James D. Griffiths

Plasma ropivacaine concentrations after ultrasound-guided transversus abdominis plane block

BACKGROUND The transversus abdominis plane block is a novel technique involving injection of local anaesthetic between the internal oblique and the transversus abdominis muscles of the abdominal wall. It is possible that injection of a large dose of local anaesthetic into a relatively vascular plane may result in toxic concentrations. One previously published study examined plasma lidocaine concentrations after transversus abdominus plane block and showed potentially toxic plasma concentrations. Although ropivacaine is most commonly used for this technique, plasma concentrations of ropivacaine after this block have not been reported previously. METHODS Adult female patients undergoing elective open gynaecological surgery received bilateral ultrasound-guided transverse abdominal plane blocks before surgical incision (3 mg kg(-1) of ropivacaine diluted to 40 ml). Venous blood was collected each 15 min for the first hour, each 30 min for the second hour, and then at 3, 4, 12, and 24 h post-block. RESULTS Twenty-eight patients were recruited. The mean (sd) peak total ropivacaine concentration occurred 30 min post-injection and was 2.54 (sd 0.75) µg ml(-1). The highest measured concentration was 4.00 µg ml(-1), also 30 min post-injection. Mean total concentrations remained above 2.20 µg ml(-1) for up to 90 min post-injection. The mean unbound peak venous concentration was 0.14 (0.05) µg ml(-1), and the peak was 0.25 µg ml(-1). CONCLUSIONS Transversus abdominus plane block using 3 mg kg(-1) of ropivacaine produces venous plasma concentrations that are potentially neurotoxic, although broadly consistent with plasma levels found after injection at other comparable sites.

Interventions at caesarean section for reducing the risk of aspiration pneumonitis.

BACKGROUND Various interventions are used as prophylaxis for aspiration pneumonitis in obstetric anaesthesia. This review, based on a Cochrane systematic review currently being updated, examines whether interventions given before caesarean section reduce the risk of aspiration pneumonitis. METHODS Twenty-two studies, involving 2658 women providing data in a usable format for meta-analysis were identified. RESULTS Compared to no treatment or placebo, there was a significant reduction in the risk of intra-gastric pH <2.5 with antacids (risk ratio (RR) 0.17, 95% confidence interval (CI) 0.09-0.32), H2 antagonists (RR 0.09, 95% CI 0.05-0.18) and proton-pump antagonists (RR 0.26, 95% CI 0.14-0.46). H2 antagonists were associated with a reduced risk of intra-gastric pH <2.5 when compared with proton-pump antagonists (RR 0.39, 95% CI 0.16-0.97), but compared with antacids the findings were unclear. Combined use of antacids plus H2 antagonists was associated with a significant reduction in the risk of intra-gastric pH <2.5 when compared with placebo (RR 0.02, 95% CI 0.00-0.15) or compared with antacids alone (RR 0.12, 95% CI 0.02-0.92). CONCLUSION The quality of evidence was weak and may not reflect a reduction in the risk of aspiration pneumonitis since none of the studies assessed substantive clinical outcomes or potential adverse effects. Further work is required to validate the suitability of surrogate markers of pH and gastric volume for clinical outcomes in the context of aspiration pneumonitis.

Abdominal Wall Blocks: Safe Practice and Management of Adverse Events

Abdominal wall blocks have gained popularity in recent years as an alternative to epidural anesthesia. Due to the vascularity of the target area, the risk of local anesthetic toxicity is heightened. The key to safe abdominal wall blockade is anatomical knowledge, ultrasound scanning skill, and adherence to local anesthetic dose limits. Although rare, trauma to the abdominal wall itself and intra-abdominal structures has been reported. Another rare complication that should be considered is inadvertent femoral nerve block. Absorption of local anesthetic following TAP block is rapid and, although peak plasma concentrations are comparable to other blocks, several reports of seizures have been published, usually following injection of large local anesthetic doses. Abdominal blocks can be challenging in certain populations, including children, the obese, pregnant women, and individuals with coagulopathy. Awareness of needle size and trajectory and local anesthetic dosing are especially critical to avoiding complications in these patients.