RATIONAL MANAGEMENT OF ASSISTED VENTILATION

Abstract

Total ventilation (VIT) of artifically ventilated infants equals mechanical ventilation (VIM) plus infant ventilation (VIB) or VIT=VIM+VIB. Since ventilation is the product of tidal volume (VT) and frequency (f) then VTTxfT=(VTMxfM)+(VTBxfB). To evaluate any change in ventilatory support it is necessary to measure all the factors in the above equation. We examined the effects of reduced PEEP on the mean values and trends in these factors with continuous measurements of ventilation during alternate 30 min. periods of PEEP at 6cm H20, or 2cm H2O. Ventilator rate, FiO2 and peak pressure (PIP) were constant. Ten studies were performed on 6 infants weighing 740 to 1000g. All breaths were analyzed, X̄=4020 breaths/hour/infant. At PEEP 2cm H2O VTM increased immediately due to a 4cm H2O increase in ΔP, then progressively decreased in all patients over time (x̄ decrease =15%). Thus at PEEP=2 VIB is less efficient (smaller VTB & increased fB) & contributes less to VIT. Optimal management of infants on assisted ventilation is not possible without continuous measurements of the above ventilatory parameters.