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Year : 2016  |  Volume : 10  |  Issue : 2  |  Page : 184-188  

Efficacy of ultrasound-guided mandibular block in predicting safer anesthetic induction

Department of Anaesthesiology, Institute of Medical Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh, India

Date of Web Publication26-Apr-2016

Correspondence Address:
Gaurav Jain
Department of Anaesthesiology, Institute of Medical Sciences, Banaras Hindu University, Varanasi - 221 005, Uttar Pradesh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0259-1162.176406

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Background: Mandibular nerve block reverses the trismus caused by pain and muscle spasm, thereby allowing for selection of a safer intubation technique.
Aims: As ultrasonographic imaging has added newer dimensions to clinical anesthesia practice, we utilized this tool in performing mandibular nerve block and evaluated its efficacy in segregating trismus patients on etiological basis, to predict safer anesthetic induction.
Settings and Design: Prospective, randomized controlled, outcome assessor blinded trial.
Materials and Methods: Sixty-eight patients with unilateral mandibular fracture, acute pain, and trismus were randomized to receive mandibular nerve block by Vazirani-Akinosi approach (Group V) or the ultrasound-guided (USG) technique (Group U) before the general anesthetic induction for corrective surgery. Visual Analog Scale (VAS) score and inter-incisor distance was measured at intervals. Primary outcome measure was blocked failure (continued pain [VAS > 30] after the block procedure).
Statistical Analysis Used: Mann–Whitney U-test and Wilcoxon signed rank test.
Results: There was a significant decrease in pain score following the block procedure, except for six patients (block failure) in Group V. Inter-incisor distance increased to near-maximal levels after the nerve blockade, except for nine patients in Group V (including all block failures) and four in Group U having continued limited mouth opening. General anesthetic induction increased the inter-incisor gap in block failures (Group V) only.
Conclusion: USG mandibular block appears to relieve reversible trismus more reliably, thereby allowing for a precise decision on a safer intubation technique.

Keywords: Anesthesia induction, intubation, mandibular block, trismus, ultrasound

How to cite this article:
Jain G, Yadav G, Singh AP, Singh Y, Singh DK. Efficacy of ultrasound-guided mandibular block in predicting safer anesthetic induction. Anesth Essays Res 2016;10:184-8

How to cite this URL:
Jain G, Yadav G, Singh AP, Singh Y, Singh DK. Efficacy of ultrasound-guided mandibular block in predicting safer anesthetic induction. Anesth Essays Res [serial online] 2016 [cited 2020 Jul 2];10:184-8. Available from:

   Introduction Top

Trismus is defined as a limitation in mouth opening ability, due to reduced mandibular mobility resulting from a wide array of etiologies. It may be precipitated by reversible causes like pain and muscle spasm secondary to local inflammation, infection, and trauma, etc. or a consequence of irreversible causes such as neoplasm, fibrosis, and trauma.[1] This makes the airway access a difficult task for the anesthesiologist. Preoperative mandibular nerve block has been suggested to reproduce maximal possible mouth opening and thus, safer anesthetic induction in such patients, by alleviating the source of reversible trismus.[2] However, a documented failure rate of around 20% may preclude this conventional technique as an ideal approach for this purpose, especially in trauma patients where anatomical location of the nerve may be disturbed.[3],[4] Furthermore, the requirement of a larger volume of local anesthetic with this technique makes the patients prone to associated complications.

The use of ultrasound may help to target the mandibular nerve more reliably, thereby reducing the amount of local anesthetic required and decreasing the incidence of complications. Use of ultrasound-guided (USG) mandibular nerve block has been described in literature but current data is limited to case reports only.[5],[6] Thus, the purpose of this study is to access the relative efficacy of USG mandibular nerve block in predicting safe anesthetic induction in unilateral mandibular fracture patients presenting with acute pain and trismus.

   Materials and Methods Top

After institutional ethical approval and written informed consent, all patients belonging to American Society of Anesthesiologist physical Status I and II, aged 18–65 years, body mass index 25–30 kg/m 2, presenting as unilateral mandibular fracture with acute pain and trismus, in between July 2014 and December 2014, were included in this prospective, randomized controlled, outcome assessor blinded trial (registered in Indian clinical trial registry). Exclusion criteria included a requirement for rapid sequence induction, hemodynamic instability, absent incisors, end-organ dysfunction, pregnancy, psychiatric disorders, history of limited mouth opening, recent analgesic, sedative or muscle relaxant consumption, and any contraindication for mandibular nerve block.

