Intra-operative assessment of human pulmonary alveoli in vivo using Sidestream Dark Field imaging: a feasibility study

BACKGROUND: In vivo videomicroscopy has been used for years to visualize subpleural alveoli in animal studies. This has led to a better understanding of alveolar physiology. We tested the hypothesis whether a novel handheld videomicroscope could be used for intraoperative detection of alveoli in surgical patients during mechanical ventilation. MATERIAL/METHODS: Using Sidestream Dark Field imaging, we observed 6 patients (3 adults and 3 children) who underwent elective cardiac surgery. In each patient, the tip of the microscope was placed on the visceral pleural surface of the left upper pulmonary lobe after weaning from cardiopulmonary bypass. The acquired images were converted into digital signals and captured on a computer. RESULTS: Although cardiac motion artifacts were present, visceral pleural microvascular blood flow could be observed in adults and infants. In infants, sub-pleural cavities (alveoli) were observed. These alveoli were remarkably similar in dimension and structure to those identified previously as true alveoli in animal studies. Quantification of these alveoli demonstrated that mean alveolar diameter, perimeter and area increased with age among the investigated infants (all parameters p <0.001). CONCLUSIONS: High-quality images of visceral pleural microvessels as well as subpleural cavities, reflecting superficial alveoli, could be obtained in infants. These findings create the opportunity to begin human intervention studies, which should investigate alveolar dynamics during mechanical ventilation in cardio-thoracic surgery in more detail