Les respirateurs d'anesthésie de nouvelle génération vont-ils modifier notre pratique chez l'enfant ?

Abstract

Because of specific paediatric respiratory physiology (mainly decreased compliance and functional residual capacity, increased O 2 demand and CO 2 production), ventilators for paediatric anaesthesia need to be powerful and able to deliver small volumes at a high rate without compression volume loss. The compensation of compliance now available on every anaesthesia machine, compensates for the volume of gas lost by compression in the circuit tubing allowing the tidal volume to reach preset commands, even for bellow in box respirators. Preset tidal volume is then totally delivered to the lung by volume-controlled ventilation because it becomes independent of total pulmonary compliance and fresh gas flow. Increased precision of electronic flowmeters and better air-tightness of circuits allow reducing with precision fresh gas flow to values approaching children's O 2 consumption and N 2O diffusion. New modes of ventilation are now available on anaesthesia machine. Pressure controlled mode, by increasing and maintaining mean airway pressures, ameliorates intrapulmonary gas distribution and compensates for the gas leak from uncuffed tracheal tubes. Unsteady tidal volume resulting from variation of total compliance, is the main drawback of pressure-controlled ventilation that may be overcome by using the “autoflow” mode (better described as a pressure controlled mode ensuring tidal volume) available with one of the last generation of ventilators. Increased accuracy and security of the mode “pressure assist” might increase the use of spontaneous ventilation in paediatric anaesthesia even for low weight children. However tidal volume remains variable with compliance and depth of anaesthesia, which may require several adjustments of ventilator's settings. The clinical conditions (mainly airway control) of pressure assist use for children less than 10 kg should be elucidated before recommending its use.