Suspected venous air embolism during thoracic limb amputation in a dog

A six-year-old dog was anaesthetised for the amputation of her left forequarter. Preoperative haematology, biochemistry and physical examination were unremarkable. Twenty minutes into surgery, a sudden decrease in end tidal carbon dioxide (50–14 mm Hg) and arterial haemoglobin oxygen saturation (95–87 per cent) was noted. After briefly excluding some differentials, an iatrogenic venous air embolism (VAE) was suspected secondary to the dissection of the axillary vein. The vein was clamped and mechanical ventilation initiated delivering 100 per cent oxygen. The surgery was completed, the dog was recovered and closely monitored. The animal was discharged three days after the event. This article discusses the pathophysiology, diagnosis, different treatments and outcome of a suspected VAE. This case emphasises the importance of an early recognition of this complication during procedures such as limb amputations.

Rhinitis following intraoperative gastro-oesophageal reflux in a dog

A four-month-old, male dog underwent surgical repair of femoral and pelvic fracture. The dog was premedicated with acepromazine combined with morphine; anaesthesia was induced with propofol to effect and maintained with isoflurane in 100 per cent oxygen. One hour after induction the dog regurgitated and gastric contents emerged through the nares. At the end of the surgery rhinoscopy and oesophagoscopy were performed. The oesophageal mucosa was apparently normal, while posterior and retrograde rhinoscopy revealed diffused hyperaemia and oedema of the nasal cavity and nasopharyngeal mucosa; food particles and moderate amount of mucous exudates were also seen. Copious lavage was performed, and administration of antibiotics, metoclopramide, cimetidine and sucralfate was initiated. Nasal mucosa was re-evaluated four days later. No abnormalities were detected in both nasal cavities and nasopharynx. The development of rhinitis following regurgitation during anaesthesia should be considered as a possible complication.

Burns Night: Combustion

Burning, more formally combustion, denotes burning in oxygen and more commonly in air (which is 20 per cent oxygen). Combustion is a special case of a more general term, ‘oxidation’, which originally meant reaction with oxygen, not necessarily accompanied by a flame. The rusting of iron is also an oxidation, but we don’t normally think of it as a combustion because no flame is involved. Oxidation now has a much broader meaning than reaction with oxygen, as I shall unfold in Reaction 5. For now, I shall stick to combustion itself. To achieve combustion, we take a fuel, which might be the methane, CH4, 1, of natural gas or one of the heavier hydrocarbons, such as octane, C8H18, 2, that we use in internal combustion engines, mix it with air, and ignite it. The outcome of the complete combustion of any hydro-carbon is carbon dioxide and water but incomplete combustion can result in carbon monoxide and various fragments of the original hydrocarbon molecule. All combustions are ‘exothermic’, meaning that they release a lot of energy as heat into the surroundings. We use that energy for warmth or for driving machinery. Another example of an exothermic combustion is provided by the metal magnesium, which gives an intense white light as well as heat when it burns in air. A part of the vigour of this reaction is due to the fact that magnesium reacts not only with oxygen but also with nitrogen, the major component of air. You should be getting a glimpse of the broader significance of the term ‘oxidation’ in the sense that the reaction need not involve oxygen; in magnesium’s case, nitrogen can replace oxygen in the reaction. Magnesium foil was used in old-fashioned photographic flashes and in fireworks. The latter now mostly use finely powdered aluminium, which is much cheaper than magnesium and reacts in much the same way. In what follows you could easily replace aluminium with magnesium if you want to think fireworks. For the whole of the following discussion you need to be familiar with oxygen, O2, 3, a peculiar molecule in several respects.

