Temperature monitoring: the consequences and prevention of mild perioperative hypothermia

Homeothermic species require a nearly constant internal body temperature. Significant deviations from “normal” internal temperature cause the metabolic function to deteriorate. Usually, the human thermoregulatory system maintains a core body temperature within 0.2°C of normal, near 37°C. Hypothermia results from exposure to cold, or exposure combined with drugs or illness that decrease thermoregulatory efficacy. Exposure to a cold operating room environment during anaesthesia and surgery commonly combines with anaesthetic-induced inhibition of thermoregulation to produce hypothermia. The prevention and management of temperature-related complications is expedited by an understanding of both normal and druginfluenced thermoregulation.Keywords: mild perioperative hypothermia; consequences; preventio

The long-term consequences of anaesthetic management

In distinct contrast to preventable anaesthetic mortality, which thankfully is now rare, all-cause postoperative mortality is surprisingly high. Approximately 5% of surgical patients die in the year following surgery. Mortality is roughly 10% in those who are older than 65 years of age.1 In other words, mortality in the year after surgery is approximately 10 000 times more common than preventable anaesthetic mortality. Thus, it is reasonable to ask to what extent anaesthetic management might influence long-term outcomes. The distinction being made here is between the classical definition of anaesthetic complications, which is restricted to the immediate perioperative period, perhaps extending to a few days after surgery, and the potential effects of anaesthetic management on events weeks, months or even years after surgery. Given that modern anaesthetic drugs are uniformly short acting, it is by no means obvious that the consequences of anaesthetic management could last more than hours or days after surgery. The long-term consequences of anaesthesia were not seriously considered until relatively recently. There is increasing evidence that some intraoperative anaesthetic management decisions have long-term consequences, and that others might as well.Keywords: long-term consequences; anaesthetic managemen

Humidity and measurement of volatile propofol using MCC-IMS (EDMON)

The bedside Exhaled Drug MONitor – EDMON measures exhaled propofol in ppbv every minute based on multi-capillary column – ion mobility spectrometry (MCC-IMS). The MCC pre-separates gas samples, thereby reducing the infuence of the high humidity in human breath. However, preliminary analyses identifed substantial measurement deviations between dry and humid calibration standards. We therefore performed an analytical validation of the EDMON to evaluate the infuence of humidity on measurement performance. A calibration gas generator was used to generate gaseous propofol standards measured by an EDMON device to assess linearity, precision, carry-over, resolution, and the infuence of diferent levels of humidity at 100% and 1.7% (without additional) relative humidity (reference temperature: 37°C). EDMON measurements were roughly half the actual concentration without additional humidity and roughly halved again at 100% relative humidity. Standard concentrations and EDMON values correlated linearly at 100% relative humidity (R²=0.97). The measured values were stable over 100min with a variance≤10% in over 96% of the measurements. Carry-over efects were low with 5% at 100% relative humidity after 5min of equilibration. EDMON measurement resolution at 100% relative humidity was 0.4 and 0.6 ppbv for standard concentrations of 3 ppbv and 41 ppbv. The infuence of humidity on measurement performance was best described by a second-order polynomial function (R²≥0.99) with infuence reaching a maximum at about 70% relative humidity. We conclude that EDMON measurements are strongly infuenced by humidity and should therefore be corrected for sample humidity to obtain accurate estimates of exhaled propofol concentrations

Validation of the cognitive recovery assessments with the Postoperative Quality of Recovery Scale in patients with low-baseline cognition

Patients with pre-surgery cognitive impairment cannot currently be assessed for cognitive recovery after surgery using the Postoperative Quality of Recovery Scale (PostopQRS),as they would mathematically be scored as recovered. The group nonetheless represent a frail cohort at high risk of recovering poorly. We aimed to validate a novel method to score cognitive recovery in patients with low baseline cognition, using the number of low-score tests rather than their numerical values. Face validity was demonstrated in 86 participants in whom both PostopQRS and an 11-item neuropsychological battery were performed. The PostopQRS agreed with neuropsychological categorization of low versus normal cognition 74% of the time, with all but 5 incorrectly coded participants deviating by only 1 neurocognitive test. Cognitive recovery over time was comparable for groups with differing baseline cognitive function, irrespective of whether PostopQRS or neuropsychological methods were used. Discriminant validation was demonstrated in a post hoc analysis of the Steroids in Cardiac Surgery (SIRS) substudy by allocating groups to normal (n=246) or low baseline cognition (n=231) stratified by cognitive recovery on day 1. Recovery was similar for participants with low and normal baseline cognition. Postoperative length of stay was longer in patients with failed cognitive recovery whether they had normal (10.4±10.0 vs. 8.0±5.9 days, P=0.02) or low baseline cognition (12.0±11.1 vs. 8.2±4.7 days, P<0.01). Overall quality of recovery, as well as cognitive, emotive, and physiological recovery in those who recovered was independent of baseline cognition. The modified scoring method for the PostopQRS cognitive domain therefore demonstrates acceptable face and discriminant validity

