Abstract
Background
To detect preload responsiveness in patients ventilated with a tidal volume (Vt) at 6 mL/kg, the Vt challenge consists in increasing Vt from 6 to 8 mL/kg and measuring the induced increase in pulse pressure variation (PPV). However, this requires an arterial catheter. The perfusion index (PI), which reflects the amplitude of the plethysmographic signal, may reflect stroke volume and its respiratory variation (pleth variability index, PVI) may be a surrogate of PPV. We assessed whether changes in PVI or PI during a Vt challenge could be as reliable as changes in PPV for detecting preload responsiveness.
Methods
In critically ill patients mechanically ventilated with Vt = 6 mL/kg and no spontaneous breathing activity, monitored with a PiCCO2 system and a Masimo SET technique (sensor placed on the finger or the forehead), haemodynamic data were recorded during a Vt challenge and a passive leg raising (PLR) test. Preload responsiveness was defined by a PLR-induced increase in cardiac index ≥ 10%.
Results
Among 63 screened patients, 21 were excluded because of an unstable PI signal and/or atrial fibrillation. Among the 42 included patients, 16 were preload responders. During the Vt challenge in preload responders, PPV (absolute change), PI measured on the finger (percent change), PVI measured on the finger (absolute change), PI measured on the forehead (percent change) and PVI measured on the forehead (absolute change) changed by 4.4 ± 1.9%, -14.5 ± 10.7%, 1.9 ± 2.6%, -18.7 ± 10.9 and 1.0 ± 2.5, respectively. All these changes were significantly larger than in preload non-responders.