described by the K/DOQI Guidelines).
7) Maintain a record of PIA for arterial and venous needles over time for each patient.
Continually increasing PIA values indicate a need for intervention.
The following is a depiction of the StenTec Gauges. There are three gauges for fistula tubing lengths
of 12 inches (with 2.3-2.6 ml internal tubing volume), each for a different range of altitude of the city.
The actual gauge is printed on clear plastic, through which the blood-air interface is clearly visible.
Another set of cards is available with green coloring for fistula tubing lengths of 16 inches (having 3.6
ml air volume):
StenTec Gauges will be sold at $2.00 per Gauge, in lots of 50. Each Gauge should be assigned to a
single patient, in order to prevent patient-to-patient contamination. The Gauges may be cleaned
with alcohol, peroxide, or hypochlorite between uses.
1 Besarab A, Moritz M, Sullivan K, Dorrell S, Price JJ. Venous access pressures and the detection of intraaccess stenosis. ASAIO J. 1992 Jul-Sep;38(3):M519-23.
2 Besarab A, Sullivan KL, Ross RP, Moritz MJ.. Kidney Int. Utility of intra-access pressure monitoring in
detecting and correcting venous outlet stenoses prior to thrombosis. Kidney Int. 1995 May;47(5):1364-73.
3 http://www.kidney.org/professionals/kdoqi/guidelines_updates/doqiupva_ii.html#doqiupva11