++
Thoracic paravertebral block (TPVB) is the technique of injecting local
anesthetic alongside the thoracic vertebra close to where the spinal nerves
emerge from the intervertebral foramen.1,2 This produces
unilateral, segmental, somatic, and sympathetic nerve
blockade,3 which is effective for anesthesia and in
treating acute and chronic pain of unilateral origin from the chest and
abdomen.1 Hugo Sellheim of Leipzig (1871–1936) is
believed to have pioneered TPVB in 1905.1,2 Kappis, in
1919, developed the technique of paravertebral injection, which is
comparable to the one in present-day use. Although paravertebral block was
fairly popular in the early 1900s, it seemed to have fallen into disfavor
during the mid and later part of the century, the reason for which is not
known. In 1979 Eason and Wyatt rekindled interest by describing a technique
of paravertebral catheter placement.4 Our understanding of
the safety and efficacy of TPVB has improved significantly in the last 25
years, and there has been a gradual renewal of interest in this technique.
Currently it is used not only for analgesia but also for surgical
anesthesia,5–7 and its application has been extended to
children.8–10
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The thoracic paravertebral space (TPVS) is a wedge-shaped space located
on either side of the vertebral column (Figure 43–1). The parietal
pleura forms the anterolateral boundary. The base is formed by the vertebral
body, intervertebral disc, and the intervertebral foramen with its contents.
The transverse process and the superior costotransverse ligament form the
posterior boundary. Lying in between the parietal pleura anteriorly and the
superior costotransverse ligament posteriorly is a fibroelastic structure,
the endothoracic fascia, which is the deep fascia
of the thorax (Figure 43–1, 43–2, and 43–3).1,11–15
Medially the endothoracic fascia is attached to the periosteum
of the vertebral body. A layer of loose areolar connective tissue, the
subserous fascia, lies between the parietal pleura and
the endothoracic fascia. Therefore there are two potential fascial
compartments in the TPVS: the anterior extrapleural
paravertebral compartment and the posterior
subendothoracic paravertebral compartment (see Figures
43–1 and 43–2). The TPVS contains adipose tissue within which lie the
intercostal (spinal) nerve, the dorsal ramus, intercostal vessels, rami
communicantes, and anteriorly the sympathetic chain. The spinal nerves are
segmented into small bundles and lie freely in the adipose tissue of the
TPVS, which make them accessible to local anesthetic solutions injected into
the TPVS.16
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The TPVS communicates with the epidural space
medially17,18 and with the intercostal space laterally.
The TPVS on either side of the thoracic vertebra also communicate with each
other through the epidural and prevertebral space.1,12,15
The cranial extension of the TPVS is challenging to define and may
significantly vary; however, we have observed direct paravertebral spread of
radiopaque contrast medium from the thoracic to the cervical paravertebral
space, indicating a direct anatomic continuity. The TPVS also communicates
caudally through the medial and lateral arcuate ligaments with the
retroperitoneal space behind the fascia transversalis, where the lumbar
spinal nerves are located.13,19–21
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Mechanism of Block & Distribution of Anesthesia
++
TPVB produces ipsilateral somatic and sympathetic nerve blockade
(Figure 43–4) due to a direct effect of the local anesthetic on
the somatic and sympathetic nerves in the TPVS, extension into the
intercostal space laterally, and the epidural space medially. The overall
contribution of epidural spread to the dermatomal distribution of anesthesia
following a TPVB is not well defined. However, some degree of ipsilateral
spread of local anesthetic toward the epidural space probably occurs in the
majority of patients, resulting in a greater distribution of anesthesia
than occurs with paravertebral spread alone.18 The
dermatomal distribution of anesthesia following a single injection of a
large volume (eg, injection of 15–25 mL of local anesthetic at one level)
varies and is often unpredictable.1,3,22 However, the
injected solutions routinely spread both cephalad and caudad to the site of
injection to some extent (Figure 43–5). Nevertheless, the
multiple-injection technique, where small volumes (3–4 mL) of local
anesthetic are injected at several contiguous thoracic levels, is preferable
over single, large-volume injection. This is particularly important when
reliable anesthesia over several ipsilateral thoracic dermatomes is desired,
such as when TPVB is used for anesthesia during breast surgery.
