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The development of a simple and reliable method for measurement of the partial pressures of the atmospheric gases offers the possibility of both basic and clinical examination of the air in natural as well as pathological or iatrogenic cavities.From measurements in nine patients a plot of the changes in pO2 and pCO2 in the pneumonectomy space from the end of the thoracotomy to the establishment of equilibrium with the blood gases was made. pCO2 equilibrated faster than pO2 (6- and 50 h respectively). The equilibrium difference between arterialp02 and pneumonectomy space p02 was 6.5 kPa (2.5-12.3 kPa) and we propose that measuring this difference may be a sensitive method for the diagnosis of bronchopleural fistula.During the study period one of the patients developed a bronchopleural fistula. The suspicion was based on X-ray findings and was supported by gas analysis from the pneumonectomy space, and conclusively confirmed by bronchoscopy.

Continuous measurement of pH, pCO2and pO2during extracorporeal circulation has become feasible using disposable fluorescence sensors (optodes). We have evaluated a commercial system: Gas-STAT (American Bentley) by reference to in-vitro measurements on discrete samples using conventional electrochemical sensors (BMS-3, Radiometer). The Gas-STAT measures at the actual temperature of the blood in the extracorporeal circuit. The reference measurements were performed at two fixed temperatures of 25 and 37 °C with interpolation of the values to the actual temperature of the Gas-STAT.10 patients undergoing coronary artery bypass grafting during hypothermic extracorporeal circulation with hemodilution were monitored in the venous as well as the arterial line with the Gas-STAT with 6–9 samplings of arterial and venous blood from each patient, a total of 136 samples.The comparisons revealed a large scatter which was due partly to inter-optode partly to intra-optode variation and partly to a memory effect which rendered the initial measurements unreliable. Omitting the first samplings, standard deviations for inter- and intra-optode variations were 0.018 and 0.030 for pH, 0.026 and 0.034 for lg pCO2, and 0.041 and 0.066 for lg pO2. There was a minor systematic difference between the Gas-STAT and the reference method for pH, the bias being 0.017; for pCO2and pO2the average bias was insignificant. The calibration slope was 0.87 for pH, 0.85 for pCO2and 1.08 for pO2(all significantly different from 1).We conclude that the calibration procedure for the Gas-STAT should be improved, for example by calibration of the pH sensor with certified pH calibration solutions, and separate calibration of the CO2and O2optodes with certified gas mixtures. The low and the high calibration values for the pO2optode should be farther apart, e.g. about 2 and 50 kPa, respectively. All 3 optodes display a memory effect, and a certain stabilization period must be allowed after establishing extracorporeal circulation. The minimum time needs to be better established. With such minor improvements the Gas-STAT would be a reliable method of continuous monitoring of pH, pCO2and pO2during extracorporeal circulation.

Modern pH and blood gas equipment, combining electrochemical and optical methods, measures pH, Pco2, po2, hemoglobin concentration, oxygen saturation, carboxy-hemoglobin, and methemoglobin. Measurements in arterial and mixed venous blood and in expired air (including measurement of expiratory ventilation) allow calculation of a series of derived quantities: concentrations of bicarbonate, total carbon dioxide, base excess, standard bicarbonate, total oxygen, 2,3-diphosphoglycerate; p50, arteriovenous CO2and O2differences, pulmonary shunting, ventilation-perfusion ratio, dead space ventilation, CO2production, O2consumption, respiratory quotient, energy metabolism, and cardiac output. Accurate measurement of carboxyhemoglobin even gives an opportunity of measuring blood volume.Equations are reviewed for these calculations including the Henderson-Hasselbalch equation for plasma and whole blood, the Van Slyke equation, the ODC-equation (hyperbolic tangent function), alveolar air equation, Bohr equation, and others. Some of the algorithms have not been previously published. The precision of the calculated quantities is evaluated on the basis of the precision of the measured quantities.

