Conventional Blood Gas Analysis Research Articles

Evaluation of an on-demand, ex vivo bedside blood gas monitor on pulmonary artery blood gas determinations.

Critically ill patients often have cardiopulmonary perturbations that require rapid and frequent assessment for optimal care, including cardiac output determinations, measurement of cardiac filling pressures, and arterial and mixed venous blood gas determinations. We evaluated the performance of a rapid, on-demand bedside blood gas monitor to determine arterial and mixed venous blood gas values. The blood gas monitor uses fluorescent optode technology to directly measure Po2, Pco2, and pH. This measurement is accomplished by aspirating blood from the artery or vein into a sampling chamber where it interfaces with the fluorescent optode. After approximately 90 s of equilibration, the blood gas values are reported. Since the blood is drawn into the sampling chamber, it can be returned to the patient, thus eliminating the need for phlebotomy. We studied 15 critically ill patients requiring systemic and pulmonary arterial catheterization. Conventional blood gas analysis was performed simultaneously. The results obtained from the blood gas monitor were compared with those obtained via traditional blood gas analysis using Bland-Altman plots and examination of bias and precision. The results were well within the expected clinical variance. During the study period, there was no interference with patient care or adverse events related to the use of the monitoring system. In conclusion, the blood gas monitor can provide rapid, accurate determinations of arterial and mixed venous blood gases allowing optimal therapeutic interventions in critically ill patients.

Clinical evaluation of a new continuous intraarterial blood gas monitoring system in the intensive care setting

The present study was designed to evaluate a new continuous intraarterial blood gas monitoring system under routine clinical intensive care conditions. Nine mechanically ventilated adult patients were enrolled in this study. A multiparameter intravascular sensor was inserted into the radial or dorsalis pedis artery through a 20-gauge cannula in each patient. The accuracy of the sensor for pH, Pco2, and Po2 values was evaluated by comparing the data simultaneously obtained from the monitoring system and from conventional blood gas analysis. Measurements were performed for 3 days for each sensor. A total of 62 blood samples were obtained for comparison. The ranges of measured variables were: pH 7.185-7.602, Pco2, 28.8-68.5 mmHg, and Po2 45.2-542.4 mmHg. The overall bias ±precision values were 0.002±0.018 for pH units, 0.53±2.04mmHg for Pco2, and -1.62±20.00 mmHg for Po2. In clinically important ranges of Po2, less than 200 mmHg in particular, the bias and precision values were -2.25±6.48 mmHg in the range of less than 100mmHg, and 0.98±14.38 mmHg in the range of 100-200 mmHg. Variations of sensor accuracy as a function of elapsed time were within the clinically acceptable range throughout the study period. These findings suggest that this new device is sufficiently useful for routine clinical settings.

Measurement of blood CO2 concentration with a conventional PCO2 analyzer.

CO2 content can be determined from the Pco2 in an acidified (forces all CO2 into solution) and diluted blood sample. However, Pco2 concentrations measured in conventional blood gas analyzers are only correct for samples with a significant buffer capacity (such as whole blood), so that mixing with the Pco2 in the rinse solution and tubing walls does not significantly change the sample Pco2. This study describes a calibration method and validation data for the Radiometer Medical ABL2 CO2 electrode system to accurately measure unbuffered blood samples used in the determination of blood CO2 content (or other aqueous fluids). Prospective, criterion standard. Laboratory. Blood samples (0.4 mL) were acidified and diluted with 0.2 M lactic acid. After measuring Pco2, CO2 content was calculated using the CO2 solubility coefficient and the dilution factor of 20. CO2 content was determined in a series of sodium carbonate (Na2CO3) solutions spanning the physiologic range of CO2 content. Regression of the measured vs. the actual CO2 content data generated a straight line with a slope of 0.796 and y-intercept of 12.5 (r2 = .99; n = 48). These coefficients were successfully used to correct CO2 content determined in blood samples into which graduated amounts of sodium carbonate were added. This calibration procedure allows accurate measurement of Pco2 in aqueous samples using the Radiometer ABL2 electrode system, and should be applicable to other blood gas analyzers. Necessary syringes and chemicals are readily available, the method is fast and simple, and the sample volume is small. In the practice of critical care medicine, accurate Pco2 measurement in aqueous acidified and diluted blood provides direct determination of blood CO2 content (useful in calculations of modified Fick cardiac output or tissue CO2 production). Determinations of absolute CO2 content in blood requiring complex methodology are not necessary. In addition, accurate measurement of aqueous gastric Pco2 can help determine gastric pH, which is an important marker of tissue perfusion.

