title: Lumbar transversus abdominis plane block: the role of local anesthetic volume and concentration-a pilot, prospective, randomized, controlled trial.
abstract: BACKGROUND
  The lumbar transversus abdominis plane (TAP) block has become an optional part of multimodal analgesia following several abdominal surgeries. There remains a lack of consensus regarding the extent of dermatomal blockade following lumber TAP block, as well as the optimal local anesthetic volumes and concentrations. The objectives of this pilot trial were to assess the feasibility of conducting a similar full-scale trial and gather information on relevant clinical outcomes, namely whether greater local anesthetic volumes would lead to more cephalad dermatomal blockade.
  
  
  METHODS
  The study was a prospective, double-blinded pilot randomized controlled trial (RCT) with three arms, each representing different local anesthetic volumes: 20 ml 0.5% ropivacaine, 30 ml 0.33% ropivacaine, and 40 ml 0.25% ropivacaine. We planned to recruit 30 females undergoing total abdominal hysterectomy for non-malignant pathology, who would then receive bilateral ultrasound-guided midaxillary TAP blocks at the completion of surgery. Randomized patients would be followed for 48 h post-block and would receive multimodal analgesia. The primary outcomes were measurements of patient recruitment and safety, to inform the feasibility of a larger trial. The main secondary outcome was the clinically pertinent endpoint of dermatomal blockade, which was assessed by loss of sensation to ice and pinprick.
  
  
  RESULTS
  Our target sample size was reached in 8 months, and the recruitment rate was 52% (31/60). A total of 58 TAP blocks were performed among 29 patients. All but one of the patients who received interventions were successfully followed and assessed up to 48 h. No patient safety-related adverse events were reported during the study period. The mean highest dermatome blocked in each group at any time point was T8. The 20 ml 0.5% ropivacaine group achieved a T9-L1 block that lasted for 48 h. The 30 ml 0.33% ropivacaine group had a sensory block from T9-L1 that regressed to T10-T12 between 24 and 48 h. The 40 ml 0.25% ropivacaine group reported an initial sensory block from T9-T12 that regressed by 24 h to include only the T12 dermatome.
  
  
  CONCLUSIONS
  This pilot study demonstrated that the study design is feasible and safe to be carried to a full-scale RCT. The preliminary clinical findings showed that increasing the volume, while maintaining a constant dose, of local anesthetic does not appear to extend the height of dermatomal blockade following midaxillary TAP block. This finding needs to be confirmed in future studies.
  
  
  BACKGROUND
  ClinicalTrials.gov registration is: NCT01307215.
authors.affiliation: Department of Anesthesia, St. Joseph's Healthcare Hamilton, McMaster University, 50 Charlton Avenue E, Hamilton, L8N 4A6 Ontario Canada.
authors.forename: Mauricio
authors.initials: M
authors.lastname: Forero
authors.affiliation: Department of Anesthesia, MUMC-2V9, McMaster University, 1280 Main Street West, Hamilton, L8S 4 K1 Ontario Canada.
authors.forename: Andrew
authors.initials: A
authors.lastname: Heikkila
authors.affiliation: Department of Anesthesia, MUMC-2V9, Hamilton Health Sciences Corporation, McMaster University, 1280 Main Street West, Hamilton, L8S 4 L1 Ontario Canada.
authors.forename: James E
authors.initials: JE
authors.lastname: Paul
authors.affiliation: Biostatistics/FORSC, St. Joseph's Healthcare Hamilton, McMaster University, Martha Wing - 3rd Floor, H325, 50 Charlton Ave. E., Hamilton, L8N 4A6 Ontario Canada.
authors.forename: Ji
authors.initials: J
authors.lastname: Cheng
authors.affiliation: Biostatistics/FORSC, Clinical Epidemiology and Biostatistics, St. Joseph's Healthcare Hamilton, McMaster University, Martha Wing - 3rd Floor, H325, 50 Charlton Ave. E., Hamilton, L8N 4A6 Ontario Canada.
authors.forename: Lehana
authors.initials: L
authors.lastname: Thabane
keywords: Dermatomal blockade; Perioperative pain management; Regional anesthesia; Transversus abdominis plane block