Plasma Lidocaine Levels Research Articles

Lidocaine infusions for refractory chronic migraine: a retrospective analysis

IntroductionPatients with refractory chronic migraine have poor quality of life. Intravenous infusions are indicated to rapidly ‘break the cycle’ of pain. Lidocaine infusions may be effective but evidence is limited.MethodsThe...

LID study: Plasma lidocaine levels following airway topicalisation for paediatric microlaryngobronchoscopy (MLB).

A dose of 5 mg/kg lidocaine is considered appropriate for paediatric airway topicalisation. Existing literature suggests that younger children are susceptible to toxic lidocaine plasma levels and achieve this at a faster rate. The primary outcome of this study was to ascertain peak plasma lidocaine levels after topicalisation for airway endoscopy. Secondary endpoints included: time to peak lidocaine plasma levels, signs of lidocaine toxicity (restricted to ECG changes or seizures when under anaesthesia) and clinical adverse events of laryngospasm, coughing or desaturation during the procedure. Data were collected prospectively over 18months at Royal Manchester Children's Hospital. Children aged 0-8years undergoing elective diagnostic or therapeutic airway endoscopy were included within the study. Standardised 2% lidocaine was used for airway topicalisation. Dose varied depending upon the practitioner's usual practice. Venous bloodsampling occurred at 5, 10, 15 and 20 min post-administration and plasma lidocaine levels (ng/ml) were analysed. A significant relationship exists between higher peak plasma levels and ages <18 months (p=.00973). Strong linear correlation exists between body weight and age for our cohort (r=.88). Higher peak plasma lidocaine levels occur with total dose volumes between 2 and 3 mls of 2% lidocaine local anaesthetic (p=.03) compared with <2 ml total dose volumes. Data suggest a potential relationship of lower body weights achieving higher peak plasma levels (p=.0516). Reduced interquartile variation of peak plasma lidocaine levels exists when lidocaine dosing is <5 mg/kg. Age and total dose volume of topicalised lidocaine have a significant relationship with plasma lidocaine levels. A dose of 5mg/kg topicalised lidocaine for paediatric airway endoscopy is safe and provides good operating conditions. Lower patient body weights trend towards higher peak lidocaine plasma concentrations and require further investigation.

Biorelevant In Vitro Skin Permeation Testing and In Vivo Pharmacokinetic Characterization of Lidocaine from a Nonaqueous Drug-in-Matrix Topical System

Recently, lidocaine topical systems utilizing nonaqueous matrices have been developed and provide efficient lidocaine delivery through the skin, such that lower concentrations of drug provide equivalent or greater drug delivery than drug-in-matrix hydrogel lidocaine patches. This study characterizes drug delivery from a nonaqueous lidocaine topical system with increasing drug load both in vitro and in vivo. Topical systems formulated with either 1.8% or 5.4% lidocaine were applied to healthy volunteers’ backs (n = 15) for 12 h in a single-center, open-label, four-treatment, four-period crossover pharmacokinetic study. Subjects were dosed with either three 1.8% systems or one, two, or three 5.4% systems in each period. Blood was collected for up to 48 h, and plasma lidocaine levels were measured with a validated HPLC method. In parallel, human and mouse skin models characterized the in vitro skin permeation profile. The pharmacokinetic profile was linear between one, two, and three lidocaine 5.4% applications. Application of three lidocaine 1.8% systems (108 mg lidocaine) was bioequivalent to one lidocaine 5.4% system (108 mg lidocaine). Both topical systems remained well adhered to the skin and irritation was mild. The 5.4% system had approximately threefold higher skin permeability than the 1.8% system in the mouse and human skin models. The results indicate increasing the drug load by three times results in triple the drug delivery both in vivo and in vitro. The relationship between the in vitro permeation and in vivo absorption correlates and is nonlinear.

Lidocaine safety after saphenous vein tumescent anesthesia.

