Influence of carbon dioxide insufflation of the neck on intraocular pressure during robot-assisted endoscopic thyroidectomy: a comparison with open thyroidectomy

BACKGROUND

Increased intraocular pressure (IOP) during surgery can result in serious ophthalmic complications. We hypothesized that carbon dioxide (CO₂) insufflation of the neck during endoscopic thyroidectomy would constrict the jugular veins mechanically, causing elevated venous pressure and thus elevated IOP. We compared IOP changes at each step of open thyroidectomy (OT) versus robot-assisted endoscopic thyroidectomy (RET) METHODS: Perioperatively, IOP was measured at six time points in patients undergoing OT (n = 18) or RET with CO₂ insufflation (n = 19). Anesthesia, ventilatory strategy, intravenous infusions, and surgical positioning were standardized

RESULTS

In both groups, induction of anesthesia reduced IOP, but surgical positioning with the neck in extension had no effect on IOP. In the OT group, IOP remained unchanged during anesthesia. In the RET group, CO₂ insufflation significantly increased IOP to an average of 3.6 ± 3.0 mmHg higher than the previous measurement (P < 0.001), and this IOP increase persisted immediately before gas deflation. These elevated IOP values during CO₂ insufflation in the RET group were significantly higher than those at corresponding time points in the OT group. However, these elevated IOP values were similar to the pre-anesthetic baseline IOP CONCLUSION: CO₂ insufflation of the neck at pressure of 6 mmHg increased the IOP significantly compared with open thyroidectomy. However, this increase in IOP could be balanced by an anesthetic-induced IOP-lowering effect, thereby having no clinical significance in patients with normal IOP undergoing robot-assisted endoscopic thyroidectomy.

A Study on the Influence of Emulsion Droplet Size on the Skin Penetration of Tetracaine

OBJECTIVES/AIMS

The influence of emulsion droplet size on the skin penetration of a model drug, tetracaine, was studied. For this purpose, in vitro dermal and transdermal delivery of tetracaine from 6 emulsions (3 macro-emulsions with droplet sizes >1 microm and 3 nano-emulsions with droplet sizes <100 nm) were tested.

METHODS

Two approaches were used: in the first one, the composition of the emulsions was kept constant, while in the second one, the surfactant concentration in the aqueous phase was kept constant by varying the overall surfactant concentration.

RESULTS

The results from emulsions differing only in droplet size did not provide statistically significant evidence for the anticipated increase in transdermal or dermal delivery (after 24 h) when reducing emulsion droplet size. The same results were obtained when the surfactant concentration in the aqueous phase was kept constant, indicating that there is no influence of emulsion droplet size on the skin penetration of tetracaine within the droplet size range studied.

CONCLUSION

This is in contrast to what has been reported in various publications that claim penetration to increase with reducing droplet size. It should be noted that the results reported so far are based on emulsions that apart from droplet size also differed in composition and/or system components.

Tetracaine-membrane interactions: effects of lipid composition and phase on drug partitioning, location, and ionization

Interactions of the local anesthetic tetracaine with unilamellar vesicles made of dimyristoyl or dipalmitoyl phosphatidylcholine (DMPC or DPPC), the latter without or with cholesterol, were examined by following changes in the drug's fluorescent properties. Tetracaine's location within the membrane (as indicated by the equivalent dielectric constant around the aromatic fluorophore), its membrane:buffer partition coefficients for protonated and base forms, and its apparent pK(a) when adsorbed to the membrane were determined by measuring, respectively, the saturating blue shifts of fluorescence emission at high lipid:tetracaine, the corresponding increases in fluorescence intensity at this lower wavelength with increasing lipid, and the dependence of fluorescence intensity of membrane-bound tetracaine (TTC) on solution pH. Results show that partition coefficients were greater for liquid-crystalline than solid-gel phase membranes, whether the phase was set by temperature or lipid composition, and were decreased by cholesterol; neutral TTC partitioned into membranes more strongly than the protonated species (TTCH(+)). Tetracaine's location in the membrane placed the drug's tertiary amine near the phosphate of the headgroup, its ester bond in the region of the lipids' ester bonds, and associated dipole field and the aromatic moiety near fatty acyl carbons 2-5; importantly, this location was unaffected by cholesterol and was the same for neutral and protonated tetracaine, showing that the dipole-dipole and hydrophobic interactions are the critical determinants of tetracaine's location. Tetracaine's effective pK(a) was reduced by 0.3-0.4 pH units from the solution pK(a) upon adsorption to these neutral bilayers, regardless of physical state or composition. We propose that the partitioning of tetracaine into solid-gel membranes is determined primarily by its steric accommodation between lipids, whereas in the liquid-crystalline membrane, in which the distance between lipid molecules is larger and steric hindrance is less important, hydrophobic and ionic interactions between tetracaine and lipid molecules predominate.

