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Articles about the
AVOXimeters Other Publications
Abstracts
Freeman, G.L., et al., Evaluation of Two Oximeters for Use in Cardiac Catheterization Laboratories. Catheterization and Cardiovascular Diagnosis 30: 51-57, 1993. We evaluated two whole-blood oximeters designed for use in the cardiac catheterization laboratory: the Oxicom 3000 and the AVOXimeter 1000. Unlike the larger CO-Oximeters which hemolyze a blood sample before analysis, these simple instruments use disposable cuvettes to allow determination of oxyhemoglobin saturation of whole blood. Thus, they eliminate the need for cleaning solutions and considerable maintenance. We evaluated the accuracy of these instruments in comparison with a Radiometer OSM3, and found them both to work well on routine samples. Of note, the AVOXimeter performed better than the Oxicom when the sample was hemolyzed and when green dye was present. Carboxy- and methemoglobin interfered with the Oxicom's measurements but not the AVOXimeter's. In addition, the AVOXimeter measures the total hemoglobin concentration and the oxygen content of each sample, eliminating errors that hemodilution introduces into the determination of cardiac output by the Fick principle. We conclude that whole-blood oximeters are accurate and useful instruments for use in the cardiac catheterization laboratory.
Gong, A.K., Near-Patient Measurement of Methemoglobin, Oxygen Saturation, and Total Hemoglobin: Evaluation of a New Instrument for Adult and Neonatal Intensive Care. Critical Care Medicine 23: 193-201, 1995. Objectives: 1) to evaluate the performance of the AVOXimeter, a compact, new instrument that uses disposable cuvettes to measure total hemoglobin concentration, oxygen content, and the relative concentrations of oxy- and methemoglobin in 50 µl blood samples; 2) to determine whether the instrument can be used for near-patient assessment of methemoglobinemia; and 3) to ascertain whether problems commonly encountered in neonatal blood samples affect the instrument's performance.Design: This is a prospective study in which the test instrument was compared with a standard method. Samples of whole blood with and without bilirubin, fetal hemoglobin, and hemolysis were analyzed on the new test instrument and on a widely used CO-Oximeter, the Radiometer OSM3 Hemoximeter.Setting: In vitro analyses of blood samples in clinical and university laboratories.Measurements and Main Results: There was a close linear correlation between the methemoglobin measurements of the test instrument and those of the reference instrument (slope = 0.989, r2 = 0.989). The average difference in mean assay values between the reference instrument and the bedside analyzer was -0.59%, i.e. less than 1% methemoglobin. Repeated measurements indicated the precision was 0.5% methemoglobin. Complete hemolysis of the sample reduced the methemoglobin reading by only 0.40%. Bilirubin (10 - 11 mg/dl) increased the methemoglobin reading by 0.23%, the oxyhemoglobin by 0.45%, and the total hemoglobin by 0.21 g/dl. Fetal hemoglobin also had minimal effects on the readings. Conclusions: The test instrument is extremely fast and easy to operate. No sample preparation or pipetting is required. To operate the instrument, the user simply connects a syringe containing the blood sample to one of the disposable cuvettes, injects 50 µl of blood into the cuvette, and inserts the cuvette into the instrument. The test instrument automatically detects the presence of the cuvette, analyzes the sample, and displays the results in less than 10 seconds. The findings in this study indicate that the test instrument has sufficient accuracy for near-patient testing in intensive care units. The errors introduced by hemolysis, fetal hemoglobin, and bilirubin were too small to be of any clinical importance. Thus, the test instrument is essentially unaffected by complications commonly encountered in neonatal blood. Its measurements of methemoglobin will make it particularly useful if inhaled nitric oxide therapy becomes a standard clinical practice.
