Konno-Mead analysis of ribcage-abdominal motion during successful and unsuccessful trials of weaning from mechanical ventilation

Respiratory muscle fatigue is considered a common cause of weaning failure but its detection is hampered by the lack of a satisfactory diagnostic test. Abdominal paradox has been proposed as a valuable clinical index of fatigue and thus its presence may lead to curtailment of weaning trials. However, sensitivity and specificity of this sign as a predictor of weaning outcome is unknown. We hypothesize that abnormal ribcage-abdominal (RC-Ab) motion is a common finding in the early stages of weaning and its presence does not inevitably imply an unsuccessful weaning outcome. We tested this hypothesis in patients undergoing a weaning trial: one group had a successful weaning outcome and were extubated (n = 10) and the other group failed the trial (n = 7). Normal RC-Ab motion was separately characterized in 17 healthy subjects. Employing a calibrated respiratory inductive plethysmograph, quantitative assessment of asynchrony and paradox was obtained by computing several indices from series of breaths at fixed time periods using the Konno-Mead method of analysis. During the weaning trial, both groups of patients displayed significant increases in asynchrony and Ab paradox compared to normal values. As a group, patients who failed the trial displayed significantly greater asynchrony and paradox of the RC and Ab than patients with a successful outcome. However, there was considerable overlap between the individual patients in the 2 study groups. Only 3 indices, inspiratory RC paradox, the ratio of maximum compartmental amplitude to tidal volume (which takes into account both asynchrony and paradox), and breath-to-breath variability in RC and Ab contribution to tidal volume, appeared to discriminate between the 2 groups. In conclusion, abnormal ribcage-abdominal motion is a common finding in the early stages of weaning from mechanical ventilation and its presence does not inevitably imply weaning failure.