Synergistically enhanced transdermal permeation and topical analgesia of tetracaine gel containing menthol and ethanol in experimental and clinical studies

The aim of this study is to observe the synergistically enhanced percutaneous penetration and skin analgesia of tetracaine gel containing menthol and ethanol through experimental and clinical studies. Four anesthetic gels containing 4% tetracaine in carbomer vehicle named T-gel (containing no menthol or ethanol), 5%M/T-gel (containing 5% menthol), 70%E/T-gel (containing 70% ethanol, an optimal concentration for antiseptic), and 5%M+70%E/T-gel (containing both 5% menthol and 70% ethanol), respectively, were fabricated. The in vitro mouse skin permeation was investigated using a Franz diffusion cell. The mouse skin morphology was examined by a scanning electron microscope. The in vivo skin analgesic effect in mice was evaluated using the von Frey tests. To determine the efficacy of tetracaine gels for managing the pain in human volunteers, a paralleled, double-blinded, placebo-controlled, randomized controlled trial design combined with verbal pain scores (VPS) was performed. The combination of menthol and ethanol (5%M+70%E/T-gel) conferred significantly higher tetracaine diffusion across full-thickness mouse skin than 5%M/T-gel, 70%E/T-gel, and T-gel. The ultra structure changes of mouse skin stratum corneum treated with 5%M+70%E/T-gel were more marked compared with those of any other tetracaine gel. von Frey tests in mice showed a synergistically enhanced effect of menthol and ethanol on the analgesia of tetracaine gel. The mean VPS were significantly lower for volunteers treated with 5%M+70%E/T-gel than those receiving other gels or the EMLA cream. 5%M+70%E/T-gel possessed the shortest anesthesia onset time, the longest anesthesia duration and the strongest anesthesia efficacy. Seventy percent ethanol in 5%M+70%E/T-gel not only improved the analgesic efficacy of the tetracaine gel through synergistically enhanced percutaneous permeation with menthol but also served as an antiseptic agent keeping drug application site from infection. 5%M+70%E/T-gel is a potential topical anesthesia preparation for clinical use.

Transdermal delivery of hydrophobic and hydrophilic local anesthetics from o/w and w/o Brij 97-based microemulsions

PURPOSE

To characterize the physicochemical properties of drug-loaded oil-in-water (o/w) and water-in-oil (w/o) Brij 97-based microemulsions in comparison to their blank counterparts and to investigate the influence of microemulsion type on in vitro skin permeation of model hydrophobic drugs and their hydrophilic salts.

METHODS

The microemulsion systems were composed of isopropyl palmitate (IPP), water and a 2:1 w/w mixture of Brij 97 and 1-butanol. The samples were characterized by visual appearance, pH, refractive index, electrical conductivity, viscosity and determination of the state of water and IPP in the formulations using differential scanning calorimetry (DSC). Transdermal flux of lidocaine, tetracaine, dibucaine and their respective hydrochloride salts through heat-separated human epidermis was investigated in vitro using modified Franz diffusion cells.

RESULTS

The physicochemical properties of drug-loaded microemulsions and their blank counterparts were generally similar; however, slight changes in some physicochemical properties (apparent pH and conductivity) were observed due to the intrinsic properties of the drugs. The o/w microemulsions resulted in the highest flux of lidocaine, tetracaine and dibucaine as compared to the other formulations with in the same group of drugs.

CONCLUSIONS

The characterization results showed that incorporation of the model drugs into the microemulsions did not change the microemulsion type. The permeation data exhibited that the nature of the microemulsions was a crucial parameter for transdermal drug delivery. The o/w microemulsions containing hydrophobic drugs provided the highest skin permeation enhancement. In addition, skin permeation was depended on the molecular weight of the model drugs.

Effect of the composition of lecithin/n-propanol/isopropyl myristate/water microemulsions on barrier properties of mice skin for transdermal permeation of tetracaine hydrochloride: In vitro

Effect of composition of lecithin water-in-oil and oil-in-water microemulsion on in vitro transdermal permeation of tetracaine hydrochloride was studied on mice model. The results were compared with an aqueous solution of tetracaine hydrochloride (2.7 mg/ml). In vitro skin flux and permeability coefficients were obtained using the Franz diffusion cell. Differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM) were used to study the mechanism of action of the microemulsion. Micrographs of TEM and CLSM studies were analyzed by using Image Pro Plus image software. Skin flux of tetracaine hydrochloride was found to be dependent on the composition of lecithin/n-propanol/isopropyl myristate/water microemulsions. At lower Km ratio (i.e. 0.5:1 and 0.8:1) of microemulsion, the rate of permeation of tetracaine hydrochloride was higher when compared to the microemulsion of higher Km ratio (1:1 and 1.5:1). Image analysis of TEM micrograph, 6h after application of lecithin microemulsion, showed 3.5+/-0.75-fold (p<0.001) increase in the intercellular space in the epidermis and 3.8+/-0.4-fold (p<0.001) enhancement in upper dermis. CLMS results show that sweat gland and hair follicles also provided path for permeation of the drug through the skin.

Modeling the pore structure of voltage-gated sodium channels in closed, open, and fast-inactivated conformation reveals details of site 1 toxin and local anesthetic binding

In this work molecular modeling was applied to generate homology models of the pore region of the Na(v)1.2 and Na(v)1.8 isoforms of human voltage-gated sodium channels. The models represent the channels in the resting, open, and fast-inactivated states. The transmembrane portions of the channels were based on the equivalent domains of the closed and open conformation potassium channels KcsA and MthK, respectively. The critical selectivity loops were modeled using a structural template identified by a novel 3D-search technique and subsequently merged with the transmembrane portions. The resulting draft models were used to study the differences of tetrodotoxin binding to the tetrodotoxin-sensitive Na(v)1.2 (EC50: 0.012 microM) and -insensitive Na(v)1.8 (EC50: 60 microM) isoforms, respectively. Furthermore, we investigated binding of the local anesthetic tetracaine to Na(v)1.8 (EC50: 12.5 microM) in resting, conducting, and fast-inactivated state. In accordance with experimental mutagenesis studies, computational docking of tetrodotoxin and tetracaine provided (1) a description of site 1 toxin and local anesthetic binding sites in voltage-gated sodium channels. (2) A rationale for site 1 toxin-sensitivity versus -insensitivity in atomic detail involving interactions of the Na(v)1.2 residues F385-I and W943-II. (3) A working hypothesis of interactions between Na(v)1.8 in different conformational states and the local anesthetic tetracaine.