Objectives For endovenous thermal ablation of the saphenous veins, tumescent lidocaine anesthesia is often used. Unfortunately, information is sparse on the pharmacokinetics of lidocaine absorption and its maximum safe dose. The aim of this study was to evaluate plasma concentration of lidocaine on 12 lead electrocardiograms (ECGs) and symptoms over time after the administration of tumescent lidocaine during endovenous thermal ablation procedures in healthy volunteers. Methods An observational study of symptoms, 12 lead ECGs, and serum lidocaine levels were obtained following the administration of either 15 mg/kg lidocaine or 35 mg/kg lidocaine in the perivenous saphenous space under ultrasound guidance. Blood was drawn at regular intervals in heparinized tubes and spun at 3000 r/min for 10 min. The plasma lidocaine levels were plotted vs. time for statistical comparisons. Results With the 35 mg/kg dose, four of 11 participants developed symptoms of lidocaine toxicity at 40 min, which resolved by 180 min. The 35 mg/kg dose resulted in a mean serum lidocaine peak of 2.55 µg/ml at 60 min. The 15 mg/kg dose did not result in any symptoms of lidocaine toxicity, and it resulted in a serum lidocaine plateau of 0.85 µg/ml at 180 min. No significant changes were seen on the 12-lead ECG after the administration of lidocaine at either dose. Conclusions The 15 mg/kg total lidocaine dose did not cause symptoms and appears to be a safe lidocaine dosage for tumescent anesthesia for saphenous endovenous thermal ablations. The 35 mg/kg lidocaine dose is associated with lidocaine toxicity. More study on the maximal safe dose of lidocaine for endovenous thermal ablations is needed.

Blood concentration of prilocaine and lidocaine after the use of topical anesthesia (Oraqix® ) in lacerated wounds.

Soft tissue injuries have been reported as being sutured using only topical anesthesia applied in the laceration wound. The objective of this study was to assess the pharmacokinetic profile of components of Oraqix® (2.5% prilocaine and 2.5% lidocaine) when applied in a laceration as compared to intact skin application in the mouse. A total of 200 BALB/c male mice were used in this study. The mice were divided into three groups: group A: shaved and laceration group (80 mice); B: shaved and intact skin group (80 mice); and C: control group (shaved, no treatment; 40 mice) which underwent the same procedures but without application of Oraqix® . Blood samples were collected over 90 min. Plasma sample analysis employing liquid chromatography coupled with the tandem mass spectrometric (LC-MS/MS) method was used to determine plasma concentrations of lidocaine and prilocaine. Pharmacokinetic analysis of mouse plasma concentrations was carried out by standard non-compartmental methods. Absorption of both lidocaine and prilocaine was rapid. Cmax and AUC values of lidocaine were significantly increased by fourfold and twofold, respectively, in lacerated mouse skin compared to intact skin. Similarly, prilocaine's Cmax and AUC values were also increased by 2.5-fold and fourfold, respectively, in lacerated skin compared to intact skin. When Oraqix® was applied directly into the skin laceration, the plasma concentration of lidocaine and prilocaine was significantly increased as compared to when applied on intact skin. The present study, albeit in mice, indicates that the plasma levels of lidocaine and prilocaine can reach very high levels when the thermosetting gel Oraqix® is placed directly in wounds.

Systemic Lidocaine Fails to Improve Postoperative Pain, But Reduces Time to Discharge Readiness in Patients Undergoing Laparoscopic Sterilization in Day-Case Surgery: A Double-Blind, Randomized, Placebo-Controlled Trial.

