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Intravenous lipid emulsion is, in some countries, the recommended treatment for local anaesthetic toxicity. Systemic local anaesthetic toxicity results in hypoxaemia and acidosis, and whether this influences the effects of lipid therapy on drug concentrations and cardiovascular recovery is currently unknown. Twenty anaesthetised pigs were given a 3-mg/kg bolus of levobupivacaine followed by a five minute phase of hypoventilation and 1 mmol/kg of lactic acid in one minute. After lactic acid infusion, pigs were treated, in randomised order, with either 20% lipid emulsion or Ringer's acetate for 30 min: a 1.5-ml/kg bolus followed by a 0.25-ml/kg/minute infusion. Haemodynamic parameters were recorded and blood samples were collected for pharmacokinetic analysis. There was no difference between the groups in the area under the plasma levobupivacaine concentration-time curve (AUC) or between that and AUC of unentrapped levobupivacaine in the Lipid group, or in the plasma half-lives. The cardiovascular outcome and normalisation of the electrocardiogram were similar in both groups. Five pigs developed marked hypotension: one in both groups died, while two in the Lipid group and one in the Ringer group needed adrenaline. Administration of lipid emulsion did not improve cardiovascular recovery from levobupivacaine toxicity exacerbated by acidosis and hypoxaemia. Lipid emulsion did not entrap levobupivacaine or affect levobupivacaine pharmacokinetics.

Intravenous lipid emulsion has been suggested as treatment for local anaesthetic toxicity, but the exact mechanism of action is still uncertain. Controlled studies on the effect of lipid emulsion on toxic doses of local anaesthetics have not been performed in man. In randomized, subject-blinded and two-phase cross-over fashion, eight healthy volunteers were given a 1.5 ml/kg bolus of 20% Intralipid(®) (200 mg/ml) or Ringer's acetate solution intravenously, followed by a rapid injection of lidocaine 1.0 mg/kg. Then, the same solution as in the bolus was infused at a rate of 0.25 ml/kg/min. for 30 min. Electroencephalography (EEG) was recorded, and 5 min. after lidocaine injection, the volunteers were asked to report subjective symptoms. Total and un-entrapped lidocaine plasma concentrations were measured from venous blood samples. EEG band power changes (delta, alpha and beta) after the lidocaine bolus were similar during lipid and during Ringer infusion. There were no differences between infusions in the subjective symptoms of central nervous system toxicity. Lidocaine was only minimally entrapped in the plasma by lipid emulsion, but the mean un-entrapped lidocaine area under concentration-time curve from 0 to 30 min. was clearly smaller during lipid than Ringer infusion (16.4 versus 21.3 mg × min/l, p = 0.044). Intravenous lipid emulsion did not influence subjective toxicity symptoms nor affect the EEG changes caused by lidocaine., (© 2014 Nordic Association for the Publication of BCPT (former Nordic Pharmacological Society).)

Reports on the efficacy and pharmacokinetics of local anesthetics in uremic patients have been controversial. Our study involved 29 uremic and 28 nonuremic patients. We performed axillary block with ropivacaine 300 mg (50 mL). Venous blood samples were drawn for 24 h for assay of total and unbound plasma ropivacaine, 3-hydroxyropivacaine, pipecoloxylidide (PPX), and serum alpha(1)-acid glycoprotein (AAG). Block quality was similar in both groups. No toxicity occurred. Plasma clearance of ropivacaine was smaller and the area under the concentration-time curve of ropivacaine, 3-hydroxyropivacaine, and PPX larger in the uremic patients. The plasma concentration of PPX increased until 24 h in uremic patients whose AAG concentrations were also larger throughout the study. The free fraction of ropivacaine in plasma was smaller in the uremic group when measured 60 min and 12 h after the block, but the unbound concentration of ropivacaine was larger in the uremic group at 12 h. Enhanced absorption of ropivacaine into circulation, increased binding to AAG, and probably reduced urinary excretion of the metabolites lead to larger total plasma concentrations of ropivacaine and its main metabolites in uremic patients.

Background and Objectives: Ropivacaine is a potent local anesthetic that, experimentally at low concentrations, produces an effective block of pain conducting nerve fibers. Therefore, it was hypothesized that 0.1% and 0.2% ropivacaine would provide clinically adequate postoperative analgesia in continuous axillary plexus block., Methods: Sixty patients (ASA I-II) scheduled for elective hand or forearm surgery received 5 mg/kg of 0.75% ropivacaine for axillary block using nerve stimulator technique. One hour later, in random order, a continuous infusion of either 0.1% ropivacaine (0.125 mg/kg/h), 0.2% ropivacaine (0.25 mg/kg/h) or saline 6 to 11 mL/h was started., Results: The mean total ropivacaine dose for the surgical block was 5.1 to 5.2 mg/kg with the supplementation. All patients were pain free for the first 12 to 15 hours after the block. The need for postoperative analgesics during the infusion was similar in all groups. After the initial block, the maximum plasma concentrations (mean 2.5 microg/mL) were measured at 45 or 60 minutes after injection. The highest individual plasma concentration was 4.2 microg/mL. Despite the high venous peak concentration, no toxic reactions were observed. The mean peak plasma concentration (Cmax) was 2.2+/-0.5 microg/mL for saline, 2.6+/-0.8 microg/mL for 0.1% ropivacaine, and 2.6+/-0.7 microg/mL for 0.2% ropivacaine. During the continuous infusion of 24 hours, the ropivacaine concentration declined steadily., Conclusions: Ropivacaine is safe and effective for axillary brachial plexus block. The continuous infusion of 0.1% or 0.2% ropivacaine was no more beneficial than an infusion of saline in relieving postoperative pain in patients having elective hand surgery. None of the infusions were sufficient to adequately treat the patients' pain without the addition of adjunct agents.

