Cardiac output assessed by arterial thermodilution during exsanguination and fluid resuscitation: experimental validation against a reference technique

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Abstract
Background and objective: The arterial thermodilution technique offers the ability to measure cardiac output using only central venous and arterial catheters. However, the technique has been reported to overestimate cardiac output because of a higher loss of cold indicator due to the increased distance between the sites of injection and measurement. In this study, the two techniques were compared with respect to conditions of low cardiac output in which a longer passage time may further increase loss of indicator. Methods: Seventeen anaesthetized dogs were studied during hypovolaemic shock and fluid resuscitation. Cardiac output measurements were carried out simultaneously by arterial and pulmonary artery thermodilution techniques. Results: One-hundred-and-two measurements were performed. The mean cardiac output was 2.28 ± 1.4 L min−1 by the pulmonary arterial technique and 2.29 ± 1.56 L min−1 by the arterial thermodilution technique. The correlation coefficient between the two measurements was 0.95, the precision −0.04 ± 0.41 L min−1 and the limits of agreement from −0.86 to 0.78 L min−1. The agreement was also consistent at low cardiac outputs. Conclusions: The arterial thermodilution technique may serve as a less invasive cardiac output monitor in conditions of severe bleeding and shock.