Associated with the contraindications for LP, are the complications of LP. The potential complications of this procedure are:

• Post LP headache
• Post LP back pain
• Seeding of infection to the CSF
• Epidermoid tumor implantation
• Uncal or transtentorial herniation and neurological deterioration
• Spinal hematoma

Post lumbar puncture headache is the most common complication of LP. The post LP headache develops in 5 – 40% of patients undergoing lumbar puncture. It is a headache that begins within 72 hours of LP and usually lasts less than 5 days. The headache is a bilateral pressure or throbbing that is intensified in the upright position and with coughing. The headache resolves when the patient is supine. The longer the patient is upright, the longer before it resolves when the patient is supine.

From a pathophysiological viewpoint, the post LP headache occurs because of the tear in the dura mater caused by the LP needle. This opening allows for the continued leakage of CSF out of the dura and this lower pressure allows the brain to shift downward. Traction on the pain sensitive bridging vessels, dura and nerves causes the headache. When supine, the pressure column of the CSF is equal and thus there is no pull on pressure sensitive structures of the brain and the headache resolves.

There are a number of ways to minimize post LP headaches in your patient. The first is to use the smallest size spinal needle possible. The smaller the needle, the smaller the tear in the dural fibres and the lower the incidence of post lumbar puncture headache. The incidence of post LP headache is about 70% with 16 – 19 gauge needles, 20 – 40% with 20 –22 gauge needles and 5 – 12% with 24 – 27 gauge needles. The LP kit carried in our hospital contains a 20 gauge needle. This module will teach you not only how to use the provided needle, but also how to utilize smaller spinal needles for LP.

Another factor that can be utilized to minimize the chance of post LP headache is the use of a stylet in the needle. This internal stylet prevents the needle from "coring" through the tissues while placing the LP needle. It is intuitive to use the stylet to prevent the needle from being blocked up with soft tissue while doing the LP. What is of interest, though, is that the replacement of the stylet into the needle prior to the needle's removal (at the end of the procedure) has been shown to reduce the incidence of post LP headache by 50%. It is theorized that during CSF collection, a strand of arachnoid fiber may enter the needle and when the needle is withdrawn the arachnoid strand is pulled out through the dural defect and produces a prolonged CSF leak. Replacement of the stylet prior to the LP needle's removal would prevent this.

Furthermore, the type of needle and the orientation of the needle's cutting edge also influence the incidence of post lumbar puncture headache. There are three main types of needles, pictured below. The Quincke needle was the first invented and has a beveled cutting tip. The Whitacre and Sprotte are "atraumatic" or pencil point needles and have blunt tips with lateral ports for CSF collection.

Figure 1. Spinal needle types

When using the Quincke needle, the orientation of the bevel influences the incidence of post lumbar puncture headache. Post LP headache is reduced by 50% or greater when the bevel is parallel to the dural fibres' long axis. To you and me this means that if the patient is lying in the lateral decubitus position, the flat portion of the bevel should point up towards the ceiling. An easy way to remember this is that when performing the LP in the lateral position, the bead on the plastic end of the stylet and therefore the notch that the stylet fits into should be pointing up at the ceiling.

Although the usual LP kit contains a Quincke needle, there is very good evidence that the atraumatic needles significantly reduce the incidence of post lumbar puncture headache. It is theorized that these needles spread the dural fibres and cut fewer fibres. This reduces the size of the hole in the dura and reduces the tendency to develop CSF leak. Numerous studies demonstrate post lumbar puncture headache rates of only 2-6% using atraumatic needles compared to rates of 18-40% using the same sized Quincke needles. Numerous direct comparisons have borne out the superiority of using atraumatic needles for reducing post LP headache.

There is considerable conflicting literature about a variety of other methods of reducing post lumbar puncture headache. Some recommend lying flat on one's back for 4 hours, some recommend lying prone and a few recommend activity right after lumbar puncture. To date, there are no post procedural interventions that seem to influence the incidence of post LP headache.

Therefore, in order to reduce post lumbar puncture headache, we recommend using small, atraumatic LP needles when doing lumbar puncture. In this module we will demonstrate the use of both types of needles, as some practitioners may not have access to small atraumatic spinal needles.

Also common after lumbar puncture is local back pain at the site of puncture. Approximately one third of patients will experience some local back discomfort after the procedure, which lasts for a couple of days. This is due to local soft tissue trauma. In rare cases, if the needle is inserted beyond the subarachnoid space, the annulus fibrosis may be damaged and the intervertebral disk can herniate. This is very rare, though.

Thankfully, other complications from lumbar puncture are much less common. The risk of introducing organisms into the CSF from a properly performed lumbar puncture is exceedingly small. This can occur with breaks in sterile technique, use of contaminated equipment and placement of the needle through infected skin. It is estimated that the incidence of such infection after lumbar puncture is about 0.2%.

Epidermoid tumor implantation is a theoretical concern that is very rare to see. The true incidence is unknown, but thought to occur when a plug of skin is carried into the spinal canal where it presents months to years later as an expanding epidermoid tumor. The use of a stylet with lumbar puncture has made this complication mostly one of historical significance.

Spinal subdural hematoma is also a rare complication reported in lumbar puncture. It is most common in those who undergo lumbar puncture while having coagulation abnormalities, including thrombocytopenia, anticoagulation and bleeding disorders. In spinal subdural hematomas, patients present with severe low back, radicular pain, sensory loss or paraparesis hours to days post LP. These symptoms in a post LP patient warrant aggressive investigation with CT/MRI and associated decompressive laminectomy if a hematoma is present. Epidural spinal hematomas may also present with the same clinical picture post LP and have the same risk factors and investigation as the spinal subdural hemorrhage.

As discussed previously, neurological deterioration due to herniation syndromes is the most dreaded complication of lumbar puncture. As previously noted, the risk of herniation is 0 –5 % in those patients who are known to have intracranial masses. The risk of herniation in the conscious, neurologically normal patient is exceedingly small. Its occurrence obviously warrants aggressive investigation and treatment.