Needle tip position influences bupivacaine concentration within the pterygopalatine fossa during suprazygomatic maxillary nerve block: a cadaveric study

PURPOSE: The primary objective was to evaluate the influence of needle tip positioning during suprazygomatic maxillary nerve block on bupivacaine concentration within the pterygopalatine fossa (PPF). The secondary objective was to correlate early injectate spread on computed tomography (CT) with PPF bupivacaine concentrations. METHODS: Suprazygomatic maxillary nerve block attempts (n=34) were performed on 17 human cadaveric heads with different needle tip positions. Each attempt involved injection of 5 mL containing 0.4% bupivacaine, iohexol, and methylene blue. Computed tomography was used to determine needle tip location and early injectate spread. PPF samples were harvested via a transmaxillary approach for bupivacaine quantification by liquid chromatography-tandem mass spectrometry. RESULTS: The highest median [Q1-Q3] bupivacaine concentrations were observed when needle tip was positioned within pterygomaxillary fissure or PPF, with 829.3 [728.1-1015.7] µg/g, and when positioned directly against maxillary tuberosity, with 535.3 [355.7-820.7] µg/g. Concentrations were highly variable with off-bone infratemporal placements (range, 0.1-335.8 µg/g). Lateral needle displacement was associated with lower bupivacaine concentrations (β=-0.193, 95% CI -0.301 to -0.086; P<0.001), whereas anterior (β=0.107, 95% CI 0.018-0.196; P=0.020) and cranial displacement (β=0.079, 95% CI 0.017-0.141; P=0.014) were associated with higher concentrations. CT contrast spread between temporalis and lateral pterygoid muscles was not associated with higher PPF bupivacaine concentrations (P=0.117). CONCLUSION: Needle tip position influenced bupivacaine concentration within PPF, with concentrations generally increasing as the needle approached PPF and with more anterior positioning, including placement at the maxillary tuberosity. More superficial or posterior infratemporal placements yielded lower and more variable concentrations. Moreover, infratemporal contrast spread on early CT imaging was not associated with higher PPF bupivacaine concentrations.