Our results showed that the FIVP could be used to estimate correctly CVP and confirmed previous published studies in adults and children in ICU [4, 5]. However, we pointed out that FIVP measurement accuracy had to be interpreted according to the intra-abdominal pressure. When intra-abdominal pressure was inferior to 14 mmHg, FIVP predicted very well CVP. When intra-abdominal pressure was more than 14 mmHg, corresponding to the first stage of intra-abdominal hypertension, FIVP did not reflect accurately CVP anymore. The difference could be large (median 4 (range 0–18)) and was always in the direction FIVP > CVP. Interestingly, this cutoff was close to the threshold (12 mmHg) that defines intra-abdominal hypertension according to the International Conference of Experts on Intra-abdominal Hypertension and Abdominal Compartment Syndrome
. It is not exactly the same value of cutoff probably because the studied population size was limited. In case of severe intra-abdominal hypertension (IAP > 20 mmHg), De Keulenaer et al.  recently reported that FIVP could be used as a surrogate measure of IAP, illustrating the link between FIVP and IAP. The consequences during severe infections, if physicians followed Survival Sepsis Campaign Guidelines for fluid administration, could be an underestimation of hypovolemia in these patients, a delay for fluid challenge and could in fine worsen patient’s prognosis . The effects of intra-abdominal pressure on FIVP measurements are relevant, because abdominal compartment syndrome is not rare in ICU (from 1–20% according to published data) and is frequently underestimated .
More generally, this study questions about the effects of intra-abdominal pressure on others hemodynamic tools used in the clinical setting to evaluate volemia. For example, passive leg raising was reported by several groups to be a good predictor of fluid responsiveness . However, Mahjoub et al. showed that the passive left raising maneuver did not accurately predict fluid responsiveness in patients with intra-abdominal hypertension .
Our study has several limitations. It is a monocentric study and results have to be confirmed in a larger population. Nevertheless, although the size of this preliminary study was not very large, it was sufficient to highlight significant results. Intra-abdominal pressure was recorded indirectly by using intra-bladder pressure, but this technique had achieved a widespread adoption worldwide. Finally, our studied population did not have severe pulmonary disease: median PEEP was 3 cmH2O (2–5) and median plateau pressure was 20 cmH2O (18–25). Therefore, our data could not be extrapolated to clinical situations with lung injury and/or high PEEP and/or high intrathoracic pressure, but we could speculate that, in these situations, agreement between central and femoroiliac venous pressure would be strongly altered. The impact of increased intra-abdominal pressure on agreement between CVP and FIVP was documented using short catheters (20-cm long) and could not be extrapolated to measurements obtained using longer catheters, which tip arise right atrium.