Decreased lung compliance increases preload dynamic tests in a pediatric acute lung injury model

Area of Science:

• Critical care medicine
• Pediatric physiology
• Respiratory mechanics

Background:

• Dynamic preload tests, including pulse pressure variation (PPV) and stroke volume variation (SVV), are vital for predicting fluid responsiveness.
• The impact of factors beyond preload on these dynamic tests, particularly in pediatric patients, remains incompletely understood.
• Assessing the influence of tidal volume (VT) on PPV and SVV under varying lung compliance conditions is crucial for accurate clinical interpretation.

Purpose of the Study:

• To evaluate the effect of different tidal volumes (VT) on PPV and SVV.
• To investigate these effects in the context of both normal and reduced lung compliance.
• To provide insights into the interpretation of dynamic preload tests in pediatric critical care.

Main Methods:

• Utilized a piglet model (n=20) for the study.
• Anesthesia and paralysis were administered, with monitoring via pulse contour analysis.
• PPV and SVV were measured during mechanical ventilation using low (6 mL/kg) and high (12 mL/kg) VT, before and after inducing acute lung injury (ALI) with polysorbate 20.

Main Results:

• Before ALI induction, changes in VT did not significantly alter PPV and SVV.
• Following ALI induction, both PPV and SVV were significantly elevated during high VT ventilation compared to low VT ventilation (P<0.01).
• Specifically, PPV increased from 8.9±1.2% to 12.4±1.1%, and SVV from 8.5±1.0% to 12.7±1.2% after ALI with high VT.

Conclusions:

• High tidal volume and reduced lung compliance, as seen in ALI, significantly increase dynamic preload test values.
• Reduced lung compliance exerts a more substantial influence on PPV and SVV than tidal volume alone.
• Clinicians must consider lung compliance when interpreting dynamic preload tests in patients with ALI.