H. Pontoppidan

Acute Respiratory Failure in the Adult

Effect of Mechanical Ventilation and Airway Pressures on Circulation and Blood Gas Exchange The ventilatory pattern is defined by: the inspiratory and expiratory flow rates and pressures, including...

Hemodynamic responses to mechanical ventilation with PEEP: the effect of hypervolemia.

The hemodynamic effects of prolonged mechanical ventilation with positive end-expiratory pressure (PEEP), with and without blood volume augmentation, were studied in 18 beagles anesthetized with halothane (0.7 per cent end-tidal). Addition of 12 cm H2O PEEP during mechanical ventilation in normavolemic dogs was associated with reductions of transmural cardiac filling pressures, cardiac index and stroke index to 50 per cent of control values. Circulatory adaptation did not occur. Filling pressures and flow remained unchanged during the ensuing 8 hours when PEEP was maintained. They returned to control levels when PEEP was discontinued, except for the transmural right ventricular end-diastolic pressure, which remained elevated above control levels. Systemic vascular resistance was unchanged, but pulmonary vascular resistance doubled upon addition of PEEP. Following autologous whole blood transfusion (25 ml/kg) during mechanical ventilation with PEEP, cardiac index returned to, and remained at, control levels. After PEEP was discontinued, cardiac index increased acutely and remained elevated for the remainder of the study period (as long as 7 hours). Comparable transfusion during mechanical ventilation without PEEP elevated cardiac index only transiently. Right atrial, pulmonary capillary wedge, and right and left ventricular end-diastolic pressures showed marked increases relative to atmospheric with PEEP and after transfusion. Calculated transmural pressures demonstrated clear reductions with application of PEEP, followed by increases to control levels with transfusion and further increases to above control when PEEP was discontinued. Study of ventricular function curves revealed that changes in filling pressures and not to changes in ventricular contractility. Transmural pulmonary arterial diastolic pressure rose throughout the 12 hours of study, despite return of pulmonary vascular resistance to control level with removal of PEEP. Thus, acute decreases in cardiac filling pressure, cardiac index, and stroke index persist consequent to application of PEEP, and circulatory adaptation does not occur. The apparent hemodynamic deterioration may be reversed by blood volume augmentation, but when PEEP is discontinued, hypervolemia with consequent increases in filling pressures and a move along a ventricular function curve will occur. Changes in cardiac index will depend upon the overall state of right and left ventricular contractility.

Continuous Positive-Pressure Ventilation in Acute Respiratory Failure

Abstract Continuous positive-pressure ventilation was used in eight patients with severe acute respiratory failure. Cardiac output and lung function were studied during continuous positive-pressure ventilation (mean end-expiratory pressure, 13 cm of water) and a 30-minute interval of intermittent positive-pressure ventilation. Although the mean cardiac index rose from 3.6 to 4.5 liters per minute per square meter of body-surface area, the mean intrapulmonary shunt increased by 9 per cent with changeover to intermittent positive-pressure ventilation. Satisfactory oxygenation was maintained in all patients during continuous positive-pressure ventilation with 50 per cent inspired oxygen or less. With intermittent positive-pressure ventilation arterial oxygen tension promptly fell by 161 mm of mercury, 79 per cent occurring within one minute. Prevention of air-space collapse during expiration and an increase in functional residual capacity probably explain improved oxygenation with continuous positive-pressur...

Ventilation and Oxygen Requirements during Prolonged Artificial Ventilation in Patients with Respiratory Failure

IN a person with normal lungs the amount of ventilation that is sufficient to eliminate the carbon dioxide produced (and thus to maintain carbon dioxide homeostasis) is predictable with considerabl...

The response of patients with respiratory failure and cardiopulmonary disease to different levels of constant volume ventilation.

The purpose of this study was to determine the effect of increasing the tidal volume on pulmonary ventilation-perfusion relations in patients with respiratory failure caused by cardiopulmonary disease. The frequent occurrence of an increased physiologic dead space (2, 3) and of increased physiologic shunting (3) in patients undergoing prolonged artificial ventilation has previously been described. These changes in ventilation-perfusion ratios mean that very large tidal volumes and high percentages of inspired oxygen are often required to maintain life during prolonged intermittent positive pressure ventilation. The aim of our study was to measure the consequences of changing the tidal volume, but not the respiratory frequency, of patients with respiratory failure secondary to either acute intrapulmonary infection or chronic pulmonary emphysema.

Arterial Oxygenation During Hypothermia

The aims of this stady were: to investigate a possible significant relation between the size of the tidal volume during constant volume ventilation and the rate of change of the alveolar-arterial oxygen tension gradient (AaDO2): to determine whether hypothermia significantly affects this relationship; and to test the accuracy of correction factors previously proposed for the effect of temperature on the oxygen tension of fully saturated blood. Ten patients were surface cooled to 30° C. for over 24 hours. Anesthesia consisted of pentobarbital sodium and d-tubocurarine. Constant volume pulmonary ventilation with 100 per cent oxygen was provided by a piston pump. A significant relationship (P < 0.01) was found between the size of the constant tidal volume and the rate of increase or decrease of the AaDO2. This relation showed little evidence of being affected by hypothermia per se. The accuracy of previously determined temperature correction factors for oxygen tension was confirmed.

Positive airway pressure in lambs spontaneously breathing air and oxygen

The effects of 10 cm H2O positive endexpiratory pressure (PEEP) were studied in 26 unrestrained Hampshire and Corriedale lambs, breathing spontaneously air or pure oxygen. No changes in lung morphology, pulmonary mechanics or arterial blood gas tensions were detected after air breathing with 10 cm H2O PEEP for one week. No changes were found in mean pulmonary artery pressure, pulmonary capillary wedge pressure, pulmonary vascular resistance or cardiac output in oxygen breathing lambs until minutes before death. Addition of PEEP to oxygen breathing accelerated the development of respiratory acidemia and death (PEEP group mean lifespan 5434 hr, without PEEP mean lifespan 7134 hr). Morphologic changes of acute oxygen toxicity were present in oxygen breathing lambs and lung water was increased. Oxygen breathing lambs died from apnea with hypercarbia and a markedly increased (A-a) DO2. An increase in pulmonary vascular resistance or right ventricular failure do not appear to be major factors in the syndrome of fulminant acute respiratory insufficiency due to oxygen toxicity in lambs.

Case 22-1966

Presentation of Case First admission. A seventy-two-year-old man entered the hospital because of dyspnea. He had been well until nine years previously, when an aneurysm of the abdominal aorta was f...