Atmospheric Chemistry of Hydrofluoroethers: Reaction of a Series of Hydrofluoroethers with OH Radicals and Cl Atoms, Atmospheric Lifetimes, and Global Warming Potentials

Atmospheric chemistry of CF3CHFCF2OCH3 (HFE-356mec3) and CHF2CHFOCF3 (HFE-236ea1) initiated by OH and Cl and their contribution to global warming

The kinetic study of the gas-phase reactions of hydroxyl (OH) radicals and chlorine (Cl) atoms with CF3CHFCF2OCH3 (HFE-356mec3) and CHF2CHFOCF3 (HFE-236ea1) was performed by the pulsed laser photolysis/laser-induced fluorescence technique and a relative method by using Fourier Transform infrared (FTIR) spectroscopy as detection technique. The temperature dependences of the OH-rate coefficients (kOH(T) in cm3s-1) between 263 and 353 K are well described by the following expressions: 9.93 × 10-13exp{-(988 ± 35)/T}for HFE-356mec3 and 4.75 × 10-13exp{-(1285 ± 22)/T} for HFE-236ea1. Under NOx-free conditions, the rate coefficients kCl at 298 K and 1013 mbar (760 Torr) of air were determined to be (2.30 ± 1.08) × 10-13 cm3s-1and (1.19 ± 0.10) × 10-15 cm3s-1, for HFE-356mec3 and HFE-236ea1, respectively. Additionally, the relative kinetic study of the Cl + CH2ClCHCl2 reaction was investigated at 298 K, as it was used as a reference reaction in the kinetic study of the Cl-reaction with HFE-356mec3 and discrepant rate coefficients were found in the literature. The global atmospheric lifetimes were estimated relative to CH3CCl3 at the tropospheric mean temperature (272 K) as 1.4 and 8.6 years for HFE-356mec3 and HFE-236ea1, respectively. These values combined with the radiative efficiencies for HFE-356mec3 and HFE-236ea1 derived from the measured IR absorption cross sections (0.27 and 0.41 W m-2 ppv-1) yield global warming potentials at a 100-yrs time horizon of 143 and 1473, respectively. The contribution of HFE-356mec3 and HFE-236ea1 to global warming of the atmosphere would be large if they become widespread increasing their atmospheric concentration.

Reaction Rates of OH Radicals with CH3OCF2CHFCF3 and CHF2CF2OCH2CF2CHF2: Measurements and Estimation Using Neural Network Method

The reaction rates of OH radicals with CH3OCF2CHFCF3 (k1) and CHF2CF2OCH2CF2CHF2 (k2) were measured over a temperature range of 250-430 K. Kinetic measurements were performed using the flash and laser photolysis methods combined with a laser-induced fluorescence technique. The Arrhenius rate parameters were determined as k1 = (2.52 ± 0.25) × 10-12·exp[-(1390 ± 30)/T], k2 = (1.83 ± 0.20) × 10-12·exp[-(1420 ± 35)/T] cm3 molecule-1 s-1. The infrared absorption spectra of the two hydrofluoroethers were measured at approximately 298 K in 760 Torr of N2. The atmospheric lifetimes of CH3OCF2CHFCF3 and CHF2CF2OCH2CF2CHF2 have been estimated as 2.5 and 3.8 years, respectively, and their global warming potentials were determined as 245 and 405, respectively. Additionally, a method, using a three-layered feed-forward neural network, for estimating the rates of the reaction of the OH radicals with alkanes, ethers, and alcohols was investigated. The ratios of the calculated reaction rates to the observed ones agreed within a factor of 2. The ability of the neural network method to predict reaction rates was examined by using a leave-one-out test.

Avoiding Regrettable Replacements: Can the Introduction of Novel Functional Groups Move PFAS from Recalcitrant to Reactive?