Perioperative systemic lidocaine provides postoperative analgesia, decreases opioid consumption, and facilitates rehabilitation in abdominal surgery. We hypothesized that systemic lidocaine has analgesic effects in women undergoing day-case laparoscopic sterilization. Eighty women were randomized in this prospective, double-blind trial to receive either lidocaine (intravenous bolus of 1.5 mg/kg at induction of anesthesia, followed by an infusion of 1.5 mg · kg · h, which was continued until 30 minutes after arrival at the postanesthesia care unit [PACU]) or placebo. The primary end point was the proportion of patients with a numeric rating scale (NRS) of greater than 3, 30 minutes after arrival at the PACU. Secondary outcomes included total opioid consumption, postoperative pain scores, incidence of postoperative nausea and vomiting, and time to readiness for discharge. This clinical trial was registered (Eudra CT 2011-001315-31). Thirty minutes after PACU admission, the proportion of patients with an NRS score of greater than 3 did not differ between the groups (lidocaine group: 59% vs placebo group: 58%). The postoperative NRS for pain over the entire observation period was not significantly different between lidocaine and placebo groups (mean, 3.1 [SD, 0.7] vs 2.8 [SD, 0.6]; P = 0.4). Groups did not differ with respect to perioperative opioid consumption. Patients in the placebo group suffered significantly less from nausea (NRS: 0.1 [SD, 0.1] [placebo] vs 0.3 [SD, 0.1] [lidocaine]; P = 0.02) and required less postoperative nausea and vomiting rescue medication (1 patient in the placebo group vs 7 in the lidocaine group; P = 0.03). The time to meet hospital discharge criteria was significantly lower in the lidocaine group (median, 177 minutes [range, 96-408 minutes] vs 221 minutes [range, 121-420 minutes]; P = 0.02). The mean lidocaine plasma levels at the end of IV lidocaine infusion was 2.5 (SD, 1.1) μg/mL. In laparoscopic sterilization, systemic lidocaine reduces time to readiness for hospital discharge.

Convulsion tardive après instillation de lidocaïne pour bronchoscopie

Lidocaine toxicity usually appears rapidly and is directly correlated with plasma concentrations of the drug. We report a case of a late neurologic toxicity occurring after instillation of lidocaine during fibre-optic bronchoscopy. A patient with bronchiolitis obliterans underwent a diagnostic bronchoscopy. She received multiples instillations of Xylocaine(®) 2% (lidocaine). Three and a half hours later, she had a tonic-clonic seizure. Seven hours later, this recurred. Lidocaine plasma levels were in the toxic range at the time of the first seizure (18.32μg/mL) with a significant decrease in the concentration noted 24hours later. The slow absorption of lidocaine into the blood from the bronchial tree explains the delayed neurologic toxicity. Our observation is a reminder that complications can occur due to high doses of lidocaïne administrated by instillation. Thus, if the recommended dose of lidocaine is exceeded, it is essential to monitor patients closely for a prolonged period, especially those with fibrosing lung disease in order to avoid possible late toxicity.

O-209 Continuous Incisional Lidocaine Infusion In Paediatric Patients Following Open Heart Surgery

Study objective To evaluate the efficacy of local incisional lidocaine infusion after heart surgery. Methods Observational prospective study including post cardiac surgery children in whom a 0,5% lidocaine elastomer was intraoperatively placed within the surgical wound. Lidocaine doses and plasma levels 48 h after administration, adverse effects, additional analgesic or sedative drugs and analgesia and sedation score were registered. All patients received intravenous metamizol and paracetamol. Results 105 patients were analysed. Median age was 66 months, with 21% of patients under 2 years of age. The most frequent surgical interventions were: Fontan surgery (26.2%), atrial septal defects (20.4%) and ventricular septal defects (10.7%). Median lidocaine administration duration was 58 h. 52.4% received fentanyl infusion (mean dose 1 mcg/kg/h, mean duration 24 h), 18.1% received midazolam infusion (1.5 mcg/kg/h, 8 h) and 12% received propofol (1.5 mg/kg/h, 4 h). Mean comfort score was 21.8 points and mean analgesia score was 1.9 (62% of patients required additional analgesia). Fentanyl infusion was less often needed in patients over 2 years old than in younger patients (45.8% vs. 77.3%; p = 0.015). Midazolam infusion was also less often required in patients over 2 years old (13.3% vs 36.4%; p = 0.025). Lidocaine plasma levels were recorded 48 h after administration in 66 patients, 46% (n = 31) were within therapeutic range (1.4–5 mcg/ml). No important side – effects attributable to lidocaine were observed. Conclusions Incisional analgesia with lidocaine is safe and effective after cardiac surgery. Children over 2 years of age require less additional analgesia and sedation.

