Ropivacaine (total and unbound) and AGP concentrations after transversus abdominis plane block for analgesia after abdominal surgery

Local anesthetic dosing and toxicity of adult truncal catheters: a narrative review of published practice

BACKGROUND/IMPORTANCE

Anesthesiologists frequently use truncal catheters for postoperative pain control but with limited characterization of dosing and toxicity.

OBJECTIVE

We reviewed the published literature to characterize local anesthetic dosing and toxicity of paravertebral and transversus abdominis plane catheters in adults.

EVIDENCE REVIEW

We searched the literature for bupivacaine or ropivacaine infusions in the paravertebral or transversus abdominis space in humans dosed for 24 hours. We evaluated bolus dosing, infusion dosing and cumulative 24-hour dosing in adults. We also identified cases of local anesthetic systemic toxicity and toxic blood levels.

FINDINGS

Following screening, we extracted data from 121 and 108 papers for ropivacaine and bupivacaine respectively with a total of 6802 patients. For ropivacaine and bupivacaine, respectively, bolus dose was 1.4 mg/kg (95% CI 0.4 to 3.0, n=2978) and 1.0 mg/kg (95% CI 0.18 to 2.1, n=2724); infusion dose was 0.26 mg/kg/hour (95% CI 0.06 to 0.63, n=3579) and 0.2 mg/kg/hour (95% CI 0.06 to 0.5, n=3199); 24-hour dose was 7.75 mg/kg (95% CI 2.1 to 15.7, n=3579) and 6.0 mg/kg (95% CI 2.1 to 13.6, n=3223). Twenty-four hour doses exceeded the package insert recommended upper limit in 28% (range: 17%-40% based on maximum and minimum patient weights) of ropivacaine infusions and 51% (range: 45%-71%) of bupivacaine infusions. Toxicity occurred in 30 patients and was associated with high 24-hour dose, bilateral catheters, cardiac surgery, cytochrome P-450 inhibitors and hypoalbuminemia.

CONCLUSION

Practitioners frequently administer ropivacaine and bupivacaine above the package insert limits, at doses associated with toxicity. Patient safety would benefit from more specific recommendations to limit excessive dose and risk of toxicity.

Plasma bupivacaine levels (total and free/unbound) during epidural infusion in liver resection patients: a prospective, observational study

INTRODUCTION

Liver resection patients may be at an increased risk of local anesthetic (LA) toxicity because the liver is essential for metabolizing LA and producing proteins (mainly α1-acid glycoprotein (AAG)) that bind to it and reduce the free (and pharmacologically active/toxic) levels in circulation. The liver resection itself, manipulation during surgery, and pre-existing liver disease may all interfere with normal hepatic protein synthesis and result in an attenuation of the increased AAG (a positive acute-phase protein) that normally occurs postoperatively. The purpose of this study was to determine whether the AAG response is attenuated postoperatively following liver resection and whether patients approach toxicity thresholds with continuous postoperative epidural infusion of bupivacaine.

METHODS

Prospective, observational study with blood drawn preoperatively, in the postanesthetic care unit, on postoperative day (POD) 2, and prior to discontinuation of epidural analgesia on POD3/POD4. Plasma was analyzed for total and unbound bupivacaine via liquid chromatography-mass spectrometry and AAG via ELISA. Signs/symptoms of local anesthetic systemic toxicity (LAST), pain, and sedation scores were also recorded.

RESULTS

For the 19 patients completed, total plasma bupivacaine was correlated with total administered, but unbound levels were not associated with the total administered. Unlike non-hepatectomy surgery where unbound LA plasma levels remain stable (or decrease) with continuous postoperative epidural administration, we observed an overall increase. Several patients approached toxicity thresholds and 47% reported at least one symptom of LAST, but no epidurals were discontinued because of LAST. In contrast to the AAG response reported following major non-liver surgery where AAG levels increase twofold, we observed a reduction until POD2 and the magnitude was proportional to resection weight.

DISCUSSION

Our results are supported by the literature in suggesting that major liver resection patients may be at an increased vulnerability for LAST. Factors such as the extent of liver disease, resection and intraoperative blood loss should be considered when using continuous postoperative epidural infusion of bupivacaine and vigilance should be used in monitoring, for signs/symptoms of LAST, even for those subtle and non-specific. Future research will be required to verify these findings.

TRIAL REGISTRATION NUMBER

NCT03145805.