Per- and polyfluoroalkyl substances (PFASs) are present in a range of commercial and consumer products. These chemicals are often high-performance surfactants or nonstick/water-repellant coatings due to their chemical stability; however, this stability leads to select PFAS being environmentally persistent. To facilitate degradation, new fluorosurfactant building blocks (F7C3-O-CHF-CF2-S-CH2-CH2-OH (FESOH), F3C-O-CHF-CF2-S-CH2-CH2-OH (MeFESOH), F7C3-O-CHF-CF2-O-CH2-CH2-OH (ProFdiEOH), F7C3-O-CHF-CF2-CH2-OH (ProFEOH), and F3C-O-CHF-CF2-O-CH2-CH2-OH (MeFdiEOH)) have been systematically developed with heteroatom linkages such as ethers, thioethers, and polyfluorinated carbons. The room temperature, gas-phase OH oxidation rate constants, and products of these chemicals were monitored in an atmospheric chamber to investigate their fate in the atmosphere. Analysis was performed using online high-resolution chemical ionization mass spectrometry (CIMS) using the iodide reagent ion and via offline UPLC-MS/MS. FESOH and MeFESOH, the thioether congeners, were observed to have the largest rate constants of kFESOH = 2.82 (±0.33) and kMeFESOH = 2.17 (±0.17) (×10-12 cm3 molecules-1 s-1, respectively). First-, second-, and third-generation products of OH oxidation were observed as a function of time, while product quantification yielded ultrashort perfluoropropionic acid (PFPrA) and short polyfluoroether acid species as the terminal products for FESOH and ProFdiEOH. There was evidence for MeFESOH being fully mineralized, demonstrating the potential benign chemical architecture.

Levels and distribution profiles of Per- and Polyfluoroalkyl Substances (PFAS) in a high Arctic Svalbard ice core

Per- and polyfluoroalkyl substances (PFAS) are a group of persistent organic contaminants of which some are toxic and bioaccumulative. Several PFAS can be formed from the atmospheric degradation of precursors such as fluorotelomer alcohols (FTOHs) as well as hydrochlorofluorocarbons (HFCs) and other ozone-depleting chlorofluorocarbon (CFC) replacement compounds. Svalbard ice cores have been shown to provide a valuable record of long-range atmospheric transport of contaminants to the Arctic. This study uses a 12.3 m ice core from the remote Lomonosovfonna ice cap on Svalbard to understand the atmospheric deposition of PFAS in the Arctic. A total of 45 PFAS were targeted, of which 26 were detected, using supercritical fluid chromatography (SFC) tandem mass spectrometry (MS/MS) and ultra-performance liquid chromatography (UPLC) MS/MS. C₂ to C₁₁ perfluoroalkyl carboxylic acids (PFCAs) were detected continuously in the ice core and their fluxes ranged from 2.5 to 8200 ng m^-2 yr^-1 (9.51-16,500 pg L^-1). Trifluoroacetic acid (TFA) represented 71 % of the total mass of C₂ - C₁₁ PFCAs in the ice core and had increasing temporal trends in deposition. The distribution profile of PFCAs suggested that FTOHs were likely the atmospheric precursor to C₈ - C₁₁ PFCAs, whereas C₂ - C₆ PFCAs had alternative sources, such as HFCs and other CFC replacement compounds. Perfluorooctanesulfonic acid (PFOS) was also widely detected in 82 % of ice core subsections, and its isomer profile (81 % linear) indicated an electrochemical fluorination manufacturing source. Comparisons of PFAS concentrations with a marine aerosol proxy showed that marine aerosols were insignificant for the deposition of PFAS on Lomonosovfonna. Comparisons with a melt proxy showed that TFA and PFOS were mobile during meltwater percolation. This indicates that seasonal snowmelt and runoff from post-industrial accumulation on glaciers could be a significant seasonal source of PFAS to ecosystems in Arctic fjords.

Understanding the insight into the mechanisms and dynamics of the OH-initiated oxidation of CHF2CF2OCHF2 and the subsequent reactions in the presence of NO and O2

The mechanism and dynamics of CHF₂CF₂OCHF₂ initiated by OH radical evaluated through the density functional theory and variflex code. The solvation pattern of PCM was utilized to analyze the influence of water on the CHF₂CF₂OCHF₂ + OH reaction. The most feasible reaction channel is resulting in the product CF₂CF₂OCHF₂ with H₂O by hydrogen abstraction. The computed rate coefficient is consistent with the experimental data. The results turned out that aqueous water act as a disincentive to the title reaction. In the atmosphere, the computation results testified that OH, H₂O, NH₃ and HCOOH could not accelerate the degradation of the CHF₂CF₂OCHF₂ through OH-initiated in view of the Gibbs free barriers. The research of the follow-up oxidation procedure of the products CHF₂CF₂OCF₂ and CF₂CF₂OCHF₂ with O₂/NO reactions indicated that CF₂O and CHF₂ were the most feasible products. The atmospheric lifetimes of CHF₂CF₂OCHF₂ were in the scope of 71.10-4.74 years in altitude of 0-12 km and at 200-300 K. This research supplies discernment into the conversion of CHF₂CF₂OCHF₂ in a complex environment.