Long-term evaluation of a continuous intra-arterial blood gas monitoring system in patients with severe respiratory failure.

The purpose of this study was to evaluate the reliability and accuracy of a new continuous intra-arterial blood gas monitoring system (IABG; PB3300, Puritan Bennett) over a prolonged period of time (> 7 days). Prospective criterion standard study. Anesthesiological intensive care unit in a university hospital. 11 sensors were tested in 10 mechanically ventilated patients with severe respiratory failure. PO2, PCO2, and pH measured using IABG were compared to values obtained from 2 conventional blood gas analyzers. The quality of blood pressure tracings was assessed using a scoring system consisting of 5 grades. The median study period was 205h/sensor (range: 169-506h). 320 blood samples were obtained. The ranges of measured parameters were: PO2 = 46-433 mmHg, PCO2 = 25-79 mmHg, pH = 7.25-7.55. The mean (SD) differences for the whole study period were: -4.3 (11.9) mmHg for PO2, for the clinically important range (PO2 < 150 mmHg) -1.9 (5.4) mmHg, -2.8 (4.5) mmHg for PCO2, and -0.03 (0.04) for the pH value. The MD (SD) in relation to the sensor lifetime were for days 1-3: -1.1 (5.1) mmHg for PO2, -0.4 (3.9) mmHg for PCO2, and -0.01 (0.03) for the pH value; for days 4-6: -1.5 (6.0) mmHg for PO2, -3.3 (4.0) mmHg for PCO2, and -0.03 (0.03) for the pH value; for days 7-9: -2.5 (4.7) mmHg for PO2, -5.1 (4.6) mmHg for PCO2, and -0.04 (0.04) for the pH value; for days > 9: -4.9 (4.4) mmHg for PO2, -5.3 (4.1) mmHg for PCO2, and -0.05 (0.03) for the pH value. The IABG reliably measured blood gases and pH values with acceptable clinical performance based on the overall results. There was, however, a decline in the agreement of the sensors and conventional values with increasing sensor lifetime. The mean differences (bias) and the standard deviation of differences (precision) of PO2, PCO2 and the pH values were acceptable for clinical purposes up to day 6. The arterial blood pressure tracings and blood withdrawal were not adversely affected. No side effects due to the sensors occurred. In summary, a prolonged sensor use for a period of up to 6 days appears to be reasonable. This system offers on-line information on oxygenation, ventilation, and acid-base status and allows immediate detection of acute and potentially life-threatening events.

Continuous Intra-arterial Blood Gas and pH Monitoring in Critically Ill Patients with Severe Respiratory Failure

HALLER, MATHIAS; KILGER, ERICH; BRIEGEL, JOSEF; FORST, HELMUTH; PETER, KLAUS Author Information

Continuous intra-arterial blood gas and pH monitoring in critically ill patients with severe respiratory failure

To evaluate the routine clinical performance of a new intra-arterial fiberoptic blood gas sensor that provides continuous PO2, PCO2, and pH monitoring. Criterion standard study under routine clinical conditions. Intensive care unit (ICU) in a university hospital. Twenty-two sensors were tested in 13 patients with acute respiratory failure, including two patients receiving veno-venous extracorporeal lung assist. Patient selection was based on the necessity of frequent blood gas monitoring. Sensor-deprived PO2, PCO2, and pH values were compared with values obtained using two different conventional laboratory blood gas analyzers located in the ICU. The median study period was 72 hrs per sensor (range 8 to 170 hrs). The quality of blood pressure readings with the sensor introduced through the arterial catheter was assessed by a grading system. Mean differences between sensor-derived values and the average values of the two conventional blood gas analyzers were as follows: PO2 -2.4 +/- 6.5 (SD) torr (-0.3 +/- 0.9 kPa), PCO2 -2.9 +/- 3.9 torr (-0.4 +/- 0.5 kPa), and pH -0.04 +/- 0.03. Correlation coefficients were 0.99 (PO2), 0.94 (PCO2), and 0.89 (pH), respectively. The agreement between the two methods for PO2 measurement was better for the clinically important range of values (PO2 < 150 torr [< 20 kPa]) than for all measured PO2 values (range 30 to 522 torr [4 to 69.6 kPa]). Blood withdrawal and pressure readings were not adversely affected by the sensor. No side effects due to the insertion of the sensor were observed. The degree of agreement of intra-arterial blood gas sensor values with conventional blood gas analysis is within an acceptable range for routine clinical purposes. Acute changes in measured values are detected reliably. Continuous intra-arterial blood gas analysis can add substantially to the safety of patients with acute respiratory failure and can reduce blood sampling requirements for blood gas analysis.

