H.13 SureTap: A medical device used to reduce blood contamination in lumbar puncture procedures

Background: A lumbar puncture (LP), or spinal tap, is a procedure to sample the cerebrospinal fluid (CSF)  that surrounds the brain and spinal cord.  It is a widely used procedure in both children and adults, most often for the evaluation of infection for cancer cells in the CSF. Normally, the CSF appears similar to water, and has a low cell count which is comprised predominantly of lymphocytes and macrophages.  If infection is suspected, the white cells are typically elevated, with a predominance of either neutrophils or lymphocytes depending on the type of infection.  If cancer cells are within the CSF, traditional chemotherapy may not penetrate the blood-brain barrier, and chemotherapy is given directly in the intrathecal space.

Sampling of the CSF is performed by inserting a needle through the lumbar vertebrae and into the intrathecal space (see diagram below).  A small amount of CSF is withdrawn in a sterile fashion, and sent to the laboratory for testing, including bacterial cultures, protein and glucose evaluation, cell count, and cytologic evaluation.  A small amount of the CSF is used to prepare a cytospin slide which is then stained and sent to a pathologist to review.  The pathologist then notes which cell types are present, including any abnormal cells, which guides therapy.

In many cases, the needle will penetrate an epidural vein prior to entering the intrathecal space, leading to blood contamination of the CSF.  This is called a traumatic tap, and presents many problems, as listed below:

1. It is difficult to distinguish if there is blood in the CSF from a true hemorrhage versus a traumatic tap.  In the laboratory, we can use a parameter called xanthochromia to see if there are red blood cell breakdown products in the CSF, which would suggest a true central nervous system (CNS) hemorrhage.  However, since it takes approximately 2 to 4 hours for xanthochromia to develop, if the bleed is very recent, it can be very difficult or impossible to distinguish the two.
2. Cells from the blood get mixed with cells from the CSF. It is essentially impossible to tell if the cells seen on the cytospin slide are coming from the blood, or if they were in the CSF to begin with.  This can make assessments of infection or the detection of cancer cells in the CSF much more difficult. There is a calculation to try to correct for CSF WBC counts which are falsely increased due to a traumatic tap, but this is still inferior to having no blood contamination at all.  
3. Most seriously, if the patient has recently been diagnosed with cancer cells in the blood, such as leukemia, a traumatic tap may introduce cancer cells into the CSF. This is especially problematic since in the sampling of the CSF to detect the presence of cancer cells, they can actually be seeded from the blood.  Patients may relapse with cancer in their CSF at a later date due to this procedure.

Figure 1: CSF is sampled from the lumbar spine with a needle inserted between the vertebrae.

Figure 2:  The CSF is collected and sent to the lab for cytologic evaluation.

Scope of the problem:

Review of the literature shows that traumatic LPs, with an RBC count of greater than 10 cells per microliter, represent approximately 29% of all pediatric LPs, and bloody LPs, defined as greater than 500 cells per microliter, were observed in 10% [1].  Taken together, almost 40% of samples showed blood contamination.  

The need:

A device is needed that can map subcutaneous blood vessels so that they can be avoided during the LP procedure.  This device would be small, lightweight, and can be placed noninvasively over the skin.  Using a combination of Doppler ultrasonography, oxygen detection, or UV light (or other means), the device will detect blood flow to the depth of the intrathecal space.  This would allow the clinician to avoid the vessels when introducing the needle.

Potential market:

Decreasing blood contamination in the CSF during the LP procedure would have widespread benefit, and the device can be marketed to hospitals and medical clinics worldwide.  According to the National Institute of health, approximately 92,533 LP procedures were done in 2018 among the Medicare population in the US alone.  This device can also be used when administering epidural anesthesia for deliveries.

Limitations:

Traumatic taps occur with more frequency in the setting of thrombocytopenia or a recent lumbar puncture procedure.  These variables cannot be controlled for.  In addition, if the needle is inserted too far, past the intrathecal space, blood contamination may result from laceration of the vertebral venous plexus as the needle hits the vertebral body.  In extreme cases, sampling of the bone marrow may be observed, and is most often seen in young infants where the thecal sac is very small. [1] This device cannot correct for over insertion of the needle. 

A product is currently on the market called Vein Finder, which presents a map of the vessels to facilitate blood draw.  The primary use of this device is to find vessels so they can be accessed.  It is unclear if this device has the sensitivity to be used on the back for the purpose to avoid the vessels to reduce blood contamination. 

References:

Figure 1: https://www.mayoclinic.org/tests-procedures/lumbar-puncture/about/pac-20394631

Figure 2: https://www.mountsinai.org/health-library/tests/csf-cell-count

1. Howard SC, Gajjar AJ, Cheng C, Kritchevsky SB, Somes GW, Harrison PL, Ribeiro RC, Rivera GK, Rubnitz JE, Sandlund JT, de Armendi AJ, Razzouk BI, Pui CH. Risk factors for traumatic and bloody lumbar puncture in children with acute lymphoblastic leukemia. JAMA. 2002 Oct 23-30;288(16):2001-7. doi: 10.1001/jama.288.16.2001. PMID: 12387652.