Lung recruitment and PEEP response in ARDS-related H1N1 virus patients
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KeywordsAcute Respiratory Distress Syndrome Respiratory Mechanic Peep Level Lung Recruitment Recruitable Lung
Starting in April 2009 the swine-origin influenza (H1N1) virus is considered a worldwide pandemic and is associated with a large number of patients admitted to intensive care. In a proportion of these patients, acute respiratory distress syndrome (ARDS) can develop. We described the case of two patients that presented ARDS related to H1N1 virus confirmed by a nasal swab tested with real-time reverse transcription-polymerase chain reaction. Using a lung CT scan we measured the potential of lung recruitment and the response to positive end-expiratory pressure (PEEP) in terms of gas exchange and respiratory mechanics.
Patients underwent a lung CT scan at an airway pressure of 5 and 45 cmH2O; lung profiles were outlined and quantitative analysis was performed with custom-made software. The potential of lung recruitment was computed as the amount of nonaerated lung tissue at 5 cmH2O in which aeration can be restored at an airway pressure of 45 cmH2O. The PEEP test was performed at two PEEP levels (5 and 15 cmH2O), maintaining constant the minute ventilation and the inspiratory oxygen fraction; gas exchange and respiratory mechanics were recorded 20 minutes after each PEEP change.
Two sedated and paralyzed subjects with acute lung injury (ALI)/ARDS (age 46 ± 5 years, BMI 38.6 ± 5.5 kg/m2, PaO2/FiO2 187 ± 30 mmHg, PEEP 17 ± 1 cmH2O; both patients were obese and one of them suffered from diabetes) were enrolled. One patient required extracorporeal membrane oxygenation support for 5 days. Lung CT scans were performed 5 ± 3 days after ICU admission. The total lung weight at 5 cmH2O was 1,598 ± 142 g. The percentage of potentially recruitable lung was 24 ± 8% of the total lung weight, corresponding to an absolute weight of 371 ± 109 g recruitable lung tissue. A 15 cmH2O compared with 5 cmH2O of PEEP improved the compliance of the respiratory system from 42.2 ± 7.0 to 46.6 ± 2.1 ml/cmH2O and the gas exchange from PaO2 62.7 ± 0.1 to 123.2 ± 61.8 mmHg and PaCO2 47.1 ± 0.9 to 45.9 ± 3.2 mmHg, respectively.
The ARDS-related H1N1 virus presented, in the early phase, a high potentially recruitable lung in which elevated PEEP levels can be beneficial.