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J B Downs

Publications and source records attributed to J B Downs.

At least 19 recordsLinked to original sources
PubMed1991

Airway pressure release ventilation during acute lung injury: a prospective multicenter trial.

OBJECTIVE: To evaluate the feasibility of airway pressure release ventilation (APRV) in providing ventilatory support to patients with acute lung injury of diverse etiology and mild-to-moderate severity. DESIGN: Prospective, multicenter, nonrandomized crossover trial. SETTING: ICUs in six major referral hospitals. PATIENTS: Fifty adult patients with respiratory failure requiring mechanical ventilation and positive end-expiratory airway pressure. INTERVENTIONS: After optimization of continuous positive airway pressure (CPAP), conventional ventilation and APRV were administered sequentially for 30 mins. During APRV, the CPAP level and airway pressure release level were adjusted to prevent hypoxemia, while the degree of ventilatory support was adjusted by altering the frequency of pressure release. MEASUREMENTS AND MAIN RESULTS: Circulatory and ventilatory pressures, arterial blood gases and pH, heart rate, and respiratory rate were measured. Alveolar ventilation was augmented adequately in 47 of 50 patients by APRV. Adjustment of APRV required an increase in mean CPAP from 13 +/- 3 (SD) to 21 +/- 9 cm H2O and a release pressure of 6 +/- 5 cm H2O. This airway pressure pattern produced a mean airway pressure comparable to that pressure achieved during conventional ventilation. Failure of APRV in three patients could be attributed to an inadequate level of CPAP or an inadequate APRV rate. While maintaining oxygenation of arterial blood and circulatory function, APRV allowed a substantial (55 +/- 17%; p less than .0001) reduction in peak airway pressure compared with conventional positive pressure ventilation adjusted to deliver a comparable or lower level of ventilatory support. CONCLUSIONS: APRV is a feasible alternative to conventional mechanical ventilation for augmentation of alveolar ventilation in patients with acute lung injury of mild-to-moderate severity.

Adult↗
PubMed1991

Distribution of ventilation and perfusion with different modes of mechanical ventilation.

We compared pulmonary gas exchange during synchronized intermittent mandatory ventilation (SIMV), pressure support ventilation (PSV), and airway pressure release ventilation (APRV). Nine subjects aged 56 to 75 yr were studied from 4 to 19 h after cardiac operations. When subjects were ready to be weaned from mechanical ventilation their ventilation-perfusion distribution was estimated using the multiple inert gas elimination technique during SIMV. The subjects then received PSV and APRV during alternating periods on a randomized basis, and the gas-exchange measurements were repeated. Vasoactive infusions and inspired oxygen fraction were held constant throughout the investigation. The results indicated that the major characteristics of the main mode of the VA/Q distributions (mean, standard deviation, and skew) were similar during all three modes. Dead space was lower during APRV (30.1 +/- 1.7% [SEM]) than during SIMV (36.2 +/- 1.5%) and PSV (37.1 +/- 2.7%) (p less than 0.05). Right-to-left shunt was significantly greater during APRV (19.9 +/- 2.3%) than during SIMV (15.4 +/- 1.7%) (p less than 0.05). Peak airway pressure (Paw) was higher during SIMV (32.8 +/- 1.3 cm H2O) than both PSV (19.4 +/- 2.1 cm H2O) and APRV (14.3 +/- 1.0 cm H2O) (p less than 0.05). Minute ventilation was lower during APRV (7.5 +/- 0.07 L/min) than during SIMV (9.4 +/- 0.6 L/min) and PSV (9.0 +/- 0.5 L/min) (p less than 0.05). Hemodynamic variables were similar during all three modes. We conclude that all three modes provide acceptable oxygenation and ventilatory support.

Aged↗
PubMed1989

A model to decrease hepatic blood flow and cardiac output with pressure breathing.

This randomized, controlled, crossover study evaluated the effect of continuous positive airway pressure (CPAP) breathing on hepatic blood flow (HBF) and cardiac output in 10 healthy male subjects. A CPAP mask was placed on the face and the subject breathed at either CPAP 12.5 cm H2O or ambient airway pressure. The estimated HBF was calculated as the ratio of indocyanine green plasma clearance to one minus the hematocrit. Cardiac output was measured with Doppler ultrasound. CPAP caused HBF to decrease in 8 of 10 subjects (14.1% +/- 15.3%, mean +/- SD, p = 0.033) and cardiac index (CI) to decrease in all subjects (14.1% +/- 5.7%, p = 0.0001). Stroke volume and respiratory rate were significantly decreased; heart rate was unchanged. These results indicate that CPAP at 12.5 cm H2O causes a small, but significant decrease in both HBF and CI.