++
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++
Segmental contralateral anesthesia, adjacent to the site of injection,
occurs in approximately 10% of patients after single-injection TPVB and
may be due to epidural or prevertebral spread. Bilateral symmetrical
anesthesia due to extensive epidural spread or unintentional intrathecal
injection into a dural sleeve may occur, particularly when the needle is
directed medially or when a larger volume of local anesthetic (>25
mL) is used. For this reason, during placement of TPVB, patients should be
monitored using the same vigilance and methods as those employed for
injection using the large-volume, single-injection epidural technique. The
ipsilateral ilioinguinal and iliohypogastric nerves may also occasionally be
involved after lower thoracic paravertebral injections. This is either due
to epidural spread or extended subendothoracic fascial spread to the
retroperitoneal space where the lumbar spinal nerves are located. The effect
of gravity on the dermatomal spread of anesthesia after TPVB is unknown, but
there may be a tendency for preferential pooling of injected solution toward
the dependent levels.3,23,24
++
It is preferable to perform TPVB with the patient in the sitting
position because the surface anatomy is better visualized and patients are
often more comfortable. However, when this is not possible or practical,
TPVB can also be performed with the patient in the sitting, lateral, or
prone position. The number and level of injections are selected according to
the desired spread of local anesthesia. In this example, description of the
TPVB for breast surgery is described. Surface landmarks are identified and
marked with a skin marker before block placement (Figure 43–6).
Skin markings are also made 2.5 cm lateral to the midline at the thoracic
levels that are to be blocked. These markings indicate the needle insertion
sites and should lie over the transverse process of the vertebra
(Figure 43–7).
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A standard regional anesthesia tray is prepared, and strict asepsis
should be maintained during block placement. A 22-gauge Tuohy- or
Quincke-tip spinal needle is used for a single- or multiple-injection TPVB
(Figure 43–8). If the needle does not have depth markings on its
shaft, a depth guard (see Figure 43–8) is recommended. An epidural set is
used if insertion of a catheter into the TPVS is planned. Multiple
injections during TPVB are uncomfortable and require a proper premedication
(eg, midazolam 2–3 mg plus fentanyl 50–100 mcg) to ensure patient acceptance
and comfort during the block placement.
++
+++
Loss‐of-Resistance Technique
++
There are several different techniques of TPVB. The classical technique
involves eliciting loss of resistance. The skin
and underlying tissue is infiltrated with lidocaine 1%, and the block
needle is inserted perpendicular to the skin in all planes to contact the
transverse process of the vertebra. Note that due to the acute angulation of
the thoracic spines in the midthoracic region, the transverse process that
is contacted is the one from the lower vertebra (Figures 43–9 and 43–10). The depth at which the transverse process is contacted
varies (3–4 cm) and depends on the build of the individual and the level at
which the needle is inserted. The depth is deeper at the cervical and lumbar
spine level and shallower at the thoracic levels. During needle insertion it
is possible to miss the transverse process and inadvertently puncture the
pleura. Therefore it is imperative to search and make contact with the
transverse process before advancing the needle too deep and risking pleural
puncture. To minimize this complication, the block needle should initially
be inserted only to a maximum depth of 4 cm at the thoracic and 5 cm at the cervical
and lumbar levels. If bone is not contacted it should be assumed that the
needle is in between two adjacent transverse processes. The needle should be
withdrawn to the subcutaneous tissue and reinserted with a cephalad or
caudad direction to the same depth (4 cm) until bone is contacted. If bone
is still not encountered, the needle is advanced a further centimeter and
the above procedure repeated until the transverse process is identified. The
needle is then walked above (these authors' preference) or below the
transverse process and gradually advanced until a loss of resistance is
elicited as the needle traverses the superior costotransverse ligament into
the TPVS (Figures 43–3 and 43–11). This usually occurs within 1
to 1.5 cm from the superior edge of the transverse process (see Figure
43–3). Although a subtle “pop” or “give” may be appreciated as the
needle traverses the superior costotransverse ligament, this should not be
entirely relied on. Instead, the depth of the needle placement should be
guided by the initial bone contact (skin-transverse process plus 1 to 1.5 cm).
Unlike localization of the epidural space, in which the loss of resistance
is typically unequivocal, loss of resistance elicited during TPVB is very
subtle and takes time to appreciate and master. The use of a glass syringe
may facilitate recognition of the loss of resistance when this method is
used.
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Predetermined Distance Technique
++
TPVB can also be performed by advancing the needle by a fixed
predetermined distance (1 cm) once the needle is
walked off the transverse process, without eliciting loss of resistance
(Figure 43–12).5–7,23 Proponents of this
technique have used it very successfully with low risk of pneumothorax. The
use of a depth marker is recommended to avoid
inadvertent pleural or pulmonary puncture.
