Performance of an Electrochemical Carbon Monoxide Monitor in the Presence of Anesthetic Gases

Objective. The passage of volatile anesthetic agents through accidentallydried CO₂ absorbents in anesthesia circuits can result in thechemical breakdown of anesthetics with production of greater than 10 000 ppmcarbon monoxide (CO). This study was designed to evaluate a portable COmonitor in the presence of volatile anesthetic agents. Methods. Two portableCO monitors employing electrochemical sensors were tested to determine theeffects of anesthetic agents, gas sample flow rates, and high COconcentrations on their electrochemical sensor. The portable CO monitorswere exposed to gas mixtures of 0 to 500 ppm CO in either 70% nitrousoxide, 1 MAC concentrations of contemporary volatile anesthetics, or reactedisoflurane or desflurane (containing CO and CHF₃) in oxygen.The CO measurements from the electrochemical sensors were compared tosimultaneously obtained samples measured by gas chromatography (GC). Datawere analyzed by linear regression. Results. Overall correlation between theportable CO monitors and the GC resulted in an r² value>0.98 for all anesthetic agents. Sequestered samples produced anexponential decay of measured CO with time, whereas stable measurements weremaintained during continuous flow across the sensor. Increasing flow ratesresulted in higher CO readings. Exposing the CO sensor to 3000 and 19 000ppm CO resulted in maximum reported concentrations of approximately 1250ppm, with a prolonged recovery. Conclusions. Decrease in measuredconcentration of the sequestered samples suggests destruction of the sampleby the sensor, whereas a diffusion limitation is suggested by the dependencyof measured value upon flow. Any value over 500 ppm must be assumed torepresent dangerous concentrations of CO because of the non-linear responseof these monitors at very high CO concentrations. These portableelectrochemical CO monitors are adequate to measure CO concentrations up to500 ppm in the presence of typical clinical concentrations of anesthetics.     

Exhaled carbon monoxide in mechanically ventilated critically ill patients: influence of inspired oxygen fraction

OBJECTIVE: To assess the feasibility of exhaled carbon monoxide (CO) measurements in mechanically ventilated critically ill adult patients and to determine the influence of inspired oxygen fraction on this measurement. DESIGN: Prospective physiologic study. SETTING: Medical ICU in a community hospital. PATIENTS: The study was performed on nine mechanically ventilated patients with varying diagnoses. MEASUREMENTS AND RESULTS: Carbon monoxide concentration was determined with an infrared CO analyzer on exhaled breath collected at the outlet of the ventilator. We assessed the stability of exhaled carbon monoxide concentration over a 4-hour period and determined its course during a 7-hour period after inspired oxygen fraction had been abruptly increased from baseline to 1. Carbon monoxide was detected in exhaled breath in each patient at a higher concentration than in inspired gas (0.64 +/- 0.1 ppm vs 0.25 ppm, approximately). Exhaled carbon monoxide did not vary during a 4-hour period in five hemodynamically stable patients. When inspired oxygen fraction was increased from baseline (0.52 +/- 0.04) to 1, exhaled carbon monoxide concentration increased abruptly from baseline (0.63 +/- 0.13 ppm) to a peak value of 1.54 +/- 0.16 ppm within 15 min and returned slowly to baseline values within 7 h. CONCLUSION: CO was easily detected in the exhaled breath of mechanically ventilated patients and CO lung excretion was markedly but transiently dependent on inspired oxygen fraction. Other studies are warranted in order to determine the different factors that might influence CO lung excretion in critically ill patients.     

Single breath CO measurements normalized to 5% CO2 in Coombs' test positive neonates

A portable, prototype instrument that measures peak CO, CO2 and H2 concentrations of breath samples was evaluated on 58 antibody positive, blood group incompatible infants. The reproducibility of 108 duplicate breath CO determinations improved when the result was normalized (CO(n)) for the simultaneously measured CO2 concentration (r = 0.97 versus r = 0.87). The average CO(n) for 18 antibody positive, ABO incompatible infants who received phototherapy was 1.2 ppm higher than the average for 32 who did not receive phototherapy (p < 0.001). There was a positive correlation between CO(n) and the duration of phototherapy (r = 0.75). Sodium acetate infusion and breath H2 did not affect the CO(n) results. In antibody positive infants, single breath CO to CO2 ratios provided more reproducible results than CO determinations that were not adjusted for the CO2 concentration. Therefore, a portable instrument that measures both gases on the same aliquot of exhaled air and that is not affected by H2 should have clinical utility as an indicator of heme catabolism and bilirubin production that is not distorted by hyper- or hypoventilation.     

