Myron B. Laver

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...

Cardiovascular Response to Large Doses of Intravenous Morphine in Man

Abstract Large doses of intravenous morphine (0.5 to 3.0 mg per kilogram of body weight) were used alone or in combination with inhalation anesthetic agents for anesthesia in over 1100 patients undergoing open-heart surgery. Morphine, 1 mg per kilogram, was administered intravenously to seven subjects with aortic-valve disease and eight without major heart or lung disease. The cardiac subjects had higher control pulse rates and lower control stroke indexes than the normal subjects. In the cardiac but not in the normal subjects, significant increases in cardiac index, stroke index, central venous pressure, and pulmonary-artery pressure, and a significant decrease in systemic vascular resistance, were observed after morphine was administered, suggesting that large doses of morphine may be used with safety in patients with minimal circulatory reserve.

Pulmonary Complications and Water Retention in Prolonged Mechanical Ventilation

Abstract In a retrospective study of 100 patients treated with prolonged mechanical ventilation, water retention without evidence of cardiac failure developed in 19. This was associated with radiologic evidence of pulmonary edema and with the following significant changes: a mean gain in weight of 2.6 kg; a mean increase in the alveolar-arterial oxygen tension gradient of 127 mm of mercury; a decrease in vital capacity of 29 per cent; a reduction in estimated compliance of 31 per cent; a fall in hematocrit of.13 percent; and a decrease in serum sodium of 5.80 mEq per liter. These changes were reversed after the institution of a negative water balance by restriction of water intake and by diuretic therapy. Radiologic improvement was usually prompt. The appearance of pulmonary edema may be related to a relative water overload, a rise in antidiuretic hormone production or subclinical cardiac failure.

Pulmonary barotrauma during mechanical ventilation

In the treatment of acute respiratory failure, pulmonary barotrauma (subcutaneous emphysema, pneumothorax, and pneumomediastinum) developed in ten patients (10%) receiving IPPV without PEEP and in seven patients (11%) receiving IPPV with PEEP. Pre-existing chronic obstructive pulmonary disease seemed to predispose to the development of pulmonary barotrauma. Necropsy findings revealed the presence of pneumonitis and pulmonary edema in the majority of patients, in addition to pulmonary emphysema in some. Available information fails to demonstrate a correlation between the incidence of pulmonary barotrauma and the magnitude of air-way pressure required for adequate mechanical ventilation. The addition of PEEP to IPPV during therapy for acute respiratory failure does not in-crease the incidence of pulmonary barotrauma.

Low Plasma Ionized Calcium and Response to Calcium Therapy in Critically Ill Man

Marked lowering of plasma ionized calcium concentrations [Ca++] occurred in eight patients (2 days to 54 years old) who required extensive pharmacologic support of the circulation. [Ca++]s ranged from 0.21 to 0.53 mM. Only one patient survived. The hypocalcemia occurred in the absence of massive transfusion of citrated whole blood or well after such transfusions had been discontinued. These abnormally low concentrations of ionized calcium were not readily corrected by intravenous administration of calcium salts in doses generally recommended. The process responsible for inadequate hemodynamic function appeared to be associated with a severe disturbance in calcium metabolism. Contribution of the latter to the severity of hemodynamic deterioration is unclear, and little benefit from intravenous calcium therapy was found. In two patients, normal [Ca++] could not be restored by administration of CaCl2 alone, but [Ca++] rose to normal following continued calcium replacement therapy in conjunction with increased isoproterenol infusion. There was no predictable relationship between total and ionized plasma calcium concentrations. Thus, measurement of total calcium provided no indication of the level of the biologically active moiety. [Ca++] was low with both normal and low plasma [Ca++] values. The data suggest that a very high infusion rate of CaCl2 may be required to restore [Ca++] to normal and that hypocalcemia occurring during low-flow states often cannot be corrected by calcium therapy alone. It is recommended that calcium replacement therapy be undertaken only with close monitoring of [Ca++].

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...

Left Ventricular Performance and Pulmonary Circulation Following Addition of Nitrous Oxide to Morphine during Coronary-artery Surgery

The effects of nitrous oxide on ventricular performance and pulmonary circulation were studied in 12 patients with angiographically demonstrated coronary-artery disease and normal ventricular contractility who had received 2 mg/kg morphine intravenously. Seventeen studies were performed intraoperatively, five before and 12 after cardiopulmonary bypass and myocardial revascularization. Recordings were obtained during oxygen breathing and during nitrous oxide administration. Fifty per cent nitrous oxide significantly decreased mean arterial pressure (P < 0.05), cardiac index (P < 0.01), stroke index (P < 0.01), left ventricular stroke work index (P < 0.01), peak left ventricular dP/dt (P < 0.05) and dP/dt/P (P < 0.01), and heart rate-systolic arterial pressure product (P < 0.01). Mean pulmonary arterial pressure (P < 0.05), pulmonary artery occluded pressure (P < 0.01). left ventricular end-diastolic pressure (P < 0.01) and pulmonary vascular resistance (P < 0.05) increased. Heart rate, right atrial pressure and systemic vascular resistance remained unchanged. When nitrous oxide was discontinued. all variables returned to control except mean pulmonary arterial pressure and pulmonary vascular resistance. Responses were similar before and after cardiopulmonary bypass and myocardial revascularization. These findings suggest that nitrous oxide depresses left ventricular performance when administered intraoperatively to patients who have received large doses of morphine for coronary-artery surgery. Nitrous oxide also increases pulmonary vascular resistance. possibly via alpha-adrenergic stimulation.

Inappropriate response to increased plasma ADH during mechanical ventilation in acute respiratory failure.

The effect of mechanical ventilation (IPPV) and positive end-expiratory pressure (PEEP) on plasma ADH was studied in eight patients with acute respiratory failure. The study was divided into two 60-minute periods, PEEP of 10 cm H2O being added to IPPV during first or second hour in random order. Mean decreases in urinary flow from 1.11 to 0.78 ml/min (P < 8.05) and cardiac index (determined in six patients) from 4.3 to 3.4 1/min/m2 (P < 0.01) were observed with PEEP. Although a twofold increase in plasma ADH (mean 8.1 to 18.8 μU/ml, P < 0.05) following PEEP was associated with a decrease in urinary flow, inconsistent changes in free-water and osmolal clearance and urinary osmolality point to an inappropriate response to increased ADH. The decrease in urinary flow and concurrent reduction in urinary sodium excretion suggest an overriding influence of the decrease in cardiac index on renal function.

The Effect of Hemodilution with Albumin or Ringer's Lactate on Water Balance and Blood Use in Open-Heart Surgery

To determine the effect of intraoperative albumin administration on blood use, water balance, and postoperative clinical course, we studied two groups of adult cardiac surgical patients. Group I (30 patients) received 25 gm of albumin during withdrawal of 2 units of blood prior to cardiopulmonary bypass (CPB) and 50 gm of albumin in the oxygenator prime. Group II (32 patients) received no albumin prior to the end of CPB. No difference in clinical course could be identified, nor was there a significant difference in blood use. Group I patients had lower hematocrit values intraoperatively from the time of blood withdrawal until the conclusion of operation. Coronary artery bypass operations were associated with greater positive water balance than were heat valve operations. Forty-three percent of the patients having coronary artery bypass grafting had a positive water balance greater than 5 liters, whereas 50% of those undergoing valve procedures had a balance less than 3 liters. We conclude that the principal effect of withholding albumin under these circumstances is to increase net positive water balance. The greater positive water balance does not appear to be detrimental.