Gravity- Versus Suction-driven Large Volume Thoracentesis

Therapeutic thoracentesis aims to drain fluid from the pleural space to alleviate
breathlessness. The amount of and speed with which the fluid can be safely drained in one
setting is unclear, and likely depends on the physiology of the pleural effusion. The
principle concern when draining a large amount of fluid quickly from the pleural space is
that excessively negative pleural pressure may be generated; this occurs if the lung is
unable to freely re-expand into the space previously occupied by fluid. Excessively negative
pleural pressure and the resulting high transpulmonary pressure gradient are thought to be
associated with several complications, including pneumothorax ex vacuo, chest discomfort, and
re-expansion pulmonary edema (REPE). Evidence suggests that monitoring pleural pressures
during thoracentesis via manometry does not mitigate this problem. In fact, data shows that
whether manometry is used or not, most patients do experience clinically significant increase
in chest discomfort during thoracentesis. Current methods for draining the pleural fluid
include suction- (via vacuum bottles, wall suction or the use of large syringes with a
one-way valve tubing system) or gravity-driven thoracentesis. Pressures generated by all
suction techniques range from -200 to -500 cmH2O, and far exceed what are considered safe
pleural pressures. Accordingly, in case of non-expandable lung, excessively negative
pressures may develop quickly, exposing patients to complications. Some clinicians advocate
for gravity drainage, which generates less negative pressures in the pleural space
(specifically defined as the vertical distance between the catheter and the drainage bag,
generally around -50 to -100 cmH20). While this technique is considered standard of care by
some as it is potentially more comfortable for patients, it is also likely associated with
longer procedures, and is not generally favored by clinicians who in general prefer suction
drainage, despite the possible higher risk of complications.The investigators propose to
study the impact of gravity- versus suction-driven large volume therapeutic thoracentesis on
the development of chest discomfort during the procedure, and consider as secondary
endpoints: the duration of the procedure, the amount of pleural fluid drained, the rate of
REPE, the rate of pneumothorax ex vacuo.

Inclusion Criteria:

1. Referral to pulmonary services for large-volume thoracentesis

2. Presence of a symptomatic moderate or large free-flowing (non-septated) pleural
effusion on the basis of:

1. Chest radiograph: effusion filling ≥ 1/3 the hemithorax, OR

2. CT-scan: maximum AP depth of the effusion ≥ 1/3 of the AP dimension on the axial
image superior to the hemidiaphragm, including atelectatic lung completely
surrounded by effusion, OR Ultrasound: effusion spanning at least three
interspaces, with depth of 3 cm or greater in at least one interspace, while the
patient sits upright.

3. Age > 18

Exclusion Criteria:

1. Inability to provide informed consent

2. Patient has already been enrolled in this study

3. Study subject has any disease or condition that interferes with safe completion of the
study including:

1. Coagulopathy, with criteria left at the discretion of the operator

2. Hemodynamic instability with systolic blood pressure <90 mmHg or heart rate > 120
beats/min, unless deemed to be stable with these values by the attending
physicians

4. Pleural effusion is smaller than expected on bedside pre-procedure ultrasound

5. Referral is for diagnostic thoracentesis only

6. Presence of more than minimal septations and/or loculations on bedside pre-procedure
ultrasound

7. Inability to sit for the procedure