General Considerations

Both the diagnostic and therapeutic thoracenteses are performed using a similar technique. The major difference is the amount of fluid removed. The proceduralist may also choose to only use the needle technique as opposed to the needle-catheter unit when obtaining fluid for diagnostic purposes only.

It is generally recommended that needle size be limited to 18-gauge or smaller to minimize risk of pneumothorax and damage to nearby structures.

US-guided thoracentesis is associated with a significantly lower rate of complications and has become the standard of care. (1)  Real-time ultrasound (US) guidance is recommended for small or loculated effusions when there is concern that the diaphragm or lung tissue is <10mm from the pleural surface. It is also recommended in patients with relative contraindications such as coagulopathies and the mechanically ventilated patient.

Approximately 60ml of fluid should be obtained for diagnostic studies. Traditional guidelines recommend that no more than 1.0-1.5L of fluid should be removed during a therapeutic procedure because hypotension and pulmonary edema may occur. However, there is ongoing debate of whether re-expansion pulmonary edema (RPE) and pneumothorax are related to significantly negative pleural pressures or absolute volume of pleural fluid removed, or neither. Pleural manometry is rarely used in the ED, and it is recommended that patient symptoms should guide decisions to abort the procedure. When large volumes of fluid must be removed, the patient's blood pressure should be monitored continuously and the procedure stopped if they develop new hypotension, chest pain, desaturations or dyspnea. (2)

Getting it Done

Equipment contained in the UCMC thoracentesis kit.

1.) Gather all of the appropriate supplies and set-up the kit within reach. Make sure that the catheter easily moves over the needle. Draw up 5-10cc of 1% lidocaine with epinephrine or other local anesthetic of choice.

2.) Place the patient on telemetry, BP and O2 sat monitor.

Landmarks for thoracentesis

3.) Have the patient in the sitting position with some lumbar flexion and with the arms resting on a bedside table for support. If the patient is unable to maintain the position on their own have an someone available to assist them. Alternatively, if the patient is unable to sit erect, place them in a supine position with the arm abducted above the head.

4.)Verify the procedure is to be performed on the correct side of the thorax using physical exam and radiography.

5.) Before prepping and draping the area, use the low frequency US transducer to identify the superior border of the effusion, the respiratory motion of the diaphragm, consolidated lung deep to the effusion and the liver or spleen caudally depending on the laterality of the procedure. Using a marking pen or the end of a needle cap, place a mark 1-2 intercostal spaces below the superior aspect of the fluid level in the mid-scapular or posterior axillary line just superior to the rib to avoid the neurovascular bundle that runs inferior to the rib. Do not mark below the 9th rib to avoid diaphragmatic or abdominal organ injury when the needle is inserted. For reference, the inferior tip of the scapula is at the 7th rib in the average, upright adult with the arms by the side. During this step, the depth of the superficial border of the pleural space and the center of the fluid collection should be measured to estimate the depth of needle insertion.

6.) The operator should then mimic the angle of insertion of the needle by placing the US transducer flush at the skin mark and verify the window is safe with the angle utilized.

7.) Once the area is appropriately marked prepare the skin with antiseptic of choice in a circular area via sterile technique. Place sterile towels or a sterile drape around the site. Also, cover the high-frequency transducer with a sterile probe cover.

8.) Using a 22 or 25-gauge needle form a skin wheel with anesthetic at the marked injection site. A longer needle than those supplied in the standard kit may be required depending on the amount of subcutaneous tissue.

9.) Using the sterile high-frequency probe, verify the location of the fluid pocket deep to the skin wheel. The proceduralist may chose to measure the depth the needle will have to be inserted to reach the effusion at this step as well. (4)

10.) Next, with the transducer in the transverse orientation, introduce the needle alongside the transducer using the “in-plane” method and visualize the needle entering the pleural space while intermittently aspirating and injecting as the needle progresses through the subcutaneous tissues to adequately anesthetize the subcutaneous tissue. Inject the remaining anesthetic at the parietal pleura which is typically the most painful portion of the procedure.

11.) Pierce the skin with a scalpel at the insertion site to ease entry of the catheter through the skin.

Thoracentesis Needle with syringe for diagnostic sample

12.) Attach the needle-catheter unit to a 10-mL syringe. Using the high-frequency probe, repeat the “in-plane” technique and advance the needle-catheter unit to the depth measured in the previous step while maintaining slight, constant negative pressure on the syringe. Alternatively, if an assistant is available to hold the US probe, grasp the needle-catheter unit with index finger and thumb of the non-dominant hand at the previous measured depth for stabilization and use the opposite hand on the syringe.

13.) Once pleural fluid is encountered stop advancing the needle and set down the US probe. Direct the needle slightly caudally and advance the catheter over the needle while holding the needle steady.

14.) Withdraw the needle. If the kit being used does not have a self-sealing valve where the needle leaves the catheter, immediately cover the open lumen of the catheter with the thumb to prevent air entry into the pleural space.

15.) Attach a 60ml syringe to the 3-way stopcock on the end of the catheter and obtain a fluid sample for analysis.

16) If a therapeutic drainage is being performed, at this point fluid may be removed by aspirating with the syringe and then expelling the fluid through a one way valve into a collection bag or by attaching the high-pressure tubing to the stopcock and allowing fluid to drain into a vacuum container. If removing the syringe or changing vacuum bottles, turn the stopcock off to the patient to prevent air entry into the pleural space

17.) Once the desired amount of fluid is removed or the flow ceases or the patient experiences any new symptoms, turn the stopcock off to the patient and slowly remove the catheter.

18.) Place a sterile bandage over the insertion site


  1. Gordon CE, Feller-Kopman D, Balk EM, Smetana GW. Pneumothorax Following Thoracentesis: A Systematic Review and Meta-analysis. Arch Intern Med. 2010;170(4):332-339. doi:10.1001/archinternmed.2009.548.
  2. Feller-Kopman, David et al. Large-Volume Thoracentesis and the Risk of Reexpansion Pulmonary Edema. The Annals of Thoracic Surgery , Volume 84 , Issue 5 , 1656 - 1661
  4. Custalow, Catherine B, James R. Roberts, Todd W. Thomsen, and Jerris R. Hedges. Roberts and Hedges' Clinical Procedures in Emergency Medicine. Philadelphia, PA: Elsevier/Saunders, 2013.