Marc A. M. Simon

A cervical anterior spinal artery syndrome after diagnostic blockade of the right C6-nerve root.

A 48-year-old man suffered from intractable neck pain irradiating to his right arm. Magnetic resonance imaging (MRI) of the cervical spine was unremarkable. A right-sided diagnostic C6-nerve root blockade was performed. Immediately following this seemingly uneventful procedure he developed a MRI-proven fatal cervical spinal cord infarction. We describe the blood supply of the cervical spinal cord and suggest that this infarction resulted from an impaired perfusion of the major feeding anterior radicular artery of the spinal cord, after local injection of iotrolan, bupivacaine, and triamcinolon-hexacetonide around the C6-nerve root on the right side.

Intravenous regional anesthesia with 0.5% articaine, 0.5% lidocaine, or 0.5% prilocaine : a double-blind randomized clinical study

Background and Objectives. The purpose of this study was to compare the effectiveness of three local anesthetic agents for intravenous regional anesthesia in the upper limb. Side effects and plasma concentrations of the drugs in the doses administered for IVRA were also studied. Methods. Thirty patients in ASA groups I and II received intravenous regional anesthesia for surgery of the upper limb. In a double‐blind prospective study, they were randomly allocated to receive one of three local anesthetics: articaine, lidocaine, or prilocaine. Patients received 40 mL of a 0.5% solution of the local anesthetic. The onset time of sensory block was assessed by pinprick and the extent of motor block was was scored as 0‐3. Plasma concentrations of local anesthetics were determined in all patients from serial arterial blood samples drawn at predetermined times before and after tourniquet release. Results. The onset time of sensory block was significantly shorter (2.5 minutes) in the articaine group than in the lidocaine group (11.1 minutes) or the prilocaine group (10.9 minutes) (Scheffe, P < .05). Development of motor block was equal in all three groups (score 2). Estimation of plasma concentrations by high performance liquid chromatography showed that the peak level in all 30 patients was reached immediately after release of the tourniquet; plasma concentrations thereafter gradually declined. Maximum concentrations of articaine, lidocaine, and prilocaine were, 1.85, 8.5, and 4.4 μg/mL, respectively. No signs of local anesthetic toxicity of the cardiovascular or central nervous systems were seen. Conclusion. Articaine had the fastest onset of sensory block and the lowest peak plasma concentration of the three local anesthetics when used for intravenous regional anesthesia.

Clinical Pharmacokinetics of R(+)-and S(−)-mepivacaine After High Doses of Racemic Mepivacaine With Epinephrine in the Combined Psoas Compartment/sciatic Nerve Block

The purpose of this study was to investigate the pharmacokinetics of R(+)- and S(-)-mepivacaine in 10 male patients after injection of a high dose (731 mg) of racemic R,S-mepivacaine for a combined psoas compartment/sciatic nerve block. Arterial blood samples were taken, and the plasma concentrations of the stereoisomers R(+)- and S(-)-mepivacaine were measured by means of high-performance liquid chromatography (HPLC) with a Chiral AGP column. The S(-) isomer reached higher plasma concentrations than the R(+) isomer. The maximal plasma concentration (Cmax) of R(+) was 1.54 +/- 0.34 micrograms/mL, whereas that of the S(-) isomer was 2.34 +/- 0.51 micrograms/mL (P = 0.00050). The time at which Cmax was reached (Tmax) was identical for both isomers. The area under the plasma concentration-time curve from t = 0 to infinity (AUC infinity) of S(-)-mepivacaine was almost double that of R(+)-mepivacaine. The elimination half-life (T1/2) was identical for both isomers (3 h), which means that the calculated total body clearance and the calculated steady-state volume of the distribution of R(+) are, respectively, 1.7 and 1.5 times larger than that of the S(-) isomer. We conclude that the plasma concentrations of the S(-)-mepivacaine isomer were higher than those of the R(+) isomer because of a smaller volume of distribution and a slower total body clearance.