Bailey, S.R., et al., Evaluation of the AVOXimeter: Precision, Long-term Stability, Linearity, and Use without Heparin. Journal of Clinical Monitoring 13:191 - 198, 1997 Objectives: Because the AVOXimeter uses disposable cuvettes and makes its measurements directly in whole blood without first hemolyzing the sample, it does not need the care and maintenance that conventional co-oximeters require, it operates faster than conventional co-oximeters, and it is less expensive. Therefore, the objectives of this study were 1) to evaluate the precision and linearity of the AVOXimeter's measurements of total hemoglobin concentration and oxyhemoglobin saturation, 2) to assess its long-term stability and thus the required interval for re-calibration, 3) to determine whether measurements can be made without anticoagulants, and 4) to assess the feasibility of storing blood samples in the disposable cuvettes.Methods: Measurements made by the test instrument were compared with those of conventional co-oximeters or with standardized hemoglobin solutions. Blood samples were also collected with and without heparin to determine whether anticoagulation is necessary.Results: Our tests confirmed the specified precision of 0.3 g/dL for total hemoglobin and 0.5% for oxyhemoglobin. The results also showed that these measurements were linear when compared with a conventional co-oximeter, and they were consistent with the specified accuracy of 0.45 g/dL for total hemoglobin and 1% for oxyhemoglobin. Weekly checks with control solutions showed that the instrument holds its calibration for a year or more. Although treating syringes with heparin caused dilution errors, heparin did not affect the measurements when dilution was avoided. When blood samples were placed in disposable cuvettes and read repeatedly at one-minute intervals for 20 minutes, the readings drifted appreciably away from the original value. This drift occurred so slowly that readings taken at the first and second minute after the cuvette was filled were within 1 or 2 % of the original reading.Conclusions: In our experience, the AVOXimeter was simple and easy to operate. It met the specifications for precision and accuracy, its measurements were highly linear, and it maintained a stable calibration for one year. If the cuvettes are filled as soon as blood is drawn, anticoagulation is unnecessary. However, the cuvettes should be read within one minute after the cuvette is filled.
Shepherd, A.P., and J.M. Steinke. CO-Oximetry interference by perflubron emulsion: comparison of hemolyzing and non-hemolyzing instruments. Clinical Chemistry 44: 2183-2190, 1998. Perflubron emulsion is expected to be in clinical use soon as a non-hemoglobin blood substitute. A preliminary report indicates that this new oxygen-carrying fluorocarbon interferes with the measurements of co-oximeters. Therefore, we have quantified the interference that perflubron causes in the measurements of eight widely used oximeters and co-oximeters. The AVL Omni 6, CC270, IL482, IL682 and OSM3 are conventional co-oximeters that hemolyze blood samples before analyzing them. By contrast, the AVOXimeters 1000 and 4000 and the IL Synthesis 35 make their measurements without hemolyzing the samples. Because perflubron is expected to be used most frequently on surgical patients in a hemodiluted state, we conducted all tests on human red blood cells suspended in plasma at a hemoglobin concentration standardized to 7 g/dL and with oxyhemoglobin saturation set at 97%. When perflubron was added to the blood samples, the non-hemolyzing co-oximeters were not seriously affected by perflubron concentrations in and above the therapeutic range. By contrast, some of the hemolyzing co-oximeters experienced concentration-dependent interference in their measurements of all analytes except total hemoglobin concentration. Thus, we conclude that the non-hemolyzing co-oximeters provide an effective means for determining whether a hemolyzing co-oximeter is experiencing clinically significant interference in blood from patients receiving perflubron.
