2. Paravertebral Space Flashcards
Intro + use
Thoracic paravertebral blocks can provide ipsilateral analgesia via a technique that is
simpler (and probably safer) than a thoracic epidural. First described as long ago as
1905, they have made a resurgence, particularly for procedures such as day case breast
surgery. Lumbar paravertebral blocks are less useful and largely have been replaced by
transversus abdominis plane (TAP) and rectus sheath blocks.
Where is it + shape
By definition there are bilateral paravertebral spaces associated with all the vertebrae;
the thoracic paravertebral space extends from the level of T1 down to T12.
The area is triangular (wedge shaped) in all directions.
Boundary
The medial wall is formed by the vertebral bodies, intervertebral discs and intervertebral
foraminae.
The anterolateral boundary consists of the parietal pleura and the innermost
intercostal membrane.
The posterior boundary consists of the transverse processes of the thoracic vertebrae,
the heads of the thoracic ribs and the superior costotransverse ligament.
Division
Contents
An endothoracic fascial layer divides the space into ventral (anterior) and dorsal
(posterior) compartments. This has relevance for the spread of local anaesthetic
within the space.
It contains spinal nerves, as the target for local anaesthetic injection; white and grey
rami communicantes; the sympathetic chain; intercostal vessels; lymphatics; and fat.
It is continuous with a number of areas: the contralateral paravertebral space via the
prevertebral fascia, the epidural space immediately medially, and the intercostal
space laterally.
Use
The extent of the thoracic paravertebral space (both thoracic and lumbar) means that
unilateral paravertebral block is a versatile analgesic technique that can be used for
surgery as diverse as mastectomy and iliac crest bone harvesting
Indications:
Indications: paravertebral block can be used to provide analgesia for
unilateral surgical operations in the thoracic and upper abdominal region
. These include
breast,
renal and
thoracic operations.
It can also be used for open cholecystectomy.
The block can be used to treat the acute pain of fractured ribs,
and may also have a place in the
management of chronic pain conditions
such as neuropathic pain and the
complex regional pain syndrome.
Contraindications:
Contraindications: absolute contraindications are typically generic and include
patient refusal and local sepsis.
Rarely the presence of a tumour in the paravertebral
space at the level of injection would also preclude the procedure.
Specific relative contraindications to thoracic paravertebral block include respiratory disease involving the diaphragm as a result of which the patient relies on intercostal function.
Coagulopathies, either innate or acquired, are relative contraindications which
require a risk-benefit assessment. However, unlike a haematoma in the epidural
space, a bleed into the paravertebral space is highly unlikely to lead to spinal cord
compression or damage to the spinal nerves themselves.
Technique of thoracic paravertebral block
spread
ventral/anterior compartment is associated with longitudinal spread along
several segments, whereas injection into the dorsal/posterior compartment results in
much more localized and limited distribution around the level of injection. If
injections are made at multiple levels, however, which probably is the more common
technique, the needle placement need not be quite as focused.
Depth
Depth: the median distance from skin to the thoracic paravertebral space is said to be
5.5 cm, but body habitus, predictably, has an influence on this depth, which can be
measured using ultrasound.
The space is also shallower in the mid-thoracic region.
The key to the efficacy and safety of this block is to limit the advance of the needle to
no more than 1.0 cm beyond the superior costotransverse ligament,
having walked off the transverse process.
USG technique
The ultrasound probe is placed transversely (axially), just lateral to the midline, aiming to identify the rib. The probe is then manoeuvred caudally to visualise the intercostal space.
The pleura should be seen along with the internal intercostal membrane which is continuous with the SCTL.
The needle is advanced in a lateral to medial direction towards the TP until it breaches the internal intercostal membrane.
Local anaesthetic is injected after negative aspiration, and the pleura should again be visualised moving downwards.
Levels required for common procedures
Levels required for common surgical procedures: these should be predictable from
knowledge of the sensory dermatomes. For example, simple mastectomy, T3–T4;
mastectomy with axillary clearance, T1–T6.
Continuous analgesia
Continuous analgesia can be provided by the insertion of a paravertebral catheter.
This should be inserted no deeper than 2.0 cm into the space so as to avoid the risk of
catheterizing the epidural space. In adults, a starting infusion rate of 0.1 ml kg hr–1
would be appropriate.
Complications:
Complications: in addition to generic complications such as vascular puncture
and neurapraxia, the complications specific to paravertebral block include
pneumothorax (which initially may go unnoticed because injected local anaesthetic
will lead to effective intrapleural analgesia), epidural anaesthesia due to
medial passage of injectate through the intervertebral foramen, and inadvertent
puncture of the dural cuff with intrathecal spread. Paravertebral injections block
sensory, motor and autonomic nerves, and so hypotension may also complicate
an effective block.
Comparison with Thoracic Epidural Analgesia
Performing an epidural in the upper thoracic region is a considerably more difficult
technique than paravertebral blockade.
A thoracic epidural cannot reliably provide unilateral analgesia. The catheter may
migrate laterally through the intervertebral foramina and into the paravertebral
space, at which point of course it become an inadvertent paravertebral block.
Otherwise the analgesia provided by the two techniques is comparable.
This analgesia comes at the expense of predictable consequences of a high bilateral
block together with the generic complications of epidural insertion. These are inadvertent
dural puncture and subsequent post-dural puncture headache, but with the
additional risk of spinal cord damage, failure, unilateral or patchy block, inadvertent
subdural block, intravascular injection, epidural haematoma or abscess. The risk of
permanent neurological sequelae is small, but in the NAP 3 report on complications
of neuraxial blockade, the greatest number of identified problems were associated
with peri-operative epidurals. There were 14 epidural abscesses reported, for
example, 10 of which were thoracic (Third National Audit Project [NAP3]. National
Audit of Major Complications of Central Neuraxial Blockade in the United
Kingdom. Royal College of Anaesthetists. 2009).
