REGIONAL ANAESTHESIA
Paravertebral block anatomy
The aim of paravertebral analgesia in thoracotomy surgery is to:
Provide continuous postoperative analgesia to the dermatomes innervating the lung surgery wounds and chest drain sites close to this wound (usually T4-T9 dermatomes)
Reduce the opioid requirements of lung surgery patients (reduce side-effects)
Enable early mobilisation and ability for deep inspiration and coughing to avoid serious respiratory complications
A paravertebral block (PVB) produces ipsilateral analgesia by the injection of local anaesthetic alongside the vertebral column, to encourage longitudinal spread [1].
The paravertebral space is a wedge-shaped area between the heads and necks of the ribs. The boundaries are:
Posteriorly: the superior costo-transverse ligament (SCTL) lies between the transverse processes medially, and continuous with the internal intercostal membrane (IICM) laterally
Anteriorly: the parietal pleura (PP)
Medially: the vertebra, intervertebral disc and intervertebral foramen
The anatomy and contents of the paravertebral space are shown in the diagram below:
Local anaesthetic, injected in the space, can therefore spread longitudinally along the heads and necks of the ribs, medially through the intervertebral foramina, and laterally in the intercostals plane. The consequence of local anaesthetic penetrating the intercostals nerve, its dorsal ramus, rami communicantes and sympathetic chain, is a unilateral somatic and sympathetic block.
Techniques for paravertebral block
The administration of a preoperative paravertebral block, using ultrasound-guidance after the induction of general anaesthesia in the patient, is a practice that has shown to reduce pain and decrease opioid requirements in the postoperative period (Appendix A).
1. Pre-surgical ultrasound-guided paravertebral block
Different methods have been described: out-of-plane, in-plane, transverse or sagittal paramedian view, using a transducer (either 5-10 MHz linear array or 5-10 MHz curved array probe). The aim is to visualise the spinous process, transverse process (TP), Superior costo-transverse ligament (and IICM laterally) and the parietal pleura in one image. Paramedian and transverse scan views are shown [2-5].
The patient is positioned as for surgery in the lateral position, and the scan and PVB is performed under aseptic technique.
Sagittal view of paravertebral space: Transverse Process (TP), Superior Costo-transverse Ligament (SCTL).
The ribs are scanned longitudinally from cranial to caudal to identify the chosen rib space for injection, and the transducer probe orientated to the desired approach, transverse or sagittal.
The following interspaces are recommended to anaesthetise the primary wound(s) and chest drain sites:
T 3/4 and T 7/8
For thoracotomy and conventional video-assisted thoracoscopy (VAT)
T3/4 and T8/9
For robotic VAT surgery
An 18G Tuohy SonoTAP (Pajunk) needle is inserted from lateral to medial to the PVB triangle; when the IICM is crossed, a faint ‘click’ is felt.
A total of 20 ml 0.5% levobupivacaine is injected (if two levels, 10ml at each level)
The correct plane of injection is confirmed by the inferior movement of the pleural interface.
Currently catheters are not placed by the ultrasound method for thoracic surgery in this institution; it has been shown that although there is a high success rate for needle-tip position, the position of catheters can be variable by this technique.
2. Intra-operative surgical placement
The technique of paravertebral catheter analgesia was introduced to Guy’s hospital 20-years ago, by Mr Jules Dussek, Consultant Thoracic surgeon. Previously, only opiate analgesia was used for thoracotomy pain. He followed a method described by Sabanathan from Bradford Infirmary in 1988 [7], where there is blunt dissection of the parietal pleura to the vertebral bodies, creating a free edge of pleura. A Tuohy needle is then advanced externally from the skin into the paravertebral space under direct vision, to allow a catheter to be placed.
The current amendment to practice at Guy’s Hospital is to use the externally introduced Tuohy needle to raise a ‘bleb’ using a few millilitres of local anaesthetic. The catheter is then introduced into the bleb, without the need of dissecting the pleura and therefore omitting a free edge altogether. This method has been used for thoracoscopy analgesia [8]:
The pocket is formed in a way that minimises the leakage of local anaesthetic from the paravertebral space and encourages the longitudinal spread of local anaesthetic for a few dermatomes above and below the injection site.