Shepherd, A.P., and C.A. McMahan. Role of oximeter error in the diagnosis of shunts. Catheterization and Cardiovascular Diagnosis 37: 435-446, 1996. We have analyzed the role that instrument error plays in the oximetric diagnosis of shunts. First, we review the accuracy specifications of instruments currently available for measuring oxyhemoglobin saturation during cardiac catheterization. Then we derive a mathematical model of a left-to-right shunt and illustrate the relationships between the magnitude of shunts and the saturation step-ups they generate. Using the shunt model and statistical methods, we show how oximeter error affects the likelihood of success in detecting shunts of a given magnitude. By computing the probabilities of false negative and false positive diagnoses, the model can be used to determine how the likelihood of successful shunt detection is influence by factors such as shunt flow, the minimum saturation step-up considered indicative of a shunt, oximeter error, hemoglobin concentration, and the number of blood samples. A spreadsheet is included for those who wish to analyze the diagnostic capabilities of their own instrumentation and clinical methods. Conclusions: 1. Modern instruments for use during cardiac catheterization analyze blood samples with a measurement error ranging from 2.5% to 1% saturation or better. 2. Until more information is available regarding the accuracy of such devices in measuring oxygen content, the detection of shunts should be made on the basis of step-ups in saturation rather than oxygen content (even though step-ups in oxygen content have the potential advantage of being independent of the oxygen-carrying capacity of blood). 3. Averaging the analyses of two or more blood samples from each site and using an oximeter with 1% error greatly improve the probability of reaching the correct diagnosis. 4. Oximeter error of 2.5% or greater is unacceptable by today's standards. 5. With the instrumentation currently available, oximetry can potentially detect saturation step-ups as small as 3.6% and still keep both false negative and false positive diagnoses below 10% if venous blood is adequately mixed.
Shepherd, A.P., J.M. Steinke, and C.A. McMahan. Effect of oximetry error on the diagnostic value of the Qp/Qs ratio. International Journal of Cardiology 61 (3): 247-259, 1997. As a quantitative assessment of the magnitude of shunting, the ratio of pulmonary to systemic blood flow (Qp/Qs) plays an important role not only in the oximetric diagnosis of intracardiac and great-vessel shunts but also in the treatment of the patient. However, the oxygen saturation measurements used to compute the Qp/Qs ratio contain errors due to physiological variability and measurement error of the oximeter used to analyze the blood samples. We have developed a mathematical model to describe the variability that oximetry errors contribute to the uncertainty in the Qp/Qs ratio. Using this model, we compute the probability of making an inappropriate recommendation regarding corrective surgery when a particular value of the ratio is the criterion for surgery, e.g. a Qp/Qs ratio > 2. This report also contains a spreadsheet that readers can use to analyze their own oximetry data by computing confidence intervals for the Qp/Qs ratio. The results presented here support the following conclusions. First, because the Qp/Qs ratio is calculated from saturation measurements at four different sites, oximetry errors make the Qp/Qs ratio less effective at detecting the presence of a shunt than the conventional step-up method that depends on samples from only two sites. Second, although oximetry errors are equally likely to cause the calculated Qp/Qs ratio to overestimate the true Qp/Qs ratio as to underestimate it, the overestimations on average have greater magnitudes than the underestimations. Third, in comparison with an oximeter that has 2.5% measurement error, using an oximeter with 1% or less error greatly reduces the uncertainty in the Qp/Qs ratio and thus increases the probability of reaching the right decision regarding corrective surgery. Fourth, the variability in apparent Qp/Qs ratios is also greatly diminished by taking multiple blood samples from each of the four requisite sites and averaging them before calculating the Qp/Qs ratio. Although increasing the number of blood samples from each site can compensate for the error of an oximeter, this approach can be impractical, particularly if the oximeter error is 2.5% or greater.