Kinetics of CF3CH2OCH3 (HFE-263fb2), CHF2CF2CH2OCH3 (HFE-374pcf), and CF3CF2CH2OCH3 (HFE-365mcf3) with OH radicals, IR absorption cross sections, and global warming potentials

Hydrofluoroethers (HFEs), like CF3CH2OCH3 (HFE-263fb2), CHF2CF2CH2OCH3 (HFE-374pcf), and CF3CF2CH2OCH3 (HFE-365mcf3), have been proposed in the last decades as the third-generation replacements of perfluorocarbons (PFCs) and hydrofluorocarbons (HFCs) because of their...

Comparison of minimal-flow sevoflurane versus desflurane anesthesia: randomized clinical trial

BACKGROUND AND OBJECTIVES

Minimal-flow anesthesia provides various advantages, such as reduced environmental pollution, proper humidification and warming of anesthetic gases, and reduced costs. The aim of this study was to compare the cost-effectiveness of minimal-flow sevoflurane and desflurane anesthesia and their effects on hemodynamics, postoperative recovery, respiratory parameters, and liver and kidney functions.

METHODS

A total of 60 ASA I-II patients aged 18-70 years who underwent posterior spinal instrumentation were included in the study. The patients were divided into Group S (sevoflurane) and Group D (desflurane). After anesthesia induction, the gas flow was initiated at a rate of 4 L.min^-1 using a concentration of 8% in Group D and 3.5% in Group S, and the time to reach 0.8 MAC was recorded. The gas flow was then switched to minimal flow. Patient hemodynamic and respiratory parameters, body temperatures and arterial blood gas levels were recorded. The integrated pulmonary index (IPI) was monitored postoperatively. Biochemical findings were recorded 12 hours after the operation. The amount of bleeding and blood transfused, and the costs involved were calculated.

RESULTS

The patients' demographic characteristics, duration of surgery, hemodynamic parameters, IPI values, body temperatures, and arterial blood gas levels were similar at all time points. Biochemical findings, amount of bleeding and amount of blood transfused were similar between the two groups. The mean cost was lower in Group S than in Group D (p = 0.007).

CONCLUSION

The study found no significant difference in terms of reliability between minimal-flow sevoflurane and desflurane anesthesia. Furthermore, the procedure was found to be more cost-effective for Group S than for Group D.

Photochemical aging and secondary organic aerosols generated from limonene in an oxidation flow reactor

Oxidation flow reactors (OFRs) are increasingly used to study the formation and evolution of secondary organic aerosols (SOA) in the atmosphere. The OH/HO₂ and OH/O₃ ratios in OFRs are similar to tropospheric ratios. In the present work, we investigated the production of SOA generated by OH oxydation and ozonolysis of limonene in OFR as a function of OH exposure and O₃ exposure. The results are compared with those obtained from the simulation chambers. The precursor gas is exposed to OH concentrations ranging from 2.11 × 10⁸ to 1.91 × 10⁹ molec cm^-3, with an estimated exposure time in the OFR of 137 s. In the environmental chambers, the precursor was oxidized using OH concentrations between 2.10 × 10⁶ and 2.12 × 10⁷ molec cm^-3 over exposure times of several hours. In the overlapping OH exposure region, the highest SOA yields are obtained in the OFR, which is explained by the ozonolysis of limonene in the OFR. However, the yields decrease with the increase of OHexp in both systems.

Unusual Fluorine Substitution Effect on S···Cl Bonding between Sulfides and Atomic Chlorine

A theoretical investigation on the interaction of various sulfides and their fluorinated counterparts (H₂S, HSF, F₂S, CH₃SH, CH₃SF, CH₂FSH, CH₂FSF, NH₂SH, NH₂SF) with atomic chlorine has been carried out using density functional theory (DFT) based LC-BLYP/aug-cc-pVTZ and sophisticated ab initio CCSD(T)/aug-cc-pVQZ methods. The present study is intended to discuss the influence of the substituents implanted at the sulfur atom on the bonding parameters. The optimized geometries reveal that intermolecular S···Cl distances are short and range between 2.423 and 2.561 Å. A strong contraction of the S-F bond is also predicted. Two-center-three-electron S···Cl bonds are formed; the interaction energies are large and range from -33.9 to -70.1 kJ mol^-1. Very surprisingly, the interaction energies are greater and the intermolecular distances are shorter for F-substituted sulfides than for unsubstituted ones. This is in complete contrast with the lower proton affinities and less negative electrostatic potentials of fluorinated sulfides. AIM analysis, the charge transfer from the sulfur atom to the Cl atom, and the spin densities on the Cl and S atoms are considered to explain this unusual behavior. The hyperconjugation energies from the LP(F) to the σ*(S-Cl) antibonding orbital can be considered as one of the stabilizing factors for the greater stability of the fluorinated complexes over the nonfluorinated ones.

Hydrogen Abstraction from Fluorinated Ethyl Methyl Ether Systems by OH Radicals

A systematic computational investigation of hydrogen abstraction by OH from the full series of fluorinated ethyl methyl ethers (EME) containing at least one H and one F, C2HnX5-nOCHmX3-m (n=0–5, m=0–3; and n=m=0 not allowed), including 147 reactants and 469 transition states, has been carried out, employing the MP2/6-31G(d) level of theory. Results for optimized geometries, including evidence of intramolecular hydrogen bonding in transition states, and barrier heights are presented. Trends pertaining to the number of fluorines substituted, key bond lengths, barrier heights, and key bond angles were found with good correlations and were investigated. An increase in the number of F increases the barrier height of the reaction. An increase in some parameters such as C–H length of TS, relative change in C–H from reactants to TS, ∠COC of reactants, ∠HOH in the TS, and relative change in ∠HOH between TS and free water bond angle also correlates with increased barrier height. An increase in other parameters like C–H length in the reactants and hydrogen bonding can decrease the barrier height.

Atmospheric Chemistry of (CF3)2CHOCH3, (CF3)2CHOCHO, and CF3C(O)OCH3

Smog chambers with in situ FTIR detection were used to measure rate coefficients in 700 Torr of air and 296 ± 2 K of: k(Cl+(CF3)2CHOCH3) = (5.41 ± 1.63) × 10(-12), k(Cl+(CF3)2CHOCHO) = (9.44 ± 1.81) × 10(-15), k(Cl+CF3C(O)OCH3) = (6.28 ± 0.98) × 10(-14), k(OH+(CF3)2CHOCH3) = (1.86 ± 0.41) × 10(-13), and k(OH+(CF3)2CHOCHO) = (2.08 ± 0.63) × 10(-14) cm(3) molecule(-1) s(-1). The Cl atom initiated oxidation of (CF3)2CHOCH3 gives (CF3)2CHOCHO in a yield indistinguishable from 100%. The OH radical initiated oxidation of (CF3)2CHOCH3 gives the following products (molar yields): (CF3)2CHOCHO (76 ± 8)%, CF3C(O)OCH3 (16 ± 2)%, CF3C(O)CF3 (4 ± 1)%, and C(O)F2 (45 ± 5)%. The primary oxidation product (CF3)2CHOCHO reacts with Cl atoms to give secondary products (molar yields): CF3C(O)CF3 (67 ± 7)%, CF3C(O)OCHO (28 ± 3)%, and C(O)F2 (118 ± 12)%. CF3C(O)OCH3 reacts with Cl atoms to give: CF3C(O)OCHO (80 ± 8)% and C(O)F2 (6 ± 1)%. Atmospheric lifetimes of (CF3)2CHOCH3, (CF3)2CHOCHO, and CF3C(O)OCH3 were estimated to be 62 days, 1.5 years, and 220 days, respectively. The 100-year global warming potentials (GWPs) for (CF3)2CHOCH3, (CF3)2CHOCHO, and CF3C(O)OCH3 are estimated to be 6, 121, and 46, respectively. A comprehensive description of the atmospheric fate of (CF3)2CHOCH3 is presented.

