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Comparison of Function of Commercially Available Pleural Drainage Units and Catheters: Patient’s pleural space

Appropriate PDC size selection is therefore key to preventing tension pneumothorax development. Because a PDU is often connected in series with a PDC, appropriate PDU selection is also key. However, when considering flow rates accommodated, the PDC is the most likely rate-limiting device when compared to the PDU (Tables 1, 2).
No formula analogous to the Fanning equation exists to determine flow rates for commercially available PDUs. This is likely due to their relatively complex structure based on the three-bottle (compartment) system. This three-bottle system is commercially condensed into a convenient and easily mobile single module of variable design incorporating the three compartments. The three compartments, sequentially, include the following: (1) the collection bottle to trap liquid material and other debris from the patient’s pleural space while allowing pleural air to pass through the next two compartments, (2) the water seal bottle to prevent air flow back to the patient’s pleural space and allow detection of an air leak (bronchopleural fistula), and (3) the manometer bottle to regulate the amount of negative pressure transmitted back to the patient from the wall suction device (or equivalent suction source). The manometer bottle has an input and output tube and a central vent tube that may be raised or lowered. Adjusting the depth of the central vent tube in the chamber water determines the negative pressure transmitted from the wall suction back to the patient’s pleural space. The water chamber device has been replaced in some commercial PDUs with a spring-loaded or similar device to regulate the negative pressure transmitted to the patient. birthcontroltab.com
Given the complexity of PDUs and their design variability, it is understandable there is no formula to calculate flow. Meantime, using the Fanning equation to mathematically derive flow rates for a PDC is onerous and impractical.