Intravenous and Intramuscular Allopregnanolone for Early Treatment of Status Epilepticus: Pharmacokinetics, Pharmacodynamics, and Safety in Dogs

Allopregnanolone (ALLO) is a neurosteroid that modulates synaptic and extrasynaptic GABAA receptors. We hypothesize that ALLO may be useful as first-line treatment of status epilepticus (SE). Our objectives were to (1) characterize ALLO pharmacokinetics-pharmacodynamics PK-PD after intravenous (IV) and intramuscular (IM) administration and (2) compare IV and IM ALLO safety and tolerability. Three healthy dogs and two with a history of epilepsy were used. Single ALLO IV doses ranging from 1-6 mg/kg were infused over 5 minutes or injected IM. Blood samples, vital signs, and sedation assessment were collected up to 8 hours postdose. Intracranial EEG (iEEG) was continuously recorded in one dog. IV ALLO exhibited dose-proportional increases in exposure, which were associated with an increase in absolute power spectral density in all iEEG frequency bands. This relationship was best described by an indirect link PK-PD model where concentration-response was described by a sigmoidal maximum response (Emax) equation. Adverse events included site injection pain with higher IM volumes and ataxia and sedation associated with higher doses. IM administration exhibited incomplete absorption and volume-dependent bioavailability. Robust iEEG changes after IM administration were not observed. Based on PK-PD simulations, a 2 mg/kg dose infused over 5 minutes is predicted to achieve plasma concentrations above the EC50, but below those associated with heavy sedation. This study demonstrates that ALLO is safe and well tolerated when administered at 1-4 mg/kg IV and up to 2 mg/kg IM. The rapid onset of effect after IV infusion suggests that ALLO may be useful in the early treatment of SE. SIGNIFICANCE STATEMENT: The characterization of the pharmacokinetics and pharmacodynamics of allopregnanolone is essential in order to design clinical studies evaluating its effectiveness as an early treatment for status epilepticus in dogs and people. This study has proposed a target dose/therapeutic range for a clinical trial in canine status epilepticus.

An IoT Solution for Online Monitoring of Anesthetics in Human Serum Based on an Integrated Fluidic Bioelectronic System

In this paper, we present the design, the implementation and the validation of a novel Internet of Things (IoT) drug monitoring system for the online continuous and simultaneous detection of two main anesthetics, e.g., propofol and paracetamol, in undiluted human serum. The described full system consists of a custom-built electronic Raspberry Pi (RPi) based Printed Circuit Board (PCB) that drives and reads out the signal from an electrochemical sensing platform integrated into a fluidic system. Thanks to the Polydimethylsiloxane (PDMS) fluidic device, the analyzed sample is automatically fluxed on the sensing site. The IoT network is supported by a Cloud system, which allows the doctor to control and share all the patient's data through a dedicated Android application and a smart watch. The validation closes with the first ever demonstration that our system successfully works for the simultaneous monitoring of propofol and paracetamol in undiluted human serum by measuring the concentration trends of these two drugs in fluxing conditions over time.

Cascaded PID controller for anaesthesia delivery

The technologies for continuous measurement of the anaesthetic agents circulating in body fluids are not mature yet, though some preliminary prototypes exist already. We present a control algorithm that based on the real measurement of propofol plasma concentration may adjust the delivery rate. This opens a possibility for a safer anesthesia when the technologies for online measurement of drug concentration will be mature enough to be combined with our model.

Separation and enhanced detection of anesthetic compounds using solid phase micro-extraction (SPME)-Raman spectroscopy

Polydimethylsiloxane (PDMS)-based solid-phase micro-extraction (SPME) was used along with Raman spectroscopy (RS) to separate and enhance the detection of five anesthetic compounds (halothane, propofol, isoflurane, enflurane, and etomidate) from aqueous and serum phases. Raman signals in the spectral ranges 250-450 cm(-1) and 950-1050 cm(-1) allowed the unique characterization of all five compounds when extracted into the PDMS phase. The SPME-RS detection of clinically relevant concentrations of aqueous propofol (6.5 μM) and halothane (200 μM) is shown. We quantify the partition coefficient for aqueous halothane in PDMS as log K = 1.9 ± 0.2. Solid-phase micro-extraction of the anesthetics makes their detection possible without the strong autofluorescent interference of serum proteins. Because of low solubility and/or weak Raman scattering, we found it challenging to detect enflurane, isoflurane, and etomidate directly from the aqueous phase, but could we do so with SPME enhancement. These studies show the potential of SPME-RS as a method for the direct detection of anesthetics in blood.

[Pharmacokinetics of anesthesia related drugs in patients with chronic kidney disease]

For anesthetic management, various kinds of drugs are administered to the patient. When unchanged drugs or their active metabolites are eliminated from the kidney, renal function has significant effects on the pharmacokinetics of the drugs. Generally, in such cases, drug or metabolite clearance shows a positive relation with glomerular filtration rate. When these drugs are administered to patients with renal impairment, drug concentrations are increased, prolonging the pharmacological effects or causing side-effects. In anesthesia related drugs, morphine, muscle relaxants, antibiotics and phosphodiesterase III inhibitors require special attention. Their dosages should be adjusted according to parameters of renal function such as creatinine clearance.

[Reliability of propofol target-controlled infusion in obese patients]

BACKGROUND

Propofol target-controlled infusion (TCI) is now commonly used for induction and maintenance of anesthesia. In this study, we measured the propofol plasma concentrations in obese patients in order to test our hypothesis that propofol TCI is reliable for use in obese patients.

METHODS

We measured plasma concentrations of propofol in 10 obese patients undergoing elective general anesthesia. Propofol TCI was commenced at a target plasma concentration of 4microg x ml(-1) using a TCI pump. The target concentration was kept at 4microg x ml(-1) for at least 3 hours. Arterial blood samples were drawn for measurement of the propofol plasma-concentration analysis at 30, 60, 90, 120 and 180 minutes after the induction of anesthesia, and at the emergence from anesthesia.

RESULTS

The measured plasma concentrations of the drug were not significantly different from the target plasma concentrations and they showed no tendency to increase during the 3 hours of anesthesia. The measured plasma concentration at emergence was lower than the estimated value.

CONCLUSIONS

We conclude that propofol TCI is a reliable method for maintaining anesthesia even in obese patients. At emergence, however, the data suggested that the plasma concentrations might be lower than the estimated values in obese patients.

Thiopental and halothane dose-sparing effects of magnesium sulphate in dogs

OBJECTIVE

To evaluate the effect of pre- and intraoperatively administered magnesium sulphate (MgSO(4)) on the induction dose of thiopental and of halothane for maintenance of anaesthesia in dogs undergoing ovariohysterectomy (OHE).

STUDY DESIGN

Prospective, double-blind, randomized, placebo-controlled study.

ANIMALS

Forty-six healthy, ASA physical status 1 dogs, scheduled for elective OHE.

