F-037
WATER SEAL'S ONE-WAY ACTION IN CHEST DRAINAGE SYSTEMS: WHEN THE PARADIGM FAILS Free

Objectives: In most traditional chest drainage systems a water reservoir serves as a one-way valve for air. During deep inspiration some patients can entrain atmospheric air and mimic a “true” air leak during the following expiration. This gives the erroneous impression that the air is leaking from the lung. We investigated this phenomenon in the laboratory focusing on its clinically relevant features.

Methods: The valves of 31 different drainage devices were tested simulating cyclic breathing patterns with controlled vacuum applied to the chest tube (0 to -160 cmH₂O). 3D modelling and computer simulations of the observed hydrodynamic process were used to correlate different structural characteristics of the valve chambers to the origin of the apparent air leak.

Results: Twenty-six systems showed reverse airflow. The amount of negative pressure and time needed to produce this varied according to the valve geometry. Despite maintaining water in the reservoir, 15 systems demonstrated reverse airflow by bending of the water surface. Average applied suction was -74 cmH₂O (range -25 to -145) for an average of 2 seconds (1-7) and an average of 12 ml of air (3-19) was entrained per inspiration. Complete emptying of the reservoir occurred in all systems and average applied suction was -68 cmH₂O (-24 to -155) for an average of 65 seconds (4-244).

Conclusions: Conditions for reverse airflow vary dramatically among systems. We identified 2 patterns. The first occurs at values easily attained by humans. Deep inspirations can create the impression of a prolonged air leak and thus likely prolonged hospital stay. The second occurs only in specific or unusual circumstances. Clinicians should acknowledge this phenomenon in order to avoid prolonged chest tube drainage. Translating these results back to the bedside and performing further research on different clinical scenarios will help improve patient care.

Disclosure: No significant relationships.