Cutaneous Sensory Block Area, Muscle-Relaxing Effect, and Block Duration of the Transversus Abdominis Plane Block: A Randomized, Blinded, and Placebo-Controlled Study in Healthy Volunteers.
OBJECTIVE
The transversus abdominis plane (TAP) block is a widely used nerve block. However, basic block characteristics are poorly described. The purpose of this study was to assess the cutaneous sensory block area, muscle-relaxing effect, and block duration.


METHODS
Sixteen healthy volunteers were randomized to receive an ultrasound-guided unilateral TAP block with 20 mL 7.5 mg/mL ropivacaine and placebo on the contralateral side. Measurements were performed at baseline and 90 minutes after performing the block. Cutaneous sensory block area was mapped and separated into a medial and lateral part by a vertical line through the anterior superior iliac spine. We measured muscle thickness of the 3 lateral abdominal muscle layers with ultrasound in the relaxed state and during maximal voluntary muscle contraction. The volunteers reported the duration of the sensory block and the abdominal muscle-relaxing effect.


RESULTS
The lateral part of the cutaneous sensory block area was a median of 266 cm2 (interquartile range, 191-310 cm2) and the medial part 76 cm 2(interquartile range, 54-127 cm2). In all the volunteers, lateral wall muscle thickness decreased significantly by 9.2 mm (6.9-15.7 mm) during a maximal contraction. Sensory block and muscle-relaxing effect duration were 570 minutes (512-716 minutes) and 609 minutes (490-724 minutes), respectively.


CONCLUSIONS
Cutaneous sensory block area of the TAP block is predominantly located lateral to a vertical line through the anterior superior iliac spine. The distribution is nondermatomal and does not cross the midline. The muscle-relaxing effect is significant and consistent. The block duration is approximately 10 hours with large variation.
From the Department of Anaesthesiology, Nordsjællands Hospital, University of Copenhagen, Copenhagen, Denmark.
Kion
K
Støving
Christian
C
Rothe
Charlotte V
CV
Rosenstock
Eske K
EK
Aasvang
Lars H
LH
Lundstrøm
Kai H W
KH
Lange
D000009:Abdominal Muscles / Q000000981:diagnostic imaging / Q000294:innervation*; D000328:Adult; D000577:Amides / Q000008:administration & dosage* / Q000009:adverse effects; D000779:Anesthetics, Local / Q000008:administration & dosage* / Q000009:adverse effects; D003718:Denmark; D004311:Double-Blind Method; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects*; D009407:Nerve Block / Q000009:adverse effects / Q000379:methods*; D017288:Pain Threshold / Q000187:drug effects*; D000077212:Ropivacaine; D012867:Skin / Q000294:innervation*; D013997:Time Factors; D016896:Treatment Outcome; D018084:Ultrasonography, Interventional; D055815:Young Adult
D000577:Amides; D000779:Anesthetics, Local; D000077212:Ropivacaine