A transverse abdominal plane (TAP\_ block will be performed by one of the investigators who is adept in using ultrasound guidance after induction of general anesthesia. The dose of bupivacaine administered will be based on the weight of the patient. This dose is consistent with routine levels of local anesthetic used for peripheral nerve blocks and is lower than toxic levels so there will be no additional change in renal or liver function. Whole blood samples will be collected on a piece of filter paper from either an arterial, central, peripheral line or heel stick. The extracts from dried blood samples (DBS; calculated volume 20 µL) collected on filter paper will be analyzed using an LC-MS/MS system in combination with online extraction (LC/LC-MS/MS). Blood samples will be obtained at 0, 5, 15, 30, 60, 120 minutes, 4, 24, 48 hours. If obtained from a heel stick, these samples will be obtained at time of glucose sampling or a clinical indication. Subjects will be considered evaluable if they have 5 samples. All sampling for the study will be based on concurrent sampling so there will be no additional blood draws.
Pain will be assessed by the bedside nurse or study research assistant using the Neonatal Infant Pain Scale (NIPS). As part of the standard of care in this institution, nurses will have the opportunity to administer additional pain medications including but not limited to intravenous fentanyl or morphine. This will be done as per standing orders if the neonate meets criteria for additional analgesia, in other words, if there is an increase in pain as indicated by the NIPS pain scores. NIPS score will be recorded prior to each blood draw and every 8 hours while the subject is enrolled in the study. The NIPS will be the primary clinical outcome measure for this study. Blood pressure and heart rate will also be recorded as a physiologic correlate for drug level at these times.
