Lumbar Puncture - Further References and Resources
Our practice should be driven by evidence, and where that is limited, by a "safe consensus" or eminence. There have been, over the years, a number of landmark papers regarding the procedure of lumbar puncture. Anna Holdgate and Karyn Cuthbert's 2001 paper 'Perils and pitfalls of lumbar puncture in the emergency department' (Emerg Med 2001 Sep;13(3):351-8) represents a clear review of evidence as it stood at the time. Interestingly, a number of the practice points such as use of pencil point needles and keeping needle size to a minimum have been slow to enter practice across the board.
LP in SAH
Evidence supports the validity of a rule out for SAH if a CT is performed and read by a Radiologist within 6 hours of symptom onset.
Perry, JJ et al. (2011) Sensitivity of computed tomography performed within six hours of onset of headache for diagnosis of subarachnoid haemorrhage: prospective cohort study. BMJ, July 2011; vol 343. [PubMedCentral link]
Historically, LP was performed by removing and reinserting the stylet of the needle every time it is advanced, even past the interspinous ligament. An alternative to this practice is to remove the stylet once the needle is well into the interspinous ligament, and advance the open needle slowly while watching for flow of CSF. Which technique should we use? Here’s a quick look at some recommendations, and the evidence behind them.
- Royal Children's Hospital Melbourne - Lumbar Puncture Procedure - Clinical Guideline
- Advance the needle into the spinous ligament (increased resistance). Continue to advance the needle within the ligament until there is a fall in resistance. Remove the stylet. If CSF is not obtained replace the stylet and advance the needle slightly then recheck for CSF.
- An alternative technique is to remove the stylet once the needle is in the ligament and advance very slowly without the stylet watching for CSF to flow back. This has the advantage of making it harder to go unintentionally past the subarachnoid space.
- Johnson, KS et al. (2016) Lumbar puncture: Technique, indications, contraindications, and complications in adults, Uptodate, October 2016
- Many physicians choose to advance the needle incrementally, removing the stylet periodically to check for CSF flow, then reinserting the stylet until the subarachnoid space is entered. However, others report a higher rate of successful LP when the stylet is removed, just after the skin is punctured and before it is passed into the subarachnoid space in order to better observe the flow of CSF upon entry of the subarachnoid space.
- Baxter, AL et al. (2006) Local anesthetic and stylet styles: factors associated with resident lumbar puncture success, Pediatrics, March 2006, vol. 117 no. 3, pp. 876-881.
- For infants < or =12 weeks of age, early stylet removal improved success rates (OR: 2.4; 95% CI: 1.1-5.2).
So why do many doctors prefer the “closed needle” approach?
- A stylet provides a leading point to the needle, making it (theoretically) easier to advance.
- At the end of the procedure, removing the needle with stylet in situ may also reduce the incidence of post-lumbar-puncture headache.
- The major concern behind conventional teaching of LP technique, however, seems to be the (small but important) risk of transplanting ectopic tissue into the spinal canal. Three cases of LP-associated intraspinal epidermoid tumours were reported in JAMA in 1977, followed by a strong recommendation in Lancet that “Until … experiments can be repeated, and the modern needles prove to have a far lower incidence of coring, a stylet should always be used”.
The already small risk relates to the coring and implantation of skin tissue, which is the most difficult to pierce, and is theoretically less for more compliant deeper tissues. Both techniques begin with stylet in situ for the initial advancement of needle through skin, and this remains the safe recommendation. Some clinicians introduce the needle through the skin puncture used for infiltrating local anaesthetic, a practice which may further decrease the risk. Additionally, newer, pencil-point and smaller needles are theoretically less likely to punch a core of tissue into the spinal canal. As with patient positioning, the best technique is likely to be the one that patient, clinician, and institution are most familiar and comfortable with.