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  • 1
    Electronic Resource
    Electronic Resource
    Accuracy of end-tidal carbon dioxide tension analyzers (1991)
    Springer
    Journal of clinical monitoring and computing 7 (1991), S. 195-208 
    Details
    ISSN: 1573-2614
    Keywords: Monitoring carbon dioxide ; Equipment infrared analyzers Raman spectrometer mass spectrometer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Medicine
    Notes: Abstract Substantial mean differences between arterial carbon dioxide tension (PaCO2) and end-tidal carbon dioxide tension (PetCO2) in anesthesia and intensive care settings have been demonstrated by a number of investigators. We have explored the technical causes of error in the measurement ofPetCO2 that could contribute to the observed differences. In a clinical setting, the measurement ofPetCO2 is accomplished with one of three types of instruments, infrared analyzers, mass spectrometers, and Raman spectrometers, whose specified accuracies are typically ±2, ±1.5, and ±0.5 mm Hg, respectively. We examined potential errors inPetCO2 measurement with respect to the analyzer, sampling system, environment, and instrument. Various analyzer error sources were measured, including stability, warm-up time, interference from nitrous oxide and oxygen, pressure, noise, and response time. Other error sources, including calibration, resistance in the sample catheter, pressure changes, water vapor, liquid water, and end-tidal detection algorithms, were considered and are discussed. On the basis of our measurements and analysis, we estimate the magnitude of the major potential errors for an uncompensated infrared analyzer as: inaccuracy, 2 mm Hg; resolution, 0.5 mm Hg; noise, 2 mm Hg; instability (12 hours), 3 mm Hg; miscalibration, 1 mm Hg; selectivity (70% nitrous oxide), 6.5 mm Hg; selectivity (100% oxygen), −2.5 mm Hg; atmospheric pressure change, 〈1 mm Hg; airway pressure at 30 cm H2O, 2 mm Hg; positive end-expiratory pressure or continuous positive airway pressure at 20 cm H2O, 1.5 mm Hg; sampling system resistance, 〈1 mm Hg; and water vapor, 2.5 mm Hg. In addition to these errors, other systematic mistakes such as an inaccurate end-tidal detection algorithm, poor calibration technique, or liquid water contamination can lead to gross inaccuracies. In a clinical setting, unless the user is confident that all of the technical error sources have been eliminated and the physiologic factors are known, depending onPetCO2 to determine PaCO2 is not advised.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01618124
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  • 2
    Electronic Resource
    Electronic Resource
    FIx Controller: An Instrument to Automatically Adjust Inspired Oxygen Fraction Using Feedback Control from a Pulse Oximeter (1997)
    Springer
    Journal of clinical monitoring and computing 13 (1997), S. 91-101 
    Details
    ISSN: 1573-2614
    Keywords: Monitoring: oxygen saturation ; Equipment: ventilators, pulse oximetry, oxygen analyzers ; Oxygen: toxicity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Medicine
    Notes: Abstract Objective. To develop an instrument to help prevent pulmonaryO2 toxicity, a syndrome that manifests itself in adultintensive care patients. Methods. We designed, built, and tested adevice that controls FIO2 exposure using oxygensaturation measured with a pulse oximeter (SpO2) in a negativefeedback control system. A target SpO2 is designated by theclinician and the system adjusts the FIO2 from amechanical ventilator so as to minimize the difference between the measuredSpO2 and the target. Important elements of the system includea conservative artifact rejection algorithm, a gain-scheduled sampled-dataproportional-integral-derivative (PID) controller, and a safety system toprevent inspired mixtures with undesirably low FIO2 dueto device failure. Results. The control system was tuned in a series ofanimal experiments. Acceptable clinical response of the system was obtainedusing a gain-scheduled controller algorithm whereby the gain of theproportional term of a PID controller was adjusted based on the error signaland measured minute ventilation. Also, the artifact rejection algorithm andsafety systems were successfully tested using simulation. Conclusions.Testing the effectiveness of this instrument will require comparison withmanual control of FIO2 in an appropriately designedtrial.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007384122804
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  • 3
    Electronic Resource
    Electronic Resource
    An electronic stethoscope is judged better than conventional stethoscopes for anesthesia monitoring (1986)
    Springer
    Journal of clinical monitoring and computing 2 (1986), S. 151-154 
    Details
    ISSN: 1573-2614
    Keywords: Monitoring ; auscultation ; Equipment ; stethoscope ; monitoring ; electronic
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Medicine
    Notes: Abstract A prototype electronic monitoring stethoscope was constructed from readily available, high-quality components. It consisted of a conventional precordial or esophageal probe connected to a microphone by a rubber adapter. The microphone was connected by lightweight wire to an amplifier and headphones. Twenty-one anesthesia clinicians evaluated the stethoscope and responded to a multiple-choice preference questionnaire. The electronic stethoscope was judged to perform better than the conventional stethoscope in most categories evaluated. The electronic device was perceived to be louder, clearer in sound reproduction, more efficacious for monitoring, and easier to use continuously, and its head-phones were considered more comfortable than the conventional carpiece. Based on our results, we conclude that amplified stethoscopes have the potential to improve monitoring. Further development of electronic stethoscope monitoring seems warranted and is continuing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01620547
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  • 4
    Electronic Resource
    Electronic Resource
    The prevalence of hypoxemia detected by pulse oximetry during recovery from anesthesia (1988)
    Springer
    Journal of clinical monitoring and computing 4 (1988), S. 16-20 
    Details
    ISSN: 1573-2614
    Keywords: Complications: hypoxemia ; Monitoring: oxygen ; Measurement techniques: pulse oximetry ; Anesthesia: post-operative period
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Medicine
