The effect of heparin on blood gas analysis.
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Blood gas analysis of chest tube drainage following thoracostomy for experimental and clinical penetrating chest injuries was evaluated to determine its usefulness in predicting the etiology of the injury. Twenty dogs were divided into four groups and sustained right chest injury as follows: Group I--closed chest lung laceration; Group II--open chest lung laceration; Group IIII-gunshot wounds; Group IV--thoracotomy and injection of autologous, mixed venous blood. All animals and 14 patients who sustained penetrating chest injury were made simultaneously from chest tube draininage, systemic artery, and central vein in all dogs and patients. Eight patients (Group A) had pneumothorax; six patients (Group B) did not. Mean control canine aortic PO2 and pulmonary arterial PO2 values in Group I did not differ significantly from those in the other three canine groups, nor from the two human groups. Group II dogs exhibited chest tube PO2 which was significantly (p less than 0.01) above aortic PO2. In Group IV, chest tube PO2 was increased significantly above pulmonary arterial blood. Patients without pneumothorax had values for PO2 in chest tube drainage and aorta which were not significantly different, whereas when pneumothorax was present, PO2 of chest tube drainage was significantly higher than that of aortic PO2. Thus blood gas determinations on chest tube drainage may reflect the nature of the injury; however, the presence of air in the pleural space can result in oxygenation of contained blood well above systemic arterial levels.
Evaluation of a new system, based on gas chromatography, providing arterial blood gas tensions without requiring drawn blood samples is continued in an animal model. A series of in vivo dog experiments is discussed evaluating flow dependence and other performance characteristics. Results confirm the laboratory bench performance reported earlier; clinical trials are now indicated.
In modern blood gas analysis heparin is used for preventing coagulation in the syringe and the analyzer. If the amount of heparin added is too large the pH of the blood sample falls and so an artificial metabolic acidosis is induced. Consequently the amount of heparin used should be just enough to prevent blood coagulation without changing appreciably the acid-base status of the sample. High concentrations of inspired oxygen have no additional effect on the ability of heparin to alter the pH values.
The literature data concerning respiratory function in cirrhosis of the liver are cited and reference is made to the results of a spirometric, gas analysis and 133-Xenon investigation of this parameter in 38 patients. Spirometry pointed to slight ventilatory incapacity of the restrictive type. Arterial gas analaysis showed respiratory alkalosis, usually accompanied by metabolic acidosis and slight hypoxyaemia. Examination with 133-Xe indicated that hypoxyaemia was not due to a shunt effect, since there was no excess of perfusion with respect to district ventilation. It was clear, on the other hand, that the pulmonary capillary reserve was almost exhausted. Such complete perfusion of the capillary bed may be due to increased cardiac output and, in part, to reduction of the respiratory surface caused by raising of the diaphragm and hypoventilation of the lung bases.
Oxygen saturation was determined non-invasively with the oxygenmet pulse wave oximeter 1471 and mathematically from the pH and pO2 of the blood gas analysis. The determination of the oxygen saturation by the aid of the oximetric method was carried out on fingers, metacarpus and wrist of 80 infants (male = 44, female = 36 - ages: 1 day - 1 year and 8 months). Blood gas analysis was done just behind the oximetric analysis and oxygen saturation was calculated from the pH and pO2. The comparison of the oxygen saturations determined non-invasively on fingers, metacarpus and wrist among themselves, showed no statistical significant differences. Also no statistical significant differences were observed between the results obtained with the pulse wave oximeter and the results calculated from the blood gas analysis. The comparison of the oxygen saturations determined with the oxygenmet oximeter (mean of fingers, metacarpus, wrist) with the oxygen saturations calculated from the blood gas analysis showed a very close correlation. The correlation coefficient was 0.930.
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We undertook an external quality control survey of blood-gas analysis in 16 laboratories at 13 hospitals. All samples were prepared in the laboratories under investigation by equilibration of blood or serum with gas mixtures of known composition. pH of serum was measured with no significant bias but with an SD of random error 0.026 pH units, which was almost twice the SD of the reference range (0.015). An acceptable random error (half SD of reference range) was not obtained in a longitudinal internal quality control suvey although there were acceptable results for buffer pH in both field and internal surveys. Blood PO2 was measured with no significant bias but with SD of random error 1.38 kPa which reduced to 0.72 kPa by excluding one egregious result. The latter value was just over half of the SD of the reference range (1.2 kPa). PCO2 of blood was also measured without significant bias but with a much smaller SD of random error of 0.28 kPa (by excluding one egregious result), which was again just over half the SD of the reference range (0.51 kPa). Measurements of blood PO2 and PCO2 seem generally acceptable in relation to their respective reference ranges but measurements of pH were unsatisfactory in both internal and external trials.
The Department of Labor has set guidelines for the use of resting arterial blood gas analysis in determination of total and permanent disability for coal workers' pneumoconiosis. To determine the prevalence with which bituminous coal miners fall below the arterial tensions of both oxygen and carbon dioxide published in the Federal Register, we studied 1012 miners who had both reproducible spirometry and arterial blood gas analysis as part of their disability evaluation. Eighty-seven percent of impaired miners could be identified by the spirometric criteria. Thirteen percent of impaired bituminous coal miners had acceptable pulmonary function but were eligible for black lung benefits by the blood gas guidelines. This population would have been missed if blood gas analysis were excluded from the evaluation process. On the other hand, approximately 25% of the blood gas analyses that were performed could be eliminated if a policy was adopted to do this test only on miners with spirometry that exceed the federal guidelines.