Adult↗
PubMed1989

The effects of hyperoxia during fulminant sepsis.

Although adequate tissue oxygenation is essential to maintain cellular metabolism, the use of hyperoxia to improve oxygen delivery or to improve metabolic performance is controversial. For example, supplemental inspired oxygen is reportedly beneficial in the treatment of some experimental infections; however, oxygen therapy also has well-documented adverse side effects. To evaluate the effect of increased inspired oxygen concentration (FIO2) in animals with fulminant sepsis, 117 Sprague-Dawley rats underwent cecal ligation and puncture. Animals were then exposed to an FIO2 of either 0.21, 0.4, or 0.8. Twenty sham-operated controls had no mortality with any FIO2. Increasing the FIO2 increased mortality from 70% to 85% in animals receiving 40% O2, and to 100% in those receiving 80% O2. Autopsies revealed mild pulmonary oxygen toxicity with 80% O2 exposure in both control and septic animals, but normal lung histologic appearance in animals receiving lower levels of oxygen. Arterial blood gases documented maintenance of oxygenation and ventilation. Thus, pulmonary oxygen toxicity does not appear to be the mechanism for increased mortality. Supplemental oxygen may worsen, rather than improve, survival after fulminant infection.

Acute Disease↗
PubMed1988

Real-time continuous estimation of gas exchange by dual oximetry.

We designed a ventilation-perfusion index (VQI) to estimate venous admixture (Qsp/Qt) in a real-time fashion by simultaneous pulse and pulmonary artery oximetry in 17 patients with acute respiratory failure. Changes in Qsp/Qt were produced by altering the level of continuous positive airway pressure. VQI correlated well with Qsp/Qt (r = 0.78). This contrasts with the poor correlation found between Qsp/Qt and the commonly used oxygen tension based indices such as PaO2/FIO2 (r = -0.51), PaO2/PAO2 (r = 0.47), and PAO2-PaO2 (r = 0.23). The use of dual oximetry to derive a VQI appears to be a reliable and accurate method for real-time assessment of pulmonary gas exchange in patients with acute respiratory failure.

Acute Disease↗
PubMed1988

Optimum versus clinically established levels of continuous positive airway pressure in respiratory therapy.

To evaluate the efficacy of our routine method of cardiopulmonary monitoring of accurate management of respiratory therapy, continuous positive airway pressure (CPAP) was titrated in 11 surgical intensive care patients within +/- 7.5 cm H2O of the clinically selected level. Cardiopulmonary data were independently and retrospectively reviewed by three experienced critical care physicians from three outside hospitals. Each physician estimated the optimum level of CPAP for each patient. Variability between reviewers was not statistically significant. The optimum CPAP level based on all reviewers' opinions (8.6 +/- 5.7 cm H2O, mean +/- SD) was significantly lower than that selected clinically (13.2 +/- 4.5 cm H2O; P less than 0.05). We conclude that current methodology for monitoring respiratory therapy is inefficient for rapid adjustment of CPAP to appropriate levels. Continuous arterial and pulmonary artery oximetry may provide an improvement in the efficacy of cardiopulmonary monitoring in the future.

Adult↗
PubMed1988

Continuous monitoring of gas exchange and oxygen use with dual oximetry.

