Experimental study of changes in oxygen concentrations during self-inflating bag ventilation

Discrepancies exist in the recommendations about the oxygen flow to deliver during manual ventilation. The aim of the present study was to determine t he effects of ventilatory frequency (FR), inspiratory pressure (P) and oxyg en flow on the concentration of the delivered oxygen (FiO(2)) to obtain FiO (2) near 1. Material and methods. - Experimental study with self-inflating resuscitatio n bag (Ambu(R) with oxygen reservoir) tested on a mono-compartmental test l ung (resistant tube and elastic bag [Draege(R)]; characteristics: complianc e = 0.6 mL/cmH(2)O; resistance = 85 cmH(2)O.L-1.s(-1)). Protocol 1: six neo natologists ventilated this model as if they were ventilating premature new born infants with RDS at various ventilatory rates from 30 to 120 bpm and a t various oxygen flows (from 2 to 12 L/min). Tidal volumes (Vt), inspirator y times (Ti), P and FiO(2) were recorded continuously during the study Prot ocol 2: a graduated manometer was added to visualize pressure. The same pro tocol was then applied. Results. - Protocol 1 (without visual control of the pressure): increase in oxygen flow delivered with the Ambu(R) increases the FiO(2) values (P < 0. 0001); the higher the ventilatory frequency, the lower the FiO(2) (P < 0.00 01). The mean value of delivered FiO(2) was related to the operator (extrem e: 47-86%) (P < 0.001). Multivariate statistical analysis showed that O-2 f low, ventilator rate and operator modulated independently the FiO(2). Ti an d Vt did not change the FiO(2). Protocol 2 (with visual control of the pres sure: the mean inflating pressures were less than those obtained without vi sual control of the pressure (26 vs 40 cmH(2)O respectively; P < 0.05). FiO (2) was independent of O-2 flow and ventilatory rate. Conclusions. - A special device for continuous visual control of airway pre ssure is recommended during neonatal manual ventilation. It prevents ventil atory rate-induced FiO(2) fluctuations and overdistention. (C) 2001 Edition s scientifiques et medicales Elsevier SAS.