Patients' characteristics, fracture side, inter-incisor distance, and pain score (using a 100-mm Visual Analog Scale [VAS]) were noted in neutral head position. Enrolled patients were randomly assigned to two equal groups by computer generated random numbers and concealed via sealed opaque envelope technique. Group V received mandibular nerve block via intra-oral Vazirani-Akinosi (VA) technique; Group U received above block via USG technique.

VA technique

With teeth occluded, lips were retracted. The needle and syringe were aligned parallel to the occlusal plane, at a level just superior to the maxillary molars. The needle penetrated the mucosa just medial to the ramus, and it was advanced to a depth of 2.5 cm. Now, a volume of 10 ml bupivacaine (0.5%) was injected on the affected site (i.e. where surgical intervention was planned) after negative aspiration.[2],[7]

Ultrasound-guided technique

A linear ultrasound probe (8–13 MHz [12 L-RS probe]; GE Healthcare LOGIQ e portable USG machine) was placed superior to the mandible in a transverse orientation on the same side of fracture site. The condyle of mandible was traced and anterior to the condyle; mandibular nerve was identified as an ovoid to round hyperechoic structure adjacent to the alveolar artery and vein [Figure 1]. A blunt tip needle (22-gauge, 5 cm length) was inserted superior to the probe using an out of plane technique and advanced until it is adjacent to the mandibular nerve. Now, 3 ml of 0.5% Bupivacaine was injected after negative aspiration. In case, the mandibular nerve was not visualized by this plane, a cardiac probe (2.8–4 MHz [3S RS probe]; GE Healthcare LOGIQ e portable USG machine) was chosen and placed in an oblique transverse position below the zygoma and anterior to the mandibular condyle. The lateral pterigoid plate was located, and posterior to the plate, the mandibular nerve was identified as a hyperechoic round to oval structure deep to maxillary and alveolar artery [Figure 2]. Now, a blunt tip needle (22-gauge, 5 cm length) was inserted posterior to the probe using an in-line technique. The needle was advanced until it is adjacent to the nerve and a volume of 3 ml bupivacaine (0.5%) was injected after negative aspiration.[5]
Figure 1: Linear transducer position and location of mandibular nerve, alveolar artery and vein

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Figure 2: Cardiac transducer position and location of mandibular artery and nerve

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After the procedure, inter-incisor distance and pain score were re-evaluated at 30 min, in both the groups. Patients with continued pain (VAS > 30) were regarded as “block failure” and any block or drug-related complications were noted. Now all patients were intubated as per ASA difficult airway algorithm, and general anesthesia (GA) was induced with propofol, fentanyl, and rocuronium. The mouth was then opened maximally, and inter-incisor distance was again measured, to reassess any further increase in above parameter after GA induction. Patients with continued limited mouth opening even after GA were regarded as “mechanical obstruction.” Data collection and monitoring were done by an investigator blinded to group allocation.

To detect a 20% difference in the block failures with an expected standard deviation of 25% estimated from initial pilot observations; power analysis, with α = 0.05, β = 0.20, show that we required to enroll 26 patients per group. Sample size was calculated with power and sample size calculator (Department of Biostatics, Vanderbilt University, USA).

Statistical analysis

Data were evaluated with Mann–Whitney U-test for unpaired variables and Wilcoxon signed rank test for paired variables, using SPSS for Windows: Version 16 (SPSS Inc., Chicago IL, USA). P < 0.05 was considered as significant.