The utility of integrated pulse and pulmonary artery oximetry, known as dual oximetry, was evaluated by monitoring 10 critically ill surgical patients for a total of 208 patient hours. The ventilation-perfusion index (VQI), an estimate of venous admixture, and the oxygen extraction index (O2EI), an estimate of tissue oxygen utilization coefficient, previously described, were calculated on-line from arterial and mixed venous oxyhemoglobin saturations using a computer. Effective monitoring was accomplished 85% of the total time. The dual oximetry device was nonfunctional owing to equipment failure only 15% of the time, even though no undue attention was given to instructing the staff on operation of the oximeters. Accuracy of VQI and O2EI was reconfirmed by this study. Drift in the saturations, VQI, and O2EI during the 6-h period between calibrations was negligible. The 95% range of random variability was +/- 2% for SaO2, +/- 3% for SvO2, +/- 5% for VQI, and +/- 0.04 for O2EI. Thirty-six episodes of arterial blood desaturation below 90% were detected by continuous oximetry. In contrast, 74 routine arterial blood samples revealed only four such episodes. Dual oximetry appears to be a technically reliable and accurate method of monitoring pulmonary gas exchange and tissue oxygen utilization. The equipment provided stable readings for at least six hours without recalibration. Random variability is sufficiently small to allow early detection of alterations in pulmonary and circulatory function without blood sampling.

Anesthesia, General↗
PubMed1988

The carbon dioxide rate of rise in awake apneic humans.

Currently available estimates of the PaCO2 rate of rise in resting humans with resting lung volume were gathered during general anesthesia. The PaCO2 rate of rise during apnea in awake subjects was determined to acquire a value that may be more applicable to awake, ventilator-dependent, critically ill patients. Clinically, apnea occurs at functional residual capacity. With FiO2 = 1.0, 20 volunteers held their breaths at functional residual capacity for 0, 10, and 20 seconds, and then for as long as possible. They exhaled through an infrared CO2 analyzer after each interval to determine end-tidal pCO2. An estimate of the logarithmic PaCO2 rise during breath holding at functional residual capacity was 7 mmHg during the first 10 seconds (43 mmHg/minute), 2 mmHg during the next 10 seconds (13 mmHg/minute), and 6 mmHg/minute thereafter. In conclusion, PaCO2 increases more rapidly in awake apneic humans than earlier thought. The values reported herein probably are better for estimating duration of apnea in conscious, critically ill patients than are values obtained during general anesthesia.

Adult↗
PubMed1988

Oxygen supplementation during electroconvulsive therapy.

The effects of ventilation with 30% and 100% oxygen were investigated on the circulatory and electrocardiographic response to electroconvulsive therapy (ECT) in 12 patients during 40 treatments. Administration of 30% oxygen resulted in a 25% decrease in seizure duration compared with 100% oxygen (P less than 0.0125). Hypoxaemia, defined as SaO2 less than 90%, occurred during five of 20 treatments with 30% oxygen and during two of 20 treatments with 100% oxygen (ns), and was associated invariably with loss of airway control. Heart rate, arterial pressure, and the incidence of cardiac arrhythmias were not affected significantly by oxygen supplementation. Inspired oxygen concentration has a significant effect on seizure activity and should be of a consistent value if a reproducible seizure is to be produced during ECT. Breathing 100% oxygen does not appear to affect adversely the cardiovascular response to ECT. However, arterial hypoxaemia may develop rapidly during or after the seizure, regardless of oxygen supplementation, if adequate control of airway and ventilation is not maintained.

Adult↗
PubMed1988

Endobronchial drainage of undiagnosed lung abscess during chest physical therapy. A case report.

Bronchial drainage, positive-pressure lung inflation, chest-wall percussion, and suctioning were performed in a patient with postoperative atelectasis, lung infection, and respiratory failure. A previously undiagnosed posterior lung abscess subsequently drained into the bronchial tree, causing dissemination of the infection and a severe deterioration of pulmonary function. Dissemination of pulmonary infection from a lung abscess is a possible complication that should be considered when prescribing and administering chest physical therapy.

Drainage↗
PubMed1988

Oxygen consumption during spontaneous ventilation with acute lung injury in anesthetized pigs.

Acute lung injury causes a restrictive pulmonary defect, decreases lung compliance, and increases the work of breathing. We wished to determine the oxygen cost of the increased elastic work of breathing associated with acute lung injury. Extracorporeal venous circulation with a membrane lung was used to extract CO2 and to induce apnea in 14 anesthetized pigs. Data were collected during 4 experimental states: during spontaneous ventilation and apnea when the animals' lungs were normal, and after acute lung injury developed because of oleic acid administration. Acute lung injury decreased lung compliance from 101 +/- 79 (mean +/- SD) to 52 +/- 25 ml/cm H2O (p less than 0.04), and increased the elastic work of breathing from 700 +/- 590 to 1,060 +/- 630 ml.cm H2O (p = 0.01). During spontaneous ventilation, the increases in total O2 consumption and the O2 cost of breathing caused by acute lung injury were sufficiently small as to be undetectable, and, therefore, less than 3 to 4% of basal O2 consumption despite markedly increased elastic work and ventilatory power requirements. The increase in O2 consumption imposed by acute lung injury was small enough (less than 3 to 4% of total O2 consumption) that it appears to be clinically insignificant.