A total of up to 30 ml 0.25% levobupivacaine is injected at the surgical PVB.
In theory, the parietal pleura pocket must be intact and undamaged for local anaesthetic to be contained and for the PVB to be effective
A catheter is placed in the space to allow postoperative PVB infusion
3. ‘Surrogate’ paravertebral blocks
These are blocks which may be considered when:
There is failure or difficulty in siting a PVB:
Paravertebral space cannot be accessed e.g. pleural displacement endpoint not achieved on injection
Imaging of PV space is difficult e.g. obese anatomy
Pleura surrounding space is not intact e.g. due to surgery, decortication
Enhanced longitudinal spread of local anaesthesia is a priority e.g. for extensive surgical incision
An epidural is contraindicated or unsuitable
These ‘surrogate’ or paravertebral ‘by proxy’ blocks are fascial plane blocks which show evidence of local anaesthetic spread to the paravertebral space. They are more superficial in anatomy to the traditional PVB, and they may be easier to administer and image. A summary of the blocks is shown below [25]:
Supplementary local anaesthetic blocks
1. Surgical intercostal blocks
Intercostal blocks are performed using a long needle at dermatomal levels T4 to T9, by the surgeon, to anaesthetise the primary wound sites and the low drain sites. In combination with the PVB it is likely to improve the spread of the subsequent PVB infusion.
2. Phrenic nerve block for shoulder pain
Shoulder pain after thoracic surgery is mediated by the phrenic nerve which is cervical dermatomal in origin, and the pain is therefore not treated by PVB [9]. The surgeon may administer a block to the phrenic nerve, at the peri-phrenic fat pad at the cardio-diaphragmatic junction intraoperatively.
Though shoulder pain can be relieved by opioid administration (patient-controlled analgesia), the opioid side-effects of sedation and respiratory depression must be avoided. Conservative measures such as a warm compress will alleviate pain.
The primary goal of analgesia is that the patient is alert, and able to cough and deeply inspire, and mobilise as soon as possible.
Factors affecting spread
A bolus volume of 15 ml will produce a somatic block spread of at least 5 dermatomes and a sympathetic block of about 8 dermatomes [1]. However, in cadaveric studies the injection of contrast in the paravertebral space results in an unpredictable distribution, ranging from cranio-caudal spread or intercostal spread. The presence of the endothoracic fascia may explain the difference: injectate placed anterior to this fascia can spread cranio-caudally without reaching the intervertebral foramen.
The paravertebral space is not an isolated compartment and communicates with adjacent intercostal and epidural spaces. Improving accuracy of administration, such as by ultrasound-guidance or direct visualisation may improve spread [6,20].
Indications and contraindications for paravertebral block
INDICATIONS:
Paravertebral catheter analgesia in thoracic surgery is indicated mainly for:
Thoracotomy analgesia (lobectomy, pneumonectomy)
- As a primary analgesia choice
- As a secondary choice where the insertion of a thoracic epidural has failed
Thoracoscopy analgesia (lobectomy, pneumonectomy)
RELATIVE CONTRAINDICATIONS:
Pleurectomy involving parietal pleura adjacent to the vertebral bodies if there is sufficient pleura here, a PVB may still be performed
Thoracotomy wound extending more than 5 dermatomal segments e.g. extensive chest wall resection.
Sepsis or tumour in the paravertebral space or chest or skin entry site
In these cases, an epidural or ESP block may be the more appropriate mode of analgesia.
On-going anticoagulation, anti-thrombotic medication or a bleeding disorder does not preclude the use of a paravertebral, as the neurological consequences of a paravertebral haematoma are small compared to that of an epidural haematoma.
PVB in thoracic surgery is excluded from the antithrombotic guideline.
