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Severity of hypoxaemia can be assessed using the partial pressure of arterial oxygen to fraction of inspired oxygen ratio (FiO2). However, in patients breathing through non-rebreather reservoir bag oxygen mask, accuracy of bedside FiO2 estimation methods remains to be tested. In a post-hoc analysis of a multicentre clinical trial, three FiO2 estimation methods were compared with FiO2 measured with a portable oxygen analyser introduced in the oxygen mask. Among 262 patients analysed, mean (SD) measured FiO2 was 65% (13). The 3%-formula (21% + oxygen flow rate in L/min × 3) was the most accurate method to estimate FiO2 Other methods overestimated FiO2 and hypoxaemia severity, so they should be avoided. [ABSTRACT FROM AUTHOR]

The use of long term domiciliary oxygen therapy in the Sheffield area from June to August 1987 has been surveyed. Of the 74 patients prescribed long term domiciliary oxygen therapy, 64 were visited at home. These had arterial blood gas tensions or oxygen saturation measured (while breathing oxygen and air), and the indications for long term domiciliary oxygen therapy were examined retrospectively. Fifty two patients had chronic bronchitis and emphysema, the remainder having pneumoconiosis, bronchiectasis, fibrosing alveolitis, and congestive cardiac failure. Of the 54 cases where indications for treatment could be compared with the Department of Health and Social Security (DHSS) guidelines, only 23 (43%) met the full DHSS criteria before the start of treatment. The median length of treatment was 16 months. At follow up 51 patients had an arterial oxygen tension (PaO2) greater than 8.0 kPa when breathing oxygen. They had a significantly higher PaO2 when breathing air than before long term oxygen therapy (6.7 (SD 1.2) kPa before oxygen treatment, 7.6 (1.4) kPa on reassessment). A similar change was seen in the 23 patients assessed as recommended by the DHSS (6.1 (0.8) kPa; 7.2 (1.2]. PaO2 during the breathing of air was less than 7.3 kPa at reassessment in only 21 (33%) patients. Thirteen patients had carboxyhaemoglobin concentrations above 2.5%, the 95th centile of the distribution in nonsmokers in the laboratory. [ABSTRACT FROM AUTHOR]

Examples of six oxygen concentrators (DeVO2, Dom 10, Econo 2, Hudson, Permox, and Roomate) were evaluated over a 9-28 day period to determine (1) the oxygen yield (% O2) over the flow range 1-4 l min-1; (2) 90% oxygen rise time (90% RT) from a cold start when they were operated at 2 l min-1; (3) accuracy and readability of the flow device; (4) static outlet pressure; (5) major components comprising the product gas (Hudson only); and (6) general characteristics. At an outlet flow of 2 l min-1 the mean % O2 generated by all models, except the Permox (which was lower, mean (SD) 90.5% (3.1%), were between 94% and 95% with a range of less than +/- 0.5%. The Dom 10, Econo 2, and Hudson consistently generated higher oxygen concentrations than the other models at flow rates greater than 2 l min-1. The 90% RT was less than 10.5 minutes for all models. Deviations of up to 22% were observed between predicted and measured flow rates in all models except the DeVO2, Hudson, and Permox. It was possible to set the orifice type flow devices fitted to the Permox and Roomate between indicated flow settings, resulting in cessation of flow. Spectral analysis of the output of one device showed that argon and oxygen were concentrated to similar extents, indicating that the maximal attainable oxygen yield for a molecular sieve concentrator is about 96%. [ABSTRACT FROM AUTHOR]

We have studied the efficacy of three devices designed to conserve oxygen delivered to patients with hypoxic chronic bronchitis and emphysema. Devices A and B are valve systems, which deliver oxygen only during inspiration. Device C is a modified nasal prongs system incorporating a "moustache reservoir" (Oxymizer, Chad Therapeutics Inc, Woodland Hills, California), which is claimed to produce a higher arterial oxygen saturation (SaO2) from a given flow of oxygen than does continuous delivery through nasal prongs. Devices A and B were found to give the same oxygen saturation as continuous flow oxygen, but only device B reduced the flow of oxygen significantly (p less than 0.01). The flow characteristics of device A were likely to be the cause of this failure to conserve oxygen. Device C produced a higher mean rise in SaO2 than did standard nasal prongs at all oxygen flow rates, and was able to achieve the same rise in SaO2 as standard nasal prongs with a small (25-33%) saving in oxygen delivery. There was, however, considerable variation between patients in the oxygen saving efficiency of device C, with little or no oxygen saving in seven of the 12 patients studied. [ABSTRACT FROM AUTHOR]

