General anaesthetic and airway management practice for obstetric surgery in England: a prospective, multi-centre observational study

There are no current descriptions of general anaesthesia characteristics for obstetric surgery, despite recent changes to patient baseline characteristics and airway management guidelines. This analysis of data from the direct reporting of awareness in maternity patients' (DREAMY) study of accidental awareness during obstetric anaesthesia aimed to describe practice for obstetric general anaesthesia in England and compare with earlier surveys and best-practice recommendations. Consenting patients who received general anaesthesia for obstetric surgery in 72 hospitals from May 2017 to August 2018 were included. Baseline characteristics, airway management, anaesthetic techniques and major complications were collected. Descriptive analysis, binary logistic regression modelling and comparisons with earlier data were conducted. Data were collected from 3117 procedures, including 2554 (81.9%) caesarean deliveries. Thiopental was the induction drug in 1649 (52.9%) patients, compared with propofol in 1419 (45.5%). Suxamethonium was the neuromuscular blocking drug for tracheal intubation in 2631 (86.1%), compared with rocuronium in 367 (11.8%). Difficult tracheal intubation was reported in 1 in 19 (95%CI 1 in 16-22) and failed intubation in 1 in 312 (95%CI 1 in 169-667). Obese patients were over-represented compared with national baselines and associated with difficult, but not failed intubation. There was more evidence of change in practice for induction drugs (increased use of propofol) than neuromuscular blocking drugs (suxamethonium remains the most popular). There was evidence of improvement in practice, with increased monitoring and reversal of neuromuscular blockade (although this remains suboptimal). Despite a high risk of difficult intubation in this population, videolaryngoscopy was rarely used (1.9%)

Lubrication and Friction of Piston and Piston Rings in Internal Combustion Engines.

A model has been developed for determining the lubrication regime under which the piston and piston rings operate in the internal combustion engine, and for calculating the friction force of each component at each crank angle. The ring is assumed to have a circular profile in the direction of motion. The profile changes in time because tilting of the ring is taken into account. In the circumferential direction two cases are examined. In the first the ring is assumed to be a perfect circle, and the bore cross-section elliptic. The Finite Element Method (FEM) is used to solve the two-dimensional Reynolds equation. In the second the clearance between ring and bore is assumed to be constant, and the one-dimensional Reynolds equation is used. The ring is treated as infinitely long, and an integration of the Reynolds equation is performed. The piston is treated like the one-dimensional case of the ring, except that a correction factor is used to take care of the fact that the piston skirt has dimensions of the same magnitude in both directions. For all cases mixed lubrication is considered when the oil film thickness becomes lower than a specified value. This value depends upon the roughness of the surfaces which are in contact. The friction coefficient for this type of lubrication is taken as a function of the oil film thickness and the surface roughness. The friction results of the model are compared with experimental friction data for a given engine under motoring conditions. The agreement between the theoretical results and the experimental data is very good. Also the effect of several parameters of the rings and of the engine on the FMEP of a ring pack is examined. These parameters are the curvature and the offset of the profile, the ring width and tension, the roughness of the surfaces, the bore ellipticity, the engine speed, the oil temperature and viscosity. Some of these parameters have an optimum value for which the FMEP is minimum. For values smaller or larger than the optimum the FMEP increases in some cases very sharply.Ph.D.Mechanical engineeringAutomotive engineeringOcean engineeringUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/161693/1/8801378.pd