US guidance is recommended by the British Thoracic Society (BTS) when undertaking any procedure on a pleural effusion in order to reduce complications. This chapter outlines the indications for draining a pleural effusion and describes the technique for using US to identify a safe site for drainage. A detailed description of how to undertake an US-guided pleural aspiration, thoracocentesis, and insertion of chest drain follows.
Role of ultrasound
Pleural effusions are frequent in the critical care setting, and pleural US is the ideal bedside imaging modality for the assessment and drainage of pleural effusions. In addition, real-time imaging of the hemidiaphragm provides information about any restriction of movement secondary to the effusion. The depth of the effusion at the most postero-lateral point allows estimation of the effusion volume (Figure 30.1), and the US characteristics of the effusion can indicate the type of fluid (transudate, exudate, empyema). Of most significance, the use of real-time US guidance to drain effusions significantly reduces the complication and failure rates of the procedure. Complications of pleural drainage include pneumothorax, procedure failure, pain, haemorrhage, and visceral injury.
The BTS guidelines recommend that all drainage procedures for pleural fluid are undertaken using US guidance. An ‘X marks the spot’ technique that is undertaken remote in time and place from the drainage procedure carries the same complication rate as performing blind drainage and should not be undertaken.
Indications for drainage
It is rare to find a patient on the critical care unit without a small pleural effusion. The decision about whether to drain or sample the pleural fluid is patient-specific and not always dependent on the effusion size. Pleural aspiration and insertion of intercostal drains are invasive procedures with associated risks; neither should be undertaken without careful clinical consideration. Common indications for drainage are discussed in the following sections.
Bedside observations, arterial blood gas results, and clinical examination indicate whether a patient is compromised by a pleural effusion. Direct observation of the movement of the hemidiaphragm on the affected side will also aid this decision (Video 3.1.1 ). Although a larger-volume effusion is more likely to compromise an individual, a pleural effusion should not be drained because of size alone. Smaller effusions (e.g. <400 mL) are unlikely to have a significant effect on respiratory function.
Suspicion of empyema
An empyema should always be drained to dryness, using an adequately sized intercostal chest drain. US assessment can aid in the differentiation between purulent fluid and a simple transudate. A diagnostic tap under US guidance can provide the definitive answer. The pH of non-purulent fluid should be measured, with a value of <7.2 indicating an empyema and the need for tube drainage of a parapneumonic effusion.
Pleural drainage can help diagnostically. Pleural fluid can be sent for microbiology, biochemistry, and cytology, all of which can provide vital diagnostic information. Light’s criteria from the results of lactate dehydrogenase (LDH) and total protein measurements in pleural fluid and serum are used to differentiate a transudate from an exudate (Box 30.1).
With atelectatic lung surrounded by effusion, drainage of the fluid will reveal if the lung is solely compressed by the surrounding fluid or if there is a proximal bronchial obstruction causing lobar collapse.
US assessment of the pleural effusion can contribute to the decision to drain. Use US to answer the following questions:
• What type of fluid makes up the effusion (purulent, exudate, transudate)?
• Is there a suitable and safe site to drain the fluid (Box 30.2)?
Assessment of site for drainage
It is recommended that the minimal fluid depth for safe drainage is at least 10 mm. A puncture site should be chosen which is not impinged by the underlying lung during inspiration. Identify any structures which may be in proximity such as the liver, spleen, or LV and it’s associated vasculature (Figure 30.2 and Videos 3.1.2 and 3.1.3 ). If loculations are present, identify the largest locule for symptomatic drainage or diagnostic sampling (Figure 30.3). Referral for video-assisted thoracoscopy may be necessary for breaking up the locules and a safer and more effective method of drainage.
The ideal site for insertion without US guidance is within the ‘safe triangle’, defined by the lateral border of the pectoralis major, the anterior border of the latissimus dorsi, and the fifth intercostal space. US imaging may identify a safe and appropriate place to access a pleural effusion which is outside the ‘safe triangle’. However, the neurovascular bundle may not lie under the inferior border of the rib posteriorly, but in the middle of the intercostal space, such that very posterior sites of drainage should be avoided.
Although US is very sensitive at identifying loculated effusions, if there is any uncertainty regarding the nature of a pleural effusion, CT imaging should be undertaken prior to any intervention. Differentiating a complex loculated effusion from consolidated lung can be very difficult, and the CT scan remains the gold standard imaging modality for the lung.