METHODS

The dogs were randomly assigned to receive a bolus of 50 mg kg(-1) MgSO(4) intravenously (IV), just before induction of anaesthesia, followed by a constant rate infusion (CRI) of 12 mg kg(-1) hour(-1) MgSO(4) intraoperatively (group Mg, n = 27) or a placebo bolus and CRI of 0.9% sodium chloride (NaCl) (group C, n = 19), approximately 30 minutes after premedication with acepromazine (0.05 mg kg(-1), intramuscularly, IM) and carprofen (4 mg kg(-1), subcutaneously, SC). Anaesthesia was induced with thiopental administered to effect and maintained with halothane in oxygen. End-tidal halothane (ET(hal)) was adjusted to achieve adequate depth of anaesthesia. Blood samples were obtained pre- and postoperatively for measurement of total serum magnesium concentration.

RESULTS

The mean dose of thiopental was statistically lower (p < 0.0005) and the mean standardized ET(hal) concentration and end-tidal carbon dioxide partial pressure (Pe'CO(2)) areas under the curve were statistically smaller (p < 0.0005 and 0.014 respectively) in group Mg. Postoperatively the mean total serum magnesium concentration was statistically higher than the preoperative value (p < 0.0005) in group Mg, but not in group C. Nausea, associated with the MgSO(4) bolus injection, was observed in six dogs in group Mg, two of which vomited prior to induction of anaesthesia.

CONCLUSIONS AND CLINICAL RELEVANCE

Magnesium sulphate administration reduced the induction dose of thiopental and ET(hal) concentration for maintenance of anaesthesia in dogs undergoing OHE. Observed side effects were nausea and vomiting.

Effects of allopregnanolone on sedation in men, and in women on oral contraceptives

Allopregnanolone is a known GABA(A) receptor agonist not previously given to men, or to women using oral contraceptives (OC). The effects of metabolites of sex hormones on the GABA(A) receptor are different between men and women. OC are known to change GABA(A) receptor subunit composition. These factors might play a role in the differential effect of allopregnanolone in men and women, and in women with or without OC. To study the sedative effect of and sensitivity to allopregnanolone in men and in women with OC, nine healthy men (mean age 24.6 years) and nine healthy women on OC (mean age 21.8 years) were given three, increasing, intravenous dosages (0.015, 0.03, and 0.045 mg/kg) of allopregnanolone. Saccadic eye velocity (SEV), subjective ratings, and electroencephalography (EEG) were used to evaluate the response to allopregnanolone. Repeated blood samples for analyses of serum allopregnanolone levels were drawn throughout the study day. Allopregnanolone decreased SEV more in women than in men, and increased subjective ratings of 'sedation'. The results in women on OC are similar to earlier results in women without OC. Subjective ratings of 'contentedness' decreased in men but increased in women. Serum levels of allopregnanolone were more highly increased in men compared to women. Other pharmacokinetic parameters were not different between sexes. On the EEG, beta power increased in men. In conclusion, men and women on OC reacted differently to allopregnanolone.

Pharmacokinetics and anesthetic activity of eugenol in male Sprague-Dawley rats

Eugenol, the principle chemical constituent of clove oil, has recently been evaluated for its anesthetic and analgesic properties in fish and amphibians. The objective of this study was to determine the pharmacokinetic (PK) and anesthetic activity of eugenol in rats. Male Sprague-Dawley rats received single i.v. doses of eugenol (0, 5, 10, 20, 40 and 60 mg/kg) and anesthetic level was evaluated with the withdrawal reflex. For the 20 mg/kg dose level, blood and urinary samples were collected over 1 h for the PK assessment. Plasma and blood concentrations of eugenol, as well as metabolite identification in urine, were determined using a novel dansyl chloride derivatization method with liquid chromatography mass spectrometry (LC/MS/MS). PK parameters were calculated using noncompartmental methods. Eugenol-induced loss of consciousness in a dose-dependent manner, with mean (+/-SEM) recovery in reflex time of 167 +/- 42 sec observed at the highest dose level. Mean systemic clearance (Cl) in plasma and blood were 157 and 204 mL/min/kg, respectively. Glucuronide and sulfate conjugates were identified in urine. Overall, eugenol produced a reversible, dose-dependent anesthesia in male Sprague-Dawley rats.

Plasma pharmacokinetics of alfaxalone in dogs after an intravenous bolus of Alfaxan-CD RTU

OBJECTIVE

To determine the pharmacokinetic parameters of alfaxalone in dogs after the intravenous (IV) administration of clinical and supra-clinical doses of a 2-hydroxypropyl-beta-cyclodextrin (HPCD) alfaxalone formulation (Alfaxan-CD RTU).

EXPERIMENTAL DESIGN

Prospective two-period crossover design. Animals Eight (four male and four female) young adult healthy Beagle dogs. Methods The steroid anaesthetic alfaxalone was administered IV at two doses in a crossover design (2 and 10 mg kg(-1)) with a washout period of 21 days. Blood samples were collected before and up to 8 hours after dosing. Plasma concentrations of alfaxalone were assayed using a liquid chromatograph/mass selective detector technique and analyzed to estimate the main pharmacokinetic parameters by noncompartmental analysis. Results were expressed as mean +/- SD.

RESULTS

The mean duration of anaesthesia from endotracheal intubation to extubation was 6.4 +/- 2.9 and 26.2 +/- 7.5 minutes, for the 2 and 10 mg kg(-1) doses, respectively. The plasma clearance of alfaxalone for the 2 and 10 mg kg(-1) doses differed statistically at 59.4 +/- 12.9 and 52.9 +/- 12.8 mL kg(-1) minute(-1), respectively (p = 0.008) but this difference was deemed clinically unimportant; the harmonic mean plasma terminal half-lives (t(1/2)) were 24.0 +/- 1.9 and 37.4 +/- 1.6 minutes respectively. The volume of distribution was between 2 and 3 L kg(-1) and did not differ between the two doses. No sex effect was observed.

CONCLUSIONS AND CLINICAL RELEVANCE

Alfaxalone, as an HPCD formulation (Alfaxan-CD RTU) administered in the dog provides rapid and smooth induction of anaesthesia, satisfactory conditions for endotracheal intubation and a short duration of anaesthesia. There was no clinically significant modification of the pharmacokinetic parameters between sexes and between the clinical (2 mg kg(-1)) and supra-clinical (10 mg kg(-1)) doses.

