Ultrasound-guided Bilateral Suprazygomatic Maxillary Nerve Block and Bimaxillary Osteotomy

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.

Therefore, in order to produce an effective anesthesia of the maxillary area, the needle can be introduced through the pterygomaxillary fissure to the pterygopalatine fossa, with risk of vascular and nerve puncture. However, with real-time vision of the ultrasound-guided block, these risks will be limited, allowing a direct localization of the maxillary artery, position of the needle and the distribution of LA within the pterygopalatine fossa. The pterygopalatine fossa is anatomically deep and surrounded by bones. The most optimal ultrasound window is the infrazygomatic path, allowing the visualization of the entire axis of the pterygopalatine fossa up to the foramen rotundum.

The usual practice for the ultrasound-guided maxillary nerve block is the placement of the ultrasound probe in an infrazygomatic position and the introduction of the needle by suprazygomatic route for better visualization of the procedure. The approach by suprazygomatic route from the frontozygomatic angle is one of the safest and recommended routes to reach the foramen rotundum. This trajectory limits the insertion of the needle in the anterior portion of the foramen rotundum, avoiding, this way, the inadvertent puncture of the intraorbital content through the infraorbital fissure.

Experienced anesthesiologists in anesthesia for maxillofacial surgery, perform bilateral ultrasound-guided blockade of the maxillary nerve by suprazygomatic route with ropivacaine for greater control of perioperative pain. These investigators avoid the use of a combination of LA for maxillary nerve block. The combination of several local anesthetics in the same nerve block is sometimes used in perioperative anesthesia with the intention of compensating the short duration of action of some agents whose start of action is fast, such as lidocaine, and the high latency of the agents that present a more lasting action, such as ropivacaine. The combination of lidocaine and ropivacaine offers clinical advantages (rapid onset, long duration). However, to date, indications for combining LA are scarce because of the use of catheters in many forms of regional anesthesia that allow to prolong the duration of the block. This is nevertheless not an extended practice among anesthesiologists in maxillofacial surgery. On the other hand, it is important to also remember avoiding the use of maximum doses of two LA combined, which is based on the erroneous belief that their toxicities are independent; on the contrary, the toxicities have an additive character.

Multiple drugs have been used to increase the time of action of LA, such as adrenaline, clonidine, dexamethasone, ketamine and dexmedetomidine, among others. To the study patients, adrenaline is always administered along with physiological serum by the surgeon at the local level to improve the surgical field, both in patients who undergo pre-incision infiltration and bilateral blockade of the maxillary nerve. The use of Clonidine is ruled out because it is not supplied in the hospital center where the investigators will carry out the study. The use of dexamethasone and ketamine is ruled out, because they will be administered intravenously in the patient's perioperative period as anti-inflammatory agents and anesthetic adjuvant, respectively. And the use of Dexmedetomidine is also ruled out in order to prolong the effect of the nerve blockade as this indication is not in the technical file.