   Results Top

The admission rate for mandibular fracture in our hospital is about 20–25 per month. All such patients admitted during the study period were screened for eligibility, with the target to include at least 26 patients per group. Of 126 patients screened for our study during the study duration, 68 patients meeting the inclusion and exclusion criteria were initially randomized into two study groups. Four patients were later excluded: In two patients, mandibular nerve could not be identified by ultrasonography (Group U), in other two patients there was hemorrhagic tap during the procedure (Group V). Thus, 64 patients (32 in each group) completed the study successfully [Figure 3].
Figure 3: Flow chart of patients studied

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Baseline demographics, ASA grade, inter-incisor distance, and VAS scores were similar among both the groups [Table 1]. There was a significant reduction in VAS score after performing nerve block in both groups (P < 0.001), except for six patients (block failures) in Group V [Table 1]. Postblock inter-incisor distance increased significantly (P < 0.001) in both groups, except for nine patients in Group V (including six block failures) and four in Group U. After GA induction, there was a significant increase in inter-incisor distance in block failures (six patients in Group V), but remaining 7 patients (3 in Group V, 4 in Group U) continued to have limited mouth opening (mechanical obstructions). The difference between postblock and postinduction inter-incisor measurements was not significant for all other patients in both groups [Table 2]. No major side effects were observed, except for itching of upper lips and ipsilateral lower eyelid (8 patients in Group V) which subsided rapidly, and did not require any intervention.
Table 1: Comparison of baseline and other measured variables among the groups (n=32)

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Table 2: Comparison of various measured variables within the groups

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   Discussion Top

Several researchers have evaluated the anesthetic efficacy of various approaches for mandibular nerve block in surgical procedures related to dentistry. Previous studies on VA technique have documented an anesthetic failure rate of about 20% with this procedure.[3],[4] However, Heard et al. reported successful nerve blockade in all six patients of the similar subset as of our study; a strong emphasis could not be laid upon such results, as it was not a suitably powered trial having a small sample size.[2] We observed significantly decreased postblock VAS scores with both the techniques, except for six block failures following the VA procedure, where patients had continued pain and limited mouth opening. Inter-incisor distance increased significantly in these patients after GA induction. Here, inter-individual anatomical variations, swelling and inflammation or blind needle placement technique, all or any of them could have contributed to displaced position of mandibular nerve leading to block failure with VA approach. Seven patients (3 with VA and 4 with USG technique) where the cause of trismus was possibly mechanical (due to trauma, swelling, or other risk factors), inter-incisor distance remained limited even after GA induction. For all other patients, the increase in inter-incisor distance after nerve blockade was nearly maximal and the postinduction inter-incisor distance did not changed significantly from the postblock values in both the compared techniques.

Reversal of trismus was likely due to pain relief and muscle relaxation in the mandibular nerve supply area, after the block procedure. Increased mouth opening then allowed the attending anesthesiologist to carry out crucial airway assessment for other predictors of the difficult airway, and direct laryngoscopy-guided endotracheal intubation was performed in majority of patients, where airway was otherwise normal. While USG technique allowed us to precisely segregate all the patients who genuinely required awake fibreoptic intubation; in VA technique a safer strategy for airway management of 6 block failures could not be predicted.

Previous trials have used 1.5–2.0 ml of local anesthetic in VA approach for performing various dental procedures.[8],[9],[10] Potocnik and Bajrovic observed that even if there is no procedural flaw, inflammation could increase the mandibular block failure rate to 45% with routine local anesthetic volume.[4],[11] Data on trismus is relatively scarce and limited to case reports only; with stated volume usage varying from 5 to 10 ml.[2],[12],[13] As the extent of inflammation and swelling is expected to be higher in trauma patients, we preferred maximally effective, safer drug volume (10 ml) documented for VA technique. We, however, acknowledge that a dose–response study could provide better insight into ideal choice of local anesthetic and its optimal dose or concentration for performing VA procedure in trismus patients. Data on USG technique are altogether uniform, so we utilized similar methodology and drug volume (3 ml) in this group.[5],[6]

Block related complication included hemorrhagic tap in two patients while performing VA technique. Above procedure was abandoned in these patients, and further management included close observation followed by awake fibreoptic intubation with no other sequel. Drug-related adverse effects included itching in upper lips and lower eyelid (25% patients) by VA technique. Previous studies have observed this side effect in 8% patients while other complications were reported rarely.[9],[10],[14] Higher incidence in our study could be attributed to larger local anesthetic volume (10 ml) injected via VA technique, which led to greater drug distribution toward the affected area, precipitating as paresis of the infraorbital nerve. No such deleterious effects were observed in any patient where USG nerve block was performed in our study. Ultrasound guidance allowed us to precisely target the mandibular nerve and reduced the dose of local anesthetic needed for nerve blockade, thereby diminishing any chance of complications related to tissue injury or drug insufflations to adjacent structures.