Effectiveness of pre-peritoneal continuous wound infusion with lidocaine for pain control following ovariohysterectomy in dogs

This study compared the post-operative analgesic efficacy of continuous lidocaine administration with that of intramuscular (IM) methadone in dogs undergoing ovariohysterectomy. Thirty-eight dogs were divided randomly into two groups. Following surgery, the lidocaine group (L) received a continuous lidocaine infusion (2 mg/kg/h) through a wound catheter inserted in the pre-peritoneal space; the control group (C) received methadone (0.2 mg/kg IM). A dynamic and interactive visual analogue scale (DIVAS), the Scale-Form Glasgow Composite Measure Scale (CMPS-SF), mechanical wound thresholds, heart rate, respiratory rate and blood pressure were assessed pre-operatively and 2, 4, 6, 18, and 24 h after surgery. The presence of the wound catheter prevented the evaluator from remaining blinded to group allocations. Plasma lidocaine and cortisol levels were measured 2, 6, 18, and 24 h after surgery.There were no intergroup differences in any pain assessment scale scores at any time point. Stable intravenous lidocaine levels were observed. Four animals in the control group but none in the lidocaine group required rescue analgesia. There were no differences in complication rates between groups. Continuous locoregional lidocaine delivered via a wound catheter between the parietal peritoneum and abdominal muscle offers effective analgesia in dogs during ovariohysterectomy and appears to be a promising analgesic option in veterinary surgery.

5% Lidocaine Medicated Plaster Use in Children with Neuropathic Pain from Burn Sequelae

Neuropathic pain is a challenge in children with burn sequelae. Although relatively infrequent, the intensity and chronicity of neuropathic pain negatively impact functionality and quality of life. The use of 5% lidocaine medicated plaster has not previously been reported in children. We explored the effectiveness and safety of 5% lidocaine medicated plaster to treat neuropathic pain in children with burn sequelae. Three-month prospective, uncontrolled study. Corporation of Aid to Burned Children (COANIQUEM), a nonprofit pediatric burn rehabilitation center in Chile. Fourteen pediatric patients with burn sequelae neuropathic pain. Demographics, burn and pain evolution (type, intensity [using Wong-Baker FACES], and Douleur Neuropathique 4 [DN4]), and patient functionality. Plasma lidocaine levels were measured at 0, 12, 36, and 60 hours after treatment commencement. Fourteen patients were evaluable for plasma lidocaine levels. Twelve patients were available for clinical assessment (two patients lost to follow-up) [mean (standard deviation)]: age, 11 years 7 months (2 years 6 months); weight, 45 kg (11.9 kg); burn evolution, 5 years 6 months (4 years); time between burn and pain onset, 3 years 6 months (3 years 2 months); time between pain onset and treatment, 5.1 months (4.8 months); lidocaine, between < and ½ plaster; initial pain intensity (FACES), 6.8 (1.6); final pain intensity, 0 in 11/12 patients; DN4, initial-6, final-2.3. All patients reported improved functionality. Plasma lidocaine levels were ≤27.45 ng/mL (>180 times below critical levels). No adverse reactions occurred. These are the first published data suggesting that 5% lidocaine medicated plaster improves patient functionality, and is effective and safe for the treatment of neuropathic pain in pediatric patients with burn sequelae.

