Microchannel technologies for artificial lungs: (2) screen-filled wide rectangular channels.

Artificial lungs with blood-side channels on a 10-40 microm scale would be characterized, similar to the natural lungs, by tens of thousands to hundreds of millions parallel blood channels, short blood paths, low pressure drops, and low blood primes. A major challenge for developing such devices is the requirement that the multitude of channels must be uniform from channel to channel and along each channel. One possible strategy for developing microchannel artificial lungs is to fill broad rectangular channels with micro scale screens that can provide uniform support and stability. The present work explores the effectiveness of 40 microm screen-filled blood-side channels and, as a comparison, 82 microm screen-filled channels. Small concept-devices, consisting of a single 69 mm wide and 3 or 6 mm long channel, were tested using 30% hematocrit blood and oxygen or air on the gas side. The measured oxygen fluxes in the devices were in the range of 4 to 9 x 10(-7) moles/(min x cm(2)), with the latter close to the theoretical membrane limit. The pressure drop was in the range of 1-6 mm Hg. Extrapolating the data to a device designed to process 4 L/min suggests a required blood prime of only 35 ml.

Microchannel technologies for artificial lungs: (3) open rectangular channels.

Lithographic techniques were used to develop patterned silicone rubber membranes that provide 15 microm high microchannels for artificial lungs. Two types of devices were fabricated as a proof-of-concept: one has a series of parallel, straight, open rectangular channels that are each 300 microm wide, separated by 200-microm walls, and 3-mm long and the other is a wide rectangular channel with support posts, also 3- mm long. Experiments with 30% hematocrit, venous, bovine blood showed average oxygen fluxes ranging from 11 x 10(-7) moles/(min x cm(2)) at a residence time of 0.04 sec to 6.5 x 10(-7) moles/(min x cm(2)) at a residence time of 0.20 sec. The average oxygen flux vs. residence time, which is due to transverse molecular diffusion, follows the same relation for all membranes tested. The corresponding increase in hemoglobin saturation ranged from 9% at the residence time of 0.04 sec to 24% at the residence time of 0.20 sec. The support-post channel membranes are attractive for designers because they can be arbitrarily wide and would be less prone to blockage.

Direct evidence of oxidized gold on supported gold catalysts.

Supported gold catalysts have drawn worldwide interest due to the novel properties and potential applications in industries. However, the origin of the catalytic activity in gold nanoparticles is still not well understood. In this study, time-of-flight secondary ion mass spectroscopy (TOF-SIMS) has been applied to investigate the nature of gold in Au (1.3 wt %)/gamma-Al2O3 and Au (2.8 wt %)/TiO2 catalysts prepared by the deposition-precipitation method. The SIMS spectrum of the supported gold catalysts presented AuO-, AuO2-, and AuOH- ion clusters. These measurements show direct evidence for oxidized gold on supported gold catalysts and may be helpful to gaining better understanding of the origin of the catalytic activity.

Acute pain services in Hong Kong: facilities, volume, and quality.

Acute pain services in public hospitals in Hong Kong were studied. Audit data on the volume and quality of acute pain services were collected prospectively from 1997 to 1999, and data on related facilities were collected in 2000. About 20% of patients undergoing a major operation received an acute pain service; of these, 78.6% were satisfied with the treatment provided. In 2000, 86% (18/21) of hospitals providing anaesthetic services were running an acute pain service. Staffing was better in hospitals providing a high volume of acute pain services, ranging from a full-time specialist anaesthesiologist assisted by a half-time trainee to a half-time specialist assisted by a full- or half-time trainee. However, only four hospitals were staffed with pain nurses. In total, 57% of patients received intravenous patient-controlled analgesia and 32% epidural analgesia. The mean duration of acute pain service treatment was 3.1 days. Currently anaesthesiologist-based acute pain services take care of a limited number of patients. To expand the coverage, there should be a move towards an anaesthesiologist-led, pain nurse-based, acute pain service. The present shortage of pain nurses should be addressed.

Anaesthetic clinical indicators in public hospitals providing anaesthetic care in Hong Kong: prospective study.

OBJECTIVES: To assess the quality of anaesthetic services as defined in the six anaesthetic clinical indicators against preset standards and to identify risk factors for adverse events in the recovery room. DESIGN: Prospective study. SETTING: All public hospitals providing anaesthetic care in Hong Kong. PATIENTS: Eighteen thousand, seven hundred and fifty-nine patients receiving elective or emergency anaesthesia administered by anaesthetists from June 1998 to July 1998. MAIN OUTCOME MEASURES: Patient demographics, American Society of Anesthesiologists status, category and nature of operation, presence of preoperative anaesthetic visit in ward, type of anaesthesia, reasons for a recovery room stay of more than a 2-hour duration, intubation to relieve respiratory distress in the recovery room, presence of hypothermia in the recovery room for operations lasting more than 2 hours, and dental or ocular injuries attributable to anaesthesia. RESULTS: There are two major findings from this study. Firstly, a high incidence of hypothermia in the recovery room was reported. Secondly, a greater risk of prolonged stay in the recovery room was identified for patients older than 65 years, major operations, and anaesthetic techniques using combined general and regional anaesthesia. CONCLUSION: The six anaesthetic clinical indicators reflected the provision of anaesthetic care in public hospitals in Hong Kong. Good compliance to the preset standard of the anaesthetic clinical indicators was achieved during the study period.

Arterial desaturation during induction in healthy adults: should preoxygenation be a routine?

We studied the haemoglobin saturation of one hundred healthy patients equally divided into two groups. Group 1 patients received three minutes of preoxygenation prior to thiopentone induction followed by inhalational anaesthetics. Group 2 patients breathed room air prior to induction. None of the patients in Group 1 showed any arterial oxygen desaturation during the five minutes of the induction period, whereas 21 patients in Group 2 showed definite desaturation (P less than 0.005), of which fifteen patients had a saturation of 90% or less (P less than 0.005) and six had a saturation of 85% or less. Since those were healthy patients and the anaesthetics were given by experienced anaesthetists, we concluded that some form of preoxygenation should be used in all patients receiving general anaesthesia.