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Placement of Thoracic Paravertebral Catheter
++
If a continuous TPVB (CTPVB) is planned, a catheter is inserted through
a Tuohy needle into the TPVS.4,22 Unlike epidural
catheterization, certain resistance is commonly encountered during insertion
of the paravertebral catheter. This can be overcome by manipulating
(rotating or angling) the needle or injecting 5–10 mL of saline to create a
space before catheter insertion. An unusually seamless passage of catheter
should arouse the suspicion of interpleural placement.
++
Perhaps the safest and simplest method of placing a catheter into the
TPVS is to place it under direct vision from within the open chest
cavity.8,25 Obviously, this requires an open thorax and is
therefore done exclusively in patients undergoing a thoracotomy. This
technique involves reflecting the parietal pleura from the posterior wound
margin onto the vertebral bodies over several thoracic segments, thereby
creating an extrapleural paravertebral pocket (Figure 43–13) into
which a percutaneously inserted catheter is placed against the angles of the
exposed ribs. The pleura is reapposed to the chest wall, and the thorax is
closed. This method can be combined very effectively with a preincisional,
single-shot, percutaneous thoracic paravertebral injection to provide
perioperative analgesia during thoracic surgery.26
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TPVB is indicated for anesthesia and analgesia for unilateral surgical
procedures in the chest and abdomen. Commonly reported indications are
listed in Table 43–1. The use of bilateral TPVB has also been
reported.
++
++
There are very few absolute contraindications for TPVB. These include
infection at the site of injection, allergy to local anesthetic drug,
empyema, and a neoplastic mass occupying the paravertebral space.
Coagulopathy, bleeding disorders, or patients receiving anticoagulant drugs
are relative contraindications for TPVB. One must exercise caution in
patients with kyphoscoliosis or deformed spines and those who have had
previous thoracic surgery. The chest deformity in the former may predispose
to inadvertent thecal or pleural puncture, and the altered paravertebral
anatomy due to fibrotic obliteration of the paravertebral space or adhesions
of the lung to the chest wall in the latter may predispose to pulmonary
puncture.
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Choice of Local Anesthetic
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Since TPVB does not result in motor weakness of the extremities,
long-lasting analgesia is nearly always desirable with TPVB. Consequently,
long-acting local anesthetic drugs are typically used. These include
bupivacaine or levobupivacaine 0.5% and ropivacaine 0.5–0.75%. For
single-injection TPVB, 20–25 mL of local anesthetic is injected in
aliquots, whereas for multiple-injection TPVB, 4–5 mL of local anesthetic
is injected at each level planned. Higher concentrations of local anesthetic
(eg, ropivacaine 0.75%) may reduce the onset time and prolong the
duration of anesthesia and analgesia. The maximum dose of local anesthetic
must be adjusted in the elderly, poorly nourished, and frail patients. The
TPVS is well vascularized, leading to relatively rapid absorption of local
anesthetic into the systemic circulation. Consequently, peak plasma
concentration of the local anesthetic agent is attained quickly. Epinephrine
(2.5–5 mcg/mL) containing local anesthetic solutions may be used during the
initial injection because it reduces systemic absorption and thereby reduces
the potential for toxicity. Epinephrine also helps in increasing the maximum
allowable dose of local anesthetic. The duration of anesthesia after TPVB
ranges from 3 to 4 h, but analgesia often lasts much longer (8–18 h). If
CTPVB is planned, eg, for postoperative analgesia after
thoracotomy or continuous pain relief for multiple fractured ribs, then an
infusion of bupivacaine or levobupivacaine 0.25% or ropivacaine 0.2%
at 0.1 to 0.2 mL/kg/h is started after the initial bolus injection and
continued for 3 to 4 days or as indicated. It is our experience that using a
higher concentration of local anesthetic (eg, bupivacaine 0.5% instead of
0.25%) for the CTPVB does not result in better quality of analgesia, and
it may increase the potential for local anesthetic toxicity.
