A study to compare the post operative analgesia and ease of performance following the surgical repair of inguinal hernias and orchidopexy in children

Ultrasound guided transversus abdominis block Once general anaesthesia has been established the primary investigator, or consultant anaesthetist experienced in ultrasound-guided regional anaesthesia in children, will perform the transversus abdominis nerve block. A Micromaxx ultrasound machine with either a hockey stick or high frequency linear (HFL) probe will be used to identify the relevant structures. Following aseptic preparation of the puncture site and the ultrasound probe, the transversus abdominis nerve block will be performed under cross-sectional continuous ultrasound imaging. A 22g spinal needle will be used. A transversely orientated ultrasound probe with an imaging depth of 4 to 6 cm is placed on the anterolateral abdominal wall where the three muscle layers are most distinct. After identification of the transversus plane between the internal oblique and transversus abdominis muscles, the probe is moved posterolaterally to lie across the mid axillary line just superior to the iliac crest. The needle is introduced anteriorly, in the plane of the ultrasound beam. The probe is moved anteriorly to identify the needle after skin puncture and then moved posteriorly in order to image the needle during its entire passage through the abdominal wall. The needle obliquely approaches the transversus abdominis plane and near perpendicular to the ultrasound beam. The needle tip is guided posterior to the mid axillary line in order to block the lateral nerve branches. Once the needle is correctly positioned a predetermined volume of 1% lignocaine and 1% Ropivacaine will be injected following a negative aspiration test. A total of 0.3ml/kg (to a maximum of 10 ml) of combined 1% lignocaine and 1% ropivacaine will be infiltrated 5 minutes prior to skin incision.