Transdermal permeation of tetracaine hydrochloride by lecithin microemulsion: In vivo

In vivo transdermal permeation of tetracaine hydrochloride encapsulated in lecithin water-in-oil and oil-in-water microemulsion was studied. The effect of the composition of the lecithin microemulsion on analgesic response of tetracaine hydrochloride was evaluated on Wistar rats by tail flick method. To find out the toxicity of lecithin/n-propanol/isopropyl myristate/water/tetracaine hydrochloride microemulsion histopathological and irritation response were measured in Swiss mice. Time course studies were also conducted for the biochemical response of microemulsion by measuring catalase, glutathione and lipid peroxidation levels of the treated mice skin. The analgesic response was found to be dependent on the drug concentration and composition of the systems. The histopathological, irritation and biochemical findings reveal that lecithin/n-propanol/isopropyl myristate/water/tetracaine hydrochloride microemulsion is a safe carrier for transdermal drug delivery systems. Confocal laser scanning microscopy observation indicated that sweat gland and hair follicle also provided the path for transdermal permeation of lecithin/n-propanol/isopropyl myristate/water microemulsion.

Menthol facilitates the skin analgesic effect of tetracaine gel

The aim of this study is to observe the effect of menthol on the percutaneous penetration and skin analgesic action of tetracaine gel (T-gel). Anesthetic gels containing 4% tetracaine in carbomer vehicle with and without menthol were prepared. The menthol penetration-enhanced gel conferred significantly higher diffusion of tetracaine across full-thickness mouse skin than non-penetration-enhanced gel, in a dose-dependent manner. The inter-cellular spaces of the stratum corneum in skin treated with menthol penetration-enhanced gel became extended as compared with those in non-penetration-enhanced gel. This may suggest that menthol's action was related to the changes of the epidermis ultra structures. An enlarged inter-cellular space, per se, would allow a better passage to tetracaine. To determine the efficacy of menthol penetration-enhanced tetracaine gel in the management of pain, a double-blind, placebo-controlled, randomized controlled trial (RCT) design was used. The mean verbal pain scores (VPS) were significantly lower in volunteers treated with penetration-enhanced tetracaine gel than those in volunteers receiving non-penetration-enhanced tetracaine gel or placebo. Menthol improved the analgesic efficacy of the tetracaine 4% gel in part through enhanced percutaneous permeation.

Rapid Human Skin Permeation and Topical Anaesthetic Activity of a New Amethocaine Microemulsion

We developed a fast-acting, topical, 4% (w/w) amethocaine microemulsion and tested its in vitro permeation in isolated human skin. Comparison with a commercial amethocaine gel (Ametop((R)) ) was performed using Franz diffusion cells. Permeability coefficient (k(p)), flux (J) and percentage permeation after 10 h of microemulsion application were, in all cases, 1.5 times higher than those of the gel. The values obtained for the P(1) parameter [1], 1.06.10(-2) cm (microemulsion) and 0.724.10(-2) cm (gel) indicate that the microemulsion excipients favour amethocaine deposition in the skin, increasing the permeability coefficient, amount of drug retained in the skin, and the flux achieved. Analgesic activity was also examined in rats made hyperalgesic or allodynic after carrageenan-induced inflammation. The rats were distributed into four groups (n = 5-9 per group), each group receiving topically either amethocaine microemulsion, amethocaine gel (Ametop), amethocaine subcutaneous infiltration or nothing (controls). In edematous paws, anti-hyperalgesic activity appeared at 4.2 and 13.8 min after application of amethocaine microemulsion and gel, respectively. These effects are lower than after 0.5% w/w amethocaine infiltration. Amethocaine microemulsion was the only topical formulation with an anti-allodynic effect, although this effect was less than with amethocaine infiltration. These results suggest that microemulsion could be a valuable formula for improving amethocaine permeation and thus bringing rapid pain relief.

A critical review of the topical local anesthetic amethocaine (Ametop) for pediatric pain

