Proportional assist ventilation in infants

Conventional patient-triggered ventilation attempts to synchronize the upstroke in ventilator pressure with the onset of spontaneous inspiration. Other parameters of the mechanical cycle such as the peak inspiratory pressure are preset by the clinician. They will be imposed on the infant regardless of the actual spontaneous respiratory drive. Proportional assist ventilation (PAV) and respiratory mechanical unloading of spontaneous breathing (RMU, resistive and elastic unloading) are based on fundamentally different concepts. In contrast to the conventional perception of the ventilator being a "pump", PAV/ RMU servo-control the applied ventilator pressure continuously throughout each inspiration. These modalities proportionally enhance the effect on ventilation of each respiratory effort. They rely on rather than interfere with the subject's respiratory control system. The patient controls all variables of the respiratory pattern while the ventilator works fully enslaved as a proportional amplifier. Backup conventional mechanical ventilation is initiated during episodes of hypoventilation and apnea. The clinician sets the degree of the assist during PAV/ RMU in terms of "gains". Selecting specific "gains" for the elastic and resistive unloading components allows to tailor the ventilator pressure waveform to the individual degree of restrictive and obstructive pulmonary disease. This results in a reduction of the transpulmonary pressure cost of ventilation compared to conventional modes. However, further studies on PAV/ RMU are required to evaluate clinically important long-term outcome variables in infants and to determine whether the benefits outweigh potential drawbacks and the complexity involved in these new modes of mechanical ventilation.