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Ultrasound-guided thoracentesis

Ultrasound-guided thoracentesis
Literature review current through: Sep 2023.
This topic last updated: Jan 23, 2023.

INTRODUCTION — Ultrasound guidance can be used for several pleural access procedures that are performed at the bedside including thoracentesis, catheter insertion, and needle aspiration biopsy of pleural or subpleural lung masses.

The use of thoracic ultrasound to guide thoracentesis and related procedures will be reviewed here. The equipment and technique of thoracic ultrasound, and imaging of pleural effusions are discussed separately. (See "Bedside pleural ultrasonography: Equipment, technique, and the identification of pleural effusion and pneumothorax" and "Imaging of pleural effusions in adults".)

INDICATIONS AND CONTRAINDICATIONS — Indications, both diagnostic and therapeutic, and contraindications for thoracentesis are provided separately. (See "Diagnostic evaluation of the hemodynamically stable adult with a pleural effusion", section on 'Thoracentesis indications and contraindications'.)

EQUIPMENT — Several thoracentesis kits are commercially available that contain items needed for thoracentesis. Some kits also contain a pleural manometer. (See "Measurement and interpretation of pleural pressure (manometry): Indications and technique".)

Items needed include:

Sterile gloves, gowns, and drapes; skin sterilizing fluid (eg, 0.05 percent chlorhexidine or 10 percent povidone-iodine solution); and sterile wound dressing materials. (See 'Site preparation and local anesthesia' below.)

Local anesthetic agent (1 to 2 percent lidocaine) with the appropriate needles (25-gauge for skin infiltration and 21- or 22-gauge for deeper tissue infiltration through the ribs) and syringe for injection.

Thoracentesis needle and drainage devices. Most kits contain an 8 French over-the-needle catheter, an 18-gauge needle, a stopcock, 35 to 60 mL syringe, and thoracentesis drainage bag/system; if a kit is not available, a similarly sized angiocatheter, syringe, and vacuum bottle (if planned) are alternatives.

If the thoracentesis is performed for diagnostic purposes only with small volume withdrawal (eg, 30 mL), an 18-gauge needle without catheter may be used.

If the thoracentesis is performed with the intent to remove much or all of the fluid, use of a needle alone for drainage is contraindicated due to risk of lacerating the visceral pleural surface. The needle is used transiently to introduce the drainage catheter using an over-the-needle catheter system or using the Seldinger technique (wire/dilator/catheter system). For drainage of a large volume pleural effusion, typical catheter size is 8 French, while Seldinger technique catheters range in size from 6 to 14 French. Larger diameter drainage tubes may be used when indicated using Seldinger technique for their insertion (16 to 36 French size). (See "Thoracostomy tubes and catheters: Placement techniques and complications", section on 'Needle thoracostomy' and "Thoracostomy tubes and catheters: Placement techniques and complications", section on 'Techniques'.)

Sedation is not typically needed. However, if the procedure is expected to be prolonged or complicated, then additional medication and monitoring may be appropriate. Conscious sedation is rarely used. (See "Procedural sedation in adults in the emergency department: General considerations, preparation, monitoring, and mitigating complications", section on 'Preparation and monitoring'.)

For a diagnostic needle thoracentesis, a 50 mL syringe and a small gauge needle (21- or 22-gauge) needle that is 40 mm in length are used. Use of larger bore needles has been associated with an increased rate of pneumothorax, although the evidence is conflicting and based upon retrospective reports [1-3]. In obese, edematous, or muscular patients, the depth of needle penetration required to access the pleural fluid may exceed 40 mm. If a longer needle is required, a 20-gauge lumbar puncture needle (typically 100 mm in length) may be required. However with the increasing use of kits, the issue of needle length is overcome by the provision of both needles and over-the-needle catheters that are at least 100 mm in length.

The following items may also be necessary and are discussed separately:

Equipment for bedside ultrasonography. Although a sterile cover for the ultrasound probe and sterile gel is typically not necessary for straightforward thoracentesis, a sterile cover is routinely incorporated into the setup for more advanced pleural procedures (eg, wire placement guidance for catheter insertion or expected loculations) or when site selection for thoracentesis needs to be reconfirmed during the procedure. (See "Bedside pleural ultrasonography: Equipment, technique, and the identification of pleural effusion and pneumothorax", section on 'Equipment'.)

Informed consent. (See "Informed procedural consent".)