Muon Colliders

Muon Colliders have unique technical and physics advantages and disadvantages when compared with both hadron and electron machines. They should thus be regarded as complementary. Parameters are given of 4 TeV and 0.5 TeV high luminosity \mumu colliders, and of a 0.5 TeV lower luminosity demonstration machine. We discuss the various systems in such muon colliders, starting from the proton accelerator needed to generate the muons and proceeding through muon cooling, acceleration and storage in a collider ring. Problems of detector background are also discussed.Comment: 28 pages, with 12 postscript figures. To be published Proceedings of the 9th Advanced ICFA Beam Dynamics Workshop, AIP Pres

Nitrous oxide does not produce a clinically important sparing effect during closed-loop delivered propofol-remifentanil anaesthesia guided by the bispectral index: a randomized multicentre study†‡

Background Nitrous oxide (N2O) offers both hypnotic and analgesic characteristics. We therefore tested the hypothesis that N2O administration decreases the amount of propofol and remifentanil given by a closed-loop automated controller to maintain a similar bispectral index (BIS). Methods In a randomized multicentre double-blind study, patients undergoing elective surgery were randomly assigned to breathe 60% inspired N2O (N2O group) or 40% oxygen (AIR group). Anaesthesia depth was evaluated by the proportion of time where BIS was within the range of 40-60 (BIS40-60). The primary outcomes were propofol and remifentanil consumption, with reductions of 20% in either being considered clinically important. Results A total of 302 patients were randomized to the N2O group and 299 to the AIR group. At similar BIS40-60 [79 (67-86)% vs 76 (65-85)%], N2O slightly decreased propofol consumption [4.5 (3.7-5.5) vs 4.8 (4.0-5.9) mg kg−1 h−1, P=0.032], but not remifentanil consumption [0.17 (0.12-0.23) vs 0.18 (0.14-0.24) µg kg−1 min−1]. For the subgroups of men, at similar BIS40-60 [80 (72-88)% vs 80 (70-87)%], propofol [4.2 (3.4-5.3) vs 4.4 (3.6-5.4) mg kg−1 h−1] and remifentanil [0.19 (0.13-0.25) vs 0.18 (0.15-0.23) µg kg−1 min−1] consumptions were similar in the N2O vs AIR group, respectively. For the subgroups of women, at similar BIS40-60 [76 (64-84)% vs 72 (62-82)%], propofol [4.7 (4.0-5.8) vs 5.3 (4.5-6.6) mg kg−1 h−1, P=0.004] and remifentanil [0.18 (0.13-0.25) vs 0.20 (0.15-0.27) µg kg−1 min−1, P=0.029] consumptions decreased with the co-administration of N2O. Conclusions With automated drug administration titrated to comparable BIS, N2O only slightly reduced propofol consumption and did not reduce remifentanil consumption. There was a minor gender dependence, but not by a clinically important amount. Clinical trial registration This study was registered at ClinicalTrials.gov, number NCT0054720

Status of Muon Collider Research and Development and Future Plans

The status of the research on muon colliders is discussed and plans are outlined for future theoretical and experimental studies. Besides continued work on the parameters of a 3-4 and 0.5 TeV center-of-mass (CoM) energy collider, many studies are now concentrating on a machine near 0.1 TeV (CoM) that could be a factory for the s-channel production of Higgs particles. We discuss the research on the various components in such muon colliders, starting from the proton accelerator needed to generate pions from a heavy-Z target and proceeding through the phase rotation and decay ($\pi \to \mu \nu_{\mu}$) channel, muon cooling, acceleration, storage in a collider ring and the collider detector. We also present theoretical and experimental R & D plans for the next several years that should lead to a better understanding of the design and feasibility issues for all of the components. This report is an update of the progress on the R & D since the Feasibility Study of Muon Colliders presented at the Snowmass'96 Workshop [R. B. Palmer, A. Sessler and A. Tollestrup, Proceedings of the 1996 DPF/DPB Summer Study on High-Energy Physics (Stanford Linear Accelerator Center, Menlo Park, CA, 1997)].Comment: 95 pages, 75 figures. Submitted to Physical Review Special Topics, Accelerators and Beam