Development of a patient-dedicated, on-demand, blood gas monitor.

A new monitor (CDI 2000) that brings blood gas measurements to the patient's bedside has been developed. To measure blood gases, blood is drawn into the patient's arterial pressure-monitoring line past in-line fluorescent-based sensors. After measurement, the blood is returned to the patient, avoiding blood loss and delays in sample turnaround and reducing the risk of infection to both patient and operator. We assessed this system's performance in vitro with tonometered bovine blood. Bias (mean difference between monitor and tonometered gas or measured pH values) +/- the standard deviation (SD) were 0.01 +/- 0.02 at pH = 7.39; 0.0 +/- 0.7 mm Hg at Pco2 = 39 mm Hg; and 2.4 +/- 3.2 mm Hg at a Po2 = 100 mm Hg (n = 54). Changes in hematocrit, blood temperature, or serum sodium concentration did not have clinically significant effects on system performance. Studies in normal volunteers, in whom large changes in blood gases were induced, showed a bias (mean difference between monitor and IL 1306 values) +/- SD of 0.00 +/- 0.02 for pH, -0.4 +/- 2.0 mm Hg for Pco2, and -3.6 +/- 7.7 mm Hg for Po2 (n = 69). We conclude from the present study that the performance of this system is comparable to that of conventional blood gas analyzers.

Inhaled nitric oxide reverses hypoxic pulmonary vasoconstriction without impairing gas exchange

Nitric oxide (NO) is an endogenous endothelium-derived relaxing factor that participates in the regulation of vascular tone. We studied the effects of inhaled NO gas on transient hypoxic pulmonary vasoconstriction and normal lungs in mechanically ventilated sheep. We measured hemodynamics and pulmonary gas exchange. For gas exchange measurements we used conventional blood gas analysis and the multiple inert gas elimination technique to estimate ventilation-perfusion heterogeneity. Our hypotheses were 1) inhaled NO reverses hypoxic pulmonary vasoconstriction, 2) the hemodynamic effects of inhaled NO are limited to the pulmonary circulation, and 3) inhaled NO does not impair pulmonary gas exchange and may redistribute blood flow to better ventilated areas of the lungs. Hypoxic pulmonary vasoconstriction was induced by using a hypoxic inspiratory gas mixture. The addition of 20 ppm NO to the hypoxic inspiratory gases returned pulmonary arterial pressure to baseline values. Systemic hemodynamics and gas exchange indexes derived from conventional blood gas analysis remained constant. Gas exchange indexes for ventilation-perfusion ratios and gas dispersions improved. The addition of 20 ppm NO to medical air (21% O2) had no such significant effects on hemodynamics or pulmonary gas exchange. Our findings show that inhaled NO reverses transient hypoxic pulmonary vasoconstriction. The hemodynamic effects of NO are limited to the pulmonary circulation; it does not impair pulmonary gas exchange. Moreover, it redistributes blood flow to better ventilated alveoli. As such, NO has potential in the treatment of lung diseases associated with pulmonary hypertension.

Continuous blood gas monitoring in haemodialysis using an electrode inserted in the extracorporeal dialysis circulation.

The aim of this study was to evaluate the usefulness of continuous gas monitoring during haemodialysis using an oxygen- and carbon dioxide-sensitive electrode inserted in the 'arterial' line from the arteriovenous fistula. We investigated 15 patients with chronic renal failure, treated with regular bicarbonate haemodialysis. The PO2 and PCO2 were measured by the new method and compared to conventional blood gas analysis of the 'arterial' blood from the dialysis circulation. We found the in situ gas sensors were stable and there was no systematic difference between gas tensions measured by in situ and conventional blood gas measurements. The standard deviations of the difference between paired measurements for PO2 and PCO2 were 1.3 and 0.4 kPa, respectively. Therefore, the method can be used to detect major changes in blood gas tensions during haemodialysis.

