Medicine

A question of safety: This Review discusses how far the human toxicological evaluation of synthetic nanomaterials has come, for which over 10000 publications have appeared since 2000. Four core themes have been analyzed: the uptake of nanomaterials by the three main pathways of the lungs, gastrointestinal tract, and skin as well as the assessment of the methods for lung exposure studies.

Perioperative resuscitation with large amounts of fluid may cause tissue edema, especially in the gut, and thereby impair its functions. This is especially relevant in sepsis where capillaries become leaky and fluid rapidly escapes to the pericapillary tissue. We assessed the effects of endotoxemia and peritonitis, and the use of high and moderate volume fluid resuscitation on jejunal contractility. We hypothesized that both endotoxemia and peritonitis impair jejunum contractility and relaxation, and that this effect is aggravated in peritonitis and with high fluid administration. Pigs were randomized to endotoxin (n = 16), peritonitis (n = 16), or sham operation (n = 16), and either high (20 mL/kg/h) or moderate volume (10 mL/kg/h) fluid resuscitation for 24 hours or until death. At the end of the experiment, jejunal contractility and relaxation were measured in vitro using acetylcholine and sodium nitroprusside reactivity, and the effect of nitric oxide synthase inhibition (NOS-I)...

Background: Bispectal index (BIS TM ) monitoring may reduce drug usage and hasten recovery in propofol and inhalation anesthesia. The faster emergence profile of desflurane may reduce the effect of BIS monitoring on recovery from desflurane compared with propofol. This study compared hypnotic drug usage, recovery, patient satisfaction and incidence of inadequate sedation in BIS monitored and nonmonitored women anesthetized with desflurane or propofol. Methods: One hundred and sixty patients scheduled for elective gynecological surgery were randomly assigned to desflurane or propofol anesthesia with and without BIS monitoring. Fentanyl, vecuronium and remifentanil were administered according to clinical criteria. The BIS monitor was used in all patients, but the monitor screen was covered in the controls. A BIS level between 45 and 55 was targeted in the BIS monitored patients whereas depth of anesthesia was assessed by clinical criteria in the controls. Results: The mean (SD) desflurane MAC-hours administered with and without BIS were 0.70 (0.15) and 0.76 (0.12), respectively, resulting in extubation times of 6.5 (4.1) and 8.3 (6.1) min. (NS). Bispectal index monitoring was associated with improved patient satisfaction, reduced postoperative nausea and antiemetic drug requirement, and fewer episodes with sustained BIS levels >60. The mean (SD) propofol infusion rates were 6.0 (1.4) and 6.6 (0.9) mg kg À1 h À1 with and without the BIS monitor (P ¼ 0.023), resulting in mean (SD) extubation times of 6.8 (4.6) and 10.5 min (5.9), respectively (P < 0.05). Conclusion: Bispectal index monitoring reduced propofol usage and hastened recovery after propofol anesthesia, whereas in desflurane anesthesia it was associated with improved patient satisfaction, probably because of decreased postoperative nausea and fewer episodes of inadequate hypnosis.

The results of pulse oximetry saturation in a patient with a high level of methaemoglobinaemia, who subsequently underwent intravenous methylene blue treatment, are presented. The reasons for the erroneously low values after treatment are explained. Pulse oximeters currently available are not helpful in patients treated with methylene blue and should be used with caution in patients who present with cyonosis of'unknown origin.

Arterial pressure is still one of the most important measures in estimating the required dose of inhaled anaesthetics. It is measured easily and reacts rapidly which makes it suitable as a variable for feedback control of depth of anaesthesia. Fuzzy logic, a novel approach to feedback control, was used to control arterial pressure in 10 patients during intraabdominal surgery by automatic adjustment of the concentration of isoflurane in fresh gas. During anaesthesia, fuzzy control periods of 45-min duration were alternated randomly with human control periods of equal duration. During the skin incision period (-3 to +12min) 48.2% of all fuzzy control pressure values were within ±10% of the desired mean arterial pressure compared with 40.4% of the human control values (P < 0.05). The corresponding values for the remainder of the operation were 78.3% and 83.2%, respectively. Thus fuzzy outperformed human control at skin incision, but was slightly inferior during the rest of the operation. We conclude that fuzzy logic is a promising new technique for control of isoflurane delivery during routine anaesthesia. (Br. J. Anaesth. 1995; 74: 66-72)

Sedation may influence the responses of some experimental pain models used to test analgesic efficacy. In this study we compared the effects of a sedative (propofol) and analgesic (alfentanil) on: nociceptive reflex to single and repeated electrical stimulations; mechanical pressure pain; and evoked potentials elicited by nociceptive (electrical and laser) and non-nociceptive (acoustical) stimulation. We studied 12 healthy volunteers with two subanaesthetic concentrations of propofol and two analgesic concentrations of alfentanil. Both propofol and alfentanil increased the threshold for nociceptive reflex to single electrical stimulations, but only alfentanil increased the threshold for nociceptive reflex to repeated electrical stimulations. The pressure pain tolerance thresholds were increased significantly by alfentanil, whereas propofol significantly decreased the thresholds (hyperalgesia). Propofol and alfentanil induced similar reductions in the amplitudes of the evoked potentials elicited by nociceptive (electrical and laser) and non-nociceptive (acoustical) stimulation, whereas only alfentanil reduced the perceived pain to nociceptive stimulations. We have shown that sedation can influence both the psychophysical and electrophysiological responses of some experimental pain tests used to measure analgesic efficacy, and that propofol in subhypnotic doses, has no analgesic effect on painful electrical and heat stimulations, but has a hyperalgesic effect on mechanical pressure pain.

In order to evaluate the performance of feedback fuzzy logic control of inspired oxygen and isoflurane concentrations, we studied 30 patients undergoing discectomy for lumbar (n = 26) or cervical (n = 4) disc herniation. Patients were allocated random to one of two groups: a standard group (n = 15) with low flow anaesthesia (1.2-1.3 litre min-1) and manual control of gas concentrations; and a fuzzy group (n = 15) with minimal flow (0.5 litre min-1) and fuzzy logic feedback control of gas concentrations. Fuzzy logic control achieved and maintained very accurately the desired isoflurane concentration. Oxygen concentration was controlled more precisely than in the standard group. Delivery and costs of oxygen and nitrous oxide were significantly lower in the fuzzy group (P &amp;lt; 0.01). Accumulation of foreign gases was observed in one patient during low flow and in 11 patients during minimal flow anaesthesia. In conclusion, fuzzy logic control of inspired oxygen and isoflurane concentration during minimal flow anaesthesia was reliable and reduced anaesthetic gas delivery and costs.

We have investigated in 10 patients the effect of extradural anaesthesia on temporal summation by comparing pain thresholds to single and repeated (five impulses at 2 Hz) electrical stimuli and compared these tests with pinprick and cold stimulation. Bupivacaine 0.5% (20 ml) was injected at L2-3. After extradural anaesthesia the threshold to repeated stimuli was significantly lower than the threshold to single stimuli (P = 0.0007). Nine patients lost cold sensation and 10 patients pinprick sensation. Pain to single electrical stimulation disappeared in six patients and pain to repeated electrical stimulation in one. Pain may be evoked by temporal summation of repeated electrical stimuli even when pinprick sensation, cold sensation and pain to single electrical stimuli are inhibited. Thus temporal summation should be taken into consideration when extradural analgesia is assessed.

We studied the clinical use of an automatic feedback control system to adjust the end-tidal anaesthetic concentration with a low-¯ow method. The end-tidal controller uses two input signals (the end-tidal and inspiratory concentrations) to control the iso¯urane concentration in the fresh gas¯ow, using a model-based algorithm. We studied 22 ASA I±III patients during elective surgery lasting more than 2 h. The anaesthetist was asked to make four step changes of the target end-tidal concentration (+0.3, +0.6, ±0.3, ±0.6 vol%), either manually (Group A) or by setting the target value for the feedback controller (Group B), and then the control was changed and the step changes were repeated, in a crossover design. Eighty step changes with each control method were compared in terms of response time, maximal overshoot and stability. The automatic control system was more accurate and stable than the human controller for step increases and step decreases, with less overshoot/undershoot and greater stability [e.g. maximal overshoot 14.7 (SD 3.7)% and 18 (8.1)% respectively for +0.6 vol% step changes, and 19.8 (3.7)% and 30.7 (13.2)% respectively for +0.3 vol% step changes]. However, the automatic control system showed a faster response time than the manual method only with large increasing steps (e.g. 149 (32) s and 205 (57) s respectively for +0.6 vol% step changes) and was not different from manual control for decreasing steps. Automatic control of the end-tidal iso¯urane concentration can be better than human control in a clinical setting, and this task could be done automatically.

demanded). The investigations were performed with premixed test gases (2.5, 5, 10 vol%, error < / % rel). Humidification (37° C) of gases were generated by a Drager Aquapor. Respiratory cycles were simulated by manually activated valves. All monitors complied with the tolerated accuracy bias in CO 2 reading (<12% or 4 mmHg of actual test gas value) for wet and dry test gases at all concentrations, except that the Marquette MGA-AS exceeded this accuracy limit with wet gases at 5 and 10 vol% CO 2 . Water condensed in the metal airway adapter of the HP M1166A at 37° C gas temperature but not at 30° C. The Servomex 2500 (nonclinical reference monitor), Passport (M-type), Multinex (Sl-type) and

Automatic controllers capable of regulating multiple patient outputs for higher-quality anesthesia treatment are described. The first steps toward the development of an autonomous anesthesia system at the authors&amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; laboratory are presented. The controllers are implemented on a real-time platform and tested on humans to quantify the benefits that may result from their use in routine practice. To date, the staff

Two new portable infrared gas analysers, the Irina (Drfigerwerke, Liibeck, Germany) and the Normac (Datex Instrumentarium Corporation, Helsinki, Finland), were tested and the results compared to those from such established methods as gaschromatography and the Beckman LB-2 (Beckman, USA) infrared gas analyser using exactly defined gas mixtures from a vaporizer developed in our laboratory. The analysers were evaluated for their accuracy and precision, noise, zero stability, gain stability and the impact of flow, overpressure, carrier gas and humidity. All three analysers showed good accuracy and precision. The noise level was acceptable except in the older version of the Normac, but this error has now been corrected by the manufacturer. Zero and gain stability are very good; gas flow and overpressure do not affect the measurement. The influence of carrier gases and humidity is negligible except for the strong N20 effect on the Beckman. We conclude that this new generation of highly sophisticated and reliable but handy analysers will meet the clinical demands.

To test the accuracy of a thermal conductivity xenon sensor in vitro and in vivo and to test the effect of xenon on other anesthetic gas analyzers as determined by a mass spectrometry gold standard. The xenon concentration was measured with a prototype of a thermal conductivity sensor and a mass spectrometer in vitro and in 6 patients. Further in vitro experiments determined the impact of xenon on the measurements of oxygen, carbon dioxide and desflurane with three commercially available anesthesia gas monitors. In vitro the thermal conductivity sensor and an associated computer, when calibrated against a mass spectrometer using a third order polynomial calibration curve measured the xenon concentration to a 95% confidence limit of -1.2 to +1.8 vol% compared to mass spectrometry. In vivo and under clinical conditions with a mixture of xenon, O2 and CO2 the 95% confidence limit was -2.5 to +1.6 vol% with a mean bias of -0.5 vol% over a concentration range of 20 to 70 vol%. Xenon indu...