Acute Disease↗
PubMed1988

Effects of expiratory flow resistance on inspiratory work of breathing.

To minimize work of breathing, airway pressure should not fluctuate during spontaneous breathing with continuous positive airway pressure (CPAP). However, flow resistance in the inspiratory limb of the breathing circuit and an inadequate continuous gas flow rate result in airway pressure fluctuation and increased work of breathing. Flow resistance of the expiratory pressure/exhalation valve also directly affects the level of airway pressure during spontaneous inhalation with CPAP (the greater the resistance of the valve, the greater the decrease in airway pressure and work of breathing). We compared this effect with three types of expiratory pressure valves: a threshold resistor with low resistance to flow, an inflatable balloon (mushroom) valve with moderate resistance to flow, and a variable-orifice flow resistor with a high resistance to flow. Work increased up to threefold with the balloon valve and more than tenfold with the flow resistor compared with the threshold resistor. To apply CPAP, expiratory pressure valves with low resistance to flow should be used to minimize fluctuations in airway pressure and, thus, in the work of spontaneous breathing.

Humans↗
PubMed1988

Cardiovascular effects of conventional positive pressure ventilation and airway pressure release ventilation.

The hemodynamic sequelae of conventional positive pressure ventilation (CPPV), airway pressure release ventilation (APRV), and spontaneous breathing were compared with continuous positive airway pressure (CPAP) in ten anesthetized dogs who had ventilatory failure with and without parenchymal lung injury. The APRV corrected respiratory acidosis without significantly effecting arterial blood oxygenation, venous admixture, cardiovascular function, or tissue oxygen utilization. Application of CPPV precipitated marked depressions in blood pressure, stroke volume, and cardiac output. A concomitant decrease in venous admixture did not compensate for these adverse cardiovascular effects. Deterioration of tissue oxygen delivery resulted in oxygen supply-demand imbalance during CPPV. The results of this experimental study indicate that if ventilatory augmentation of subjects who require CPAP is desired, APRV will enhance alveolar ventilation without compromising circulatory function and tissue oxygen balance, whereas CPPV will impair cardiovascular function significantly.

Animals↗
PubMed1988

Airway pressure release ventilation (APRV). A human trial.

After operative coronary revascularization, 14 consenting adults received conventional positive pressure ventilation (PPV). When they were hemodynamically stable, data were collected during PPV and then during airway pressure release ventilation (APRV). During APRV, airway pressure (Paw) was reduced periodically at the lowest frequency which produced normal PaCO2. As anesthesia resolved, the rate of APRV breaths was decreased until patients breathed only with CPAP. During PPV and APRV, pHa, PaO2/FIO2, and hemodynamic variables were similar. All patients were weaned from APRV without complication. Optimal ventilator design for patients with acute lung injury would provide CPAP as a primary intervention and secondarily would augment alveolar ventilation. The APRV supported oxygenation and ventilation in patients with mild acute lung injury, yet with much lower peak airway pressure than produced by PPV.

Airway Resistance↗
PubMed1987

Estimation of oxygen utilization by dual oximetry.

Total body oxygen utilization coefficient was estimated using continuous pulse and pulmonary artery oximetry (dual oximetry) in 17 patients with respiratory failure. Change in arterial and mixed venous oxygen saturations was induced by altering airway pressure. Continuous measurement of mixed venous oxygen saturation provided an accurate and linear estimate of oxygen utilization coefficient (r = -0.92), the true values being overestimated by 0.05 +/- 0.06 (mean +/- SD). Addition of pulse oximetry improved the correlation (r = 0.93) and decreased the difference between absolute values (0.02 +/- 0.06). Oxygen utilization coefficient can be estimated reliably in an online fashion using pulmonary artery oximetry. However, the use of dual oximetry will further improve the estimate.

Adult↗