Reliability of Waveform Analysis as an Adjunct to Loss of Resistance for Thoracic Epidural Blocks

Abstract

Epidural waveform analysis (with pressure transduction through the needle) provides a simple adjunct to LOR for thoracic epidural blocks. Although its use was devoid of complications, further confirmatory studies are required before its routine implementation in clinical practice.

Reliability of pressure waveform analysis to determine correct epidural needle placement in labouring women

“…In this observational trial of lumbar epidural analgesia, pressure waveform analysis through the epidural needle resulted in a higher sensitivity and positive predictive value than noted previously for thoracic epidural placement (91.1% and 94.9%, respectively), but a lower specificity and negative predictive value (83.8% and 73.8%, respectively) [10]. However, this should be interpreted with caution, as an unexpectedly low failure rate [1] of 3% means that the calculations of specificity and negative predictive values are derived from just a few individuals.…”

“…Pressure waveform analysis provides a simple confirmatory adjunct to loss-of-resistance; when the needle (or catheter) is correctly positioned inside the epidural space, a pulsatile waveform synchronised with arterial pulsations will be seen [2]. In a recent trial of 160 patients having thoracic epidural placement, we observed 91% sensitivity and 84% specificity when waveform analysis was used to verify the correct placement of the epidural needle [10]. Subsequently, in a study involving two academic centres, we demonstrated that thoracic epidural needle placement using loss-of-resistance, confirmed with pressure waveform analysis, was associated with a 2% failure rate compared with 24% for loss-of-resistance alone (p = 0.002) [11].…”

“…Fifteen minutes after the local anaesthetic injection through the needle, a blinded investigator assessed the presence of an epidural block using ice. A successful block was defined as a bilateral complete loss of cold sensation in at least two dermatomes between T1 and L5 [10]. When the effects of the lidocaine bolus subsided, as shown by the return of pain during contractions, the treating anaesthetist administered a catheter test dose of 10 ml bupivacaine 0.125%.…”

“…The equipment for waveform analysis was prepared before the start of the epidural procedure [10]. A pressurised 500 ml saline 0.9% bag was connected to a pressure transducer kit (Transpac â IV Monitoring Kit; icumedical, San Clemente, CA, USA).…”

“…Thus, in this observational study, we investigated the reliability of pressure waveform analysis during epidural insertion for labour analgesia, using similar methodology to our previous trial during thoracic epidural placement [10].…”