Effects of Ultrasound-guided Maxillary Nerve Block Performed After Bimaxillary Osteotomy in Adult Patients

Bimaxillary osteotomy is a surgical procedure in the field of orthognathic surgery (from Latin; "orthos" rectum and "gnathos" mandible) for the correction of dentofacial deformities, both for functional and aesthetic reasons. The incidence of this deformity is estimated to be in the order of 5-10% of the population; and its origin is still unknown, and genetic, environmental and embryonic factors are postulated. The surgical technique is complex, with the performance of mandibular and upper jaw osteotomies that allow these bones to be advanced, retracted, impacted and rotated, 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, it is said that bimaxillary osteotomy is a frequent and potentially painful surgery in adults. Bimaxillary surgery under general anesthesia is common practice. And isolated non-ultrasound-guided peripheral nerve blocks and surgical field infiltration are widely used practices by surgeons. These minor blockages and infiltrations are used to avoid the unwanted effects of anesthetics and analgesics; particularly the adverse respiratory effects of opioids. The practice of loco-regional anesthesia therefore provides perioperative pain control in a multimodal way, showing effective postoperative analgesia and minimizing respiratory depression due to excessive use of opioids.

The introduction of loco-regional nerve blocks in the last three decades has meant a revolution in the management and control of perioperative pain for the anesthesiologist. The expansion of the practice of loco-regional nerve blocks has been seen in both the upper and lower limbs, as well as the trunk and abdomen. Conversely, facial blocks, superficial and deep, have not experienced the same; relegating its practice to the surgeon, or to the anesthesiologist who works in the field of chronic pain. The subsequent introduction of ultrasonography (USG) in the 1990s in the perioperative period was also an important advance for the anesthesiologist, both in terms of safety and in terms of ease of handling catheterizations of the venous and arterial lines, and the practice of loco-regional blocks.

Consequently, anesthesiologists already experienced at the USG have recently published on the use of ultrasound (US) for facial nerve block in children and adults undergoing maxillofacial surgery. USG devices are becoming more accessible, more portable, cheaper, and more secure; And therefore, its introduction in the field of perioperative pain management of maxillofacial surgery still has a long way to go.

The maxillary nerve, like the ophthalmic nerve, is only sensory. It is detached from the anterolateral border of the trigeminal ganglion, laterally to the ophthalmic. From its origin, it heads anteriorly, traverses the foramen round, and penetrates the background of the infratemporal fossa until it enters the pterygopalatine fossa (except for the middle meningeal nerve, all its branches reach the pterygopalatine fossa before reaching the facies). In the pterygopalatine fossa, the maxillary nerve is located at the top of the cavity and passes superiorly to the maxillary artery and superolaterally to the pterygopalatine ganglion. The maxillary nerve receives and conducts through its endings the sensitivity of the skin of the cheek, lower eyelid, wing of the nose and upper lip. Its deep branches conduct the sensitivity of the mucosa of the lower part of the nasal cavities or respiratory area, of the tooth roots and of the gums of the maxilla.

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

To carry out the maxillary nerve block, several approaches have been described. However, placing the ultrasound probe in an infrazygomatic position, and introducing the needle suprazygomaticly from the frontozygomatic angle is one of the safest and most recommended routes to reach the round foramen. This trajectory limits the insertion of the needle into the anterior portion of the foramen round, thus preventing inadvertent puncture of the intraorbital contents through the infraorbital fissure.

In general, in bimaxillary surgery it is the surgeon who performs the infiltrations with local anesthetic (AL) in a pre-incisional way to block the terminal branches of the maxillary nerve intraorally and intranasally. The choice of LA is influenced by considerations such as onset of action, duration, and toxicity. A wide range of LA have been used in maxillofacial surgery, such as lidocaine and bupivacaine, among others. The two LAs produce a reversible blockade of the sodium channel of the neuronal membrane, and are synthetic derivatives of cocaine. Both have three essential functional units (hydrophilic tertiary amide chain, linked by an intermediate amide chain to another lipophilic aromatic ring-portion). That is, they are both AL of the amide type; but even though they belong to the same group of LA, there are great differences in terms of initiation of action, duration of action and toxicity. Lidocaine has a faster onset of action (short latency) than bupivacaine, and has an antiarrhythmic effect. Bupivacaine is more potent and has a longer duration of action than lidocaine, although more cardiotoxic than other AL teams such as ropivacaine.

To date, the gold standard anesthetic technique has not been described, nor is the ideal time to perform it in patients who have undergone bimaxillary osteotomy surgery. The investigators now propose the performance of bilateral maxillary nerve block ultrasounded by suprazygomatic route with bupivacaine after bimaxillary osteotomy surgery for greater control of postoperative pain. In this way, the researchers aim to maintain the pre-incisional infiltration of LA with lidocaine plus bupivacaine and adrenaline in the surgical field performed by the surgeon with its well-known benefits and to perform the ultrasound-guided block of the maxillary nerve with bupivacaine after surgery, before extubation to prolong its effect even more in the immediate postoperative period.

The investigators use a combination of LA (lidocaine and bupivacaine) for pre-incisional infiltration of the surgical field. The combination of several local anesthetics in the same nerve block is sometimes used in perioperative anesthesia with the intention of compensating for the short duration of action of some agents with a rapid onset of action, such as lidocaine, and the high latency of agents with a longer action, such as bupivacaine. The combination of lidocaine and bupivacaine offers clinical advantages (rapid onset, long duration). This is a widespread practice among professionals in maxillofacial surgery. It is also a way to avoid the use of maximum doses of these LAs.

By performing the bilateral ultrasound-guided maxillary nerve block with bupivacaine after the surgical incision, the researchers were able to extend the effect of the nerve block for greater control of postoperative pain. Postoperative pain control is a key factor in achieving greater patient satisfaction, better rehabilitation and shorter hospital stays. Current clinical guidelines recommend the management of postoperative pain control in a multimodal manner; and this includes the use of LA for infiltration of the surgical field and the performance of peripheral nerve blocks.

To date, studies describing maxillary nerve block prior to surgeries of the middle third of the face (orthognathic surgery, cleft palate, trauma) have been described; However, there are no studies of the practice of maxillary nerve block at the end of surgery, prior to extubation. If the investigators assume that the patient receives general anesthesia (with their respective analgesics in the form of opioids, anti-inflammatories, paracetamol and other adjuvants) together with the infiltration of LA from the surgical field before starting surgery, and that this implies sufficient intraoperative analgesic coverage, the investigators propose with this study that anesthesiologists could postpone the maxillary nerve block at the end of surgery. for a greater long-term benefit of the patient in the immediate postoperative period.