LAUSR

by Morparia et al. [5], investigating respiratory variation in peak aortic velocity (ΔVpeak) and PPV in children undergoing general anaesthesia, is very much appreciated. The authors studied 22 patients (13 responders and 9 nonresponders) and demonstrate that ΔVpeak, as measured by bedside ultrasound, can predict responsiveness to volume resuscitation in an intraoperative setting. Values greater than 12.3% were predictive of fluid responsiveness, with a specificity of 89% and an area under the ROC curve of 0.90. Interestingly, the authors did not find PPV to be useful for predicting fluid responsiveness in the paediatric population studied. These results are comparable to those of prior studies in various paediatric cohorts. The authors also adequately strove to rationalize their results. Indeed, the failure of PPV to be predictive, despite ΔVpeak showing a strong prediction of fluid responsiveness, was explained by the related increased vascular compliance observed in children compared to adults (a greater “Windkessel effect”) [5]. Indeed, this decrease in arterial elastance induces a huge attenuation of the pulse pressure wave measured by a peripheral catheter [6]. Nevertheless, even though the authors should be applauded regarding their well explained mechanistic study, a consistent limitation should be recognized. In particular, the authors documented a good correlation between baseline ΔVpeak and percent changes in stroke volume after volume infusion, but interestingly, both stroke volume and ΔVpeak were measured simultaneously by the same ultrasound method. And in this regard, the good correlation observed between these two haemodynamic parameters may have been biased if we assume a haemodynamic steady state during all measurements. Indeed, the Doppler spectral analysis was a shared variable in the calculations of both stroke volume (flow velocity time integral) and ΔVpeak (Vpeak max and Vpeak min) [7]. Consequently, A frequent question in the intensive care setting is whether fluid resuscitation or volume expansion administered to a hypotensive patient will increase that patient’s cardiac output [1]. In this regard, the assessment of preload, and especially the preload dependency state, is not always simple [1], specially in case of latent hypovolemia [2]. Among all indices available, static parameters of preload (central venous pressure, pulmonary artery occlusion pressure), which are influenced by various other physiologic parameters (heart function, heart chamber extramural pressure), do not allow adequate prediction of fluid responsiveness. In contrast, dynamic parameters such as pulse pressure variation (PPV) and stroke volume variation (SVV), which are based on the influence of cardiopulmonary interactions on heart preload, have been found to be accurate indices [1]. Methods for detecting a decreased preload and predicting whether cardiac output will increase with volume expansion have been sought for many years. Respiratory changes in systolic arterial pressure and pulse pressure have been shown to predict an increase in cardiac output in response to volume loading in adult patients [1], so one could presume the same finding in a paediatric population under controlled positive pressure ventilation. However, the several studies that have been performed in the paediatric population have yielded controversial results [3, 4]. In addition, more research in children is needed before incorporation of dynamic parameters into clinical practice. In this regard, as part of the present issue of the Journal of Clinical Monitoring and Computing, the study published