A topical formulation of the ester-type local anesthetic amethocaine (tetracaine) [Ametop ] is currently available for reducing pain from cutaneous procedures such as venipuncture. The Ametop mark preparation contains 40 mg of amethocaine base (4% w/w) and produces anesthesia within 30-45 minutes of application; duration of action ranges from 4 to 6 hours. Clinical studies have demonstrated the superiority of the 4% amethocaine preparation over placebo in pediatric populations for indications such as intravenous cannulation, vaccination, and venipuncture. Amethocaine has been shown to produce anesthesia comparable to that of 5% lidocaine-prilocaine for procedures such as venipuncture and accessing centrally placed devices; in general, anesthesia was achieved more rapidly with amethocaine than lidocaine-prilocaine. In the neonatal population amethocaine was found to be ineffective at reducing the pain of heel prick and peripherally inserted central catheters. Depending on the type of procedure, amethocaine application times between 30 and 60 minutes have produced clinically acceptable anesthesia; application times <30 minutes have not been associated with reliable anesthesia. The 4% amethocaine preparation is well tolerated; the most commonly reported local skin reaction is transient local erythema while local edema and itching have been reported more rarely. There have been no accounts of systemic toxicity with topical use of the preparation. Several cases of sensitization have been described in adults upon repeated exposure to topical amethocaine. In summary, the novel preparation of 4% amethocaine gel has been shown to be clinically effective for managing pain associated with minor cutaneous procedures while maintaining a good tolerability profile. Amethocaine has also demonstrated similar efficacy to lidocaine-prilocaine when appropriate application times are used; the more rapid onset of action and extended duration of action of amethocaine may make it more useful than lidocaine-prilocaine in busy clinical settings.

Development of the Bioadhesive Tetracaine Gels for Enhanced Local Anesthetic Effects

To develop the new local anesthetic formulations with a suitable bioadhesive property, hydroxypropyl methylcellulose (HPMC)-based gel was formulated. As the drug concentration in the gels, and the temperature of surrounding solutions increased, the drug release increased. The activation energy of tetracaine permeation was 4.47 kcal/mol. The effects of permeation enhancers on the permeation rate of drug through skin were studied using various enhancers, such as the glycols, the nonionic surfactants, and the bile salts. Among the enhancers used, polyoxyethylene 2-oleyl ether showed the highest enhancing effects on drug permeation through skin. The analgesic activity was examined using a tail-flick analgesimeter. In the AUEC (area under the efficacy curve) of the rat-tail flick test, tetracaine gel containing polyoxyethylene 2-oleyl ether showed about 3.2-fold increase in analgesic activity compared with the control. The results of this study support that the tetracaine gels with efficient anesthetic effects could be developed using HPMC and poloxamer with combination of enhancer and vasoconstrictor.

A Raman spectroscopic investigation of bioadhesive tetracaine local anaesthetic formulations

Raman spectroscopy at 785 nm has been employed to characterise the properties of tetracaine in bioadhesive gel and patch formulations. In the first study, interactions between the drug and excipients in novel bioadhesive patch systems were characterised. It was determined that the drug did not interact with any of its formulation components, and that this was an important factor in its clinical performance, particularly the rapid onset of anaesthesia. Investigations of drug uptake in the stratum corneum from a gel formulation suggested that tetracaine rapidly undergoes a phase-change upon application to the skin. The intensity of the tetracaine Raman bands at approximately 1600 cm(-1) suggests that the local anaesthetic is rapidly absorbed into the skin. Decreases in Raman tetracaine band intensities, along with an absence in the concomitant alteration in the internal standard spectra, indicates an decrease in the tetracaine concentration present in the gel. Further, a baseline indicating complete tetracaine absorption appears to be reached after approximately 40 min of exposure. After this time little further absorption was observed, suggesting that the stratum corneum "reservoir" was saturated with tetracaine at this time. This is consistent with the optimum application time required for tetracaine gels to attain maximum clinical efficacy. This study has indicated the effectiveness of Raman spectroscopy in the analysis of gel-based pharmaceutical preparations, showing it to be a simple, rapid, virtually non-invasive technique for determination of tetracaine.

Effect of receptor solution specific conductivity on iontophoresis of tetracaine hydrochloride

AIM

To examine the quantitative relationship between solution specific conductivity and the permeability of tetracaine HCl, and to investigate the effect of receptor solution specific conductivity on the iontophoretic transport.

METHODS

An in vitro study was carried out to determine the iontophoretic permeability of tetracaine hydrochloride through rat skin. Iontophoretic flux of tetracaine hydrochloride through excised rat skin was determined using Valia-Chien two-chamber diffusion cells with a constant d.c. current and Ag/AgCl electrodes. The specific conductivities of donor and receptor solution were also measured.

RESULTS

Iontophoretic flux of tetracaine hydrochloride increased with a decrease of anion (chloride ion) concentration in receptor. And the iontophoretic permeability (ER, ER is the enhancement ratio, and ER = iontophoretic flux/passive flux) for tetracaine hydrochloride was directly related to the conductivity of receptor solution when other conditions were held constant. Linear regressions confirmed that ER was related to inverse of overall specific conductivity of donor and receptor solution [1/(ks.d + ks.r), ks.d and ks.r are the specific conductivity of donor and receptor solution].

CONCLUSION

The results suggest that specific conductivity of receptor solution may be a important factor for the iontophoretic permeability of a solute.

Distribution of tetracaine and its metabolite in rabbits after high versus normal spinal anesthesia

High spinal anesthesia is one cause of sudden death associated with the spinal anesthesia. We did animal experiments to verify high spinal anesthesia by analyzing tetracaine and its metabolite, p-butylaminobenzoic acid in tissue samples. Tetracaine (0.25% in 10% glucose solution) 0.21-0.28 mg/kg was administered to two groups of rabbits to induce high and normal spinal anesthesia. Tetracaine and the metabolite in rabbit tissues were analyzed by gas chromatography-mass spectrometry, as a free base for tetracaine and as tert-butyldimethylsilyl derivative for the metabolite. In the group given high spinal anesthesia, levels of the metabolite in the brain stem were higher than in the cerebrum, cerebellum and whole blood. On the other hand, in the group given normal spinal anesthesia, the opposite results were obtained. Therefore, high spinal anesthesia induced by tetracaine can be diagnosed by comparing the concentrations of metabolite in whole blood, cerebrum, cerebellum and brain stem.

