Synchronizing thermodilution cardiac output measurements with spontaneous breathing does not improve precision.
BACKGROUND
Measuring cardiac output (CO) with the pulmonary artery catheter intermittent bolus thermodilution technique (PAC-IBTD) is less precise with spontaneous breathing compared to controlled ventilation. We aimed to test if precision could be improved in spontaneous breathing by synchronizing the measurement with respiration or using instructed respiration in 18 post-operative cardiac surgery patients.


METHODS
We performed eight CO measurements with PAC-IBTD using cold saline in three different situations; in random order: 1) random compared to respiration, 2) timed to the start of expiration, and 3) synchronized with a slow exhalation through a PEP-flute. We calculated the standard deviation (SD), coefficient of variation (CV), and precision in the total material and in the three situations using a linear mixed effects model.


RESULTS
A total of 408 CO measurements were performed in 17 included patients. There were no differences between the three study situations regarding mean or precision. The overall CO was 6.0 ± 1.4 l/min (mean ± SD), CV 6.2% and precision 12.2% for single measurements. Averaging three measurements increased the precision to 7.0%.


CONCLUSIONS
We could not improve the precision of PAC-IBTD in spontaneously breathing patients by synchronizing the measurements with respiration.
Department of Circulation and Medical Imaging, Norwegian University of Science and Technology, Trondheim, Norway.|Department of Anaesthesia and Intensive Care Medicine, Trondheim University Hospital, Trondheim, Norway.
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Kjetså
Department of Circulation and Medical Imaging, Norwegian University of Science and Technology, Trondheim, Norway.|Department of Anaesthesia and Intensive Care Medicine, Trondheim University Hospital, Trondheim, Norway.
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Skjaervold
Department of Circulation and Medical Imaging, Norwegian University of Science and Technology, Trondheim, Norway.|Department of Anaesthesia and Intensive Care Medicine, Trondheim University Hospital, Trondheim, Norway.
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Skogvoll
Department of Circulation and Medical Imaging, Norwegian University of Science and Technology, Trondheim, Norway.|Department of Anaesthesia and Intensive Care Medicine, Trondheim University Hospital, Trondheim, Norway.
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Kirkeby-Garstad
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002302:Cardiac Output; D002407:Catheterization, Swan-Ganz; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012119:Respiration; D013815:Thermodilution