Morales, R., M.B. Kirkpatrick, and P. Hoffman. Agreement in total hemoglobin and oxyhemoglobin and carboxyhemoglobin saturations between a point-of-care (Avoximeter 4000®) and a standard (OSM3®) co-oximeters. Chest 118 (4 Suppl): 273S, 2000. PURPOSE: Prior to introducing the point-of-care co-oximeter AVOXimeter 4000® (Diametrics Medical, Inc.) at our hospital, we wanted to compare the agreement of its results with the standard bench co-oximeter OSM3® (Radiometer). Both co-oximeters use absorption spectrophotometry for calculating the total hemoglobin (Hb), the oxihemoglobin saturation (OHb%) and carboxihemoglobin saturation (COHb%). METHODS: 95 samples of blood were analyzed by both co-oximeters. The bias, or mean difference, and the limits of agreement for the bias between the results given by the two co-oximeters were calculated by the statistical method described by Bland and Altman for comparing methods of measurement. To determine the interchangeable use of the co-oximeters, we assessed clinically the 95% Confidence Intervals (CI) of the limits of agreement. RESULTS: For total Hb the bias is - 0.73 g/dl with upper limit of agreement (ULA) of 0.76 g/dl (95% CI 1.0,0.4) and lower limit of agreement (LLA) of - 2.2 g/dl (95% CI - 1.92, -2.47). For OHb% the bias is 0.6% with ULA of 3.34% (95% CI 3.84, 2.83) and LLA of - 2.1% (95% CI - 1.59, - 2.6). For COHb% the bias is 1.14% with ULA of 4 (95% CI 3.5, 4.5) and LLA of - 1.7% (95% CI - l.2, - 2.2). CONCLUSION: The limits of agreement between the AVOXimeter 4000® and the OSM3® in calculating total Hb, OHb% and COHb%, are not clinically significant. CLINICAL IMPLICATIONS: The point-of-care technology allows bedside analysis of blood samples, reducing the cost of laboratory. The AVOXimeter 4000® and the OSM3® can be used interchangeably for the calculation of total Hb, OHb% and COHb%. Polito, F., et al. Electronic Archival and Compliance System for a Point-of-Care Instrument Not Connected to the Hospital Information System. Point of Care. Journal of Near-Patient Testing & Technology: 3:187-190, 2004. Many of the point-of-care (POC) instruments in use today are not connected to central hospital information systems. Therefore, maintaining sufficient records to demonstrate regulatory compliance can be laborious and time-consuming. The cardiac catheterization labs at Dartmouth-Hitchcock Medical Center have several AVOXimeter 1000E oximeters that are used regularly to diagnose intracardiac and great-vessel shunts. Multiple blood samples are typically drawn from each patient, and each oximeter can store up to 100 readings* in non-volatile memory. The data stored in the oximeter's memory consist of both patient data and quality-control (QC) readings. Consequently, it was necessary for a POC coordinator to visit the cath labs regularly and manually transcribe or print out the QC readings in order to maintain proof of regulatory compliance, for example, to show that QC procedures were performed at specified intervals. Therefore, we developed an interface that enables the POC coordinator to upload the oximeter's stored data to a personal computer (PC) for review and electronic archival. Developing the interface required modifying the oximeter's software and writing a program for the computer receiving the data from the oximeter's serial port (RS-232C). The program called ‚"OxyReview" ** enables a POC coordinator 1) to establish serial communications with the AVOXimeter 1000E, 2) to query the oximeter to determine which software version the oximeter is using, 3) to find out how many readings are stored in the oximeter's memory, 4) to upload a user-specified number of readings, 5) to review the transferred data on the computer monitor, and 6) to store the transferred data on hard disk in a format that can be read by spreadsheet programs such as Excel® . If the oximeter is using software version vE.1.1 or later, OxyReview automatically segregates quality-control readings from patient data. The AVOXimeter sends each reading in a format based on ASTM standard 1381-91 along with a checksum that OxyReview compares with its own checksum to verify the validity of transferred data. Each reading on a patient sample consists of a sample number, operator and patient identifiers, oxyhemoglobin saturation, total hemoglobin concentration, a time-date stamp, and an optional label for the anatomical site from which the blood sample was drawn, e.g. aorta, right ventricle, pulmonary artery, etc. OxyReview runs under most recent versions of Windows. Our experience at Dartmouth-Hitchcock Medical Center indicates that this type of interface to a PC provides a paperless archive that is clinically useful to the cath lab staff and that makes it easier for the POC coordinator to demonstrate regulatory compliance. *The instruments currently store up to 500 readings in memory. **Avoximeter customers can obtain free copies of ‚"OxyReview" by sending an email request to OxyReview@avoxsystems.com |
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