Nitric oxide synthesis inhibition modifies the cardiotoxicity of tetracaine and lidocaine

Suppression of nitric oxide (NO) production alters the toxicity of cocaine and bupivacaine. We undertook this study to determine whether the systemic toxicity of two other local anesthetics that differ in antiarrhythmic activity, plasma clearance, and biotransformation are similarly affected by nitric oxide synthase (NOS) inhibition. Sprague-Dawley rats anesthetized with 70% N2O and 0.5% halothane mixed with O2 were pretreated with saline (0.2 mL x kg(-1) x min(-1) i.v.) or N(omega)-nitro-L-arginine methyl ester (L-NAME; a competitive inhibitor of NOS) (2 mg x kg(-1) x min(-1) i.v.) for 30 min. The animals were then given tetracaine (3 mg x kg(-1) x min(-1) i.v.) or lidocaine (8 mg x kg(-1) x min(-1) i.v.) until cardiac arrest (asystole). Doses of lidocaine or tetracaine that produced arrhythmias, seizures, isoelectric encephalogram, and asystole were determined. Hemodynamic recordings were performed throughout the experiments, and plasma was collected to measure the concentration of lidocaine or tetracaine. L-NAME decreased tetracaine and lidocaine doses that produced arrhythmias (> or = 2 degrees atrioventricular conduction block) (tetracaine 14 +/- 2 mg/kg; lidocaine 102 +/- 9 mg/kg) versus saline treatment (tetracaine 28 +/- 2 mg/kg; lidocaine 136 +/- 9 mg/kg; P < 0.05). The tetracaine and lidocaine doses required to produce asystole were also smaller in animals with L-NAME pretreatment than those in saline-pretreated animals. L-NAME reduced the arrhythmia dose of tetracaine more than the arrhythmia dose of lidocaine (28 of 14 = 2.0 fold and 136 of 102 = 1.3-fold). The plasma concentration of lidocaine, but not tetracaine, was significantly higher at each sample time in L-NAME-pretreated animals than in saline-pretreated animals. Inhibition of NOS by L-NAME enhances the cardiotoxicity of lidocaine and tetracaine, with a greater effect on tetracaine than on lidocaine. Altered drug clearance by L-NAME was insufficient to explain these findings because L-NAME pretreatment increased the plasma levels of only lidocaine, not tetracaine.

IMPLICATIONS

Inhibition of nitric oxide production in rats markedly enhances the cardiovascular toxicity of lidocaine and tetracaine. Altered drug clearance by N(omega)-nitro-L-arginine methyl ester was insufficient to explain these findings because N(omega)-nitro-L-arginine methyl ester pretreatment increased the plasma levels of only lidocaine, not tetracaine.

[Diffusion if lidocaine after intracameral injection]

PURPOSE

To determine the lidocaine diffusion space, we compared lidocaine aquous humor concentration in topical anesthesia with 1% lidocaine intracameral injection and in peribulbar anesthesia with 2% lidocaine prior phacoemulsification.

MATERIAL AND METHOD

A gas chromatography technique of analyzing 100 microliters aqueous humor was used to detect the presence of lidocaine prior to phakoemulsification cataract surgery in two groups of patients: group A: after peribulbar anesthesia with 10 ml 2% lidocaine, group B: after 1% tetracaine topical anesthesia and 0.5 ml intracameral injection of 1% preservative-free lidocaine. The intracameral volume was estimated mathematically in group B. Endothelial cells loss was analyzed in two groups with non contact specular microscopy.

RESULTS

Lidocaine was detected in aqueous humor with a good reliability. The mean concentration after intracameral injection was 6,300 micrograms/ml and was higher than after peribulbar injection. This concentration was near than theorical intracameral rate, suggesting that there was no diffusion in the posterior segment. There was no significant difference in the 2 groups in endothelial cells loss.

CONCLUSION

Intracameral injection of lidocaine is an effective technique to anesthetize intracameral structures without diffusion in posterior segment prior to phakoemulsification.

[Spread of spinal anesthesia with 3 different hyperbaric solutions used in Japan]

We studied the spread of spinal anesthesia with 3 different hyperbaric solutions commercially available in Japan. Percamin-S [0.3% dibucaine in 5% hyperbaric saline] (P), Neo-Percamin.S [0.24% dibucaine with 0.12% T-caine in 9.5% glucose] (N) and 0.5% Tetcaine [tetracaine] in 10% glucose (T) were studied. Two ml of each solution was administered intrathecally using a 25 gauge Quincke needle. Patients (n = 90) were allocated to one of 9 groups receiving 2 ml of P, N or T at L 2-3, L 3-4 or L 4-5 interspace. Both N and T produced significantly higher spread of analgesia than P at any of L 3-4 and L 4-5 interspaces. P and N have the same specific gravity, even though significant differences were found in spread of segmental analgesia. Local anesthesic agents and solvent solutions themselves are considered to influence the spread of spinal anesthesia as the specific gravity of hyperbaric solution does.

