Chest Drainage Systems

In 1967, Deknatel introduced the first integrated
disposable chest drainage unit based on the threebottle
system. Now that we have reviewed normal
anatomy, physiology, and pathophysiology, let’s
discuss each of the three chambers in detail.


At the right side of the unit is the collection chamber
(figure 13, D). The patient tubing connects the
drainage unit directly to the chest tube. Any drainage
from the chest flows into this chamber. The collection
chamber is calibrated and has a write-on surface to
allow for easy measurement and recording of the
time, date, and amount of drainage.


The middle chamber of a traditional chest drainage
system is the water seal. The main purpose of the
water seal is to allow air to exit from the pleural
space on exhalation and prevent air from entering
the pleural cavity or mediastinum on inhalation.
When the water seal chamber is filled with sterile fluid
up to the 2 cm line, a 2 cm water seal is established
(figure 14). To maintain an effective seal, it is
important to keep the chest drainage unit upright at
all times and to monitor the water level in the water
seal to check for evaporation.

Bubbling in the water seal chamber indicates an air
leak. The patient air leak meter indicates the approximate degree of air leak from the chest cavity
(figure 14). The meter is made up of numbered
columns, labeled from 1 (low) to 7 (high). The higher
the numbered column through which bubbling
occurs, the greater the degree of air leak. By
documenting the number, the clinician can monitor
air leak increase or decrease.

The water seal chamber also has a calibrated
manometer to measure the amount of negative
pressure within the pleural cavity (figure 13, F). The
water level in the small arm of the water seal rises as
intrapleural pressure becomes more negative.
If there is no air leak, the water level should rise and
fall with the patient’s respirations, reflecting normal
pressure changes in the pleural cavity. During
spontaneous respirations, the water level should rise
during inhalation and fall during exhalation. If the
patient is receiving positive pressure ventilation, the
oscillation will be just the opposite — the water level
should fall with inhalation and rise with exhalation.
This oscillation is called tidaling and is one indicator
of a patent pleural chest tube.

At the top of the water seal chamber is a high
negativity float valve and high negativity relief
chamber (figure 13, C). These safety features maintain
the water seal in the event of high negative pressures.

Three situations can cause high negative pressure:
1. The patient in respiratory distress, coughing
vigorously, or crying;
2. Chest tube stripping;
3. Decreasing or disconnecting suction .

High negativity is indicated by rising water in the
small arm of the water seal chamber. If the water rises
beyond –20 cm, the high negativity float valve will
rise and impede the flow of water, allowing the
patient to develop as much negativity as needed for
inspiration. In instances of falsely imposed high
negative pressure, such as stripping chest tubes,
water will continue to rise, filling the high negativity
relief chamber. The relief chamber automatically vents
excessive negative pressure, thus preventing
respiratory compromise from accumulated negativity.

Vigorous milking or stripping can create dangerously
high negative pressures. Research has documented
negative pressures as high as –450 cm H2O. Pleurevac
prevents accumulation of excessive high
negative pressure as discussed above; however, the
transient high negative pressures created by vigorous
stripping can put the patient at risk for mediastinal
trauma and graft trauma. Use extreme caution and
follow your hospital policy.

A manual high negativity relief valve is located on top
of chest drainage systems (figure 15). Depressing the
high negativity relief valve allows filtered air into the
system, relieving negativity and allowing the water
level to return to baseline in the water seal. Use the
high negativity relief valve with caution. If suction is
not operative, or if operating on gravity drainage,
depressing the high negativity relief valve can reduce
negative pressure within the collection chamber to
zero (atmosphere) with the resulting possibility of a


The chamber on the left side of the unit is the suction
control chamber (figure 13, H). Traditional chest
drainage units regulate the amount of suction by the
height of a column of water in the suction control
chamber. Note: it’s the height of water, not the
setting of the suction source, that actually limits the
amount of suction transmitted to the pleural cavity. A
suction pressure of –20 cm H2O is commonly
recommended. Lower levels may be indicated for
infants and for patients with friable lung tissue, or if
ordered by the physician.

In a wet suction control system such as the Pleur-evac®
A-7000/A-8000 series, fill the suction control chamber
to the desired height with sterile fluid. Connect the
short suction tubing to a suction source, and adjust
the source suction to produce gentle bubbling in the suction control chamber. Increasing suction at the
suction source will increase airflow through the
system, but will have minimal effect on the amount
of suction imposed on the chest cavity.
Excessive source suction not only causes loud
bubbling (which can disturb patients and caregivers),
but also hastens evaporation of water from the
suction control chamber. This results in a lower
amount of suction applied to the patient as the level
of water decreases. Self-sealing diaphragms are
provided to adjust the water level in this chamber.



The next step in the evolution of chest drainage units
was the development of dry suction control
chambers. Dry suction control systems provide many
advantages: higher suction pressure levels can be
achieved, set-up is easy, no continuous bubbling
provides for quiet operation, and there is no fluid to
evaporate which would decrease the amount of
suction applied to the patient.