    Notes: Abstract Pulse oximetry was used to assess the prevalence of hypoxemia (arterial oxygen saturation of 90% or less) at various times in the immediate postoperative period: five minutes after arrival, 30 minutes later, and just before discharge. Among 149 inpatients studied, one or more hypoxemic measurements were made in 21 (14%) during their postoperative course. Of 92 outpatients, 1 (1%) was found to be hypoxemic. For inpatients, the prevalence of hypoxemia preoperatively, 5 minutes after arrival in recovery, 30 minutes later, and at discharge was 2%, 4%, 6%, and 9%, respectively. Patient factors associated with a significantly higher prevalence of hypoxemia were obesity (22%), body cavity surgical procedures (24%), age over 40 years (18%), American Society of Anesthesiologists physical status (I, 7%; II, 17%; III, 18%; IV, 100%), duration of anesthesia longer than 90 minutes (18%), and intraoperative administration of greater than 1,500 ml of fluid (20%). Unrecognized hypoxemia in postsurgical inpatients with or without these risk factors is common. Therefore routine monitoring of these patients with a pulse oximeter is suggested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01618102
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  • 5
    Electronic Resource
    Electronic Resource
    The theoretical effect of carboxyhemoglobin on the pulse oximeter (1989)
    Springer
    Journal of clinical monitoring and computing 5 (1989), S. 246-249 
    Details
    ISSN: 1573-2614
    Keywords: Blood: carboxyhemoglobin ; Oxygen: saturation ; Measurement techniques: pulse oximetry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Medicine
    Notes: Abstract The relationship between arterial oxygen saturation as measured by the pulse oximeter (SpO2) and the fractional arterial oxygen saturation (SaO2) in the presence and absence of carboxyhemoglobin (COHb) has been derived according to the theory of absorption spectroscopy. We find that our theoretically derived correction equation is similar to that found in the technical literature of Nellcor. However, the correction equations presented by Barker and Tremper and the technical literature of Ohmeda differ substantially from our equation when sufficient quantities of reduced hemoglobin are present and the fractional COHb saturation (SaCO) is high. Our approximated equation, derived from the Lambert-Beer law, is SaO2=SpO2(1−0.932 SaCO)+0.032 SaCO. The equation of Barker and Tremper is SaO2=SpO2−0.9 SaCO. The Nellcor equation is SaO2=SpO2(1−SaCO).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01618255
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  • 6
    Electronic Resource
    Electronic Resource
    Arterial-Line Monitoring System Simulation (2000)
    Springer
    Journal of clinical monitoring and computing 16 (2000), S. 547-552 
    Details
    ISSN: 1573-2614
    Keywords: Simulation ; monitoring
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Medicine
    Notes: Abstract Objective. We sought to improve the realism of our patient simulation environment by developing a simulation of the arterial-line monitoring system. Properties of the system we wished to depict were: electro-mechanical delay between ECG and radial artery pressure, beat to beat amplitude variability and respiratory variation, realistic looking pulse pressure in hypertensive and hypotensive states, a functional link to the stopcock and transducer flush, and filtering characteristics of the measurement system. Methods. A standard clinical pressure transducer and stopcock were modified to provide data about their state to a personal computer. A software program was written to modify the arterial pressure waveform from a patient simulator according to the pressure transducer and stopcock state as well as user settings to produce a new waveform. Results. All of the desired improvements in the realism of the arterial waveform were implemented.Conclusions.The realism of scenarios using the patient simulator is enhanced by having the arterial-line monitoring system more accurately simulated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1011434028338
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  • 7
    Electronic Resource
    Electronic Resource
    The effects of bronchodilator-inhaler aerosol propellants on respiratory gas monitors (1991)
    Springer
    Journal of clinical monitoring and computing 7 (1991), S. 175-180 
    Details
    ISSN: 1573-2614
    Keywords: Measurement techniques: mass spectrometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Medicine
    Notes: Abstract Spurious readings from a mass spectrometer have been reported following the administration of aerosol bronchodilators. We quantified the response of various respiratory gas analyzers to the aerosol propellant of albuterol inhalant (Proventil). The mass spectrometer systems tested, two Advantage systems, a SARA system, and a Model 6000 Ohmeda system, all displayed artifactual readings in response to the albuterol propellant. Each metered dose of the Proventil brand of albuterol contains 4 ml of Freon 11 (trichloromonofluoromethane) and 11 ml of Freon 12 (dichlorodifluoromethane). The concentration of propellant was expressed in doses/L, where each liter of gas contains 0.4 vol % of Freon 11 and 1.1 vol % of Freon 12 per dose. In proportion to the concentration of albuterol propellant, the two Advantage systems showed substantial readings of isoflurane (%) when no isoflurane was present (13% and 16% per dose/L) and reduced readings of enflurane (−8% and −10% per dose/L) and carbon dioxide (CO2) (−3 and +5 mm Hg per dose/L). The SARA system showed substantial CO2 readings when no CO2 was present (5 mm Hg per dose/L) and displayed small enflurane readings (0.1% per dose/L) when no enflurane was present. The Model 6000 unit showed CO2 readings when no CO2 was present (5 mm Hg per dose/L). Neither the Raman spectrometer, the infrared spectrometers, nor the piezoadsorptive analyzer we tested showed an artifactual effect of albuterol propellant on any of its readings. Simulation and clinical tests demonstrated that a single dose of albuterol propellant into a breathing circuit at the onset of inspiration resulted in concentrations of 0.8 and 0.3 dose/L, respectively. The phenomenon may be clinically useful, by allowing the anesthetist to verify the uptake of an inhalant into a patient.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01618119
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