Effect of Liposomal Lidocaine and Sucrose Alone and in Combination for Venipuncture Pain in Newborns

To determine the relative effectiveness of liposomal lidocaine, sucrose, and their combination for reducing pain in term newborns. Ours was a double-blind, randomized, controlled, double-dummy trial of 330 healthy term newborns. Before venipuncture for the newborn screening test, neonates received (1) 1 g of liposomal lidocaine cream topically, (2) 2 mL of 24% sucrose solution orally, or (3) sucrose and liposomal lidocaine. The facial grimacing score (0-100) was used to assess pain. Adverse events and lidocaine levels were used to assess safety. Infant characteristics did not differ among groups. Facial grimacing scores were lower in the sucrose group compared with those in the liposomal lidocaine group (mean difference: -27 [95% confidence interval (CI): -36 to -19; P < .001) and for the sucrose plus liposomal lidocaine group compared with those in the liposomal lidocaine group (mean difference: -23 [95% CI: -31 to -14]; P < .001). The sucrose and sucrose plus liposomal lidocaine groups did not differ (mean difference: -5 [95% CI: -13 to 4]; P = .3). Local skin reactions were not observed, and the incidence of spitting up did not differ between sucrose-exposed and non-sucrose-exposed infants (1.4% vs 2.7%, respectively; P = .22). The mean (SD) plasma lidocaine level was 44.6 (55.3) ng/mL. Sucrose was more effective than liposomal lidocaine for reducing pain during venipuncture in newborns. The addition of liposomal lidocaine to sucrose did not confer any additional benefit to sucrose alone. There was no evidence of harm from liposomal lidocaine or sucrose.

Airway topicalisation using atomisation of lidocaine

We read the recent article of Woodruff et al. [1] with interest. A major advantage of the atomisation with lidocaine used in this study is the rapidity with which the airway can be anaesthetised, but this is achieved at the expense of administration of a large dose over a short time (about 5 min). We have concerns over the safety of this topicalisation method in general clinical practice, particularly when the drug is rapidly administered to non-obese patients. The British Thoracic Society has recommended a maximum lidocaine dosage of 8.2 mg.kg−1 for airway topical anaesthesia during bronchoscopy [2], but these drugs are administered in fractional doses at different sites in the airway over a prolonged time period. Compared with a large dose used in a shorter time, fractional doses sprayed over a longer period result in a lower plasma drug level [3]. Moreover, we do not agree that a large dose of lidocaine is safe in routine clinical practice for two reasons. First, lidocaine pharmacokinetics are complex, being affected by many factors, so the plasma lidocaine concentration achieved in a particular patient is often unpredictable. Even with recommended doses, patients may still sometimes achieve an unexpectedly high plasma concentration [4]. After large doses of lidocaine (7.1–14.8 mg.kg−1) administered by a spray-as-you-go technique, 36–92% of subjects report symptoms attributable to lidocaine toxicity [5, 6]. In addition, a healthy volunteer has died from lidocaine toxicity after fibreoptic bronchoscopy [7]. Second, lidocaine toxicity can occur even when the plasma lidocaine levels are in a ‘safe’ range [3, 8]. The authors suggest that airway topicalisation using nebulisation requires a long preparation time and may interfere with rapid turnover of patients. However, this technique can be safely performed in the holding area. We would also like to call the authors’ attention to the two papers in which low doses of nebulised lidocaine (100 or 160 mg) achieved adequate airway anaesthesia in most patients [9, 10]. We appreciate the reference to our recent article [3], but believe that Woodruff et al. have misrepresented our time (> 20 min) for airway topicalisation. As the main aim of our study was to compare the safety and efficacy of 2% and 4% lidocaine to produce airway topical anaesthesia with a spray-as-you-go technique, the repeated lidocaine sprays in the airway were performed at a 3–5 min interval to provide adequate penetration of local anaesthetic into the mucosa for maximal effect, and the whole airway topicalisation protocol required 19.2–28.2 min. The authors think that this prolonged time for airway topicalisation may sometimes be unacceptable. However, we feel that, as with other local anaesthetic methods, ‘tincture of time’ is a useful supplement to the application of airway topical anaesthesia. Inadequate airway topical anaesthesia due to the slow onset of the maximal effect can often result in larger doses' being given or repeated drug delivery in a short time, leading to overdose.

