Effects of Ultrasound-guided Bilateral Suprazygomatic Maxillary Nerve Block on Postoperative Pain After Elective Bimaxillary Osteotomy in Adult Patients

Bimaxillary osteotomy is a surgical procedure in the field of orthognathic surgery (from Latin, "ortho" straight and "gnatho" jaw) for the correction of dentofacial deformities, both for functional and aesthetic reasons. The incidence of this deformity is estimated to be around the 5-10% of the population. Genetic, environmental and embryonic factors are postulated to be the origin of such deformity, though its origin is still unknown. The surgical technique is complex, with the performance of mandibular and upper jaw osteotomies that allow to advance, retrude, impact and rotate these bones, to align the facial axes. For all these reasons, the anesthetic management of these patients is a challenge. First, the foreseeable difficulty of managing the patient's airway; and second, the control of the patient's pain in the perioperative period.

Therefore, bimaxillary osteotomy is a frequent surgery and potentially painful in adults. Bimaxillary surgery under general anesthesia is the common practice. And peripheral non-ultrasound-guided peripheral nerve blocks are widely used by surgeons. These minor blockades are used to avoid the undesired effects of anesthetics and analgesics; mainly the adverse respiratory effects of opioids. The practice of loco-regional anesthesia provides a control of perioperative pain in a multimodal way showing effective postoperative analgesia and minimizing the respiratory depression caused by the excess use of opioids.

In general, during bimaxillary surgery the surgeon performs the infiltrations with local anesthetic (LA) in a pre-incisional manner for the blockade of the terminal branches of the maxillary nerve intraorally and intranasally. The choice of LA is influenced by considerations such as the start of action, duration and toxicity. A wide range of LA has been used in maxillofacial surgery, such as lidocaine and ropivacaine among others. Both LA produce a reversible blockade of the sodium channel of the neuronal membrane, and are synthetic derivatives of cocaine. Both possess three essential functional units (hydrophilic tertiary amide chain, linked by an intermediate amide chain, to another lipophilic aromatic ring-portion). This means, both LA are amide type; but even if they belong to the same group of LAs there is still great differences in the beginning of action, duration of action and toxicity. Lidocaine has a faster start of action (short latency) than ropivacaine, and has an antiarrhythmic effect. Ropivacaine is more potent, the action last longer than lidocaine, and is less cardiotoxic than other equipotent LA such as bupivacaine and levobupivacaine.

Subsequently, the introduction of loco-regional nerve blocks has meant for the anesthesiologist, in the last three decades, a revolution in the management and control of perioperative pain. The expansion of the practice of loco-regional nerve blocks has been seen in both upper and lower limbs, as well as in trunk and abdomen. On the contrary, the facial blockages (both superficial and deep) have not experienced the same; laying its practice to the surgeon, or to anesthesiologists working on the chronic pain domain. The subsequent introduction of ultrasonography (USG) in the 1990s in the perioperative period also represented an important advance for anesthesiologist both in terms of safety and in terms of ease of management of venous and arterial catheterizations, and practice of loco-regional blockages. Consequently, USG experienced anesthesiologists have recently published in regards to the use of ultrasounds (US) for the blockage of facial nerves in children and adults undergoing maxillofacial surgery. USG devices are increasingly accessible, more portable, cheaper and safer; and therefore, its introduction in the field of perioperative pain management of maxillofacial surgery has still a long way to go.

The maxillary nerve, just like the ophthalmic, is only sensitive. It is detached from the anterolateral border of the trigeminal ganglion, laterally to the ophthalmic. From its origin, it goes above, crosses the foramen rotundum and penetrates into the background of the infratemporal fossa until it enters the pterygopalatine fossa (except the middle meningeal nerve, all its branches reach the pterygopalatine fossa before reaching the facies). In the pterygopalatine fossa the maxillary nerve is located in the upper part of the cavity and passes superiorly to the maxillary artery and superolaterally to the pterygopalatine ganglion. The maxillary nerve receives and conducts the sensitivity of the skin of the cheek, the lower eyelid, the wing of the nose and the upper lip. Its deep branches drive the sensitivity of the mucosa of the lower part of the nasal cavities or respiratory area, and of the dental roots and the gums of the maxilla.