The mean age of the pediatric patients was 8.7±5.6 years (median: 5.7 years) with a mean weight of 27.9☒2.9 kg (median: 17 kg). The mean age of the infant population was 2.8☒.3 months (median: 2.8 months), and the mean weight was 4.6☓.3 kg (median: 3.8 kg).

Seventy patients were ventilated using infant circuits and 28 patients were ventilated using pediatric circuits. The pneumotachometer was placed between the ventilator circuit and the endotracheal tube.

Respiratory parameters were measured both at the expiratory valve of the ventilator and using a pneumotachometer connected to a respiratory mechanics monitor. Cannon et al 2 studied 98 conventionally ventilated infants and children. Significant differences in ventilator-determined Vts, pneumotachometer-determined Vts, and calculated effective Vts exist, especially in neonates, infants, and young children who require small Vts. When Vts are measured using a pneumotachometer positioned between the ventilator circuit and the endotracheal tube, the ventilator circuits compliance and the confounding circuit variables are no longer pertinent factors. Therefore, calculating the delivered Vt using an expiratory-valve measurement and the circuit-compliance factor would not be expected to give an accurate determination of the Vt actually delivered to the patients lungs. The circuit-compliance factor does not consider uncontrolled variables such as heaters, in-line suction devices, adapters for end-tidal carbon dioxide monitors, changes in temperature, secretions, or condensation. 1 This equation, however, is based on a circuit-compliance factor that is derived using the circuit as it is packaged at room temperature in a manufacturing facility. Theoretically, the effective Vt is defined as the Vt measured at the expiratory valve minus the volume of gas lost due to the distensibility of the circuit, calculated as the figure for peak inspiratory pressure minus positive end-expiratory pressure (PEEP) multiplied by circuit compliance. To determine the actual Vt delivery, one can employ a mathematical equation to correct for the circuits compliance. The compliance factor of a ventilator circuit is printed on its package or can be obtained from the circuits manufacturer. The volume of gas lost due to distensibility of the ventilator circuit is partially attributable to the compliance of the circuit. Vt determination at the endotracheal tube is more likely to represent the actual Vt of the patients lungs accurately than is Vt measured at the expiratory valve of the ventilator. Since a significant volume of the gas that is delivered by the ventilator may be lost due to circuit conditions, it is essential to measure the Vt that reaches the endotracheal tube accurately in infants and small children. The determined values of these ventilators are often used clinically for important patient-care decisions however, due to multiple circuit variables (such as circuit compliance, heaters, in-line suction devices, secretions, and condensation), the Vt measured at the expiratory valve of a ventilator does not accurately represent the Vt truly delivered.Ī determination of Vt at the expiratory valve of a ventilator does not compensate for the volume of gas lost due to the distensibility of the ventilator circuit, nor does it compensate for the many different variations in the circuit setup. Many conventional ventilators measure Vt at the expiratory valve. Considering the small Vts used in ventilating infants and young children, small inaccuracies in Vt determination may result in significantly adverse conditions. Accurate measurement of delivered tidal volumes in infants and children is essential during mechanical ventilation.Īn accurate determination of the tidal volume (Vt) delivered to a patients lungs is essential when mechanically ventilating infants and children.

Calculating tidal volume