Healthcare and Medicine Reference
In-Depth Information
Box 7.2 Symptoms and signs of increased ICP
Decreased consciousness
Focal neurology
pulse - late sign
Ligamentum flavum
Figure 7.2 Spinal needles.
in the shape of the tip of the needle and in the location of the
opening at the tip. The different designs have been produced
to try to reduce the incidence of postdural puncture headache
(see 'Complications'). The pencil point tips of the Whitacre and
Sprotte needles are designed to split apart the fi bres of the dura
on insertion, rather than cutting a hole in them. This allows
the fi bres to come together again on needle withdrawal, sealing
the hole and preventing further CSF leakage which can lead to
The narrower-gauge spinal needles have an introducer to pass
the needle through. This helps to prevent the needle bending too
much on insertion and not following the desired course.
Stylets are included to add stiffness to the needle for insertion
and block the opening at the needle tip so that it doesn't become
blocked with skin or subcutaneous tissue during insertion.
Spinal needle
Posterior longi-
tudinal ligament
Anterior longitudinal
Dura and arachnoid
Figure 7.1 Sagittal anatomy of lumbar spine.
L1 (L3 in children), and so insertion of the needle must be below
this level to avoid possible spinal cord injury.
The spinal cord is surrounded by the three meninges which
stretch from the foramen magnum to the sacral level (S2). The
dura mater forms a tough fi broelastic outer layer with the arach-
noid mater attached to it beneath. There is then a space, the
subarachnoid space, before the pia mater which is closely adher-
ent to the cord itself. The CSF is located within this subarachnoid
space. The pia mater extends caudally as the fi lum terminale and
anchors the spinal cord and dura to the coccyx.
In order to reach the subarachnoid space the lumbar puncture
needle needs to pass through skin, subcutaneous tissue, vertebral
ligaments, the dura and the arachnoid mater. The ligaments are
the supraspinous ligament running between the tips of the verte-
bral spines, the interspinous ligament stretching between adjacent
spines, and the ligamentum fl avum which forms a tough ligament
that connects adjacent laminae. The dura lies immediately deep
to the ligamentum fl avum, although there is a potential space
between these structures that can be expanded by injecting fl uid
or air. This is the epidural space and is where the catheter for an
epidural anaesthetic is inserted.
Patient positioning
Lumbar puncture can be performed with the patient sitting or lying
in a lateral position. The sitting position allows easier identifi ca-
tion of the midline (especially in obese patients where the vertebral
spines can be diffi cult or impossible to feel); however, the patient
may be too ill to sit up.
Both positions require the patient to fl ex their lumbar spine so
that the intervertebral spaces open up maximally to allow easier
needle passage. This is achieved by asking the patient to put their
chin on their chest, bring their knees as far up to their chest as they
can and push their lumbar spine backwards.
For the sitting position, ask the patient to sit on the bed with
their feet placed on a stool, adjusting the height of the bed or
stool until the patient's hips are adequately fl exed. Ask them
to lean forward over a pillow to produce arching of the back
(Figure 7.3).
For the lateral position, ask the patient to lie on their left side if
you are right-handed and vice versa, with their head supported on
a pillow so that their spine is in a horizontal line. Their back should
be along the edge of the bed and must be perpendicular to the bed
in the vertical plane. Then ask them to curl up as described above
(Figure 7.4).
Lumbar puncture requires specialised spinal needles (Figure 7.2)
which are long and relatively narrow gauge (18-29G). They differ
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