Neuroventilatory efficiency and extubation readiness in critically ill patients
1 Department of Critical Care Medicine, Nanjing Zhong-Da Hospital, Southeast University School of Medicine, 87 Dingjiaqiao Street, Nanjing 210009, China
2 Department of Critical Care, St. Michael's Hospital, Keenan Research Centre in the Li Ka Shing Knowledge Institute of St. Michael's Hospital, 30 Bond Street, Toronto, Ontario, M5B1W8 Canada
3 Department of Pediatrics, University of Toronto, Hospital for Sick Children, 555 University Avenue, Toronto, Ontario M5G 1X8 Canada
4 Department of Medicine, Interdepartmental Division of Critical Care Medicine, University of Toronto, Ontario M5G 1X8 Canada
Critical Care 2012, 16:R143 doi:10.1186/cc11451
See related letter by Wang and Bai, http://ccforum.com/content/16/6/461Published: 31 July 2012
Based on the hypothesis that failure of weaning from mechanical ventilation is caused by respiratory demand exceeding the capacity of the respiratory muscles, we evaluated whether extubation failure could be characterized by increased respiratory drive and impaired efficiency to generate inspiratory pressure and ventilation.
Airway pressure, flow, volume, breathing frequency, and diaphragm electrical activity were measured in a heterogeneous group of patients deemed ready for a spontaneous breathing trial. Efficiency to convert neuromuscular activity into inspiratory pressure was calculated as the ratio of negative airway pressure and diaphragm electrical activity during an inspiratory occlusion. Efficiency to convert neuromuscular activity into volume was calculated as the ratio of the tidal volume to diaphragm electrical activity. All variables were obtained during a 30-minute spontaneous breathing trial on continuous positive airway pressure (CPAP) of 5 cm H2O and compared between patients for whom extubation succeeded with those for whom either the spontaneous breathing trial failed or for those who passed, but then the extubation failed.
Of 52 patients enrolled in the study, 35 (67.3%) were successfully extubated, and 17 (32.7%) were not. Patients for whom it failed had higher diaphragm electrical activity (48%; P < 0.001) and a lower efficiency to convert neuromuscular activity into inspiratory pressure and tidal volume (40% (P < 0.001) and 53% (P < 0.001)), respectively. Neuroventilatory efficiency demonstrated the greatest predictability for weaning success.
This study shows that a mixed group of critically ill patients for whom weaning fails have increased neural respiratory drive and impaired ability to convert neuromuscular activity into tidal ventilation, in part because of diaphragm weakness.
Clinicaltrials.gov identifier NCT01065428. ©2012 Liu et al.; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0 webcite), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.