Positioning (typically in the seated upright position with the arms resting on a surface but alternatives may be required). (See "Bedside pleural ultrasonography: Equipment, technique, and the identification of pleural effusion and pneumothorax", section on 'Patient position'.)

TECHNIQUE — Pleural effusions are usually detected by physical examination or by thoracic imaging studies (eg, ultrasonography, chest radiograph, or chest computed tomography [CT]). Most thoracenteses are typically performed by ultrasound-guidance at the bedside. CT imaging-guidance is used for effusions that are small, or those that cannot be readily accessed or have failed ultrasound-guided access (eg, loculated effusions).

Identify anatomical structures — All the typical anatomic structures including the diaphragm with underlying liver or spleen, lung, chest wall, heart, and descending aorta (if the left lower posterior chest wall is the intended site) should be identified. It is important to document the presence and location of lung sliding before the procedure (best assessed using a >5 MHz vascular probe) because the disappearance of lung sliding or B-lines after the procedure confirms the interval development of a pneumothorax. (See "Bedside pleural ultrasonography: Equipment, technique, and the identification of pleural effusion and pneumothorax", section on 'Identification of pleural effusion using ultrasonography' and "Bedside pleural ultrasonography: Equipment, technique, and the identification of pleural effusion and pneumothorax", section on 'Evaluation for pneumothorax'.)

Site selection — Ultrasonography improves the accuracy of site selection for needle insertion, thereby improving safety and increasing the likelihood of a successful procedure [4-13]. It is very important that the patient not move between the time of site selection and needle insertion since the position of the fluid may move considerably within the thorax with minor movement of the patient [14]. Similarly, if time has elapsed between prior ultrasonography and the thoracentesis, it is mandatory to repeat the ultrasonography to ensure the pleural effusion is still present (eg, intervening diuresis may have reduced effusion size).

Locating fluid — Using ultrasound, a thoracentesis puncture site can usually be quickly identified and marked. The equipment, machine setup, landmarks and typical appearance of pleural fluid on ultrasound are discussed separately. (See "Bedside pleural ultrasonography: Equipment, technique, and the identification of pleural effusion and pneumothorax".)

When the pleural fluid is free-flowing, an intercostal space is chosen (typically posteriorly in the upright position) that will allow the needle to be inserted at an angle perpendicular to the chest wall and directly into pleural fluid, without risk of lung puncture [2]. Several respiratory cycles are observed to ensure that no intervening lung could potentially move near or into the proposed needle path during some part of the respiratory cycles [2]. A few rib spaces are examined to optimize safe site selection. There is no definite rule as to the minimum allowable depth of pleural fluid at the needle insertion site but greater than 10 mm is considered by most experts as a reasonable estimate of a safe distance [2].

When pleural fluid is loculated, selection of a safe needle insertion site should follow similar steps, although particular care is needed to identify adjacent structures correctly when accessing fluid in unfamiliar locations, such as the anterior chest. Correlation with computed tomographic images may be helpful. If the operator is unsure of the anatomy, a more experienced ultrasonographer should be consulted.

Misidentification of the presence of pleural fluid when none is actually present can create a dangerous situation, such as subdiaphragmatic needle/device insertion, pneumothorax, or vascular injury. Subdiaphragmatic needle/device insertion can lead to organ laceration (liver or spleen) with catastrophic consequences (bleeding). The most common source of this error is that the ultrasonographer incorrectly identifies the hepatorenal recess or the splenorenal recess as the diaphragm and mistakes the liver or spleen for pleural fluid. The best way to avoid this problem is to have an absolute rule that the diaphragm and underlying organs be positively identified before any needle insertion. (See "Bedside pleural ultrasonography: Equipment, technique, and the identification of pleural effusion and pneumothorax", section on 'The anatomic boundaries'.)

A less dangerous situation occurs when the examiner is not able to identify the effusion with ultrasonography, even though it is actually present. Sometimes, the pleural effusion and surrounding organs are difficult to discern with ultrasonography, such as when the chest wall is thickened due to obesity, increased thoracic muscle mass, or edema. Some effusions (eg, hemothorax, empyema) are hyperechoic, rather than the usual hypo- or anechoic appearance, and are of sufficient density so as to ablate the dynamic changes seen in most effusions during respiration. An experienced ultrasonographer should be consulted when thoracic ultrasound does not locate pleural fluid that is believed to be present; advanced image interpretation skills may allow identification of the effusion.

