Ultrasonographic Assessment of Lung Aeration and Recruitment with use of Prone Position in Acute Respiratory Distress Syndrome

OBJECTIVES: To evaluate alteration in lung density with the help of lung ultrasound (LUS) and its correlation with oxygenation and outcomes in patients with acute respiratory distress syndrome (ARDS). MATERIALS AND METHODS: This prospective, cross-sectional, observational study was done in the intensive care unit (ICU) of Manipal Hospital, Bengaluru for a period of 8 month. Study included 50 patients with moderate to severe ARDS who were admitted to the ICU and required ventilation. Sufficient sedation and analgesia were provided, and neuromuscular blocking agents were used as per unit protocol. Data collected included hemodynamics, ventilatory parameters, ABG analysis and LUS at various time during prone ventilation. Data thus collected was subjected to statistical analysis and results were drawn. RESULTS: The mean age of patients with ARDS in this study was 55.56±15.95 years and 60% of them were male. The mean APACHE II score was 19.84±6.47 and the mean SOFA score was 6.70±2.40. Majority of the patients presented with APACHE-II score <25 (82%) and SOFA score within 9 (86%). Diabetes Mellitus (DM) (54.0%) was the most frequent co-morbidity followed by Hypertension (HTN) (46.0%) observed in the study patients. The mean heart rate decreased significantly over time after admission. The mean level of SPO2, ABG-pH and BE increased significantly over time, while the mean level of PaCO2 decreased significantly over time after admission. The mean P/F Ratio increased significantly till prone position at 2–4 hours before re-supination and then decreased significantly at 2–4 hours after re-supination, whereas the mean LUS decreased significantly over time after admission. The correlation between P/F Ratio and LUS was positive at all time intervals but it was statistically significant only at prone position after 2- 4 hours and 2- 4 hours before resupination. Driving pressure (DP) has significantly decreased over time after prone positioning. The mean duration of ICU stay in our study was 12.20±9.37 days. 28 Day Mortality of the patients was 42%. The mean DP was lower in survivors when compared to non-survivors. Vasopressor was required in 88% of the patients while RRT was required in only 38% of the patients. Secondary sepsis developed in 26% of the study patients. CONCLUSION: Prone position in severe ARDS brings about improved oxygenation and a consistent CO2 reduction in majority. In this study oxygen responders are 100% and CO2 responders are 2/3rd. These changes are not correlated with changes in LUS. We hypothesise that the changes to chest wall compliance and homogeneity of the perfusion of available lung volumes (functional baby lung) may have played an important role in oxygenation and ventilation change. In absence of recruitment manoeuvres and very high PEEP level (>15), LUS is less likely to detect changes in lung density that could correlate with oxygenation and ventilation indices.