Mixed venous blood gases are superior to arterial blood gases in assessing acid-base status and oxygenation during acute cardiac tamponade in dogs.

Recent reports using anesthetized ventilator-dependent animal models, have suggested that in certain shock states, a disparity exists between arterial and mixed venous blood gases with regard to acid-base status and oxygenation. In a chronically instrumented unanesthetized canine model of acute cardiac tamponade breathing room air, we studied the effect of a graded decline in cardiac output on arterial and mixed venous pH, PCO2, and PO2. Cardiac tamponade resulted in a profound arterial respiratory alkalosis, whereas mixed venous pH, PCO2, and calculated serum bicarbonate levels remained relatively unchanged. As intrapericardial pressure increased and cardiac output declined, the difference between arterial and mixed venous PCO2 progressively increased. Further, whereas arterial oxygenation improved as cardiac output declined, mixed venous oxygenation steadily worsened. This disparity began early in cardiac tamponade (reductions in cardiac output of 20-40%) long before arterial blood pressure began to fall and progressively worsened as hemodynamic deterioration and lactic acidosis developed. Our findings are consistent with the hypothesis that a reduction in blood flow, resulting in decreased CO2 delivery to the lungs, is the primary mechanism responsible for the difference in pH and PCO2 observed between arterial and mixed venous blood. In this conscious, spontaneously breathing animal model, mixed venous blood gases thus are superior to arterial blood gases in assessing acid-base status and oxygenation, even early in acute cardiac tamponade when the decline in cardiac output is in the range of 20 to 40% and arterial blood pressure has not changed significantly.     

Ionized calcium during plateletpheresis

The concentration of ionized calcium (Ca++) during platelepheresis was monitored when donors received 461 ± 95 (mean ± S.D.) ml of anticoagulant acid-citrate-dextrose (ACD), N.I.H. formula A. Most donors experienced mild subjective symptoms (perioral tingling) during reinfusion of autologous blood. The concentration of serum Ca++ before the procedure was 4.19 ± 0.203 (mean ± S.D.) mg/dl and it decreased to 3.27 ± 0.391 (mean ± S.D.) mg/dl after the procedure. Two of the 79 donors experienced more severe symptoms (nausea, lightheadedness) while ionized calcium was lower than 3 mg/dl. Mild hypocalcemic effects could be demonstrated by electrocardiography in most donors. When donors received 414 ± 28 (mean ± S.D.) ml of ACD, N.I.H. formula B, only some of them experienced perioral tingling during reinfusion of the autologous blood. The concentration of Ca++ before the procedure was 4.18 ± 0.14 (mean ± S.D.) mg/dl and it decreased to 3.66 ± 0.14 (mean ± S.D.) mg/dl after the procedure. These data indicated that ACD N.I.H. formula B promotes greater donor comfort and safety than does ACD, formula A. The data showed that hemodilution occurred immediately following the withdrawal of one unit of blood, prior to infusion of any intravenous fluids. The analysis of the data revealed also that both magnesium and calcium entered the intravascular compartment during plateletpheresis. Although the origin of the calcium ion entering the plasma could not be established, it appeared that at least part was derived from calcium-citrate complexes.     

Ionized calcium in normal serum, ultrafiltrates, and whole blood determined by ion-exchange electrodes

