Is Barotrauma Related to Airway Pressures?
Is Barotrauma Related to Airway Pressures?
ABSTRACT & COMMENTARY
High airway pressures have been blamed for the development of air leaks and worsening of outcome in acute respiratory distress syndrome (ARDS). Nonuniform distribution of involved areas in ARDS has led to a belief that small tidal volume ventilation with low peak airway pressures might protect the lung from further damage. This has led to nonconventional modes of ventilation in an attempt to prevent this form of iatrogenic "ventilator-induced lung injury." The data analyzed in this paper came from a prospective, randomized, controlled study demonstrating no effect on outcome of aerosolized synthetic surfactant in sepsis-induced adult ARDS (Anzueto A, N Engl J Med 1996;334:1417-1421).
Data from the 725 patients enrolled in the surfactant study were re-examined for the development of air leak using conventional chest radiography. Respiratory variables had been collected every eight hours throughout the period of mechanical ventilation, and the worst values were identified in the control patients (no air leak) and compared to the values immediately preceding the detection of air leak in the barotrauma patients. All patients in the original surfactant study were included.
There were 77 patients (10.6%) who developed any kind of air leak, including 50 with pneumothorax (6.9%). Patients with air leaks were younger (45 vs 52 years), smaller (72 vs 76 kg), and more likely to be female. There was no difference in highest peak airway pressure (47 vs 46 cm H2O), mean airway pressure (24 cm H2O in both groups), PEEP level (12.6 vs 11.5 cm H2O), tidal volume in relation to body weight (11.4 vs 11.7 mL/kg), or 30-day mortality (45.5% vs 39%). There were also no differences between the groups with respect to degree of illness as measured by APACHE III scores, highest FiO2, or oxygenation as measured by PaO2/FiO2 ratio. Serum albumin nadir was slightly lower in the air-leak group (2.2 vs 2.4 g/dL). In evaluating the relationship between increasing airway pressures and ventilation volumes, no relationship to air leak was demonstrated.
In this study using conventional ventilation strategies, no relationship between pressure or volume and development of barotrauma was seen. Most importantly, no increase in mortality was associated with barotrauma or pneumothorax. (Weg JG, N Engl J Med 1998;338(6):341-436.)
COMMENT BY CHARLES G. DURBIN, Jr., MD, FCCM
This is a provocative study that casts doubt on the "baby lung," small-volume ventilation, "lung-protective" strategy being promoted for managing patients with ARDS. The study has several significant faults. Most significant among these is that the study assumes that conventional markers of barotrauma act as surrogates to identify the proposed "volutrauma" insult of the "baby lung" theory. More subtle injuries from over-stretching alveolar walls and capillaries, such as worsening pulmonary edema (alveolar capillary leak) and lung compliance, are more reasonable pathophysiological markers; air leaks may not be sensitive at this level of damage. Since all these patients were ventilated with high tidal volumes and high airway pressures (if they were required), no conclusions about protection from low tidal volumes can be reached.
The study was not designed to test the hypothesis of an association between airway pressures and air leaks. Intrinsic problems with post-hoc analysis such as performed in this study limit the strength of the conclusions. The pressure risk factors were assumed to be only the worst value (highest peak, PEEP, and mean airway pressure) in the control group, and these were compared to the value immediately preceding the barotraumatic event. A more reasonable risk would be the time spent at high levels of pressure or some average of airway pressures throughout the entire risk period. This analysis was not performed in this study.
Other important information is missing in the analysis. No values for lung compliance were presented. The fact that females and smaller patients had a higher incidence of air leak suggests that over-distention may well play a role in barotrauma. This could be examined in more detail in this population. Whether any of the "barotraumatic" injuries were related to central line placement was not indicated. The only valid conclusion from this study is that no additional mortality is incurred by sustaining air leak or pneumothorax in these ARDS patients.
Subscribe Now for Access
You have reached your article limit for the month. We hope you found our articles both enjoyable and insightful. For information on new subscriptions, product trials, alternative billing arrangements or group and site discounts please call 800-688-2421. We look forward to having you as a long-term member of the Relias Media community.