There are spinal nerves in the location sampled, but they have room to move away from the needle. There is the potential for the needle to contact a small vein on the way in. While this is not ideal, it may occur a certain percentage of the time. The evaluation of your results will take this into account. Blood from the collection procedure spinal tap may contaminate the first portion of CSF sample that is collected. However, there are usually three or more separate tubes used to collect CSF samples during one spinal tap procedure.
The last tube that is collected during a spinal tap is least likely to have blood cells present due to the procedure and is usually the sample used to test for the presence of blood cells in the CSF.
The flow is caused by the action of cilia extending from cells that line these spaces. These provide a beating motion that sweeps the fluid along. The rate of CSF production must be met by an equal rate of CSF reabsorption to prevent any build-up of fluid in the brain and spinal cord. The fluid is reabsorbed by arachnoid villi which return it to the venous blood before it leaves the head Blows, These values, and the concentration of potassium, calcium and bicarbonate in CSF, are lower than the equivalent values found in blood plasma.
CSF has a pH of about 7. The total volume of CSF is ml at any given time. This volume is replaced three to four times a day at roughly eight-hourly intervals. About ml of CSF is produced every day. Normal CSF pressure measured with a manometer is mm of water. These may occur when a space occupying lesion SOL develops. The differential in production and absorption of CSF, along with changes in blood flow through the brain, help to prevent any major increase in intracranial pressure as an SOL grows in size.
Such compensation can be effective only for a limited time, depending on the rate of growth of the SOL;. This is usually a safe procedure undertaken to acquire a sample of CSF for analysis, and is also sometimes done to measure CSF pressure or to introduce drugs into the CSF, a procedure known as intrathecal injection.
The insertion of a needle under local anaesthetic requires careful positioning to prevent injury to the spinal cord. Since the spinal cord ends as a solid structure around the level of the second lumbar vertebra L2 the insertion of a needle must be below this point, usually between L3 and L4 Fig 2.
The spinal cord continues below L2 down into the sacrum as many separate strands of nerve pathways, the cordae equina, bathed in CSF. Putting a needle into the spaces between the strands to collect fluid is much safer than taking the risk of hitting the solid cord higher up the spine. The spinal vertebrae are held together by ligaments. Those penetrated in a lumbar puncture are the interspinous ligaments which bind adjacent spinous processes together and the ligamentum flavum which binds adjacent vertebral laminae together and, in so doing, lines the posterior wall of the spinal canal.
Lumbar puncture must be carried out as a sterile procedure, with full aseptic precautions to prevent the introduction of outside organisms into the spinal canal and the contamination of the specimens collected. The patient must be either:. The latter position curves the spine anteriorly, providing the maximum room between the vertebral processes to allow the insertion of the needle. It may be necessary for the nurse to assist the patient into this position, and give them support to maintain it during the procedure.
Placing the patient towards the edge of the bed gives the doctor easy access. These packs contain sterile hand towels, gown, fenestrated drape, swabs, trays, spinal needle 25G Whitacre with introducer, syringes and needles.
These are used as standard for performing spinal anaesthesia but are suitable for diagnostic lumbar punctures as well. A wide range of spinal needles is available. They vary in length, diameter and tip design. The standard length is 90 mm and this is long enough for most patients. Morbidly obese patients may require a mm needle to access the subarachnoid space.
Spinal needles have clear hubs that allow CSF to be easily seen. Most will come with an inner obturator with or without a shorter introducer needle. There are two main types of needle tips: the cutting tip e.
Quincke and the pencil-point Sprotte or Whitacre Figure 1. We recommend the use of a narrow gauge pencil-point needle. It is associated with lower incidence of post-dural puncture headaches. A narrow gauge e. Cutting tip needles of wider gauge e. Figure 1. A Cutting tip needle Quincke. B Sprotte or Whitacre pencil-tip needle. C Ball-point tip. The types of collection bottles, number of samples, volume of CSF and the test required may depend on the suspected diagnosis.
Prior to setting up you should order your tests on ICE. Focal neurological deficit; Altered level of consciousness; a history of seizures new in the last week or Papillodema should undergo a CT scan first. All others should have LP as soon as possible. If in the first hour of presentation then delay antibiotics until after BUT do not delay treatment longer if not possible to perform then. On the right there is a heading for ID: Lumbar Puncture. Select all. You require drops in each bottle.
CSF glucose goes in a normal grey tube. You will also need to request a normal blood glucose sample. CSF glucose will be in a normal grey tube. All samples with a large B on the sticker go to micro and the others to biochemistry.
Xanthochromia MUST be protected from light- ask a porter to take this and place inside a normal brown envelope. Patient position is crucial to the success of the procedure and this should be explained to the patient.
The optimal position will flex the lumbar spine which opens up the spaces between the spinous processes and improves success rate. An assistant who can help with positioning, with reassuring the patient, and with help with equipment is invaluable.
The sitting position is useful for identifying the anatomical landmarks in the technically challenging patient.
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