Chapter 40 - Single breath lung mechanics during mechanical ventilation of very low birthweight infants

Abstract

This chapter discusses a study to elaborate the single breath lung mechanics during mechanical ventilation of very low birthweight infants. Ten infants weighing less than 1500 g were studied on one or more occasions in the newborn period. All infants were intubated with a Coles pattern PVC endotracheal tube and ventilated using a pressure limited, time-cycled ventilator. Airway pressure changes were measured at the end of the endotracheal tube. To avoid adding dead space to the infant's breathing circuit, flow was measured using two identical heated pneumotachographs, linear to 12 1/minute placed in the bias flow pathway on either side of the endotracheal tube connection. The correlation coefficients for the slope of the flow/volume plot were high supporting the assumption that the released expiratory flow volume relationship is linear and that compliance and resistance can be expressed as single values. This was despite the infant's upper airway being replaced by a linear resistive endotracheal tube, and held true even in the presence of known linear resistive loads. The estimated resistance of the load was calculated at the infant's mean flow rate and the change in resistance between the mean flow rate and zero flow as estimated in the laboratory was small in relation to the infant's total respiratory resistance.