If no ultrasound is available, diagnostic or therapeutic thoracentesis is performed only for free-flowing effusions. Clinicians traditionally locate the site using clinical landmarks as described below. (See 'Choosing and marking the needle site' below.)

Choosing and marking the needle site — Once the fluid is identified by ultrasound, the optimal intercostal space is selected and the exact needle site is chosen. The ideal intercostal space is one that will allow the safe removal of fluid without puncturing the lung. As an example, for small volume thoracentesis an intercostal space that is one rib space below the superior margin of the fluid may be appropriate while a space that is two to three ribs below the superior margin may be more optimal if a large volume thoracentesis is planned, provided it is not too close to the diaphragm. In contrast, the choice of intercostal space may be limited when fluid is loculated.

Once the intercostal space is chosen, the needle insertion site is marked using firm indentation with a needle cap. This method is preferred over marking with a pen, because ink may be removed during application of skin sterilizing fluid. The insertion site should be immediately cephalad to the rib margin to avoid puncturing the neurovascular bundle, which generally lies inferior to the rib [15-20]. In elderly patients the intercostal vessels (particularly those close to the spine) are often tortuous and may extend inferiorly into the intercostal space, below the inferior margin of the rib. Thus, needle insertion should not be performed within 10 cm of the spine, because there is increased risk of puncturing aberrantly positioned intercostal vessels in this region [16]. Some experts recommend that the planned needle trajectory for thoracentesis also be examined using color Doppler in order to identify aberrantly positioned intercostal vessels that could be injured during the procedure. [18,19].

If no ultrasound is available, clinicians traditionally locate the site of access using imaging (chest radiograph or computed tomography) and the physical examination to select the puncture site, using the following landmarks:

One to two interspaces below the level at which breath sounds decrease or disappear on auscultation, percussion becomes dull, and fremitus disappears.

Above the ninth rib, to avoid subdiaphragmatic puncture.

Midway between the spine and the posterior axillary line, because the ribs are easily palpated in this location.

Angle and depth of needle insertion — Following the identification of the needle insertion site, the examiner determines the best angle for needle insertion that will access the fluid and avoid adjacent organs. The transducer angle defines the angle at which the needle/syringe assembly will be held at the time of actual needle insertion. Ideally, this is achieved by selecting an angle that is perpendicular (rather than oblique) to the skin surface, which is easier to duplicate with the needle/syringe assembly. It is important that the operator has memorized the angle of the transducer, as it must be duplicated by the needle/syringe assembly following sterile skin preparation (real-time needle ultrasound guidance during needle insertion is not required).

Once the angle is determined, the depth for needle penetration is measured from a frozen image on the screen using the machine caliper function (see "Bedside pleural ultrasonography: Equipment, technique, and the identification of pleural effusion and pneumothorax", section on 'Machine setup'). If the estimated fluid depth is deeper than the length of the thoracentesis needle (typically 40 mm), a longer needle will need to be used.

Needle or catheter insertion — This part of the procedure is not performed under real-time ultrasound guidance. However, it can be done if the clinician deems it necessary (eg, loculated fluid pocket), in which case a sterile transducer cover should be used. An assistant may hold the transducer in place.

Site preparation and local anesthesia — After identifying the pleural fluid, marking the needle site and trajectory, and maintaining the patient in the same position, the operator should sterilize a wide area surrounding the puncture site with 0.05 percent chlorhexidine or 10 percent povidone-iodine solution. Sterile drapes are placed around the puncture site.

Local anesthetic (eg, 1 or 2 percent lidocaine without epinephrine; max 3 mg/kg) should be administered. The epidermis is initially infiltrated with anesthetic using a syringe and 25-gauge needle.

Next, a syringe attached to a small gauge needle (20- to 22-gauge) loaded with 1 or 2 percent lidocaine is inserted through the skin and advanced toward the upper border of the rib along the trajectory defined by the ultrasonography examination. To avoid intravascular injection of the lidocaine, whenever the needle is advanced forward, the plunger of the syringe is pulled. If no blood is aspirated during the forward movement of the needle, an aliquot of lidocaine is injected.

Once the rib is reached and anesthetic administered to the periosteum (done using tapping movements that inject small amounts of anesthetic), using the same intermittent aspiration technique, the needle is advanced cephalad over the rib, through the parietal pleura and into the pleural space; pleural fluid return indicates that the needle has entered the pleural space and additionally determines/confirms the distance from the skin to the pleural fluid collection.

The needle is then withdrawn slightly and additional anesthetic injected to anesthetize parietal pleural nerve endings (ie, the area that produces the most pain during the procedure) and then the needle is withdrawn.

