83 (95% CI 0.68, 0.93), 0.78 (95% CI 0.61, 0.88), 0.76 (95% CI 0.59, 0.89), and 0.58 (95% CI 0.41, 0.75), respectively. There were no statistical differences between the AUC for cIVC2 and E wave velocity, VTI, E/A ratio, and E/Ea ratio (P = 0.46, 0.99, 1.00, and 0.26, respectively).DiscussionBecause the AUC of the ROC curve for cIVC was 0.77 (95% Rucaparib CAS CI 0.60, 0.88), the present study shows that cIVC cannot reliably (inferior limit of CI < 0.75) predict fluid responsiveness in spontaneously breathing patients with ACF. More precisely, a cIVC value below 40% cannot exclude fluid responsiveness while patients with cIVC above 40% are more likely to respond to fluid challenge. The 40% cutoff value is in agreement with recent studies [22].The first explanation for these imperfect results is that, as previously suggested, cIVC is a dynamic preload index.

In contrast with findings reported in mechanically ventilated septic patients, dynamic parameters have been shown to be ineffective to predict fluid responsiveness in spontaneous breathing patients [6,7]. Spontaneous ventilation implies a very wide range of breathing patterns. In patients with spontaneous ventilation, respiratory variations are highly variable from one cycle to another in a given patient and between different patients. Then, influence of breathing pattern on cIVC is also variable. The present results indirectly confirm that spontaneous breathing is a natural limit for the use of a dynamic parameter.

Because previous studies have reported a good correlation between cIVC and blood volume removal during hemodialysis [17,24] or during blood donation [41], the inability of cIVC to predict fluid responsiveness may be surprising in spontaneously breathing patients with ACF. However, monitoring blood volume during blood removal is not the same as predicting fluid responsiveness. It has been shown that there is a good correlation between high cIVC value and low CVP value [21,22,42]. A low CVP value (< 7 mmHg) could be considered a good indicator of fluid responsiveness [11], corresponding to high values of cIVC (specificity = 80%). In contrast, lower values of cIVC values are poorly predictive, corresponding to higher values of CVP [8,9].The conditions of measurement of cIVC could be discussed. In the present study, the IVC diameter was measured by M mode at 2 or 3 cm from the right atrium, as described in previous studies [17,18,22].

Carfilzomib However, Wallace et al. [43] recently showed that in spontaneously breathing healthy volunteers, variations of IVC diameter were significantly lower when recorded closed to the right atria (cIVC = 20%) than when recorded 2 cm caudal to the hepatic vein inlet (cIVC = 30%, P = 0.03) or at the level of the left renal vein (cIVC = 30%, P = 0.002) [43]. This finding would explain our high rate of false negative results. This hypothesis needs to be tested in further studies.