ObjectivesA recent update of the definition of acute respiratory distress syndrome (ARDS) proposed an empirical classification based on ratio of arterial partial pressure of oxygen to fraction of inspired oxygen (PaO2/FiO2) at ARDS onset. Since the proposal did not mandate PaO2/FiO2 calculation under standardised ventilator settings (SVS), we hypothesised that a stratification based on baseline PaO2/FiO2 would not provide accurate assessment of lung injury severity.DesignA prospective, multicentre, observational study.SettingA network of teaching hospitals.Participants478 patients with eligible criteria for moderate (100300).Primary and secondary outcomesGroup severity and hospital mortality.ResultsAt ARDS onset, 173 patients had a PaO2/FiO2≤100 but only 38.7% met criteria for severe ARDS at 24 h under SVS. When assessed under SVS, 61.3% of patients with severe ARDS were reclassified as moderate, mild and non-ARDS, while lung severity and hospital mortality changed markedly with every PaO2/FiO2 category (p<0.000001). Our model of risk stratification outperformed the stratification using baseline PaO2/FiO2 and non-standardised PaO2/FiO2 at 24 h, when analysed by the predictive receiver operating characteristic (ROC) curve: area under the ROC curve for stratification at baseline was 0.583 (95% CI 0.525 to 0.636), 0.605 (95% CI 0.552 to 0.658) at 24 h without SVS and 0.693 (95% CI 0.645 to 0.742) at 24 h under SVS (p<0.000001).ConclusionsOur findings support the need for patient assessment under SVS at 24 h after ARDS onset to assess disease severity, and have implications for the diagnosis and management of ARDS patients.Trial registration numbersNCT00435110 and NCT00736892.

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Neutral ruthenium hydrides Ru(CO)ClH(L)(PPh3)2 bearing one N-donor ligand react with 1-alkynes at 23 °C to yield neutral alkenyl complexes Ru(CO)Cl(CHCHR)(L)(PPh3)2. Under similar conditions, cationic hydrido complexes [Ru(CO)H(L)2(PPh3)2]PF6 with pyridine-type N-donor ligands yield alkynyl complexes [Ru(CO)(CH≡CHR)(L)2(PPh3)2]PF6 as a result of the reaction of the intermediate labile alkenyl with a second molecule of alkyne. Under more forcing conditions, 1-alkynyl complexes could also be prepared from the neutral ruthenium hydrides. Cationic ruthenium hydrides with bidentate N-donor ligands are unreactive toward 1-alkynes. Neutral alkenyl complexes Ru(CO)Cl(CHCHR)(L)(PPh3)2 (R = p-MeC6H4, CMe3; L = pyridine, isoquinoline) reacted smoothly with 1-alkynes to afford the corresponding σ-alkynyl ruthenium derivatives Ru(CO)Cl(C≡CR)(L)(PPh3)2.

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The reaction of Ru{CO)ClH{PPh3)3 with 1-alkynes in 1,2-dichloroethane under reflux conditions provides the coordinatively unsaturated butenynyl complexes [Ru{C(C=CR)=CHR}(CO)Cl(PPh3)2j in good yield. These and related butenynyl complexes were also prepared by starting from the corresponding alkenylor alkynylruthenium complexes. Hydrogenolysis of [Ru-{C(C=CPh)=CHPh}(CO)Cl( PPh3)2] in the presence of pyridine gave (Z)-l,4-diphenylbutenyne and Ru(CO)-ClH(py){PPh3)2.The reaction of ruthenium hydrides, such as Ru(CO)-ClH(PPh3>3 (1), with alkynes usually results in the formation of -alkenyl derivatives by insertion of the alkyne into the Ru-H bond (hydroruthenation).1 However, the cationic hydrides [Ru(CO)H(py)2(PPh3)2]A (A = CIO*, BF4, PF6) react with 1-alkynes to give ( -alkynyl)ruthenium derivatives.2 In this process, labile alkenyl complexes were formed first, which react with another molecule of alkyne to give alkynyl complexes and 1-alkenes.2 On the other hand, phenylacetylene reacts in the presence of a catalytic amount of these hydrides to give (Z)-l,4-diphenyl-l-buten-3-yne as the major product.3 These results, as well as related work reported in the literature,4 suggest that -alkynyl complexes are inter-

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