Effect of ventilation on breath hydrogen measurements

Measurement of hydrogen (H2) in expired air by interval sampling after oral administration of carbohydrate detects sugar malabsorption. Standard breath H2 tests require comparison of H2 concentrations in expired air samples obtained immediately before and after delivery of a test substrate. Comparison of interval samples assumes that minute ventilation (VE) remains constant unless H2 is independent of VE. Because healthy individuals have variable VE, we determined how H2 is influenced by changes in VE. H2 concentration was studied at different ventilatory rates in eight healthy adults. It varied inversely with VE in all subjects. We also compared the effect of changes in VE on the relationship between H2 and carbon dioxide (CO2) concentrations in expired air samples. At constant VE, the relationship between H2 and CO2 was linear (r = 0.95, P less than 0.001). As VE changed, the relationship between H2 and CO2 became nonlinear. Changes in VE altered methane concentrations in expired air samples from two subjects in a manner comparable to the effect on H2. These results demonstrate that breath H2 concentrations vary with ventilatory rate. Under conditions where frequent changes in VE are likely, independent measures for ensuring constant VE over sampling times are necessary. Use of CO2 as an internal standard to normalize H2 values to an alveolar concentration is appropriate only under conditions of constant VE.     

Using a refrigerant leak detector to monitor waste gases from halogenated anesthetics.

Although halogenated gas anesthetics are indispensable in laboratory animal medicine, they are hazardous when present in the working environment. A simple technique of real-time leak detection and environmental spot monitoring can provide valuable adjunct information to current techniques of time-weighted monitoring. We investigated the minimal limit of detection of halothane, isoflurane, sevoflurane, and desflurane of a leak detector for halogenated gas refrigerants which provides a qualitative response only. We connected a container to an infrared gas analyzer to create a 135-l closed-circuit system and injected liquid halothane, isoflurane, sevoflurane, and desflurane to create calculated gas concentrations of 0.7 to 3.4 parts per million (ppm). The infrared absorbance and response of the leak detector were recorded, and a total of 5 measurements were made per concentration. The actual gas concentrations were calculated by comparison with the agent-specific absorbance standard curve. The leak detector clearly and consistently responded to halothane, isoflurane, sevoflurane, and desflurane from minimal concentrations of 2.1 +/- 0.2, 1.4 +/- 0.04, 0.8 +/- 0.04, and 1.2 +/- 0.4 ppm, respectively, as determined by infrared analysis. Although the detector does not provide numerical and time-weighted results, leak testing of equipment and repeated monitoring of the environment (spot monitoring) can provide valuable real-time information. In addition, with appropriate consideration of the methodological limitations, spot monitoring can be used to predict the likelihood of compliance with time-weighted exposure recommendations. A leak detector therefore represents a simple, effective, and inexpensive instrument for monitoring the leakage of halogenated anesthetic gases from equipment and into the working environment.     

Improved gas chromatographic quantitation of breath hydrogen by normalization to respiratory carbon dioxide.

A gas-solid chromatographic system using tandem silica gel and molecular sieve columns is described for the measurement of hydrogen, carbon dioxide, oxygen, and nitrogen in samples of respiratory gases. This system has a detection limit of 2 ppm of hydrogen in a 1 ml sample and can measure 120 ppm H2 and 5% CO2 with relative standard deviations of 1.3% and 1.7%, respectively. Improved sample storage and withdrawal techniques are described that give reproducible values for up to 6 weeks after collection. Finally we show that normalization of breath hydrogen values to an alveolar concentration, using the observed carbon dioxide concentrations, substantially reduces the range and variance of apparent H2 concentrations in human subjects. Normalization eliminates the need for rebreathing or end-expiratory collection techniques and substantially increases the reliability and clinical utility of hydrogen breath measurements in noninvasive tests of carbohydrate malabsorption.     