Impact of oxygen concentration and laser power on occurrence of intraluminal fires during shared-airway surgery: an investigation

Objectives:Airway fires pose a risk during laser microlaryngoscopy, and neurosurgical cotton patties, used to prevent tissue injury from stray laser beams, are a potential ignition source. Using a configuration approximating clinical practice, we experimentally assessed the relative impact of changing different ‘fire triad’ components on the occurrence of airway fires, in order to better inform patient care.Methods:The relative effects of wet vs dry neurosurgical patties, oxygen concentration and laser power setting on the patty ignition time were studied in a cadaveric porcine model. Data were analysed using t-test and two-way analysis of variance.Results:Dry patties ignited after 2.3 ± 1.2 seconds (average ± standard deviation) of continuous 5 W laser fire at 50 per cent oxygen concentration, compared with 63.9 ± 27.8 seconds for wet patties under the same laser and oxygen settings (p < 0.0001). There was a statistically significant reduction in the time to patty ignition when laser power settings were increased from 5 to 7.5 W, but no further reductions occurred when the power was further increased to 10 W (p < 0.05; Tukey test for multiple comparisons; two-way analysis of variance). There was no significant reduction in the time to ignition between oxygen concentrations of 50 and 75 per cent, but the time to ignition fell significantly when the oxygen concentration was further increased to 100 per cent.Conclusion:We suggest that surgical patties should always be soaked and should be used for relatively short periods, in order to prevent drying. If at all possible clinically, prolonged laser use at high power settings and ventilation with 100 per cent oxygen should be avoided.

Characteristics of low temperature and low oxygen diesel combustion with ultra-high exhaust gas recirculation

Ultra-low NOx and smokeless operation at higher loads up to half of the rated torque is attempted with large rates of cold exhaust gas recirculation (EGR). NOx decreases below 6 ppm (0.05 g/kW h) and soot significantly increases when first decreasing the oxygen concentration to 16 per cent with cold EGR. However, after peaking at 12–14 per cent oxygen, soot then decreases sharply to essentially zero at 9–10 per cent oxygen while maintaining ultra-low NOx, regardless of fuel injection quantity and injection pressure. However, at higher loads, with the oxygen concentration below 9–10 per cent, the air-fuel ratio has to be over-rich to exceed half of the rated torque, and thermal efficiency, CO, and THC deteriorate significantly. As the EGR rate increases, exhaust gas emissions and thermal efficiency vary with the intake oxygen content rather than with the excess air ratio. Longer ignition delays due to either advancing or retarding the injection timing reduced the smoke emissions, but advancing the injection timing has the advantages of maintaining the thermal efficiency and preventing misfiring. A reduction in the compression ratio is effective to reduce the in-cylinder temperature and increase the ignition delay as well as to expand the smokeless combustion range in terms of EGR and i.m.e.p. (indicated mean effective pressure).

Computer Simulation of Human Interaction with Underwater Breathing Equipment

A mathematical model of the human respiratory system is being developed in order to simulate manned diving operations using various types of breathing equipment. A simulation study is presented of a human diving to a depth of 50 m, using a semi-closed re-breathing system with two different oxygen flow settings. A gas supply with 32.5 per cent oxygen concentration results in a safe dive whereas a 60 per cent setting indicates a dangerous diving condition. Typical respiratory model input data are illustrated for the lung, together with dimensional details for the re-breathing counterlung. The simulation results show variations in alveolar and pleural pressures, gas concentrations and partial pressures in the equipment and in the human respiratory system.

High-Intensity Burners with Low Nox Emissions

Experimental combustion and NOx emissions results are summarized for a range of jet shear layer combustion systems that have rapid fuel and air mixing, short intense flames, a high turn-down ratio and low NOx characteristics. Two burner sizes of 76 and 140 mm are investigated for propane and natural gas. Three jet shear layer burners are compared with axial and radial swirlers. The combustion techniques were developed for application to low NOx combustion systems for industrial gas turbines, where NOx emissions as low as 10 ppm at 15 per cent oxygen have been demonstrated. It is shown that at one bar pressure, gas turbine combustors and high-intensity burners operate at similar air flow, blockage and pressure loss conditions.