An intercostal nerve block provides anesthesia and analgesia of portions of the thoracic wall innervated by the intercostal nerves. The block does not provide anesthesia nor analgesia to the thoracic viscera. Use of an intercostal nerve block for lateral thoracotomy has been shown to improve blood gas parameters compared to systemic opioids, as well as providing an equivalent level of analgesia.

An intercostal nerve block may be used for procedures such as thoracic wall surgery, thoracotomy, chest drain placement, sternotomy (bilateral nerve blocks) and for analgesia for thoracic wall trauma.

Advantages of this procedure include reduction or prevention of sympathetic response to noxious surgical stimulation, post-operative analgesia, it’s straightforward to perform and can be performed without nerve location or ultrasound guidance. Disadvantages include multiple injection points, it can be difficult to deposit local anesthetic in the correct fascial plane between the parietal pleura and the internal intercostal musculature without ultrasound visualization, leading to failure of nerve block and if not performed dorsally enough (that is, the proximal portion of the rib) the innervation of the skin (lateral cutaneous branch of the ventral branch of the spinal nerve) may not be blocked.

Possible complications include hematoma, hemothorax, pneumothorax, allergic reaction to local anesthetic and local anesthetic toxicity.

Preparation

Aim for the patient to be calm and provide analgesia for the planned procedure. Drug choice and dose will depend on the patient’s physical status and behavior. The patient should be heavily sedated or anesthetized, in lateral recumbency, with the hemithorax blocked uppermost. Alternatively, if a bilateral block is to be performed, or the patient’s respiratory status is compromised in lateral recumbency, it can be performed in sternal recumbency. The patient will require additional analgesia beyond the duration of action of the intercostal nerve block, this should be appropriate for the patient and procedure. Rescue analgesia should be available should there be partial or complete block failure.

Local anesthetic choice and dose

Dose of local anesthetic should be calculated keeping in mind the recommended safe dose for the local anesthetic to be used for that species (see below) – the toxic dose of local anesthetics being lower in cats than in dogs, as well as being cumulative between agents in all species.

• Lidocaine: 3 mg/kg dog; duration of action: 1-2 h.

• Bupivacaine: 1-2 mg/kg dog; duration of action 4-6 h.

• Ropivacaine: 3 mg/kg dog; duration of action 4-6 h.

The volume per injection site for the intercostal nerve block should be calculated by dividing the local anesthetic volume by the number of injection sites and using at least 0.25ml for each site. Local anesthetic can be diluted to allow a greater volume to be used (commonly with sterile water for injection or 0.9% saline, though data sheets should be checked for each formulation to ensure compatibility). Dilution decreases the concentration of the local anesthetic solution, which can decrease the effectiveness of the block as blockade of nerve impulse conduction by local anesthetics is concentration dependent.

The procedure

Two nerves cranial and caudal to the intended site should be blocked. Hair should be clipped away from the site and skin should be aseptically prepared.

Using a sterile technique, fill the syringe with the desired amount of local anesthetic and dilute if required. Prime the needle. The intercostal nerve runs in close proximity to the intercostal vein and artery in a neurovascular bundle, which is located caudal to the caudal border of the corresponding rib. The local anesthetic should be deposited as dorsal as it is possible to palpate the rib confidently, ideally within the proximal third of the rib, in order to desensitize as much of the thoracic wall as possible. Two nerves caudally and cranially in addition to the desired intercostal nerve should be blocked. Introduce the needle through the skin and musculature at the identified site immediately caudal to the caudal border of the rib at a 90-degree angle to the skin. It can be easier to position the needle without the syringe connected initially, or with the use of a T-port connector or other extension set between the needle and syringe allowing manipulation of the needle only. Extensions will require priming before needle placement and injection. Aspirate before injection of local anesthetic to check for air (needle within the thorax) or blood (needle within a blood vessel). If either is present, the needle needs to be withdrawn, and repositioned. Inject the desired volume of local anesthetic, before withdrawing needle. Repeat for each intercostal nerve to be blocked.

Monitoring

Respiratory and cardiovascular monitoring should be in place, consisting of respiratory rate and effort, capnography (if available), heart rate and arterial blood pressure. Intravenous fluid therapy as determined by the patient and procedure.

References 

• Intercostal nerve block

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