Continuous Infusion Pressure Measurement in Predefined Interfascial and Intramuscular Tissue Conditions: An Ex Vivo Pilot Study

Background: Perineural catheter migration is a clinically relevant cause of continuous block failure, but the present study was not designed to model true clinical displacement. Instead, we investigated whether low-rate infusion pressure differs between two predefined catheter–tissue environments, interfascial and intramuscular, under controlled ex vivo conditions. Methods: Sixty porcine thigh specimens were studied. Under ultrasound guidance, a catheter-over-needle system with a multi-orifice catheter was placed either in the interfascial plane or intramuscularly, with one measurement obtained from each specimen. After baseline recording outside the tissue, saline was infused at 5 mL/h for 10 min. Pressure recordings were normalized to baseline. For each trace, a representative value was obtained using a predefined automated stable-segment algorithm, and between-group differences were assessed using Welch’s t-test. Results: Mean normalized pressure was higher during intramuscular than interfascial infusion (0.3346 ± 0.0635 PSI [17.3 ± 3.3 mmHg] vs. 0.1917 ± 0.0285 PSI [9.9 ± 1.5 mmHg]). The between-group difference was significant (mean difference: 0.1430 PSI [7.4 mmHg], 95% CI: 0.1181 to 0.1679 PSI; p = 7.22 × 10−15), with a very large standardized effect size (Hedges’ g = 2.87), reflecting strong statistical separation between the two predefined groups under controlled ex vivo conditions rather than clinical discriminative ability. However, the absolute pressure difference remained small. Conclusions: Under controlled ex vivo conditions, mean normalized infusion pressure differed between predefined interfascial and intramuscular catheter positions. However, the absolute difference was small. This binary model does not represent real catheter displacement, and the findings do not support current clinical applicability, individual-level interpretation, or the definition of a clinically usable threshold. The results should be considered exploratory and hypothesis-generating.