The selected article for discussion during the month of October is:

“Comparison of Procedural Times for Ultrasound-Guided Perineural Catheter Insertion in Obese and Nonobese Patients” (Mariano and Brodsky)

Access the article here

Questions for discussion:

1. The technique used in this study relies on in-plane needle guidance and the insertion of a flexible epidural-type catheter.  If you have experience with other techniques, how do your results compare with those of this study?

2. Trainees placed nearly all of the perineural catheters included in this study. Do you think this factor influenced study results?

3. According to the authors, future research to determine the optimal ultrasound-guided perineural catheter equipment and insertion technique for obese and nonobese patients is warranted. Do you agree? How would you design such a study?

4. Do you have questions or comments for these authors?

The Practice Gap

Obese patients presenting for eligible surgery may benefit considerably from regional anesthesia techniques. Unfortunately, obesity is associated with technical difficulty in performance of these techniques, as well as higher failure rates, compared to those of nonobese patients. 

Compared to the traditional stimulating catheter technique, an exclusively ultrasound-guided approach results in high success rates for catheter insertion and reduces the procedural time. However, it remains unknown whether this new approach results in high success rates and reduced procedural time in obese compared to non-obese patients.

Research study design

A retrospective analysis of an existing data set of 240 patients who participated in 5 previous randomized clinical trials comparing ultrasound- and stimulation-guided perineural catheter insertion techniques* (see references below).

• The authors performed a pooled analysis of previously published clinical trial data to test the hypothesis that obese patients require more time for perineural catheter insertion compared to nonobese patients despite using an ultrasound-guided technique.

Study participants

Inclusion criteria: Catheters inserted using exclusively ultrasound guidance.

120/240 patients met the criteria.

• 51 obese (body mass index [BMI] ≥ 30 kg/m²)
• 69 non-obese (BMI <30 kg/m²).

(Of note: obese patients were older)

Outcome Measurements

• Primary outcome:
  • Procedural time for perineural catheter insertion
• Secondary outcomes:
  • Block efficacy and procedure-related pain on a numeric rating scale of 0–10 immediately after catheter placement
  • Fluid leakage, vascular puncture, and catheter dislodgment reported on postoperative day 1.

Results

• All obese patients had successful catheter placement per the protocol
• The time for perineural catheter insertion was 7 (4–12) minutes for obese patients versus 7 (4–15) minutes for nonobese patients.
• Procedure-related catheter insertion pain was similar for obese and nonobese patients. There were no statistically significant differences in other secondary outcomes.

Statistical Analysis

• Normality of distribution: Kolmogorov-Smirnov test
• Normally distributed data, comparisons of independent samples:  Student t test
• Continuous data in distributions other than normal: Mann-Whitney U test
• Further analysis of association, if any, between the BMI and procedural time: Simple linear regression
• Comparisons of categorical variables: the z test or Fisher exact test (n < 5 in any category)
• Two-sided P < .05 was considered statistically significant for the primary outcome.
• Post hoc calculation to determine the power of the study to detect a 5-minute difference between groups.

* Data from 5 previously published randomized clinical trials comparing ultrasound- and stimulation-guided perineural catheter insertion techniques:

Mariano ER, Cheng GS, Choy LP, et al. Electrical stimulatin versus ultrasound guidance for popliteal-sciatic perineural catheter insertion: a randomized controlled trial. Reg Anesth Pain Med 2009; 34:590–59.

Mariano ER, Loland VJ, Bellars RH, et al. Ultrasound guidance versus electrical stimulation for infraclavicular brachial plexus perineural catheter insertion. J Ultrasound Med 2009; 28:1211–1218.

Mariano ER, Loland VJ, Sandhu NS, et al. Ultrasound guidance versus electrical simulation for femoral perineural catheter insertion. J Ultrasound Med 2009, 28:1453–1460.

Mariano ER, Loland VJ, Sandhu NS, et al. A trainee-based randomized comparison of stimulating inerscalene perineural catheters with a new technique using ultrasound guidance alone. J Ultrasound Med 2010; 29:329–336.

Mariano ER, Loland VJ, Sandhu NS, et al. Comparative efficacy of ultrasound-guided and stimulating popliteal-sciatic perineural catheters for postoperative analgesia. Can J Anaesth 2010; 57:919–926.