Monitoring and controlling lung stress and diaphragm effort has been hypothesized to limit lung injury and diaphragm injury. The occluded inspiratory airway pressure (Pocc) and the airway occlusion pressure at 100 ms (P0.1) have been used as noninvasive methods to assess lung stress and respiratory muscle effort, but comparative performance of these measures and their correlation to diaphragm effort is unknown. The authors hypothesized that Pocc and P0.1 correlate with diaphragm effort and lung stress and would have strong discriminative performance in identifying extremes of lung stress and diaphragm effort.
Change in transdiaphragmatic pressure and transpulmonary pressure was obtained with double-balloon nasogastric catheters in critically ill patients (n = 38). Pocc and P0.1 were measured every 1 to 3 h. Correlations between Pocc and P0.1 with change in transdiaphragmatic pressure and transpulmonary pressure were computed from patients from the first cohort. Accuracy of Pocc and P0.1 to identify patients with extremes of lung stress (change in transpulmonary pressure > 20 cm H2O) and diaphragm effort (change in transdiaphragmatic pressure < 3 cm H2O and >12 cm H2O) in the preceding hour was assessed with area under receiver operating characteristic curves. Cutoffs were validated in patients from the second cohort (n = 13).
Pocc and P0.1 correlate with change in transpulmonary pressure (R2 = 0.62 and 0.51, respectively) and change in transdiaphragmatic pressure (R2 = 0.53 and 0.22, respectively). Area under receiver operating characteristic curves to detect high lung stress is 0.90 (0.86 to 0.94) for Pocc and 0.88 (0.84 to 0.92) for P0.1. Area under receiver operating characteristic curves to detect low diaphragm effort is 0.97 (0.87 to 1.00) for Pocc and 0.93 (0.81 to 0.99) for P0.1. Area under receiver operating characteristic curves to detect high diaphragm effort is 0.86 (0.81 to 0.91) for Pocc and 0.73 (0.66 to 0.79) for P0.1. Performance was similar in the external dataset.
Pocc and P0.1 correlate with lung stress and diaphragm effort in the preceding hour. Diagnostic performance of Pocc and P0.1 to detect extremes in these parameters is reasonable to excellent. Pocc is more accurate in detecting high diaphragm effort.
- Recent research suggests that optimization of diaphragmatic effort and avoidance of excessive lung stress may facilitate liberation from mechanical ventilation in critically ill patients
- Low diaphragmatic effort has been associated with rapid development of disuse atrophy, and excessive effort may result in muscle injury, increased lung stress, and pendelluft (displaced ventilation from recruited to nonrecruited lung regions)
- Monitoring transdiaphragmatic and transpulmonary pressures may facilitate accurate assessment of diaphragmatic effort and lung stress, respectively, but requires esophageal and gastric manometry, an overly complex process for routine clinical practice
- A secondary analysis of two previous studies evaluated the ability of two transient inspiratory airway occlusion maneuvers (Pocc, the total drop in airway pressure during an occlusion, and P0.1, the drop in the first 100 ms) obtained from the mechanical ventilator to predict either diaphragm effort or lung stress
- Neither P0.1 nor Pocc should be used to predict exact values for diaphragm effort or lung distending pressure
- However, both maneuvers can reliably identify patients with low or high extremes in diaphragm effort and lung stress, where Pocc outperforms P0.1 based on the areas under the receiver operating characteristic curves
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