A quantitative analysis was performed of the CT images relative to 7 normal human subjects and to 22 patients affected with ARF (Acute Respiratory Failure). The CT scanner image quality was investigated, and the unit was checked with quality control procedures, in order to assure reliability and reproducibility. In every patient the lung was scanned at 3 different levels--basis, hilum and apex. The frequency distribution of CT numbers was studied. The lung areas were calculated for the different conditions, and the data correlated with functional lung data. A method was then tested to evaluate lung weight; the data obtained did not differ from literature data. All the patients were treated with different positive and expiratory pressure (PEEP). For different PEEP values, the quantitative data from CT analysis were correlated with morphofunctional indices.

Adult↗

PubMed1988

Relationships between lung computed tomographic density, gas exchange, and PEEP in acute respiratory failure.

Twenty-two patients with acute respiratory failure underwent lung computed tomography (CT) and physiological measurements at 5, 10, and 15 cm H2O positive end-expiratory pressure (PEEP) to investigate the relationship between morphology and function. Lung densities were primarily concentrated in the dependent regions. From the frequency distribution of CT numbers (difference in x-ray attenuation between water and lung) and lung gas volume measurements the authors obtained a quantitative estimate of normally inflated, poorly inflated, and non-inflated lung tissue weight. This estimated average lung weight was increased twofold above normal and excess lung weight correlated with the mean pulmonary artery pressure (P less than 0.01). Venous admixture correlated with the non-inflated tissue mass (P less than 0.01). Increasing PEEP caused progressive clearing of radiographic densities and increased the mass of normally inflated tissue (anatomic recruitment), while reducing venous admixture. The cardiac index decreased after increasing PEEP while oxygen delivery was unchanged. The authors conclude that CT scan lung density and oxygen exchange efficiency are correlated; the main effect of augmenting PEEP is to recruit perfused alveolar units that were previously collapsed.

Acute Disease↗

PubMed1988

Pulmonary microthrombosis in severe adult respiratory distress syndrome.

Pulmonary microvascular occlusive disease has been investigated using balloon occlusive pulmonary angiography in 31 patients with severe adult respiratory distress syndrome (ARDS) of different origins (14 patients with pneumonia, nine with multiple injury, eight with sepsis). Multiple pulmonary artery filling defects (PAFD) were detected in 13 (42%) patients, with a seven (78%) in nine incidence among those with posttraumatic ARDS. The presence of PAFD did not correlate with the severity of the respiratory failure, with the pulmonary hemodynamic alterations (pulmonary hypertension and increased vascular resistance), or with the final outcome (mortality rate was 54% among patients with PAFD and 61% among those with normal angiograms). These findings suggest that widespread pulmonary microthrombosis is a common event in patients with polytrauma and respiratory failure, with an important pathophysiologic role in the onset of posttraumatic ARDS.

Adolescent↗

PubMed1988

Inflammatory pulmonary edema and positive end-expiratory pressure: correlations between imaging and physiologic studies.

The anatomic and physiologic response to positive end-expiratory pressure (PEEP) was investigated using computed tomography (CT) in patients with adult respiratory distress syndrome (ARDS). The lesions (densities) in ARDS are distributed inhomogeneously but tend to concentrate in the dependent regions. The estimated lung weight (by CT scan, quantitative analysis, and lung gas volume measured with helium dilution) is, on the average, 200% higher than expected. Changing the body position from supine to prone causes a change in the density distribution in response to gravitational forces. The main effect of PEEP is to clear the densities through alveolar anatomic recruitment. Anatomic recruitment changes the mechanical characteristics of the lung and parallels the improvement in gas exchange. The effects of PEEP on pulmonary arterial pressure appear to be related to anatomic recruitment.

Humans↗

PubMed1988

The prone position in ARDS patients. A clinical study.

The gas exchange and hemodynamics were evaluated before, during, and after a two-hour period of prone position in 13 moderate-severe ARDS patients. Lung computerized tomography was obtained in both the supine and prone positions in two of these patients. Average arterial oxygenation improved after prone positioning (p less than 0.01). A PaO2 improvement of at least 10 mm Hg after 30 minutes of prone position was used as a criterion to discriminate between responders and nonresponders to the postural change. Eight patients met the "responders" group criterion, and in the five nonresponder patients, the PaO2 did not change significantly throughout the study. Computerized tomograms in the prone position showed disappearance of posterobasal densities and appearance of new densities in the anterior regions, in both patients studied. One of these was a responder, the other a nonresponder. A brief test period in prone position is indicated in ARDS patients to identify those who may benefit from this postural treatment. The definite mechanism of the arterial oxygenation improvement observed remains to be clarified.

Adult↗

PubMed1988

[Bronchoalveolar lavage in acute respiratory insufficiency].

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Adolescent↗

PubMed1987

Volume/pressure curve of total respiratory system in paralysed patients: artefacts and correction factors.

The volume/pressure (V/P) curve of the total respiratory system in paralysed patients is drawn assuming that volume changes of the respiratory system (delta V resp) equals volume displacement of the measuring apparatus (delta V syr), usually a supersyringe. However, in 93 VP curves we found that O2 removed from the lung-syringe system during the procedure (proportional to the time) largely exceeds the CO2 added to the lung-syringe system (delta V gas). This results in a net loss of volume from the system (delta V resp less than delta V-syr). Deflation compliance, hysteresis area and ratio are significantly affected by this phenomenon. Inflation compliance is less influenced by delta V gas, partially compensated by the intrapulmonary gas expansion due to the temperature changes. We conclude that the parameters computed on the deflation limb of V/P curve are misleading if proper correction of the volume scale is not introduced.

Adolescent↗

PubMed1987

Hypermetabolic response after hypothermic cardiopulmonary bypass.

Sixteen patients undergoing hypothermic cardiopulmonary bypass for open heart surgery were studied prospectively. Oxygen consumption and CO2 production showed a marked increase during the first 6 h postoperatively. Consequently, the measured resting energy expenditure was markedly elevated compared to the predicted energy expenditure. This hypermetabolic response occurred simultaneously with maximum spontaneous rewarming after the end of surgical procedures. Ventricular function was low throughout the postoperative period, and no cardiac response to increased energy requirements was recorded. On the contrary, marked increases in arteriovenous oxygen and CO2 difference were observed during the period of highest resting energy expenditure. We conclude that the first hours after hypothermic cardiopulmonary bypass represent the period of highest risk for decompensation. The continuous monitoring of CO2 production is suggested as a useful clinical method to detect postoperative changes in metabolic rate.

Aged↗

PubMed1987

Pressure-volume curve of total respiratory system in acute respiratory failure. Computed tomographic scan study.

To investigate the relationship between lung anatomy and pulmonary mechanics in acute respiratory failure (ARF), 20 patients with ARF underwent computerized tomography (CT) at 3 levels of positive end-expiratory pressure (PEEP) (5, 10, and 15 cm H2O). The static pressure-volume curve of the total respiratory system and the lung volumes (helium dilution method) were also measured. By knowing the lung volumes and analyzing the CT number frequency distribution, a quantitative estimate of normally aerated, poorly aerated, and nonaerated lung tissue was obtained at each level of PEEP. The recruitment was defined as the percent increase of normally aerated tissue from 5 to 15 cm H2O. We found that the different compliances (starting compliance, inflation compliance, and deflation compliance) were correlated only with the amount of normally aerated tissue present in the range of pressures explored by a given compliance (5 cm H2O for starting compliance and 15 cm H2O for inflation and deflation compliances). No relationship was found between the compliances and the poorly aerated and nonaerated tissue. The specific compliance was in the normal range, whereas the amount of recruitment was related to the ratio of inflation compliance to starting compliance. Our data suggest that (1) the pressure-volume curve parameters in ARF investigate only the residual healthy zones of the lung and do not directly estimate the "amount" of disease (poorly or nonaerated tissue), (2) the pressure-volume curve may allow an estimate of the anatomic recruitment, and (3) the residual normally aerated zones of the ARF lung seem to maintain a normal intrinsic elasticity.

Adult↗

PubMed1987

ECMO revisited.

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Humans↗

PubMed1986

Low-frequency positive-pressure ventilation with extracorporeal CO2 removal in severe acute respiratory failure.

Forty-three patients were entered in an uncontrolled study designed to evaluate extracorporeal membrane lung support in severe acute respiratory failure of parenchymal origin. Most of the metabolic carbon dioxide production was cleared through a low-flow venovenous bypass. To avoid lung injury from conventional mechanical ventilation, the lungs were kept "at rest" (three to five breaths per minute) at a low peak airway pressure of 35 to 45 cm H2O (3.4 to 4.4 kPa). The entry criteria were based on gas exchange under standard ventilatory conditions (expected mortality rate, greater than 90%). Lung function improved in thirty-one patients (72.8%), and 21 patients (48.8%) eventually survived. The mean time on bypass for the survivors was 5.4 +/- 3.5 days. Improvement in lung function, when present, always occurred within 48 hours. Blood loss averaged 1800 +/- 850 mL/d. No major technical accidents occurred in more than 8000 hours of perfusion. Extracorporeal carbon dioxide removal with low-frequency ventilation proved a safe technique, and we suggest it as a valuable tool and an alternative to treating severe acute respiratory failure by conventional means.

Acute Disease↗

PubMed1986

Morphological response to positive end expiratory pressure in acute respiratory failure. Computerized tomography study.

Ten patients with acute respiratory failure (ARF), (4 pneumonia, 4 sepsis, 2 polytrauma), underwent computerized tomography (CT) of the lungs, (apex, hilum, base), at 5, 10, 15 cm H2O positive end expiratory pressure (PEEP). The ARF lungs, on CT scan, appeared as a patchwork of normal and dense areas with generally well defined boundaries. Most of the densities were found in the dependent regions. The areas of density were correlated with PaO2 (r = 0.51). The PEEP increase resulted in a significant expansion of total cross-sectional lung surface area. The dense areas decreased significantly at the hilum and base when increasing PEEP while the changes at the apex were not significant. The changes of density with PEEP were highly correlated with the changes in oxygenation (r = 0.91). In the individual patient, however, the modifications of gas exchange can not be entirely predicted from morphological changes, possibly due to a diversion of pulmonary blood flow.

Acute Disease↗

PubMed1986

Adult respiratory distress syndrome profiles by computed tomography.

Ten patients with full-blown ARDS, on mechanical ventilation with PEEP underwent lung CT. Seven normal subjects were also studied. Three tomographic levels (apex, hilum, and base) were selected. The most consistent morphologic finding in ARDS was the presence of densities in the dependent regions of the lung. Assuming that the three levels were a representative sample of the whole lung, the lung weight was computed from the mean CT number and lung gas volume. Analysis of the CT number frequency distribution revealed three definite patterns of distribution: type 1, bimodal, with one mode in the normal CT number range; type 2, unimodal narrow distribution, with the mode in the CT range of water; and type 3, unimodal broad distribution in the abnormal CT number range.

Humans↗

PubMed1985

The importance of the circuit capacity in the administration of CPAP.

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Humans↗