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Changes in cardiac output and intrathoracic blood volume: a mathematical coupling of data?
W Buhre1, S Kazmaier, H Sonntag
1Klinik für Anaesthesiologie, Medizinische Einrichtungen der RWTH Aachen, Georg-August Universität, Göttingen, Germany. Wolfgang.Buhre@post.rwth-aachen.de
Insights
High-dose esmolol significantly altered cardiac output (CO) but not intrathoracic blood volume (ITBV) in MIDCAB patients. These findings suggest thermodilution measurements of ITBV are reliable despite CO fluctuations.
Area of Science:
- Cardiovascular Physiology
- Critical Care Medicine
- Surgical Hemodynamics
Background:
- Intrathoracic blood volume (ITBV) is crucial for assessing cardiac preload and investigating cardiac output (CO) alterations.
- A potential mathematical coupling exists between CO and ITBV measurements, raising concerns about data reliability.
- This study addresses whether CO variations influence ITBV thermodilution measurements, particularly in the context of beta-blockade.
Purpose of the Study:
- To prospectively investigate if induced variations in cardiac output (CO) affect transpulmonary thermodilution measurements of intrathoracic blood volume (ITBV).
- To evaluate the reliability of ITBV measurements during significant CO changes caused by high-dose beta-blockade in patients undergoing minimally invasive coronary artery bypass grafting (MIDCAB).
Main Methods:
- Sixteen patients undergoing elective MIDCAB surgery were enrolled.
- Transpulmonary thermodilution was used for simultaneous ITBV and CO measurements.
- Measurements were taken before, during high-dose esmolol-induced beta-blockade, and post-beta-blockade.
Main Results:
- Cardiac output (CO) decreased by 33% during esmolol administration, while intrathoracic blood volume (ITBV) remained unchanged.
- Following esmolol withdrawal, CO increased by 79%, with ITBV showing no significant alteration.
- These results indicate ITBV measurements were unaffected by substantial CO fluctuations.
Conclusions:
- Substantial changes in cardiac output (CO) induced by high-dose esmolol do not impact thermodilution measurements of intrathoracic blood volume (ITBV).
- The findings suggest that thermodilution-derived ITBV is a reliable parameter, even with significant CO variations unrelated to preload changes.
- This supports the use of ITBV measurements in clinical settings where CO may fluctuate.
Background:
Measurements of intrathoracic blood volume (ITBV) provide volumetric information about cardiac preload and are used to investigate the cause of alterations in cardiac output (CO). On the other hand, CO is required to calculate ITBV. Thus, concerns have been raised with respect to a mathematical coupling of data. The aim of this prospective, clinical study was to investigate whether a variation in CO induced by high-dose beta-blockade influences thermodilution measurements of ITBV in the absence of changes in intravascular volume in patients undergoing minimally invasive coronary artery bypass grafting.
Methods:
Sixteen patients undergoing elective minimally invasive direct coronay artery bypass (MIDCAB) surgery were studied. Transpulmonary thermodilution measurements of ITBV and CO were simultaneously performed before bypass grafting, during beta-blockade induced by high-dose esmolol and at the end of surgery.
Results:
During esmolol administration, CO significantly decreased by 33%, whereas ITBV remained unchanged compared to control values (876+/-46 ml m-2 during control versus 860+/-61 ml m-2 during esmolol administration). After the end of esmolol administration, CO significantly increased by 79%. Again, ITBV remained virtually unchanged (860+/-61 ml m-2 during esmolol administration versus 911+/-38 ml m-2 after esmolol administration).
Conclusions:
The results of the present study demonstrate that substantial alterations in CO as a consequence of high-dose esmolol infusion are not associated with changes in ITBV. Because haemodynamic changes were induced by factors other than variation of preload, these findings suggest that changes in cardiac output do not influence thermodilution measurements of ITBV in this setting.
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