GABA(A) receptor changes in acute allopregnanolone tolerance

To study acute tolerance, rats were anesthetized with interrupted i.v. allopregnanolone infusions where the "silent second" in the electroencephalogram (EEG) was the target. Animals were killed either directly at the first silent second or at the silent second level after 30 or 90 min of anaesthesia. Acute tolerance was demonstrated at 90 min of anaesthesia as earlier shown. In situ hybridization showed a decreased expression of the gamma-aminobutyric acid(A) (GABA(A)) receptor subunit alpha4mRNA amount in the thalamus ventral-posteriomedial nucleus of the tolerant rats. A parallel change in the abundance of the alpha4 subunit was detected with immunohistochemistry. The increase in maintenance dose rate (MDR) was significantly negatively correlated with the alpha4mRNA in the thalamus ventral-posteriomedial nucleus, and positively correlated with alpha2mRNA in different hippocampal subregions. There was also a positive relationship between the alpha1mRNA amounts in the different hippocampal subregions, with significant differences between groups. These changes in GABA(A) receptor subunits mRNA expression and protein (alpha4) might be of importance for the development of acute tolerance to allopregnanolone.

Characterization of the stereoselective biotransformation of ketamine to norketaminevia determination of their enantiomers in equine plasma by capillary electrophoresis

A robust CE method for the simultaneous determination of the enantiomers of ketamine and norketamine in equine plasma is described. It is based upon liquid-liquid extraction of ketamine and norketamine at alkaline pH from 1 mL plasma followed by analysis of the reconstituted extract by CE in the presence of a pH 2.5 Tris-phosphate buffer containing 10 mg/mL highly sulfated beta-CD as chiral selector. Enantiomer plasma levels between 0.04 and 2.5 microg/mL are shown to provide linear calibration graphs. Intraday and interday precisions evaluated from peak area ratios (n = 5) at the lowest calibrator concentration are < 8 and < 14%, respectively. The LOD for all enantiomers is 0.01 microg/mL. After i.v. bolus administration of 2.2 mg/kg racemic ketamine, the assay is demonstrated to provide reliable data for plasma samples of ponies under isoflurane anesthesia, of ponies premedicated with xylazine, and of one horse that received romifidine, L-methadone, guaifenisine, and isoflurane. In animals not premedicated with xylazine, the ketamine N-demethylation is demonstrated to be enantioselective. The concentrations of the two ketamine enantiomers in plasma are equal whereas S-norketamine is found in a larger amount than R-norketamine. In the group receiving xylazine, data obtained do not reveal this stereoselectivity.

Low serum allopregnanolone levels in girls with precocious pubarche

Allopregnanolone, a neuroactive steroid, increases during pubertal development and high concentrations are present in subjects with precocious puberty. The aim of the present study was to evaluate serum allopregnanolone levels in girls with precocious pubarche (PP). Basal gonadotropins and steroid hormones were assessed in 17 girls with PP, 22 girls with central precocious puberty (CPP), 25 girls with normal puberty at the same pubertal stage of CPP ones, and 17 prepubertal girls. Adrenocorticotropin hormone (ACTH) and gonadotropin-releasing hormone (GnRH) stimulation tests were performed in all subjects with PP, and in 12 out of 22 with CPP. All girls with normal puberty underwent to GnRH test, while ACTH test was performed in 17 out of 25. Basal dehydroepiandrosterone sulfate (DHEAS) concentrations resulted significantly higher in PP and normal pubertal girls than in prepubertal ones. Allopregnanolone, gonadotropins and estradiol levels were significantly lower in PP group with respect to CPP (P<0.05), while they were comparable among PP, normal pubertal and prepubertal groups. After ACTH administration, allopregnanolone concentrations significantly increased in all groups (P<0.05). After GnRH stimulation, its levels significantly increased in CPP and normal pubertal controls (P<0.05), while no incremental rise was found in PP girls. In conclusion, our study shows that in girls with PP basal and GnRH-stimulated levels of allopregnanolone are significantly lower than in CPP girls. These data suggest that this neurosteroid may be considered a new marker of pubertal development.

Post-ictal circulating levels of allopregnanolone in children with partial or generalized seizures

INTRODUCTION

Allopregnanolone (3alpha-hydroxy-5alpha-pregnan-20-one) is a neurosteroid with a potent modulating activity on the gamma-aminobutyric acid (GABA)(a) receptor complex. It plays a key role in the epileptogenesis of partial seizures. Serum allopregnanolone concentrations significantly increase in the postcritical phase. In the present study we investigated the post-ictal serum allopregnanolone levels in children with partial seizures and generalized seizures, respectively.

PATIENTS AND METHODS

Three groups of subjects were included in the study. Group 1 consisted of 18 children affected by complex partial seizures. Group 2 consisted of 11 children presenting with generalized epilepsy. Group 3 consisted of 20 healthy age-matched subjects. Serum allopregnanolone levels were assayed in the inter-ictal phase and within 30 min after an epileptic event.

RESULTS

The data we obtained suggest that circulating allopregnanolone level significantly increases in the post-ictal phase. However, we found no significant differences in the post-ictal serum allopregnanolone concentrations between patients with partial seizures and those with generalized seizures.

CONCLUSIONS

Further studies are needed to establish if allopregnanolone is a reliable circulating marker of epileptic seizures. However, our observations seem to indicate that post-ictal circulating allopregnanolone level is not useful in differentiating focal and generalized epilepsy events.

Effect of clonidine pre-medication on propofol requirements during lower extremity vascular surgery: a randomized controlled trial

BACKGROUND

Pre-medication with clonidine reduces the requirement for volatile agents during general anaesthesia. This may also be true for anaesthesia with propofol, but the amount of dose reduction has not been measured. Because clonidine also affects cardiac output and thus regional blood flow it could alter the pharmacokinetics of propofol. This randomized, double-blind placebo-controlled trial aimed to study the effect of clonidine pre-medication on dose requirement for propofol during lower extremity vascular surgery using the bispectral index (BIS) as a measure of anaesthetic depth.

METHODS

After oral pre-medication with either clonidine 3 microg kg(-1) or placebo, 39 subjects had lower limb vascular surgery using propofol infusion for anaesthesia. Anaesthetic depth was adjusted to a BIS of 45. Predicted plasma propofol concentrations were noted every 30 min from a target-controlled propofol infusion pump and arterial samples were taken at the same time for propofol measurements.

RESULTS

Patients in both groups were anaesthetized to similar depths of anaesthesia as indicated by BIS readings (P=0.44). The groups had comparable mean (95% CI) arterial concentrations of propofol, 4.8 (3.5-6.1) microg ml(-1) in the patients given clonidine, and 4.6 (3.4-5.7) microg ml(-1) in the patients given placebo (P=0.81). However, the average plasma concentration predicted by the target-controlled infusion was less in the clonidine group [3.2 (2.9-3.5)] than in the group given placebo [3.6 (3.3-3.9)] microg ml(-1) (P<0.05).

CONCLUSIONS

Pre-medication with clonidine reduces the requirement for propofol, which is a pharmacokinetic effect and not a pharmacodynamic central sedative effect.