Role of the gut in shock and resuscitation

Summary Data from animal experiments supported by circumstantial evidence from patients indicate that anaesthesiologists have the potential to reduce the morbidity and mortality from surgery and in the critically ill by preventing or limiting in duration the development of an intramucosal acidosis in the stomach. An intramucosal acidosis in the stomach is one of the earliest manifestations of compensated shock, a condition in which there is inadequate tissue oxygenation in a patient who appears by conventional criteria to be adequately resuscitated. The intramucosal pH in the stomach may be conveniently measured with a TRIP-tonometer combined with a conventional nasogastric tube, a sample of arterial blood and access to a conventional blood gas analyser. The intramucosal pH in the stomach is linearly related to the intramucosal pH in the small and large gut and to the lactate concentration in hepatic venous blood. An inadequacy of oxygen delivery, an increased metabolic demand for oxygen and an impaired ability to extract and utilize the oxygen are important causes of an intramucosal acidosis. The development of an intramucosal acidosis induces an increase in mucosal permeability and superficial mucosal injury, and thereby promotes the translocation of enteric bacteria and toxins and the associated release of toxic mediators. These substances are the putative causes of the low cardiac output syndrome, nosocomial infections from enteric organisms and multiple systems organ failure, the most common cause of morbidity and mortality in the critically ill today. By definition, resuscitation from compensated shock can only be complete when all evidence of defective tissue oxygenation, including the associated intramucosal acidosis in the gut, has been eliminated. Empirical efforts designed to prevent the development of compensated shock improve outcome. In many patients with defective tissue oxygenation, increasing oxygen delivery restores the adequacy of tissue oxygenation. In some patients evidence of defective tissue oxygenation persists or even increases despite hyperresuscitative efforts. Novel and aggressive therapeutic approaches are justified in ICU patients and in those having cardiovascular operations whose intramucosal pH remains low for 5–12 hours, for the mortality in these circumstances approaches 100%. Novel therapeutic strategies being considered in these circumstances include ACE inhibitors, monoclonal antibodies to endotoxin, gut lavage, selective decontamination of the gut, abdominal exploration for infarcted gut, and resection or exteriorization and gut lavage for those without transmural infarction.

Evaluation of a new instrument offeringsodium, potassium, and ionized calcium incombination with haematocrit, pH and bloodgas analysis; the performance of the NovaStat Profile 1

The Nova Stat Profile 1 analyser, a combined sodium, potassium, ionized calcium, haematocrit and conventional blood gas analyser, was evaluated over a four month period. In addition to assessing and demonstrating that the instrument met analytical requirements, an appreciation of the use of ionised calcium (iCa) was made. Prospective costs were characterised and practical problems of iCa measurement addressed.

Optimizing ventilatory settings using pulse oximetry in the transition between life and death

In the patient with catastrophic lung disease intra- and extrapulmonary factors interact to determine the O2-delivery to the peripheral lifethreathened organs. The therapeutic strategy will take into account both settings on the ventilator that are not harmful to the patient i.e. avoiding high peak airway pressures and high inspired oxygen fractions and circulatory support keeping the cardiac output adequate. Usually the arterial blood gases are frequently monitored as parameters determining optimal therapy. Recently pulse oximetry has been suggested as a noninvasive continuous monitoring method. It could be looked upon as an indicator and monitor of both ventilatory and circulatory optimality, because the parameter tells what “the sensor sees.” This might not be identical to the “true arterial saturation”, but it can be argued that this does not matter as long as the trend observed is useful in therapeutic decision making.In this study 25 patients with catastrophic lung disease i.e. a) panlobar alveolar infiltrates, b) a PaO2 >7.00 kPa with an FIO2 > 0.8 with 15 cm H2O PEEP and a cardiac index above 3.5 L/min/m2 and c) an effective compliance below 25 ml/cm H2O were studied and ventilatory and circulatory adjustments were made in order to reduce peak airway pressure to below 50 cm H2O and the FIO2 to below 0.6. Fourteen patients were randomised to monitoring with pulse oximetry and eleven to conventional arterial blood gas analysis. Using pulse oximetry the median time for optimization was 45 min with a range of 20–120, without pulse oximetry the median time was 95 min with range 60–240, p <0.05.It is concluded that pulse oximetry is a fast, reliable index of peripheral O2-delivery and can be regarded a “new parameter” in optimizing ventilatory strategy.