Detection of Carbon Monoxide Production as a Result of the Interaction of Five Volatile Anesthetics and Desiccated Sodalime with an Electrochemical Carbon Monoxide Sensor in an Anesthetic Circuit Compared to Gas Chromatography

OBJECTIVES: There is a continuing risk of production of toxic levels of carbon monoxide (CO) as a result of interaction of volatile anesthetics and desiccated strong base carbon dioxide absorbents like soda lime. The aim of this study is to establish the reliability of detection of CO levels by an electrochemical carbon monoxide sensor compared to gas chromatography. METHODS: Completely desiccated sodalime was conducted through a circle anesthesia system connected to an artificial lung. For different rates of CO production, a low flow anesthesia with a oxygen/nitrous oxide mixture was maintained using five volatile anesthetics. For quantification of CO production, a portable gas chromatograph (GC) was connected to this setup, as well as a Bedfont EC40 electrochemical carbon monoxide sensor (ES) with a claimed reliable sensitivity of 0-200 parts per million (ppm) and a maximum detection range of more than 5500 ppm. To assess the agreement between the GC and ES measurements the intra class correlation coefficient (ICC) and the 95% limits of agreement were calculated. Bland and Altman scatterplots were made to visualize the difference between measurements. RESULTS: For concentrations up to 200 ppm, no significant differences between the GC and ES mean CO measurements were found in the halothane experiments. However CO was not accurately measured at every moment during these experiments by the ES. For concentrations above 200 ppm the results of the two instruments differed significantly. The ES malfunctioned when exposed to sevoflurane and desiccated sodalime. CONCLUSIONS: From these data we conclude that the ES can only be used as an indicator of CO production. When this sensor is used with sevoflurane and desiccated sodalime it is not capable of normal operation. The use of a strong base free carbon dioxide absorbent is therefore recommended.     

Monitoring of isoflurane and desflurane breakdown: interfering gases and infrared detection

Objective.The reaction of isoflurane, enflurane or desflurane with dried CO₂ absorbents produces carbon monoxide (CO), a highly toxic gas which cannot be detected by gas monitors typically available in the operating room. Trifluoromethane (CHF₃) is produced along with CO when this reaction occurs with isoflurane and desflurane, and can be detected by gas monitors. This study will determine the ability of a modified SAM module (Smart Anesthesia Multi-gas Module, GE/Marquette Medical Systems, Milwaukee, WI) to identify the presence of CHF₃, and provide a clinically useful indirect warning of CO production. Methods.Isoflurane (1.5%) and desflurane (7.5%) were reacted under clinical conditions with desiccated absorbents resulting in CO production. CO and CHF₃ concentrations were measured using gas chromatography. The CHF₃ concentrations measured by a modified SAM monitor were compared with the measurements obtained by gas chromatography. Alarm limits set on the SAM monitor were used to warn of the presence of CHF₃. Results.A concentration of 0.25% CHF₃, as measured by the SAM monitor, corresponds to an average CO concentration of 780 ppm for isoflurane and1700 ppm for desflurane. Lowering the threshold to 0.05%CHF₃ would result in an average CO concentration of 155 ppm CO for isoflurane and 345 ppm CO for desflurane. Conclusions.We have shown that the SAM module is capable of measuring CHF₃due to anesthetic breakdown. With appropriate changes in the display programming and reference cell spectra the monitor would be able to provide an early warning of CO exposure, although the amount of CO would not be reported. This revised version was published online in July 2006 with corrections to the Cover Date.     

