Updated: Sep 18, 2019
Pain is personal. Pain is emotional. Pain is what you say it is.
Painful sensory information that reaches the spinal cord causes instantaneous - and potentially prolonged - chemical and anatomic changes that can result in an exaggerated and lasting response. Controlling pain decreases suffering, improves the patient experience, and minimizes the catabolic perioperative stress response.
Effective analgesia just makes good sense.
Local anesthetics are the only analgesic agents that can block conduction of all sensory information from the periphery to the central nervous system. (1) Other analgesics decrease inflammation or tamp down the afferent noxious signal but are unable to abolish painful information completely. In humans, the use of local and regional anesthesia can reduce perioperative opioid requirements, leading to reduced nausea, better gastrointestinal function, shorter hospital stays, and improved patient satisfaction. The incidence of chronic pain states may be reduced with regional anesthetic techniques and there is some evidence that regional anesthesia may reduce the incidence of tumor recurrence and metastasis in oncologic surgery, though this is far from settled. (2)
By incorporating local analgesia into your current acute pain management approach, you can provide a multimodal, effective analgesic strategy. Using local and regional techniques can help reduce the need for opioids in painful procedures and disease states and can help patients feel better faster.
Here are 3 easy regional techniques that you can start using today:
You are probably familiar with a retrobulbar block, in which a small amount of local anesthetic is placed inside the extraocular muscle cone. This block can be difficult to perform correctly and comes with the risk of hemorrhage, intradural spread of local anesthetic, and trauma to the nerves and other structures in the retrobulbar space. An alternative is the peribulbar block, which relies on a larger volume of local anesthetic place outside the extraocular muscle cone. A short needle is used for this block, thus avoiding risk of traumatic injury to extraocular structures, including the optic nerve. It is also technically easier because there is not as much need to be precise with placement of the larger volume of local anesthetic.
The New York School of Regional Anesthesia has gone so far as to say "...given that there is no situation in which a retrobulbar block would be preferred over a peribulbar block, it seems unlikely that retrobulbar blocks will remain part of the repertoire of the modern anesthesiologist."
In cats, a 25 gauge needle is inserted along the orbital rim at the dorsomedial eyelid and advanced, hugging the orbital rim and avoiding the globe. Inject 2 mg/kg bupivacaine or ropivacaine diluted to 3 mL total volume.
In dogs, two injections along the orbital rim - one at the dorsomedial eyelid and the other at the ventrolateral eyelid – may result in more reliable ophthalmic anesthesia.
An awesome free full text review of the anatomy and performance of a variety of ophthalmic locoregional techniques in small animal patients can be found here:
Intravenous Regional Anesthesia
This is one that you may recognize if you’ve done any large animal work. Also known as a Bier block, this technique allows complete anesthesia of the distal limb and is perfect for digit amputations or mass removals.
After exsanguination of the limb by wrapping from distal to proximal with a tight bandage (ie VetWrap), a tourniquet is placed with an inflation pressure of about 100 mmHg greater than systolic BP. Pneumatic cuffs with a manometer are available but in veterinary medicine, a Penlon drain with a hemostat is often used as the tourniquet. The bandage is removed and lidocaine 2 - 3 mg/kg is injected into the catheter. Reliable surgical anesthesia of the distal extremity occurs within 5 to 10 minutes, developing in a distal to proximal fashion. The IVC can be removed during this time period and pressure applied to the site.
To avoid systemic signs associated with lidocaine, it is generally recommended to leave the tourniquet inflated for at least 20 to 30 minutes. The maximum time a tourniquet should be left in place is 60 - 90 minutes because tourniquet-associated pain and tissue ischemia can develop. Intravenous regional anesthesia can be used in cooperative, sedated, or anesthetized dogs and cats. (3, 4)
Similar to a garden soaker hose, this technique involves placing a piece of tubing with multiple holes into a surgical incision at the time of closure. Commercial soaker catheters are available http://www.milainternational.com/index.php/diffusion-catheter-wound-catheter.html but they can also be made by sealing a red rubber urinary catheter or butterfly catheter shut at the distal end and poking holes along it with a 25 to 27-gauge needle. These catheters should be placed in the deepest layer of closure. Lidocaine can be administered as an infusion but it is simpler to bolus bupivacaine or ropivacaine every 4 to 6 hours. Although potentially any incision could have a soaker catheter placed, these are particularly helpful with limb amputations, extensive mastectomies, and large fibrosarcoma resections.
Here’s a link to one way to make a soaker catheter:
Next time, Dr. Hofmeister will discuss local anesthetic agents and whether or not it makes sense to mix them.