Transconjunctival Oxygen Monitoring as a Predictor of Hypoxemia During Helicopter Transport

As the use of helicopters for air transport of critically ill patients increases, the availability of monitoring devices for physiological parameters during flight becomes important. It has long been known that arterial PO2 (PaO2) decreases during unsupplemented, non-pressurized flight. In this study, the authors examined the use of the transconjunctival oxygen (cjO2) monitor for assessing the adequacy of arterial oxygenation during helicopter flight in four healthy volunteers. Arterial PaO2 as measured by conventional blood gas analysis was compared with cjO2 at ground level, 5,000 feet, and 10,000 feet altitude. Mean PaO2 dropped significantly from 93.5 to 81.5 to 58.5 mm Hg, respectively (P less than 0.001, analysis of variance with repeated measures). Mean cjO2 also decreased significantly from 63.8 to 52.0 to 34.8 mm Hg, respectively (P less than 0.001, analysis of variance with repeated measures). Within individual subjects, cjO2 was an accurate predictor of PaO2 (P less than 0.001, multiple regression analysis). The relationship between cjO2 and PaO2 was linear with a regression coefficient of 1.147. The authors conclude that the transconjunctival O2 monitor may be useful for monitoring the adequacy of arterial oxygenation during helicopter flight in hemodynamically stable patients. The results of study also support the use of supplemental oxygen in all patients subjected to helicopter transport.

Correlation of gas exchange impairment to development of atelectasis during anaesthesia and muscle paralysis

Pulmonary gas exchange and the development of atelectasis were studied in eight essentially lung-healthy patients, awake and during halothane anaesthesia with mechanical ventilation. Gas exchange was evaluated by a multiple inert-gas elimination technique and conventional blood-gas analysis, and atelectasis was studied by computerized tomography (CT). Ventilation and lung perfusion were well matched in the majority of the patients when awake. In two patients there was low perfusion of poorly ventilated regions (low VA/Q). One patient had a shunt corresponding to 4% of cardiac output. None of the patients showed signs of atelectasis on the CT scans. After 15 min of anaesthesia, shunt had appeared in all patients, ranging from 1% in two patients (unchanged from the awake state) to 17%. The major VA/Q mode was widened and ventilation of poorly perfused regions (high VA/Q) was noted in seven patients. Densities in dependent lung regions (interpreted as atelectasis) were seen on the CT scans in six patients. The extent of atelectasis was significantly correlated both to the magnitude of shunt (r = 0.93, P less than 0.01) and to the impairment of arterial oxygenation (r = 0.99, P less than 0.001). The findings indicate that atelectasis in dependent lung regions during halothane anaesthesia creates shunting of blood flow and that atelectasis is the major or sole cause of impaired gas exchange in the lung-healthy, anaesthetized subject.

Transconjunctival oxygen monitoring as a predictor of hypoxemia during helicopter transport

As the use of helicopters for air transport of critically ill patients increases, the availability of monitoring devices for physiological parameters during flight becomes important. It has long been known that arterial P O 2 (Pa O 2 ) decreases during unsupplemented, non-pressurized flight. In this study, the authors examined the use of the transconjunctival oxygen (cjO 2 ) monitor for assessing the adequacy of arterial oxygenation during helicopter flight in four healthy volunteers. Arterial Pa O 2 as measured by conventional blood gas analysis was compared with cjO 2 at ground level, 5,000 feet, and 10,000 feet altitude. Mean Pa O 2 dropped significantly from 93.5 to 81.5 to 58.5 mm Hg, respectively (P 2 also decreased significantly from 63.8 to 52.0 to 34.8 mm Hg, respectively (P 2 was an accurate predictor of Pa O 2 (P 2 and Pa O 2 was linear with a regression coefficient of 1.147. The authors conclude that the transconjunctival O 2 monitor may be useful for monitoring the adequacy of arterial oxygenation during helicopter flight in hemodynamically stable patients. The results of study also support the use of supplemental oxygen in all patients subjected to helicopter transport.

Continuous intra-arterialPo2monitoring with a surface heparinized catheter electrode

Surface-heparinized catheter PO2 electrodes were used for continuous intra-arterial monitoring in non-heparinized dogs. During one-day experiments the read-out of the electrode monitoring unit was compared with that of conventional blood gas analysis. Furthermore, the electrodes were studied after long-term implantation. The intra-arterial PO2 electrodes have previously been reported to be linear in the gas phase, water phase and in heparinized blood. The present study demonstrates that the catheter electrodes remain linear after surface heparinization. As compared with the conventional blood gas analysis it was found that the desk analyser in the range PaO2 greater than 18 kPa underestimated the actual PaO2 as compared to the invasively monitored PaO2, but in the range below 7 kPa the desk analyser overestimated the PaO2. Surface-heparinized PO2 catheter electrodes were studied after up to 23 days of implantation. No coagulation phenomenon was found around the catheters, neither macroscopically nor by scanning electron microscopy. The electrical function withstood 7 days of implantation. After more extended periods the electrical leads were broken without any damage to the catheter itself. When compared with acutely implanted surface-heparinized electrodes, there was no difference in monitoring characteristics between the acutely implanted and the long-term implanted PO2 electrodes.