Plasma lidocaine levels associated with use of local anesthesia (1% lidocaine with 1:100,000 epinephrine) during Mohs micrographic surgery

Plasma lidocaine levels associated with use of local anesthesia (1% lidocaine with 1:100,000 epinephrine) during Mohs micrographic surgery

An assessment of the clinical utility of transperineal urethrosphincteric block (TUSB) in outpatient rigid cystoscopy: a single-blind, randomized study

Pain control in outpatient rigid cystoscopy is often achieved via the application of intraurethral lidocaine jelly. This clinical trial was designed to test the effectiveness and safety of a new method to provide local anesthesia, transperineal urethrosphincteric block (TUSB), prior to rigid cystoscopy. Male patients posted for outpatient rigid cystoscopy were randomized to receive TUSB (group A) using 10-20 ml of 1% lidocaine, intraurethral 30 ml of 2% lidocaine jelly (group B) or intraurethral 30 ml of neutral jelly (group C) as a method of pain control. Following the procedure, plasma concentrations of lidocaine were measured in group A patients. Outcome assessments included mean urethral and sphincteric numerated pain scores (0-10), overall discomfort level (0-4) and plasma lidocaine levels. One hundred and fifty patients were recruited, 50 in each group. When the three groups were compared, the ratio of group A patients with sphincteric pain score >or=2 was significantly the least. Also, the ratio of group A patients with discomfort level >or=2 was significantly less than the same ratio in either group B or C. Plasma lidocaine concentrations were within nontoxic levels and never exceeded 2.83 microg/ml in 39 subjects. This study demonstrates that TUSB is an effective and safe method in significantly relieving the pain associated with outpatient rigid cystoscopy. TUSB may offer urologists and anesthetists an alternative way to achieve pain control besides intraurethral lidocaine jelly during rigid cystoscopy.

C-fiber spontaneous discharge evoked by chronic inflammation is suppressed by a long-term infusion of lidocaine yielding nanogram per milliliter plasma levels

Nociceptors innervating inflamed tissue acquire an abnormal spontaneous discharge that is believed to be at least part of the reason for the persistent spontaneous pain, allodynia, and hyperalgesia that accompany inflammation. Recent studies suggest that patients with chronic inflammatory pain may obtain an analgesic effect with transdermal application of lidocaine that yields very low plasma levels (130–225ng/ml). The aim of this study was to investigate whether a 7-day exposure to such low plasma levels of lidocaine had an effect on inflammation-evoked spontaneous discharge in the rat. Seven days after a hind-paw injection of Complete Freund’s Adjuvant (CFA), we confirmed the presence of myositis, pain hypersensitivity, and a significant increase in the incidence of spontaneous discharge in A-fibers and C-fibers innervating both muscle and skin. We then compared the incidence of spontaneous discharge in muscle and cutaneous fibers in CFA-injected animals treated with a 7-day infusion of saline or lidocaine. The lidocaine infusion yielded a plasma level of 210ng/ml. The muscle C-fiber discharge was completely inhibited by the lidocaine infusion and the cutaneous C-fiber discharge was suppressed by 50%. Lidocaine infusion had no effect on the incidence of spontaneous discharge in muscle or cutaneous A-fibers. Lidocaine infusion reduced mechano-hyperalgesia but had no effect on mechano-allodynia or heat-hyperalgesia. We conclude that the analgesic effects seen clinically with transdermal lidocaine administration yielding low plasma levels may be due to a systemic drug action on spontaneously active C-fibers.

