title: Technical report: optimal quantity of saline for epidural pressure waveform analysis.
abstract: OBJECTIVE
  Epidural waveform analysis (EPWA) is a simple test to confirm the optimal placement of an epidural catheter. It relies on the transmission of the thecal pressure waveform through the epidural catheter. Little is known about the optimal volume of catheter injectate needed to optimize the EPWA test.
  
  
  METHODS
  In a randomized controlled trial we compared three different catheters: stimulating, open-ended hole [S1]; stimulating, three-hole [S3]; non-stimulating three-hole [NS3]) in 60 patients in an unblinded pilot study. After catheter insertion using a loss of resistance to air technique, we recorded the dose response curve of EPWA and the presence of epidural pressure wave transmitted through the catheter to repeated injections of 2.5 mL saline boluses in the catheter to a total volume of 10 mL. All patients were followed by the acute pain service to confirm adequacy of postoperative epidural analgesia.
  
  
  RESULTS
  The S3 catheters were significantly more responsive (able to transmit a pulsatile waveform) compared to the S1 [P = 0.003 (S3) and P = 0.012 (NS3)] at low injectate volume, while there was no differences between the S3 catheters in their ability to transmit a waveform for EPWA (P = 0.25). There was no increase in responsiveness after 2.5 mL injected for S3 catheters and 5 mL for the S1 catheter. Three patients had soft catheters that did not transmit an epidural pulsative waveform.
  
  
  CONCLUSIONS
  For EPWAs, S3 epidural catheters are superior to S1 catheters for determining pulsative waveform transmission at low injectate volume. The optimal initial quantity of saline for EPWA is 5 mL regardless of the catheter type used.
authors.affiliation: Département d'anesthésiologie du Centre Hospitalier Universitaire de Sherbrooke, Sherbrooke, Québec, Canada. estria1@globetrotter.net
authors.forename: Etienne
authors.initials: E
authors.lastname: de Médicis
authors.forename: Jocelyn
authors.initials: J
authors.lastname: Pelletier
authors.forename: René
authors.initials: R
authors.lastname: Martin
authors.forename: Marie-Josée
authors.initials: MJ
authors.lastname: Loignon
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Tétrault
authors.forename: Lucie
authors.initials: L
authors.lastname: Laroche
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015360:Analgesia, Epidural / Q000379:methods*; D002404:Catheterization / Q000295:instrumentation* / Q000379:methods; D004824:Epidural Space; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010149:Postoperative Pain / Q000188:drug therapy*; D010865:Pilot Projects; D011312:Pressure; D011673:Pulsatile Flow; D012965:Sodium Chloride / Q000008:administration & dosage*
chemical_list: D012965:Sodium Chloride