Comparison of the effects and disposition kinetics of articaine and lidocaine in 20 patients undergoing intravenous regional anaesthesia during day case surgery

The aim of this investigation was to assess the effects and dispostion kinetics of the local anaesthetic drugs (±)articaine and lidocaine during intravenous regional anaesthesia (IVRA). The mean onset time of surgical analgesia of articaine was 2.5±1.1 min and that of lidocaine 11.2 ± 5.1 min (p = 0.0006). None of the patients exhibited objective symptoms of toxicity, either local or systemic, during injection of articaine or lidocaine, nor were there any subjective complaints. No changes in blood pressure, heart rate or oxygen saturation were observed with these local anesthetics at any time during the procedure, nor after deflation of the tourniquet. After releasing the tourniquet, articaine appears in the blood and is rapidly eliminated with a t1/2a of 5±3 min and a t1/2β of 59±39 min due to hydrolysis. Lidocaine is rapidly and biexponentially eliminated with similar half‐lives of t1/2a of 4±2 min and a t1/2β of 79±31 min. Total body clearance of articaine (8.9±3.5 L/min) is ten times greater than that of lidocaine (0.9±0.4 L/min; p = 0.0005). We concluded that both (±)articaine and lidocaine are suitable and safe agents for IVRA with rapid onset of good surgical anaesthesia. Articaine is a racemic mixture, which is nowadays considered as less favourable. After releasing the tourniquet, articaine is eliminated with a t1/2β of 60 min and lidocaine with a t1/2β of 80 min. Quicker onset and shorter elimination time favours (±)articaine over lidocaine for IVRA in day case settings so that patients treated with articaine will be ‘drug free’ more quickly than those who receive lidocaine. Faster elimination and more rapid onset are important advantages for articaine in IVRA for day‐case procedures.

Similar Motor Block Effects and Disposition Kinetics between Lidocaine and (±)Mepivacaine in Patients Undergoing Axillary Brachial Plexus Block during Day Case Surgery

The aim of this investigation was to compare the clinical effects and pharmacokinetics of lidocaine (one metabolite) and mepivacaine (two metabolites) in 2 groups of 15 patients undergoing axillary brachial plexus anaesthesia. The study had a randomised design. The 30 patients were divided into 2 groups. The patients received either lidocaine (600 mg = 2.561 mMol + 5 μg ml-1 adrenaline) or mepivacaine (600 mg = 2.436 mMol + 5 μg ml-1 adrenaline), injected via the axilla near the brachial plexus over a period of 30 s. Onset of surgical analgesia was defined as the period from the end of the local anaesthetic injection to the loss of pinprick sensation in the distribution of the ulnar, radial, and median nerve. Motor block was measured. Onset of motor block was similar for both drugs. Lidocaine is eliminated biexponentially with a t1/2α of 9.95 ± 14.3 min and a t1/2β of 2.86 α 1.55 h. Lidocaine is metabolised into MEGX (tmax 2.31 α 0.84 h; Cmax 0.32 α 0.13 mg l-1; t1/2β 2.36 α 2.35 h; total body clearance was 67.9 α 28.9 l h-1). Mepivacaine is eliminated rapidly and monoexponentially with a t1/2 of 4.78 α 2.38 h, a Cmax of 3.89 α 0.83 mg l-1, and a tmax of 0.41 α 0.19 h. The total body clearance of mepivacaine is 50% of that of lidocaine, 26.9 α 10.6 l h-1 vs. 67.9 α 28.9 l h-1, respectively (p <0.0001). (α)Mepivacaine is metabolised into (α)4-OHmepivacaine (Cmax 0.45 α 0.25 mg l-1; t1/2β 6.48 α 6.57 h) and (α)2,6-pipecoloxylidide (Cmax 0.56 α 0.30 mg l-1; t1/2b 1.48 α 0.74 h). For the axillary brachial plexus block, lidocaine and mepivacaine show similar pharmacodynamic and pharmacokinetic behaviour, despite the number of metabolites, and can therefore be used to the clinical preference for this regional anaesthetic technique.

Comparison of the disposition kinetics of lidocaine and (±)prilocaine in 20 patients undergoing intravenous regional anaesthesia during day case surgery

Objective: The aim of this investigation was to compare the pharmacokinetics of lidocaine and prilocaine in two groups of 10 patients undergoing intravenous regional anaesthesia.

Comparison of the effects and disposition kinetics of lidocaine and (+/-)prilocaine in patients undergoing axillary brachial plexus block during day case surgery.