Comparison of the Hemodynamic Effects of a Single 5 mg/kg Dose of Lidocaine With or Without Epinephrine for Thoracic Paravertebral Block

Epinephrine is often added to local anesthetic solutions to minimize and slow the systemic absorption of local anesthetics, and thus reduce the possibility of adverse effects of these drugs. In an earlier study we found that the injection of 5 mg/kg of lidocaine via the paravertebral route depressed myocardial contractility by up to 30%, with practically no changes in heart rate or blood pressure. In the present study we investigated whether these alterations are due to systemic absorption of the local anesthetic, and whether such absorption can be minimized by adding epinephrine to the local anesthetic solution. A prospective, blind, and randomized study was made of 50 patients subjected to lung resection surgery. The subjects were divided into two groups: Lid group (5 mg/kg bolus dose of lidocaine in the thoracic paravertebral space) and Lid+E group (addition of 5 mcg/mL of epinephrine to the local anesthetic). The anesthetic solution was administered through a paravertebral catheter ipsilateral to the operative side. In addition to routine hemodynamic monitoring (heart rate and radial artery blood pressure), an aortic transpulmonary thermodilution catheter was inserted into the femoral artery for recording of the following variables: cardiac index, cardiac function index, maximum pressure derivative, global end diastolic volume, and intrathoracic total blood volume index. Data collection was carried out immediately before administration of the anesthetic solution and 15, 30, and 45 minutes after administration. Measurements were made of the plasma lidocaine levels at those same postparavertebral injection time points. Prior to paravertebral dosing there were no differences in terms of the hemodynamic variables studied. However, 15 minutes after dosing in the Lid+E group, lesser reductions in contractility, cardiac function index, and cardiac index were recorded, compared with the Lid group, with a significant reduction in cardiac filling volumes. Blood lidocaine levels were 53% and 34% lower in Lid+E group, as recorded 15 and 30 minutes after injection. The patients who, 15 minutes after paravertebral injection, had blood lidocaine levels greater than 3 mcg/mL (independently of the type of anesthetic solution used) had a significant reduction in mean blood pressure, cardiac function index, cardiac index, and maximum pressure derivative, compared with the patients with lower blood lidocaine concentrations. Addition of epinephrine to lidocaine when performing thoracic paravertebral block, attenuates the cardiodepressive effects associated with the systemic absorption of lidocaine and also, as a result of the beta-adrenergic consequences of epinephrine, systemic absorption from the paravertebral space.

Postoperative methemoglobinemia following infiltrative lidocaine administration for combined anesthesia in pediatric craniofacial surgery

Infiltrative anesthesia of the scalp with lidocaine was used in an attempt to reduce blood loss and anesthetic requirements during pediatric craniofacial surgery. Lidocaine, however, has the potential to cause methemoglobinemia. In this retrospective cohort-study we analyzed the incidence and effects of postoperative methemoglobinemia following subcutaneous lidocaine administration. During 1999-2006, 50 infants (age: 3-31 months) undergoing elective craniofacial surgery were analyzed. All infants received general anesthesia and routine monitoring, including invasive arterial blood pressure measurement. Prior to incision, the scalp was infiltrated with 6-15 ml lidocaine 1% (with epinephrine 1 : 200.000). Blood loss and blood transfusions were recorded. Methemoglobin (Met-Hb) levels were determined postoperatively using co-oximetry. Twenty percent of the operated infants showed elevated Met-Hb levels (median of maximal levels: 6%; range: 2.2-18%) at admission on the PICU. In 80% of these methemoglobinemia resolved spontaneously within 12 h, only two children received methylene blue because of visible cyanosis. The intra- and postoperative course was otherwise uneventful in all the children despite significant total blood loss (median of blood loss as percentage from total estimated blood volume: 43%; range: 11-110%). Lidocaine was the only substance identified to have the potential to cause methemoglobinemia. However, the average administered dose of lidocaine was not significantly different between patients with or without methemoglobinemia (13 +/- 3.1 vs 12 +/- 3.5 mg.kg(-1); P = 0.37). Even though we did not measure lidocaine plasma levels, lidocaine was the most likely cause of postoperative methemoglobinemia. Despite a high incidence, methemoglobinemia occurred sporadically and was without dangerous consequences.