One membrane oxygen enricher (Oxygen Enrichment Company OE-4E) and four molecular sieve (MS) concentrators (Mountain Medical Econo2, De Vilbiss MINI DeVO2, Cryogenic Roomate III, and Mountain Medical Mini O2) have been studied to assess technical and clinical performance. During four weeks of continuous operation at a flow rate of 2 l min-1 (6 l min-1 for OE-4E) consistent oxygen levels were delivered by all machines (mean greater than 93% for MS concentrators, 36.5% for OE-4E). At flow rates of up to 21 mm-1 all four MS machines delivered oxygen concentrations greater than 92%, but at 3 l min-1 (Econo2 89.6%, MINI DeVO2 93.9%, Roomate III 92.0%, Mini O2 85.0%) and at 4 l min-1 (Econo2 78.0%, Mini DeVO2 84.7%, Roomate III 83.3%, Mini O2 69.1%) the two newer machines gave higher oxygen concentrations. In 20 hypoxic patients the mean oxygen saturation levels achieved when they were breathing oxygen from the MS concentrators at a flow rate of 2 l min-1 were similar (Econo2 92.6%, MINI DeVO2 92.5%, Roomate II 92.6%), but the level achieved when they were breathing from the OE-4E, at the equivalent flow rate of 6 l min-1, was lower (91.0%, p less than 0.005). The performance of concentrators in service (Econo2, MINI DeVO2, Mini O2) was satisfactory when judged by patients' oxygen saturation levels and delivered oxygen concentrations. The OE-4E may be indicated for a small number of patients who require oxygen with high humidification. The four MS concentrators studied are all suitable for domiciliary use, but the MINI DeVO2 and Roomate III have advantages in terms of better performance at high flow rates and reduced size and weight. [ABSTRACT FROM AUTHOR]

, , 371-376. An oxygen enrichment attachment is described which fulfils the basic requirements for intubated patients. Using values for tidal volume and inspiratory time found in the type of patients for whom the attachment is intended, a range of mean inspired oxygen concentration has been given for 2, 4, 6, 8, and 10 1/min oxygen flow. [ABSTRACT FROM PUBLISHER]

Six commercially available devices were tested to determine the alveolar oxygen concentration that is achieved and the volume of rebreathing that can occur in conditions simulating clinical use. All were tested at zero oxygen flow, since failure and interruption of the oxygen supply to such devices can occur in clinical use. In patients whose cardiorespiratory reserve is exhausted, any increase in dead space will be detrimental; for such patients devices should be selected which cannot cause rebreathing under any circumstances. Three of the devices tested could cause appreciable rebreathing, Oxyaire (B.L.B. pattern), Pneumask, and the M.C. mask. Claims made for the Pneumask and the M.C. mask were not substantiated in this study. With administration by nasal catheter changes in alveolar oxygen concentrations were found to be dependent on the percentage of mouth breathing by the subject. The Ventimask produced a consistent elevation of the alveolar oxygen percentage and did not cause any increase in the dead space. [ABSTRACT FROM PUBLISHER]

Oxygen administration via a nasal cannula incorporating a small collapsible reservoir (Oxymizer, Chad Therapeutics Inc, California) was compared with delivery via a standard nasal cannula. Twelve patients with chronic, stable hypoxaemia (arterial oxygen tension less than 60 mm Hg (8.0 kPa)) were studied. Transcutaneous oxygen and carbon dioxide tensions were recorded by skin electrodes and oxygen saturation by ear oximetry. Baseline measurements during the breathing of air were compared with those made during the breathing of oxygen at flow rates of 0.5, 1.0, and 2.0 l/min via each device. Increases in saturation and transcutaneous oxygen tension were significantly greater at each flow rate with the reservoir device than with the conventional cannula. To produce similar improvements in oxygenation the reservoir device required an oxygen flow rate about half that of the conventional cannula. Use of the reservoir device may reduce the inconvenience and perhaps the cost of supplying domiciliary oxygen, and prolong the time during which patients may rely on a portable cylinder. [ABSTRACT FROM AUTHOR]