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Mass spectrometers are used in ICUs and ORs to measure the concentration of medical and anesthetic gases gathered from multiple sites. This investigation was designed to determine the accuracy of a clinical system, which included 12 ICU bedside stations monitored by a medical mass spectrometer (Perkin-Elmer RMS III, Pomona, CA). Each site station was connected to the analyzing unit via two Teflon tubes, one permanently installed, 30-m long, and the second disposable, 2.4-m long. A gas mixture containing 95% O2 and 5% CO2, alternating with room air, was delivered to a solenoid valve and from there to the connecting tubes. Gas flow-rate, delay time, rise time, and peak and trough concentrations were determined for each gas at solenoid cycling frequencies of 25, 50, and 100/min. After the first set of measurements, the 30-m tubes were thoroughly cleaned and all measurements repeated. In addition, the authors also measured CO2 delay and rise times when the gas was delivered to the mass spectrometer through an unused 30-m tube or a new 2.4-m tube. Gas flow-rate increased from 143 +/- 12 ml/min (mean +/- SD) to 238 +/- 9 ml/min after the tubes were cleaned. Delay time was identical for all gases at all solenoid cycling rates but decreased significantly (P less than 0.05), from 11.5 +/- 0.3 to 4.8 +/- 0.7 s after the ceiling tubes were cleaned. As solenoid valve rate increased, the difference between measured and actual gas concentration increased. The lowest accuracy was 63.6 +/- 2.1%, for CO2 at 100 cycles/min.(ABSTRACT TRUNCATED AT 250 WORDS)

High frequency jet ventilation (HFJV) is an incompletely studied technique of mechanical respiratory support. The authors have built a ventilator based on a solenoid valve, that allows independent selection of respiratory rate and inspiratory/expiratory ratio. The ventilator can be synchronized to the heart rate. Hum-idification is provided by warm saline dripped in front of the injector nozzle, so that the jet stream itself acts as a nebulizer. Tube diameter, length, and deformability are fundamental determinants of inspiratory flow rate and wave form. Cannula kinking and inadequate humidifi-cation were the most significant sources of complications.

We used indirect calorimetry to measure oxygen consumption (VO2) and carbon dioxide production in 29 mechanically ventilated patients. These data were compared to VO2 measured simultaneously by a standard thermodilution technique. A good correlation was demonstrated between the methods, but VO2 measured by indirect calorimetry was 15% higher than VO2 measured by thermodilution.

Since the introduction of the Electrosurgical Unit (ESU) as an effective tool in the OR and clinic, there has been a need to measure accurately the output of these devices in order to verify their safety, calibration, and performance. This article presents review of ESU measurement techniques, along with an analysis of their advantages and shortcomings. An alternative method is advanced that improves accuracy and resolution, provides extremely flexible selection of load resistance values and current measurement paths, and directly measures Crest Factor, a significant electrosurgical parameter.

A variety of technical decisions are required for the proper selection and safe and efficacious application of high-frequency jet ventilation (HFJV). Criteria for analyzing the performance of an HFJV system are presented, along with discussions of some of the more common respiratory measurements and their applicability to HFJV.