Small-Volume Diagnostic Paracentesis or Thoracentesis

I've alluded to a technique I use to obtain a small amount of pleural or ascitic fluid for laboratory analysis. This technique is much faster, easier and less cumbersome than using the large-volume trays designed to drain liters of fluid. Having this technique in your bag of tricks makes it much easier for you to do the right thing in the middle of the night and get your patient tapped and fully worked up rather than waiting for the interventional radiologist to do your dirty work.

This is also a great technique if your patient has coagulopathy and you are concerned about post-procedure bleeding. Obviously, bleeding risk is not eliminated but this is a relatively atraumatic technique compared to the larger-bore needles and catheters used in large-volume techniques.

PREPARATION

Obtain informed consent as you usually would. Examine the patient and find landmarks as you would for a large-volume tap.

SUPPLIES

Not pictured: alcohol swabs, skin prep (iodophor or chlorhexidine), 2x2 gauze, skin tape, 1% lidocaine with or without epinephrine for local anesthesia, 3 or 5cc syringe for lidocaine, 18G needle to draw up lidocaine, 23G needle for subcutaneous infiltration.

Basic set-up:

• 1, 2: anaerobic and aerobic culture bottles
• 3: Vacutainer single-use blood collection tube holder/bell adapter (BD item #366487)
• 4: 2 red-top tubes
• 5: 2 lavender-top tubes
• 6: arterial blood gas syringe
• 7: Vacutainer multiple sample luer adapter (BD item #367290)
• 8: Spinal needle, 18 or 20 gauge. This is a 3.5 inch 18G Quincke needle, but the type/shape doesn't matter

The key to the basic set-up is #7, the multiple sample luer adapter (affectionately known as "the blue thing"). This permits you to attach the spinal needle directly to the bell adapter, which in turn means you can collect fluid directly into evacuated tubes/bottles.

TECHNIQUE

1. Recheck landmarks and mark the spot you plan to sample.
2. Prep skin with antiseptic of choice. Allow to dry.
3. Draw up lidocaine into 3 or 5cc syringe. Raise a wheal at your marked site.
4. Insert multiple sample luer adapter into Vacutainer bell adapter. Remove stylet from spinal needle.



5. Attach spinal needle to end of multiple sample luer adapter.
6. Insert red-top tube into Vacutainer.



7. Keeping tube applied to Vacutainer, insert spinal needle into infiltrated skin. The vacuum in the tube will draw fluid into the tube when you are in the right location. Once you have fluid entering the tube, stop advancing the spinal needle.
8. Obtain fluid into red-top (chemistries), lavender-top (cell count and differential), and culture bottles.
9. To collect fluid into blood gas syringe (for pH)^*, remove cap on syringe, remove Vacutainer with multiple sample luer adapter from spinal needle, attach blood gas syringe to spinal needle, obtain sample and replace cap on blood gas syringe. Or use alternate technique, below.
10. Dress injection site.

^*You can also order pH from your chemistries tube, but I was taught to collect it in a blood gas syringe and old habits die hard.

ALTERNATE TECHNIQUE

If you do not have a multiple sample luer adapter available, you may obtain fluid sample directly into 30cc syringes. You will need a blood transfer device (BD Item #364880) pictured with alternate technique supplies below:

1. Recheck landmarks and mark the spot you plan to sample.
2. Prep skin with antiseptic of choice. Allow to dry.
3. Draw up lidocaine into 3 or 5cc syringe. Raise a wheal at your marked site.
4. Remove stylet from spinal needle and insert into infiltrated skin.
5. When you are in the right spot, fluid will drip from the open end of the spinal needle. Attach a 30cc syringe.



6. Draw back on syringe until full, and repeat with a second 30cc syringe.
7. Remove cap from blood gas syringe, attach to spinal needle port, obtain sample, then replace cap.
8. Remove spinal needle and dress injection site.
9. Obtain a blood transfer device and attach one of the filled 30cc syringes.
10. Apply evacuated collection tubes and bottles into Vacutainer to fill.

Now your tubes and culture bottles are all ready to label and send to lab. I taught this technique to all my interns, so they never had any excuse to dodge a procedure in the middle of the night, so I think all interns should learn this method of quick, bedside diagnostic sampling.