Underwater Seal Chest Drainage System


A system that allows drainage of the pleural space using an airtight system to maintain subatmospheric intrapleural pressure; the underwater seal acts a one-way valve


  • drainage of pleural air, blood or other fluid to allow re-expansion of lung


3 bottle system


1 bottle system

  • essentially the water-sealed bottle of the 3 bottle system directly attached to the intercostal catheter, with a second tube open to air


3-bottle system

  • a trap or collection bottle is interposed between the intercostal catheter and the underwater-seal bottle and a third bottle, called the manometer or pressure-regulating bottle, is added after the underwater-seal bottle
  • modern drains incorporate three separate bottles into one unit
  • bottle A = fluid trap or collection bottle, can be independently emptied and allows accurate record of drainage amount
  • bottle B = underwater seal drain, maintained at a predetermined level whilst still allowing for drainage of pleural fluid (if bubbling continuously -> bronchopleural fistula)
  • bottle C = manometer or pressure-regulating bottle allows suction to be attached and should bubble continuously
  • The maximum negative pressure (in cm H2O) generated by suction equals to the distance (in cm) the vent tube is below the water line (this can be adjusted)
  • The negative pressure generated by the vent tube is independent of the amount of pleural drainage that is collected in the trap bottle

1-bottle system

  • chest drain is connected by collecting tubing to a tube approximately 3 cm under water (the seal) in the underwater-seal bottle
  • another vent tube is open to atmosphere
  • 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
  • A disadvantage of this single bottle system is that, as liquid content (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


Safety features

  • first tube connecting drain to drainage bottles must be wide to decreased resistance
  • volume capacity of this tube should exceed ½ of patient’s maximum inspiratory volume (otherwise H2O may enter chest)
  • volume of H2O in bottle B should exceed ½ patient’s maximum inspiratory volume to prevent indrawing of air during inspiration
  • drain should always stay at least 45cm below patient (prevention of removed fluid or H2O refluxing into patient)
  • clamp drain when moving
  • H2O level above tube in the manometer bottle determines the amount of suction applied before air drain through tube (safety suction limiting device)
  •  if suction is turned off then tubing must be unplugged -> so air can escape into atmosphere (otherwise a tension pneumothorax)
  • should not be applied following pneumonectomy


  • Kinking
  • occlusion
  • retrograde flow of fluid may occur if the collection chamber is raised above the level of the patient
  • clamping may cause a tension pneumothorax
  • the drains must be maintained upright to maintain the seal
  • glass bottles can break

Heimlich valves

  • unidirectional flutter valve used to replace underwater seal drains (e.g. when being transported)
  • consists of a tubing assembly and sealed transparent housing with tubing connection ends to attach to the chest drain and a collection bag

CCC 700 6

Critical Care


Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of three amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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