Kinetics and mechanism of gas-phase reaction of CF3OCH2CH3 (HFE-263) with the OH radical — a theoretical study

In the present study, the density functional method with recently developed M06 functionals has been used to study the reaction of CF3OCH2CH3 with the OH radical. All possible hydrogen abstraction and displacement reaction channels have been modeled. The minimum energy path on the respective potential energy surface and energetics were calculated at the M06-2X/6-311++G(d,p) level of theory. Two different reaction mechanisms were considered: (i) reactant and product complexes called the complex mechanism and (ii) the direct mechanism (reactant → transition state → product). Tunneling corrections were made using the Eckart unsymmetrical potential. The overall rate constant calculated by the complex mechanism (keff = 1.8 × 10−13 cm3 molecule−1 s−1) has been found to be in good agreement with the experimentally determined value (1.5 ± 0.25 × 10−13 cm3 molecule−1 s−1), while the rate constant calculated by the direct mechanism (kD = 7.6 × 10−14 cm3 molecule−1 s−1) is about two times lower than the experimental value. The theoretical studies show that hydrogen atom abstraction from the –CH2– site is the most favorable reaction pathway and the reaction involves prereactive and product complexes before leading to stable product formation.

Theoretical studies on kinetics, mechanism and thermochemistry of gas-phase reactions of HFE-449mec-f with OH radicals and Cl atom

A theoretical study on the mechanism and kinetics of the gas phase reactions of CF3CHFCF2OCH2CF3 (HFE-449mec-f) with the OH radicals and Cl atom have been performed using meta-hybrid modern density functional M06-2X using 6-31+G(d,p) basis set. Two conformers have been identified for CF3CHFCF2OCH2CF3 and the most stable one is considered for detailed study. Reaction profiles for OH-initiated hydrogen abstraction are modeled including the formation of pre-reactive and post-reactive complexes at entrance and exit channels. Our calculations reveal that hydrogen abstraction from the CH2 group is thermodynamically and kinetically more facile than that from the CHF group. Using group-balanced isodesmic reactions, the standard enthalpies of formation for HFE-449mecf and radicals generated by hydrogen abstraction, are also reported. The calculated bond dissociation energies for CH bonds are in good agreement with experimental results. The rate constants of the two reactions are determined for the first time in a wide temperature range of 250-450K. The calculated rate constant values are found to be 9.10×10(-15) and 4.77×10(-17)cm(3)molecule(-1)s(-1) for reactions with OH radicals and Cl atom, respectively. At 298K, the total calculated rate coefficient for reactions with OH radical is in good agreement with the experimental results. The atmospheric life time of HFE-449mec-f is estimated to be 0.287 years.

Theoretical investigation on gas-phase reaction of CF3CH2OCH3 with OH radicals and fate of alkoxy radicals (CF3CH(O•)OCH3/CF3CH2OCH2O•)

Detailed theoretical investigation has been performed on the mechanism, kinetics and thermochemistry of the gas phase reactions of CF3CH2OCH3 (HFE-263fb2) with OH radicals using ab-initio and DFT methods. Reaction profiles are modeled including the formation of pre-reactive and post-reactive complexes at entrance and exit channels, respectively. Our calculations reveal that hydrogen abstraction from the CH2 group is thermodynamically and kinetically more facile than that from the CH3 group. Using group-balanced isodesmic reactions, the standard enthalpies of formation for CF3CH2OCH3 and radicals (CF3CHOCH3 and CF3CH2OCH2) are also reported for the first time. The calculated bond dissociation energies for the CH bonds are in good agreement with experimental results. At 298K, the calculated total rate coefficient for CF3CH2OCH3+OH reactions is found to be in good agreement with the experimental results. The atmospheric fate of the alkoxy radicals, CF3CH(O)OCH3 and CF3CH2OCH2O are also investigated for the first time using the same level of theory. Out of three plausible decomposition channels, our results clearly point out that reaction with O2 is not the dominant path leading to the formation of CF3C(O)OCH3 for the decomposition of CF3CH(O)OCH3 radical in the atmosphere. This is in accord with the recent report of Osterstrom et al. [CPL 524 (2012) 32] but found to be in contradiction with experimental finding of Oyaro et al. [JPCA 109 (2005) 337].

