Page 510 - Cardiac Nursing

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486 P A R T III / Assessment of Heart Disease
DISPLAY 21-7 PA Thermodilution CO
Factor Notes
Catheter position • Distal port (catheter tip) must be in the PA (confirm by observing PA waveform)
• Proximal port should be positioned in RA (verify by observing RA waveform)
• Ensure catheter not wedged
Injection port • Inject into the proximal port (RA), venous infusion port, or RV port
• Injections through side-port less accurate than injections through infusion port
• Ensure exit of proximal port is outside of introducer sheath
Calibration constant (CC) (see • A factor that corrects for the gain of heat from the tubing and thermistor
manufacturer’s insert for • Specific to (1) catheter type, (2) volume (5 vs. 10 mL), (3) temperature (iced vs. room
catheter-specific CC) temperature), (4) solution type (D5W vs. NS)
Injection technique
• Injection rate of 4 seconds • Injection rate demonstrated to produce accurate results 5 to 10 mL injectate
• Avoid handling syringe barrel • Heat transfer from hands will alter accuracy of measurements
•Inject at end-expiration or • Respiratory-induced changes in CO, with up to 30% variability between
throughout respiratory cycle inspiration/expiration
• Allow 60 seconds between • Measurements obtained at end-expiration decrease variability in measures (may
measures (monitor will overestimate CO by 1–1.5 times)
indicate “READY”) • Measurements obtained with random injection throughout respiration increases
• Perform four TDCO validity of measures
measurements (may require • To determine the CO, average three measurements that are within 10% of median
more with room temperature value (e.g., if median value 5 L/min, include all measures 4.5–5.5 L/min) or average
injectate or 5 mL vs. 10 mL) the four measurements to provide 95% confidence that the CO is within 5% of “true”
CO 299
Injectate temperature/volume Iced injectate (0–5 C) Room temperature (19–25 C)
• Temperature between injectate • 5 mL 10 mL • 10 mL RT 10 mL IT
and blood should be 10 C • Low and high CO • CO within normal limits (5 mL IT 10 mL RT)
• There is increased variability • Hyperdynamic patients • Normothermia (5 mL if fluid restricted)
in CO measurements between • 10 mL iced is considered the • Hyperdynamic patients
cold and room temperature standard * •Hypothermia
injectate particularly in patients
with a low EF ( 30%) 300
Concomitant infusion • Increased variability with concomitant infusion
• Consider discontinuation of infusion if there is not risk to the patient
• Avoid performance of TDCO during bolus infusion 301
• Remove all vasoactive medications from proximal port to avoid inadvertent bolus
Patient position • Reproducible TDCO measures with backrest up to 20 degrees (Note: CCO
reproducible up to 40 degrees backrest elevation) 302
• 250 to 500 mL/min position-related change CO in 20-degree sidelying position
• Compare sidelying CO to supine CO
Concurrent use of sequential • Note the effect of SCDs on CO measurements—decrease CO an average of 24% during
compression devices (SCDs) inflation cycle 303
It is not necessary to prime the catheter with cold solution before CO measurements

CO Measurement During Therapeutic needed to determine the most accurate method for CO measure-
Hypothermia ment during therapeutic hypothermia.
There is limited research on the effect of therapeutic hypothermia
on CO measurement. During rapid changes in core body tem- Clinically Important Changes in CO
perature there may be thermal instability or thermal noise in PA
blood temperature, which increases the error in CO measure- In general, a change of greater than 10% to 15% in CO is con-
ments most likely due to baseline drift in temperature immedi- sidered to be physiologically important. This criterion is based on
ately preceding the CO measurement. In cardiac surgery patients, studies that demonstrate that on average normal physiological
TDCO and CCO were similar pre- and postoperatively, but dur- variability ranges from approximately 4.8% to 9.9%, 307,308 al-
ing the early phase of bypass when there was a decrease in core though individual variation may be larger. 309 In atrial fibrillation,
temperature the TDCO and CCO were significantly different; where there is increased CO variability, two sets of measurements
however, determining which method was most accurate was not must vary more than 15% before one can be 95% confident that
possible. 304 A newer technology (TPTD—PiCCO), which uses a a real change has occurred. 310 In assessing changes in CO, it is im-
cold injectate to calibrate the system, was found in two case stud- portant to evaluate technical (Display 21-7), physiological, and
ies to have clinically significant increase in variability at colder pathophysiological factors related to the CO. The characterization
core temperature, which resolved with normothermia. 305,306 Re- of a CO change as clinically important should not be based on the
warming may also increase thermal noise. Further research is absolute change in CO, but rather the patient’s tolerance to the