Atul Palkar

Diaphragm Excursion-Time Index: A New Parameter Using Ultrasonography to Predict Extubation Outcome

Background The diaphragmatic response to increased mechanical load following withdrawal of mechanical ventilation is critical in determining the outcome of extubation. Using ultrasonography, we aimed to evaluate the performance of the excursion‐time (E‐T) index—a product of diaphragm excursion and inspiratory time, to predict the outcome of extubation. Methods Right hemidiaphragm excursion, inspiratory time, and E‐T index were measured by ultrasonography during mechanical ventilation: (1) on assist‐control (A/C) mode during consistent patient‐triggered ventilation, (2) following 30 min during a spontaneous breathing trial (SBT), and (3) between 4 and 24 h following extubation. These measurements were correlated with the outcome of extubation. Patients in the “failure” group required reintubation or noninvasive ventilation within 48 h of extubation. Results Of the 73 patients studied, 20 patients failed extubation. During SBT, diaphragm excursion was 1.65 ± 0.82 and 2.1 ± 0.9 cm (P = .06), inspiratory time was 0.89 ± 0.30 and 1.11 ± 0.39 s (P = .03), and the E‐T index was 1.64 ± 1.19 and 2.42 ± 1.55 cm‐s (P < .03) in the “failure” and “success” groups, respectively. The mean change in E‐T index between A/C and SBT was –3.9 ± 57.8% in the failure group and 59.4 ± 74.6% in the success group (P < .01). A decrease in diaphragmatic E‐T index less than 3.8% between A/C and SBT had a sensitivity of 79.2% and a specificity of 75%, to predict successful extubation. Conclusions Diaphragm E‐T index measured during SBT may help predict the outcome of extubation. Maintenance or increase in diaphragm E‐T index between A/C and SBT increases the likelihood of successful extubation.

Ventilator Weaning and Excursion Time Index: One Step Closer to the Quantum Leap?

We thank Drs. De Santo and Equinas for their comments. The patients selected for our observational study had diverse causes of respiratory failure with the most common ones being septic shock, pneumonia, neuromuscular depression, and cardiac arrest or failure. This allows our study findings to be potentially applicable to a broad group of critically ill patients. 7 out of 20 patients in the “failure” group following extubation were initiated on pre-emptive non-invasive ventilation as per the discretion of the treating ICU team. These patients, similar to other patients in the “failure” group, were found to have lower diaphragmatic excursion on serial ultrasonography during spontaneous breathing trials compared to that during assist control mode of ventilation. The “success” and “failure” groups were similar with regards to their comorbidities, the severity of critical illness as determined by the APACHE IVa score, and had potentially similar factors influencing the outcome of extubation. Dissimilar extubation outcomes between “success” and “failure” groups were more likely to be a sequel of their disparate diaphragm function as measured by ultrasound [1]. Extubation outcome is influenced by several factors in addition to diaphragmatic dysfunction such as alterations in airway resistance or respiratory system compliance, cardiac decompensation, excess mechanical load, or simply the inability to clear secretions due to poor cough, or depressed mental status [2]. We agree it is unlikely that a single parameter focused solely on respiratory muscle dysfunction would be sufficient to predict extubation failure. Our objective was to observe whether any differences in diaphragm function could be detected during weaning trials between patients who are extubated successfully versus those who fail extubation. Our ultrasonography findings did not influence the decision making for weaning or indication for non-invasive support or re-intubation. It would require a much complex randomized trial to examine whether ultrasound has an impact on weaning outcomes and duration of mechanical ventilation. Weaning from mechanical ventilation takes both data analysis and clinical acumen. Weaning outcomes are strongly influenced by the response of muscles of respiration, mainly the diaphragm, the heart and lung, to increased mechanical loads after withdrawal of positive pressure support. A better understanding and surveillance of these factors may allow us to foresee extubation outcomes. The excursion time index may prove to be a useful tool in accessing muscle function during the holistic decision-making process of weaning and extubation. Yes, a “slice of salami” perhaps; but integrated with pepperoni, mortadella, and provolone, as part of the larger Panini sandwich. Ultrasonography may have other roles in guiding the clinician when managing patients with respiratory failure. It has been used to monitor alveolar de-recruitment during weaning from mechanical ventilation and predict extubation outcome [3]. By adding diaphragm or lung ultrasonography to current clinical-based algorithms, we may be able to improve upon the current excessive extubation failure rate of 20–30%. The enigma of accurately foretelling extubation outcome may soon change due to better tools and a growing understanding of its underpinning factors.