Effect of Medial vs Traditional Approach to US-guided Transverse Abdominis Plane (TAP) Blocks on Analgesia After Open Inguinal Hernia Repair

This study is a prospective, open, randomized trial. Subjects will be randomized using a computer-generated table of random numbers into 2 groups to receive pre-incisional ipsilateral ultrasound-guided TAP block using classic or medial approach. Group assignments will be sealed in sequentially numbered, opaque envelopes that would be opened by an anesthesiologist performing the block. The research nurse, not involved with patient care after the subject signed written informed consent, will provide postoperative data collection. Study subjects and other anesthesia care providers will also be blinded to group allocation.

All patients will be premedicated with 1-2mg IV midazolam and 50-150 mcg IV fentanyl. In the OR, propofol infusion will be started at 75mcg/kg/hr and titrated for patient comfort. After patient is adequately sedated, ultrasound guided TAP block will be performed in all subjects using a linear 6-15MHz ultrasound probe on a portable ultrasound machine (SonoSite, Bothell, WA). Classic approach group will receive a TAP block as previously described (Hebbard P, 2007). For the medial approach, once the external oblique abdominal, the internal oblique abdominal, and the transversus abdominal muscles were visualized using the ultrasound transducer between the costal margin and the iliac crest at the level of the anterior axillary line (classic approach), the transducer would be moved medially to the point where internal oblique muscle disappears. The injection target area will be within 1 inch lateral to that point.

The place of needle insertion will be prepped with Chlorhexidine gluconate 2% antiseptic solution, and 21G 90-mm StimuQuik needle (Arrow International, Reading, PA) will be used to inject 20ml of Ropivacaine 0.5% in the proper place once it is identified. Each subject will receive local infiltration with 20ml of Lidocaine1% : Bupivacaine 0.25% 1:1 mix prior to the incision by the surgeon as well as 1000 mg of IV acetaminophen and 8 mg IV dexamethasone intraoperatively.

In the postanesthesia care unit (PACU), the patient will be asked to rate their pain at rest upon arrival and at regular intervals on a 0 to 10 numeric rating scale (NRS), where 0 means no pain and 10 is the worst pain imaginable. Hydromorphone 0.5 mg IV will be administered every 5 minutes to maintain an NRS pain score <4 of 10. In cases of postoperative nausea or vomiting, subjects will receive 4mg IV ondansetron, followed by 12.5 mg IV Diphenhydramine if necessary. The Aldrete Recovery Score will be used to transfer the patients from Phase I of recovery, which focuses on providing a transition from a totally anesthetized state to one requiring less intervention. Aldrete Scoring System assesses respiration, oxygen saturation, consciousness, circulation and activity. Each item is scored on a 0 to 2 scale with higher score representing more advanced recovery. Once the score of 9 or higher is reached, the subjects will be transferred to Phase II recovery, which focuses on preparing the patient for dicharge. At discharge, subjects will be instructed to take a combination of oxycodone 5mg and acetaminophen 325mg orally every 4-6 hours for NRS pain score>4 of 10. Postoperative opioid consumption for the 48 hours will be converted to an equivalent dose of oral hydromorphone.

Subjects will be contacted by telephone by a research nurse or one of the investigators not involved in their care, and will be asked about their pain and amount of pain medication they consumed since discharge or since the last phone call respectively. In case of a potential problem, the matter will be referred to a physician.