Ropivacaine-induced convulsion immediately after epidural administration--a case report

Ropivacaine is a new long-acting amide-type local anesthetic with less toxic effects compared with bupivacaine. Here, we report a case who sustained convulsion immediately after administration of epidural ropivacaine. A 75-year-old woman was scheduled for total knee replacement. Epidural catheter was inserted smoothly. After aspiration test and injection of a test dose of 3 ml of 2% lidocaine containing 15 micrograms epinephrine, 160 mg ropivacaine was administered epidurally. Unfortunately, a generalized tonic-clonic convulsion of sudden onset occurred right after ropivacaine injection. After he was given 100% oxygen and intravenous thiopental 150 mg, the patient recovered uneventfully. During the episode of convulsion sinus tachycardia at a rate of 120 beats/min without the interposal of other form of cardiac arrhythmia was noted, and respiration remained intact. This suggests that ropivacaine offers a good cardiovascular stability. This example serves as another evidence to remind us that even with a negative aspiration following epidural catheter placement and an uneventful test dose injection, inadvertent intravascular injection may still happen, particularly in the elderly.     

The obturator nerve block

During transurethral electroresection in the posterolateral bladder neck, trigone and posterior urethra, unintentional contractions of the thigh-adductor muscles may occur due to irritation of the obturator nerve. The sudden displacement of the bladder wall against the cutting loop may cause a perforation of the bladder. The authors describe the topographic relation of the bladder wall to the passage of the obturator nerve in the minor pelvis. The technique of obturator nerve block by local anaesthesia is described and its efficacy is demonstrated in 21 patients.     

Ultrasound-guided obturator nerve block

We reviewed the technique and anatomy for the ultrasound-guided obturator nerve block, especially interadductor approach. Although it is sometimes difficult to observe obturator nerve in the ultrasound image, obturator nerve block is completed observing three muscle layers, adductor longus muscle, adductor blevis muscle and adductor magnus muscle, in the ultrasound image. Local anesthetics are injected between the muscle layers confirming the needle tip and spread of the solution. This technique will reduce incomplete effect or side effects of the obturator nerve block.     

闭孔神经阻滞的研究进展

背景闭孔神经阻滞（obturator nerve block,ONB）可用于缓解大腿内收肌痉挛及髋关节疼痛、抑制经尿道膀胱肿瘤电切术中闭孔神经反射等。近年来,随着人们对神经阻滞麻醉的再度关注,ONB的应用与研究也随之增多。目的概述及评价ONB适应证及穿刺方法,为临床及研究工作提供参考。内容阐述ONB的适应证,荟萃分析ONB的不同穿刺入路及方法。趋向随着ONB临床应用的不断普及,更具优势的阻滞方法也会不断涌现。     

An evaluation of the cutaneous distribution after obturator nerve block.

In 1973, Winnie et al. introduced the inguinal paravascular three-in-one block, which allegedly provides anesthesia of three nerves--the femoral, lateral cutaneous femoral, and obturator nerves--with a single injection. This concept was undisputed until the success of the obturator nerve block was reassessed by using evidence of adductor weakness rather than cutaneous sensory blockade, the latter being variable in its distribution and often absent. We performed this study, therefore, to evaluate the area of sensory loss produced by direct injection of local anesthetic around the obturator nerve. A selective obturator nerve block with 7 mL of 0.75% ropivacaine was performed in 30 patients scheduled for knee surgery. Sensory deficit and adductor strength were evaluated for 30 min by using sensory tests (cold and light-touch perception) and the pressure generated by the patient's squeezing a blood pressure cuff placed between the knees. Subsequently, a three-in-one block was performed, and the sensory deficit was reassessed. The obturator nerve block was successful in 100% of cases. The strength of adductors decreased by 77% +/- 17% (mean +/- SD). In 17 patients (57%), there was no cutaneous contribution of the obturator nerve. The remaining 7 patients (23%) had an area of hypoesthesia (cold sensation was blunt but still present) on the superior part of the popliteal fossa, and the other 6 (20%) had sensory deficit located at the medial aspect of the thigh. The three-in-one block resulted in blockade of the lateral aspect of the thigh in 87% of cases, whereas the anteromedial aspect was always anesthetized. By use of magnetic resonance imaging in eight volunteers, we demonstrated that the obturator nerve has already divided into its two branches at the site of local anesthetic injection. However, the injection of blue dye after having simulated the technique in five cadavers showed that the fluid regularly spread to both branches. We conclude that after three-in-one block, a femoral nerve block may have been assessed as an obturator nerve block in 100% of cases when testing the cutaneous distribution of the obturator nerve on the medial aspect of the thigh. IMPLICATIONS: Previous studies reporting an incidence of obturator nerve block after three-in-one block may have mistaken a femoral nerve block for an obturator nerve block in 100% of cases when the cutaneous distribution of the obturator nerve was assessed on the medial aspect of the thigh. The only way to effectively evaluate obturator nerve function is to assess adductor strength.     

Accurate obturator nerve block in transurethral surgery

Twenty-two patients with ureteral stones underwent twenty-four-hour urinary excretion studies of calcium, phosphorus, and uric acid before and after stone elimination from the urinary tract. Comparison of pre- and post-stone elimination studies showed no significant differences suggesting that the presence of stones in the urinary tract has little influence on the twenty-our-hour urinary excretion of calcium, phosphorus, and uric acid.     