Ion-exchange calcium electrodes represent the first practical method for the direct measurement of ionized calcium [Ca⁺⁺] in biologic fluids. Using both “static” and “flow-through” electrodes, serum [Ca⁺⁺] was within a rather narrow range: 0.94-1.33 mmoles/liter (mean, 1.14 mmoles/liter). Within a given individual, [Ca⁺⁺] varied only about 6% over a several month period. Consistent pH effects on [Ca⁺⁺] were observed in serum and whole blood, [Ca⁺⁺] varying inversely with pH. Less consistent pH effects were also noted in ultrafiltrates, believed to largely represent precipitation of certain calcium complexes from a supersaturated solution. Heparinized whole blood [Ca⁺⁺] was significantly less than in corresponding serum at normal blood pH, related to the formation of a calcium-heparin complex. [Ca⁺⁺] in ultrafiltrates represented a variable fraction (66.7-90.2%) of total diffusible calcium. There was no apparent correlation between serum ionized and total calcium concentrations. Thus, neither serum total calcium nor total ultrafiltrable calcium provided a reliable index of serum [Ca⁺⁺]. Change in serum total calcium was almost totally accounted for by corresponding change in protein-bound calcium [CaProt]. About 81% of [CaProt] was estimated to be bound to albumin and about 19% to globulins. From observed pH, serum protein, and [CaProt] data, a nomogram was developed for estimating [CaProt] without ultrafiltration. Data presented elsewhere indicate that calcium binding by serum proteins obeys the mass-law equation for a monoligand association. This was indicated in the present studies by a close correspondence of observed serum [Ca⁺⁺] values with those predicted by the McLean-Hastings nomogram. While these electrodes allow study of numerous problems not possible previously, they have not been perfected to the same degree of reliability obtainable with current pH electrodes. The commercial (Orion flow-through) electrode is: (a) expensive. (b) requires periodic replacement of membranes, and (c) has not yet been thermostated. As with blood pH measurements. (d) electrode response is logarithmic, i.e. small potential errors generate rather large [Ca⁺⁺] errors. (e) loss of CO₂ should be prevented, and (f) errors due to other cations must be considered under certain conditions. Despite these limitations, we believe the electrode represents a major advance in calcium metabolism.     

Differences in systemic and myocardial blood acid-base status during cardiopulmonary resuscitation

Simultaneous arterial (aortic), mixed venous (pulmonary artery), and myocardial venous (great cardiac vein) blood gas and lactate concentrations were obtained in 12 dogs before and during cardiac arrest and CPR. We observed marked mixed venous and myocardial venous acidosis and increased PaCO2 but normal pHa and reduced PaCO2. Furthermore, the pH was significantly lower and the PCO2 significantly higher at the myocardial venous site compared to the mixed venous site, and marked myocardial lactate production occurred during CPR. Calculated bicarbonate and CO2 content (CCO2) did not increase during CPR from any site compared to control values and actually decreased significantly in arterial and myocardial venous samples. Changes in hydrogen ion concentration in both mixed venous and myocardial venous blood correlated with changes in lactate concentration but not total CCO2. Our results during CPR demonstrate a) a significant discrepancy between arterial and mixed venous blood gases but also a large and significant discrepancy between mixed venous and myocardial venous blood gases, b) significant anaerobic systemic and myocardial metabolism, and c) that mixed venous and myocardial venous acidosis is possibly a result of lactic acidosis.     

Relationships of glucose concentrations in capillary whole blood, venous whole blood and venous plasma

We studied the difference in glucose levels between capillary and venous whole blood during 75-g oral glucose tolerance test (OGTT) in 75 healthy subjects. Capillary and venous whole blood glucose values were measured by HK-G6PD method after deproteinization. The post-loaded glucose levels in capillary blood were significantly higher than those in venous blood, and the mean values of capillary and venous difference at 30, 60, 90, 120 and 180 min were 1.37, 1.40, 1.07, 0.95 and 0.52 mmol/l, respectively, with the maximum difference at 60 min. No correlation was found in the magnitude of the differences in glucose between capillary and venous blood specimens. We determined the inaccuracy of six self-monitoring blood glucose devices relative to the reference method using venous plasma, venous whole blood and capillary whole blood from 31 diabetic patients. The differences of mean values of venous whole blood and capillary whole blood, and venous whole blood and venous plasma, and capillary whole blood and venous plasma were 9.6%, 11.3% and -3.2%, respectively. The range of bias and Sy/x were 0.31-1.06 mmol/l and 0.71-1.07 mmol/l, respectively, compared to the reference method using venous plasma.     

Electrocardiogram, arterial and central venous pressure during laparoscopy under local anaesthesia.

Cardiovascular hazards of laparoscopy performed under local anaesthesia and with room air pneumoperitoneum are not well known. Therefore we have recorded electrocardiogram, arterial blood pressure and central venous pressure in 63 consecutive liver patients undergoing this procedure. Electrocardiographic changes were found in 34 cases, and consisted in transistory tachycardia and bradycardia, ectopic supraventricular and ventricular beats, ST segment depression and flattening of T wave. Blood pressure did not change significantly, but five patients had transitory hypotension during the procedure. Central venous pressure did not vary immediately after inflation, but a significant increase was found during the performance of laparoscopy and it was still observed after deflation. Our findings show that cardiovascular changes during laparoscopy under local anaesthesia are minimal, and that they are probably due to neurogenic factors.     

