Introduction: The aim of this study was to evaluate dynamic indices of fluid responsiveness in a model of intra-abdominal hypertension.
Methods: Nine mechanically-ventilated pigs underwent increased intra-abdominal pressure (IAP) by abdominal banding up to 30 mmHg and then fluid loading (FL) at this IAP. The same protocol was carried out in the same animals made hypovolemic by blood withdrawal. In both volemic conditions, dynamic indices of preload dependence were measured at baseline IAP, at 30 mmHg of IAP, and after FL. Dynamic indices involved respiratory variations in stroke volume (SVV), pulse pressure (PPV), and systolic pressure (SPV, %SPV and Δdown). Stroke volume (SV) was measured using an ultrasound transit-time flow probe placed around the aortic root. Pigs were considered to be fluid responders if their SV increased by 15% or more with FL. Indices of fluid responsiveness were compared with a Mann-Whitney U test. Then, receiver operating characteristic (ROC) curves were generated for these parameters, allowing determination of the cut-off values by using Youden's method.
Results: Five animals before blood withdrawal and all animals after blood withdrawal were fluid responders. Before FL, SVV (78 ± 19 vs 42 ± 17%), PPV (64 ± 18 vs 37 ± 15%), SPV (24 ± 5 vs 18 ± 3 mmHg), %SPV (24 ± 4 vs 17 ± 3%) and Δdown (13 ± 5 vs 6 ± 4 mmHg) were higher in responders than in non-responders (P < 0.05). Areas under ROC curves were 0.93 (95% confidence interval: 0.80 to 1.06), 0.89 (0.70 to 1.07), 0.90 (0.74 to 1.05), 0.92 (0.78 to 1.06), and 0.86 (0.67 to 1.06), respectively. Threshold values discriminating responders and non-responders were 67% for SVV and 41% for PPV.
Conclusions: In intra-abdominal hypertension, respiratory variations in stroke volume and arterial pressure remain indicative of fluid responsiveness, even if threshold values identifying responders and non-responders might be higher than during normal intra-abdominal pressure. Further studies are required in humans to determine these thresholds in intra-abdominal hypertension.