INTRODUCTION: It is an important element to have a detailed view of the procedure known as Lumbar puncture which is also known as the Spinal Tap.
It is mostly used as a diagnostic procedure by which a sample of CSF can be obtained, (which is known as the Cerebrospinal Fluid, the fluid found in the brain and spinal cord.) which is used for bacterial or microscopic examination in the case of meningitis, as well as providing a way for injecting drugs like in the case of chemotherapy. Anesthetic drugs and antibiotics are also injected into the Cerebrospinal fluid via the Spinal tap. This procedure also provides a means of measuring the pressure in the Cerebrospinal fluid with the help of a manometer.
Cerebrospinal Fluid is a clear colorless fluid produced by the choroid plexus and assisted by the ependymal cells. It contains inorganic salts like chloride, glucose few lymphocyte cells and trace amounts of protein. The pressure range of cerebrospinal fluid measured by the manometer is said to be about 60 – 150mm water and the rate of the production of cerebrospinal fluid is 0.5ml/min. (Snells Neuroanatomy)
The basic function of cerebrospinal fluid is to cushion or protect the brain from any mechanical trauma. It also provides buoyancy to the brain due to the increased density of the cerebrospinal fluid. The fluid also acts as a source of nourishment for the underlying nervous tissue and also acts as a pathway for the pineal secretions from the pituitary gland.
Method: The patient, on whom the lumbar puncture is to be performed should lie in a lateral Recumbent position i.e. on the side or even in a prone or sitting position depending on the preference of the health caregiver or a clinician. The vertebral column should be well flexed and the lamina in the lumbar region should be opened to the maximum.
There is an imaginary line which is obtained by joining the highest points on the iliac crests and when joined passes over the fourth lumbar vertebrae. From L3 to the lower border of the S2 vertebrae the subarachnoid space filled with cerebrospinal fluid is accessible and safe to penetrate as the spinal cord in an adult already terminates at the level of L1 and L2 vertebrae, thus making the lumbar region an ideal site to perform the Spinal tap.
The physician then uses a careful aseptic technique and the patient is provided with local anesthesia. The lumbar puncture needle that is the Quincke spinal needles 22G which may be of size 1.5 for infants and newborn, 2.5 for children and 3.5 for adults, fitted with a stylet is passed through anatomical structures like the skin, superficial fascia, Supraspinous ligament, Interspinous ligament, Ligamentum flavum, areolar tissue (which contains the internal vertebral venous plexus), Dura mater and the Arachnoid mater, ending in the subarachnoid space which contains the cerebrospinal fluid. It is from here that we are able to aspirate a sample of cerebrospinal fluid. The needle will pass through these structures to a depth of 1inch (2.5cm) in a normal adult and less in a child, however, in the case of an obese patient a depth of 4 inches is required.
When the stylet is withdrawn and if few drops of blood are seen, it is then due to the fact that the needle has only entered the internal vertebral plexus and might still be in the areolar tissue. The patient would experience a fleeting discomfort in a muscle or a dermatome if the nerve roots of the cauda equina were stimulated. If the needle is in the lumbar cistern and the stylet is withdrawn the cerebrospinal fluid would start flowing and escapes at a rate of approximately one drop per second. The cerebrospinal fluid’s normal pressure is about to 60 -150mm of water and if the subarachnoid pressure is high then the fluid would escape out as a jet.
Anesthetic drugs are also given in the extradural space and in the subarachnoid space in order to anesthetize the nerve roots of the lumbar and sacral area, which is helpful in operations of the pelvic and the leg. The patient is advised to be in an erect position during these surgeries as if the patient is in a recumbent position then the anesthesia would be only effective unilaterally and if the patient is in a head-down position the anesthetic could pass cranially and affect respiration.
Some of the complications include Post-dural puncture headache, infection, cerebral herniation, bleeding and back pain. It is contraindicated when there is an increased intracranial pressure, thrombocytopenia or any brain abscess.
Types of equipment used:
1% lidocaine solution
22G or 25G needle
5ml disposable syringe
Spinal needle with stylet
Manometer with 3 way stopcock
A labeled sterile specimen container