This technique anesthetizes the skin, rib periosteum, and parietal pleura, thereby minimizing pain during procedure [21].

Fluid removal — The following description is geared toward over-the-needle catheter thoracentesis using commercially available kits that typically have a syringe, stopcock, and an over-needle catheter. Details for bedside small bore catheter tube thoracostomy placement are discussed separately. (See "Thoracostomy tubes and catheters: Placement techniques and complications", section on 'Seldinger technique' and "Thoracostomy tubes and catheters: Indications and tube selection in adults and children".)

Once the selected insertion site is anesthetized, the operator makes a cut through the epidermis using the #11 scalpel blade provided by most kits. The cut is made with vertical movement of the scalpel blade using a stabbing action. The cut is through the full thickness of the epidermis. If the depth of the incision is not adequate, the catheter will get "hung up" at the skin surface, impeding its penetration through the skin. If the patient has a thick epidermis, a cruciate cut (cross-shaped) may be required to allow easy insertion of the needle-catheter assembly. Alternatively, some experts fully advance the scalpel and then, angle the blade 180 degrees and cut while withdrawing the blade; this makes a rectangular shaped hole at the dermis (not a triangular shaped hole in the same size/shape as the blade).

Generation over-the-needle catheters have a three-way stopcock permanently affixed to the catheter. The stop cock is pre-orientated in a position that is closed to the patient; with this type of system, when the needle is removed from the stopcock, there is no risk of pneumothorax from entrainment of air into the pleural space during inspiration. We recommend using this type of system to avoid inadvertent entry of air into the pleural space though an open stopcock. Older design catheter over needle devices required attachment of the stopcock to the catheter following insertion of the catheter into the pleural space; this type of system could result in entrainment of air.

With the stopcock attached, the over-the-needle catheter is inserted through the skin while continuous negative pressure is applied to the syringe. When fluid is aspirated, the needle is inserted another 5 mm to assure that both the needle and the catheter are positioned within the pleural fluid collection. The needle introducer is held stationary while the catheter is pushed forward over the needle to the desired depth or until the catheter hub is against the skin (whichever comes first). The needle is then removed (through the stopcock) and the catheter and stopcock remain in place.

If pleural pressure is to be measured to evaluate possible trapped or entrapped lung, the manometer can be attached to the side port of the stopcock. If manometry is not planned or is completed and the manometry device removed, fluid can be drained as described in the bullet below. The technique of pleural manometry is discussed separately. (See "Measurement and interpretation of pleural pressure (manometry): Indications and technique".)

Generation over-the-needle catheter device kits include a Y shaped drainage tubing set that simplifies therapeutic thoracentesis. One way valves are positioned in the tubing set such that the operator may draw fluid into the 50 mL syringe and then push it out into the collection bag. When properly attached, the tubing set is a closed system, so it offers the advantage of a convenient means of fluid drainage with no risk of inadvertent air entrainment into the pleural space during fluid removal.

With the stopcock open to the patient and the syringe, 50 mL of pleural fluid is withdrawn for analysis. More fluid may be removed if required for additional tests.

Common tests performed on pleural fluid include cell count, protein, lactate dehydrogenase, pH, glucose, amylase, gram stain, culture, and cytology. The pleural fluid should be immediately placed in the appropriate specimen tubes and bottles, and sent to the laboratory for analysis. (See "Pleural fluid analysis in adults with a pleural effusion".)

For the measurement of pH, a fresh 3 mL syringe pre-coated with heparin (<0.4 mL or approximately 8 units) or a 3 mL arterial blood gas syringe that comes pre-coated with heparin is attached to the thoracentesis catheter to draw pleural fluid directly from the patient. Any air bubbles in the syringe should be immediately expelled from the syringe and the syringe placed on ice. Fluid should be analyzed by a blood gas analyzer within one hour of collection [22]. Collection of pleural fluid for measurement of pH requires careful technique because the admixture of air, lidocaine, or heparin with pleural fluid alters the measured pH. The syringe used to anesthetize the thoracentesis site should, therefore, not be used to collect pleural fluid because even a small volume of residual lidocaine will affect pH. (See "Arterial blood gases", section on 'Sources of error'.)

Once a sample of fluid is removed for analysis, there are three methods to remove additional fluid (if that is desired).

