Determinants of point-of-care ultrasound lung sliding amplitude in mechanically ventilated patients.

BACKGROUND: Although lung sliding seen by point-of-care ultrasound (POCUS) is known to be affected to varying degrees by different physiologic and pathologic processes, it is typically only reported qualitatively in the critical care setting. Lung sliding amplitude quantitatively expresses the amount of pleural movement seen by POCUS but its determinants in mechanically ventilated patients are largely unknown. METHODS: This was a single-center, prospective, observational pilot study examining 40 hemithoraces in 20 adult patients receiving mechanical ventilation. Each subject had lung sliding amplitude measured in both B-mode and by pulsed wave Doppler at their bilateral lung apices and bases. Differences in lung sliding amplitude were correlated with anatomical location (apex vs base) as well as physiologic parameters including positive end expiratory pressure (PEEP), driving pressure, tidal volume and the ratio of arterial partial pressure of oxygen (PaO2) to fraction of inspired oxygen (FiO2). RESULTS: POCUS lung sliding amplitude was significantly lower at the lung apex compared to the lung base in both B-mode (3.6 ± 2.0 mm vs 8.6 ± 4.3 mm; p < 0.001) and the pulsed wave Doppler mode (10.3 ± 4.6 cm/s vs 13.9 ± 5.5 cm/s; p < 0.001) corresponding to expected distribution of ventilation to the lung bases. Inter-rater reliability of B-mode measurements was excellent (ICC = 0.91) and distance traversed in B-mode had a significant positive correlation with pleural line velocity (r2 = 0.32; p < 0.001). There was a non-statistically significant trend towards lower lung sliding amplitude for PEEP ≥ 10 cmH2O, as well as for driving pressure ≥ 15 cmH2O in both ultrasound modes. CONCLUSION: POCUS lung sliding amplitude was significantly lower at the lung apex than the lung base in mechanically ventilated patients. This was true when using both B-mode and pulsed wave Doppler. Lung sliding amplitude did not correlate with PEEP, driving pressure, tidal volume or PaO2:FiO2 ratio. Our findings suggest that lung sliding amplitude can be quantified in mechanically ventilated patients in a physiologically predictable way and with high inter-rater reliability. A better understanding of POCUS derived lung sliding amplitude and its determinants may aid in the more accurate diagnosis of lung pathologies, including pneumothorax, and could serve as a means of further reducing radiation exposure and improving outcomes in critically ill patients.

Role of Point-of-Care Ultrasound in the Management of Mechanical Ventilation

Ultrasound (US) became an essential tool in the hands of the intensivist and is now recommended both for procedural guidance and diagnostic purposes. Point-of-care ultrasound (POCUS) is an immediately available and repeatable, non-irradiating bedside tool integrating the clinical examination. Recent years were characterized by a growing interest in the fields of lung ultrasound (LUS) and diaphragm ultrasound (DUS). The combination of these two ultrasound techniques with critical care echocardiography (CCE) may integrate the classical approach to mechanically ventilated patients, both for monitoring and diagnostic purposes, finally contributing to the titration of mechanical ventilation and to the management of respiratory disease. Lung, diaphragm, and cardiac US provide significant information to improve the management of the critical patient under mechanical ventilation, from the initial assessment, through the ventilation setting (like PEEP) and its complication diagnosis (like pneumothorax, atelectasis), until the weaning process. LUS is of particular help in COVID-19 patients. It is potentially able to distinguish between the two phenotypes (type H and type L) of COVID-19, based on the different signs and patterns and also the assessment of prone positioning effects and lung recruitment maneuvers in these patients. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2022.