Abstract
BackgroundRecent studies in haemodynamic management have focused on fluid management and assessed its effects in terms of increase in cardiac output based on fluid challenges or variations in pulse pressure caused by cyclical positive pressure ventilation. The theoretical scope may be characterised as Starling-oriented. This approach ignores the actual events of right-sided excitation and left-sided response which is consistently described in a Guyton-oriented model of the cardiovascular system.AimBased on data from a previous study, we aim to elucidate the primary response to crystalloid and colloid fluids in terms of cardiac output, mean blood pressure and right atrial pressure as well as derived and efficiency variables defined in terms of Guyton venous return physiology.MethodRe-analyses of previously published data.ResultsCardiac output invariably increased on infusion of crystalloid and colloid solutions, whereas static and dynamic efficiency measures declined in spite of increasing pressure gradient for venous return.DiscussionWe argue that primary as well as derived and efficiency measures should be reported and discussed when haemodynamic studies are reported involving fluid administrations.
Highlights
Recent studies in haemodynamic management have focused on fluid management and assessed its effects in terms of increase in cardiac output based on fluid challenges or variations in pulse pressure caused by cyclical positive pressure ventilation
Cardiac output invariably increased on infusion of crystalloid and colloid solutions, whereas static and dynamic efficiency measures declined in spite of increasing pressure gradient for venous return
We introduce the calculation of power efficiency, Power efficiency (Epower) showing the same pattern as Heart efficiency (Eh) and Volume efficiency (Evol): slightly declining and with great variance in the crystalloid group and rather stable with low variance in the colloid group
Summary
Recent studies in haemodynamic management have focused on fluid management and assessed its effects in terms of increase in cardiac output based on fluid challenges or variations in pulse pressure caused by cyclical positive pressure ventilation. We observe the increase in CO with a cut-off at 10–15% (dictated by minimum discernible difference of CO monitor) in response to a volume increment of 250–500 mL of fluid It is, often unspecified which type of fluid and whether the volume should be fixed, related to body size or adapted to the vascular compliance of the patient and which infusion rate should be used. Often unspecified which type of fluid and whether the volume should be fixed, related to body size or adapted to the vascular compliance of the patient and which infusion rate should be used Inotropy is another option increasing CO, and guidelines usually refer the clinician to the use of inotropic therapy when the preloading option does not confer a CO increase > 10%. In the Starling model, there is no option for quantifying the ‘cost’ of volume resuscitation, ɔ: how efficiently added volume results in an increase in cardiac power ((MAP − CVP) × CO), nor numerically characterise heart efficiency and changes therein
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