Instead of regulating the level of suction with a
column of water, the dry suction units are controlled
by a self-compensating regulator. A dial to set the
suction control setting is located on the upper left
side of each unit. To set the suction setting, rotate
the dial until the red stripe appears in the
semi-circular window at the prescribed suction level
and clicks into place. Suction can be set at –10, –15,
–20, –30, or –40 cm of water. The unit is pre-set at
–20 cm of water when opened (figure 16).

Connect the short suction tubing or suction port to
the suction source. Source suction must be capable
of delivering a minimum of 16 liters per minute
(LPM) air flow. Increase suction source until the
orange float appears in the suction control indicator

The unique design of the Pleur-evac dry suction control
immediately responds to changes in patient pressure
(patient air leak) or changes in suction pressure
(surge/decrease at the suction source). The setting of
the suction control dial determines the approximate
amount of suction imposed regardless of the amount
of source suction — as long as the orange float
appears in the indicator window.

Patient situations that may require higher suction
pressures of –30 or –40 cm H2O include: a large air
leak from the lung surface, empyema or viscous pleural
effusion, a reduction in pulmonary compliance, or
anticipated difficulty in expansion of the pulmonary
tissue to fill the hemithorax.

In the presence of a large air leak, air flow through
the Pleur-evac may be increased by increasing source
suction, WITHOUT increasing imposed negativity. It is
not necessary to change the suction setting on the
Pleur-evac unit to accommodate high air flows.
The suction control level can be changed at any time
as prescribed by simply rotating the dial to the new
suction setting. Confirm that the orange float remains
in the suction control indicator window at the new
suction setting. If suction setting is changed from a
HIGHER to a LOWER level, the patient negativity may
remain at the higher level unless the negativity is
relieved. Use the manual high negativity relief valve to
reduce negativity to desired level.

Both the wet suction and dry suction series of Pleurevac
have a positive pressure relief valve that opens
with increases in positive pressure, preventing
pressure accumulation (figure 15). Normally, air exits
through the suction port. Obstruction of this route
(i.e. a bed wheel rolls on top of the suction tube, or
the suction port is capped after suction discontinued)
could cause accumulation of air in the system leading
to tension pneumothorax. This safety feature allows
venting of the positive pressure automatically, thus
minimizing the risk of tension pneumothorax.


In the Pleur-evac Sahara®, (figure 17) a one-way valve
replaces the traditional water seal. No water is
required to establish the one-way seal. Just connect
the patient tube to the patient’s thoracic catheter and
the patient seal is established for patient protection.
The one-way valve maintains the patient seal even if
the unit is tipped over. Unlike a water seal system in
which the seal may be lost when the unit is tipped,
the Sahara dry seal protects the patient from
atmospheric air.

If air leak diagnostics are desired, the patient air leak
meter must be filled to the “Fill” line. The fluid in the
patient air leak meter is used for air leak detection as
described earlier and is not a water seal.

In the Pleur-evac Sahara, negative pressure exists in
the collection chamber when the YES can be seen in
the indicator window (figure 18). During gravity
drainage before normal negative pressure has been
re-established in the pleural cavity, the indicator may
intermittently indicate negative pressure with patient
respiration. During suction drainage, the pressure
indicator should indicate a negative pressure
continuously. The negative pressure indicator does
not confirm drainage tube patency. Routinely check
the drainage tube patency.

The Pleur-evac Sahara system also has an automatic
high negative pressure relief valve to limit the
negative pressure to approximately –50 cm of H2O. A
manual high negativity relief valve is also provided to
vent excessive negativity as described earlier.


Not all patients require suction. Suction may be
discontinued to transport a patient; it may also be
discontinued 24 hours before chest tube removal.
Consult hospital policy to determine if an order is
needed to institute or discontinue suction. If suction is
discontinued, the suction tube or port should remain
UNCAPPED and free of OBSTRUCTIONS to allow air
to exit and minimize the possibility of tension


The decision whether to clamp a chest tube when
the drainage system has been knocked over and
disconnected or otherwise disrupted is based on your
initial assessment of the water seal chamber and air
leak meter. If there has been no bubbling in the
water seal, you can deduce there is no air leak from
the lung. Therefore, the tube may be clamped for the
short time it takes to reestablish drainage. If there has
been bubbling and your assessment has determined
there is an air leak from the lung, you MUST NOT
clamp the chest tube. Doing so will cause air to
accumulate in the pleural cavity since the air has no
means of escape. This can rapidly lead to tension

The few times you should clamp a chest tube are
when: 1) You are performing a physician-ordered
procedure such as sclerosing, 2) Assessing for a leak,
or 3) Prior to removing the chest tube to determine if
the patient can do without the chest tube (with a
physician order).

You should never clamp a chest tube during patient
transport unless the chest drainage system becomes
disrupted during patient movement, and then only if
there is no air leak.