Background and Goal of the Study
The transversus abdominis plane (TAP) block is a technique used for analgesia after abdominal surgery in adults. However, data on optimal injected dose regimen and volume are limited.
The goal: to evaluate the character of dye spread in TAP, according to the volume injected.
Materials and Methods
Research Ethics Committee approval for the study protocol was obtained.
The study was conducted on 15 fresh, unembalmed adult cadavers. Only subjects that cause of death was other than abdominal pathology were enrolled. Written informed consent was obtained from first-degree relatives or legal representatives of all subjects for dye injection and autopsy.
Cadavers were divided into three groups (5 per group), according to the amount of dye injected (10, 20 or 40 mL). Bilateral USG guided injections were performed. Injection point was in the mid axillary line in the space between costal margin and iliac crest.
After the dissection of the cadaver, the spread of the dye was assessed on both abdominal wall sides. The end points were the maximum length of dye spread in cephalo-caudal and medial-lateral direction. Statistics: one way ANOVA with Duncan posttest. Data are presented as mean and (95% CI).
Results
All 15 cadavers were examined bilaterally (30 samples, 10 per group). There were no issues in USG location of TAP. The dye was present in all samples. 
Cephalo-caudal length of spread:
for (A) 40 mL – 12.8 (11.7 to 13.9) cm; 
for (B) 20 mL – 11.8 (10.5 to 13.0) cm;
for (C) 10 mL – 6.2 (5.5 to 6.8) cm.
(A vs. B: p=0.109; A vs. C: p=0.00006; B vs. C: p=0.00014).
Medio-lateral length of spread:
for (D) 40 mL – 9.6 (8.1 to 10.9) cm; 
for (E) 20 mL – 10.2 (8.9 to 11.5) cm; 
for (F) 10 mL – 5.8 (5.1 to 6.4) cm. 
(D vs. E: p=0.38; D vs. F: p=0.00015; E vs. F: p=0.000065).
Conclusion
There were no differences in the maximum length of cephalo-caudal and medio-lateral spread of the dye in the transversus abdominal plane after injection of a volume of 40 mL and 20 mL, but there were significant differences after a 10 mL injection.

Spread of dye after single injection of transversus abdominis plane in adults: a cadaveric study