[Infrared A radiation-controlled permeation of tetracaine in vitro and in vivo]

Waterfiltered infrared light (IR-A) was investigated as permeation enhancer for transdermal drug delivery systems on biological membranes. Due to the IR-A-radiation pulse on human keratinocytes (HaCaT) a clear increase in the permeability of tetracaine was recognizable. In vivo studies showed IR-A-supported enhanced local analgesia of tetracaine hydrogel in the pin prick test. The study leads to the conclusion, that IR-A-radiation can specifically be used to optimize transdermal drug permeation.

Acid-base state of cerebrospinal fluid during pregnancy and its effect on spread of spinal anaesthesia

To assess the possible relationship between changes in acid-base state of cerebrospinal fluid (CSF) and enhanced spread of spinal anaesthesia during pregnancy, we have measured CSF pH, carbon dioxide tension (PCO2) and HCO3- values in 73 women undergoing spinal anaesthesia with hyperbaric amethocaine 8 mg. Patients were allocated to one of four groups according to gestational period: non-pregnant group (n = 13), first trimester group (8-13 weeks, n = 19), second trimester group (14-26 weeks, n = 11) and third trimester group (27-39 weeks, n = 30). The pH of the CSF was greater in the second and third trimester groups than in the non-pregnant group. CSF PCO2 decreased by 0.53-0.8 kPa throughout pregnancy. CSF HCO3- was decreased throughout pregnancy. Overall, no clinically significant correlation was found between maximum cephalad spread of analgesia and CSF pH, PCO2 or HCO3-. We conclude that pregnancy-induced changes in acid-base state of CSF have little effect on the spread of spinal anaesthesia, although there is a clinically different spread of spinal anaesthesia between non-pregnant and pregnant states.

Pharmacodynamics of a liposomal preparation for local anaesthesia

A phospholipid containing formulation with tetracaine (CAS 94-24-6) for topical anaesthesia was developed. In vitro drug liberation as well as in vivo efficacy and duration of the anaesthetic effect were investigated. The in vitro liberation constant was 0-.626 +/- 0.005 mg/(cm2.square root of h for a liposomal gel formulation containing 2% (m/l) tetracaine. The gel showed high efficacy in anaesthetizing the skin after topical application. After 60 min of application complete anaesthesia of the skin was observed with all volunteers. The duration of anaesthesia after removing the application system was 150 min on average. The determination of the in vivo penetration rate resulted in values between 0.010 and 0.015 mumol/min.cm2 tetracaine.

Cerebrospinal fluid progesterone in pregnant women

To assess the possible relationship between an increase in progesterone concentration in cerebrospinal fluid (CSF) and enhancement of spread of spinal anaesthesia, we have measured CSF progesterone concentrations in 134 patients undergoing spinal anaesthesia with hyperbaric amethocaine 8 mg. Patients were allocated to one of five groups according to the gestational period: non-pregnant group (n = 13), first trimester group (8-12 weeks, n = 16), second trimester group (13-24 weeks, n = 18), third trimester group (25-36 weeks, n = 38) and term group (37-41 weeks, n = 49). Progesterone concentration in CSF was higher in the third trimester and term groups than in the non-pregnant, first trimester and second trimester groups. Maximum cephalad spread of analgesia was higher in the second trimester, third trimester and term groups than in the non-pregnant and first trimester groups. Although an increase in CSF progesterone concentration in the second trimester group was similar in magnitude to that observed in the first trimester group, enhanced spread of spinal anaesthesia, comparable in magnitude with that observed in the term group, occurred in the second trimester group. There was no significant correlation between CSF progesterone concentration and spread of spinal anaesthesia in any of the groups. These data suggest that not only a minimum level of progesterone in CSF but also a certain duration of exposure to elevated CSF progesterone concentrations may be necessary for enhancement of spread of spinal anaesthesia, and that values of CSF progesterone concentration do not correlate directly with enhancement of spread of spinal anaesthesia.

Spread of subarachnoid hyperbaric amethocaine in adolescents

We have compared the spread of subarachnoid hyperbaric amethocaine in adolescents with that in adults. Amethocaine 8 mg in 2 ml of 10% glucose was injected through a 25-gauge spinal needle inserted at the L3-4 interspace in 21 adolescents aged 12-16 yr and in 111 adults aged 17-82 yr. Although we found no differences in height, weight or body mass index between the adolescents and adults, maximum spread of analgesia was significantly higher in the adolescents (median T3 (range T4-C5) than in the adults (T4 (T9-C7)). We conclude that subarachnoid injection of hyperbaric amethocaine produces an unexpectedly higher level of analgesia in adolescents than in adults.

Influence of duration of lateral decubitus on the spread of hyperbaric tetracaine during spinal anesthesia: a prospective time-response study

Searching for a differential spinal block between dependent and nondependent sides, we evaluated a prospective randomized time-response study of the influence of the duration of lateral decubitus on the spread of hyperbaric local anesthetic solution during spinal anesthesia in 60 patients undergoing lower limb surgery. In a lateral position with the operated side dependent, all patients received 12 mg of lyophilized tetracaine with 0.2 mg epinephrine in 2.5 mL 10% dextrose and were randomized into four groups according to the duration of lateral decubitus after spinal injection: Group 0, patients immediately turned supine after spinal injection; Group 6, 6 min in lateral decubitus then supine; Group 12, 12 min in lateral decubitus then supine; Group 18, 18 min in lateral decubitus then supine. There was no difference in maximum sensory level between both sides in the same group nor between the four groups. In all four groups a comparable number of patients had a Grade 4 motor block on the dependent as well as on the nondependent side. A positive correlation found between duration of lateral decubitus and duration of sensory block on the dependent side suggested a preferential spread of hyperbaric local anesthetics. This differential spread was confirmed by the positive correlation between the duration of lateral decubitus and the difference in duration between dependent and nondependent sides of both sensory and motor blocks. However, because of the minimal differences between groups, we believe there is no reason to routinely maintain patients in the lateral position after performing spinal anesthesia.

