Point of View: A Holistic Four-Interface Conceptual Model for Personalizing Shock Resuscitation

Abstract

The resuscitation of a patient in shock is a highly complex endeavor that should go beyond normalizing mean arterial pressure and protocolized fluid loading. We propose a holistic, four-interface conceptual model of shock that we believe can benefit both clinicians at the bedside and researchers. The four circulatory interfaces whose uncoupling results in shock are as follows: the left ventricle to arterial, the arterial to capillary, the capillary to venular, and finally the right ventricle to pulmonary artery. We review the pathophysiology and clinical consequences behind the uncoupling of these interfaces, as well as how to assess them, and propose a strategy for approaching a patient in shock. Bedside assessment of shock may include these critical interfaces in order to avoid hemodynamic incoherence and to focus on microcirculatory restoration rather than simply mean arterial pressure. The purpose of this model is to serve as a mental model for learners as well as a framework for further resuscitation research that incorporates these concepts.

Keywords: coherence; hemodynamics; microcirculation; resuscitation; sepsis; shock.

Figure 1

Diagrammatic representation of the four main circulatory interfaces.

Figure 2

Theoretical response surface model for a given mean arterial pressure (70 mmHg) according to different combinations of vascular resistance, cardiac output, and preload. MAP: mean arterial pressure; MSFP: mean systemic filling pressure. Note that cardiac output can be adequate or inadequate for the same MAP when it is maintained by a higher resistance.

Figure 3

Forrester–Kenny diagram showing the four phenotypic quadrants as well as dynamic phenotypes. Note that different parameters of forward flow and venous congestion may be used depending on available technology and physician familiarity.

Figure 4

Basic and advanced assessment alternatives for each interface (note that this may evolve with further research to include new parameters). Abbreviations: TAPSE—tricuspid annular plane systolic excursion; PASP—pulmonary artery systolic pressure; S’—tissue Doppler velocity; RV—right ventricle; FAC—fractional area change; Ees/Ea—end-systolic elastance/arterial elastance; JVP—jugular venous pulse; CVP—central venous pressure; LVEF—left ventricular ejection fraction; VTI—velocity time integral; VExUS—venous excess ultrasound; RVSI—renal venous stasis index; JV—jugular venous; MSFP—mean systolic filling pressure; NIRS—near infrared spectroscopy; VOT—vascular occlusion test.

Figure 5

Clinical scenario illustrating the evolution of a patient undergoing resuscitation in a framework of both congestive and forward flow parameters.