Availability of end-tidal carbon dioxide on change in stroke volume in spontaneous breathing subjects

ABSTRACT

OBJECTIVE: Stroke volume (SV) measurements have been used to guide fluid management. Noninvasive, indirect, and convenient measurements of the SV for fluid therapy are required for most patients during spontaneous breathing (SB). On the other hand, the preferred method for an indirect prediction of the SV is unclear. This study examined the best of the indirect and predictable parameters responding to a SV variation during SB. METHODS: Hemodynamic parameters, such as collapsibility of the inferior vena cava (cIVC), peak velocity variation in the common carotid artery (pvvCCA), collapsibility of the internal jugular vein (cIJV), and end-tidal carbon dioxide (ETCO₂) were measured 180 times (6 different positions each in 30 normal subjects). The variables changed with the SV at the upper body elevation of 60°and 30°, in the supine position, at the lower body elevation of 60°and 30°, and lumbar elevation. RESULTS: The SV showed the highest value at 30°of lower body elevation. Following fixed position changes, the ETCO₂ during SB was the factor most correlated with the SV when compared to cIVC, cIJV, and pvvCCA (β coefficient, 2.432 vs. −0.41, −0.033, and −0.654; P=0.004). The adjusted ETCO₂ showed a significant change with the SV, even though the change in ETCO₂ was not large. CONCLUSION: ETCO₂ was less influenced by the SB than cIVC, pvvCCA, and cIJV because the ETCO₂ change was in accordance but the variations of the other blood vessels did not coincide with a SV change. Therefore, ETCO₂ monitoring for predicting the SV would be more important than the variations in the vessels during SB.