Grand mal convulsion after an accidental intravenous injection of ropivacaine

A 36-yr old, ASA physical status I patient scheduled for hip arthroplasty under regional anesthesia received at the end of surgery an i.v. injection of approximately 200 mL of a 0.15% ropivacaine solution (300 mg = 4.6 mg/kg) in approximately 5 min. The bag prepared for postoperative epidural infusion was accidentally connected to a peripheral i.v. line. The patient developed grand mal convulsions, hypotension, and respiratory arrest. No arrhythmias were observed. Twenty minutes after the event, the arterial plasma concentration of ropivacaine was 3.10 microg/mL. Using a pharmacokinetic model, the peak plasma concentration at the time of the accidental administration was estimated at 17.04 microg/mL. The patient recovered uneventfully. IMPLICATIONS: An accidental i.v. injection of approximately 300 mg of ropivacaine was followed by seizures without any arrhythmia. The patient recovered uneventfully.     

Ropivacaine-induced toxicity with overdose suspected after axillary brachial plexus block

Ropivacaine has a high threshold for systemic toxicity. We report and highlight a rare case in which an overdose of ropivacaine was suspected of leading to a generalized convulsion following the injection of this agent for axillary brachial plexus block (ABPB). A 25-year-old woman (height, 153 cm; weight, 48 kg; American Society of Anesthesiologists physical status I) was scheduled for finger surgery with ABPB. The perivascular sheath was identified by fascial clicks. We administered 300 mg (6.25 mg·kg⁻¹) ropivacaine, while confirming that no blood flow was observed in the injection line by repeated negative aspiration tests. Ten minutes after the injection, most sensory and motor nerves were blocked effectively. Thirteen minutes after the administration, the patient lost consciousness and convulsed suddenly. No severe symptoms of cardiovascular toxicity occurred. The concentration of ropivacaine in a venous blood sample taken 28 min after the ropivacaine injection was 3.65 μg·ml⁻¹. She recovered with no sequelae. Limited cases have indicated high efficacy and sufficient safety for the use of 300 mg ropivacaine for ABPB. However, the toxic threshold of ropivacaine remains unclear, and the dose should be calculated in relation to the weight of the patient to prevent severe toxic complications.     

膀胱肿瘤电切术中行闭孔神经阻滞防止闭孔神经反射的效果分析

目的 探讨经尿道膀胱肿瘤电切术中采用闭孔神经阻滞防止闭孔神经反射的临床效果.方法 对214例膀胱癌患者行经尿道电切术,治疗组113例在腰-硬联合麻醉基础上进行闭孔神经阻滞,而对照组101例仅行单纯腰-硬联合麻醉.结果 治疗组闭孔神经反射发生率（9.7%）明显低于对照组（22.8%）（P〈0.05）,两组复发率差异无统计学意义（21.2% vs 25.7%,P＆gt;0.05）.结论 在经尿道膀胱肿瘤电切术中采取闭孔神经阻滞能明显减少闭孔神经反射的发生,提高手术的安全性和有效性,临床效果良好.     

Adding a selective obturator nerve block to the parasacral sciatic nerve block: an evaluation

Our aim was to objectively evaluate the efficacy of obturator nerve anesthesia after a parasacral block. Patients scheduled for knee surgery had a baseline adductor strength evaluation. After a parasacral block with 30 mL 0.75% ropivacaine, sensory deficit in the sciatic distribution (temperature discrimination) and adductor strength were assessed at 5-min intervals. Patients with an incomplete sensory block (defined as a temperature discrimination score of less than 2 in the 3 cutaneous distributions of the sciatic nerve tested) 30 min after the parasacral block were excluded from the study. Subsequently, a selective obturator block was performed with 7 mL 0.75% ropivacaine and adductor strength was reassessed at 5 min intervals for 15 min. Finally, a femoral block was performed using 10 mL 0.75% ropivacaine. Patient discomfort level during each block was assessed using a visual analog scale (VAS). Thirty-one patients completed the study. Five patients were excluded as a result of inadequate sensory block in the sciatic distribution 30 min after the parasacral block (success rate of 89%). Thirty min after the parasacral block, adductor strength decreased by 11.3% +/- 7% compared with baseline (85 +/- 24 versus 97 +/- 28 mm Hg, P = 0.002). Fifteen min after the obturator nerve block, adductor muscle strength decreased by an additional 69% +/- 7% (16.6 +/- 15 versus 85 +/- 24 mm Hg, P < 0.0001). VAS scores were similar for all blocks (26 +/- 19, 28 +/- 24, and 27 +/- 19 mm for parasacral, obturator, and femoral respectively). Four parasacral blocks were simulated in 2 fresh cadavers using 30 mL of colored latex solution. The spread of the die in relation to the obturator nerve was assessed. Injection of 30 mL colored latex into cadavers resulted in spread of the injectate restricted to the sacral plexus. These findings demonstrate the unreliability of parasacral block to achieve anesthesia of the obturator nerve. A selective obturator block should be considered in the clinical setting when this is desirable.