Effects of Inspiratory Flow Waveforms on Preload

Arterial Pulse Pressure Variation and Inferior Vena Cava Distensibility Affected by Inspiratory Flow Waveforms in Mechanically Ventilated Patients: Time for a Change

The clinical usefulness of inspiratory flow pattern manipulation during mechanical ventilation remains unclear. The aim of this study was to investigate the effects of different inspiratory flow waveforms, i.e. constant and decelerating, on cardiac preload in mechanically ventilated patients assessed by arterial pulse pressure variation (PPV) and inferior vena cava distensibility.

During mechanical ventilation the lungs can be inflated with different pressure and flow waveforms. Originally the piston-driven mechanical ventilators generated a quasi-sinusoidal flow waveform, whereas the newer electronically controlled ventilators can also produce constant and decelerating waveforms. According to several theoretical,animal and clinical studies,the inspiratory flow waveform affects the distribution of the inspired gas as well as respiratory mechanics and gas exchange. However, other studies failed to show any significant effect.But there is no study interested to the effects of inspiratory flow waveforms on cardiac preload. Thus, the clinical usefulness of inspiratory flow pattern manipulation remains unclear, though the capacity for selection of different inspiratory flow waveforms is provided by most modern, microprocessor-equipped ventilators. Therefore, the purpose of this study was to compare the effects of flow patterns (sinusoidal, constant and decelerating) on dynamic measurements of cardiac preload dependence such as arterial pulse pressure variation (ΔPP) and distensibility index of the inferior vena cava (dIVC).

inspiratory flow pattern, mechanical ventilation, cardiac preload, arterial pulse pressure variation, inferior vena cava collapsibility

patients admitted to a 18-bed medical surgical intensive care unit of the military hospital of Tunisia and were mechanically ventilated fully adapted to their ventilator and in sinus rhythm. intervention:varying inspiratory flow waveforms

inspiratory flow waveform was changed, in a randomized sequence using a computer ,to one of the following modalities: 1) constant inspiratory flow; 2) decelerating inspiratory flow Each inspiratory flow waveform was maintained for 30 min. During the last 5 min of this period the physiological signals were collected and measures were performed.

change in pulse pressure variation (ΔPP) and distensibility index of the inferior vena cava (dIVC)when varying inspiratory flow waveforms

Inclusion Criteria: mechanical ventilation Volume AssistControl Ventilation sinus rhythm Exclusion Criteria: pressure mode arrhythmia