LOCAL ANESTHESIA | Wounds Africa

Local anesthesia in wound care

Image 1. We often need to inject local anesthetics around wounds to debride them properly. Other areas of use are numbing a wound to take biopsies or a toe to treat an ingrown toenail. While you may be quite comfortable using local anesthetics, we hope this chapter includes a few new pearls. image: shutterstock

Topical anesthetics

Local anesthetics can be found in creams, ointments, sprays, and gels. Be aware that most producers of these products specify that the products should only be used on intact skin. In other words, these products are not made to be used in open wounds. However, worldwide, millions of patients receive topical anesthetics into their wounds every year, for lack of an alternative. Every caregiver we know in wound care uses these products off-label directly in wounds. Most producers acknowledge off-the-record that this practice exists and that it seems to be safe.

Be aware of the following aspects to use topical anesthetics safely:

Topical anesthetics have dose limits beyond which they are toxic. Although the absorption through a wound surface is low, we must account for some absorption. We therefore use the same dose limits as we would for subcutaneous injections.

Potent local anesthetics like prilocaine are particularly toxic for infants. In small children, it is essential to double-check the maximum allowed doses.

The larger the wound surface, the more likely the product will be absorbed. When using topical anesthetics on extensive wounds like burns, for example, the maximum allowed dosages must be absolutely respected.

Some topical anesthetic gels and sprays contain alcohol and can burn intensely upon application. Read the label and do not use products containing alcohol on these wounds.

You can drip regular local anesthetic, which is meant for injection, onto the wound and use it topically. If you can inject it under and around the wound, it must be safe to drip it into the wound, right? This is, therefore, the least controversial method of using topical anesthetics.

Image 2. Topical analgesics come in many different formulations. Most are based on lidocaine. 1. Lidocaine cream often comes in 4% or 5% strengths. As it is lipophilic, it penetrates slightly better than lidocaine gel. 2. Lidocaine gel often comes in strengths of 2%. The type of lidocaine gel used to numb the urethra before catheterization is also suitable. 3. Note that some formulations contain high concentrations of lidocaine, and you must use them cautiously when treating extensive wound areas such as burns. Nr 3. In the diagram is J-Caine, marketed as a local analgesic before tattoos. 4. Lidocaine spray often contains additives that burn! We do not recommend using these unless you have no other alternatives. 5. Emla cream stands out as the most effective topical analgesic. Be aware, though, that it is toxic for infants < 3 months!

None of the topical anesthetics numbs the tissue deeply. At best, they might anesthetize tissue a millimeter beneath the wound bed. The prilocaine/lidocaine combination is probably the most potent topical product as it penetrates slightly deeper than other formulations. If the wound surface is covered by necrotic tissue or a thick fibrin layer, the anesthetic will not reach nerve endings well. Debride what you can first without causing the patient pain. Stop and apply the anesthetic when the patient starts to feel discomfort. You have to be patient with topical anesthetics- they work slowly. Apply them to the wound- cover with a nonabsorptive dressing and let the anesthetic dwell in the wound for at least 15-20 minutes.

Topical anesthetics do not work sufficiently if extensive debridements are required. In these cases, it is more effective to inject the anesthetic in or around the ulcer or as a local or regional block. The latter techniques will be discussed at the end of the chapter.

Using anesthetics for subcutaneous injections in wound care

1% Lidocaine is relatively cheap and usually available even in remote clinics in Africa. In most cases, you only need 0,5%. You can dilute the 1% Lidocaine with equal sterile saline to make 0,5%, which will save you money and is equally effective. It may take a couple of minutes longer for the 0,5% solution to work, and the effect may dissipate earlier. Still, by that time, you are already done with the debridement. We rarely use bupivacaine or other more potent anesthetics in wound care.

We rarely use local anesthetics with epinephrine/adrenaline. The exception may be patients using strong blood-thinning medication, where we would like to take a biopsy. There is no documentation that the temporary blood vessel constriction caused by epinephrine/adrenaline is detrimental to wound healing. Still, we usually see no need to use it. When we went to medical school we were taught that the use of epinephrine/adrenaline was contraindicated in fingers/toes, nose and ears and around the penis, as it could cause irreversible necrosis of tissues in these anatomical areas. It turned out that this was somewhat of a medical myth. Today, we are not concerned about using epinephrine/adrenaline in these areas.

