Predicting Fluid Responsiveness Using Transiently Increased Intrathoracic Pressure in Mechanically Ventilated Patients

Once an eligible subject is identified and written or telephone consent is obtained from the patient or surrogate as appropriate, we will record demographic data and clinical information including age, sex, height, actual body weight, predicted body weight (PBW), APACHE II on admission, primary diagnosis, reason for ICU admission, and dose of vasopressors.

Patients will be intubated and on assist-control volume ventilation receiving low tidal volumes. Sedation will be titrated per current MICU protocol to minimize patient discomfort and minimizing ventilator dyssynchrony. In keeping with standard practice, the dose of vasoactive medications will be kept constant during the intervention period. The standard practice is to titrate vasopressor therapy every five minutes, so keeping vasoactive medications constant for sixty seconds is in keeping with the standard of care. All subjects will be in an ICU setting and monitored per standard of care (vital signs, telemetry, ventilator data) by a respiratory therapist, pulmonary and critical care fellow or faculty member, and critical care nurse at the bedside throughout the entire intervention.

A point of care (POC) echocardiogram will be performed by the investigator performing the intervention in order to measure the stroke volume index (surrogate for cardiac output).

Subjects will be randomized to either undergo the PEEP challenge or tidal volume challenge first. After the initial challenge, subjects will cross over to whichever challenge has not yet been performed.

The simple changes to the ventilator we are proposing to use as challenges in this study are done frequently and routinely in the ICU with or without the supervision of a physician, but we will have a physician present throughout the entire proposed intervention. For the subjects undergoing PEEP challenge first, we will do the following: