Abstract: The authors report on a 64-year-old woman with a huge recurrent skull base hemangiopericytoma, in whom they encountered severe difficulty in attaining intraoperative hemostasis. Standard surgical hemostatic methods and the administration of fresh-frozen plasma and prothrombin complex concentrates failed to stop diffuse bleeding from an inoperable tumor remnant. At a critical point during the operation, the intravenous administration of recombinant activated factor VII, combined with mechanical compression, finally led to satisfactory hemostasis. The rationale for using recombinant activated factor VII in situations of uncontrolled bleeding during neurosurgical procedures is discussed, along with the literature in which the use of recombinant activated factor VII as a maneuver of last resort is reported for hemostasis in other surgical fields.
Abstract: BACKGROUND: Previous studies in which volatile anesthetics were exposed to small amounts of dry soda lime, generally controlled at or close to ambient temperatures, have demonstrated a large carbon monoxide (CO) production from desflurane and enflurane, less from isoflurane, and none from halothane and sevoflurane. However, there is a report of increased CO hemoglobin in children who had been induced with sevoflurane that had passed through dry soda lime. Because this clinical report appears to be inconsistent with existing laboratory work, the authors investigated CO production from volatile anesthetics more realistically simulating conditions in clinical absorbers. METHODS: Each agent, 2.5 or 5% in 2 l/min oxygen, were passed for 2 h through a Dräger absorber canister (bottom to top) filled with dried soda lime (Drägersorb 800). CO concentrations were continuously measured at the absorber outlet. CO production was calculated. Experiments were performed in ambient air (19-20 degrees C). The absorbent temperature was not controlled. RESULTS: Carbon monoxide production peaked initially and was highest with desflurane (507 +/- 70, 656 +/- 59 ml CO), followed by enflurane (460 +/- 41, 475 +/- 99 ml CO), isoflurane (176 +/- 2.8, 227 +/- 21 ml CO), sevoflurane (34 +/- 1, 104 +/- 4 ml CO), and halothane (22 +/- 3, 20 +/- 1 ml CO) (mean +/- SD at 2.5 and 5%, respectively). CONCLUSIONS: The absorbent temperature increased with all anesthetics but was highest for sevoflurane. The reported magnitude of CO formation from desflurane, enflurane, and isoflurane was confirmed. In contrast, a smaller but significant CO formation from sevoflurane was found, which may account for the CO hemoglobin concentrations reported in infants. With all agents, CO formation appears to be self-limited.
Abstract: Pharmacokinetic parameters of inhaled anaesthetics have previously been assessed experimentally in healthy volunteers. In contrast, we developed a method to estimate pharmacokinetic parameters under clinical conditions. We obtained data from the continuous routine monitoring of fractional concentration and ventilation during anaesthesia with desflurane, isoflurane and sevoflurane. By simulation studies, we assessed the effects of several sources of variation, including the noise of measurement, the second gas effect and rounding errors or a limited number of displayed digits. Stable fits to a two-compartment model were obtained for both real and simulated data sets in all cases. The most stable parameter was the intercompartmental clearance, and the most sensitive parameter was the volume of distribution. The bias in pharmacokinetic parameters caused by adding errors to measured concentrations was similar for the different compounds. We conclude that the model allows the estimation of an alternative set of pharmacokinetic parameters that can reliably describe the behaviour of volatile anaesthetics under clinical conditions, and allow comparison between agents.
Abstract: The pharmacokinetic characteristics of desflurane, isoflurane and sevoflurane (16 patients for each anaesthetic) were estimated from measurements of inspired and end-expired agent concentrations and ventilation, obtained during routine anaesthesia in patients undergoing maxillofacial surgery (mean age 38 yr, duration of anaesthesia approximately 2 h). A two-compartment model described the data adequately. Although isoflurane and sevoflurane have almost the same tissue/blood partition coefficients, significant differences between substances were observed for the peripheral volume of distribution (medians and ranges: desflurane, 612 (343-1850) mlvapour kgbw-1; isoflurane, 4112 (1472-9396) mlvapour kgbw-1; sevoflurane, 1634 (762-8843) mlvapour kgbw-1) and the transport clearance from the central to the peripheral compartment (desflurane, 7.0 (4.4-11.1) mlvapour kgbw-1 min-1; isoflurane, 30.7 (15.9-38.7) mlvapour kgbw-1 min-1; sevoflurane, 13.0 (9.8-22.4) mlvapour kgbw-1 min-1). Thus, during clinical anaesthesia the important characteristics of the compounds could be obtained and compared between substances from simple data.
Abstract: BACKGROUND: In an open-labelled clinical trial, the effect of desflurane anaesthesia on liver function markers in paediatric patients was monitored. METHODS: Fifty infants and children, 37 male, scheduled for elective cleft plate surgery were included in the study. Median age was 0.57 (0.25-5.45) years (range), mean desflurane exposure was 2.29 +/- 0.75 MAC-h. Function markers were determined within 24 h prior to and within 24-48 h after anaesthesia. Complete data sets were available for total bilirubin 29, aspartate aminotransferase (ASAT) 36, alanine aminotransferase (ALAT) 35, and for alkaline phosphatase (AP) 28. Pre- and postanaesthetic function tests were compared by means of Wilcoxon's matched-pairs test. RESULTS: Only for AP could a statistically significant reduction of the postanaesthetic values be observed, while the other parameters showed no significant changes. Postanaesthetic ASAT and ALAT were clearly reduced in three children who had unspecific highly elevated preanaesthetic values. After the study, this observation could be repeated in at least one child, who received a further anaesthesia with desflurane within 3 months. CONCLUSION: The data suggest that desflurane does not affect excretory or structural liver integrity in infants and children.
Abstract: In a prospective, randomized parallel study, 60 ASA I-III children aged 1-17 years, scheduled for elective strabismus surgery, were anaesthetized with desflurane without prophylactic antiemetic medication. The objective of the study was to determine the incidence of postoperative nausea and vomiting after general anaesthesia with desflurane. To decide whether nitrous oxide further influences these symptoms, the patients were randomly assigned to two groups of 30 patients each. One group received desflurane in oxygen/air and a second group received desflurane in oxygen/nitrous oxide. In all children, after intravenous induction and tracheal intubation, anaesthesia was administered as minimal flow anaesthesia with oxygen and nitrous oxide or air according to the random plan. The patients were observed for 48 postoperative hours until their discharge from the ward. The overall incidence of nausea was found to be 37%, and vomiting was seen in 32% of all patients. No statistical correlation was found between the incidence of postoperative emesis and the administration of nitrous oxide or the duration of general anaesthesia. Instead, the incidence of vomiting was 2.5-fold higher when surgery was performed on both eyes compared with one eye. The relatively low incidence of postoperative nausea and vomiting, as well as the quick recovery from anaesthesia, permitting an early discharge from the postoperative care unit to the ward, show desflurane to be a suitable volatile anaesthetic in strabismus surgery in children.
Abstract: There are some case reports about excessive heat production in the absorbent canister when sevoflurane or enflurane are washed into a circle containing dried soda lime. This observation was often made in the DRAGER ISO 8 circle system with the gas inlet upstream of the soda lime canister with the gas-flow from bottom to top. METHODS: The temperature in the center of an absorbent canister was measured 3.0 cm and 7.5 cm above the bottom. Soda lime (DRAGERSORB 800) was dried in an O2 stream for 2-3 days until there was no further loss in weight. 5 Vol% of desflurane, enflurane, isoflurane and sevoflurane in 2 1/min O2 or 4 Vol% of halothane in 2.5 I/min O2 were continuously fed into the canister. The concentration of the respective inhalational agents were measured after the soda lime canister using a DATEX Capnomac. Experiments were performed at ambient temperatures of 20-22 degrees C. RESULTS: A considerable temperature increase was achieved with all anaesthetics. The highest temperatures were measured at the upper sensor with 56-58 degrees C for desflurane, 76-80 degrees C for enflurane and isoflurane, 84-88 degrees C for halothane and 126-130 degrees C for sevoflurane. IR-detection for some agents was considerably delayed or the time course indicated that other compounds might have formed which absorb at the wavelength monitored. DISCUSSION: The high temperatures indicate the degradation rather than absorption of the volatile anaesthetics. CO is known to be degradation product of all currently used volatile anaesthetics except sevoflurane. Sevoflurane, however, produced the highest temperatures passing through dried soda lime. There are no reports about new specific breakdown products for sevoflurane on dried soda lime.