AbstractObjective: The aim of this investigation was to compare the clinical effects and pharmacokinetics of lidocaine and prilocaine in two groups of 15 patients undergoing axillary brachial plexus anaesthesia. Methods: The study had a randomised design. Patients were allocated to one of the two groups of 15. Each group received either lidocaine (600mg = 2.56 mmol/L + 5 mg/L adrenaline) or prilocaine (600mg = 2.72 mmol/L + 5 mg/L adrenaline), injected over a period of 30 seconds. Onset of the surgical analgesia was defined as the period from the end of the injection of the local anaesthetic to the loss of pinprick sensation in the distribution of all three nerves. Results: The mean onset time of surgical analgesia of both lidocaine and prilocaine was 10 minutes. Lidocaine was biexponentially eliminated with a rapid elimination phase half-life (t½α) of 9.95 ± 14.3 minutes and a terminal elimination phase half-life (t½β) of 2.86 ± 1.55 hours. Lidocaine was metabolised to MEGX (monoethylglycylxylidide); time to reach maximum plasma concentration (tmax) 2.3 ± 0.8 hours; maximum plasma concentration (Cmax) 0.32 ± 0.13 mg/L; t½β 2.4 ± 2.4 hours. Lidocaine total body clearance was 67.8 ± 28.8 L/h. Prilocaine was rapidly and biexponentially eliminated with a t½α of 9.4 ± 18.4 minutes and a t½β of 2.12 ± 1.28 hours. The total body clearance of prilocaine (150 ± 53 L/h) was higher than that of lidocaine (p = 0.0255). Both compounds demonstrated a comparable volume of distribution (Vd), while the volume of distribution at steady-state (Vss) and the volume of distribution in the second compartment (Vβ) values of prilocaine were a factor of 1.6 higher than those of lidocaine (p < 0.001). Both compounds showed a comparable t½α (p > 0.8) and a comparable t½β (p = 0.26). Conclusion: Following axillary administration, lidocaine and prilocaine demonstrated similar pharmacokinetic behaviour and could therefore be used as the clinical preference for this regional anaesthesia technique.

Comment on ‘A cervical anterior spinal artery syndrome after diagnostic blockade of the right C6-nerve root’, PJAM Brouwers et al., PAIN 91 (2001) 397–399

tible with a cauda equina lesion. I have also been aware of three similar cases following root sleeve injections of local anaesthetic and steroid. I do not know the details of the first case, but have recently been asked to comment on a case with persisting neurological sequelae after injection at C3, with hemiparesis and sensory deficit, and a further patient with urinary incontinence following root sleeve injections unilaterally at L4, L5 and S1, although it is doubtful that this was due to the injection. The anatomy of the blood supply to the cord is well described. Dommisse et al. (1980) have performed anatomical dissection of 50 human cadavers. The cord is totally dependent on the three longitudinal arterial trunks, which run from the medulla to the conus medullaris. The anterior spinal artery overlies the median sulcus of the cord, and gives off anterior perforators that supply the cord. The paired posterolateral trunks are small and tortuous, being intertwined between the posterior rootlets. The posterior perforators penetrate the cord in the company of the nerve rootlets. Ligation of the anterior vessel distal to the artery of Adamkiewicz usually leads to paraplegia in the rhesus monkey. The medullary feeder arteries supply and maintain the long arterial trunks. These are variable in number and level of supply. They arise from the segmental arteries (which supply the segmental nerves, and arise at every segmental level). There are usually more than nine (two to 17) supplying the anterior and more than 15 (six to 25) supplying the posterior trunks. The artery of Adamkiewicz (arteria radicalis anterior magna) is the largest medullary feeder and occurs on the left side in 80% of cases between T7 and L4, especially T9–T11. The intervertebral foraminae are of critical value in the blood supply of the cord, as the feeder vessels pass through the foraminae alongside the nerve root. However, Dommisse does show that there are arteri-arterial anastomoses between the segmental intervertebral arteries in the thorax. They are potential sources of alternative supply to the cord. Dommisse proposed surgical guidelines to prevent postoperative paraplegia. He stated that neither cautery nor tight plugging nor heavy retraction should be applied to the intervertebral foramen, lest a single essential feeder vessel be destroyed. Two decades on, we should heed his advice, and treat the foramen with respect. Trauma to the feeding vessels from the introduction of needles to the foramen can produce vasospasm, and the potential for consequent cord ischaemia. We have an obligation to warn our patients of the risk, however small, of such a catastrophic complication when we perform such procedures.