EQUINE VETERINARY EDUCATION / AE / MAY 2015
275
Critically Appraised Topic Which nerve blocks will help me with a tooth extraction?
N. du Toit Tulbagh Equine Dentistry, Tulbagh, South Africa. Corresponding author email:
nixdutoit@hotmail.com
Clinical scenarios and question refinement
With the advent of modern sedatives and analgesics, there has been an increase in the number of surgical procedures that can be performed in the standing horse. The use of regional anaesthesia is essential to decrease the pain perception and facilitate these procedures, including dental extractions. The use of an inferior alveolar (mandibular) nerve block and maxillary nerve block to perform mandibular and maxillary cheek teeth extractions in horses has been well described in the literature (Tremaine 2007). There is the potential for complications with dental nerve blocks such as arteriopuncture, neuropraxia, cellulitis and inadvertent anaesthesia of the lingual nerve (Caldwell and Easley 2011). More than one technique has been described for each of these blocks. When choosing which technique to use for the maxillary and mandibular nerve blocks it is important to know firstly, which techniques are more accurate and which techniques have less complications/side effects.
Search strategy
A literature search using PubMed and Google Scholar was conducted of studies relating to equine maxillary and mandibular nerve blocks or dental local anaesthesia.
Quantity of evidence
There were 2 papers describing and/or comparing different techniques for the maxillary nerve block and mandibular nerve block each.
Quality of evidence
Maxillary nerve block The papers examining the methods for maxillary nerve blocks used cadavers (Staszyk et al. 2008; Bardell et al. 2010), with only 2 live horses used in the study by Staszyk et al. (2008). Bardell et al. (2010) used the technique inserting the needle ventral to the zygomatic arch, and compared an angled method to a perpendicular method. Methylene blue dye was used in cadaver heads, which were dissected to determine the correct location of dye deposition. There was no significant difference in the 2 methods with complete and partial nerve contact in about 80% of the blocks performed. Staszyk et al. (2008) used the same perpendicular method,
but varied the depth of the needle insertion; deeper penetration up to contacting bone (Palatine Bone Insertion: PBI) compared to injecting into the extraperiorbital fat body (EFBI). Contrast medium was injected into 5 cadaver heads and 2 live horses, and the local distribution of the contrast medium was assessed using computed axial tomography (CAT). The PBI technique was performed 9 times and the EFBI only 4 times. Both methods were shown to be effective at
achieving distribution of the contrast medium to the maxillary nerve. However, due to the anatomical location of the structures in the pterygopalatine fossa, the PBI technique did pose a greater risk for inadvertent needle puncture of the infraorbital artery, descending palatine artery and deep facial vein.
Mandibular nerve block The first study assessing the inferior alveolar nerve block used 11 cadaver heads to compare an angled to a perpendicular method (Harding et al. 2012). Each block was performed 22 times using coloured dyes and a full hit was achieved 73% of the time with the angled approach compared to 59% with the perpendicular approach. However, there was no statistically significant difference. This study also radiographically assessed the topographical markers used to determine the location of the mandibular foramen and found this to be relatively accurate with no significant difference in the methods. The study by Henry et al. (2014) assessed the accuracy of
an intra-oral approach to anaesthetising the inferior alveolar nerve. Twenty-six skulls were measured to determine the correct anatomical location and 4 cadaver heads were used to perform the nerve block, which was assessed by CAT. The block was then performed in 43 live cases having procedures done requiring anaesthesia of the mandibular quadrant. This was shown to be a successful technique and it was believed that this would reduce the potential complication of anaesthetising the lingual nerve.
Can this evidence be applied in my case scenario/clinical scenario?
These studies have demonstrated that techniques described for performing dental nerve blocks in horses are relatively accurate. Although, there was no difference in the accuracy of the maxillary nerve block techniques, the study by Staszyk et al. (2008) did demonstrate that the EFBI technique had reduced the risk of potential complications. Based on the paper by Harding et al. (2012) it would appear that the mandibular nerve blocks are accurate in about 80% of cases. The more recent paper by Bardell et al. (2010) described a new intraoral approach with successful anaesthesia of the nerve in live patients following the intraoral nerve block, but the assessment of successful nerve block was subjective.
Clinical message and primary data sources
There appears to be no significant difference in the techniques used to perform dental nerve blocks and, if the correct topographical landmarks are identified, dental nerve blocks in horses can be performed successfully.
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