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Biomedical subjects

J B Downs

Publications and source records attributed to J B Downs.

At least 19 recordsLinked to original sources
PubMed1979

Alteration of oxygen tension and oxyhemoglobin saturation. A hazard of sodium bicarbonate administration.

The administration of sodium bicarbonate solution, which has been advocated for the treatment of metabolic acidosis, may have detrimental side effects. We evaluated oxyhemoglobin saturation and oxygen tensions in eight anesthetized swine before and after freshwater near-drowning and after a rapid intravenous infusion of 7.5% sodium bicarbonate solution (8 mEq/kg). After freshwater aspiration, arterial and venous oxygen tensions and oxyhemoglobin saturation decreased. Administration of sodium bicarbonate resulted in decreased venous and increased arterial, oxygen tensions. Arterial, but not venous, oxyhemoglobin saturation increased. These findings suggest that sodium bicarbonate caused a distinct leftward shift in the oxyhemoglobin dissociation curve, which could impair tissue oxygenation. Therefore, to avoid detrimental effects, sodium bicarbonate should be administered slowly and in a dose sufficient just to correct metabolic acidosis.

Acidosis↗
PubMed1979

Lung expansion, airway pressure transmission, and positive end-expiratory pressure.

Transmission of airway pressure to the intrapleural space and change in functional residual capacity by positive end-expiratory pressure (PEEP) were measured in ten anesthetized swine. Measurements and calculations were performed with varying lung and chest wall compliances. When both compliances were normal, approximately half of the applied airway pressure was transmitted. Aspiration of hydrochloric acid reduced lung compliance approximately fourfold and decreased airway pressure transmission. Increased thoracic compliance also reduced airway pressure transmission. When acid aspiration reduced lung compliance and sternotomy simultaneously increased thoracic compliance, pressure transmission was maximally reduced. Decreases in either thoracic or lung compliance reduced the volume-expanding effects of PEEP. Positive end-expiratory pressure was least effective when thoracic and lung compliances were reduced simultaneously. Careful assessment of both lung and thoracic compliances may be helpful in treating patients requiring elevated airway pressure.

Animals↗
PubMed1979

Renal function and cardiovascular responses during positive airway pressure.

The authors determined cardiovascular, renal, and hormonal responses to increased airway pressure during continuous positive-pressure ventilation (CPPV) and continuous positive airway pressure (CPAP). Nine healthy, hydrated laboratory swine had appropriate catheters placed to allow for measurement of intrapleural, aortic, inferior vena caval, and left ventricular end-diastolic pressures; cardiac output; and urinary flow. Samples of arterial blood were analyzed for oxygen and carbon dioxide tensions, pH, plasma vasopressin, osmolality, and creatinine and sodium concentrations. Urine was analyzed for osmolality and creatinine and sodium concentrations, and volume was recorded. Intrapleural pressure was subtracted from left ventricular end-diastolic pressure to calculate transmural pressure, a reflection of left ventricular filling pressure. Glomerular filtration rate and urinary free-water and osmolal clearances were also calculated. Expiratory left ventricular filling pressure was decreased equally by CPAP and CPPV. However, inspiratory left ventricular filling pressure and cardiac output were decreased by CPPV only. Urinary flow and glomerular filtration rate were decreased equally by CPAP and CPPV. Sodium excretion was decreased and plasma vasopressin increased by CPPV, but not by CPAP. Urinary free water and osmolal clearances were not changed by either ventilatory pattern. Although many of the renal-function variables were affected similarly by CPPV and CPAP, these alterations were not influenced solely by cardiac output or vasopressin, because only CPPV depressed cardiac output and increased vasopressin levels.

Animals↗
PubMed1979

Comparison of assisted and controlled mechanical ventilation in anesthetized swine.

We compared assisted mechanical ventilation with controlled mechanical ventilation with and without PEEP in 10 anesthetized swine. Catheters were placed to measure airway, intrapleural, and blood pressure; PaO2 and PaCO2; arterial pH; total minute ventilation; and mixed exhaled oxygen and carbon dioxide tensions. We calculated the ratio of physiological dead space to tidal volume, alveolar minute ventilation, CO2 production, VO2, and RQ. We found no clinically or statistically significant difference between assisted and controlled ventilation.

Anesthesia↗
PubMed1979

Instantaneous blood flow responses to positive end-expiratory pressure with spontaneous ventilation.

Variable hemodynamic responses to positive end-expiratory pressure (PEEP) with spontaneous ventilation have been reported. To clarify these responses, 15 awake patients were studied using a catheter-tip velocity transducer to record phasic aortic root blood flow continuously before, during and after PEEP (10 cm H2O) applied with a face mask. Central blood volume and effective ventricular filling pressures were measured. Phasic pulmonary artery blood flow was also simultaneously recorded in three of these patients. PEEP produced an acute aortic blood flow reduction, detected within one respiratory cycle. Stroke volume decreased 12%, and since heart rate was unchanged, cardiac output also declined (p less than 0.05). Inspiratory-to-expiratory aortic flow changes were less during PEEP. In contrast, inspiratory-to-expiratory pulmonary artery flow alterations were exaggerated due to a marked flow decline during expiration. Central blood volume and effective left ventricular filling pressure decreased 9% and 19%, respectively (p less than 0.05 in all patients). The decrease in pulmonary artery flow was associated with a decrease in central blood volume in the three patients in whom pulmonary flow was measured. PEEP promptly reduces cardiac output during spontaneous ventilation, related to a decrease in pulmonary flow in expiration.

Adult↗
PubMed1979

Prolonged endotracheal intubation.

The advisability of prolonged oral or nasotracheal intubation is of continuing concern to physicians caring for patients requiring prolonged mechanical ventilatory assistance. Currently, in many health care centers, prolonged intubation is defined as being in excess of seven days. We treated a patient who required mechanical ventilatory assistance and in whom oral endotracheal intubation was maintained for two months without significant pathologic sequelae.

Aged↗
PubMed1979

Measuring exhaled volume with continuous positive airway pressure and intermittent mandatory ventilation. Techniques and rationale.

When patients breathe spontaneously through a ventilator circuit, a fall in airway pressure during the inspiratory cycle may increase inspiratory effort. A system of delivery which incorporates a distensible reservoir bag and delivers a constant flow of gas that is two or three times the patient's minute volume will prevent a significant drop in inspiratory airway pressure. Unfortunately, the constant flow of gas mixes with the patient's exhaled gas and makes continuous monitoring of exhaled volumes difficult. Two modifications of circuits are described which allow accurate continuous measurement of volume. One of these circuits allows analysis of the concentrations of expired gases. When spontaneous ventilation occurs, tidal volume and minute ventilation demonstrate an intact connection between the ventilator and the patient, continuously indicate the patient's ability to sustain independent ventilation, and give early warning of a change in respiratory status.

Humans↗
PubMed1978

Evaluation of criteria for discontinuing mechanical ventilatory support.

Thirty-three patients who required short-term postoperative mechanical ventilatory support were studied to compare different criteria established to initiate weaning from mechanical ventilation. Intermittent mandatory ventilation criteria (i.e., decreasing mechanical respirator rate as long as the arterial (pHa) remains above 7.35) and conventional criteria (ie, vital capacity greater than 15 ml/kg and peak negative pressure greater than 20 cm H2O) were compared to determine which would more rapidly predict a patient's ability to sustain total spontaneous respiration. All patients were eventually weaned from mechanical ventilation and had their tracheas extubated. Twenty-one patients maintained a pHa of greater than 7.35 during total spontaneous ventilation before they would, or could, meet conventional criteria for initiating a trial of spontaneous respiration (P less than .001). Seven patients simultaneously met both criteria for maintaining total spontaneous ventilation and the remaining five patients met conventional criteria before intermittent mandatory ventilation criteria. In the latter group, the pHa decreased below 7.35 during spontaneous respiration but in only one patient did it fall below 7.30. Our findings suggest that a patient's ability to maintain a pHa of greater than 7.35 while decreasing the frequency of mechanical ventilator breaths is more accurate than peak negative pressure and vital capacity for predicting ability to sustan adequate spontaneous respiration.

Adolescent↗
PubMed1977

Pulmonary function following severe acute respiratory failure and high levels of positive end-expiratory pressure.

In an 18-month period, we treated 561 patients with mechanical ventilation. Fifty-four (10 percent) of these patients had acute respiratory failure, requiring treatment with positive end-expiratory pressure (PEEP) in excess of 20 mm Hg (range, 20 to 40 mm Hg). All patients were allowed to breathe spontaneously between volume-limited mechanical breaths delivered at a rate sufficient to maintain an arterial pH greater than or equal to 7.35. PEEP was applied until calculated pulmonary venous admixture was minimized. Forty-three (80 percent) of these 54 patients were alive and asymptomatic three months after dischage from the hospital, and tests of pulmonary function were performed on ten patients within one year after hospitalization. Abnormalities in pulmonary function appeared to be reversible, and pulmonary function gradually approached normal within one year. It appears that neither acute respiratory failure nor exposure to high airway pressures caused significant permanent pulmonary damage in the ten patients studied.

Acute Disease↗
PubMed1976

Treatment of bronchopleural fistula during continuous positive pressure ventilation.

Pneumothorax as a complication of continuous positive pressure ventilation may result in the formation of bronchopleural fistula. If positive end-expiratory pressure cannot be sustained, the functional residual capacity and the ratio of alveolar ventilation to perfusion may decrease, and pulmonary gas exchange may be severely impaired. Recommended therapy includes removal of positive airway pressure and institution of negative intrapleural pressure via thoracostomy tube, but this may cause severe hypoxemia in patients with acute respiratory failure in spite of potentially toxic inspired oxygen concentrations. We applied positive intrapleural pressure equal to the end-expiratory airway pressure of three patients who developed bronchopleural fistula during therapy for acute respiratory failure. Positive intrapleural pressure facilitated resolution of the bronchopleural fistula in each case.