However, we are cautious when we do a toe block in patients with critical ischemic disease. First, we would never use a local anesthetic with epinephrine/adrenaline in these patients. Second, we would use a needle as thin as possible ( preferably 27G) to avoid damaging the remaining blood vessels in the toe. Third, we would use as little anesthetic solution as possible. Avoid pressing large volumes into these delicate areas. The pressure in the tissues from the injected volume can severely reduce blood circulation for several hours!

When we use local anesthetic to numb the tissues before a wound biopsy, we usually only need very minute amounts of the anesthetic. Half a milliliter is generally more than enough for each biopsy site.

How do we numb an entire wound for deeper debridement? Here we can use several injection techniques. Firstly, since we only need the numbing effect to last 20-30 minutes, 0,5% Lidocaine is usually sufficient. The most effective method of numbing the wound would be to inject at several sites around the wound through the intact skin. This will often be the most painful way to do the injections! The gentlest method is to carefully inject Lidocaine through the necrotic wound bed (the dead tissue is without sensation) to just below the necrotic layer. You do not know where the necrotic tissue /healthy tissue interface is, but often you can feel it in the resistance of the needle as you gently push it deeper.

We use this technique in most cases. Always be patient when using a local anesthetic. Make it a rule to wait at least 10 minutes for the product to work sufficiently.

Table 1: Some of the properties of different types of local anesthetics. Note that maximum doses are dependent on whether epinephrine/adrenaline is added. For most purposes in wound care, lidocaine is sufficient, and we can often dilute it to 0,5% with saline.

Image 3. Hypodermic needles come in different thicknesses and lengths. Understandably, the thinner the needle, the less painful the injection. We often use 27G needles for local anesthesia. The challenge when using such a thin needle is to press the local anesthetic through the needle. Using a small syringe makes this a lot easier. See image 5.

Image 4. The laws of physics tell us that it will be easier to press the anesthetic through the thin 27G needle if we use a smaller syringe with a lower diameter piston. When using a 27 G needle, it is best to use a 2.5ml syringe or even a 1ml syringe. This means that you may have to pull up the anesthetic several times, but it will make it so much easier to inject.

Buffering Local Anesthetics: Rationale and Technique

The administration of local anesthetics is a routine aspect of wound care, minor surgical procedures, and regional anesthesia. While generally safe and effective, one of the most frequently reported patient complaints during infiltration is the burning or stinging sensation upon injection. This discomfort is primarily attributed to the acidity of commercially prepared local anesthetic solutions.

Most local anesthetics—particularly lidocaine and bupivacaine—are prepared with a relatively low pH (typically between 3.5 and 5.5) to ensure chemical stability and shelf life. However, this acidic environment can cause significant discomfort when injected into tissue, especially when the surrounding area is inflamed or hypersensitive, as is often the case in wound care settings. Moreover, acidic pH delays the onset of anesthesia by maintaining the anesthetic in its ionized, less membrane-permeable form.

Buffering the local anesthetic by raising its pH closer to physiological levels offers a simple and effective method for reducing pain on injection and accelerating the onset of action. This is typically achieved by adding sodium bicarbonate to the anesthetic solution, which raises the pH and increases the proportion of non-ionized (lipid-soluble) anesthetic molecules, enhancing their ability to penetrate nerve membranes and initiate nerve blockade more rapidly.

The clinical advantages of buffering are well documented. Patients receiving buffered anesthetics report significantly less pain during infiltration, and the block typically takes effect more quickly. This is particularly valuable in settings such as wound care, where tissue manipulation may already be uncomfortable and where minimizing procedure time is often a priority. Buffered solutions may also reduce the need for additional injections, improving patient experience and clinical efficiency.

How to Buffer Local Anesthetic: A Practical Recipe

The most commonly buffered local anesthetic is 1% or 2% lidocaine, with or without epinephrine. Bicarbonate must be added cautiously and in appropriate ratios to avoid precipitation, especially in solutions containing epinephrine, which are more acidic and less stable.

The standard buffering ratio is:

1 part of 8.4% sodium bicarbonate to 10 parts of lidocaine solution

For example:

Mix 1 mL of 8.4% sodium bicarbonate with 10 mL of 1% lidocaine
For 2% lidocaine, some clinicians use a 1:20 ratio to reduce precipitation risk

When epinephrine is present, buffering must be done just before administration, as the more alkaline environment reduces the shelf life of the epinephrine and may cause visible precipitation over time. Buffered solutions should ideally be used within 1 hour.