Monitoring pulmonary function with superimposed pulmonary gas exchange curves from standard analyzers

Objective.A repetitive graphic display of the single breath pulmonary function can indicate changes in cardiac and pulmonary physiology brought on by clinical events. Parallel advances in computer technology and monitoring make real-time, single breath pulmonary function clinically practicable. We describe a system built from a commercially available airway gas monitor and off the shelf computer and data-acquisition hardware. Methods.Analog data for gas flow rate, O₂, and CO₂ concentrations are introduced into a computer through an analog-to-digital conversion board. Oxygen uptake (VO₂) and carbon dioxide output (VCO₂) are calculated for each breath. Inspired minus expired concentrations for O₂ and CO₂ are displayed simultaneously with the expired gas flow rate curve for each breath. Dead-space and alveolar ventilation are calculated for each breath and readily appreciated from the display. Results.Graphs illustrating the function of the system are presented for the following clinical scenarios; upper airway obstruction, bronchospasm, bronchopleural fistula, pulmonary perfusion changes and inadequate oxygen delivery. Conclusions.This paper describes a real-time, single breath pulmonary monitoring system that displays three parameters graphed against time: expired flow rate, oxygen uptake and carbon dioxide production. This system allows for early and rapid recognition of treatable conditions that may lead to adverse events without any additional patient measurements or invasive procedures. Monitoring systems similar to the one described in this paper may lead to a higher level of patient safety without any additional patient risk.     

A deep breath method for noninvasive estimation of cardiopulmonary parameters

A specific ventilation pattern incorporating a single deep breath is used to demonstrate the possibility of estimating six cardiopulmonary parameters by measuring respiratory flow and expired oxygen and carbon dioxide concentrations at the mouth. Equations are derived from both alternating and continuous ventilation models of gas exchange which allow the six parameter estimates to be computed. The results indicate that pulmonary capillary blood flow, functional residual capacity, equivalent lung volume, mixed venous P_O2 and P_CO2, and pulmonary tissue plus capillary blood volume can be estimated in subjects with normal gas exchange.The use of a mechanical ventilator to provide a uniform ventilation pattern before and after the ventilator induced deep breath is the key to the methods simplicity. This allowed parameter estimates to be obtained which could then be analyzed for accuracy and precision. The feasibility of estimating these parameters, demonstrated by the present study, suggests that a recursive least squares estimation procedure could be used to recover the time variation of each parameter during exercise stress testing of subjects with normal or nearly normal gas exchange.     

Single-breath CO2 analysis as a predictor of lung volume change in a model of acute lung injury

OBJECTIVE: To examine the utility of single-breath CO2 analysis as a measure of lung volume change in a model of acute lung injury. SETTING: Animal laboratory in a university-affiliated medical center. DESIGN: Prospective, animal cohort study comparing 21 variables derived from single-breath CO2 analysis with lung volume measurements determined by nitrogen washout. SUBJECTS: Seven lambs with saline lavage-induced acute lung injury. METHODS: Animals were treated with repetitive saline lavage to achieve a uniform degree of acute lung injury (PaO2 < 100 torr [13.32 kPa] on FiO2 of 1.0). Twenty-one derived components of the CO2 expirogram were evaluated as predictors of lung volume change. Lung volume was manipulated by 3-cm H2O incremental increases in positive end-expiratory pressure from 0 to 21 cm H2O and ranged between 90 and 765 mL. MEASUREMENTS AND MAIN RESULTS: Fifty-five measurements of lung volume were available for comparison with derived variables from the CO2 expirogram. Stepwise linear regression identified five variables that were most predictive of lung volume change: a) dynamic lung compliance; b) the slope of phase III; c) the slope of phase II divided by the mixed expired CO2 concentration; d) airway deadspace; and e) PaO2/FIO2 ratio. The multivariate equation was highly statistically significant and explained 94% of the variance (adjusted r2 = .94, p < .0001). The bias and precision of the calculated lung volume were 10.9 and 55.9, respectively. The mean percentage difference for the lung volume estimate derived from the single-breath CO2 analysis station was 3.3%. CONCLUSIONS: Our data indicate that analysis of the CO2 expirogram can yield accurate information about lung volume in animals with saline lavage-induced acute lung injury. Specifically, five variables derived from a plot of expired CO2 concentration vs. expired volume predict changes in lung volume in healthy lambs with an adjusted coefficient of determination of 0.94. We hope to further define the utility of this technique by prospective application of this methodology in the clinical setting.     

