Objective: The use of respiratory mechanics to optimise ventilator settings has become more common since the integration of pressure and flow transducers into modern ventilators. However, values of respiratory resistance (R(rs)) and compliance (C(rs)) can be overestimated in the presence of tracheal tube leak and clinical decisions based on these figures would be misinformed. This study aimed to assess the influence of tracheal tube leak on measurements of C(rs), R(rs) and expired tidal volume (V(TE)) in ventilated children in order to establish when such measurements were reliable in this population.
Design: Respiratory function was monitored for at least five consecutive hours during which normal medical procedures were performed. The magnitude and variability of tracheal tube leak was assessed during these periods.
Setting: The paediatric and cardiac intensive care units at Great Ormond Street Hospital for Children, NHS Trust, London.
Patients: Seventy-five paralysed, fully ventilated infants and children.
Results: Ten children had a mean leak greater than 20% (range: 22%-65%). Amongst this group there were wide fluctuations with respect to leak magnitude, V(TE), C(rs) and R(rs). Leaks of less than 20% appeared necessary to obtain reliable measurements of C(rs) and R(rs) and to ensure consistent and adequate ventilation.
Conclusions: Leaks larger than 20% result in inconsistent tidal volume delivery and gross overestimation of C(rs) and R(rs) irrespective of ventilation mode. The magnitude of tracheal tube leak needs to be accurately displayed on all ventilatory equipment to verify reliable measures of respiratory function so that appropriate clinical decisions can be made and ventilatory management optimised.