Ultrasound-Guided Continuous Serratus Anterior Plane Block vs Dexmedetomidine Infusion in Patients With Rib Fractures.

In thoracic trauma patients with rib fractures, the ability to cough and clear secretions is impaired by pain, leading to an increased risk of atelectasis, retention of secretions, chest infections and prolonged ICU stay thereby leads to significant morbidity, mortality and cost of treatment.Hence, aggressive pain management is a vital component of rib fracture management for the healing of rib fractures, improvement of pulmonary functions, and pulmonary rehabilitation.

The number of rib fractures >3, rib fracture locations, bilateral rib fractures, intraparenchymal pulmonary injuries, flail chest, and a first rib fracture influence the mortality rates.

The involvement of acute pain services in Multiple rib fractures (MRFs) is based on "Rib Fracture score". Rib fracture score = (breaks × sides) + age factor. "Breaks" is the total number of fractures to the rib. Score of 1 is for unilateral fractures and 2 for bilateral fractures. Age is factored into the equation due to an increased risk of complications (age factor = 0 if <50 years; 1 if 51-60 years; 2 if 61-70 years; 3 if 71-80 years; 4 if above 80 years). A score >7, requires the involvement of acute pain team.

There is a wide variety of strategies for treating acute pain , including multimodal opioid and non-opioid systemic analgesics, regional anesthesia including thoracic epidural analgesia (TEA), paravertebral blocks (PVB),intercostal nerve blocks and a recent expansion in the use of novel fascial plane blocks.

Ultrasound-guided Serratus Anterior Plane (SAP) block is an ultrasound (US) guided interfascial plane block which has been used in managing pain due to MRFs. It is a relatively recent technique, first described in 2013, that provides almost complete analgesia for the thoracic wall by blocking the lateral branches of the intercostal nerves from T2 to L2. Two planes were described, one superficial to serratus anterior muscle and second underneath the muscle and above the rib. It is a safe, simple to perform block with no significant contraindications or side effects. It can be performed in patients lying supine, rendering it particularly useful in polytrauma patients who are unable to sit up or turn lateral for regional blocks on the back. It can be safely given to polytrauma patients who may be having hemodynamic instability or coagulopathy, unlike epidural and paravertebral. There is a theoretical possibility of local anesthetic toxicity and hematoma such as other interfacial plane blocks. Pneumothorax is a potential complication, but under ultrasound guidance, it would be a remote possibility as the injection is far from the pleura between two muscles or above the rib.

Use of continuous techniques using catheters has the benefit of providing prolonged analgesia titrated to patient response.

Dexmedetomidine is a highly selective α-2 adrenoceptor agonist. It has sympatholytic, sedative, amnestic, and analgesic properties. It provides a unique analgesia, without respiratory depression best described as opioid- sparing. The analgesic properties of α-2 agonists are mediated by Supraspinal (locus ceruleus) and spinal (dorsal horn) mechanisms. Also it decreases sympathetic outflow through a central action in a dose-dependent manner, and these presynaptic sites of action are clinically significant because they modulate the release of norepinephrine. This inhibitory effect on neurotransmitter release is mediated by the blockage of calcium entry into nerve terminals. Systemic administration of the α-2 agonists has been tested in the perioperative period. The reduced opioid requirement was a feature of the administration of such group of medications. This feature is indirect evidence that these drugs have analgesic action. However, the perioperative period involves many conflicting factors. Clearly, the sedative effect may be the reason behind the reduced opioid requirements.