Validity of a disposable end-tidal carbon dioxide detector in verifying endotracheal tube position in piglets

BACKGROUND AND METHODS: the most reliable methods for confirming endotracheal tube placement are direct visualization of passage through the vocal cords and documentation of CO2 in the expired gas. We evaluated the use of a disposable colorimetric CO2 detector for verifying endotracheal tube position in small animals. The end-tidal CO2 (Petco2) detector was tested in 11 piglets with the endotracheal tube sequentially in the trachea, the esophagus, the esophagus with a carbonated beverage in the stomach, the esophagus after bag-mask ventilation. Endotracheal tube position was confirmed in all cases by direct visualization and capnometry. RESULTS: The Petco2 detector identified the tube placement accurately in all 54 (21 tracheal, 33 esophageal) intubations (p less than .001). CONCLUSIONS: This disposable Petco2 detector is highly sensitive and specific for verifying endotracheal tube placement in this nonarrest piglet model.     

Development of a protocol to measure volatile organic compounds in human breath: a comparison of rebreathing and on-line single exhalations using proton transfer reaction mass spectrometry

Analysis of volatile organic compounds (VOCs) on human breath has great potential as a non-invasive diagnostic technique. It is, therefore, surprising that no single, standard procedure has evolved for breath sampling. Here we present a novel repeated-cycle isothermal rebreathing method, where one cycle comprises five rebreaths, which could be adopted for breath analysis of VOCs. For demonstration purposes, we present measurements of three common breath VOCs: isoprene, acetone and methanol. Their concentrations measured in breath are shown to increase with number of rebreaths until a plateau value is reached by at least 20 rebreaths. The average ratio of plateau concentration to single mixed expired breath concentration was found to be 1.92 +/- 0.57 for isoprene, 1.25 +/- 0.13 for acetone and 1.12 +/- 0.12 for methanol (mean +/- standard deviation). Measurements from on-line single exhalations are presented which demonstrate a positive slope in the time-dependent expirograms of isoprene and acetone. The slope of the isoprene expirogram is persistently linear and the end-expired concentration of isoprene is highly variable in the same subject depending on the duration of exhalation. End-expired values of acetone are not as sensitive to the length of exhalation, and are the same to within measurement uncertainty for any duration of exhalation for any subject. It is concluded that uncontrolled single on-line exhalations are not suitable for the reliable measurement of isoprene in the breath and that rebreathing can be the basis of an easily tolerated protocol for the reliable collection of breath samples.     

Pulsatile uptake of CO in the human lung

The instantaneous uptake of CO in the lungs was measured with a water-filled body plethysmograph in normal man. First, control measurements of plethysmograph pressure were made while the subject held his breath for 7 sec after breathing gas mixtures prepared to bring his alveolar P(O2) and P(CO2) close to mixed venous levels. Then, CO uptake measurements were made while he held his breath after inhaling the same gas mixtures with added CO (2.0%). The change in lung volume on CO minus the change in lung volume during the control measurement was a measure of the CO uptake in the lungs. Cardiopneumatic changes in lung gas volume were subtracted electrically. All of five subjects showed pulsatile CO uptake. The mean CO uptake was 103 ml/min. A peak uptake of 2.0 (range 1.6-2.3) times the mean uptake occurred 0.3-0.4 sec after the R wave of the EKG and a minimum uptake of 0.4 (range 0.2-0.5) times the mean uptake occurred during the tenth of a second before the R wave of the EKG. These results suggest that pulmonary capillary blood volume is pulsatile during the cardiac cycle.     

The [14C]-triolein breath test is not valid as a test of fat absorption.

The [14C]-triolein breath test is used as a test of fat absorption. However, its validity has not been established. The aim of this study was to investigate, whether the absorption of [14C]-triolein could be estimated from the breath test, and whether the breath test could be useful as a clinical test. The [14C]-triolein absorption was estimated from faecal measurements, using 51CrCl3 as non-absorbable marker. The breath test was done according to the standard technique with hourly estimations of the 14CO2 expiration. Fifty-one patients participated. A nearly perpendicular, curvilinear relation between the 6-h cumulative 14CO2 expiration and the [14C]-triolein absorption was found, and no obvious cut-off level for normal 14CO2 expiration could be identified. Accordingly, the diagnostic sensitivity of the breath test was 80% at the expense of a specificity of 45%. In 19 patients duplicate measurements were done. A high intra- and inter-individual variation in the fraction of absorbed [14C]-triolein, expired within 6 h, was found. It is concluded that expiration of 14CO2 is influenced by factors other than the absorption of [14C]-triolein, and that the [14C]-triolein breath test is not useful as test of fat absorption.     