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The effect of heparin on the measurement of blood gases is mainly caused by dilution, which substantially reduces the PCO2 and HCO3- values. Excess heparin will change the pH, PCO2 and 3- as a consequence of an alternation in H+ ionconcentration. The effect of dilution on electrolytes depends on the respective electrolyte concentration in diluent. Dilution reduces the glucose value, but to a higher degree as could be expected from a dilution effect. Heparin binds electrolytes and influences the results, especially the calcium ion. As a result of this investigation we recommend the 20IU or less heparin be used for multi-electrolyte determination with or without blood gas analysis, and that the dilution of sample be maintained at less than 5%. In other words, at least a 3ml or 2ml blood sample should be collected in a 5ml or 2ml glass syringe, the corresponding heparin concentration is 400kU/L or less.
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In 61 patients with chronic cor pulmonale with compensation and decompensation of circulation, the stroke and minute heart volume were studied as well as the indices, characterizing the blood-gas contents and acid-base blood state. The minute heart volume in the patients examined proved to be with normal values. Stroke heart volume is decreased in all patients examined with chronic cor pulmonale. The acceleration of heart activity enables the maintenance of normal minute volume. Hypoxemia has a cardiac depressive effect as regards minute volume and heart rate. The moderate hypercapnia has a certain stimulating effect on heart. A direct proportional correlation exists between the hypercapnia degree and the tendency of minute volume increase and especially of heart rate. The campaign against hypoxemia is an essential element in the prophylaxis and early treatment of chronic cor pulmonale.
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Benzodiazepines for sedation may decrease the PaO2, the arterial O2 saturation (SaO2), and the CO2 response more in the elderly than in the young. The purpose of this study was to assess changes in blood gases due to i.v. midazolam or sublingual flunitrazepam given as premedication in elderly patients for unilateral cataract surgery. METHODS. Fifty patients over 65 years of age with treated arterial hypertension and other co-existing diseases (ASA III-IV) were randomly assigned to have: (1) i.v. midazolam titrated until they became drowsy (17 patients; 2.85 +/- 0.84 mg [mean +/- SD]); (2) sublingual flunitrazepam (16 patients; 0.005 mg/kg); or (3) no sedation (17 patients; controls). On entering the operating theatre, the radial artery was cannulated and the first blood gas analysis was obtained. The premedication was then given. At 5, 10, 20, and 30 min after premedication, before and 10 min after retrobulbar block, before operation, 5 and 15 min after the beginning of the operation, 10 and 20 min after administration of 500 mg acetazolamide i.v. during the operation, and 10 and 20 min after the operation additional arterial blood samples were analysed (a total of 15 measuring points). Pulse oximetry, invasive blood pressure, and ECG were continuously monitored. All patients received oxygen 3 l/min during the operation by nasal cannula. Differences between the three groups were analysed by Student's t-test or U-test and a P value < 0.05 was considered significant. RESULTS. The patient demography, including duration of anaesthesia and operation, was similar in the three groups (Table 1). No significant differences were seen in heart rate, mean arterial pressure, PaO2, pulse-oximetric oxygen saturation (SpO2), base excess, or serum bicarbonate levels. The PaCO2 increased in patients after midazolam (P < 0.01) and flunitrazepam (P < 0.05) until the beginning of the operation compared with the control group (Fig. 3); 20 min after the operation there was still a significant difference between the midazolam group and the controls. SaO2 was significantly (P < 0.05) lower in the midazolam group 10 and 20 min after administration of premedication compared with the control group, but was within physiological limits (Fig. 5). Despite titration, 2 patients had severe respiratory insufficiency 3 min after midazolam: the SpO2 decreased below 85% and the paO2 below 55 mmHg. The paCO2 was higher (P < 0.05) in the midazolam group 10 min after acetazolamide compared with the controls. CONCLUSIONS. The results of the study show the potential hazards of i.v. midazolam in the elderly. If sedation is required for cataract surgery under local anaesthesia, we recommend sublingual flunitrazepam or the use of benzodiazepines with lower hypnogenic effects in the elderly. A thorough preoperative discussion of anaesthesia and the operation might be an adequate substitute for any premedication in high-risk patients; the best blood gas analysis results were obtained in the control group.
Forty-two interns and residents on the staff of a community teaching hospital were questioned to assess their understanding of blood gas abnormalities. Misunderstandings were such that 24% of the residents and interns might have given inadequate care had their interpretations dictated practice. Few therapeutic misadventures in fact occurred, largely because of supervision. Even without supervision, it is unlikely that much harm would have come about, partly because pattern recognition and rules of thumb provided adequate guidance and partly because no notice was taken of the results of the blood gas analysis anyway. Those who wish to promote rational practice should direct their educational efforts to improved understanding of the mechanisms of hypoxaemia and of the chemical, physiological and pathophysiological interactions of PCO2, bicarbonate and pH in the various acid-base disorders.