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Consequences of postoperative alterations in respiratory mechanics.

Abstract In patients undergoing extrathoracic surgical procedures, upper abdominal operations led to the most significant reductions in vital capacity, tidal volume, and functional residual capacity. The degree of fall in vital capacity correlated with the development of a clinical pulmonary complication. After upper abdominal surgery there was a delay of sixteen hours prior to a fall in the functional residual capacity. Decrease in surfactant activity is the mechanism proposed for this volume change. In a series of seriously ill patients, changes in the functional residual capacity were related to the degree of arterial hypoxemia. Elevation in the functional residual capacity toward normal resulted in a decrease in the physiologic shunt. Failure to correlate hypoxemia with radiologic evidence of segmental atelectasis is consistent with peripheral alveolar collapse or decrease in alveolar ventilation because of small airway closure.

Transfusion of 2,3 DPG-Enriched Red Blood Cells to Improve Cardiac Function

Attempts were made to enhance oxygen availability in patients undergoing coronary artery bypass operations by transfusing red blood cells enriched in 2,3 diphosphoglycerate (2,3 DPG) to 150% of normal. In this study of 22 patients, 11 received red blood cells with high 2,3 DPG levels and 11 received red blood cells with 70% of normal 2,3 DPG levels (control). Immediately following cardiopulmonary bypass the 11 patients who received high 2,3 DPG red blood cells had a P50 value of 31.6 mm Hg; the value in control patients was 28.3 mm Hg (p less than 0.05). Oxygen consumption values were 135 and 106 ml/min/m2, respectively (p less than 0.05). Mixed venous oxygen tensions were similar in the two groups, but the arteriovenous content difference was higher in the high 2,3 DPG group (p less than 0.05). Cardiac indices increased significantly in response to a fluid load in the high 2,3 DPG group compared with controls at comparable filling pressures. We believe the improved myocardial performance in response to a fluid challenge is a result of increased oxygen availability.

Cardiac Output Measurement by Thermodilution during Cardiac Operations

Measurement of cardiac output by the thermodilution (COTD) technique through a flow-advanced pulmonary artery catheter is simple, reliable, and practical at the bedside. Rapid repeat determinations are possible, facilitating dynamic description of myocardial performance through construction of ventricular function curves. Replicate determinations of cardiac output indicate that the thermodilution method is more accurate than the indocyanine green technique. Examples of the clinical application of COTD in cardiac surgical patients are provided.

The risks in abdominal and thoracic surgery in copd

Most pulmonary complications following surgery in patients with COPD result either from failure to recognize the presence of the lung disease beforehand or from relative neglect during the first few hours after operation.

Indicator Dilution Measurements of Lung Volumes and Alveolar Air Exchange During Breathing

A new triple tracer indicator dilution technique has been used to measure alveolar ventilation as well as air and tissue volumes in the lungs of experimental animals and man. The tracers indocyanine green, [(121)I]antipyrine and xenon-133 were rapidly injected into the right atrium, while sampling was carried out from a peripheral artery. Blood flow and tissue volumes were obtained by classical analysis of the indocyanine green and antipyrine concentration-time curves. A double exit-port, constant air flow model was used to analyze the xenon curves, because ventilatory loss led to incomplete recovery of the gas tracer in effluent blood. Uniform ventilation and perfusion were assumed. This analysis permitted calculation of alveolar ventilation (VA(Xe)) and functional residual capacity (FRC(Xe)) during normal breathing. In control studies, VA(Xe) was similar to VA(co2), obtained with the steady-state CO(2) method (r = 0.87), while in critically ill patients the xenon measurement was significantly lower, averaging 54% of VA(co2). In theory, underestimates in VA(Xe) and decrease in the ratio VA(Xe)/VA(co2) relate to nonuniformity in regional ventilation and perfusion. The effect is greatest for the slightly soluble gas, xenon. The significant inverse correlation between VA(Xe)/VA(co2) and the physiologic shunt is consistent with this postulate.FRC(Xe) was similar to the predicted FRC in animals but was 76% of the helium measured FRC in patients. FRC(Xe) was significantly lower than the xenon measured air volumes during breath-holding when nonuniformity of ventilation was not operative. Lung tissue volumes in animals were 83% of gravimetric lung weights, while in patients the volumes were much lower than predicted. Nonhomogeneous lung function, including failure to perfuse the entire capillary bed, with resultant incomplete penetration of tracers into all segments of lung air and tissue, may explain these findings. The resultant errors can be significant in sick patients, and may themselves be used to study nonhomogeneities in the distribution of ventilation and volume.

P50 Determinations: Techniques and Clinical Importance

The oxyhemoglobin dissociation curve demonstrates the relationship between the partial pressure of oxygen and the percent hemoglobin carrying oxygen. The decrease in this percentage as blood passes from the arterial to venous side of tissue is indicative of the amount of oxygen delivered to that tissue. The four controlling factors governing oxygen delivery to tissue are: oxyhemoglobin concentration, blood flow, tissue PO2 and hemoglobin affinity for oxygen.1 If the affinity of hemoglobin increases, then compensation must occur or there will be a corresponding decrease in oxygen delivery to the tissue. The forms of compensation are increased blood flow (cardiac output), increased oxyhemoglobin concentration or decreased tissue PO2.1 P50 is the PO2 at which hemoglobin is 50% saturated with oxygen. It’s value defines relative changes in oxygen-hemoglobin affinity. To test the hypothesis that decreases in P50 are potentially harmful to an acutely ill individual, we developed procedures for rapidly and easily determining P50.