Non-invasive measurement of cardiac output in heart failure patients using a new foreign gas rebreathing technique

Values of effective pulmonary blood flow (Q(EP)) and cardiac output, determined by a non-invasive foreign gas rebreathing method (CO(RB)) using a new infrared photoacoustic gas analysing system, were compared with measurements of cardiac output obtained by the direct Fick (CO(FICK)) and thermodilution (CO(TD)) methods in patients with heart failure or pulmonary hypertension. In 11 patients, of which three had shunt flow through areas without significant gas exchange, the mean difference (bias) and limits of agreement (+/- 2 S.D.) were 0.6 +/- 1.2 litre x min(-1) when comparing CO(FICK) and Q(EP), and -0.8 +/- 1.3 litre x min(-1) when comparing CO(FICK) and CO(TD). When correction for intrapulmonary shunt flow was applied (i.e. calculation of CO(RB)) in all 11 patients, the bias between CO(FICK) and CO(RB) was 0.1 +/- 0.9 litre x min(-1), primarily because agreement improved in the three patients with significant shunt flow. In the eight patients without significant shunt flow, the agreement between Q(EP) and CO(FICK) was 0.3 +/- 0.9 litre x min(-1). In conclusion, a foreign gas rebreathing method with a new infrared photoacoustic gas analyser provided at least as reliable a measure of cardiac output as did thermodilution. In the absence of significant shunt flow, measurement of Q(EP) itself provides a reliable estimate of cardiac output in heart failure patients. The infrared photoacoustic gas analyser markedly facilitates clinical use of the rebreathing method in general, which makes the method available to a larger group of clinicians working with patients with cardiovascular diseases.     

Subcutaneous measurements of133 Xe disappearance with portable CdTe(CI) detectors: elimination of interference from combined convection and diffusion

Summary. Portable, solid state, cadmium telluride [CdTe(C1)] detectors were used for measurements of ¹³³Xe-disappearance rate constants as a measure of subcutaneous (s.c.) blood flow. To eliminate the disturbance on the measurements from combined local convection and diffusion of xenon in the s.c. tissue, two methods were demonstrated to be feasible in both control persons and anaesthetized rabbits. A small volume (50–80 μ1) was injected into the s.c. tissue at a depth of 5 mm and the CdTe(C1) detector elevated 20 mm above the skin surface. In this situation identical disappearance rate constants were recorded by the CdTe(C1) detector and the Nal(T1) reference detector at 15–20 cm from the depot. Similar results were obtained when either a large volume ( 800 μ1 of Xe in humans) was injected into the s.c. tissue or the labelling was performed with a smaller volume in an atraumatic uniform manner to obtain a constant Xe concentration exceecling the field of view of the CdTe(C1) detector, which in these cases was attached directly to the skin surface. The coefficients of variation (CV) of the disappearance rate constants measured by the CdTe(C1) detector were 9% and 11%, and these values did not differ significantly from each other (P>0·2), or from CV-values calculated from measurements with NaI(T1) detectors.     

Systematic instrumental errors between oxygen saturation analysers in fetal blood during deep hypoxemia