Absorption of liposome-encapsulated tetracaine versus nonliposome-encapsulated tetracaine from open wounds in rabbits

The plasma tetracaine concentration versus time profiles for liposome-encapsulated tetracaine (LET) versus nonliposome-encapsulated tetracaine (NLET) were determined after topical application to open wounds in six rabbits (three in LET and three in NLET). H3-tetracaine preparations of LET or NLET were applied randomly to uniform dermal lacerations in anesthetized rabbits. Plasma tetracaine concentrations (ng/mL) of arterial blood samples obtained were measured at predetermined intervals (0.25, 0.5, 1.0, 2.0, and 24 hours) by isotope tracer assay. Results (mean +/- standard deviation) showed the peak plasma tetracaine concentration (Cmax) and the time to Cmax were 40.8 +/- 5.1 ng/mL and 40.1 +/- 7.3 minutes for LET, and 117.8 +/- 9.7 ng/mL and 49.1 +/- 50.2 minutes for NLET. Plasma tetracaine concentrations at all samples times were significantly lower for LET versus NLET. Liposome encapsulation of topically applied tetracaine significantly decreases both the peak and overall plasma tetracaine concentrations compared with the nonencapsulated form. The data suggest that liposome encapsulation of topically applied local anesthetics such as a solution of tetracaine, adrenaline, and cocaine, might reduce the potential systemic toxicity caused by rapid absorption of these compounds.

Evaluation of local anesthesia provided by transdermal patches containing different formulations of tetracaine

Topical formulations of tetracaine in vehicles of propylene glycol and saline are tested on human volunteers with standard occlusive, adhesive, transdermal patches. The effects of formulation composition, dose, and onset time are investigated. Dose-response studies indicate that the optimum formulation for the diffusion of tetracaine in vivo is 60% free base and 40% acid salt (w/w) in 40% propylene glycol and 60% saline (v/v). A concentration of 0.3 M [8.3% (w/v)] tetracaine is sufficient to reach the dose plateau. Time-response studies indicate that high concentrations of tetracaine in the optimum formulation [1.1 and 1.8 M, 30 and 50% (w/v), respectively] can produce statistically significant analgesia relative to a placebo after 45 min. Comparison of these in vivo data with earlier in vitro data indicate that the optimum formulation with regard to clinical studies is identical to that for in vitro diffusion through hairless mouse skin [60% free base and 40% acid salt (w/w) in 40% propylene glycol and 60% saline].

New patch delivery system for percutaneous local anaesthesia

We have assessed the release of amethocaine from a new patch delivery system and subsequent drug diffusion through human stratum corneum and whole skin. We found that the patch system was more efficient than an amethocaine gel preparation. It was also observed, both in vitro and in vivo, that the stratum corneum acted as a reservoir for amethocaine. A double-blinded clinical trial, using 30- and 60-min application times, indicated that there was no statistical difference between patch and gel formulations in onset of percutaneous local anaesthesia. Furthermore, a 30-min application of the patch was sufficient to provide profound and prolonged topical anaesthesia in all volunteers. In contrast, although a 60-min application of EMLA was necessary to ensure satisfactory onset of percutaneous anaesthesia, the duration of action was much shorter than that of the amethocaine patch.

Plasma cocaine and tetracaine levels following application of topical anesthesia in children

STUDY OBJECTIVES

To measure plasma cocaine and tetracaine levels in children after standardized application of a solution of tetracaine 0.5%, epinephrine 0.05%, and cocaine 11.8% (TAC) to lacerations requiring suture repair.

DESIGN

Nonrandomized, controlled trial over a five-month period.

SETTING

University hospital emergency department.

TYPE OF PARTICIPANTS

Stable children less than 16 years of age with uncomplicated lacerations.

MEASUREMENTS AND MAIN RESULTS

Blood was obtained at either 15 or 20 minutes (early; 32) or 45 or 60 minutes (late; 45) for measurement of plasma cocaine and tetracaine levels. Analysis for cocaine and tetracaine concentrations was performed using gas chromatography-mass spectroscopy with a limit of detection for both assays of 0.5 ng/mL. Serum cocaine levels were low but measurable at both times in 75% of children. No tetracaine was measurable. Median cocaine levels were 1 ng/mL (range, 0 to 112 ng/mL) for the early group and 2 ng/mL (range, 0 to 274 ng/mL) for the late group (P = NS). Only two children had levels of more than 100 ng/mL. No significant correlation between patient or laceration characteristics and cocaine levels was detected. No significant change in heart rate or blood pressure was detected. Children who required additional local anesthesia had nonfacial lacerations and lower cocaine levels than children with facial lacerations.

CONCLUSION

Application of 3 mL of standard TAC solution for 15 minutes results in low but measurable plasma cocaine levels in 75% of children.

