Ropivacaine Plasma Concentrations and Pharmacokinetics Following Erector Spinae Plane Block in the Pediatric Population
Phase: PHASE4
Conditions: Anesthesia, Local
Sponsor: Baylor College of Medicine

Pharmacokinetic Modeling of Ropivacaine Following Single Shot Erector Spinae Plane 
Block in Anesthetized Children 
 
 
 
NCT: 04298099 
 
 
Date: 1/20/2021 (original protocol document date) 
 
 
 
 

Protocol  
 
This pilot study was a prospective, observational investigation approved by the Baylor College of 
Medicine IRB (H-4638).  In compliance with the EQUATOR network, all reporting was conducted 
under the STROBE guidelines. Written informed consent (with assent where applicable) was 
obtained by the parent(s) or legal guardian(s) for all enrolled participants.  Eligibility criteria 
included patients aged 6 months to 18 years weighing more than 4kg, scheduled to undergo 
minimally invasive video-assisted thoracoscopic surgery at Texas Children’s Hospital.  Exclusion 
criteria included allergy to local anesthetics, liver or renal dysfunction, pre-existing 
hypoalbuminemia, tumor or infection/abscess at the injection site, and a BMI > 95th percentile.    
 
Patients received an inhalational or intravenous induction with a general endotracheal tube 
anesthesia at the discretion of the attending anesthesiologist.  After the airway was secured, 
patients were placed in the lateral decubitus position and a single-shot unilateral ultrasound-guided 
ESP block, as all the procedures were unilateral incisions, was performed as previously described 
1-2 dermatomal levels above the surgical incision site.7  All patients received Ropivacaine 0.5% 
at 0.3ml/kg (1.5mg/kg) in the fascial plane deep to the erector spinae muscle.  Since there are no 
standardized dosing guidelines for ESP blocks in children, we chose a slightly higher dose from 
the previously published Ropivacaine dosing for TAP blocks of 0.25-0.75mg/kg but remaining 
within the consensus maximum dosing of 1.5mg/kg for peripheral nerve blocks.2,8  Post-anesthesia 
care unit (PACU) dermatomal assessments to ice were performed to validate ESP block accuracy.  
Intraoperative morphine equivalents (mg/kg) were additionally collected. Total and free serum 
Ropivacaine concentrations were obtained at baseline and the following time point after block 

injection: 30, 60, and 90-minutes and 2, 4, and 6-hours. These time-points reflect those previously 
noted in the literature, recognizing that serum capture of Ropivacaine is likely undetectable beyond 
6-hours.8-10 A baseline alpha-1 acid glycoprotein (AAG) was also collected.      
 
Samples were centrifuged for 15-minutes at 1100G within 2-hours of collection and the plasma 
was frozen at -80°C for processing at Lab ExperTox Inc.  We applied the same laboratory analysis 
as previously described, demonstrating the reproducibility of total and free  Ropivacaine levels 
with liquid chromatography/mass spectroscopy (LC-MS/MS).8-12 The LC-MS/MS analysis was 
performed with the Agilent Technologies 6460 mass spectrometer connected with the Agilent 
1200 series HPLC system via electrospray ionization mode.  The samples were analyzed in 
positive ionization mode with the voltage set at 3000V.  Data acquisition and data analysis were 
performed with the Agilent Mass Hunter software (Version B.07.00).  The total Ropivacaine 
concentrations were measured after protein precipitation in methanol.  The free Ropivacaine 
concentrations were measured with the same technique after ultracentrifugation of the samples 
with Vivaspin 2, 10 KDa molecular weight cut-off Concentrators (GE Healthcare, UK).  The assay 
was validated by spiking negative serum with known concentrations of Ropivacaine.  The assay 
method was linear over the concentration range 5 -3000 ng/mL, with a limit of detection of 1 
ng/mL and a limit of quantification of 5 ng/ml.  
 
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