Subjective and objective measurement of tidal volume in critically ill patients

Subjective assessment of the respiratory rate and the adequacy of tidal ventilation are the oldest and most widely practiced forms of respiratory monitoring in critically ill patients. Surprisingly, this method of assessment has itself never been evaluated in patients. The estimation of tidal volume in nine patients was performed by full-time intensive care unit (ICU) personnel and compared to the objective measurement of using a calibrated and validated respiratory inductive plethysmograph (RIP). Linear correlation analysis was performed. Poor correlation between clinical estimation by ICU personnel and actual measurement by RIP was revealed in all cases. A widespread and potentially dangerous tendency to overestimate tidal volume was noted. These data suggest that subjective assessment of tidal volume is inaccurate in critically ill patients and that the development of techniques of continuous, nonobtrusive and objective monitoring are to be encouraged.