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Practical Management of Thoracic Paravertebral Block
++
Thoracic paravertebral injection of local anesthetic at multiple levels
(C7 through T6) in conjunction with intravenous sedation is effective for
surgical anesthesia during major breast surgery (Figure
43–14).5,6,27 The C7 spinous process is the most
prominent cervical spinous process; the inferior border of the scapula
corresponds to T7. Compared with patients who receive only general
anesthesia (GA), patients who receive a multiple-injection TPVB for major
breast surgery have less postoperative pain, require fewer analgesics, and
have less nausea and vomiting after surgery. However, to effectively use the
multiple-injection TPVB technique for anesthesia during breast surgery, one
must understand the complex innervation of the breast. The anterior and
lateral chest wall receives sensory innervation from the anterior and
lateral cutaneous branches of the intercostal nerves (T2 through T6), the
axilla (T1 to T2), the infraclavicular region from the supraclavicular
nerves (C4 to C5), and the pectoral muscles from the lateral (C5 to C6) and
medial (C7 to C8) pectoral nerves. There also may be overlapping sensory
innervation from the contralateral side of the chest. This complex
innervation of the breast from the C4 to T6 spinal segments explains why
TPVB may not provide complete anesthesia for dissection over the pectoral
muscle or the infraclavicular region. However, this can be overcome with
proper sedation during surgery as well as by injections of local anesthetic
by the surgeon intraoperatively into the sensitive areas. Injection of a
local anesthetic subcutaneously along the inferior border of the clavicle or
to perform an ipsilateral superficial cervical plexus block, in order to
anaesthetize the supraclavicular nerves (C4 to C5) will minimize discomfort
and sedative and analgesic requirements during surgery. A combination of
midazolam, or propofol infusion, or IV opioid can be used to provide comfort
to the patients intraoperatively. Dexmedetomidine, a highly selective
α2-adrenoceptor agonist, with its sedative,
analgesic, and minimal or no respiratory depression properties is a useful
alternative for sedation during breast surgery under TPVB.
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When combined with general anesthesia, a single-injection TPVB with
ropivacaine (2 mg/kg diluted to 20 mL with 0.9% saline) with 1:200,000
epinephrine, performed prior to the induction of GA can be used. This
provides excellent postoperative analgesia, reduces postoperative analgesic
requirement, reduces postoperative vomiting, facilitates the earlier
resumption of oral fluid intake, reduces the postoperative decline in
respiratory function, and augments the recovery of postoperative respiratory
mechanics.
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Postthoracotomy Pain Relief
++
CTPVB is an effective method of providing analgesia after thoracotomy
(Figure 43–15). Ideally, TPVB should be established before the
thoracotomy incision, via a catheter that is inserted percutaneously, and
continued for 4 to 5 days after surgery. However, if an extrapleural
paravertebral catheter is being placed under direct vision from within the
chest during surgery, then a single-injection TPVB can be performed at the
level of the thoracotomy incision before the surgical incision, and a
continuous infusion of local anesthetic is commenced after the catheter
placement. Either method provides effective perioperative analgesia.
++
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It is important to note that CTPVB is inadequate on its own for complete
pain relief after a thoracotomy and must be combined with an opioid [best as
intravenous patient-controlled analgesia (IVPCA)] and a NSAID to provide
optimal analgesia.26 Analgesia achieved by CTPVB is
comparable to epidural analgesia but with less hypotension, urinary
retention, and the side effects commonly seen with epidural opioid
administration.1,26,28,29 The opioid requirement with such
an approach is significantly reduced by the CTPVB, and analgesia is superior
to IVPCA alone.1,30
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Multiple Fractured Ribs
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TPVB is an effective method of providing pain relief in patients with
unilateral multiple fractured ribs.1,22,23 A single
thoracic paravertebral injection of 25 (SD 5) mL of bupivacaine 0.5%
produces pain relief for a mean duration of 9.9 (SD 1.2) h and improves
respiratory function and arterial blood gases.1,23 To
avoid recurrence of pain and deterioration in respiratory function, a
thoracic paravertebral catheter can be inserted midway between the highest
and the lowest fractured rib, and a CTPVB can be commenced after
administration of the initial bolus injection. CTPVB in combination with a
NSAID provides continuous pain relief and produces a sustained improvement
in respiratory parameters and arterial oxygenation.22
Since TPVB does not cause urinary retention or affect lower limb motor
function, it is useful in patients with multiple fractured ribs who also
have concomitant lumbar spinal trauma since it also allows continuous
neurologic assessment for signs of spinal cord
compression.31
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Pharmacokinetic Considerations
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Relatively large doses of local anesthetics are commonly used during
CTPVB. Therefore there is the potential for local anesthetic toxicity, and
patients should be closely monitored during CTPVB and the infusion stopped
if signs develop. During a prolonged thoracic paravertebral infusion there
is progressive accumulation of local anesthetic in the plasma, and the
plasma concentration of the drug may exceed the threshold for central
nervous system toxicity (eg, 2–4.5 mcg/mL for bupivacaine). Despite the
systemic accumulation, local anesthetic toxicity is rare. This may be the
case because, although the total plasma concentration of the local
anesthetic increases postoperatively, the free fraction of the drug remains
unchanged32 and may be due to the postoperative increase
in α1-acid glycoprotein
concentration,32 the protein that binds to local
anesthetic drugs. There is also a greater increase in the
S-bupivacaine enantiomer,33,34 which is associated with
lower toxicity, than the R-enantiomer. Due to concerns of systemic
accumulation and local anesthetic toxicity with prolonged paravertebral
infusion, it is preferable to use a local anesthetic with lower potential
for toxicity, such as ropivacaine. One must also exercise caution in the
elderly and frail patients as well as in patients with impaired hepatic and
renal function.
