Sit the patient on the edge of the bed, arms folded in front of the body and leaning forward across a hospital table (Fig. 11).
Before putting on your gloves, check the site of the effusion on the chest x-ray and percuss down the chest. Place a cross on the lateral posterior aspect of the chest,
Fig. 11 Position of the patient for pleural tap. (Adapted from McLatchie, G. Oxford Handbook of Clinical Surgery. 1st edition. 1990, Oxford University Press)
3–5 cm below the level at which you can first percuss the effusion. Your cross should be in an intercostal space, over the top surface of a rib.
Do not proceed if you cannot confidently percuss the effusion; get an ultrasound scan to mark the position.
Put on your gloves, place sterile towels below the target area and clean the skin with antiseptic.
Draw up 5–10 ml of lidocaine and raise a bleb under the skin with a 27-gauge needle.
Infiltrate local anesthetic using a 21-gauge needle, slowly working down perpendicular to the skin. Aim over the top surface of the rib, pulling back before injecting anesthetic. Stop when you aspirate fluid (Fig. 12).
For a diagnostic tap, attach a fresh 21-gauge needle to a 20-ml syringe, insert along the anesthetized track at right angles to the skin, and advance while at the same time pulling the plunger back. When fluid is first aspirated, stop – do not advance any further – and pull the plunger back until the syringe is full. Withdraw the needle and press over the site with a gauze pad.
For a therapeutic tap, attach a 50-ml Luer-lock syringe to a three-way stopcock. Attach a length of tubing to the side port of the three-way stopcock (a giving set works reasonably well). Put the other end of the tubing in a large sterile jug.
Insert a 16-gauge cannula along the anesthetized track at right angles to the skin. When you see a fluid flashback, advance the cannula a little further, then push the plastic cannula as far into the thorax as it will go, keeping the stylet still. As you withdraw the stylet, put a thumb over the end of the cannula – this prevents a pneumothorax. If possible, ask the patient to breathe out and hold the breath in expiration as you withdraw the stylet.
Attach the three-way stopcock to the cannula, ensuring that the cannula does not kink. You can now either allow the fluid to drain under gravity, or you can withdraw 50 ml using the syringe, then turn the three-way stopcock, and expel the contents of the syringe into the tubing.
Once you have drained 1–1.5 L of fluid, remove the cannula and the attached equipment and press over the site with a gauze pad for 1 minute.
No fluid aspirated: try angling the needle down a little, to the side a little, or withdraw the needle a little. If you still fail to aspirate fluid, start again by percussing out the level of the effusion again. If you still cannot aspirate fluid, give up and request an ultrasound scan to locate the effusion
The patient is obese: for a diagnostic tap, try using a 16G or 18G cannula, or a 21G lumbar puncture needle; they are longer than a standard 21G needle. For a therapeutic tap, try using a long 14G cannula, or even better a cannula over stylet central line – rare, but very useful if you can find one!
Blood is aspirated: a small flash of blood is not unusual; this is caused by nicking blood vessels in the skin. Red fluid is either blood or a bloody effusion; put a little in a dish and see if it clots. If it doesn't clot, it is likely to be a bloody effusion. If it does clot, get out and seek help
The flow rate slows down during aspiration: some effusions, especially malignant effusions with a high protein content, can be very viscous. This can result in the cannula becoming narrowed during aspiration, which leads to difficulty aspirating fluid. You might need to use a new cannula
The patient is uncomfortable: if the discomfort occurs on inserting the needle, more local anesthetic is needed. If cough or discomfort occurs during a therapeutic aspiration, this suggests that the lung has re-expanded and the visceral pleural is in contact with the needle. Stop the aspiration if this occurs
The patient becomes unwell: vasovagal reactions are not uncommon during pleural taps; if the patient feels faint, stop, withdraw the needle immediately, and lie the patient down. Adequate local anesthetic can help to avoid this. Less commonly, the shift of the lung and mediastinum can lead to changes in autonomic tone, or to circulatory collapse. Do not aspirate more than 1–1.5 L of fluid in a single sitting.
Send the fluid for microscopy, culture and sensitivity, cytology, and for protein and lactate dehydrogenase (LDH) levels. If tuberculosis (TB) is at all possible, request acid-fast staining. If the effusion accompanies a pneumonia, place some of the fluid on ice and request the pH of the fluid – this is vital for deciding whether a chest drain is required.
Order a chest x-ray, even after a diagnostic or failed tap, to check for pneumothorax. A small pneumothorax does not need aspirating but might require another x-ray in a few hours to ensure that it is not increasing in size. Write a brief note in the patient's chart regarding the procedure.