Welch Allyn 1500 Patient Monitor v.1.4.X - User Manual - Manual (Page 82)

78 Monitoring and Measurements Welch Allyn 1500 Patient Monitor
Cardiac output (option)
Introduction
The WA 1500 patient monitor uses the thermodilution method of measuring cardiac
output. A pulmonary artery catheter (PAC) is inserted into the right side of the heart. The
PAC is balloon tipped and is inflated to help it through the right ventricle to occlude a
smaller branch of the pulmonary artery system. The balloon is deflated and the PAC
injects a small amount (10ml) of cold injectate at a known temperature into the pulmonary
artery. The temperature is then measured at a known distance using the same catheter.
The cardiac output can be calculated from the measured temperature curve. Low cardiac
output will change the temperature slowly, and high cardiac output will change the
temperature rapidly. The degree of change in temperature is directly proportional to the
cardiac output.
Usually three to five repeated measures are averaged to improve accuracy.
CO Units
Cardiac output is expressed as liters / minute:
• Cardiac Output (CO) = Stroke volume × Heart rate
where: Stroke volume = End Diastolic Volume (EDV) - End Systolic Volume (ESV)
Heart rate = beats per minute
The cardiac index is expressed as liters / minute / m
2
:
• Cardiac Index (CI) = Cardiac output/ BSA
where: BSA is Body Surface Area in square meters.