Abstract: Closed-system anaesthesia provides the best prerequisites for optimal warming and humidification of anaesthetic gases. The PhysioFlex anaesthesia machine fascilitates quantitative closed-system anaesthesia. Furthermore, its design may improve the climatization of the anaesthetic gases by revolving the system volume at 70 l/min, using a small soda-lime canister to allow optimal usage of the heat and moisture generated by CO2 absorption and by integrating all system components in thermally isolating housing. To determine the capacity of the PhysioFlex to climatize anaesthetic gases, we evaluated the heat and humidity profile at four characteristic places in the anaesthetic circuit under standardised conditions in a model. MATERIALS AND METHODS: In an air-conditioned room at 19-20 degrees C ambient temperature, the PhysioFlex was operated with a fresh gas flow of less than 500 ml/min, similar to quantitative closed-system anaesthesia in adults. With a respiratory rate of 10/min and a tidal volume of 600 ml, a humidifier was ventilated, that delivered humidity-saturated gas at 33-34 degrees C; 200 ml/min CO2 were added to the system at the humidifier to mimic the heat, moisture, and CO2 input of a patient into the anaesthetic circuit. A total of six series were performed, each starting with a cold and dry anaesthetic circuit. For 2 h the time-courses of temperature and humidity of the anaesthetic gases were measured at four distinct places: (1) in the soda-lime canister (M1); (2) at the outlet of the anaesthesia machine (M2); (3) at the inlet of the anaesthesia machine (M3); and (4) in the inspiratory limb close to the Y-piece (M4). Capacitive humidity sensors (VAISALA Type HMM 30 D without a protective cap) and very small thermocouples were used to measure relative humidity (rH) and temperature. The data were recorded at 5 min intervals. Due to the continuous gas stream in the system, the response time of the sensors, which is in the range of a few seconds, did not affect the accuracy of the measurement. With the temperature-dependent humidity content of 100% rH obtained from equation 1, absolute humidity was calculated. RESULTS: The time courses of temperature and humidity at the different measuring points are depicted in Figs. 2 and 3, respectively. The steepest increase in temperature and humidity was observed at M1. Within 10 min 100% rH was achieved at all measuring points. Initially, there was a considerable temperature gradient between M1 and M2; this became gradually smaller, indicating system components with high heat capacities. There was only a small gradient between M2 and M4, indicating that there was only a small heat loss compared to the heat input. The recommended minimal climatization of the anaesthetic gases of 20 mg H2O/l [20] was obtained within 10 min at M4. During the whole measuring period heat and humidity increased in the system, reaching a maximum at M4 after 120 min with average values of more than 28 degrees C and 27 mg H2O/l, respectively. CONCLUSION: With the PhysioFlex anaesthesia machine employing closed-system conditions, minimal climatization of anaesthetic gases was reached within 10 min. After a period of 120 min, the anaesthetic gases were nearly climatized to the extent recommended for long-term respiratory therapy. To date, no comparable temperature and humidity level has been reported with conventional anaesthesia machines. The time course of the gradient between M1 and M2 may give an opportunity for further optimising the system in reducing heat loss after the soda-lime canister, the active heat and moisture source in the circuit. At about 32 degrees C, the temperature in the soda-lime canister is 10-15 degrees C less than in conventional anaesthesia machines. Thus, the use of thermally instable volatile anaesthetics in the PhysioFlex under closed-system conditions may be less critical than in conventional anaesthesia machines under minimal-flow conditions.
Abstract: Oscillating membrane potentials that generate rhythmic impulse patterns are considered to be of particular significance for neuronal information processing. In contrast, noise is usually seen as a disturbance which limits the accuracy of information transfer. We show here, however, that noise in combination with intrinsic oscillations can provide neurons with particular encoding properties, a discovery we made when recording from single electro-sensory afferents of a fish. The temporal sequence of the impulse trains indicates oscillations that operate near the spike-triggering threshold. The oscillation frequency determines the basic rhythm of impulse generation, but whether or not an impulse is actually triggered essentially depends on superimposed noise. The probability of impulse generation can be altered considerably by minor modifications of oscillation baseline and amplitude, which may underlie the exquisite sensitivity of these receptors to thermal and electrical stimuli. Additionally, thermal, but not electrical, stimuli alter the oscillation frequency, allowing dual sensory messages to be conveyed in a single spike train. These findings demonstrate novel properties of sensory transduction which may be relevant for neuronal signalling in general.
