Venous return and mean systemic filling pressure: physiology and clinical applications

Abstract

Venous return is the flow of blood from the systemic venous network towards the right heart. At steady state, venous return equals cardiac output, as the venous and arterial systems operate in series. However, unlike the arterial one, the venous network is a capacitive system with a high compliance. It includes a part of unstressed blood, which is a reservoir that can be recruited via sympathetic endogenous or exogenous stimulation. Guyton’s model describes the three determinants of venous return: the mean systemic filling pressure, the right atrial pressure and the resistance to venous return. Recently, new methods have been developed to explore such determinants at the bedside. In this narrative review, after a reminder about Guyton’s model and current methods used to investigate it, we emphasize how Guyton’s physiology helps understand the effects on cardiac output of common treatments used in critically ill patients.

Feasibility to estimate mean systemic filling pressure with inspiratory holds at the bedside

“…Our results are in line with previous studies demonstrating the effect of a fluid bolus on MSFP ( Keller et al, 2011 ; Guerin et al, 2015 ). Although MSFP is thought central for the characterization of the circulation, the subsequent derived values such as Vs and Csys are subject to physiologic variability, though if accurate, of potentially greater clinical value ( Rothe, 1993 ; Vos et al, 2020 ; Persichini et al, 2022 ).…”

“…Furthermore, if knowing accurate Vs and Csys is required, then defining the optimal fluid type (colloid vs. crystalloid) and the minimal volume challenge needed to determine Vs and Csys needs to be assessed. Being able to quickly and reliably calculate MSFP, Csys and Vs could be beneficial in guiding hemodynamic care in various types of patients ( Rothe, 1993 ; Vos et al, 2020 ; Persichini et al, 2022 ). For example, in current sepsis resuscitation, first fluids are administered and subsequently (after >2 L of fluids is added in a normal sized adult patient), a vasopressor is started.…”

“…For example, in current sepsis resuscitation, first fluids are administered and subsequently (after >2 L of fluids is added in a normal sized adult patient), a vasopressor is started. Based on a Guytonian approach to the circulation, however, it would make more sense to start a vasopressor earlier in the treatment to recruit unstressed to the stressed volume ( Adda et al, 2021 ; Persichini et al, 2022 ). Recruiting unstressed to stressed volume is an important survival mechanism of the human body.…”

“…Recruiting unstressed to stressed volume is an important survival mechanism of the human body. Measuring MSFP, Vs, and Csys might lead to a reduction in the total amount of fluids administered for resuscitation ( Ospina-Tascón et al, 2020 ; Persichini et al, 2022 ). Despite the use of invasive hemodynamic monitoring options available in the ICU, we still lack direct and repetitive estimation of the effective circulating volume (Vs).…”

“…MSFP has helped to better understand the effects of vasopressors, propofol, and hyperoxia ( Maas et al, 2013 ; de Wit et al, 2016 ; Helmerhorst et al, 2017 ; Adda et al, 2021 ). MSFP and the derived parameters could potentially be beneficial to guide hemodynamic care in patients admitted to the intensive care unit (ICU) ( Rothe, 1993 ; Vos et al, 2020 ; Persichini et al, 2022 ).…”