In practice, buffering is quick and straightforward. Draw up the desired amount of lidocaine in a syringe, then add the appropriate volume of sodium bicarbonate using a separate syringe or via a mixing port. The solution should appear clear and mix easily. If cloudiness or crystallization occurs, the solution should be discarded.

Key Considerations

Do not buffer bupivacaine routinely, as it is more prone to precipitation
Buffered solutions should not be stored; mix only what is needed for immediate use
Warming the anesthetic to body temperature can further reduce injection pain and may be combined with buffering for enhanced comfort

In conclusion, buffering local anesthetics is a low-cost, high-impact intervention that improves the patient experience during tissue infiltration procedures. In wound care, where repeated injections are common and tissues are often hyperalgesic, this technique can make a meaningful difference in patient tolerance and procedural success. As with all modifications of injectable solutions, proper technique and compatibility awareness are essential to ensure safety and efficacy.

Image 5: Sodium Bicarbonate is usually available at an 8.4% concentration at most clinics. We also use this concentration to buffer local anesthetics, like lidocaine.

Local and regional blocks

Local blocks

A local anesthetic block numbs a smaller area of tissue. Local blocks are often used to numb an entire finger or toe. Regional blocks are very useful for numbing larger anatomical regions. A regional hand block, for example, can numb the whole hand.

As mentioned above, local blocks, also called ring blocks, are often used around the toes or fingers. Only about 2-3 milliliters of lidocaine are usually necessary on each side of the toe/finger. Wait 10 minutes to ensure that the anesthetic has had enough effect.

Important! The correct method is to inject the lidocaine from the dorsal side of the finger or toe! We have seen many examples on the internet where caregivers inject from the inside of the foot or hand. The number of nerve endings on the insides of the feet or hands is much higher here. Subsequently, piercing the skin with a needle from the plantar/palmar side is so much more painful! Do not do this!

Regional blocks

Many caregivers often forget the possibility of using a regional block to numb larger anatomical areas. While some regional blocks, like a plexus block of the upper extremity, require quite some training, blocks in other anatomical regions can be easier to learn. If you work in an off-grid clinic without an anesthesiologist, you should at least be familiar with wrist and ankle blocks. The popliteal block is a little more challenging to learn but extremely useful for more demanding procedures on the lower leg. The most elegant way to place the blocks is by using an ultrasound-guided technique. In this manner, you can often visualize the nerves or other anatomical landmarks and deliver the local anesthetic very precisely. However, an ultrasound machine is usually unavailable in rural clinics, and it takes some training to recognize the required anatomical landmarks. All these blocks can also be done without ultrasound, but this requires larger volumes of local anesthetic since we are placing the anesthetic in "approximately" the correct location.

1. Regional wrist block

A regional hand block makes numbing an entire hand relatively easy. To achieve this, you need to inject lidocaine at the sites of the radial, median, and ulnar nerves. Note that the median and ulnar nerves are injected from the volar side of the wrist. For the radial nerve, you only need to block the superficial radial nerve on the dorsoradial side of the wrist. Injecting on the volar side for the radial nerve is unnecessary and potentially harmful, risking artery or tendon injury. For more details about these techniques, please refer to the two videos below:

2. Regional ankle block

An ankle block is a regional anesthesia technique that provides surgical anesthesia or analgesia to the foot by blocking five terminal branches of the sciatic and femoral nerves at the ankle level. This technique is particularly useful for minor foot procedures, such as wound debridement, toe amputation, or podiatric surgery, and can be performed safely without the need for imaging guidance. Because the nerves at this level are relatively superficial, the block is typically performed using anatomical landmarks and a small-gauge needle.

The foot receives sensory innervation from five nerves: the posterior tibial, saphenous, superficial peroneal, deep peroneal, and sural nerves. These nerves course around the ankle in relatively predictable positions, making the ankle block a reliable and effective method of achieving regional anesthesia.

To perform an ankle block, the patient should be positioned supine with the foot resting comfortably and slightly dorsiflexed. The skin around the ankle is cleaned with an appropriate antiseptic solution and draped using a sterile technique. A 25—or 27-gauge needle is typically used, and 3 to 5 milliliters of local anesthetic are injected at each nerve site.

The posterior tibial nerve, which is the terminal branch of the tibial division of the sciatic nerve, lies posterior to the medial malleolus and adjacent to the posterior tibial artery. It is best anesthetized by palpating the artery and injecting local anesthetic just posterior to it, after aspirating to avoid intravascular injection. This nerve supplies the sole of the foot and contributes to the sensation of the plantar toes.