Gravity Drainage – The operator places the end of the drainage tube below the level of the catheter insertion and the stopcock is opened to allow flow from the patient to the collection bag. The vertical distance between the end of the drainage tube and the catheter insertion site establishes a hydrostatic gradient that causes fluid to drain passively from the pleural space. The advantage of this method is that the operator can control the degree of negative pressure that is used to draw fluid from the pleural space (the degree of pressure is determined by the vertical distance between the insertion site and the end of the drainage catheter). There are no guidelines that define the safe limit for pressure application or for rate of fluid removal. Our practice is to limit the negative pressure gradient to approximately 30 cm of vertical distance (ie, -30 cm H2O). While this may result in a relatively slow flow rate, it avoids an excessive pressure gradient.

Syringe Drainage – The operator can repeatedly fill and empty the 50 mL syringe that is attached to the commercial drainage tubing set; this requires manipulation of the stopcock catheter only to ensure safe removal and disposal of fluid. If the stopcock system is not available, the operator can withdraw individual 50 mL aliquots and inject them manually into the collection bag; however, this runs the risk of catheter dislodgement and air entrainment each time the syringe is detached from the catheter. Thus, we recommend use of a valved/stopcock tubing set.

Vacuum Bottle Drainage – A commercially available vacuum bottle may be attached to the drainage catheter. This method is convenient and allows rapid removal of fluid. One concern is that the operator has no knowledge of the negative pressure within the vacuum bottle and therefore, a possibility of non-physiologic negative pressure application to the pleural space, although this concern may be theoretical only [23]. With the advent of valved/stopcock tube drainage systems, vacuum bottle drainage is no longer widely in use.

One study reported no difference in the safety of gravity drainage compared with active drainage (ie, suction) [24]. However, gravity drainage takes a little longer.

Fluid is typically removed up to a pre-determined volume (typically less than 1 to 1.5 L, occasionally more), until flow slows or stops, or the patient experiences symptoms (eg, chest discomfort and cough may indicate a drop in pleural pressure). (See "Procedures for tissue biopsy in patients with suspected non-small cell lung cancer", section on 'Thoracentesis- cytology' and "Large volume (therapeutic) thoracentesis: Procedure and complications", section on 'Determining the volume of fluid to be removed'.)

Once the desired volume is removed, the catheter should be removed. With the syringe and stopcock still attached to the catheter, the catheter is removed while the patient holds his or her breath at end expiration. Pressure should be placed over the catheter site using a finger with subsequent placement of occlusive dressing.

Dry tap — A thoracentesis is "dry" (ie, with no pleural fluid return) in 7.4 percent of procedures [25]. There are several possible reasons for a "dry" tap, including the following:

Skin indentation artifact – If the patient has significant edema at the scan site, the transducer may indent the skin during the ultrasound study, decreasing the measured distance to the effusion. Subsequently, during site sterilization and draping, if the skin rebounds to its usual position, the distance required to penetrate into the pleural space is more than that originally measured. The solution to this problem is to observe for indentation while scanning and to factor it into the depth measurement.

Skin movement artifact – Skin is mobile, so that the skin mark may move if the operator places asymmetric force on the skin while placing the site mark. In releasing the skin, the mark may move to a new position relative to the desired pleural entry point. The solution to this problem is to avoid any skin traction when marking the site.

Poor angle replication – The angle of the needle/syringe assembly must replicate the angle of the transducer, or the tip of the needle will miss the intended spot, possibly leading to a dry tap or laceration of adjacent organs. The solution to this problem is to scan the patient again and to improve the angle of insertion. This process is simplified by choosing a perpendicular angle of insertion, when possible.

Patient movement – If the patient moves between the time of ultrasonography and needle insertion, the relationship between the skin mark and the pleural effusion may change. The solution to this problem is to perform the procedure immediately following the scan without any change in patient position.

Needle blockage – Complex pleural effusions may contain thickened viscous fluid, septations, or cellular debris that may block the needle. A clue that the needle is blocked is that a small amount of fluid may be aspirated initially, but the free flow then stops abruptly. The solution to this problem is to use a larger needle or to identify a window where there is relatively less complexity of the pleural effusion.

Visceral pleural impingement – The tip of the needle or catheter may abut the visceral pleural membrane. Causes of pleural impingement include insertion of the needle too far into the effusion with consequent movement of the lung into the needle path during respiration. Characteristically, the needle blockage is intermittent and cycles with respiration. The solution to this problem is to withdraw the needle, check that the calculated distance and trajectory is correct, and scan the patient for a location with greater depth of pleural fluid and absence of intervening lung at deep inspiration.

