A strong relationship between respiratory variations in pulse pressure (PPV) and airway pressure in fluid nonresponders: a potential explanation for false positive PPV values

Respiratory variations in pulse pressure (PPV) during mechanical ventilation predict fluid responsiveness when the tidal volume is >8 ml/kg [1]. The effect of airway pressure on the ability of PPV to predict fluid responsiveness is less explored. In patients undergoing major abdominal surgery, we found low specificity of PPV and therefore explored the relation between peak airway pressure (Paw) and PPV in fluid challenge nonresponders.

Twenty-five patients scheduled for open abdominal surgery with volume controlled ventilation 8 ml/kg, I:E ratio 1:2 and PEEP 5 cmH₂O were included. Fluid challenges of 250 ml colloid were administered at the discretion of the anesthesiologist. PPV, hemodynamic variables, Paw and stroke volume (SV) measured by oesophageal Doppler were recorded before and after fluid challenges. Responders were defined by an increase in SV >15%.

In this study on patients undergoing open abdominal surgery ventilated with 8 ml/kg, specificity of PPV was low. Paw and PPV were strongly correlated and false positive PPVs were associated with high Paw. This finding indicates that not only tidal volume, but also airway pressures may affect the ability of PPV to predict fluid responsiveness.