Critically ill patients often have complex cardiovascular problems that reduce the delivery of oxygen to the tissues, causing organs to fail. A crucial step in treatment is monitoring tissue perfusion and identifying the main patterns of blood flow (hemodynamic patterns) to guide resuscitation and break this harmful cycle.

In emergency settings, such as the emergency department or the intensive care unit, and in places with limited resources, initial resuscitation decisions might have to be based on very basic clinical information. Furthermore, many treatments given in the intensive care unit, including fluids, diuretics, drugs that affect blood vessel tone (vasoactive drugs), and maneuvers related to the ventilator, can negatively affect the stroke volume in ways that may go unnoticed because specific hemodynamic monitors are not used on all patients.

Recently, capillary refill time, a quick and simple clinical tool used at the bedside, has been suggested as a way to evaluate tissue perfusion or even as a goal for treating septic shock. Capillary refill time is appealing because it is free of cost, noninvasive, and easy to use in many clinical situations.

Unfortunately, there is no simple and widely available clinical monitor that provides similar information about overall blood flow (macrohemodynamic perspective), especially to detect a potentially low stroke volume. This low stroke volume could be due to the underlying circulatory problem or an unwanted side effect of common intensive care unit treatments.

The text explores the question of whether monitoring pulse pressure at the bedside can be useful for detecting very low values of stroke volume or tracking its changes. Pulse pressure has a strong basis in physiology as a reflection of stroke volume. The authors question the limitations and factors that could affect the relationship between pulse pressure and stroke volume, which would help clinicians use pulse pressure as an early warning sign.

The most important clinical question is whether monitoring pulse pressure after intensive care unit admission can detect a low stroke volume so that corrective actions can be taken while more advanced testing, such as pointofcare ultrasound, is being performed. If this simple and costless tool can be validated, it could become a firstline approach for assessing overall blood flow, which would be particularly valuable in resource limited settings or where advanced monitoring is not immediately accessible.

Research Questions and Objectives

Research Question

• In critically ill patients, does pulse pressure, measured through an invasive arterial line, accurately predict stroke volume, as measured by bedside echocardiography (ultrasound)?

• Hypothesis: Pulse pressure will be able to adequately detect low values of stroke volume and track its changes during commonly used dynamic cardiovascular interventions.

Primary Objective

• To determine how well pulse pressure can predict a low stroke volume, assessed by bedside ultrasonography, in critically ill patients.

Secondary Objectives

• To assess the ability of pulse pressure to predict low stroke volume in different clinical situations in intensive care unit patients, such as those with acute respiratory distress syndrome, after surgery, or with septic shock.

• To evaluate the impact of various factors (like mechanical ventilation, vasoactive medication, age, and the position of the arterial line) on the predictive ability of pulse pressure to estimate stroke volume.

• To determine the capacity of pulse pressure to track changes in stroke volume during common intensive care interventions such as the passive leg raising maneuver, fluid challenges, starting or adjusting vasoactive drugs, or ventilator related maneuvers like adjusting positive end expiratory pressure and recruitment maneuvers.