Nonexpandable lung – In some cases, a dry tap results when the lung cannot expand; this is most often due to pleural pressure which becomes negative with fluid removal (entrapped) or is negative prior to fluid removal (trapped), thereby prohibiting further drainage. It may be recognized by measuring pleural pressure in those in whom lung entrapment or trapped lung is suspected (typically on chest computed tomography). (See "Diagnosis and management of pleural causes of nonexpandable lung".)

Inappropriately short needle – In some patients (eg, obesity), the needle is too short. The need for a longer needle can be anticipated when measuring the distance from the skin to the fluid by ultrasound prior to the procedure and use of kits that provide long needles.

In many of the above cases (except for nonexpandable lung), the needle can be adjusted in its position or withdrawn, and reinserted in a slightly different angle if the patient tolerated the initial attempt. A second dry tap warrants reevaluation of the patient with ultrasound (bedside or formal) and/or CT. The risk of pneumothorax increases if more than one needle pass is required [26].

Certain findings may provide clues to the cause of a dry tap. Aspiration of air implies that the lung has been punctured because the needle was inserted superior to the effusion or too deeply. Aspiration of a small amount of blood suggests that the needle may have been inserted inferior to the effusion (ie, subdiaphragmatically) or into an intercostal vessel. Failure to aspirate anything implies that the needle may have been too short to penetrate the pleura, especially in an obese patient, the fluid is too viscous to flow through the needle, or no pleural fluid exists along the selected needle path. Aspiration of a small amount of pleural fluid that quickly stops flowing may indicate a nonexpandable lung, which may be established by the measurement of pleural pressure. (See "Measurement and interpretation of pleural pressure (manometry): Indications and technique".)

FOLLOW-UP — Following thoracentesis, the ipsilateral chest is examined for pneumothorax by ultrasound and findings documented. The presence of lung sliding at multiple interspaces is a sensitive finding that rules out a procedure-related pneumothorax. It is advisable to document the presence and location of lung sliding prior to any procedure associated with a risk of pneumothorax because the disappearance of lung sliding or B-lines after the procedure suggests the interval development of a pneumothorax and should prompt either a chest radiograph or immediate intervention (eg, if symptoms suggest tension pneumothorax). The ultrasound appearance of pneumothorax and data that support ultrasonography for the detection of pneumothorax are provided separately. (See "Bedside pleural ultrasonography: Equipment, technique, and the identification of pleural effusion and pneumothorax", section on 'Evaluation for pneumothorax'.)

A routine chest radiograph after thoracentesis is not indicated for most asymptomatic, nonventilated patients, especially if ultrasound suggests that no pneumothorax is present [27-30]. For example, in a prospective cohort study, only 1 percent of 488 asymptomatic patients were found to have a pneumothorax on a post-thoracentesis chest radiograph [27]. However, a chest radiograph is indicated if the ultrasound suggests one or is ambiguous, air was aspirated during the procedure, symptoms or signs of pneumothorax develop, ultrasonography imaging was poor, the machine is unable to store images in durable format (ie, for documentation purposes), or multiple needle passes were required [21].

Whether a post-thoracentesis chest radiograph is needed for mechanically ventilated patients is controversial [31]. Approximately 1 to 7 percent of thoracenteses performed with ultrasound-guidance in mechanically ventilated patients develop pneumothorax [32-34]. While we follow a similar practice to that in nonventilated patients, other experts routinely perform chest radiography in this population, since its detection increases the risk that a tension pneumothorax may rapidly develop.

COMPLICATIONS — Potential complications of thoracentesis include pain at the puncture site, bleeding (eg, hematoma, hemothorax, or hemoperitoneum), pneumothorax, empyema, soft tissue infection, spleen or liver puncture, vasovagal events, seeding the needle tract with tumor, adverse reactions to the anesthetic or topical antiseptic solutions, shortness of breath, cough, and re-expansion pulmonary edema [35-39]. Cases of retained intrapleural catheter fragments were reported in the past [40] but are rare since the introduction of over-the-needle catheter devices.

Pneumothorax – Pneumothorax is the most common complication that is clinically important and develops in approximately 0.3 to 3 percent of patients or less when ultrasound guidance is used. Without use of ultrasound guidance, prospective observational studies indicate that pneumothorax occurs in up to 30 percent of thoracenteses, although most studies found rates less than 12 percent [10,41-43].

