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Panelists then participated in a survey assigning a score to each peripheral nerve and interfascial plane block according to a newly proposed bleeding risk Critical, Intervention, and Assessment (CIA) scoring system4 (Table 1) as a starting point of discussion and consensus formation. This CIA system is organized around three parameters: 1) whether the block is performed in proximity to a critical structure; 2) whether a bleeding complication would potentially require invasive intervention; and 3) whether it would be difficult to assess the severity of the bleeding complication. A score of 0 or 1 was assigned to each parameter depending on whether it was absent or present, with the total score ranging from 0 to 3. From the total score, the associated risk can be categorized as low risk (CIA = 0), intermediate risk (CIA = 1), or high risk (CIA = 2 or 3). The results of panelist CIA scores are summarized in the Appendix.
The literature search was conducted in May 2018 using the MEDLINE (January 1966 to April 2018) and EMBASE (January 1980 to April 2018) databases. Search strategies for the respective procedures are summarized as follows:
The occipital nerves are located in an area that is easily compressible should bleeding occur. Even were significant bleeding to occur, the posterior scalp is devoid of any major structure that would be at risk from the mass effect of a hematoma. The evidence confirms that the occipital nerve block is a safe procedure with a low risk of bleeding complications as all bleeding/hematoma cases in the literature were self-limiting and required no interventions. The panel therefore recommends that the occipital nerve block be classified as low risk for bleeding complications.
The bleeding risk for deep cervical plexus block is less clear. While there are no reports of significant bleeding directly resulting from deep cervical plexus blocks, various critical anatomical structures are at potential risk of injury when the needle penetrates the prevertebral fascia. These include blood vessels such as the vertebral artery, dorsal scapular artery, and suprascapular artery. There are reports of direct injection of local anesthetic into the vertebral artery18,19,20 and subarachnoid space20,21 during deep cervical plexus blocks. Bleeding from these deeper vessels may be occult, difficult to tamponade non-invasively, and the mass effect from an expanding hematoma in the neck could have significant consequences. The panel therefore recommends that the deep cervical plexus block be classified as high risk for bleeding complications.
Despite the superficial location, there are many arterial structures in the interscalene region of the neck, including the dorsal scapular, transverse cervical, and vertebral arteries, any of which may be punctured during needle advancement.
In large (> 200 patients) prospective and retrospective databases, there is a low incidence of vascular puncture during interscalene block, with reported rates between 0 and 0.63%.23,24,25,26,27,28,29 These databases together captured more than 5,700 interscalene blocks and reported no cases of hematoma. Nevertheless, it is possible that the incidence of both vascular puncture and hematoma are under-reported. There are three case reports of hematoma30,31,32 after interscalene block, though none of these occurred using an ultrasound-guided technique. There have been six spinal cord injuries33,34,35,36 reported after interscalene block, representing severe injury to a critical structure in close proximity to the needle position. Again, none of the reported spinal cord injuries occurred in the context of an ultrasound-guided technique.
In large (> 200 patients) prospective and retrospective databases, the incidence of vascular puncture during supraclavicular block was noted to be between 0 and 0.4% with no reported hematomas.23,37 Similarly, there are no published case reports of hematoma following supraclavicular block.
The infraclavicular brachial plexus lies deep and inferior to the clavicle. While surrounding vascular structures including the axillary artery, axillary vein, and cephalic vein can routinely be anticipated, visualized, and avoided using ultrasound guidance, the risk of vascular puncture remains.
In large (> 200 patients) prospective and retrospective databases, the incidence of vascular puncture during infraclavicular block was noted to be between 0 and 6.6% with nerve stimulator guidance40,41,42 while it was 0.7% with ultrasound guidance,43 with no reports of hematoma formation.
Despite substantial vascularity in the region, the literature review would suggest a low incidence of vascular puncture and bleeding complications. With appropriate education and training, common vascular structures may be anticipated, visualized, and avoided with ultrasound guidance.61 If vascular puncture does occur, pressure can be readily applied to limit bleeding. Nevertheless, if a large expanding hematoma does occur, it could have serious consequences, including airway compromise. The panel therefore recommends that the interscalene and supraclavicular brachial plexus blocks be classified as intermediate risk for bleeding complications.