Anesthetic effects of progesterone are undiminished in progesterone receptor knockout mice

Progesterone has sedative and anesthetic effects but the underlying molecular mechanisms remain unclear. The two possible mechanisms by which progesterone affects the function of the brain include binding to intracellular progesterone receptors (PR) and metabolism to GABA(A) receptor-modulating neurosteroids. In this study, PR knockout (PRKO) mice were used as model to study the role of PRs in the anesthetic activity of progesterone. The progesterone-induced anesthetic activity was undiminished in female PRKO mice (ED50, 172 mg/kg) as compared to their wild-type littermates (ED50, 167 mg/kg). The progesterone-induced anesthetic activity was highly correlated with increased plasma allopregnanolone levels. Pretreatment of PRKO mice with the 5alpha-reductase inhibitor finasteride significantly reduced the progesterone-induced anesthetic activity. Allopregnanolone also evoked dose-dependent anesthetic activity in PRKO mice, which was similar to those of wild-type mice. Thus, the anesthetic activity of progesterone is not mediated by its interaction with PRs. The neurosteroid allopregnanolone partially mediates the anesthetic activity of progesterone by potentiation of GABA(A) receptor function.

A model for differential volatile anesthetic delivery to the upper and lower torso of the rabbit

INTRODUCTION

We have developed a model that permits differential delivery of volatile anesthetics to the upper and lower torso of the rabbit.

METHODS

Rabbits were anesthetized with isoflurane (n = 4) or halothane (n = 3), and blood was drained from a carotid cannula into a membrane oxygenator and reinfused via a renal artery cannula into the lower torso circulation using a roller pump. Bypass of the lower torso circulation was achieved by tightening a ligature around the aorta at the level of the renal arteries. Blood concentrations of anesthetic (assessed by gas chromatography) and cardiovascular responses to noxious stimulation were determined with and without anesthetic delivery to the membrane oxygenator.

RESULTS

When the anesthetic was removed from the oxygenator gas flow, the arterial concentration of isoflurane in the lower torso was 28 +/- 15 microg/ml, while it was 133 +/- 28 microg/ml in the upper torso circulation; the corresponding values for the halothane-anesthetized rabbits were 63 +/- 8 and 270 +/- 49 microg/ml. There was a significant correlation (r=.92-.99) between pump flow and lower torso pressure in each individual rabbit. When anesthetic was delivered to both upper and lower torso, noxious electrical stimulation of the tail or hindpaw did not affect lower torso pressures (52 +/- 10 to 54 +/- 12 mmHg). Decreasing the anesthetic concentration in the lower torso resulted in significant increases in lower torso blood pressure during noxious stimulation (82 +/- 19 to 131 +/- 35 mmHg, P < .05).

DISCUSSION

The results indicate that volatile anesthetics isoflurane and halothane can be differentially delivered to the upper and lower torso of the rabbit, with an approximate 75-80% reduction in the anesthetic concentration in the lower torso when the anesthetic is eliminated from the gas flow to the oxygenator. This preparation can be used to study the pharmacological properties of volatile anesthetics.

New trends in sample preparation: on-line microextraction in packed syringe (MEPS) for LC and GC applicationsPart III: Determination and validation of local anaesthetics in human plasma samples using a cation-exchange sorbent, and MEPS–LC–MS–MS

The need for on-line sample preparation for high-throughput applications in bioanalysis has increased during the past decade. In this paper a robust and on-line sample preparation technique, micro extraction in packed syringe (MEPS) has been developed and validated. The method is a miniaturized, fully automated, solid-phase extraction (SPE) technique that can be connected on-line to GC or LC without any modification of the chromatographs. The performance of MEPS as sample preparation method is illustrated by the determination of local anaesthetics in human plasma samples on-line with high performance liquid chromatography (HPLC) and tandem mass spectrometry. The sampling sorbent was 1mg silica based benzenesulphonic acid cation exchanger that was inserted in a 250 microl syringe. Ropicavine and two of its metabolites (PPX and 3-OH-ropivacine), lidocaine and bupivacine were used as model substances. The accuracy values of quality control samples (QC) were between 95% and 109%, and precision (relative standard deviation, R.S.D.) had a maximum deviation of 9% for the analytes.

On the use of multivariable piecewise-linear models for predicting human response to anesthesia

The standard modeling paradigm used to describe the relationship between input anesthetic agents and output patient endpoint variables are single-input single-output pharmacokinetic-pharmacodynamic (PK-PD) compartment models. In this paper, we propose the use of multivariable piecewise-linear models to describe the relations between inputs that include anesthesia, surgical stimuli and disturbances to a variety of patient output variables. Subspace identification methods are applied to clinical data to construct the models. A comparison of predicted and measured responses is completed, which includes predictions from PK-PD models, and piecewise-linear time-invariant models.

Oxidative stress and mitochondrial glutathione in human lymphocytes exposed to clinically relevant anesthetic drug concentrations

STUDY OBJECTIVE

To evaluate the potential of compounds commonly used in anesthesia practice to affect the intracellular oxidant-antioxidant homeostasis of peripheral blood lymphocytes at clinically relevant concentrations; and to study the changes in reactive oxygen species production and measure the mitochondrial glutathione content.

DESIGN

Prospective, in vitro study.

SETTING

Experimental medical research laboratory at a University Hospital.

MEASUREMENTS

Lymphocytes were isolated from the peripheral blood of 15 healthy donors and incubated for 12 hours at 37 degrees C with the following drug concentrations: thiopental sodium 20 mmoL/mL, droperidol 130 micromol/mL, propofol 60 mmoL/mL, and succinylcholine 17 mmoL/mL. Reactive oxygen species (ROS) generation was determined by hydroethidine and 2',7'-dichlorofluorescein diacetate methods. Mitochondrial glutathione level was assessed using monobromobimane staining.

MEASUREMENTS AND MAIN RESULTS

Thiopental-treated lymphocytes exhibited an overgeneration of ROS, but no change was detected in mitochondrial glutathione quantity. Propofol and droperidol could not induce any perturbative effect on the oxidative state of T cells, whereas succinylcholine was found to markedly affect lymphocyte oxidative state both by impairing glutathione content and promoting exaggerated production of ROS.

CONCLUSION

Drugs commonly used in anesthesia practice may significantly alter the oxidative state of peripheral T cells. This mechanism could contribute to the immune suppression that occurs transiently in the early postoperative period.

The two-compartment recirculatory pharmacokinetic model'an introduction to recirculatory pharmacokinetic concepts

BACKGROUND

Some limitations of traditional ("mamillary") compartmental pharmacokinetic models of anaesthetic related drugs arise from representing the blood as a central compartment. Recirculatory pharmacokinetic models overcome these limitations. It is proposed that the simplest recirculatory model has only two compartments, and that understanding the properties of this model is a useful introduction to recirculatory pharmacokinetic concepts.

METHODS

The compartments of the model are the lungs and the remainder of the body. The traditional rate constants (e.g. k12 and k21) are replaced by terms that include cardiac output. Drug infusion is into the lung compartment, and drug clearance is from the "body" compartment. The "total" drug concentrations can be thought of as the sum of the first-pass and recirculated drug concentrations at any time. Equations for both first-pass and total drug concentrations in arterial and mixed venous blood are presented. The effects of cardiac output and injection time on these concentrations were analysed.