Blood pH, pCO2and pO2were measured at 37 °C and 25 °C and the temperature coefficients were calculated as δpHδT; δlg pCO2δT, and δln pO2δT.A total of 204 blood specimens were obtained from 10 patients undergoing coronary artery bypass grafting with extracorporeal circulation including hypothermia and hemodilution. Multivariate regression analysis gave the following equations:The constants in the parentheses are the mean values of the variables. There is a significant negative correlation between the two temperature coefficients. Unfortunately pH(37) and pCO2(37) were so closely correlated that it is impossible to separate the individual effects of the two, and the same applies to cHb and the plasma protein concentration. Therefore it may be fortuitous that the pH-temperature coefficient appears to vary with pCO2(not pH) while the pCO2-temperature coefficient appears to vary more with pH than with pCO2.The pO2-temperature coefficient was found to vary with pO2and cHb as previously predicted. At a very high pO2the temperature coefficient drops to an average value of 0.013; at low pO2it increases to about 0.069. Ahigh hemoglobin concentration results in a higher temperature coefficient especially at intermediate pO2values.Accurate correction of pH and blood gas values measured at 37 °C to values referring to the temperature of the patient, or conversion of values measured at the actual temperature (using extracorporeal or catheter tip continuous monitoring) to values referring to 37 °C requires more accurate temperature coefficients than are currently employed in most commercial equipment.

Modern pH and blood gas equipment, combining electrochemical and optical methods, measures pH, Pco2, po2, hemoglobin concentration, oxygen saturation, carboxy-hemoglobin, and methemoglobin. Measurements in arterial and mixed venous blood and in expired air (including measurement of expiratory ventilation) allow calculation of a series of derived quantities: concentrations of bicarbonate, total carbon dioxide, base excess, standard bicarbonate, total oxygen, 2,3-diphosphoglycerate; p50, arteriovenous CO2 and O2 differences, pulmonary shunting, ventilation-perfusion ratio, dead space ventilation, CO2 production, O2 consumption, respiratory quotient, energy metabolism, and cardiac output. Accurate measurement of carboxyhemoglobin even gives an opportunity of measuring blood volume.Equations are reviewed for these calculations including the Henderson-Hasselbalch equation for plasma and whole blood, the Van Slyke equation, the ODC-equation (hyperbolic tangent function), alveolar air equation, Bohr equation, and others. Some of the algorithms have not been previously published. The precision of the calculated quantities is evaluated on the basis of the precision of the measured quantities.

Blood pH, pCO2 and pO2 were measured at 37 °C and 25 °C and the temperature coefficients were calculated as δpH/δT; δlg pCO2/δT, and δln pO2/δT. A total of 204 blood specimens were obtained from 10 patients undergoing coronary artery bypass grafting with extracorporeal circulation including hypothermia and hemodilution. Multivariate regression analysis gave the following equations: [image omitted] The constants in the parentheses are the mean values of the variables. There is a significant negative correlation between the two temperature coefficients. Unfortunately pH(37) and pCO2(37) were so closely correlated that it is impossible to separate the individual effects of the two, and the same applies to cHb and the plasma protein concentration. Therefore it may be fortuitous that the pH-temperature coefficient appears to vary with pCO2 (not pH) while the pCO2-temperature coefficient appears to vary more with pH than with pCO2.The pO2-temperature coefficient was found to vary with pO2 and cHb as previously predicted. At a very high pO2 the temperature coefficient drops to an average value of+ 0.013; at low pO2 it increases to about 0.069. Ahigh hemoglobin concentration results in a higher temperature coefficient especially at intermediate pO2 values.Accurate correction of pH and blood gas values measured at 37 °C to values referring to the temperature of the patient, or conversion of values measured at the actual temperature (using extracorporeal or catheter tip continuous monitoring) to values referring to 37 °C requires more accurate temperature coefficients than are currently employed in most commercial equipment.

Continuous measurement of pH, pCO2 and pO2 during extracorporeal circulation has become feasible using disposable fluorescence sensors (optodes). We have evaluated a commercial system: Gas-STAT (American Bentley) by reference to in-vitro measurements on discrete samples using conventional electrochemical sensors (BMS-3, Radiometer). The Gas-STAT measures at the actual temperature of the blood in the extracorporeal circuit. The reference measurements were performed at two fixed temperatures of 25 and 37 °C with interpolation of the values to the actual temperature of the Gas-STAT.10 patients undergoing coronary artery bypass grafting during hypothermic extracorporeal circulation with hemodilution were monitored in the venous as well as the arterial line with the Gas-STAT with 6-9 samplings of arterial and venous blood from each patient, a total of 136 samples.The comparisons revealed a large scatter which was due partly to inter-optode partly to intra-optode variation and partly to a memory effect which rendered the initial measurements unreliable. Omitting the first samplings, standard deviations for inter- and intra-optode variations were 0.018 and 0.030 for pH, 0.026 and 0.034 for lg pCO2, and 0.041 and 0.066 for lg pO2. There was a minor systematic difference between the Gas-STAT and the reference method for pH, the bias being +0.017; for pCO2 and pO2 the average bias was insignificant. The calibration slope was 0.87 for pH, 0.85 for pCO2 and 1.08 for pO2 (all significantly different from 1).We conclude that the calibration procedure for the Gas-STAT should be improved, for example by calibration of the pH sensor with certified pH calibration solutions, and separate calibration of the CO2 and O2 optodes with certified gas mixtures. The low and the high calibration values for the pO2 optode should be farther apart, e.g. about 2 and 50 kPa, respectively. All 3 optodes display a memory effect, and a certain stabilization period must be allowed after establishing extracorporeal circulation. The minimum time needs to be better established. With such minor improvements the Gas-STAT would be a reliable method of continuous monitoring of pH, pCO2 and pO2 during extracorporeal circulation.

