Question 24.2

Identify A, B, C, D & E in the figure below and explain the principles of a three-bottle drainage system compared with a one-bottle drainage system.

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College Answer

A = Trap or Collection Bottle

B = Underwater Seal Bottle

C = Manometer Bottle

D = Distance below water is equal to the negative pressure generated when suction is applied

E = Adjustable Vent tube

In the 1-bottle system the chest drain is connected by collecting tubing to a tube approximately 3 cm under water (the seal) in the underwater-seal bottle while another vent tube is open to atmosphere. In this system pleural pressure greater than + 3 cm water will force air or fluid from the pleural space into the bottle while negative pressure in the pleural space will suck fluid up the tube. As long as the underwater-seal bottle is well below the patient (e.g., on the floor beside the patient), the hydrostatic pressure of the fluid column in the tube will counterbalance the negative pleural pressure and prevent water from being sucked into the pleural space. The hydrostatic pressure is proportional to the height of the fluid column. Therefore a disadvantage of this single bottle system is that, as liquid contents (blood, pus, effusion fluid) is expelled from the pleural space and collects in the underwater-seal bottle, the seal tube becomes immersed deeper under water and the pressure required to force more contents into the bottle increases thus impeding the clearance of the pleural collection.

In a 3-bottle system, a trap or collection bottle is interposed between the drain tube and the underwater-seal bottle and a third bottle, called the manometer bottle, is added after the underwater-seal bottle. This manometer bottle has a vent tube under water to regulate the negative pressure generated by suction. The maximum negative pressure (in cm H2O) generated by suction equals to the distance (in cm) this vent tube is below the water line (represented by D in the figure above).

The negative pressure generated by the vent tube (D) is independent of the amount of pleural drainage that is collected in the trap bottle (A).


So, how are the three-bottle systems different to the one-bottle system?


  • The single-bottle system is just the underwater seal bottle
  • The underwater seal provides counterpressure to pleural pressure
  • As long as this bottle remains well below the patient, no fluid will get sucked up into the chest.
  • The more fluid drains out of the patient, the deeper the tip of the tube, and the more pressure will be required to force further fluid/gas out of the pleural cavity.
  • In contrast, in a three-bottle system the depth of the vent tube determines the negative pressure, and the amount of fluid collecting in the collection bottle does not determine the pressure.

In case there is any interest, here is a diagram of our dearly beloved Atrium system, with labels.

underwater seal drain diagram


NSW Health: Chest Drain - Set up of Atrium Oasis Dry Suction Under-Water Seal Drainage

Atrium have published their instructions online.

Additionally, they provide this training document which is surprisingly full of useful information.