Analgesic regimen for thoracic and lung cancer surgery
BEFORE SURGERY, after induction:
Pre-surgical ultrasound-guided PVB* by anaesthetist
PVB injection of a total of 20 ml 0.5% plain levobupivacaine (Chirocaine) 10ml at each injection site if two dermatome administration
DURING SURGERY
Intravenous opioids administered by anaesthetist according to clinical need
Prescribe: PVB, Patient Controlled Analgesia (PCA), regular paracetamol, regular ibuprofen if not contraindicated and the patient is under 60 years old
Direct surgical placement of PVB, intercostal and phrenic nerve blocks
Injection of up to 30 ml total of 0.25% plain levobupivacaine (Chirocaine)
Start immediately after PVB catheter placement in theatre*
PVB INFUSION of 0.125% plain bupivacaine at 3-10 ml per hour administered as a pre-packed 500ml bag via a locked programmable dedicated paravertebral infusion pump. Prescribe paravertebral regimen on MedChart. Click administer on PVB regimen; record the batch number in MedChart.
2.*The dosing for bolus and infusion rates for PVB also apply to the ‘paravertebral by proxy’ blocks.
RECOVERY WARD
A MORPHINE OR FENTANYL PCA co-administered with the PVB infusion as per pain protocol
If patient is in pain,
Assess pain at BOTH the site of surgery and ipsilateral shoulder
If pain is at the wound site, a PVB bolus of up to 10ml 0.25% plain levobupivacaine may be administered by the anaesthetist*
Conservative management of shoulder pain may be employed
e.g. warm compress
Administer IV opioid boluses as per pain protocol such that:
The patient is alert, able to cough and deeply inspire
Moderate shoulder pain is acceptable
THORACIC WARD
Continue PCA until oral fluids tolerated (usually overnight), then wean to ORAL OPIOIDS, PRN ONLY. Do not prescribe regular oral opioids.
Continue PVB infusion until after chest drain removal, up to a maximum of 5 days
The aim is to mobilise the patient on the day of surgery
AFTER the chest drains have been removed,
ï Stop and remove the PVB catheter IN THE MORNING
ï Continue regular oral analgesia
The above regimen ensures that the recommended manufacturer’s maximum dose of Bupivacaine 400mg per 24 hours, is not exceeded. The continuous paravertebral infusion is prescribed on MedChart. The patient should be monitored for signs of local anaesthetic toxicity as per the existing trust acute pain guidelines –(LINK TO BE ADDED).
Information of the treatment of local anaesthetic toxicity can be found here:
AAGBI Management of Local Anaesthetic Toxicity
Efficacy
FOR THORACOTOMY SURGERY:
There is no significant difference in pain score and morphine consumption between PVB and TEA up to 48 hours [5].
Side effects occurred less often with PVB than TEA (expressed as odds ratio (OR)):
Pulmonary complications (OR 0.36)
Urinary retention (OR 0.23)
Nausea and vomiting (OR 0.47)
Hypotension (OR 0.23)
Failed technique (OR 0.28)
PVB has been shown to be effective in the reduction of pain scores when compared to intravenous opioids alone for at least 3 days postoperatively [6].
There is no evidence as to which method of catheter placement is best (surgical or anaesthetic).
When using a solution of local anaesthetic plus opioid, TEA is associated with lower pain scores in the early postoperative period than PVB. However, PVB provides analgesia comparable to TEA when local anaesthetic is used alone and therefore can be recommended as a bolus and infusion for 2 to 3 days with fewer adverse effects.
Compared to paravertebral blockade, thoracic epidural analgesia has a higher incidence of pulmonary complications, urinary retention, nausea, itching, and hypotension [15]. Additionally, epidurals have an incidence of serious complications, albeit low, such as epidural abscess, meningitis, vertebral canal haematoma, nerve injury, cardiovascular collapse and death [18]. Epidural analgesia was associated with an increased risk of major complications in pneumonectomy patients, compared with paravertebral blockade [19].
Preoperative paravertebral blockade
Pre-emptive analgesia describes the aim of minimising central and spinal pain transmission by noxious stimuli arising from events at surgery, by administering an analgesic technique prior to surgical incision. Early evidence shows that preoperative PVB may prevent acute and chronic persistent surgical pain after thoracic surgery [21-24].