pH and blood gases were measured in simultaneous samples of arterial blood from the radial artery and mixed venous blood from the pulmonary artery using an ABL300 and OSM3 (Radiometer A/S, Denmark). Cardiac output was measured by thermodilution. The patients were suffering from chronic obstructive pulmonary disease or adult respiratory distress syndrome. The data indicate that patients respond to a decreased arterial oxygen availability by allowing the mixed venous pO2 to fall rather than by increasing the cardiac output to maintain a normal mixed venous pO2. In other words, the arterial oxygen extraction tension and the oxygen compensation factor were both highly correlated to the mixed venous pO2 but unrelated to the cardiac index. For this reason the arterial oxygen extraction tension appears to be a more relevant parameter of the overall arterial oxygen availability than the oxygen compensation factor.Comparison of the arterial and mixed venous data confirms the accuracy of the Oxygen Status Algorithm for calculating the various oxygen parameters, including the p50, the estimated 2,3-diphosphoglycerate concentration, and the estimated physiological shunt, on the basis of a single arterial blood sample.ABLTM and OSMTM are trademarks of Radiometer A/S, Denmark.

We measured pH, pCO2, pO2, oxygen saturation, total hemoglobin concentration, and fractions of carboxy-and methemoglobin in arterial blood samples from 35 healthy adults. We used a new algorithm to calculate active hemoglobin concentration, total oxygen concentration, actual half-saturation tension, 2,3-di-phospho-glycerate concentration, estimated functional shunt, oxygen extraction tension px (for extracting 2.3 mmol of oxygen per liter of blood, values below 4.5 kPa indicating risk of tissue hypoxia), and the oxygen compensation factor Qx (the factor by which the cardiac output should rise to maintain a normal mixed venous pO2 of 5.0 kPa, factors above 1.5 indicating an extra burden on the heart). Analytical precision was evaluated by duplicate determinations. The accuracy of the half-saturation tension was evaluated by comparison with values for simultaneously drawn venous blood, the accuracy of the calculated concentration of 2,3-diphosphoglycerate by comparison with direct enzymatic measurements. We conclude that all the variables may be determined with sufficient accuracy and precision in healthy adults, provided the oxygen saturation is less than 0.97 and the measurements are performed according to the highest state of the art.

The new generation of very accurate multiwavelength oximeters, e.g. OSM3, for in vitro measurement of the hemoglobin oxygen saturation, total hemoglobin concentration, and carboxy-and methemoglobin fractions opens new aspects of oxygen monitoring. Combined with the data from the blood gas analyzer (e.g. ABL300) these very accurate measurements allow the calculation of several derived oxygen parameters on the basis of a set of newly developed calculation algorithms.The traditional parameters obtained from an arterial sample are the oxygen tension (pO2) and the hemoglobin oxygen saturation (sO2). Clinical examples illustrate that the pO2 and the sO2 even in combination may give misleading information. The new algorithm calculates three extra oxygen parameters. 1) The oxygen extraction tension, px, defined as the tension required to extract 2.3 mmol of oxygen per liter blood. It signals the mixed venous pO2 level on the assumption that the arterio-venous oxygen difference is normal (2.3 mmol/L). 2) The concentration of extractable oxygen, cx, defined as the concentration of oxygen extracted at a tension of 5.0 kPa. 3) The oxygen compensation factor, Qx, derived as (2.3 mmol/L)/cx. It may be interpreted as the increase in cardiac output necessary to maintain a normal mixed venous pO2 of 5 kPa. These three parameters indicate the oxygen availability of the blood and summarize important properties of the arterial blood in relation to oxygen supply of the tissues, including the arterial pO2, the 'active' hemoglobin concentration (equivalent to the oxygen capacity), and the hemoglobin oxygen affinity (p50).The set of data measured with the blood gas analyzer, e.g. the ABL300 combined with the data measured with the OSM3 contains much more information than is routinely utilized. This information is extracted and summarized by our calculation algorithm. Omitting the calculation of the extra oxygen parameters involves a risk of losing valuable information.ABLTM and OSMTM are trademarks of Radiometer A/S, Denmark.