Pharmacokinetics of High-Dose Diluted Lidocaine in Local Anesthesia for Facelift Procedures

The maximal recommended local anesthetic dose of lidocaine is 7 mg/kg; higher doses are used in tumescent liposuction. The objective of this study was to characterize the pharmacokinetics of high-dose diluted lidocaine administered together with epinephrine for local anesthesia in facelift procedures. This was a prospective study of six female patients undergoing elective facelift surgery. The local anesthetic solution consisted of 0.33% lidocaine, 0.07% sodium bicarbonate, and 1:600,000 epinephrine in normal saline. Plasma lidocaine levels were determined in the course of 24 hours and were subjected to pharmacokinetic analysis. Patients' age was 58.5 +/- 8 years and weight 68.5 +/- 18.7 kg. Mean lidocaine dose was 21.6 +/- 3.6 mg/kg (range, 17.5-26.3 mg/kg) infiltrated subcutaneously over 20 minutes or less. No lidocaine-related adverse effects were recorded. Major bleeding was not observed. Postoperative analgesia was required only at 11.8 +/- 4.6 hours after surgery. Pharmacokinetic analysis was peak concentration 1.41 +/- 0.4 microg/mL, time to reach peak concentration 9.3 +/- 1.6 hours, terminal half-life 6.2 +/- 1.5 hours, area under the curve from time zero to last data point 1379.8 +/- 470 microg/min/mL, and area under the curve from time zero to infinity 1530.6 +/- 471.6 microg/min/mL. Plasma lidocaine concentrations formed almost a plateau between 2 and 12 hours (ie, at approximately 1.2 microg/mL) after infiltration. It is concluded that local anesthesia with diluted lidocaine at a dose 3.1 times higher than the currently recommended dose (7 mg/kg) administered with epinephrine yielded a peak plasma lidocaine level that was 72% below the level considered safe (5 microg/mL).

Airway topicalisation in morbidly obese patients using atomised lidocaine: 2% compared with 4%*

We evaluated the technique of airway anaesthesia using atomised lidocaine for awake oral fibreoptic intubation in morbidly obese patients using two doses of local anaesthetic. Morbidly obese patients were allocated to receive either 2% or 4% lidocaine (40 ml) for oral airway anaesthesia using an atomiser with high oxygen flow. Patients were carefully sedated using midazolam and fentanyl. Outcomes included patient tolerance to airway manipulation, haemodynamic parameters, and serial plasma lidocaine concentrations. In all, 27 patients were enrolled in the study (2% cohort n = 14, 4% cohort n = 13). Patient characteristics and time for topicalisation and airway management were similar. Haemodynamic parameters did not change significantly. Tolerance to insertion of the Ovassapian airway, bronchoscopy, and tracheal tube positioning was excellent (12 vs 12 patients, 12 vs 12 patients, and 8 vs 12 patients had no response, respectively, 2% vs 4%). Differences did not reach statistical significance. Peak plasma lidocaine concentration was significantly lower in the 2% group (2.8 (0.8) microg.ml(-1) compared with 6.5 (1.0) microg.ml(-1), p < 0.05). Airway anaesthesia using atomised lidocaine for awake fibreoptic intubation in the morbidly obese is efficacious, rapid, and safe. Compared with 4% lidocaine, the 2% dose provides acceptable intubating conditions in most cases and produces lower plasma lidocaine levels.

Plasma Concentrations of Lidocaine in Dogs Following Lidocaine Patch Application

Transdermal absorption of lidocaine was determined by measuring plasma lidocaine concentrations following skin application of 5% lidocaine patches. Two lidocaine patches were placed on the ventral abdominal midline of seven dogs for 72 hours. Lidocaine was detectable in plasma 12 hours after patch application, and it reached steady-state concentrations between 24 and 48 hours. Plasma lidocaine levels decreased dramatically at 60 hours post-application. Low plasma lidocaine concentrations remained for 6 hours after patch removal. No clinically significant side effects were noted.