Peak Plasma Levels of Bupivacaine After an Erector Spinae Block (ESP)
Condition: Pharmacokinetics; Anesthesia, Local
Study type: Observational

Summary: 
      The primary objective of the study is to measure plasma levels of bupivacaine following
      erector spinae (ESP) regional block in patients undergoing mastectomy.
    

Detailed description: 
      Breast cancer is one of the most frequent types of cancer in women. Mastectomy is important
      in treating these cases; however, sometimes it is associated with acute and chronic pain.
      Multimodal analgesia, combining drug therapy and regional anesthesia, can help in preventing
      acute and perhaps chronic pain in breast cancer patients undergoing mastectomy.

      Erector spinae block is a new regional anesthesia technique that has emerged to treat
      thoracic pain following thoracic and breast surgery. It consists of injecting local
      anesthetics in the space located between the erector and paravertebral muscles using
      ultrasound guidance. The injection can be done at the level of T5 allowing distribution of
      the drug to upper and lower dermatomes.

      The dose of local anesthetic injected after erector spinae block should aim to maximize
      analgesia while minimizing the chance of toxic systemic concentrations. Defining the rate of
      absorption of local anesthetics into the blood after an erector spinae block will therefore
      help anesthesiologists determinate optimal analgesic doses, in terms of both safety and
      effectiveness.

      This observational study will determine bupivacaine pharmacokinetics after single shot
      erector spinae block with bupivacaine, to further define the right dose and duration of
      surveillance in post-anesthesia care.

      Methods:

      For the erector spinae block, the patient will be placed in the sitting position. Using an
      ultrasound machine with a high frequency linear probe (Sonosite, HFL50 15-6MHz) placed in the
      parasagittal plane, 3cm away from the midline, the anesthesiologist will position an
      insulated hyperechoic needle (50-80 mm, 22 gauge, SonoPlex STIM, Nanoline, Pajun, Germany) at
      the level of the 5th thoracic vertebrae, between the erector spinae and the paravertebral
      muscles. The anesthesiologist will confirm the correct position of the needle with the
      injection of 1 mL of 5% dextrose. Then, after negative aspiration, he will inject bupivacaine
      0.5% with epinephrine 5 mcg/mL in 5 ml aliquots for a total dose of 2mg/kg of ideal body
      weight (maximum of 150mg).

      The end of injection will be considered as T0. Collection of 4.5mL of blood will be performed
      at T10min, T20min, T30min, T45min, T60min, T90min, T120min, T180min, and T240min.

      Blood tubes will be immediately placed on ice to be ultimately sent to the laboratory for
      centrifugation and measurement of bupivacaine level using liquid chromatography-tandem mass
      spectrometry (LC-MS/MS) for each of the samples.

      General anesthesia will then be induced in the operating room with no additional bupivacaine
      allowed by the anesthesiologist or the surgeon. After surgery, in the Post-Anesthesia Care
      Unit, the level of the sensory block will be identified by pinprick and the quality of
      analgesia will be evaluated using a verbal numerical rating scale, and opioid consumption
      will be noted.
    

Intervention name(s): Collection of blood samples
Intervention type(s): Other
Intervention description(s): Nine blood samples will be collected to determine bupivacaine pharmacokinetics at T10min, T20min, T30min, T45min, T60min, T90min, T120min, T180min, and T240min. T0 will be defined as the end of bupivacaine injection.
Observational model: Cohort
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        Patients undergoing unilateral mastectomy under general anesthesia and erector spinae block
        for post-operative pain management.