From the FDA Drug Label
To avoid intravascular injection, aspiration should be performed before the local anesthetic solution is injected The needle must be repositioned until no return of blood can be elicited by aspiration. Note, however, that the absence of blood in the syringe does not guarantee that intravascular injection has been avoided
You do not aspirate blood when performing a hematoma block because the needle is repositioned until no return of blood can be elicited by aspiration. This suggests that the needle is placed in a location where blood is not present, or the hematoma is not communicating with the needle. However, it is essential to note that the absence of blood in the syringe does not guarantee that intravascular injection has been avoided 1.
From the Research
You may not aspirate blood when performing a hematoma block because the blood within the hematoma has often clotted, making aspiration difficult. The hematoma consists of a mixture of clotted blood and serum, rather than freely flowing blood. Additionally, the needle tip might be positioned in a section of the hematoma that has already clotted or in the surrounding tissue rather than in a fluid-filled pocket. To perform an effective hematoma block, identify the fracture site using anatomical landmarks or imaging guidance, prepare the skin with antiseptic solution, and inject 1-2% lidocaine (typically 5-10 mL depending on the size of the fracture) directly into the fracture hematoma, as seen in a case report from 2. Even without blood return on aspiration, the anesthetic will still diffuse through the hematoma and surrounding tissues to provide pain relief. The block typically takes effect within 5-10 minutes and lasts 1-2 hours. Always monitor for signs of local anesthetic toxicity such as perioral numbness, metallic taste, or cardiac arrhythmias, though this is rare with properly administered hematoma blocks, as noted in a study from 3. It is also important to consider the potential for systemic neurological symptoms, as reported in a case study from 2, and to take necessary precautions to minimize the risk of complications. The efficacy and safety of the hematoma block have been demonstrated in various studies, including one from 4, which found that the hematoma block is an effective and safe method of providing anesthesia for fracture reduction in select patients. However, it is crucial to prioritize the most recent and highest quality study, which in this case is 2, to guide clinical decision-making and ensure optimal patient outcomes.
Some key points to consider when performing a hematoma block include:
- Using anatomical landmarks or imaging guidance to identify the fracture site
- Preparing the skin with antiseptic solution
- Injecting 1-2% lidocaine directly into the fracture hematoma
- Monitoring for signs of local anesthetic toxicity
- Considering the potential for systemic neurological symptoms and taking necessary precautions. Overall, the hematoma block is a valuable technique for providing pain relief in patients with fractures, and by following proper protocols and guidelines, clinicians can minimize the risk of complications and ensure optimal patient outcomes, as supported by the most recent evidence from 2.