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Biomedical subjects

S L Snowdon

Publications and source records attributed to S L Snowdon.

At least 37 records · Page 2Linked to original sources
PubMed1988

Predicted and measured oxygen concentrations in the circle system using low fresh gas flows with oxygen supplied by an oxygen concentrator.

An oxygen concentrator based on a zeolitic molecular sieve has been used to supply piped oxygen in a District General Hospital; such oxygen contains 5% argon. If concentrator oxygen is used in the closed circuit, argon accumulates. The present investigation defines the extent and time course of argon accumulation in partially and fully closed breathing systems. A theoretical model is presented which predicts the extent and rate of inert gas accumulation. The predictions have been tested in a volunteer under laboratory conditions and in five anaesthetized patients. It is recommended that concentrator oxygen may be used for low flow anaesthesia of indefinite duration, provided the fresh oxygen flow to the circuit is at least twice the oxygen consumption. If the circuit is totally closed, periodic opening of the circuit is necessary.

Adult↗
PubMed1987

Potentiation of the neuromuscular blockade produced by alcuronium with halothane, enflurane and isoflurane.

The potentiation of alcuronium by halothane, enflurane and isoflurane was investigated using electromyography. In the first study, cumulative dose-response curves were constructed in four groups of 10 patients anaesthetized with one of the inhalation agents and nitrous oxide, or with fentanyl and droperidol (control). All three agents reduced the ED50 of alcuronium; the effect was marked with isoflurane (P less than 0.005) but less so with halothane (P less than 0.05) and enflurane (ns). In the second part of the investigation, designed primarily to test the duration of action of alcuronium with each agent, a single bolus dose of alcuronium 0.2 mg kg-1 was given to four similar groups (n = 5). The duration of action was significantly prolonged by enflurane (P less than 0.01) and isoflurane (P less than 0.05), but not by halothane. The possible reasons for this are discussed.

Action Potentials↗
PubMed1987

Pre-oxygenation and the parturient patient.

The effects of pre-oxygenation were studied by continuous expired oxygen analysis in twenty pregnant patients and ten nonpregnant controls. The Magill system and a demand valve breathing system were both studied with tidal and vital capacity breathing. Rapid pre-oxygenation was possible with the demand valve system but the technique was associated with air leaks around the mask. Vital capacity breathing with the Magill system was inefficient in practice because of rebreathing and air leaks, and the recently proposed four vital capacity breath technique provided suboptimal alveolar oxygenation in pregnant subjects. Oxygenation in pregnant subjects was significantly faster than in nonpregnant controls and was achieved after just 2 minutes of tidal breathing from a standard Magill system with a prefilled reservoir. Care was necessary to ensure a gas-tight seal around the facemask.

Adult↗
PubMed1986

Medical gas probes.

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Equipment Safety↗
PubMed1986

Experimental investigation of the cardiovascular and respiratory effects of increasing concentrations of isoflurane in the dog.

The cardiovascular and respiratory effects of the new inhalational anaesthetic agent isoflurane were investigated in dogs. Anaesthesia was induced with thiopentone after premedication with acepromazine. Isoflurane was administered with nitrous oxide and oxygen by spontaneous ventilation after base line values had been determined. Arterial blood pressure decreased as the concentration of administered isoflurane increased. Isoflurane produced a profound and dose related respiratory depression as measured by the increase in end tidal carbon dioxide levels. Isoflurane administration did not produce any visible muscle twitching.

Animals↗
PubMed1985

Fresh gas flow economics of the Waters (to-and-fro) system in small animal anaesthetic practice.

The Waters (to-and-fro) system is a commonly used anaesthetic system in small animal clinical practice. Although it may be used as a totally closed system, it has been recommended that it be used as a semi-closed system with relatively high fresh gas flow rates. The performance of the Waters system was studied with reference to wastage of neat, unused fresh gas flow. The results were compared with the performance of a modified Waters system. Using a fresh gas flow rate of 2 litres/minute considerable wastage of fresh gas flow and volatile agent was noted using the Waters system; the wastage was less with the modified system. Marked savings of fresh gas flow and volatile agent could result by reducing the fresh gas flow to 0.5 litres/minute. The findings are discussed in the light of current small animal clinical anaesthetic practice.

Anesthesia, Inhalation↗
PubMed1984

Respiratory resistance of tracheostomy tubes.

One of the main results of tracheostomy is to reduce the airflow resistance and power of breathing. The airflow dynamics of three types of commonly used tracheostomy tubes were studied. A generator was used to produce a sinusoidal airflow wave to simulate normal breathing. The flow resistance and the power required to overcome this resistance were measured. A difference was observed in the flow resistance and the power of breathing between the inspiratory and expiratory phase of all the tubes. It was also observed that the Portex and Jackson tubes have a lower flow resistance and power of breathing than the similar gauge Shiley tube. This difference was due to the greater length, shorter radius of curvature, and rougher inner surface of the Shiley tube.

Airway Resistance↗
PubMed1984

A comparison between iohexol and metrizamide, two nonionic contrast media, in aorto-femoral angiography.

Iohexol, a recently developed non-ionic contrast medium, is shown to be well tolerated on aorto-femoral angiography. The aortic injection of 40 ml of iohexol (350 mg I/ml) was usually associated with a moderate sensation of heat and an absence of pain. A transient fall in blood pressure, no different from that resulting from metrizamide, was associated with some increase in heart rate.

Adult↗
PubMed1982

An assessment of iopamidol, a non-ionic contrast medium, in aorto-femoral angiography.

Iopamidol, a recently developed non-ionic contrast medium, was used for aorta-femoral angiography in a concentration of 370 mg of iodine/ml. The injection of 35-40 ml was painless in most cases and was never severe. A sensation of heat in the legs accompanied all injections. A fall in systolic and diastolic blood pressure and an increase in heart rate occurred, these effects being greater than with metrizamide. The image quality was satisfactory. Iopamidol is well tolerated and preferable to conventional hyperosmolar contrast media in aorto-femoral angiography.

Aorta↗
PubMed1981

Bain circuit.

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Adult↗