Canine left ventricular volume response to mechanical ventilation with PEEP

Area of Science:

• Cardiovascular Physiology
• Respiratory Mechanics
• Critical Care Medicine

Background:

• Positive End-Expiratory Pressure (PEEP) is commonly used in mechanical ventilation.
• PEEP can affect cardiac output (CO) and hemodynamics.
• The precise mechanism of CO reduction by PEEP requires further elucidation.

Purpose of the Study:

• To investigate the cause of decreased cardiac output (CO) during mechanical ventilation with PEEP.
• To assess the role of left ventricular preload in PEEP-induced CO reduction.
• To evaluate the adequacy of transmural left ventricular end-diastolic pressure (TMLVEDP) as a preload indicator.

Main Methods:

• Hemodynamic and pulmonary parameters were monitored in nine dogs.
• Radiographic estimates of left ventricular volumes were obtained.
• Measurements were taken under control, PEEP, and PEEP with intravascular volume expansion conditions.

Main Results:

• PEEP application decreased cardiac index (CI), stroke volume index (SI), and left ventricular stroke work index (LVSWI) by approximately 30%.
• Ejection fraction remained unchanged.
• Intravascular volume expansion restored CI, SI, and LVSWI to baseline levels, while TMLVEDP did not significantly change.

Conclusions:

• Reduced left ventricular preload is the primary cause of decreased cardiac output associated with PEEP.
• Transmural left ventricular end-diastolic pressure is an inadequate measure of preload under PEEP conditions.
• Volume expansion can effectively counteract PEEP-induced reductions in cardiac output.