Background and Objectives: Earlier studies of the use of articaine in intravenous regional anesthesia (IVRA) are conflicting. In fact, despite similar physicochemical properties and regional anesthetic action, significant differences between articaine and prilocaine in IVRA have been reported. Articaine, being a potent local anesthetic with low degree of toxicity and being rapidly metabolized by esterases, could be a useful local anesthetic particularly in IVRA and, perhaps, could challenge prilocaine, the present local anesthetic of choice for this technique., Methods: A double-blind, cross-over study of IVRA of the upper extremity in 10 healthy volunteers was performed. There was at least a 1-week interval between the use of the two anesthetics in each volunteer. After exsanguination with an Esmarch bandage, IVRA was induced either with preservative-free 0.5% articaine (5% Ultracaine, Hoechst, Germany, diluted with 0.9% NaCl) or 0.5% prilocaine (Citanest, Astra, Södertälje, Sweden) (35-50 mL, according to weight), injected in 2 minutes. Sensation at defined skin spots that were innervated by the median, musculocutaneous, radial, and ulnar nerves was tested by pinprick; motor function was tested by the movements of the wrist. After 20 minutes, the tourniquet cuff was deflated in one step. Circulatory, toxic, and skin reactions were registered. At least 1 week after the second IVRA intracutaneous allergy testing with 0.5% articaine, 0.5% prilocaine, histamine, and saline was performed., Results: There were no significant differences between the two local anesthetics in the onset of analgesia or anesthesia, degree of motor block, and recovery of IVRA. Onset of analgesia occurred 4.2-5.6 minutes, on average, after the injection. One volunteer had short-lasting tinnitus after tourniquet cuff deflation when prilocaine was used. Erythematous nonitching skin rashes developed in 8 of 10 volunteers when articaine was used, and two volunteers had rashes when prilocaine was used. These rashes disappeared within an hour, and negative intracutaneous test results confirmed their nonallergic origin., Conclusion: Both 0.5% articaine and 0.5% prilocaine, in a median dose of 40 mL in adults, injected in 2 minutes, are effective and equipotent local anesthetics in IVRA of the arm. An earlier reported four-time faster onset time of the block by articaine in comparison with prilocaine may be caused by a very rapid injection rate (40 mL/30 sec) by the investigators of that study. The erythematous skin rashes after IVRA, in particular when articaine was used, may be a sign of venous endothelial irritation.

Background and Objectives: The use of thin single-hole pencil-point (SHPP) spinal needles may be a reason for subarachnoid maldistribution of local anesthetic. A new double-hole pencil-point (DHPP) needle may be preferable because of a theoretic more uniform initial distribution of local anesthetic., Methods: This was a prospective, double-blinded study of 50 patients randomly selected to have spinal anesthesia using either single-hole 27-gauge (B. Braun, Melsungen, Germany) or double-hole 26-gauge (A.L.B. Medical Inc., U.S.A.) pencil-point needles. The former were inserted with the side port directed caudally and the latter with openings in both caudal and cranial direction. Two milliliters of hyperbaric 0.5% bupivacaine were injected in 1 minute, and sensory and motor block were studied at regular intervals during spinal anesthesia. All patients were interviewed on the first (personal) and the seventh (mailed questionnaire) postoperative day. Furthermore, microscopic inspection of the spinal needles was performed., Results: There were no statistically significant differences in sensory or motor block levels between the two needle types at any time during spinal anesthesia. Likewise, there was no difference in the duration of spinal block. The postanesthetic side effects (headache, backache, pricking, numbness, weakness) were similar in both groups. Light and electron microscopic examination showed resistance of the SHPP needles to tip damage. On the other hand, the DHPP needle tips seemed to be distorted quite frequently, and, even in unused needles, the tip was blunt and asymmetric., Conclusion: There was no difference between the spread of analgesia using either SHPP or DHPP spinal needles. The DHPP needles appear to be vulnerable to tip damage from mechanical contact.

The analgesic effect of topical application of local anaesthetics on the gingival mucosa and the absorption of the local anaesthetics into the blood were investigated in healthy volunteers by using a 5% eutectic mixture of the local anaesthetics lignocaine (100 mg) and prilocaine (100 mg) plus emulsifier (EMLA) or 10% lignocaine (200 mg) spray (Xylocain). The pain threshold on labial gingiva was measured by using the stimulator of an EMG-apparatus and a pair of stimulating electrodes, specially constructed for this purpose. There were no differences between the two methods in producing analgesia which was at its maximum in 13 to 14 minutes, on average. Sensation of the gingiva (pain thresholds), had usually returned to normal within 30 minutes. In the dosages used, the absorption of the local anaesthetics was more rapid after the mixture application than after spray application. No toxic reactions occurred.