PolarographicpO2sensors with heparinized membranes forin vitroand continuousin vivoregistration

The membranes of the pO2 sensor in a conventional blood gas analyser and a commercially available catheter pO2 electrode were coated with a glutardialdehyde stabilized heparin layer. It was analysed whether or not the "non-thrombogenic" heparin surface could improve the accuracy of in vitro pO2 registration and continuous in vivo paO2 monitoring. The in vivo experiments were performed on anaesthetized and non-anticoagulated dogs. Two identical blood gas analysers were used, one furnished with a heparin coated pO2 membrane and the other with a standard pO2 membrane. In vitro pO2 determinations exhibited--when simultaneously analysing the same blood sample--identical mean values. For repeated pO2 determinations, however, the standard deviation was significantly lower on the analyser furnished with a heparinized membrane. The non-heparinized catheter pO2 electrode showed a marked deterioration in accuracy with time as compared with blood-gas analysis on reference blood samples. Falsely low paO2 values were presented. The heparinized catheter electrode monitored values in full agreement with those of the conventional blood gas analyser using standard membranes. It is concluded that the heparin surface on the oxygen diffusible membranes diminishes the variability of the diffusion characteristics both at contact with anticoagulated blood in vitro and during in vivo paO2 monitoring. The "non-thrombogenic" heparin surface prevents diffusion impeding clot formations when an arterial catheter pO2 sensor is used.

ON-LINE Po2 AND PN2o ANALYSIS WITH AN IN VIVO CATHETER ELECTRODE

A technique was developed for the in vivo determination of PO2 and PN2O with a catheter electrode using double-pulse polarography. The method was evaluated in dog studies comparing readings from the electrode with those from a mass spectrometer employing an in vivo probe. The oxygen readings obtained from the catheter electrode were also compared with values obtained by conventional blood-gas analysis. Good agreement was observed between the electrode and the mass spectrometer for both PO2 and PN2O. Similar agreement was found between the electrode readings and blood-gas analysis for PO2. In the presence of halothane, the electrode over-read for both PO2 and PN2O; a remedy is suggested. The in vivo electrode provides an effective, less expensive, alternative to the mass spectrometer for the on-line measurement of PO2 and PN2O in vivo.

Continuous variability of fetal Po2 in the chronically catheterized fetal sheep

A method of continuous monitoring of fetal intravascular Po2 at various sites in the circulation in the chronically catheterized fetal sheep for up to 41 days (mean 11.1 days) has been compared with values obtained in blood samples measured extracorporeally in a standard blood gas analyzer. A double-blind comparison of the two methods showed that there was no bias between the two methods and correlation was 0.94. The stability of the electrodes was superior to that of a conventional blood gas analyzer. In every animal there was continuous variability of fetal vascular Po2. In the period from 105 to 126 days' gestation we noted the presence of slow increases in basal uterine tone that we have called “contractures.” The frequency of these contractures was very regular at approximately one per hour. There is a statistically significant related fall in fetal vascular Po2 in relation to these contractures. Well-coordinated uterine contractions during labor also produced a fall in fetal vascular Po2 that was related to the uterine activity.

Quality-Control System for Blood pH and Gas Measurements, with Use of a Tonometered Bicarbonate—Chloride Solution and Duplicate Samples of Whole Blood

Abstract We describe a procedure for the simultaneous quality control of pH, pco2,and po2 measurement. A solution of NaCl (150 mmol/liter) and NaHCO3 (50 mmol/liter) is equilibrated at room temperature (24 ± 2 °C) with a gas having the composition 21% O2, 12% CO2, 67% N2. When this solution is analyzed at 37 °C in a conventional blood-gas analyzer, a pH of 7.20, a pco2 of 110 mmHg (14.6 kPa) and a po2 of 170 mmHg (22.6 kPa) are obtained. We show that data from such an analysis, performed daily, can be simply used to meet many of the unique demands of quality control in blood pH and gas determinations. This same approach may also become the basis for devising an ideal aqueous system for blood gas calibration.