Frank-Starling and Guyton together at bedside during a fluid challenge

Abstract

Introduction According to Guyton, the difference between mean systemic filling pressure (Pms) and right atrial pressure (RAP) is the venous pressure gradient (VP). This is proportional to venous return and cardiac output (CO). According to the Frank-Starling law a fluid challenge successfully increases the stroke volume if the preload increases in the ascending part of the curve. The aim of this study was to assess the significance of the analogue of the Pms (Pmsa) measured with the NavigatorTM (Applied Physiology, St Leonards, Australia), the central venous pressure (CVP) (as a surrogate of RAP) and the VP during a fluid challenge. Methods A prospective observational study was performed in postsurgical patients. Patients were monitored with a central venous catheter, an arterial line, a calibrated LiDCOTMplus (LiDCO, Cambridge, UK) and the NavigatorTM. A 250 ml fluid challenge was used to maximise the stroke volume (SV). Data were recorded before and after the fluid challenge which was given over 5 minutes. A positive response to the fluid challenge was defined as either a stroke volume or CO increase of 10% or more. Results Twenty-five fluid challenges in 14 patients were observed. In seven cases (28%), the fluid challenge increased SV (and CO) by >=10% (Table 1). At baseline there were no differences between HR, Pmsa, CVP or DELTAVP for responders or nonresponders. The responders had greater changes in DELTAVP in response to the challenge. (Table presented) Conclusion Our study demonstrates that the NavigatorTM may be used to monitor the effect of fluid challenges by assessing the change in VP to the challenge.