Relationship Between Pulse Pressure and Stroke Volume in the Critically Ill Patients: The ANDROMEDA-PEGASUS Study

Critically ill patients often present complex cardiovascular derangements that impair oxygen delivery to the tissues leading to progressive organ dysfunction. Monitoring tissue perfusion and identifying the predominant hemodynamic patterns are key clinical objectives to implement resuscitative strategies and revert this vicious cycle. However, in different stages of acute circulatory dysfunction at the emergency department (ED) or the intensive care unit (ICU), or resource-limited settings, initial resuscitative decisions may be taken with basic clinical information only. In addition, many therapeutic interventions in the ICU such as fluids, diuretics, vasoactive drugs, and ventilatory-related maneuvers, among others, may jeopardize stroke volume (SV) in different ways, a fact that may evolve undetected due to the absence of specific hemodynamic monitors in all patients.

Unfortunately, there is no simple, costless, and universally available clinical monitor to detect low SV. There have been, however, physiological implications to use blood pressure components as a surrogate for SV. Although pulse pressure (PP) has been observed to be largely determined by SV in experimental conditions, the key issues remain to be clarified: can PP monitoring at the bedside be useful to detect extreme values, or track changes, in underlying SV? Moreover, what are the limitations, the contexts, the technical aspects, among other factors, that can affect this relationship, and thus help clinicians to potentially use PP as an early warning signal or a trigger for initial resuscitative or therapeutic interventions?

From a clinical point of view, the most relevant question is if PP monitoring can detect a low SV so that corrective measures might be implemented, while more advanced confirmatory monitoring, including point-of-care ultrasound, is pending. In addition, what are the potential confounders for this assumption? If these questions are answered, this simple and costless tool may be used as a first-line approach for macrohemodynamic profiling and clinical decision-making, which could be especially valuable in resource-limited settings and in sites where ultrasound or advanced cardiac output monitoring is not immediately available. In this multicenter, observational, cross-sectional study, we aim at answering the following research question:

Research Question

• In critically ill patients, does pulse pressure, measured through an invasive arterial line, have an adequate predictive capacity to estimate stroke volume, as assessed by bedside echocardiography?
• We hypothesize that pulse pressure will be able to adequately detect low values of stroke volume, and to track changes of stroke volume during commonly used dynamic cardiovascular interventions.

Primary Objective

• To assess the predictive capacity of pulse pressure to detect low stroke volume, evaluated by bedside ultrasonography in critically ill patients.

Secondary Objectives

• To assess the predictive capacity of PP to detect low SV in different clinical contexts in ICU patients, such as in those with acute respiratory distress syndrome (ARDS), postoperative states, or septic shock, among others.
• To assess the impact of several demographic, clinical and technical issues on the predictive capacity of PP to estimate SV, such as mechanical ventilation, vasoactive medication, age, position of the arterial line, among others.
• To determine the capacity of PP to track changes of SV during common intensive care interventions such as passive leg raising (PLR) maneuver or fluid challenges.

Inclusion criteria

• 18 years
• Admitted to ICU
• Functioning arterial line in place

Exclusion criteria

• Pregnancy
• Inadequate arterial line transduction (see below)
• Refusal of consent
• Patient who requires extracorporeal circulation