The saphenous nerve, a terminal sensory branch of the femoral nerve, runs superficially along the medial aspect of the ankle and foot. It is blocked with a subcutaneous local anesthetic infiltration along the medial side of the ankle, anterior to the medial malleolus.

The superficial peroneal nerve, which provides sensation to the dorsum of the foot and most of the dorsal toes, lies subcutaneously in the lateral anterior ankle. It can be blocked by raising a subcutaneous wheal of local anesthetic across the anterior aspect of the ankle, approximately at the level of the malleoli, from the lateral edge of the tibia to the lateral malleolus.

The deep peroneal nerve runs alongside the anterior tibial artery between the tendons of the extensor hallucis longus and extensor digitorum longus muscles. This nerve innervates the first web space between the first and second toes. To block it, the needle is inserted just lateral to the extensor hallucis longus tendon at the anterior aspect of the ankle, and 2 to 3 milliliters of local anesthetic is injected at a depth of 1 to 2 centimeters.

Lastly, the sural nerve, which provides sensation to the lateral side of the foot and fifth toe, is found posterior to the lateral malleolus. Subcutaneous local anesthetic infiltration just behind the lateral malleolus blocks it.

After the injections are completed, the foot should be monitored for the onset of sensory blockade, which typically occurs within 10 to 20 minutes, depending on the local anesthetic used. Because none of these nerves carry significant motor function at this level, an ankle block provides purely sensory anesthesia, allowing patients to retain mobility of the ankle and leg.

An ankle block is valuable for clinicians managing foot injuries or performing minor surgical procedures. It is easy to learn, carries a low complication rate, and provides excellent patient comfort without the systemic effects of sedation or general anesthesia.

We have selected several videos ( both the "landmark" and ultrasound-guided approach) to demonstrate this technique because every video explains it slightly differently. If you are new to this technique, we recommend you watch all the videos.

3. Popliteal block

The popliteal block is a regional anesthesia technique that targets the sciatic nerve in the popliteal fossa, proximal to its bifurcation into the tibial and common peroneal nerves. This block provides dense anesthesia and analgesia to the lower leg below the knee, excluding the medial aspect, which is supplied by the saphenous nerve, a branch of the femoral nerve. The popliteal block is commonly used for surgical procedures on the foot and ankle and for postoperative management. It is highly effective and versatile, with the advantage of preserving motor function at the level of the thigh.

Depending on the operator's preference, the patient is usually prone or lateral. In the prone position, the foot is positioned with the sole facing upward, while in the lateral decubitus position, the side to be blocked faces upward with the knee slightly flexed to expose the popliteal fossa. The area is cleaned with antiseptic solution and sterilely draped.

The popliteal fossa lies posterior to the knee joint and is bounded by the biceps femoris tendon laterally and the tendons of the semimembranosus and semitendinosus muscles medially. The sciatic nerve typically divides into its two terminal branches approximately 5 to 10 centimeters above the popliteal crease, although this can vary significantly. For this reason, the goal of the popliteal block is to anesthetize the sciatic nerve before its bifurcation to ensure blockade of both the tibial and common peroneal components.

Palpation of the popliteal artery in the fossa helps orient the operator, although ultrasound guidance has become the standard of care due to the variable anatomy and improved accuracy. Using ultrasound, a high-frequency linear probe is placed transversely in the popliteal crease and slowly moved proximally until the sciatic nerve is visualized as a hyperechoic oval or figure-of-eight structure, usually superficial and lateral to the artery and vein. As the probe is moved further proximally, the two components of the sciatic nerve begin to merge into a single trunk, indicating the optimal injection site.

Once the nerve is identified, a block needle is inserted using an in-plane or out-of-plane approach, depending on the operator’s experience and orientation of the ultrasound probe. The needle is advanced under direct visualization toward the sciatic nerve sheath. After careful aspiration to rule out vascular puncture, 20 to 30 milliliters of local anesthetic (such as 0.5% bupivacaine or 1.5% mepivacaine) is injected incrementally. Ideally, the anesthetic should surround the nerve in a circumferential pattern to ensure complete blockade of both branches.

