[Experimental study of changes in FiO2 during manual ventilation].
Discrepancies exist in the recommendations about the oxygen flow to deliver during manual ventilation. The aim of the present study was to determine the effects of ventilatory frequency (FR), inspiratory pressure (P) and oxygen flow on the concentration of the delivered oxygen (FiO2) to obtain FiO2 near 1.


METHODS
Experimental study with self-inflating resuscitation bag (Ambu with oxygen reservoir) tested on a mono-compartmental test lung (resistant tube and elastic bag [Draeger]; characteristics: compliance = 0.6 mL/cmH2O; resistance = 85 cmH2O.L-1.s-1). Protocol 1: six neonatologists ventilated this model as if they were ventilating premature newborn infants with RDS at various ventilatory rates from 30 to 120 bpm and at various oxygen flows (from 2 to 12 L/min). Tidal volumes (Vt), inspiratory times (Ti), P and FiO2 were recorded continuously during the study. Protocol 2: a graduated manometer was added to visualize pressure. The same protocol was then applied.


RESULTS
Protocol 1 (without visual control of the pressure): increase in oxygen flow delivered with the Ambu increases the FiO2 values (P < 0.0001); the higher the ventilatory frequency, the lower the FiO2 (P < 0.0001). The mean value of delivered FiO2 was related to the operator (extreme: 47-86%) (P < 0.001). Multivariate statistical analysis showed that O2 flow, ventilator rate and operator modulated independently the FiO2. Ti and Vt did not change the FiO2. Protocol 2 (with visual control of the pressure: the mean inflating pressures were less than those obtained without visual control of the pressure (26 vs 40 cmH2O respectively; P < 0.05). FiO2 was independent of O2 flow and ventilatory rate.


CONCLUSIONS
A special device for continuous visual control of airway pressure is recommended during neonatal manual ventilation. It prevents ventilatory rate-induced FiO2 fluctuations and overdistention.
Diependaele
J F
JF
Smur pédiatrique-Samu de Lille, Lille, France.
Rakza
T
T
Truffert
P
P
Abazine
A
A
Riou
Y
Y
Goldstein
P
P
Lequien
P
P
Storme
L
L
D004867:Equipment Design; D006801:Humans; D007231:Infant, Newborn; D010100:Oxygen / Q000008:administration & dosage*; D011312:Pressure; D012121:Respiration, Artificial / Q000379:methods*; D012129:Respiratory Function Tests
D010100:Oxygen