Plethysmographic dynamic indices predict fluid responsiveness in septic ventilated patients

In septic patients, reliable non-invasive predictors of fluid responsiveness are needed. We hypothesised that the respiratory changes in the amplitude of the plethysmographic pulse wave (ΔP_PLET) would allow the prediction of changes in cardiac index following volume administration in mechanically ventilated septic patients.

Prospective clinical investigation.

An 11-bed hospital medical intensive care unit.

Twenty-three deeply sedated septic patients mechanically ventilated with tidal volume ≥ 8 ml/kg and equipped with an arterial catheter and a pulse oximetry plethysmographic sensor.

Respiratory changes in pulse pressure (ΔPP), ΔP_PLET and cardiac index (transthoracic Doppler echocardiography) were determined before and after volume infusion of colloids (8 ml/kg).

Twenty-eight volume challenges were performed in 23 patients. Before volume expansion, ΔPP correlated with ΔP_PLET (r ² = 0.71, p < 0.001). Changes in cardiac index after volume expansion significantly (p < 0.001) correlated with baseline ΔPP (r ² = 0.76) and ΔP_PLET (r ² = 0.50). The patients were defined as responders to fluid challenge when cardiac index increased by at least 15% after the fluid challenge. Such an event occurred 18 times. Before volume challenge, a ΔPP value of 12% and a ΔP_PLET value of 14% allowed discrimination between responders and non-responders with sensitivity of 100% and 94% respectively and specificity of 70% and 80% respectively. Comparison of areas under the receiver operator characteristic curves showed that ΔPP and ΔP_PLET predicted similarly fluid responsiveness.

The present study found ΔP_PLET to be as accurate as ΔPP for predicting fluid responsiveness in mechanically ventilated septic patients.