Comparison of venous and arterial blood sampling for the assessment of platelet aggregation with whole blood impedance aggregometry

Platelet monitoring is presently under evaluation in the clinic as a tool to improve antiplatelet treatment in patients with coronary artery disease (CAD). Measuring platelet function has, however, many inherent problems. It is important not only to evaluate the method used, but also to evaluate and standardize sampling and sample handling. As platelet monitoring is often performed in connection to coronary angiography and percutaneous coronary interventions, arterial sampling may be more convenient. However, in the outpatient follow-up setting venous sampling is, for obvious reasons, more practical and convenient. In the present study we compared platelet aggregation in blood collected from the arterial sheath to blood collected from the antecubital vein using multiple electrode aggregometry in whole blood in 28 patients with CAD. We found that sampling from artery and vein give similar data and that an identical number of patients with insufficient antiplatelet responses ('low responders' to aspirin and clopidogrel, respectively, according to predefined criteria) were detected with respect to adenosine diphosphate induced and arachidonic-acid induced aggregation. Thus both arterial and venous blood samples can be used in the monitoring of platelet function when multiple electrode aggregometry is applied to detect 'low responders'.     

Using arterial blood gases to interpret acid-base balance

Arterial blood gas (ABG) interpretation can be a source of concern. However with use of the review and principles discussed in this article, the nurse's role in blood gas interpretation can become much easier.     

Acid base changes in arterial and central venous blood during cardiopulmonary resuscitation.

Twenty-seven patients in cardiopulmonary arrest had simultaneous measurements of arterial and central venous blood gases during cardiopulmonary resuscitation (CPR) with a pneumatic chest comparison and ventilation device. Mean central venous and arterial hydrogen ion concentrations, PCO2 and calculated bicarbonate concentrations were significantly different (P less than 0.01) at all sampling times (0, 10 and 20 min). Central venous blood samples predominantly showed a respiratory acidosis in contrast to a mixed disturbance in arterial samples inclined towards a metabolic acidosis. The mean difference between central venous PCO2 (pcv CO2) and arterial PCO2 (pa CO2) ranged from 5.18 to 5.83 kPa reflecting the low blood flow in patients undergoing CPR. Measurement of arterial Po2 indicated adequate oxygenation using the pneumatic device. Arterial blood gas analysis alone does not reflect tissue acid base status. Bicarbonate administration during CPR may have adverse effects and any decision as to its use should be based on central venous blood gas estimations.     

Correlation between acid-base parameters measured in arterial blood and venous blood sampled peripherally, from vena cavae superior, and from the pulmonary artery.

OBJECTIVE: In intensive care units arterial blood sampling is routine for analysing acid-base and oxygenation status. In nonintensive departments arterial blood sampling is seldom performed. Venous blood sampling is routine but not usually analysed for acid-base and oxygenation status. This study describes the correlation between arterial and peripheral, central and mixed venous pH, PCO2 and PO2 in a wide range of adult patients. METHODS: Arterial and venous blood samples were taken anaerobically and simultaneously. The values of pH, PCO2 and PO2 were compared using Bland-Altman plots. RESULTS: A total of 103 patients were included. The arteriovenous difference (bias+/-SD) for pH was 0.026+/-0.023 and for PCO2 -0.60+/-0.57 kPa (peripheral venous blood), 0.036+/-0.014 and -0.79+/-0.26 kPa (central venous blood) and 0.026+/-0.010 and -0.67+/-0.22 kPa (mixed venous blood). The arteriovenous difference for PO2 for peripheral, central and mixed venous blood was 6.27+/-4.36, 8.33+/-3.94 and 11.00+/-4.87 kPa, respectively. CONCLUSION: The venous values of pH, corrected for bias, can give arterial values which are within reasonable laboratory and clinical acceptance criteria. For PCO2 this is also true, except for peripheral blood, where the standard deviation is outside laboratory acceptance criteria but within clinical acceptance criteria. For PO2 the arteriovenous differences are not randomly distributed and even for PO2相似文献