Manual Aspiration vs Gravity Drainage

Manual Aspiration Conditions like congestive heart failure, pneumonia, cancer, and lupus can cause excess fluid to accumulate in the pleural space or area between the lungs and chest wall. To aspirate fluid from a pleural effusion, a medical procedure known as thoracentesis is performed to treat the condition and remove excess pleural fluid.

A thoracentesis procedure can be performed through gravity drainage. In this method, the patient is positioned upright while the fluid is slowly drained. However, this process poses several issues the most important of which is a prolonged drainage time.

A recent randomized, controlled trial known as the GRAVITAS trial has demonstrated that manual aspiration may be a faster alternative to gravity drainage. 

Let’s explore the results of this trial and the implications of its findings in the practice of thoracentesis.

What Is Thoracentesis?

Thoracentesis involves the insertion of a hollow needle or catheter into the thorax though the optimal location may vary from patient to patient. The patient is required to sit upright while leaning slightly forward on a table. The excess fluid accumulated in the pleural space is then drained through the catheter and collected with a bag.

This occurs over a period of several hours depending on the amount of fluid present in the pleural space. The process typically depends on the force of gravity that pulls the fluid from the pleural space to the bag.

What Is Manual Aspiration in Thoracentesis?

Manual aspiration is an alternative method for thoracentesis. It involves the use of a syringe to draw fluid from the pleural space and is performed by a medical professional.

Unlike gravity drainage, manual aspirations provide greater control over the rate of fluid removal. This can result in faster drainage and a more comfortable experience for the patient. 

Rundown of GRAVITAS Trial

The GRAVITAS trial was a randomized, controlled trial with a sample size of 142 patients of which 140 were included in the final analysis. 

During the blind trial, patients had to undergo manual aspiration or gravity drainage until the excessive fluid was completely removed. Thoracentesis was only halted prior to complete drainage when patients experienced persistent chest discomfort, intractable cough, a vagal reaction, hypotension or worsening dyspnea.

Eligible patients were 18 years old and older with at least 500ml of symptomatic pleural effusions. They were randomly assigned to the manual aspiration or gravity drainage group. The final analysis was based on 62 patients in the gravity drainage group, and 78 in the manual aspiration group. 

Once allocated, the overlying skin was anesthetized. For patients undergoing gravity drainage, the bag was placed approximately 100 cm below the site where the catheter was inserted. For manual aspiration, the pleural fluid was actively removed with the help of a 60-milliliter syringe. 

After completing the procedure, patients underwent a thoracic ultrasound to check if any plural fluid remained. A chest radiograph was also conducted to determine the degree to which the lungs had re-expanded and to assess pneumothorax and reexpansion pulmonary edema (REPE).

The results of the trial showed that discomfort and dyspnea in both procedures did not differ while the volumes of fluid drained from the participants of each group were also equal.

It was concluded that both drainage methods were safe and had comparable levels of discomfort. The results also indicated similar improvements in dyspnea. The significant difference between both procedures was the amount of time it took to perform them and extract the same volumes of fluid from each group.

Manual aspiration required less time to extract the same amount of fluid as gravity drainage. This means that the two methods can be used interchangeably. Manual aspiration is more appropriate for patients who cannot sit for long hours at a stretch. However, it is important to note that manual aspiration required more “hands-on” time while gravity drainage was considered more convenient due to its more “hands-off” approach. 

Gravity vs Manual Aspiration: Which Is Better?

In a note to the editor of the CHEST journal, a group of medical professionals highlighted some important considerations concerning the trial.

The most significant observation was that the rate of fluid aspiration in the manual method was vague. This could impact the safety of the procedure in case those performing it are not cautious enough about the potential complications that may arise due to the pressure applied during extraction. In such an instance, the gravity-assisted method may prove safer and less uncomfortable or painful despite the fact that it takes longer to perform.

Another 2021 study comparing gravity drainage with forced suction among patients who had undergone surgery for lung cancer had similar inconclusive findings. It added that the risks for extended hospital stays, post-operative pneumothorax, duration of chest tube drainage, and prolonged air leaks were the same for both procedures.

This raises an interesting predicament if you consider the fact that the only way that manual aspiration is better is because it requires less time. If manual aspiration had been more uncomfortable and unsafe for patients, its ability to drain fluids faster may make it less relevant in clinical settings than gravity drainage. However, the fact that manual aspiration is as safe as gravity drainage and can be accomplished at a much faster rate makes this the ideal method of therapeutic thoracentesis at this time. Of note, connecting the thoracentesis catheter to an evacuated container or to wall suction should not be performed as this has led to increased rates of pneumothorax and reexpansion pulmonary edema (REPE) compared with manual aspiration.

Final Thoughts

The world of medicine is constantly changing. Alternative treatments and methods are studied constantly. The GRAVITAS trial can be extremely helpful in helping professionals determine whether gravity drainage or manual aspiration may be the preferred mode of treatment for patients requiring thoracentesis. However, the findings have certain loopholes that must be further studied before a thorough conclusion is made.


Which Procedure Uses Gravity to Remove Excess Fluids From the Lungs?
Thoracentesis is a procedure to remove fluid or air from around the lungs.


Senitko,M. Ray, A. Murphy, T. Araujo, K. Bramley, K and others. Safety and Tolerability of Vacuum vs Manual Drainage During Thoracentesis: A Randomized Trial. J Bronchology Interv Pulmonol. 2019 Jul; (3): 166–171

Lentz, R. Shojaee, S. Grosu, H. Rickman, O. The Impact of Gravity versus Suction-driven Therapeutic Thoracentesis on Pressure-related Complications: the GRAVITAS Multicenter Randomized Controlled Trial. Chest 2020. Mar 157(3). 702-711

Madam, M. Mittal, S. Tiwari, P. Hadda, V. Mohan, A. Gravity vs Active Aspiration for Thoracentesis. 2020. 423-424

Li, Y. Argaez, C. Gravity Drainage Versus Forced Suction Drainage for Patients With Excess Fluid in Pleural or Peritoneal Spaces. CADTH Health Technology Review.

Read all articles in Chest Tube, Featured, medical procedures, Thoracentesis
Tags: GRAVITAS Trial, Gravity in Thoracentesis, Manual Aspiration in Thoracentesis

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