Several nonrandomized studies demonstrate that use of ultrasound guidance in nonventilated patients reduces the rate of pneumothorax following thoracentesis to less than 3 percent when performed by adequately trained operators [39,44-46]. Although one meta-analysis of observational studies, suggested no benefit to ultrasound [25], a small randomized trial of 160 patients undergoing thoracentesis by skilled operators demonstrated that ultrasound decreased pneumothorax rates from 12.5 to 1.3 percent [47]. In a meta-analysis that included 6605 diagnostic or therapeutic thoracenteses, the rate of pneumothorax was lower in those in whom ultrasound guidance was used compared with those without ultrasound guidance (9 versus 4 percent) [12]. Other studies also confirm a similar low incidence of ultrasound-guided thoracentesis [1,48-52]. Real-time ultrasound guidance has also been shown to be associated with lower rates of pneumothorax compared with ultrasound marked thoracentesis (0.63 versus 4.43 percent), particularly in mechanically ventilated patients [53].

The pneumothorax rate in ventilated patients is traditionally thought to be higher than in nonventilated patients but rates vary among studies from 1 to 7 percent [26,32-34]. Because of the positive airway pressure in mechanically ventilated patients, it is reasonable to think that a pneumothorax in ventilated patients can more frequently lead to a tension pneumothorax than in nonventilated patients, although no data support this claim. The safety of ultrasound-guided diagnostic and therapeutic thoracentesis performed by critical care physicians was examined in 211 patients receiving mechanical ventilation. A pneumothorax complicated 3 out of 232 thoracenteses (<2 percent) [32]. Thoracentesis was unsuccessful in three patients with chest wall thicknesses over 15 cm.

A pneumothorax caused by thoracentesis is usually small and resolves spontaneously, although up to one-third of patients require tube thoracostomy drainage [12]. Tube thoracostomy should be considered if the pneumothorax is large, the pneumothorax is progressive, the patient is symptomatic, or the patient is mechanically ventilated. (See "Thoracostomy tubes and catheters: Indications and tube selection in adults and children" and "Pneumothorax in adults: Epidemiology and etiology".)

When ultrasound guidance is used for thoracentesis, most pneumothoraces are not caused by laceration of the visceral pleural surface from poor site, angle, and/or depth selection by the operator but rather from the presence of non-expandable lung [1]. One study reported that among 102 thoracenteses, one pneumothorax occurred from lung puncture and eight were thought to be due to nonexpandable lung. Other studies report a correlation between the volume of fluid drained and the risk of pneumothorax, even with ultrasound guidance [1,50]. As an example, among 736 ultrasound-guided thoracenteses in 471 patients, the risk of pneumothorax after drainage of 1.8 to 2.2 L was increased compared with drainage of 0.8 to 1.2 L (odds ratio [OR] 3.8) and drainage of 2.3 L or more was even higher (OR 5.7) [50]. Other factors that contribute to ultrasound-guided pneumothorax include deeper needle penetration due to an incorrectly calculated distance from the skin surface and the fluid.

Infection – Infectious complications are exceptionally rare. In one observational study, there were no serious infections following 2489 ultrasound-guided thoracenteses performed by radiologists [54].

Liver or spleen puncture – The liver or spleen may be punctured when the patient is not sitting absolutely upright, because as a patient moves toward recumbency, the abdominal viscera move cephalad. The outcome can be catastrophic but is generally favorable if a small bore needle was used and the patient is not receiving anticoagulants and does not have a bleeding diathesis.

Bleeding – Rates of bleeding appear to be low (<0.2 percent), even among patients taking anticoagulants or antiplatelet agents [26,35,55,56]. However, higher are generally only seen in patients undergoing more invasive pleural procedures (eg, biopsy) [57]. Further data are provided separately. (See "Diagnostic evaluation of the incidental pulmonary nodule", section on 'Transthoracic needle biopsy'.)

Complication rates for thoracentesis can be reduced by recognizing risk factors for complications that include patient variables (small effusions <250 mL, obesity, multiple loculations, supine patient positioning, coagulopathy, mechanical ventilation, and intrapleural adhesions), procedural factors (operator inexperience, absence of ultrasound guidance, and large volume drainage), and systems factors (poor coordination of the thoracentesis team, nonstandardized equipment, lack of quality metrics, and lack of routine quality reviews) [36,50,58]. Recognition and improvement of modifiable risk factors decrease patient risk [58].

