Continuous Needle Tip Injection Pressure During Hydrodissection in Four Fascial Plane Blocks: A Fresh Human Cadaver Study

Background/Objectives: Continuous injection-pressure monitoring may provide quantitative insight into fascial plane hydrodissection, but comparative data remain limited. This study compared baseline-corrected mean pressure and linear pressure trends during PECS I block (interpectoral plane block) versus superficial parasternal intercostal plane (SPIP) block and rectus sheath block (RSB) versus transversus abdominis plane block (TAPB). Methods: Each ultrasound-guided technique was performed once in 10 fresh, unfrozen human cadavers. Saline was infused at 10 mL/min, and pressure was recorded continuously. A deterministic signal-processing algorithm estimated the onset of the post-puncture pressure plateau; the subsequent 40 s segment was analysed after subtraction of the pre-insertion baseline. Paired t-tests were used, with exact sign-flip permutation tests as sensitivity analyses and with Holm adjustment for multiplicity. Results: Mean pressure was 4.99 psi for PECS I and 5.09 psi for SPIP, with no significant difference between techniques (mean paired difference, 0.09 psi; 95% confidence interval [CI], −0.67 to 0.85; p = 0.790). TAPB showed a higher mean pressure than RSB (5.50 versus 4.47 psi, respectively; mean paired difference, 1.03 psi; 95% CI, 0.36 to 1.69; p = 0.0134; paired effect size, d = 1.11). Permutation analyses were concordant. Linear pressure trends did not differ for SPIP versus PECS I (p = 0.484) or TAPB versus RSB (p = 0.742). Conclusions: Continuous pressure monitoring was used to characterize the hydrodissection pressure of four fascial plane block techniques. PECS I and SPIP yielded closely aligned mean values, whereas TAPB was associated with higher pressure than RSB. These findings provide quantitative reference data and support further clinical evaluation of continuous injection-pressure monitoring.