The available literature suggests that lower extremity blocks targeting nerves or plexi situated deep to the skin and close to vital non-compressible structures (e.g., kidney, retroperitoneum, pelvic organs) be considered high risk. These areas are richly vascularized, not easily compressible in the event of vascular puncture, and the clinical diagnosis of an expanding hematoma can be difficult. The panel therefore recommends that lumbar plexus and parasacral sciatic nerve blocks be classified as high risk for bleeding complications.
Blocks targeting superficial nerves allow ease of compressibility in the event of bleeding. As such, vascular puncture occurring during performance of the femoral nerve, femoral triangle, adductor canal, lateral femoral cutaneous nerve, infrainguinal fascia iliaca, popliteal sciatic nerve, and ankle blocks should not cause significant bleeding complications if detected and treated early. The incidence of vascular puncture will also depend on the guidance modality (e.g., neurostimulation vs ultrasound guidance). The advantage of ultrasonography to visualize normal and aberrant vessels has been highlighted for the popliteal sciatic location,71 and may allow the operator to plan for a safer needle trajectory or to select an alternative approach. The risk assessment should be modified in obese patients in whom the structures may lie much deeper than usual; this increases the risk of inadvertent vascular puncture and may hinder effective compression of the bleeding site.
The literature search identified 1,207 publications. After manual review, only reports of bleeding or aneurysmal complications and visceral or peritoneal injury were retained, yielding 16 relevant publications.72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87 The reported complications from these articles are summarized in Table 8. A majority of the studies that prospectively examined complications following interfascial blocks were unclear in their approach to measurement and were excluded because data was lacking. Most reports of complications during interfascial blocks are therefore derived from case series and case reports.
While the TAP blocks, IIN/IHG blocks, PECS block, serratus anterior blocks, and the rectus sheath blocks are superficial, serious complications such as bleeding, visceral injury, peritonitis, and hematoma have been reported in the literature. In applying the CIA scoring tool, blood vessels within the fascial plane and the viscera deeper may be deemed critical structures. Furthermore, the complications noted with many of these blocks were not immediately detected and were either recognized at laparotomy or following CT imaging for symptomatic patients. Most of the complications were managed conservatively and did not need additional interventions.
The quadratus lumborum block, on the other hand, is a deeper block with a needle trajectory into a non-compressible space. The risk of bleeding complications and visceral injury may thus be considered similar to that of the lumbar plexus block, although there are sparse published data to either support or refute this. The panel therefore currently recommends that the quadratus lumborum block be classified as high risk for bleeding complications.
Based on the location of injection deep to the pectoral muscles, and the presence of nearby vascular structures such as the thoracoacromial artery, the panel recommends that these blocks be classified as intermediate risk for bleeding complications.
Bleeding complications or visceral injury with newer blocks, such as retrolaminar or erector spinae plane blocks, have not been reported. Hence, because there are no critical structures in close proximity, the panel recommends that these blocks be classified as low risk for bleeding complications.
The intercostal nerves run in close approximation to the vascular bundle of the intercostal artery and vein, along the intercostal groove on the ventral caudal surface of each rib.127 While the location of these structures is superficial relative to the skin, the thoracic cavity below the pleura represents a large and hidden compartment in which blood may accumulate.
The paravertebral space is a non-accessible and non-compressible space with a number of critical structures in close proximity. As such it has all the characteristics of a high-risk regional technique. In addition, bleeding within the space, or into the thoracic cavity is not readily detectable on clinical examination.116 The panel therefore recommends that paravertebral blocks be classified as high risk for bleeding complications. Nevertheless, we note that numerous authors have employed this block specifically as an alternative to neuraxial blockade in patients at high risk of bleeding complications.101,102 There may be circumstances where this block is an appropriate choice, even in patients at elevated risk of bleeding complications. Nevertheless this decision should be taken after careful consideration of the risk:benefit ratio and the expertise of the practitioner. 2b1af7f3a8