Adolescent↗
PubMed1976

Acute respiratory failure and intravascular coagulation.

The possible association between acute respiratory failure and disseminated intravascular coagulation was examined in eight patients with severe acute respiratory failure--a condition characterized by tachypnea, right to left intrapulmonary shunting of blood greater than 30 per cent of cardiac output, increased pulmonary artery pressure with low or normal pulmonary artery wedge pressure and roentgenologic interstitial pulmonary edema. Treatment consisted of mechanical ventilation with positive end expiratory pressure sufficient to minimize intrapulmonary shunting. There was no abnormality in platelet concentration fibrin split product concentration, fibrinogen concentration, prothrombin time or activated partial thromboplastin time during the period of most severe respiratory failure in any patient. However, mean platelet concentration fell to 90,000+/-9,000 per cubic millimeter, less than 0.001, and mean fibrin split product levels rose to 60+/-10 micrograms per milliliter, p less than 0.05, the fourth day after the onset of acute respiratory failure. No significant change occurred in other coagulation parameters. Disseminated intravascular coagulation developed in none of the patients nor was there any correlation between coagulation abnormalities and severity of acute respiratory failure that would suggest a cause and effect relationship.

Acute Disease↗
PubMed1975

High level positive end expiratory pressure (PEEP) in acute respiratory insufficiency.

Twenty-eight patients developed severe, progressive acute respiratory insufficiency despite aggressive application of conventional respiratory therapy. Application of increased PEEP (18 torr or greater) resulted in a significant decrease in QA/QT. Selection of the optimal levle of PEEP for each patient required serial determinations of QA/QT and measurement of cardiovascular response. The overall survival rate was 61 percent. Acute respiratory insufficiency was a proximate cause of death in only one patient. Four of the patients (14 percent) developed a pneumothorax following institution of high PEEP therapy. Cardiac output was not affected adversely at any level of PEEP up to 32 torr (44 cm H2O). We conclude that high levels of PEEP can be therapeutic for patients with refractory respiratory failure when combined with intermittent mandatory ventilation and careful cardiovascular monitoring. As with any therapy, the optimum dose should be tailored to each patient according to his needs and response.

Acute Disease↗
PubMedDate not supplied

Thermodilution and Fick cardiac index determinations following cardiac surgery.

With the thermodilution technique, repeated determination of cardiac index (CI) has become a rapid, easily accomplished, safe procedure. We paired 77 CI determinations measured by direct Fick and thermodilution techniques in 21 patients who underwent myocardial revascularization. Commercially available thermistor-tipped catheters and a cardiac output computer were used to determine CI according to the manufacturer's instructions. Oxygen consumption and arterial-venous oxygen content differences were measured directly to determine CI by the Fick method. Comparisons were made during mechanical ventilation with and without positive end-expiratory pressure (PEEP) and during spontaneous ventilation with and without PEEP. Cardiac indices measured by the two techniques were within +/- 0.5 L/min/m2 of each other only 76% of the time and within +/- 1.0 L/min/m2 96% of the time, if CI greater than or equal to 4.0 L/min/m2 were omitted. Ventilatory pattern had no apparent effect on results.

Cardiac Output↗
PubMedDate not supplied

Pulmonary effects of ventilatory pattern following cardiopulmonary bypass.

Twenty-one patients who underwent cardiopulmonary bypass for myocardial revascularization received postoperatively controlled mechanical ventilation (CMV) or intermittent mandatory ventilation (IMV), with or without positive end-expiratory pressure (PEEP). Functional residual capacity (FRC), right-to-left intrapulmonary shunt, dynamic compliance, physiological dead space, and arterial and mixed venous blood gases were measured during mechanical ventilation and spontaneous ventilation following weaning. Controlled ventilation increased physiological dead space and arterial pH. FRC correlated positively with dynamic compliance, but not with right-to-left intrapulmonary shunt. Postoperatively, FRC was significantly lower than normal when patients were ventilated without PEEP, but was normal when patients received PEEP. Arterial oxygen tension (PaO2), intrapulmonary shunt, and dead space were unaffected in spite of higher FRC, suggesting that patients who received PEEP had fewer atelectatic and fewer unperfused "silent" lung units than those who had not received PEEP.

Cardiopulmonary Bypass↗
PubMedDate not supplied

A new transport ventilator: an evaluation.

Transportation of patients requiring continuous ventilatory support and increased inspired oxygen concentrations may be cumbersome, inefficient, and dangerous. We evaluated a new time-cycled transport ventilator, which provided simple operation, ample inspired oxygen concentration, and adequate minute ventilation in every patient tested.

Evaluation Studies as Topic↗