Clinical evaluation of a spinal catheter technique in femoro-popliteal graft surgery

The use of a 24-gauge catheter for continuous spinal anaesthesia was evaluated in 20 patients undergoing femoro-popliteal graft surgery for occlusive disease. The catheter was inserted through either a Tuohy or Quincke-tip needle and isobaric amethocaine used for the initial injection. In five patients identification of the subarachnoid space was not straightforward, but clear difficulty with catheter insertion was encountered in only one. The range of blocks seen was wider than expected, but it was adequate for surgery 15 minutes after injection in 16 of the 20 patients. In another three the injection of a small dose of hyperbaric bupivacaine produced the necessary extension of block. Two patients (10%) required a general anaesthetic, one because of grossly inadequate spread of solution, the other because the catheter kinked and prevented injection of a second dose after the start of surgery.

[A comparative evaluation of the permeability of the dura mater in parturients and the efficacy of epidural anesthesia using morphine following cesarean section]

Spinal dura mater permeability has been compared in 15 women dead in labour or of severe multiple combined traumas. The quantitative index for the assessment of transmeningeal morphine and dicaine diffusion was permeability coefficient calculated according to Fick's equation. It has been shown that in late pregnancy dura mater permeability for morphine and dicaine increases by 18.6% and 23.5%, respectively. However, a decrease of the diffusion barrier is not clinically manifested during epidural morphine analgesia due to an equivalent increase in the rate of intravascular opiate adsorption. The conclusion is made that it is advisable to add the usual adrenaline dose (1:200,000) to the anesthetic solution to enhance the degree of anesthesia adequacy and to decrease the danger of the onset of general narcotic and respiratory depression on the fetus in the early neonatal period.

[The effect of concurrent atherosclerosis on the permeability of the dura mater and the efficacy of epidural analgesia with morphine and dicain]

The permeability of spinal dura mater (SDM) was examined for morphine and tetracaine hydrochloride in 7 suddenly died patients with profound morphological manifestations. Atherosclerosis was found to show an average 37% increase in SDM permeability. With this, the efficiency of postoperative epidural analgesia (EA) with morphine was studied in 32 surgical patients with concurrent atherosclerosis. EA was demonstrated to be not only beneficial for this category of patients, unlike control patients, but followed by a significant decrease in respiratory center sensitivity to CO2. It was concluded that the regularities found should be taken into account during EA with narcotic analgesics in patients with concurrent atherosclerosis.

Concentration-response analysis of percutaneous local anaesthetic formulations

The percutaneous absorption of amethocaine has been measured for different concentrations of the drug in three different formulations, A, B and C. Statistical analysis indicated that a concentration of 4% produced effective percutaneous local anaesthesia to pin-prick, together with an acceptable onset time of approximately 40 min. Increasing the concentration did not reduce the onset time further, although there was some increase in the duration of anaesthesia. Formulations A and B were hydrophilic, whereas C was an oil-in-water cream. Effective anaesthesia with formulation C required a higher drug concentration (12%), perhaps because of partitioning of the lipophilic anaesthetic into the lipid phase of the vehicle. The rate-limiting step was considered to be diffusion by the lipophilic anaesthetic through the stratum corneum, shown by onset of anaesthesia after removal of the formulation from the test site.

[Mechanism of the development of epidural analgesia using opiates and anesthetics]

A special model was used in order to investigate the morphine and dikain permeability of dura mater (DM) in 33 people after sudden death at the age of from 20 to 79. The morphine permeability of spinal DM was found to be 20.5% greater than that of the root DM, while the dikain permeability was 28.5% greater irrespective of the age. The quantitative evaluation of perineural diffusion of morphine and dikain is first given along the pathway of dorsal and ventral roots. A conclusion was made that the perineural pathway of spread of opiates and local anesthetics is of great significance in the mechanism of development of this kind of anesthesia.

Fatality secondary to misuse of TAC solution

The death of a 7 1/2-month-old girl from the misuse of tetracaine/adrenalin/cocaine solution for wound anesthesia is reported. Ten milliliters of the solution inappropriately came into contact with nasal mucous membranes, causing excessive drug absorption. The patient's death probably was due to cocaine toxicity (post-mortem blood level, 11.9 mg/L).

Comparative in vivo and in vitro assessment of the percutaneous absorption of local anaesthetics

The percutaneous absorption of local anaesthetics in a standard formulation has been compared in vitro and in vivo. In vitro data were obtained with a modified Sartorius absorption system and silastic as a lipophilic barrier membrane. With this system the greatest steady-state flux values and permeability coefficients were obtained with amethocaine and lignocaine. These drugs also performed best in an in vivo volunteer trial. However, statistical analysis revealed that amethocaine was significantly better at producing full-depth anaesthesia to the challenge of insertion of a sterile needle. An optimized amethocaine formulation may therefore be expected to meet most closely the ideal profile for a percutaneous local anaesthetic preparation.

[Experimental evaluation of dura mater permeability on a model of peridural analgesia with morphine and dikain]

The permeability of spinal dura mater (DM) in 14 people after sudden death was studied on the model of peridural analgesia with morphine and dikain. The DM permeability was found to linearly increase in caudal direction and within the limits of 10 segments of thoracolumbar section of the peridural space (from T2-3 to L1-2) it is increased by 170% for morphine and 200% for dikain. The diffusion of 14-18% of the epidurally injected dosage of morphine and 18-27% of dikain through the dura mater takes place depending on the segmentary level. This correlation should be taken into account for the achievement of the most pronounced antinociceptive effect and prevention of complications.