Today in #WCHAMreport we spoke about a patient who was referred for a pleural effusion.
Pleural effusions are dramatic clinical and radiographic diagnoses. Depending on the time course of presentation, patients may have significant cardio-respiratory compensation and may not even have resting or exertional hypoxia.
What is the differential diagnosis for a pleural effusion?
| Exudative | Transudative |
| Malignancy | Heart failure |
| ARDS | Atelectasis |
| Tuberculosis | CSF leak into pleural space |
| Pancreatitis | Hepatic hydrothorax |
| Eosinophilic granulomatosis with polyangiitis | Hypoalbuminemia |
| Granulomatosis with polyangiitis | Nephrotic syndrome |
| Lupus | Peritoneal dialysis |
| Lung abscess | Urinothorax |
| Chylothorax | |
| Sarcoidosis | |
| Hypothyroidism | |
Knowing the differential can help guide your history taking.
Does the patient have symptoms of malignancy or night sweats? Do they have up to date cancer screening? Has there been a recent infection? Do they have a history of heart failure or ischemic heart disease? Is there a history of connective tissues disease or rheumatologic conditions? Are there TB risk factors?
How do you determine between an exudative and a transudative effusion?
Calculation of Light’s criteria provides a systematic, validated approach to evaluating pleural fluid studies. To meet this criteria the fluid must meet at least 1/3 characteristics:
-
- Pleural fluid protein / Serum protein >0.5
- Pleural fluid LDH / Serum LDH >0.6
- Pleural fluid LDH > 2/3 * Serum LDH Upper Limit of Normal
This can save the clinician significant time and avoid unnecessary additional workup. Remember, however, that Light’s criteria is more sensitive than specific test for exudative effusions.
What should you order?
- Cell count
- Protein
- LDH
- pH
- Glucose
How does technique alter pleural fluid analysis?
A study looking at pleural fluid collection technique showed that pH is very challenging to measure accurately(1):
- air in the syringe increased pleural fluid pH by 0.08
- Residual lidocaine, even at minimal volume, decreased pH (e.g., 0.2 mL of lidocaine lowered pH by 0.15); at larger volumes, the decrease was greater.
- Retaining the heparin pre-loaded in the analysis syringe caused a decline of 0.02.
- No change from baseline pH value was seen when specimens were analyzed within 1 hour, but pH increased by 0.03 at 4 hours (P=0.07) and by 0.05 at 24 hours (P<0.001).
For pleural fluid glucose concentration, neither air nor a 4-hour delay in analysis had a significant effect; changes caused by lidocaine, heparin, and a 24-hour delay in analysis were statistically but not clinically significant.
What should you monitor for after the procedure?
In the era of ultrasound guided thoracentesis, routine chest x-rays are no longer required. However if there is a change of respiratory status, a complicated procedure
If you are looking for an interactive, step by step guide, several Toronto GIM staff and residents have created a great website to guide you through everything from the consent process to the clean up. I highly recommend checking it out before your next tap, we can all brush up on our skills:
http://www.gimprocedures.com/module/thoracentesis/#home
If you are at Women’s, please message me if you want help with any procedures and I will do my best to be available to you!
- Rahman NM et al. Clinically important factors influencing the diagnostic measurement of pleural fluid pH and glucose. Am J Respir Crit Care Med 2008 Sep 1; 178:483.