Perform an LP and analyze the results to dx bacterial meningitis

No Comments
Test Your Knowledge Which of the following maneuvers decreases post-LP headaches?
A. Bedrest
B. Reduced number of attempts
C. Smaller gauge atraumatic needles
D. IV fluids
E. Patient positioning
F. Clinician experience
G. All of the above

The Setup:
You are working a busy evening shift with a bright-eyed fourth-year medical student who presents you with a case of suspected meningitis.  He is excited because he feels competent to perform this invasive procedure. After explaining the risks and potential yield of the procedure, the student turns to you to see if you have any tips on reducing the risk of PDPH as well as what lab analysis should be ordered on the CSF.

You have a choice. You can inform your eager student that tonight heíll have the pleasure of watching your experienced hands perform your 2013th LP. You can consult your friendly neighborhood interventional radiologist to perform the LP since you are too busy to assist the inexperienced student with procedures. Or, at the expense of patient thoroughfare, you can grit your teeth and oblige your young apprentice with a detailed description of the methods, equipment, and common pitfalls for obtaining CSF in suspected CNS infections. Assuming, that is, that you know the most recent data.

The Evidence:

Straus SE, Thorpe KE, Holyroyd-Ledue J.  How Do I Perform a Lumbar Puncture and Analyze the Results to Diagnose Bacterial Meningitis? JAMA. 2006;296: 2012-2022.2

The Big Idea
Roughly 20% of patients who receive lumbar punctures experience postdural puncture headaches (PDPH, also commonly called a ìspinal headacheî). These can be quite debilitating, sometimes even requiring hospitalization. The use of small gauge atraumatic needles and reinsertion of the stylet before needle removal reduces the risk of PDPH while immobilization does not. In addition to typical serologies, cerebrospinal fluid (CSF) gram stain and culture, the following CSF markers can aid significantly in the diagnosis of bacterial meningitis in adults: CSF blood glucose ratio ≤ 0.4, CSF WBC count ≥ 500/µL, and a CSF lactate ≥ 31.53 mg/dL.1

The Data
The data at hand comes from the rational clinical exam series in JAMA. The authors used fairly rigorous criteria to generate their summative conclusions. To answer the two central questions, they selected only randomized controlled trials with predominately adult patients (age > 18). In terms of minimizing the risk of PDPH, five trials with 587 patients met inclusion criteria looking at needle design and replacement of the stylet before needle removal.  Pertinent findings were as follows:

Reinsertion of the stylet before needle removal was associated with a statistically significant decrease in the rate of headache (NNT = 9) 

 A non-significant difference in the occurrence of PDPH was found when an ëatraumaticí needle was used versus a standard cutting one (NNT = 8).  Atraumatic needles are commonly used by anesthesiologists.  They are designed with a pencil tipped end as compared to the sharp beveled end of a cutting needle (this is the typical needle provided in an ED LP tray).  It should be noted that these findings may be limited by sample size and the exclusion of large anesthesia trials that show a significant reduction in risk when atraumatic needles are used.3-5

Interestingly, several factors often touted to impact the development of PDPH were not found to be statistically significant:
Number of LP attempts
Administration of oral or intravenous
Patient positioning
Clinician experience

Four studies met inclusion criteria for the predictive ability of CSF markers for the diagnosis of bacterial meningitis. Three biochemical markers were shown to have statistically significant predictive value (see table 1).

Table 1: Biochemical Markers with statistically significant predictive values

CSF-blood glucose ratio less than or equal to 0.4 (LR+=18; 95% CI: 12 to 27;
LR-=0.31; 95% CI: 0.21 to 0.45)

CSF white blood cell count (WBC) equal to or greater than 500/µL
(LR+=15, 95% CI: 10 to 22; LR-=0.30; 95% CI: 0.20 to 0.40.)

CSF lactate greater than or equal to 31.53 mg/dL (≥ 3.5 mmol/L; LR+=21; 95%
CI: 14 to 32; LR-=0.12; 95% CI: 0.07 to 0.23).

The Caveats
So why are cutting needles (Quincke) the standard for ED LP trays?  It could be that these needles are fractionally more expensive.  It is more likely that cutting needles are used because they always have been.  For more information on atraumatic needles in prepackaged LP kits, you can explore the following websites:

The Outcome
After reviewing the evidence, you find solace in the fact the clinical experience will probably not affect the development of procedural complications and champion the studentís fervor to practice ìreal emergency medicineî.  The key teaching points should reinforce the use of a small gauge spinal needle (preferably 22 gauge but no larger than 20 gauge) that is designed to be atraumatic (e.g. Sprotte or Whitacre needles).  He should also be cautioned to replace the stylet before needle removal.  In terms of CSF serologies, the standard lab set of cell count, gram stain, culture, protein, and glucose should be augmented with lactate (if available and cost effective in your ED).

Rawle A Seupaul,  MD, is an associate professor of emergency medicine at the Indiana University School of Medicine

1. Seupaul RA. Evidence-based emergency medicine/rational clinical examination abstract. How do I perform a lumbar puncture and analyze the results to diagnose bacterial meningitis? Ann Emerg Med. Jul 2007;50(1):85-87.

2. Straus SE, Thorpe KE, Holroyd-Leduc J, et al. How do I perform a lumbar puncture and analyze the results to diagnose bacterial meningitis?[see comment]. JAMA. Oct 25 2006;296(16):2012-2022.

3. Buettner J, Wresch KP, Klose R, et al. Postdural puncture headache: comparison of 25-gauge Whitacre and Quincke needles. Regional Anesthesia. May-Jun 1993;18(3):166-169.

4. Halpern S, Preston R, Halpern S, et al. Postdural puncture headache and spinal needle design. Metaanalyses. Anesthesiology. Dec 1994;81(6):1376-1383.

5. Tourtellotte WW, Henderson WG, Tucker RP, et al. A randomized, double-blind clinical trial comparing the 22 versus 26 gauge needle in the production of the post-lumbar puncture syndrome in normal individuals. Headache. Jul 1972;12(2):73-78.

Leave A Reply