Choice of procedure and size of drain
This will depend on the nature and estimated volume of the pleural collection. If drainage over a number of days is required, a large-gauge surgical drain is inserted for a haemothorax, while a small-gauge Seldinger drain is used to drain transudates. Traditionally, larger-gauge drains are inserted to manage an empyema, although BTS guidance recommends insertion of an image-guided small-gauge Seldinger drain in the first instance. The Seldinger technique is not recommended for large drains (24 French gauge and above) when a surgical blunt dissection method is most appropriate. Treatment of smaller effusions and diagnostic sampling are undertaken by aspiration, using a small-gauge needle or cannula without placement of a drain.
Preparation and consent
Documented consent should be obtained prior to all pleural procedures, which should encompass the indications for the procedure and all common or serious possible complications. All equipment should be collected and prepared in advance. Pleural drainage is an invasive procedure and should follow locally developed standards to ensure safe practice that are based on national safety standards. A peri-procedural checklist, equivalent to the World Health Organization surgical safety checklist that is now a standard of care for all surgical procedures, can ensure compliance with local standards and improve safety.
Clotting disorders and anticoagulation
Any non-urgent pleural procedures should wait until the patient’s international normalized ratio (INR) is below 1.5 and the platelet count is above 50. For patients on direct-acting oral anticoagulants, ensure an appropriate delay since the last dose. Advice should be sought about the best way to correct any coagulation abnormalities, if they exist, prior to attempting pleural aspiration or chest drain insertion.
‘X marks the spot’ ultrasound technique
Carefully position the patient in the position you will be performing the diagnostic tap. Using US, identify the safest and most appropriate areas to puncture and drain, identifying the characteristics previously described. Using a curvilinear probe, obtain a still image in the longitudinal plane at the proposed puncture site, and measure the depth of the skin and the depth of the effusion. Now obtain a transverse still at the proposed puncture site by rotating the probe 90 degrees, and measure the depth of the skin and the depth of the effusion. Carefully note any significant changes in measurements, and also look for solid structures within the pleural fluid that were not visible in the alternative plane. Mark the site using an indelible pen or by applying pressure with a narrow, blunt object.
Ensure the patient remains in the same position.
Direct real-time ultrasound technique
For loculated or small effusions, it is recommended that aspiration is performed under direct US guidance, visualizing the needle as it is advanced into the pleural space. Use a sterile probe cover and sterile US gel. An ‘in-plane’ approach, using a high-frequency linear array probe, is recommended for most patients.
Diagnostic aspiration and therapeutic drainage are undertaken as an aseptic technique, using sterile gloves, a sterile dressing pack, cleaning solution (chlorhexidine in alcohol), and an appropriate range of syringes and an aspiration kit, if planned. Insertion of a chest drain is undertaken with full aseptic barrier precautions (surgical gown, hat, face mask, sterile gloves), using a proprietary Seldinger chest drain insertion kit or with surgical blunt dissection.
1. Diagnostic aspiration
Ensuring that the patient is in the same position as when the US was performed and using an aseptic technique, a 20-mL syringe with a 21G needle attached is passed through the skin at the marked site. Once the skin is punctured, advance the needle, keeping the syringe under negative pressure. On puncturing the pleura, there will be a rush of fluid. Do not advance the needle any further. Obtain an adequate sample for diagnostic purposes (20–50 mL).
Apply a sterile dressing to the puncture site.
2. Therapeutic aspiration (thoracocentesis)
The aspiration kit should be put together before scanning the patient, in order to minimize the time between US and puncture. US scan is undertaken as described previously, and ensure that the patient’s position remains unchanged.
Infiltrate local anaesthetic down to the pleura (pleural puncture is painful) until pleural fluid is aspirated. Using a 5- or 10-mL syringe attached to the intravenous cannula, puncture the skin at the marked and anaesthetized site. Advance the cannula, keeping the syringe under negative pressure. On puncturing the pleura, there will be a rush of fluid. Advance the cannula over the needle into the pleural space. Remove the needle and attach the three-way tap. Using the 50-mL syringe, withdraw pleural fluid and flush it away through the free port of the three-way tap attached to intravenous infusion giving-set tubing. Ensure that a sample is taken for analysis. Once an adequate amount of fluid has been drained, remove the cannula from the pleural space and apply a sterile dressing.
Therapeutic aspiration can also be performed by inserting a small-gauge chest drain that is removed immediately after the effusion has been drained. The puncture site is larger than with using a cannula, thereby increasing the risk of pneumothorax. It will need closing with a suture. Following completion of therapeutic aspiration, repeat the US examination and store an image to allow comparison with pre-procedure images (Figure 30.4).