RESULTS

The first-pass arterial concentrations were shown to make a significant contribution to the total concentrations for high-clearance drugs and/or bolus drug administration. There was an inverse relationship between these first-pass concentrations and cardiac output, and a direct relationship with bolus injection rate. Thus, the total arterial concentrations are affected by these factors in these circumstances.

CONCLUSIONS

The two-compartment recirculatory model is the simplest tool available for elaborating recirculatory pharmacokinetic concepts. The recirculatory approach may provide a conceptual framework of drug disposition that better matches the clinical experience of anaesthetists.

Pharmacokinetic and pharmacodynamic properties of metomidate in turbot (Scophthalmus maximus) and halibut (Hippoglossus hippoglossus)

Metomidate was administered to halibut (Hippoglossus hippoglossus) and turbot (Scophthalmus maximus) intravenously at a dose of 3 mg/kg bodyweight, as a bath treatment at a dose of 9 mg/L water for 5 min to study the disposition of metomidate, and as bath treatment (9 mg/L) for 10 min to study the absorption and effect of metomidate on respiration and balance/motor control. Additionally, turbot were given metomidate orally at a dose of 7 mg/kg. The studies were performed in seawater at a temperature of 10.3 +/- 0.4 degrees C (halibut) and 18.0 +/- 0.3 degrees C (turbot). Pharmacokinetic modeling of the data showed that metomidate had shorter elimination half-life and higher plasma concentrations in turbot compared with halibut, both species displaying a rapid uptake, distribution and excretion. Following intravenous administration, the volumes of distribution at steady state (Vd(ss)) were 0.21 L/kg (halibut) and 0.44 L/kg (turbot). Plasma clearances (Cl) were 0.099 L/h.kg in halibut and 0.26 L/h.kg in turbot and the elimination half-lives (t(1/2)lambdaz) were calculated to be 5.8 h and 2.2 h in halibut and turbot, respectively. Mean residence times (MRT) were 2.2 h in halibut and 1.7 h in turbot. Following oral administration, the t(1/2)lambdaz was 3.5 h in turbot. The maximum plasma concentration (Cmax) was 7.8 mg/L in turbot 1 h after administration. The oral bioavailability (F) was calculated to 100% in turbot. Following 5 min bath the maximum plasma concentrations (Cmax), which were observed immediately after end of the bath, were 9.5 mg/L and 13.3 mg/L in halibut and turbot, respectively. Metomidate rapidly immobilized the fish, with respiratory depression, reduced heart rate, and loss of balance/motor control within 1 min (mean). Recovery was slow, with resumed balance/motor control after 26.4 min. Opercular respiration movements were resumed more rapidly with a recorded mean of 1.7 min. Oral administration was demonstrated to be a way of immobilizing fish, for example in large aquariums, without exposing them to unwanted stress.

[Anaesthesia for caesarean section. Comparison of two general anaesthetic regimens and spinal anaesthesia]

OBJECTIVES

The study was undertaken to compare different anaesthetic techniques for scheduled or urgent caesarean section with respect to maternal circulatory parameters, maternal and fetal endocrine stress response, fetal vitality parameters and further clinical parameters such as recovery and analgesic demand.

METHODS

After ethical approval,patients scheduled for general anaesthesia were randomly allocated to the esketamine group ( n=21; induction with 0.5 mg/kg BW esketamine and 1.5 mg/kg BW methohexitone, ventilation until cord cutting with FiO(2) 1.0) and the sevoflurane-group ( n=21; induction with 1.5-2.0 mg/kg BW methohexitone, ventilation until uterotomia with N(2)O/O(2) [FiO(2) 0,5] and endtidal sevoflurane concentrations about 1.0 vol%). After fetal development, all patients received 2.5 microg/kg BW fentanyl and sevoflurane (about 1.0 vol% endtidal) during ventilation with N(2)O/O(2) (FiO(2) 0.33). As a further control, a group with spinal anaesthesia ( n=22; 2.6-3.0 ml isobaric bupivacaine 0.5 %) was investigated. Maternal circulatory and endocrine plasmatic stress parameters were investigated at five time points and fetal parameters once after development.alpha< or =0.05 was considered significant.

RESULTS

Biometric data were comparable in all groups. Systolic arterial pressure was higher in the esketamine group ( p=0.008), whereas the heart rate was lower during spinal anaesthesia ( p<0.001). Plasma noradrenaline decreased in all collectives ( p<0.001) and mean group levels of noradrenaline ( p=0.04) and adrenaline ( p<0.001) were lower during spinal anaesthesia. In all groups, antidiuretic hormone (ADH) remained within the normal range or was slightly increased. Adrenocorticotropic hormone (ACTH) initially increased in all groups and decreased in later time course ( p<0.001). Cortisol increased in all groups ( p<0.001) but group levels were lower during spinal anaesthesia ( p<0.001). In the groups with general anaesthesia, no significant differences in recovery times were obvious, and neither recall nor dream reactions were observed. Postoperative hypoxic incidents (psaO(2) <90%) were comparable between the groups. After spinal anaesthesia, first analgesic demand was later than in the controls ( p=0.001), and the total amount of piritramide was lower ( p=0.02). Nausea and vomiting were more frequent during spinal anaesthesia ( p=0.03). All patients were content with their regimen. Apgar scores, pH-values and adrenaline, noradrenaline and cortisol in plasma were comparable in all groups of children (69 children, 5 gemini). The fetal concentration of esketamine (251 ng/ml) was lower than the corresponding maternal values (493 ng/ml).

CONCLUSIONS

When compared with methohexitone, sevoflurane and N(2)O for caesarean section, initial total intravenous anaesthesia with esketamine and methohexitone mediated specific antinociception without negative maternal or fetal effects and not taking invasion kinetics or elimination between uterotomia and cord cutting into consideration. Avoidance of N(2)O allows optimal oxygenation of the fetomaternal unit. Stress protection and hemodynamic responses were well balanced, and intraoperative recall or negative dream reactions were lacking. Superior postoperative pain protection was advantageous after spinal anaesthesia, but in contrast, nausea and vomiting were more frequent in this group.

Context-sensitive half-times: what are they and how valuable are they in anaesthesiology?

The context-sensitive half-time is the time required for blood or plasma concentrations of a drug to decrease by 50% after discontinuation of drug administration. The context-sensitive half-time often cannot be predicted by the elimination half-life (a measure of the time needed for actual drug metabolism or elimination) since it also depends on drug distribution. The context-sensitive half-time is a function of the duration of drug administration and may only be estimated by computer simulation. It is more relevant than other isolated pharmacokinetic parameters to understanding the kinetics of drug concentrations. However, understanding the kinetics of drug effect requires concomitant consideration of pharmacodynamics.

Comparison of HPLC and GC-MS methods for determination of embutramide (a component of Tanax or T-61) in biological specimens

Tanax or T-61, a euthanasia solution commonly used in veterinary medicine, has been often involved in suicide attempts (humans) and malicious intoxications (animals). For forensic reasons, the identification of one or more of the three components (embutramide, mebenzonium iodide, and tetracaine hydrochloride) of Tanax is needed to confirm the hypothesis of intoxication. This study was performed with new high-performance liquid chromatographic and gas chromatographic-mass spectrometric methods to identify embutramide in biological matrices (blood, liver, kidney) from different animal species. The good sensitivity and specificity of both methods recommend their use in toxicological analysis in both human and veterinary medicine.

Theoretical electroencephalogram stationary spectrum for a white-noise-driven cortex: evidence for a general anesthetic-induced phase transition

We present a model for the dynamics of a cerebral cortex in which inputs to neuronal assemblies are treated as random Gaussian fluctuations about a mean value. We incorporate the effect of general anesthetic agents on the cortex as a modulation of the inhibitory neurotransmitter rate constant. Stochastic differential equations are derived for the state variable h(e), the average excitatory soma potential, coherent fluctuations of which are believed to be the source of scalp-measured electroencephalogram (EEG) signals. Using this stochastic approach we derive a stationary (long-time limit) fluctuation spectrum for h(e). The model predicts that there will be three distinct stationary (equilibrium) regimes for cortical activity. In region I ("coma"), corresponding to a strong inhibitory anesthetic effect, h(e) is single valued, large, and negative, so that neuronal firing rates are suppressed. In region II for a zero or small anesthetic effect, h(e) can take on three values, two of which are stable; we label the stable solutions as "active" (enhanced firing) and "quiescent" (suppressed firing). For region III, corresponding to negative anesthetic (i.e., analeptic) effect, h(e) again becomes single valued, but is now small and negative, resulting in strongly elevated firing rates ("seizure"). If we identify region II as associated with the conscious state of the cortex, then the model predicts that there will be a rapid transit between the active-conscious and comatose unconscious states at a critical value of anesthetic concentration, suggesting the existence of phase transitions in the cortex. The low-frequency spectral power in the h(e) signal should increase strongly during the initial stage of anesthesia induction, before collapsing to much lower values after the transition into comatose-unconsciousness. These qualitative predictions are consistent with clinical measurements by Bührer et al. [Anaesthesiology 77, 226 (1992)], MacIver et al. [ibid. 84, 1411 (1996)], and Kuizenga et al. [Br. J. Anaesthesia 80, 725 (1998)]. This strong increase in EEG spectral power in the vicinity of the critical point is similar to the divergences observed during thermodynamic phase transitions. We show that the divergence in low-frequency power in our model is a natural consequence of the existence of turning points in the trajectory of stationary states for the cortex.

Retention of nociceptor responses during deep barbiturate anesthesia in frogs

Bullfrogs (Rana catesbeiana) anesthetized with a large dose of thiopental (42.8 mg/kg) retained movement responses to nociceptor stimuli despite an average plasma drug level of 51 mg/l, of which 63% was bound to plasma proteins. This concentration, when corrected to include only unbound and uncharged drug, was 2-fold greater than those reported to abolish nociceptor response (NR) during surgical anesthesia in man. The median anesthetic dose (AD50) for loss of the righting reflex was 11.2 mg/kg by s.c. injection into the abdominal lymph sac; however, at 54.0 mg/kg, all frogs retained NRs, although otherwise deeply anesthetized. The ratio of NR-blocking dose to light AD was thus > 4.8, as compared to < 2 in mammalian studies. Whole body levels of thiopental determined at 3 h after intralymphatic injection showed that about half the injected drug had been eliminated by this time and that termination of anesthesia was chiefly due to drug elimination. Even though the pharmacokinetics of thiopental appears to differ markedly in frogs and men, the poor analgesia seen in the present study frequently has been reported during clinical barbiturate anesthesia. Since this deficiency is much more pronounced in the bullfrog than in man, its neurophysiological basis might profitably be studied using the bullfrog as a model; however, the high mortality associated with deep thiopental anesthesia in the frog should preclude its use as a practical anesthetic in amphibia.

A fatality related to the veterinary anesthetic telazol

A 45-year-old male veterinarian was found dead in bed. Police investigation showed no evidence of trauma or other suspicious circumstances. Autopsy was unremarkable except for cardiomegaly and hepatosplenomegaly. Toxicological analysis revealed the presence of Telazol and ketamine. Telazol is a veterinary anesthetic agent that is composed of equal parts of tiletamine and zolazepam. Tiletamine is a disassociative anesthetic similar to ketamine and phencyclidine, and zolazepam is a diazepine derivative tranquilizer used to minimize the muscle hypertonicity and seizures associated with tiletamine. Quantitation of tiletamine and zolazepam was performed using gas chromatography-mass spectrometry in the selected ion monitoring mode following a solid-phase extraction. Postmortem blood, urine, and liver concentrations of tiletamine were 295 ng/mL, 682 ng/mL, and 196 ng/g, respectively, whereas postmortem concentrations of zolazepam for the same tissues were 1.71 microg/mL, 1.33 microg/mL, and 15.5 microg/g, respectively. Blood and urine ketamine levels were 37 ng/mL and 381 ng/mL, respectively. The cause of death was ruled an acute mixed drug intoxication of tiletamine, zolazepam, and ketamine with the manner of death ruled as unclassified.

Effect of intravenous lidocaine on halothane minimum alveolar concentration in ponies

This study investigated the effect of lidocaine i.v. on halothane minimum alveolar concentration (MAC) in ponies. Six ponies were anaesthetised with thiopentone and succinylcholine, intubated and anaesthesia maintained with halothane. Ventilation was controlled and blood pressure maintained within clinically acceptable limits. Following a 2 h equilibration period, baseline halothane MAC was determined. The ponies were then given a loading dose of lidocaine (2.5 or 5 mg/kg bwt) or saline over 5 min, followed by a constant infusion of lidocaine (50 or 100 microg/kg/min, or saline, respectively). The halothane MAC was redetermined after a 60 min infusion of lidocaine or saline. The baseline halothane MAC for the control group was mean +/- s.d. 0.94 +/- 0.03%, and no significant decrease occurred following saline infusion. Lidocaine decreased halothane MAC in a dose-dependent fashion (r = 0.86; P < 0.0003). The results indicate that i.v. lidocaine may have a role in equine anaesthesia.

Determination of sedatives and anesthetics in plasma by liquid chromatography-mass spectrometry with a desalting system

Though liquid chromatography-mass spectrometry (LC-MS) is a powerful tool for analysis of drugs and their metabolites, it does not allow the use of a non-volatile buffer such as phosphate buffer. We used a column-switching desalting system in combination with atmospheric pressure chemical ionization LC-MS for analysis of sedatives and anaesthetics. The drugs examined were flumazenil, butorphanol, midazolam, lorazepam, phenobarbital and flunitrazepam. The separation was carried out on a reversed-phase column using acetonitrile-0.1 M phosphate buffer as a mobile phase. The mass spectra are almost the same as those obtained by direct analysis and the molecular ions were clearly observed. In the analysis, phosphate buffer was completely removed with the trapping column and did not interfere with ionization of the drugs in MS. The chiral separation of lorazepam was achieved on a chiral column with UV, optical rotatory detection and MS. This method is sufficiently sensitive and accurate for the pharmacokinetic studies of these drugs in biological samples.

A positron emission tomography study of cerebral blood flow and oxygen metabolism in healthy male volunteers anaesthetized with eltanolone

BACKGROUND

The effects of eltanolone anaesthesia in humans on regional cerebral blood flow, regional cerebral metabolic rate of oxygen and oxygen extraction ratio were to be evaluated using positron emission tomography (PET).

METHODS

Six healthy male volunteers were studied. Series of PET-measurements with 15O and H2(15)O were carried out in the awake state (baseline)(n = 6), during eltanolone anaesthesia (n = 5) and during early recovery (n = 5), when the subjects were oriented with respect to person, place and time. Eltanolone was given as a programmed infusion.

RESULTS

Cerebral blood flow (rCBF) was reduced in almost all cortex regions studied by 31 +/- 16% (mean +/- SD, P < 0.01). During recovery rCBF increased to 109 +/- 26% of pre-anaesthetic baseline levels (P < 0.01). Eltanolone in the doses administered lowered oxygen metabolism (rCMRO2) by 52 +/- 8% (P < 0.01) in cortex regions. During recovery rCMRO2 increased to 90 +/- 13% of baseline (P < 0.01). The oxygen extraction (OER) in cortical regions decreased by 32 +/- 23% (P < 0.01) during anaesthesia and returned to 82 +/- 10% of baseline (P < 0.01) during recovery. Less reduction in cortical blood flow during eltanolone anaesthesia was seen in the uncus (P < 0.01), though no differences in the depression of oxygen metabolism were seen. Oxygen extraction remained homogeneous throughout the brain.

CONCLUSION

Eltanolone anaesthesia was shown to reduce cerebral oxygen metabolism and cerebral blood flow in healthy volunteers. There were no signs of ischaemic effects.

Gas chromatographic-mass spectrometric identification and quantitation of benzyl alcohol from human serum and postmortem blood after derivatization with 4-carbethoxy hexafluorobutyryl chloride: a novel derivative

Benzyl alcohol is commonly used as an antibacterial agent in a variety of pharmaceutical formulations. Several fatalities in neonates have been linked to benzyl alcohol poisoning. Most methods for measuring benzyl alcohol concentrations in serum utilize direct extraction followed by high performance liquid chromatography. We describe a novel derivatization of benzyl alcohol using 4-carbethoxyhexafluorobutyryl chloride after extraction from human plasma, and subsequent analysis by gas chromatography-mass spectrometry (GC/MS). The derivative was eluted at a significantly higher temperature and the method was free from interferences from more volatile components in serum and hemolyzed specimens. However, with postmortem specimens, we observed multiple peaks which were eluted at a very high temperature, long after derivatized benzyl alcohol and the internal standard. Therefore, baking the column at 310 degrees C is recommended after analysis of a postmortem specimen. Another advantage of this derivatization technique is the conversion of low molecular weight benzyl alcohol (MW 108) to a high molecular weight derivative (MW 358). The positive identification of benzyl alcohol can be easily achieved by observing a distinct molecular ion at m/z 358 as well as other characteristic ions at m/z 107 and 91. Quantitation of benzyl alcohol in human serum can easily be achieved by using 3,4-dimethylphenol as an internal standard. The within run and between run precisions (using serum standard of benzyl alcohol: 50 mg/L) were 2.2% (mean = 50.6, SD = 1.1 mg/L), and 6.9% (mean = 50.8, SD = 3.5 mg/L). The assay was linear for the serum benzyl alcohol concentrations of 5 mg/L to 200 mg/L and the detection limit was 1 mg/L. We observed no carry-over problem in our assay as when 2 microL ethyl acetate was injected into the GC/MS after analyzing serum specimens containing 200 mg/L of benzyl alcohol, we observed no peak for either benzyl alcohol or the internal standard in the total ion chromatogram.

Gas chromatography in anaesthesia. I. A brief review of analytical methods and gas chromatographic detector and column systems

Practical applications and relevant studies involving the anaesthetic gases, have been extensively described in the literature. Many eminent analytical methods have already been developed for medical practice where routine analysis of anaesthetics is frequently needed, particularly during anaesthesia, and in related and respiratory research programmes. The determination of halothane, isoflurane, enflurane and nitrous oxide concentrations from vaporizers, in exhaled and inhaled gas mixtures, in body fluids and tissues is necessary to control anaesthetic concentrations, and thus, the relevant and adverse effects successfully. Therefore, a literature review, with particular emphasis on gas chromatography would provide important information for investigators in the search for a suitable analytical method for the analysis of multi-component mixtures of anaesthetic gases.

High-volume, zero-balanced hemofiltration to reduce delayed inflammatory response to cardiopulmonary bypass in children

BACKGROUND

In previous studies, researchers suggested a beneficial role of hemofiltration performed during cardiopulmonary bypass in children. This study was performed to assess both clinical effects and inflammatory mediator removal by high-volume, zero-fluid balance ultrafiltration during rewarming (Z-BUF).

METHODS

Twenty children undergoing cardiac surgery were assigned randomly to Z-BUF or a control group. Plasma C3a, interleukin (IL)-1, IL-6, IL-8, IL-10, tumor necrosis factor, myeloperoxidase, and leukocyte count were measured before (T1) and after (T2) hemofiltration and 24 h later (T3). The intensive care unit staff was blinded to the patient's group. Postoperative alveolar-arterial oxygen gradient, time to extubation, body temperature, and postoperative blood loss were monitored.

RESULTS

Ultrafiltration rate was 4,972 (3,183-6,218) mL/m2 (median [minimum-maximum]) in the Z-BUF group, where significant reductions were observed in postoperative blood loss, time to extubation (10.8[9-18] vs. 28.2 [15-58] h) and postoperative alveolar-arterial oxygen gradient (320 [180-418] vs. 551 [485-611] mmHg at T3). In the Z-BUF group, significant removal of tumor necrosis factor, IL-10, myeloperoxidase, and C3a were observed at T2. Interleukin 1, IL-6, IL-8, and myeloperoxidase were decreased at T3, suggesting earlier removal of factor(s) that may trigger their release.

CONCLUSIONS

These results suggest that hemofiltration exerts some beneficial clinical effects that are not due to water removal. The role of the early removal of factors triggering the inflammatory response, rather than a direct removal of cytokines, deserves further investigation.

A measure of association for assessing prediction accuracy that is a generalization of non-parametric ROC area

There is a need for a measure of prediction accuracy that generalizes non-parametric receiver operating characteristic (ROC) area to polytomous ordinal patient state. We describe such a measure, prediction probability PK derived from Kim's measure of association. We show that the value of PK equals the value of non-parametric ROC area for dichotomous patient state and is a meaningful generalization of non-parametric ROC area for polytomous state.

[Pharmacokinetics and effects of xylazine (Rompun) in dogs]

Six beagle dogs were treated with xylazine hydrochloride (1 mg/kg i.m.). The plasma xylazine concentration was measured by HPLC. Additionally, clinical effects were registered (cardiac rate, respiratory activity, electrocardiogram, body temperature, motoric activity, attention, analgesia). Maximum plasma concentrations were measured after 15 minutes (476 ng/ml). The plasma half-life was 24 minutes. Sedation was registered over one hour (xylazine concentration of more than 150 ng/ml). Within the first 30 minutes after treatment (xylazine concentration of more than 300 ng/ml), a low-grade analgesia was observed. In contrast, cardiac and respiratoric depression and also significantly diminished body temperature were registered over 2 to 3 hours.

Relationship of inspired anesthetic concentration to plasma concentration and urinary excretion of sevoflurane metabolites in rats

In patients, plasma concentrations of sevoflurane metabolites may be independent of inspired sevoflurane concentration over a defined dose range. In contrast, studies using rabbits have found that plasma concentrations and urinary excretion of fluoride ion are dose-dependent up to 3% inspired sevoflurane. We measured sevoflurane metabolite concentrations in adult male Sprague-Dawley rats and related them to inspired sevoflurane concentrations. When plasma concentrations and urinary excretion of metabolites were measured in vivo, they were dependent on inspired anesthetic concentration at concentrations less than 1.25%, but became less dose-dependent at higher anesthetic concentrations. Sevoflurane metabolism by precision-cut liver slices in vitro became dose-independent at more than 10-30 microM sevoflurane. No evidence of substrate inhibition was observed. These data provide evidence that sevoflurane metabolite concentrations are almost independent of inspired anesthetic concentration over at least part of the clinically used concentration range.

Determination of embutramide in biological matrices by gas chromatography with nitrogen-phosphorus detection

Embutramide is a general anesthetic having a strong narcotic effect on the central nervous system where it paralyzes the brain center that controls respiration. It is a constituent of T61, a veterinary euthanasia drug. This paper describes a gas chromatographic procedure using nitrogen-phosphorus detection for the determination of embutramide in biological matrices. The drug and the internal standard (ambucetamide) are extracted with dichloromethane under alkaline conditions. The method is linear from 100 to 3000 ng/ml. The within-day and day-to-day coefficients of variation range from 5.1 to 5.7% and from 9.1 to 10.0%, respectively. The recovery is above 80% while the minimum detectable level under the conditions described is 40 ng/ml analyzing a 1-ml or a 1-g aliquot of a sample (blood or tissue). The method is also applied to different samples from dogs euthanized with T61.

Intravenous infusion anaesthesia and delivery devices

During the past decade, major advances have taken place with regard to intravenous infusion anaesthesia. New opioid analgesics, iv anaesthetics, and muscle relaxants have become available, which are characterized by a rapid onset of action, short duration of clinical effect, and favourable side effect profiles. Optimal administration of these drugs is often best achieved by continuous infusion, rather than a more traditional technique of intermittent bolus administration. New concepts in pharmacokinetic modelling also provide an enhanced appreciation of the factors which determine rates of recovery upon discontinuation of an intravenous infusion. Pharmacokinetic principles guide rational selection of the iv anaesthetic drugs according to both procedure and patient-specific requirements. In addition, improvements in the new programmable syringe infusion pumps provide a degree of simplicity and accuracy in operation, which make iv infusion of one, two or three components of the anaesthetic state a simple and practical reality for most procedures. In this CME article, these issues will be reviewed according to the following outline: Historical considerations; Rationale for continuous infusion of iv anaesthetic drugs; Pharmacokinetic and pharmacodynamic considerations; Infusion schemes; New techniques, new indications; IV anaesthetic delivery systems; Pharmacoeconomic considerations; Conclusions.

Anaesthetic agents and excretion in breast milk

This review is an update on anesthetic agents and their excretion into breast milk; it presents the reported effects on suckling infants, and discusses the precautions which should be considered. For most anaesthetic agents, there is very sparse information about breast milk excretion and even less published knowledge about the possible effects on the suckling infant. Generally, when an anaesthetic agent is given on a single-dose basis, there is no evidence that it is excreted in breast milk in clinically significant amounts, even if there are detectable concentrations of the drug in the milk. Most anaesthetics are rapidly cleared from the mother, and, consequently, it should be possible to allow suckling as soon as practically feasible after surgery. However, repeated administration of certain opiates and benzodiazepines has been reported to cause adverse effects in neonates, with premature neonates apparently being more susceptible. Thus, in long-term treatment with these drugs, the importance of uninterrupted breast feeding should be assessed against possible adverse drug effects in the neonate.

Chronic administration of an alpha 2 adrenergic agonist desensitizes rats to the anesthetic effects of dexmedetomidine

alpha 2 adrenergic agonists are being administered perioperatively to facilitate the anesthetic management of the surgical patient. In some clinical settings, use of alpha 2 adrenergic agonists has been extended into the postoperative period to prolong the patients' sedative and stress-free state. We studied whether the administration of alpha 2 adrenergic agonists over an extended period of time would result in "desensitization" to the central actions of alpha 2 adrenergic agonists. Male Sprague-Dawley rats were administered dexmedetomidine, a highly selective alpha 2 adrenergic agonist, at rates varying between 1 and 10 micrograms.kg-1.h-1 via a chronically implanted SC osmotic pump. Spontaneous locomotor activity, tested in an open-field box, was significantly lower in both 3- and 10-micrograms.kg-1.h-1 treatment groups but returned to normal by the second or sixth day, respectively. The hypnotic response to dexmedetomidine IP was decreased in the 10-micrograms.kg-1.h-1 dose group from the second day, and by the fourth day in the 3-micrograms.kg-1.h-1 group. Recovery from the desensitized state was rapid and occurred on the third day after pump removal in the 3-micrograms.kg-1.h-1 group and by the fifth day after pump removal in the 10-micrograms.kg-1.h-1 dose group. By using a higher dose of dexmedetomidine IP (250 micrograms.kg in lieu of 100 micrograms/kg) at day 7 in "tolerant" rats, the hypnotic response could partially be "restored" towards normal. An attenuated hypnotic response could still be demonstrated even when dexmedetomidine was administered directly into the locus coeruleus (LC) in rats pretreated chronically with dexmedetomidine.(ABSTRACT TRUNCATED AT 250 WORDS)