[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)