3. Chest drain insertion
The technique of US-guided Seldinger drain insertion is similar to that described previously for therapeutic aspiration. Once the pleural space is entered, a guidewire is passed through the cannulating needle. Direct real-time US may be used to allow confirmation of the correct guidewire position within the pleural space before proceeding to dilatation and chest drain insertion. The dilator should be inserted with caution to ensure that it just enters the pleural space when a distinct ‘give’ will be felt. Inserting an excessive length of dilator may damage the underlying lung. Following dilatation, the chest drain with a stiffening insert is passed over the guidewire. The distal end of the guidewire must be visible at all times to prevent inadvertent loss into the thoracic cavity. Once the drain is inserted to an appropriate length, the guidewire and stiffening insert are withdrawn together. The drain should then be attached to an appropriate drainage system, including an underwater seal. The volume of fluid drained should be monitored and drainage temporarily stopped if >1500 mL is drained or the patient develops chest pain or cough. A detailed explanation of the insertion technique for both types of chest drain can be found within the BTS pleural procedures and thoracic US pleural disease guideline 2010. Insertion of chest drains should only be performed by staff who have been trained and assessed as competent in the procedure.
Pleural drainage using US guidance has been shown to be considerably safer than using a blind technique. The benefit of US in these circumstances is determined by the ability of the observer to accurately interpret the US images obtained in order to correctly identify the presence of pleural fluid.
Potential pitfalls in US interpretation include:
• Differentiating pleural effusion from pleural thickening
• Differentiating complicated pleural effusions from consolidated lung
• Mistaking ascitic for pleural fluid.
The size of an effusion may be overestimated if the plane of the US scan is not perpendicular to the chest wall, but angled posteriorly to cut through a dependent posterior collection. Always obtain views in two planes (longitudinal and transverse) when assessing the size of an effusion.
Once the US has identified the appropriate site for drainage, ensure that the patient’s position is not changed before completing the drainage procedure. Fluid will move under the effect of gravity, and changes in posture can have a marked effect on the depth and position of an effusion.
When undertaking chest drain insertion for a pleural effusion, it is essential that pleural fluid is aspirated during the infiltration with the local anaesthetic agent as a confirmatory step prior to proceeding. If no pleural fluid is obtained, stop and re-evaluate.
1. When undertaking US-guided pleural aspiration or drainage:
A Ensure that the puncture site is within the ‘safe triangle’
B Choose a site where the pleural depth is at least 10 mm
C Effusions with an estimated volume of >400 mL should be drained
D An empyema can be managed in the first instance with a small-gauge Seldinger drain
E A CT scan is more sensitive at identifying loculations within a pleural collection
2. When investigating the underlying cause of a pleural effusion:
A Purulent fluid should have pH measured by a blood gas machine
B A pH of <7.2 indicates a collection that requires tube drainage
C Light’s criteria defines a serum:pleural LDH ratio of >0.6 as an exudate
D Therapeutic aspiration should be undertaken with a large-gauge cannula
E Real-time US guidance is recommended for diagnostic aspiration of loculated effusions
1. When undertaking US-guided pleural aspiration or drainage:
A FALSE. US may identify an appropriate point outside the safe triangle. The safest site is determined by direct visualization of effusion depth, character, and underlying structures.
B TRUE. To minimize trauma to local structures.
C FALSE. Size alone should not dictate the need for drainage.
D TRUE. BTS guidance is to attempt US-guided Seldinger drainage.
E FALSE. US is more sensitive for this. However, a CT scan should be undertaken if there is any uncertainty regarding the nature of an apparent pleural collection.
2. When investigating the underlying cause of a pleural effusion:
A FALSE. Unnecessary if frankly purulent and will damage the blood gas machine.
B TRUE. A pH of <7.2 is an indication for tube drainage of a parapneumonic effusion.
C FALSE. A pleural:serum LDH ratio of >0.6 indicates an exudate.
D FALSE. BTS guidance is to use a small-gauge cannula to reduce risk of pneumothorax.
E TRUE. Due to the increased risk of inadvertent injury, real time ultrasound will allow direct visualization of the needle during the procedure.
Havelock T, Teoh R, Laws D, Gleeson F; BTS Pleural Guideline Group. Pleural procedures and thoracic ultrasound: British Thoracic Society Pleural Disease Guideline 2010. Thorax 2010;65(Suppl 2):ii61–76.Find this resource:
Hooper C, Lee YCG, Maskell N; BTS Pleural Guideline Group. Investigation of a unilateral pleural effusion in adults: British Thoracic Society Pleural Disease Guideline 2010. Thorax 2010;65(Suppl 2):ii4–17. Find this resource: