Ultrasound-guided rectus sheath block or wound infiltration in children: a randomized blinded study of analgesia and bupivacaine absorption

Abstract

Background: Rectus sheath block can provide analgesia following umbilical hernia repair. However, conflicting reports on its analgesic effectiveness exist. No study has investigated plasma local anesthetic concentration following ultrasound-guided rectus sheath block (USGRSB) in children.

Objectives: Compare the effectiveness and bupivacaine absorption following USGRSB or wound infiltration (WI) for umbilical hernia repair in children.

Methods: A randomized blinded study comparing WI with USGRSB in 40 children undergoing umbilical hernia repair was performed. Group WI (n = 20) received wound infiltration 1 mg·kg(-1) 0.25% bupivacaine. Group RS (n = 20) received USGRSB 0.5 mg·kg(-1) 0.25% bupivacaine per side in the posterior rectus sheath compartment. Pain scores and rescue analgesia were recorded. Blood samples were drawn at 0, 10, 20, 30, 45, and 60 min.

Results: Patients in the WI group had a twofold increased risk of requiring morphine (hazard ratio 2.06, 95% CI 1.01, 4.20, P = 0.05). When required, median time to first morphine dose was longer in the USGRSB group (65.5 min vs. 47.5 min, P = 0.049). Peak plasma bupivacaine concentration was higher following USGRSB than WI (median: 631.9 ng·ml(-1) IQR: 553.9-784.1 vs. 389.7 ng·ml(-1) IQR: 250.5-502.7, P = 0.002). Tmax was longer in the USGRSB group (median 45 min IQR: 30-60 vs. 20 min IQR: 20-45, P = 0.006).

Conclusions: USGRSB provides more effective analgesia than WI for umbilical hernia repair. USGRSB with 1 mg·kg(-1) 0.25% bupivacaine is associated with safe plasma bupivacaine concentration that peaks higher and later than WI. Caution against using larger volumes of higher concentration local anesthetic for USGRSB is advised.

Keywords: age, outpatient; ambulatory, local anesthetics; drugs; drugs, regional; pain, child; pharmacokinetics; ultrasound, regional.

Figure 1

Ultrasound-guided rectus sheath block. The needle tip is visualized in the posterior rectus sheath with tissue plane hydrodissection from local anesthetic spread.

Figure 2. Patient allocation and disposition

Figure 3

The Kaplan Meier curve demonstrates that patients in the wound infiltration group were twice as likely to require morphine for post-operative pain relief (p<0.05).

Figure 4

Plasma Bupivacaine concentrations over time. Peak plasma concentrations were higher following USGRSB than WI (median: 631.9 ng/ml IQR: 553.9 – 784.1 vs 389.7 ng/ml IQR: 250.5-502.7, p= 0.002). The time to peak concentration was longer in the USGRSB group (median 45 min IQR: 30 - 60 vs 20 min IQR: 20 – 45, p= 0.006). No measured concentration exceeded 1 mcg/ml.