title: Continuous elastomeric pump-based ropivacaine wound instillation after open abdominal aortic surgery: how reliable is the technique?
abstract: BACKGROUND
  We aimed at quantifying the impact of continuous wound infusion with ropivacaine 0.33% on morphine administration and subjective pain relief in patients after open abdominal aortic repair in a double-blind, placebo-controlled study.
  
  
  METHODS
  Before closing the abdominal wound, 2 multihole ON-Q® Soaker Catheters™ (I-Flow Corporation, Lake Forest, California, USA) were placed pre-peritoneally in opposite directions. Either ropivacaine 0.33% or saline 0.9% was delivered by an elastomeric pump at a rate of 2 mL/h for 72 hours in each of the catheters. Postoperative pain and morphine administration were assessed using the numerical rating scale (NRS) in 4-hour intervals. Total plasma concentrations of ropivacaine, unbound ropivacaine, and α1-acid glycoprotein (AAG) were measured daily. Mean arterial pressure, pulse rate, oxygen saturation, total amount of morphine administration, ventilation time, and length of stay in the intensive care unit (ICU) were recorded. At the end of the study period, the wound site and the condition of the catheters were assessed.
  
  
  RESULTS
  The study was terminated prematurely due to a malfunction of the elastomeric balloon pump resulting in toxic serum levels of total ropivacaine in 2 patients (11.4 μmol/L and 10.0 μmol/L, respectively) on the second postoperative day. Six patients had been allocated to the ropivacaine group, and 9 patients had been allocated to the control group. Demographic and surgical data were similar in both groups. During the first 3 postoperative days, no difference between the ropivacaine and the control group was found in NRS (P = .15, P = .46, and P = .88, respectively) and morphine administration (P = .48). Concentrations of unbound serum ropivacaine (0.11 ± 0.08 μmol/L) were below toxic level in all patients.
  
  
  CONCLUSIONS
  Continuous wound infusion of ropivacaine 0.33% 2 mL/h using an elastomeric system was not reliable and did not improve postoperative pain control in patients after open abdominal aortic surgery.
authors.affiliation: Institute of Anesthesiology, University Hospital Zurich, Rämistrasse 100, Zurich, Switzerland. werner.baulig@usz.ch
authors.forename: Werner
authors.initials: W
authors.lastname: Baulig
authors.forename: Konrad
authors.initials: K
authors.lastname: Maurer
authors.forename: Oliver Michel
authors.initials: OM
authors.lastname: Theusinger
authors.forename: Valentin
authors.initials: V
authors.lastname: Hinselmann
authors.forename: Barbara
authors.initials: B
authors.lastname: Baulig
authors.forename: Donat Rudolph
authors.initials: DR
authors.lastname: Spahn
authors.forename: Marco Piero
authors.initials: MP
authors.lastname: Zalunardo
mesh_terms: D000368:Aged; D000577:Amides / Q000008:administration & dosage*; D000779:Anesthetics, Local / Q000008:administration & dosage; D001012:Aorta, Abdominal / Q000601:surgery*; D020724:Elastomers; D005260:Female; D006801:Humans; D007260:Infusion Pumps; D008297:Male; D010147:Pain Measurement / Q000187:drug effects*; D010149:Postoperative Pain / Q000517:prevention & control*; D015990:Placebo Effect; D000077212:Ropivacaine; D016896:Treatment Outcome; D014656:Vascular Surgical Procedures / Q000009:adverse effects*
chemical_list: D000577:Amides; D000779:Anesthetics, Local; D020724:Elastomers; D000077212:Ropivacaine