Transversus Abdominis Plane Block

In this narrative review article, the authors discuss the anatomy, nomenclature, history, approaches (posterior vs. lateral vs. subcostal), techniques, pharmacology, indications, and complications of transversus abdominis plane blocks, as well as possible alternative truncal blocks.

Despite the scarcity of evidence and contradictory findings, certain clinical suggestions can nonetheless be made. Overall transversus abdominis plane blocks appear most beneficial in the setting of open appendectomy (posterior or lateral approach). Lateral transversus abdominis plane blocks are not suggested for laparoscopic hysterectomy, laparoscopic appendectomy, or open prostatectomy. However, transversus abdominis plane blocks could serve as an analgesic option for Cesarean delivery (posterior or lateral approach) and open colorectal section (subcostal or lateral approach) if there exist contraindications to intrathecal morphine and thoracic epidural analgesia, respectively.

Future investigation is required to compare posterior and subcostal transversus abdominis plane blocks in clinical settings. Furthermore, posterior transversus abdominis plane blocks should be investigated for surgical interventions in which their lateral counterparts have proven not to be beneficial (e.g., laparoscopic hysterectomy/appendectomy, open prostatectomy). More importantly, because posterior transversus abdominis plane blocks can purportedly provide sympathetic blockade and visceral analgesia, they should be compared with thoracic epidural analgesia for open colorectal surgery. Finally, transversus abdominis plane blocks should be compared with newer truncal blocks (e.g., erector spinae plane and quadratus lumborum blocks) with well-designed and adequately powered trials.

Local anesthetic systemic toxicity: current perspectives

Local anesthetic systemic toxicity (LAST) is a life-threatening adverse event that may occur after the administration of local anesthetic drugs through a variety of routes. Increasing use of local anesthetic techniques in various healthcare settings makes contemporary understanding of LAST highly relevant. Recent data have demonstrated that the underlying mechanisms of LAST are multifactorial, with diverse cellular effects in the central nervous system and cardiovascular system. Although neurological presentation is most common, LAST often presents atypically, and one-fifth of the reported cases present with isolated cardiovascular disturbance. There are several risk factors that are associated with the drug used and the administration technique. LAST can be mitigated by targeting the modifiable risk factors, including the use of ultrasound for regional anesthetic techniques and restricting drug dosage. There have been significant developments in our understanding of LAST treatment. Key advances include early administration of lipid emulsion therapy, prompt seizure management, and careful selection of cardiovascular supportive pharmacotherapy. Cognizance of the mechanisms, risk factors, prevention, and therapy of LAST is vital to any practitioner using local anesthetic drugs in their clinical practice.

Continuous transversus abdominis plane block vs intermittent bolus for analgesia after abdominal surgery: a randomized trial

BACKGROUND

Continuous and intermittent bolus techniques of transversus abdominis plane (TAP) blocks have been used for analgesia after abdominal surgery. Although both are effective, there are no studies comparing them. The aim of this study is to compare analgesia and cost-effectiveness between these groups.

METHODS

After obtaining ethical approval, 20 American Society of Anesthesiologists ASA grade I to III patients undergoing elective abdominal surgery were recruited with 10 patients allocated to each arm. Bilateral ultrasound-guided TAP blocks were performed with an initial bolus of 0.5% ropivacaine 20 mL per side, followed by catheter insertion. After surgery, the continuous infusion group received 0.2% ropivacaine 8 mL/hour on each side and the intermittent bolus group received doses of 0.2% ropivacaine 20 mL per side every 8 hours for 48 hours. Both groups received intravenous fentanyl patient-controlled analgesia and regular oral paracetamol. Parameters recorded included numerical rating scores for pain and post-operative analgesic consumption at baseline (time 0) and at 1 hour, 1 day and 2 days post-operatively. The duration of catheter insertion, complications, patient satisfaction and information regarding costs were also recorded. Patient satisfaction was assessed utilizing a 4-point "Likert" scale on day 2 and on day 30. Pain and Likert scores were analysed by non-parametric sum rank test and all two-sampled t-tests assumed unequal variances.

RESULTS

There was no difference between duration of TAP block, anesthetic and surgical technique and length of stay (p=0.23). Primary outcomes: pain scores at rest and cough were not significantly different (p=0.20) between the groups. Satisfaction scores were similar at day 2 and 30 (p=0.77). However, the bolus group was more cost-effective (AU$347.98 vs AU$429.43).

CONCLUSION

Continuous or bolus TAP blocks are effective analgesic techniques in abdominal surgery, with bolus technique being more economical.