Blood concentration of lidocaine during continuous epidural blockade

Injectable microparticle-gel system for prolonged and localized lidocaine release. I.In vitro characterization

Current treatment protocol for postoperative pain is to infuse anesthetic solution around nerves or into the epidural space. This clinical practice is beset by the short duration of the anesthetic effect unless the infusion is continuous. Continuous infusion, however, requires hospitalization of the patients, thereby increasing medical costs. In addition, it also causes systemic accumulation of the drug. We reported herein a novel treatment for the postoperative pain by applying to the surgical site a biodegradable microsphere-gel system for prolonged and localized release of encapsulated anesthetic drugs. This lidocaine-containing biodegradable poly(D,L-lactic acid) (PLA) microsphere system, although being established previously by other investigators, was hindered by a burst release and a followed rapid release of the drug within several hours in vitro. In this article, we demonstrated that by a step-by-step modification of the formulation, prolonged release of lidocaine, up to several days in vitro, could be achieved. Differential scanning calorimetry revealed a lower glass transition temperature for these lidocaine-loaded microspheres comparing to that of lidocaine-free microspheres. This decreased Tg explained for the tendency of the lidocaine-loaded microspheres to physically fuse at higher temperatures. In vitro studies showed that microspheres, when loaded with 35% lidocaine, yielded a threefold increase in the degradation rate. The molecular weight of PLA of the drug-loaded microspheres was reduced by 50% within a period of 1 month. Based on the results (of prolonged lidocaine release and rapid PLA microsphere degradation), this lidocaine-loaded PLA microsphere system could offer a simple solution to the treatment of postoperative pain.

Safety and efficacy of using high-dose topical and nebulized anesthesia to obtain endobronchial cultures

We evaluated the safety and efficacy of high-dose topical and nebulized airway anesthesia in normal volunteers and in patients undergoing diagnostic fiberoptic bronchoscopy. Lidocaine solution (4 percent) was used for gargling, for spraying the palate and oropharynx with an atomizer, and for nebulization with an air-powered nebulizer (mean total dose, 1,682 mg) and 2 percent lidocaine (Xylocaine) jelly for anesthetizing nasal passages. In six normal subjects and in eight patients, lidocaine blood levels were measured at baseline, after gargling, after spraying, after nebulization, and then at 5, 10, 15, 30, and 60 min; 19 normal subjects and ten patients underwent the same anesthesia protocol but had no blood drawn. Fiberoptic bronchoscopy was performed in 21 normal volunteers and in 18 patients and cultures obtained using the protected specimen brush. Additional endobronchial lidocaine (mean 256 mg) was given to the 18 patients after collecting the microbiology specimens. Peak lidocaine blood levels remained below 6 micrograms/ml in all cases. Cough and discomfort during bronchoscopic examination was absent or minimal in 17 of 21 normal subjects (80 percent) and in 14 of 18 patients (77 percent) and was severe in only one instance (5 percent). There were no related complications. Using only topical and nebulized anesthesia is safe and effective for performing fiberoptic bronchoscopy, especially when bacterial cultures are to be obtained and endobronchial instillation of lidocaine must be avoided.

Plasma bupivacaine concentrations during postoperative continuous epidural analgesia

Postoperative analgesia and plasma concentrations of bupivacaine were evaluated in six patients receiving intermittent epidural bupivacaine for a period of 72 hours following large bowel surgery. Repeated doses were administered every hour by a new automatic, specially designed pump. Venous plasma bupivacaine concentrations showed accumulation for up to 48-60 hours during administration and were mostly less than 2 micrograms/ml except in an elderly, frail patient in whom a peak of 3.9 micrograms/ml was observed. This convenient, low-dose, pulsed technique provided excellent analgesia although special care may be necessary in the elderly and frail patient if potentially toxic levels are to be avoided.

The combination of general anaesthesia and epidural block I: The effects of sequence of induction on haemodynamic variables and blood gas measurements in healthy patients

The haemodynamic effects of epidural block, administered before or after general anaesthesia, were investigated in twelve healthy women scheduled for elective gynaecological surgery. The effects of 10° head down tilt and administration of atropine 0.6 mg intravenously were also determined. Haemodynamic measurements included systolic (SAP), diastolic (DAP) and mean (MAP) arterial pressure, heart rate (HR), cardiac output (CO) and systemic vascular resistance (SVR). In those receiving general anaesthesia first (Group A) (thiopentone/suxamethonium/N2O/O2) significant changes occurred only at the time when epidural block and general anaesthesia were both present: SAP, DAP and MAP (-22%, p < 0.001) were reduced compared to awake control values, however changes in HR, CO and SVR were not significant. In those receiving epidural block first (Group B) (1.5% lignocaine, mean dose 270 mg), MAP was reduced by 20% (p < 0.01) from awake control values after epidural block and there was a further reduction to 35% below control (p < 0.001) when general anaesthesia was induced. These changes were accompanied by a significant reduction in SVR.

Comparison of all variables between Group A and Group B showed no clinically significant differences, indicating that the order of performance of epidural block (before or after general anaesthesia) did not affect haemodynamic variables. Head down tilt resulted in no haemodynamic changes in the presence of general anaesthesia or epidural block alone and only minimal changes when the two were combined. In contrast, intravenous atropine (0.6 mg) resulted in a return of arterial pressures to essentially baseline values in both Group A and Group B (HR increased 84%, p < 0.001; MAP increased 37%, p < 0.001; CO increased 70%, p < 0.001).

Plasma levels of lidocaine following nebulized aerosol administration

The venous (plasma) levels of lidocaine were measured in five subjects following nebulization of a 280-mg dose via intermittent positive pressure breathing (IPPB) and nebulization of a 400-mg dose via ultrasound. Even though a lower dose of lidocaine was given by IPPB, this system of delivery produced higher plasma concentrations of the drug than ultrasound and also was more effective in eliminating the gag reflex. In the entire study, plasma concentrations of lidocaine did not exceed 1.1 mug/ml, which is far below toxic levels. Aerosolized lidocaine, administered by IPPB, is a safe and effective topical anesthetic agent which may be useful for instrumentation of the upper airway.

Arterial and venous blood lidocaine concentrations after local anaesthesia of the respiratory tract using an ultrasonic nebulizer

Arterial and venous blood lidocaine concentrations were intermittently measured in 15 bronchoscopy patients in whom local anaesthesia was induced by an inhalation technique. A DeVillbiss ultrasonic nebulizer model 3574 was used. The anaesthetic was 10 ml of 4% lidocaine without adrenaline. Blood concentrations were measured 5 min after commencement of inhalation, on completion of inhalation, and then after 10, 30 and 60 min. Statistically significantly higher concentrations were found in the arterial blood at the first two sampling times (P less than 0.01 and P less than 0.05, respectively). The highest average concentration in both arterial and venous blood eas reached 10 min after completion of anaesthesia. After 30 min, there was no difference between the arterial and venous samples; and after 60 min, the concentration was higher in venous blood. The highest individual concentration was 2.8 mug/ml in arterial blood and 2.1 mug/ml in venous blood, well below that reported to cause systemic toxic symptoms. Thus, the inhalation technique may be considered a safe means of inducing anaesthesia in the respiratory tract.