TRAINING — Clinicians who perform thoracentesis or related procedures should have experience and have competence in performing the procedure [49,51,59]. Resident trainees at teaching hospitals self-report comfort in performing thoracentesis after 5 to 6 procedures [60]. However, survey studies demonstrate that residents have considerable gaps in knowledge and skills in conducting thoracentesis [61]. Standardized curricula and training programs for teaching thoracentesis with structured proficiency and competency standards have been shown to improve bedside thoracentesis knowledge and skills [45,62,63].

Studies also demonstrate that skills-based training programs, such as simulation-based mastery learning and other short-term but formalized teaching programs, can train residents, hospitalists, and pulmonary physicians in using ultrasound at the point of care to improve the success of thoracentesis [52,64]. Programs and assessment tools exist to recognize clinical competence for performing ultrasound-guided thoracentesis and to set standards for training [65,66]. A position paper from the Society of Hospital Medicine proposes pathways for credentialing hospitalist physicians in ultrasound guidance of thoracentesis with assessment of competence through direct observation of thoracentesis on actual patients [67].

RELATED PROCEDURES — Thoracic ultrasonography may be used to guide other procedures, such as transthoracic needle aspiration biopsy of lesions of the pleura or subpleural lung [68-71] as well as of the anterior mediastinum [72-75].However, compared with thoracentesis, these procedures are not commonly performed at the bedside and require additional expertise.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Pleural effusion".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

Beyond the Basics topics (see "Patient education: Thoracentesis (Beyond the Basics)")

SUMMARY AND RECOMMENDATIONS

Definition – Thoracentesis is a percutaneous procedure where pleural fluid is removed from the pleural space. It should only be performed by clinicians with experience and who demonstrate competency with the procedure. (See 'Introduction' above.)

Equipment – Thoracentesis is a sterile procedure that requires informed consent. Several thoracentesis kits are commercially available that contain skin sterilizing fluid (eg, 0.05 percent chlorhexidine), sterile drapes, sterile wound dressing material, local anesthetic, an 18-gauge over-the-needle catheter, stopcock, 35 to 60 mL syringe, and thoracentesis drainage bag/system. (See 'Equipment' above.)

Technique – Thoracenteses should be performed with ultrasound guidance. Before the procedure, the operator rules out pneumothorax with ultrasonography and positively identifies key structures that need to be avoided during needle insertion including the diaphragm with underlying liver or spleen, lung, chest wall, heart, and descending aorta. The procedure is performed immediately following the ultrasonography examination without any patient movement between the time of site selection and needle insertion. (See 'Technique' above and "Bedside pleural ultrasonography: Equipment, technique, and the identification of pleural effusion and pneumothorax".)

Ultrasound should guide the selection of the puncture site by identifying an intercostal space with underlying pleural fluid that is of sufficient depth that the lung will not be pierced by the needle during aspiration (typically >10 mm). (See 'Site selection' above and 'Angle and depth of needle insertion' above and 'Needle or catheter insertion' above.)

The site is marked with a needle cap, angle and depth of penetration memorized, skin and ribs anesthetized, and fluid removed. In general, 50 mL is sufficient for diagnostic purposes while larger volumes can be removed for therapeutic purposes. (See "Large volume (therapeutic) thoracentesis: Procedure and complications".)

Follow-up – Following thoracentesis, the ipsilateral chest is examined for pneumothorax by ultrasound. A routine chest radiograph after thoracentesis is not indicated for most asymptomatic, nonventilated patients, especially if ultrasound suggests that no pneumothorax is present. However, a chest radiograph is indicated if the ultrasound suggests one or is ambiguous, air was aspirated during the procedure, symptoms or signs of pneumothorax develop, ultrasonography imaging was poor, the machine is unable to store images in durable format (ie, for documentation purposes), or multiple needle passes were required [21]. While we typically apply the same practice to ventilated patients, some experts routinely obtain chest radiography in this population. (See 'Follow-up' above.)

Complications – Potential complications of thoracentesis include pain at the puncture site, bleeding (eg, hematoma, hemothorax, or hemoperitoneum), pneumothorax, empyema, soft tissue infection, spleen or liver puncture, vasovagal events, seeding the needle tract with tumor, adverse reactions to the anesthetic or topical antiseptic solutions, shortness of breath, cough, and re-expansion pulmonary edema. Pneumothorax, the most common complication that is clinically important, develops in approximately 3 percent of patients or less when ultrasound guidance is used; tube thoracostomy is rarely required for treatment. (See 'Complications' above.)

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