A theoretical investigation on the conformation and the interaction of CHF₂OCF₂CHF₂ (desflurane II) with one water molecule

The conformation and the interaction of CHF₂OCF₂CHF₂ (desflurane II) with one water molecule is investigated theoretically using the ab initio MP2/aug-cc-pvdz and DFT-based M062X/6-311++G(d,p) methods. The calculations include the optimized geometries, the harmonic frequencies of relevant vibrational modes along with a natural bond orbital (NBO) analysis including the NBO charges, the hybridization of the C atom and the intra- and intermolecular hyperconjugation energies. In the two most stable conformers, the CH bond of the F2HCO- group occupies the gauche position. The hyperconjugation energies are about the same for both conformers and the conformational preference depends on the interaction between the non-bonded F and H atoms. The deprotonation enthalpies of the CH bonds are about the same for both conformers, the proton affinity of the less stable conformer being 3 kcal mol−1 higher. Both conformers of desflurane II interact with water forming cyclic complexes characterized by CH…O and OH…F hydrogen bonds. The binding energies are moderate, ranging from −2.4 to −3.2 kcal mol−1 at the MP2 level. The origin of the blue shifts of the ν(CH) vibrations is analyzed. In three of the complexes, the water molecule acts as an electron donor. Interestingly, in these cases a charge transfer is also directed to the non bonded OH group of the water molecule. This effect seems to be a property of polyfluorinated ethers.

Strong hyperconjugative interactions in isolated and water complexes of desflurane: a theoretical investigation

Ab initio MP2/aug-cc-pvDZ and density functional B3LYP calculations with the 6-311++G(d,p) basis set are performed to investigate the conformation of desflurane (CHF2OCHFCF3), its acidity/basicity and its interaction with one water molecule. The calculations include the optimized geometries, the harmonic frequencies of relevant vibrational modes, the binding energies with water, and a detailed natural bond orbital (NBO) analysis Iincluding the NBO charges, the hybridization of the C atoms and the intra- and intermolecular hyperconjugations. The relative energies of the two most stable conformers are discussed as a function of the total hyperconjugative energies resulting from the interaction of lone pairs of the O and F atoms to the different antibonding orbitals of desflurane. The proton affinity is the same for both conformers but the acidity of the CH bond is larger for the less stable conformer. The binding energies of the complexes of two desflurane conformers with one water molecule range from -2.75 to -3.23 kcal mol(-1). Depending on the structure of the complexes, the CH bonds involved in the interaction are contracted or elongated. The σ*(CH) occupation predominates over the hybridization effect in determining the CH bond length. There is an unexpected charge transfer to the external OH bond of the water molecule. This effect is in good agreement with theoretical data on the complexes between fluorinated dimethyl ethers and water and seems to depend on the number of F atoms implanted on the ether molecule.

Assessment of theoretical methods for the study of hydrogen abstraction kinetics of global warming gas species during their degradation and byproduct formation (IUPAC Technical Report)

Global climate change is a major concern as it leads to an increase in the average temperature of the earth’s atmosphere. The existence and persistence of some gaseous species in the atmosphere contribute to global warming. Experimental techniques are used to study the kinetics and degradation of global warming gases. However, quantum mechanical methods are also useful for the kinetic and radiative forcing study of global warming species and can precede experimental investigations. Research has also been targeted to develop more adapted procedures using ab initio and density functional theory (DFT) methods. This report provides a global perspective, in simplified manner, of the theoretical studies of the degradation of gas species in the atmosphere with an emphasis on the hydrogen abstraction kinetics of global warming gas species during their degradation and byproduct formation. En route, the results obtained from these studies are analysed and compared with experimental data where available. Our analyses indicate that the theoretical predictions are in agreement with experimental findings but the predicted parameters are dependent on the method being used. Theoretical methods are used to predict the thermodynamic parameters of reactions, and, with relevance to this report, the global warming potential (GWP) index can also be calculated. This report can be useful for future investigations involving global warming gaseous species while providing suggestions on how computations can fill in data gaps when experimental data are unavailable.

The safety and efficacy of minimal-flow desflurane anesthesia during prolonged laparoscopic surgery

BACKGROUND

Minimal-flow anesthesia can meet the demands of a modern society that is more sensitive to environmental protection and economic burdens. This study compared the safety and efficacy of minimal-flow desflurane anesthesia with conventional high-flow desflurane anesthesia for prolonged laparoscopic surgery.

