Continuous Transversus Abdominis Plane Nerve Blocks: Does Varying Local Anesthetic Delivery Method—Automatic Repeated Bolus vs. Continuous Basal Infusion—Influence the Extent of Cutaneous Analgesia?
Background. The superiority of repeated intermittent bolus doses over a continuous basal infusion has been demonstrated in some studies for various ultrasound-guided perineural catheter locations,1,2 yet not others.3-5 As with other aspects of continuous peripheral nerve blocks, effects often vary depending upon the anatomy of the catheter location. The relationship between administration strategy and ensuing effects remains unexamined for transversus abdominis plane (TAP) catheters. We therefore tested the hypothesis that when using TAP catheters, providing local anesthetic in repeated bolus doses increases the cephalad-caudad cutaneous effects compared with a basal-only infusion.
Methods. This study followed Good Clinical Practice and was conducted within the ethical guidelines outlined in the Declaration of Helsinki. The trial was prospectively registered at clinicaltrials.gov (NCT02662023). The University of California San Diego Institutional Review Board (San Diego, California) approved all study procedures and provided oversight of the data and safety issues for the duration of the trial. Written, informed consent was obtained from all participating subjects. Bilateral TAP catheters were inserted in 24 healthy volunteers followed by ropivacaine 0.2% administration for a total of 6 hours using electronic infusion pumps (Nimbus Ambulatory Pump, Zyno Medical, Natick, Massachusetts) capable of providing automated bolus doses as well as a continuous basal infusion. The right side was randomly assigned to either a basal infusion (8 mL/h) or bolus doses (24 mL administered every 3 hours) in a double-masked manner. The left side received the alternate treatment. The primary endpoint was the extent of sensory deficit as measured by cool roller along the axillary line at Hour 6 (6 hours after the local anesthetic administration was initiated). Secondary endpoints included the extent of sensory deficit as measured by cool roller and von Fray filaments (5.46) along the axillary line and along a transverse line at the level of the anterior superior iliac spine at Hours 0-6. The basal-bolus difference at each time point was assessed with paired t-tests (i.e., one-sample t-tests of basal-bolus differences for each subject). The primary hypothesis pertains to the 6 hour time point with significance level 5%.
Results. While there were statistically significant differences between treatments within the earlier part of the administration period (Figures 1-3), by Hour 6 the difference in extent of sensory deficit to cold failed to reach statistical significance along the axillary line (mean=0.9 cm; SD=6.8; 95% CI -2.0, 3.8; p=0.515). Similarly, differences between treatments were not statistically significant at Hour 6 for cold in the transverse line or von Frey filaments in both the axillary and transverse lines (Figures 1-3).
Conclusion. No evidence was found to support the hypothesis that changing the local anesthetic administration technique (continuous basal versus hourly bolus) when using ropivacaine 0.2% and TAP catheter at 8 mL/h and 24 mL every 3 hours significantly influences the cutaneous effects after 6 hours of administration. Additional research is required to determine whether changing variables (e.g., local anesthetic concentration, basal infusion rate, bolus dose volume and/or interval) would provide different results.
1. Thapa D, Ahuja V, Verma P, Gombar S, Gupta R, Dhiman D: Post-operative analgesia using intermittent vs. continuous adductor canal block technique: a randomized controlled trial. Acta Anaesthesiol Scand 2016; 60: 1379-1385
2. Hillegass MG, Field LC, Stewart SR, Borckardt JJ, Dong L, Kotlowski PE, Demos HA, Del Schutte H, Reeves ST: The efficacy of automated intermittent boluses for continuous femoral nerve block: a prospective, randomized comparison to continuous infusions. J Clin Anesth 2013; 25: 281-8
3. Charous MT, Madison SJ, Suresh PJ, Sandhu NS, Loland VJ, Mariano ER, Donohue MC, Dutton PH, Ferguson EJ, Ilfeld BM: Continuous femoral nerve blocks: Varying local anesthetic delivery method (bolus versus basal) to minimize quadriceps motor block while maintaining sensory block. Anesthesiology 2011; 115: 774-81
4. Hamdani M, Chassot O, Fournier R: Ultrasound-guided continuous interscalene block: the influence of local anesthetic background delivery method on postoperative analgesia after shoulder surgery: a randomized trial. Reg Anesth Pain Med 2014; 39: 387-93
5. Monahan AM, Sztain JF, Khatibi B, Furnish TJ, Jaeger P, Sessler DI, Mascha EJ, You J, Wen CH, Nakanote KA, Ilfeld BM: Continuous adductor canal blocks: Does varying local anesthetic delivery method (automatic repeated bolus doses versus continuous basal infusion) influence cutaneous analgesia and quadriceps femoris strength? A randomized, double-masked, controlled, split-body volunteer study. Anesth Analg 2016
Figure 1. Effects of local anesthetic administered via transversus abdominis plane catheters on cutaneous deficits to cold as measured with a cool roller.
Figure 2. Effects of local anesthetic administered via transversus abdominis plane catheters on cutaneous deficits to mechanical pressure as measured with von Frey filaments.