Without ultrasound, the block can be performed using a landmark and nerve stimulation technique. With the patient prone, a point is identified approximately 7 to 10 centimeters proximal to the popliteal crease and midway between the tendons of the biceps femoris and semitendinosus muscles. After inserting the needle perpendicularly to the skin, a nerve stimulator is used to elicit motor responses—either plantar flexion (tibial nerve) or dorsiflexion/foot eversion (common peroneal nerve). Once an appropriate motor response is obtained with a low current (typically <0.5 mA), local anesthetic is slowly injected after negative aspiration.

A successful popliteal block results in anesthesia of the foot and most of the lower leg, sparing only the medial skin supplied by the saphenous nerve. Therefore, if complete anesthesia of the lower leg is required, a separate saphenous nerve block (often performed at the level of the knee or ankle or popliteal block is an effective technique with a high success rate, particularly when performed under ultrasound guidance. It provides excellent intraoperative anesthesia and prolonged postoperative analgesia while preserving the quadriceps' motor function, making it especially useful in ambulatory surgery settings. Like all peripheral nerve blocks, it should be performed with careful attention to sterile technique, anatomical variation, and appropriate monitoring for signs of local anesthetic systemic toxicity.

4. Femoral block

The femoral nerve block is a well-established regional anesthesia technique that targets the femoral nerve as it passes below the inguinal ligament. It provides sensory and partial motor blockade to the anterior thigh, most of the femur, the knee joint, and the medial aspect of the lower leg via the saphenous nerve, one of its terminal branches. Traditionally used in surgical settings for procedures involving the anterior thigh and knee, the femoral nerve block also holds significant value in wound care, particularly for managing pain during debridement, dressing changes, or minor surgical interventions in patients with complex or chronic wounds.

The femoral nerve arises from the lumbar plexus (L2–L4) and courses through the psoas major muscle before emerging from its lateral border. It travels beneath the inguinal ligament and enters the femoral triangle, which lies lateral to the femoral artery and vein. At this level, it divides into multiple branches that innervate the anterior thigh muscles, the skin over the anterior and medial thigh, and the knee joint. Importantly, the saphenous nerve—its longest purely sensory branch—descends along the medial leg to the ankle, providing cutaneous innervation without motor function.

To perform a femoral nerve block, the patient is positioned supine with the leg slightly abducted and externally rotated to expose the femoral crease. The skin is cleaned with antiseptic, and the area is prepared using sterile technique. Traditionally, the femoral artery is palpated just below the inguinal ligament, and the femoral nerve is approached immediately lateral to the artery. However, with the widespread use of ultrasound, visualization of the nerve has dramatically improved the precision and safety of the technique.

Using a high-frequency linear transducer placed transversely over the femoral crease, the femoral artery is identified as a pulsatile, anechoic structure. Lateral to the artery, the femoral nerve appears hyperechoic, triangular or oval-shaped, often partially partitioned into fascicles. A block needle is introduced using an in-plane approach from the lateral side, directed toward the femoral nerve under real-time visualization. Once the needle tip is adjacent to the nerve sheath, and after careful aspiration, 10 to 20 milliliters of local anesthetic is injected in small increments, observing for circumferential spread around the nerve.

The resulting block typically takes effect within 10 to 20 minutes and provides excellent analgesia for the anterior thigh, knee, and medial leg via the saphenous nerve. While motor weakness of the quadriceps is expected, this may be of limited concern in patients who are already immobile due to wounds or illness.

In wound care, femoral nerve blockade can be beneficial. Patients with chronic or infected wounds of the anterior thigh, knee, or medial leg often experience significant pain that can complicate essential interventions such as debridement, dressing changes, or negative pressure therapy. In such cases, systemic analgesia may be inadequate or poorly tolerated, particularly in elderly or frail patients. A femoral nerve block offers a targeted, temporary solution that improves patient comfort while allowing for effective wound care procedures. Moreover, combined with a sciatic or adductor canal block, it can provide even more comprehensive anesthesia for lower extremity wounds.

In palliative or long-term wound care, repeated femoral blocks or catheter-based continuous infusion may also be considered to provide sustained pain relief, reduce opioid requirements, and improve overall patient cooperation and outcomes. Importantly, femoral nerve blocks should always be performed with an awareness of the patient’s coagulation status, infection risk, and mobility needs, especially when motor blockade may contribute to falls.

In summary, the femoral nerve block is a valuable surgical anesthesia and also in the nuanced field of wound care. Its ability to deliver localized, potent analgesia makes it a safe and effective option for improving the quality of life in patients with pain in the anterior thigh, knee, or medial lower leg.