METHODS

Forty-six male patients (ASA physical status II or III) undergoing laparoscopic urologic surgery for more than 6 hours were randomly divided into two groups: the high-flow (HF) group and the minimal-flow (MF) group. The HF group was continuously administered a fresh gas flow of 4 L/min. In the MF group, a fresh gas flow of 4 L/min was administered for the first 20 minutes and was thereafter lowered to 0.5 L/min. Inspiratory and expiratory desflurane concentrations, respiratory variables, and hemodynamic variables were continuously monitored during administration of anesthesia. Measurements of carboxyhemoglobin (COHb) concentration and arterial blood gas analysis were performed every 2 hours during anesthesia. Serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), blood urea nitrogen (BUN) and creatinine were measured on the first and second day after the surgery.

RESULTS

Demographic data and duration of anesthesia were not different between the two groups. Significant differences were not observed between the two groups in terms of hemodynamic variables, respiratory variables, and inspiratory and expiratory desflurane concentrations. Inspiratory O(2) concentration was maintained lower in the MF group than in the HF group (43-53% vs. 53-59%; P < 0.05). Compared with the HF group, COHb concentrations was higher (P < 0.05), but not increased from the baseline value in the MF group. Serum AST, ALT, BUN, and creatinine were not significantly different between the two groups.

CONCLUSIONS

In prolonged laparoscopic surgery, no significant differences were found in safety and efficacy between minimal-flow and high-flow desflurane anesthesia.

Atmospheric chemistry of isoflurane, desflurane, and sevoflurane: kinetics and mechanisms of reactions with chlorine atoms and OH radicals and global warming potentials

The smog chamber/Fourier-transform infrared spectroscopy (FTIR) technique was used to measure the rate coefficients k(Cl + CF(3)CHClOCHF(2), isoflurane) = (4.5 ± 0.8) × 10(-15), k(Cl + CF(3)CHFOCHF(2), desflurane) = (1.0 ± 0.3) × 10(-15), k(Cl + (CF(3))(2)CHOCH(2)F, sevoflurane) = (1.1 ± 0.1) × 10(-13), and k(OH + (CF(3))(2)CHOCH(2)F) = (3.5 ± 0.7) × 10(-14) cm(3) molecule(-1) in 700 Torr of N(2)/air diluent at 295 ± 2 K. An upper limit of 6 × 10(-17) cm(3) molecule(-1) was established for k(Cl + (CF(3))(2)CHOC(O)F). The laser photolysis/laser-induced fluorescence (LP/LIF) technique was employed to determine hydroxyl radical rate coefficients as a function of temperature (241-298 K): k(OH + CF(3)CHFOCHF(2)) = (7.05 ± 1.80) × 10(-13) exp[-(1551 ± 72)/T] cm(3) molecule(-1); k(296 ± 1 K) = (3.73 ± 0.08) × 10(-15) cm(3) molecule(-1), and k(OH + (CF(3))(2)CHOCH(2)F) = (9.98 ± 3.24) × 10(-13) exp[-(969 ± 82)/T] cm(3) molecule(-1); k(298 ± 1 K) = (3.94 ± 0.30) × 10(-14) cm(3) molecule(-1). The rate coefficient of k(OH + CF(3)CHClOCHF(2), 296 ± 1 K) = (1.45 ± 0.16) × 10(-14) cm(3) molecule(-1) was also determined. Chlorine atoms react with CF(3)CHFOCHF(2) via H-abstraction to give CF(3)CFOCHF(2) and CF(3)CHFOCF(2) radicals in yields of approximately 83% and 17%. The major atmospheric fate of the CF(3)C(O)FOCHF(2) alkoxy radical is decomposition via elimination of CF(3) to give FC(O)OCHF(2) and is unaffected by the method used to generate the CF(3)C(O)FOCHF(2) radicals. CF(3)CHFOCF(2) radicals add O(2) and are converted by subsequent reactions into CF(3)CHFOCF(2)O alkoxy radicals, which decompose to give COF(2) and CF(3)CHFO radicals. In 700 Torr of air 82% of CF(3)CHFO radicals undergo C-C scission to yield HC(O)F and CF(3) radicals with the remaining 18% reacting with O(2) to give CF(3)C(O)F. Atmospheric oxidation of (CF(3))(2)CHOCH(2)F gives (CF(3))(2)CHOC(O)F in a molar yield of 93 ± 6% with CF(3)C(O)CF(3) and HCOF as minor products. The IR spectra of (CF(3))(2)CHOC(O)F and FC(O)OCHF(2) are reported for the first time. The atmospheric lifetimes of CF(3)CHClOCHF(2), CF(3)CHFOCHF(2), and (CF(3))(2)CHOCH(2)F (sevoflurane) are estimated at 3.2, 14, and 1.1 years, respectively. The 100 year time horizon global warming potentials of isoflurane, desflurane, and sevoflurane are 510, 2540, and 130, respectively. The atmospheric degradation products of these anesthetics are not of environmental concern.