The limitations of our study include a relatively small sample size in proportion to the burden of problem. Our results may vary from studies done on other ethnic groups owing to variations in jaw texture, and subjective anesthetic sensitivity. Further trails could investigate the utility of mandibular nerve block in trismus patients with multiple facial fractures.

We conclude that USG mandibular nerve block can effectively predict safer anesthetic induction in patients presenting with acute trismus. It helped in segregating patients on the basis of postblock results and decision on a safer airway management procedure was then attained precisely, by assessing other predictors of a difficult airway.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

   References Top

Dhanrajani PJ, Jonaidel O. Trismus: Aetiology, differential diagnosis and treatment. Dent Update 2002;29:88-92, 94.  Back to cited text no. 1
Heard AM, Green RJ, Lacquiere DA, Sillifant P. The use of mandibular nerve block to predict safe anaesthetic induction in patients with acute trismus. Anaesthesia 2009;64:1196-8.  Back to cited text no. 2
Malamed SF. Techniques of mandibular anesthesia. In: Handbook of Local Anesthesia. 6th ed. Missouri, USA: Mosby; 2014. p. 225-40.  Back to cited text no. 3
Yadav P, Kumar VR. Evaluation of local anaesthetic failures in dental practice. J Int Oral Health 2010;2:16-21.  Back to cited text no. 4
Bigeleisen PE. Ultrasound-guided maxillary and mandibular block. In: Ultrasound Guided Regional Anesthesia and Pain Medicine. 1st ed. Philadelphia, USA: Lippincott Williams and Wilkins; 2012. p. 217-9.  Back to cited text no. 5
Krishna S, Anis S. Case report of ultrasound-guided mandibular N blockade. Int J Perioper Ultrasound Appl Technol 2012;1:45-6.  Back to cited text no. 6
Haas DA. Alternative mandibular nerve block techniques: A review of the Gow-Gates and Akinosi-Vazirani closed-mouth mandibular nerve block techniques. J Am Dent Assoc 2011;142 Suppl 3:8S-12S.  Back to cited text no. 7
Lenka S, Jain N, Mohanty R, Singh DK, Gulati M. A clinical comparison of three techniques of mandibular local anaesthesia. Adv Hum Biol 2014;4:13-9.  Back to cited text no. 8
Martínez González JM, Benito Peña B, Fernández Cáliz F, San Hipólito Marín L, Peñarrocha Diago M. A comparative study of direct mandibular nerve block and the Akinosi technique. Med Oral 2003;8:143-9.  Back to cited text no. 9
Mishra S, Tripathy R, Sabhlok S, Panda PK, Patnaik S. Comparative analysis between direct conventional mandibular nerve block and Vazirani-Akinosi closed mouth mandibular nerve block technique. Int J Adv Res Technol 2012;1:1-6.  Back to cited text no. 10
Potocnik I, Bajrovic F. Failure of inferior alveolar nerve block in endodontics. Endod Dent Traumatol 1999;15:247-51.  Back to cited text no. 11
Meaudre E, Pernod G, Gaillard PE, Kaiser E, Cantais E, Ripart J, et al. Mandibular nerve blocks for the removal of dentures during trismus caused by tetanus. Anesth Analg 2005;101:282-3.  Back to cited text no. 12
Takemura H, Masuda Y, Yatsushiro R, Yamamoto N, Hosoyamada A. Mandibular nerve block treatment for trismus associated with hypoxic-ischemic encephalopathy. Reg Anesth Pain Med 2002;27:313-5.  Back to cited text no. 13
Donkor P, Wong J, Punnia-Moorthy A. An evaluation of the closed mouth mandibular block technique. Int J Oral Maxillofac Surg 1990;19:216-9.  Back to cited text no. 14


  [Figure 1], [Figure 2], [Figure 3]

  [Table 1], [Table 2]

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