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 Q1. Why do I need to use the Flow QC tubing set?
A. The Flow-QC tubing set provides a safe injection port for rapid
injection of the CO measurement bolus. A bolus injection at another site, such as the bubble trap, would become too long and the software program
may not be able to separate the timing of the first pass of the saline bolus from subsequent passes.
The Flow-QC tubing set also provides a Transonic-controlled, consistent
measurement environment. The ultrasonic and mechanical properties of these tubing sets are controlled to guarantee measurement accuracy,
eliminate measurement variability from blood line brands, and reduce the need for periodic sensor calibration. Use of these tubing sets is therefore
also recommended for access flow studies.
Q2. Why do I need to enter the patient's height and body weight?
A. These parameters are needed to calculate the patient's body surface
area (BSA), and thus CI. The CO measurement protocol can be executed without these values, but the software would not calculate the CI and CBVI.
Q3. Do I have to enter pressures?
A. You may skip the entry of pressures, but then the software will not
calculate the peripheral resistance.
Q4. Why do we recommend setting the pump to 200 ml/min during CO measurements?
A. Injecting 30 ml of saline over 6 seconds increases the outflow rate of the
venous blood line temporarily by 300 ml/min. Lowering the pump setting reduces the chance of pump stoppage during venous pressure elevation and
also reduces the chance of the saline injection triggering recirculation.
Q5. Why must there be 0% recirculation during the CO measurement?
A. For an accurate CO measurement, the full saline injection must reach the
heart in a single bolus. The CO calculation is based on a bolus volume of 30 ml. When recirculation is present, a part of the bolus will disappear back into
the arterial bloodline and the lost saline would introduce a measurement error. Flow-QC monitoring software will recognize recirculation during the CO
measurement injection and will warn the user to repeat the measurement at a lower pump flow setting.
Q6. Why must the saline injection be pre-warmed?
A. The transit-time of ultrasound changes with temperature. When CO is
measured, the saline bolus travels through the cardiovascular circuit before returning to the arterial line ultrasonic sensor. Saline must be pre-warmed to
body temperature so there will be no additional thermal changes to the saline indicator bolus on its passage through the body.
Q7. How can I pre-warm the saline?
A. Use the Transonic Syringe Warmer to maintain a saline temperature of 33
- 38º C. Never use a microwave to warm the saline.
Q8. How accurately must I pre-warm the saline?
Q9. How should I inject the 30 ml?
A. The 30 ml injection is made into the injection port on the venous side of
the Flow-QC tubing. It must be injected in one single pass fairly rapidly (4 to 7 seconds). Software automatically identifies and reports injection errors
(direct recirculation, micro-bubble, incorrect saline temperature).
Q10. What are normal values for CO, CI, SV, CBV and PR in the hemodialysis population?
- A. CO (cardiac output) 4 to 8 L/min (weight & height dependent)
- CI (cardiac index) 2.5 to 4.2 L/min/m2
- CBV (central blood volume) 0.8 to1.6 L (weight dependent)
- CBVI (central blood volume index) 11 - 17 ml/kg
- PR (peripheral resistance) 12 - 20 mmHg/L/min
Q11. How accurate is the Transonic CO measurement method?
A. Transonic CO measurements are the greater of 15% of the true cardiac
output, or ± 0.5 L/min.
Q12. How do I know if the measurement is free of technical errors?
A. If no error message on the screen appears, the measurement is good. A
suspect measurement is indicated by a "REPEAT" error message on the screen.
Q13. Why is there a difference in readings between two consecutive CO measurements?
A. Transonic indicator dilution technology has a repeatability of ± 4%: this
means that two consecutive measurements may vary an average of 4% from their mean. Also, CO varies during the course of a respiratory cycle,
over the course of the hemodialysis treatment, and with the patient's level of arousal.
Q14. What is the difference between CO and CI?
A. CO varies greatly with body size, sex, and physique of the patient. For
example, the heart of a baby pumps adequately but at a flow that is less than that of an adult. CI is the CO normalized by an individual's body
surface area. Therefore, CI reflects the patient's heart function, independent of body size.
Q15. Why is a CO measurement not possible with Central Venous Catheters?
A. CO measurements require recording of a dilution curve in any artery after
the introduction of an intravenous indicator (saline). In the instance of indicator injection through a central venous catheter, the indicator does not
have the proper mixing conditions to dilute with the entire cardiac flow. Therefore, CO measurements are not possible. However, CO can be
measured in an A-V catheter configuration.
Q16. How often should a clinic measure Cardiac Function Parameters?
A. Patient profiling should be performed to establish the adequacy of the
medication dosages and the hemodialysis prescription (see CHP, Chapter 3). Such a profiling measurement should be repeated until an adequate
hemodialysis and medication prescription has been confirmed. A cardiovascular baseline may then be established for a patient by measuring
CO for several more months, for instance, every time the patient's access flow is measured. This baseline must be established when a patient originally
is entered into the Transonic monitoring program and when the patient returns from a hospitalization. The baseline period may consist of monthly
measurements over two consecutive months.
After the baseline period the nephrologist should determine a measurement
regimen for each patient. This regimen includes a prescribed testing interval (i.e., quarterly, monthly), whether an analysis of fluctuations in
cardiovascular parameters induced by hemodialysis should continue, and the threshold at which changes in critical cardiac parameters should be brought
to the attention of the nephrologist. The nephrologist will base this on an estimate of how rapidly the patient's cardiovascular condition may
deteriorate. As a rule, the measurement interval should be at one-fourth the possible deterioration period. For instance, if the cardiovascular status of
the patient may critically deteriorate over a 4-month period, monthly CO measurements should be maintained to reflect the current status of the
cardiovascular parameters. Quarterly measurement may suffice for patients stable enough to expect critical changes only over a 1-year period.
Q17. Can I save the measurements and review them later?
Yes. All the patient records are saved automatically on the laptop hard
-drive. Playback is very simple. On the HD01Plus, go to "Playback" at the top of the program screen and the software will guide you. On the HD02,
double-click on the measurement line on the patient's data table.
Q18. Can I send measurements data by e-mail?
All graphics and measurements can easily be sent by e-mail:
1) for HD01Plus: find the file name of the data you want to send and attach
it to an e-mail message. The file name is composed of the first 6 letters of the patient name and a sequential number. There is also a daily log file of all
measurements (named: "date.log") that lists all measurements of that day, the measured values, and the respective file names.
2) for HD02: use option "Copy Curve to Disk."
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