Determining Plasma Bupivacaine Levels Following Pectoral Nerve Blocks: A Prospective Observational Study

Regional anesthesia techniques are common modalities used to provide analgesia following both upper and lower extremity surgeries. It is also often used for truncal procedures for the same purpose. A relatively new truncal block, first described in 2012 by Blanco, called the pectoralis nerve block (PECS I and II block) has been used successfully for breast surgery1-3. Despite its description and success in clinical practice, the extent of systemic absorption from this truncal plane block has not been described to date. However, in a study published in the British Journal of Anesthesia, this has been done for another truncal plane block, the transverse abdominus plane (TAP) block where the local anesthetic was noted to peak and had a mean total concentration of ropivacaine occurring at 30 minutes after the block4. During this study, samples were taken at 10, 20, 30, 45, 60, 90, 120, 180, and 240 minutes. The investigators anticipate that since this is a similar truncal plane block, absorption will be comparable in terms of timing. However, the concentration of drug absorbed may be different given the proximity to the ribs, intercostal and thoracic vasculature, and a higher concentration of local given the smaller plane for local anesthetic spread. Given that the investigators want to find the peak of the curve and the peak concentration of bupivacaine from the PECS block, the investigators feel will need 5 samples at the times outlined below. This number of samples was chosen to approximate a study published in 2004 where ten subjects received ropivacaine for scalp blocks and serum ropivacaine levels were measured at 15, 30, 45, 60, 90, and 120 minutes5. The investigators feel that the 120 minute measurement is well beyond the peak plasma level of bupivacaine given the findings in the TAP and scalp studies. Therefore,the investigators will collect the following samples at these times after the block is completed: 5, 10, 20, 40, 60, and 90 minutes. The purpose of this study is to determine peak plasma bupivacaine concentrations in a similar fashion for PECS I/II blocks. The investigators hypothesis is that the mean peak plasma levels for our patients undergoing PECS I/II blocks will be less than the levels reported to cause early neurotoxicity of [2.2 (0.9) micrograms/ml]6 in patients receiving intravenous bupivacaine infusions.