A multicenter study including 10079 arterial blood gas measurements were used to describe the clinical variation in the hemoglobin-oxygen dissociation curve i.e. the relationship between measured values of oxygen tension (pO2) versus oxygen saturation (sO2) and the concentration of total oxygen (ctO2).Very large variations in the actual in vivo hemoglobin-oxygen dissociation curve were found. At pO2 = 8 ± 0.5 kPa the sO2 range was 69.7 % to 99.4 %, and at sO2 = 90 ± 2 % the pO2 extremes were 3.82 and 18.3 kPa. The actual p50 varied from 2.15 to 6.44 kPa. Arterial pO2 versus oxygen content i.e. at pO2 = 8 ± 0.5 kPa the total oxygen concentration ranged from 2.04 to 10.76 mmol/L.The results indicate that it is essential to know the actual position of the hemoglobin-oxygen dissociation curve, as well as the hemoglobin concentration in the individual patient, for correct interpretation of pO2 or sO2 in arterial blood.

Measurements of pO2, pCO2and pH by optical fluorescence microsensing technology has recently become available for monitoring blood gases during extracorporeal circulation (ECC). We have compared simultaneous measurements with fiber-optic sensors (Gas-Stat®, Bentley) and electrochemical sensors (ABL-4®, Radiometer) on discrete samples.In 10 patients undergoing coronary artery bypass grafting during hypothermic (25 °C) ECC and hemodilution (hemoglobin concentration 4 mmol · 1-1) arterial and venous pO2, pCO2and pH were measured in-line in the extracorporeal circuit at the actual blood temperature. Simultaneous and anaerobically collected blood samples in glass syringes were analyzed within five minutes at 37 °C in the ABL-4.Linear regression analysis of the values at actual temperature shows the following equations: Gas-Stat Y, ABL-4 X: pO2(kPa): Y1.04 X0.5 r 0.95 n 136 pCO2(kPa): Y0.71 X 1.5 r 0.79 n 136 pH: Y 0.788 Y 1.590 r 0.76 n 136The advantage of the Gas-Stat is continuous monitoring of blood gas parameters during ECC. The present study shows that measurements of pO2, pCO2and pH with fiber-optic chemical sensors may be reliable. The differences between the two principles of measurement may be due to unknown factors interfering with the in-line measurements or to variations in sensitivity and stability of the individual sensor.

Measurements of pO2, pCO2 and pH by optical fluorescence microsensing technology has recently become available for monitoring blood gases during extracorporeal circulation (ECC). We have compared simultaneous measurements with fiber-optic sensors (Gas-Stat®, Bentley) and electrochemical sensors (ABL-4®, Radiometer) on discrete samples.In 10 patients undergoing coronary artery bypass grafting during hypothermic (25 °C) ECC and hemodilution (hemoglobin concentration 4 mmol · 1-1) arterial and venous pO2, pCO2 and pH were measured in-line in the extracorporeal circuit at the actual blood temperature. Simultaneous and anaerobically collected blood samples in glass syringes were analyzed within five minutes at 37 °C in the ABL-4.Linear regression analysis of the values at actual temperature shows the following equations: Gas-Stat = Y, ABL-4 = X: pO2 (kPa): Y=1.04 X+0.5 r = 0.95 n = 136 pCO2(kPa): Y=0.71 X + 1.5 r = 0.79 n = 136 pH: Y = 0.788 Y + 1.590 r = 0.76 n = 136The advantage of the Gas-Stat is continuous monitoring of blood gas parameters during ECC. The present study shows that measurements of pO2, pCO2 and pH with fiber-optic chemical sensors may be reliable. The differences between the two principles of measurement may be due to unknown factors interfering with the in-line measurements or to variations in sensitivity and stability of the individual sensor.