Theoretical study and rate constants calculation for the reactions X + CF3CH2OCF3 (X = F, Cl, Br)

The multiple-channel reactions X + CF3CH2OCF3 (X = F, Cl, Br) are theoretically investigated. The minimum energy paths (MEP) are calculated at the MP2/6-31 + G(d,p) level, and energetic information is further refined by the MC-QCISD (single-point) method. The rate constants for major reaction channels are calculated by canonical variational transition state theory (CVT) with small-curvature tunneling (SCT) correction over the temperature range 200–2000 K. The theoretical three-parameter expressions for the three channels k1a(T) = 1.24 x 10(-15T1.24)exp(-304.81/T), k2a(T) = 7.27 x 10(-15T0.37)exp(-630.69/T), and k3a(T) = 2.84 x 10(-19T2.51)exp(-2725.17/T) cm3 molecule(-1) s(-1) are given. Our calculations indicate that hydrogen abstraction channel is only feasible channel due to the smaller barrier height among five channels considered.

Global warming potential of inhaled anesthetics: application to clinical use

BACKGROUND

Inhaled anesthetics are recognized greenhouse gases. Calculating their relative impact during common clinical usage will allow comparison to each other and to carbon dioxide emissions in general.

METHODS

We determined infrared absorption cross-sections for sevoflurane and isoflurane. Twenty-year global warming potential (GWP(20)) values for desflurane, sevoflurane, and isoflurane were then calculated using the present and previously published infrared results, and best estimate atmospheric lifetimes were determined. The total quantity of each anesthetic used in 1 minimal alveolar concentration (MAC)-hour was then multiplied by the calculated GWP(20) for that anesthetic, and expressed as "carbon dioxide equivalent" (CDE(20)) in grams. Common fresh gas flows and carrier gases, both air/oxygen and nitrous oxide (N2O)/oxygen, were considered in the calculations to allow these examples to represent common clinical use of inhaled anesthetics.

RESULTS

GWP(20) values for the inhaled anesthetics were: sevoflurane 349, isoflurane 1401, and desflurane 3714. CDE(20) values for 1 MAC-hour at 2 L fresh gas flow were: sevoflurane 6980 g, isoflurane 15,551 g, and desflurane 187,186 g. Comparison among these anesthetics produced a ratio of sevoflurane 1, isoflurane 2.2, and desflurane 26.8. When 60% N2O/40% oxygen replaced air/oxygen as a carrier gas combination, and inhaled anesthetic delivery was adjusted to deliver 1 MAC-hour of anesthetic, sevoflurane CDE(20) values were 5.9 times higher with N2O than when carried with air/O2, isoflurane values were 2.9 times higher, and desflurane values were 0.4 times lower. On a 100-year time horizon with 60% N2O, the sevoflurane CDE(100) values were 19 times higher than when carried in air/O2, isoflurane values were 9 times higher, and desflurane values were equal with and without N2O.

CONCLUSIONS

Under comparable and common clinical conditions, desflurane has a greater potential impact on global warming than either isoflurane or sevoflurane. N2O alone produces a sizable greenhouse gas contribution relative to sevoflurane or isoflurane. Additionally, 60% N2O combined with potent inhaled anesthetics to deliver 1 MAC of anesthetic substantially increases the environmental impact of sevoflurane and isoflurane, and decreases that of desflurane. N2O is destructive to the ozone layer as well as possessing GWP; it continues to have impact over a longer timeframe, and may not be an environmentally sound tradeoff for desflurane. From our calculations, avoiding N2O and unnecessarily high fresh gas flow rates can reduce the environmental impact of inhaled anesthetics.