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Complications & How to Avoid Them
++
Based on published data the incidence of complications after TPVB is
relatively low and varies from 2.6 to 5%.1,5,35,36
These include vascular puncture (3.8%), hypotension (4.6%), pleural
puncture (1.1%), and pneumothorax (0.5%).35 Unlike
with thoracic epidural anesthesia, hypotension is rare in normovolemic
patients after TPVB because the sympathetic blockade is unilateral. However
TPVB may unmask hypovolemia and result in hypotension. Therefore TPVB should
be used with caution in patients who are hypovolemic or hemodynamically
labile. Nevertheless, hypotension is rare even after bilateral TPVB,
probably owing to the segmental nature of the bilateral sympathetic
blockade.
++
Pleural puncture and pneumothorax are two complications that often
dissuade anesthesiologists from performing a TPVB. Inadvertent pleural
puncture is uncommon after TPVB and may or may not result in a pneumothorax,
which is usually minor and can be managed conservatively. Clues that suggest
pleural puncture during a TPVB are a gritty pleural pop sensation,
irritating cough, onset of sharp chest or shoulder pain, or sudden
hyperventilation. Contrary to common belief, air cannot be aspirated
through the needle unless the lung is also inadvertently punctured or air
that may have entered the pleural cavity during removal of the stylet is
aspirated. Such patients should be closely monitored for the possible
development of a pneumothorax. It should be kept in mind that pneumothorax
may be delayed in onset and a chest radiograph taken too early to exclude a
pneumothorax may not be conclusive. Even a radiologic contrast study using a
chest radiograph may be difficult to interpret because the intrapleural
contrast disperses rapidly, does not define any specific anatomic plane, and
tends to spread to the diaphragmatic angles or horizontal fissure.
++
Systemic local anesthetic toxicity can occur due to inadvertent
intravascular injection or from using an excessive dose of local anesthetic.
The local anesthetic solution must be injected in aliquots, and the dosage
must be adjusted in the elderly and frail patient. An epinephrine-containing
local anesthetic solution is suggested to enable the recognition of
intravascular injection and reduce the systemic absorption of the local anesthetic.
++
Inadvertent epidural, subdural, or intrathecal injection and spinal
anesthesia can also occur. Published data suggest that these complications
are more frequent when the needle is directed medially but may also occur
with a normally positioned needle due to the close proximity of the needle
to the dural cuff and intervertebral foramen. Therefore the needle must
never be directed medially, and care must be taken to exclude intrathecal
injection by routinely performing an aspiration test before injection.
Transient ipsilateral Horner syndrome can occasionally develop after TPVB.
This is due to cephalad spread of the local anesthetic to the stellate
ganglion or to the preganglionic fibers of the first few segments of the
thoracic spinal cord. Bilateral Horner syndrome has also been reported and
may be due to epidural spread or prevertebral spread to the contralateral
stellate ganglion. Sensory changes in the arm and lower extremity may also
occur after a TPVB. The former is due to spread of local anesthetic to the
lower components of the ipsilateral brachial plexus (C8 and T1), and the
latter is due to extended subendothoracic fascial spread to the ipsilateral
retroperitoneal space where the lumbar spinal nerves are located (discussed
earlier), but epidural spread as a cause cannot be excluded. Motor blockade
or bilateral symmetrical anesthesia involving the lower extremity is rare.
It generally suggests significant epidural spread and may be more common if
large volumes of local anesthetic (>25–30 mL) are injected at a
single level. Therefore if a wide segmental spread of anesthesia is desired,
it is preferable to perform the multiple-injection technique or inject a
smaller volume of local anesthetic at several levels a few dermatomes apart.