BACKGROUND: During a study of artificially produced deep hypoxemia in fetal cord blood, systematic errors of three different oxygen saturation analysers were evaluated against a reference CO oximeter. Methods: The oxygen tensions (PO2) of 83 pre-heparinized fetal blood samples from umbilical veins were reduced by tonometry to 1.3 kPa (10 mm Hg) and 2.7 kPa (20 mm Hg). The oxygen saturation (SO2) was determined (n=1328) on a reference CO oximeter (ABL625, Radiometer Copenhagen) and on three tested instruments (two CO oximeters: Chiron865, Bayer Diagnostics; ABL700, Radiometer Copenhagen, and a portable blood gas analyser, i-STAT, Abbott). The CO oximeters measure the oxyhemoglobin and the reduced hemoglobin fractions by absorption spectrophotometry. The i-STAT system calculates the oxygen saturation from the measured pH, PO2, and PCO2. The measurements were performed in duplicate. Statistical evaluation focused on the differences between duplicate measurements and on systematic instrumental errors in oxygen saturation analysis compared to the reference CO oximeter. RESULTS: After tonometry, the median saturation dropped to 32.9% at a PO2=2.7 kPa (20 mm Hg), defined as saturation range 1, and to 10% SO2 at a PO2=1.3 kPa (10 mm Hg), defined as range 2. With decreasing SO2, all devices showed an increased difference between duplicate measurements. ABL625 and ABL700 showed the closest agreement between instruments (0.25% SO2 bias at saturation range 1 and -0.33% SO2 bias at saturation range 2). Chiron865 indicated higher saturation values than ABL 625 (3.07% SO2 bias at saturation range 1 and 2.28% SO2 bias at saturation range 2). Calculated saturation values (i-STAT) were more than 30% lower than the measured values of ABL625. CONCLUSION: The disagreement among CO oximeters was small but increasing under deep hypoxemia. Calculation found unacceptably low saturation.     

Carbon monoxide … the silent killer with an audible solution

Carbon monoxide (CO) is responsible for more poisoning fatalities each year than any other toxic agent. The often insidious nature of the symptom progression and its ability to imitate many common illnesses may result in the failure to diagnose a potentially fatal outcome. CO detectors equipped with an audible alarm can alert potential victims of CO poisoning before toxic sequelae develop. A study was conducted in which all calls to 911 concerning a CO detector in alarm or regarding possible CO poisoning were investigated by a paramedic crew; 101 possible CO exposures were investigated. CO detectors with audible alarms were the genesis of 59.4% of the calls. Detectable CO levels were found in 69.3% of the investigations, and 80% of the homes with detectors had verifiable CO concentrations. The mean CO concentration in homes with detectors was 18.6 ppm, compared with 96.6 ppm when no detector was available; 63.4% of the victims with no alarm were symptomatic, compared with 13.3% of victims with alarms. CO detectors with audible alarms were effective in alerting the potential victims of CO poisoning to its presence. Persons with CO detectors were less likely to become symptomatic from a CO exposure than those who did not have CO detectors.     

Inaccuracy of lipid measurements with the portable Cholestech L.D.X analyzer in patients with hypercholesterolemia.

BACKGROUND: Although total cholesterol concentrations measured by portable lipid analyzers have acceptable bias and precision in young and middle-aged adults, clinically relevant differences in HDL-cholesterol (HDL-C) and triglyceride values have been described. Furthermore, the accuracy of portable lipid analyzers in older hyperlipidemic individuals, who have a high incidence of coronary heart disease, has not been validated. This study determined the biases and variability in portable lipid measurements in older patients with hypercholesterolemia and related them to National Cholesterol Education Program Adult Treatment Panel III guidelines. METHODS: Participants were > or =70 years of age with fasting serum LDL-cholesterol (LDL-C) concentrations > 1.40 g/L. Fasting fingerstick samples were analyzed on a Cholestech L.D.X desktop analyzer. Antecubital venous samples were analyzed in a proficiency-certified clinical laboratory. RESULTS: Portable measurements systematically overestimated triglycerides (0.296 g/L; P <0.001) and HDL-C (0.015 g/L; P = 0.026). LDL-C concentrations were underestimated (0.043 g/L; P = 0.046). Total and non-HDL cholesterol calculations based on the portable lipid device provided unbiased estimates, but wide variability was present. Significant variability in lipid determinations limited their clinical usefulness in individual patients, especially because 2 SD of the mean bias between the laboratory and the portable determinations of LDL-C and non-HDL cholesterol exceeded the 0.30 g/L cutoff that defines treatment targets in the current lipid guidelines. CONCLUSIONS: Lipid values obtained from portable lipid analyzers may be useful for screening, but they should not be used to make clinical decisions regarding the diagnosis and management of dyslipidemia in individual patients.