Bedside estimation of nonaerated lung tissue using blood gas analysis.

OBJECTIVES: Studies correlating the arterial partial pressure of oxygen to the fraction of nonaerated lung assessed by CT shunt yielded inconsistent results. We systematically analyzed this relationship and scrutinized key methodological factors that may compromise it. We hypothesized that both physiological shunt and the ratio between PaO2 and the fraction of inspired oxygen enable estimation of CT shunt at the bedside. DESIGN: : Prospective observational clinical and laboratory animal investigations. SETTING: ICUs (University Hospital Leipzig, Germany) and Experimental Pulmonology Laboratory (University of São Paulo, Brazil). PATIENTS, SUBJECTS AND INTERVENTIONS: Whole-lung CT and arterial blood gases were acquired simultaneously in 77 patients mechanically ventilated with pure oxygen. A subgroup of 28 patients was submitted to different Fio2. We also studied 19 patients who underwent repeat CT. Furthermore we studied ten pigs with acute lung injury at multiple airway pressures, as well as a theoretical model relating PaO2 and physiological shunt. We logarithmically transformed the PaO2/Fio2 to change this nonlinear relationship into a linear regression problem. MEASUREMENTS AND MAIN RESULTS: We observed strong linear correlations between Riley's approximation of physiological shunt and CT shunt (R = 0.84) and between logarithmically transformed PaO2/Fio2 and CT shunt (R = 0.86), allowing us to construct a look-up table with prediction intervals. Strong linear correlations were also demonstrated within-patients (R = 0.95). Correlations were significantly improved by the following methodological issues: measurement of PaO2/Fio2 during pure oxygen ventilation, use of logarithmically transformed PaO2/Fio2 instead of the "raw" PaO2/Fio2, quantification of nonaerated lung as percentage of total lung mass and definition of nonaerated lung by the [-200 to +100] Hounsfield Units interval, which includes shunting units within less opacified lung regions. CONCLUSION: During pure oxygen ventilation, logarithmically transformed PaO2/Fio2 allows estimation of CT shunt and its changes in patients during systemic inflammation. Relevant intrapulmonary shunting seems to occur in lung regions with CT numbers between [-200 and +100] Hounsfield Units.

Diagnostic value of ADC in patients with prostate cancer: influence of the choice of b values.

OBJECTIVES: To evaluate the influence of the choice of b values on the diagnostic value of the apparent diffusion coefficient (ADC) for detection and grading of prostate cancer (PCa). METHODS: Forty-one patients with biopsy-proven PCa underwent endorectal 3-T MRI before prostatectomy. Different combinations of b values (0-800 s/mm(2)) were used to calculate four representative ADC maps. Mean ADCs of tumours and non-malignant tissue were determined. Tumour appearance on different ADC maps was rated by three radiologists as good, fair or poor by assigning a visual score (VS) of 2, 1 or 0, respectively. Differences in the ADC values with the choice of b values were analysed using one-way ANOVA. RESULTS: Choice of b values had a highly (P < 0.001) significant influence on the absolute ADC in each tissue. Maps using b = [50, 800] and [0, 800] were rated best (VS= 1.6 ± 0.3) and second best (1.1 ± 0.3, P < 0.001), respectively. For low-grade carcinomas (Gleason score ≤ 6, 13/41 patients), only the former choice received scores better than fair (VS = 1.4 ± 0.3). Mean tumour ADCs showed significant negative correlation (Spearman's ρ -0.38 to -0.46, P < 0.05) with Gleason score. CONCLUSIONS: Absolute ADC values strongly depend on the choice of b values and therefore should be used with caution for diagnostic purposes. A minimum b value greater than zero is recommended for ADC calculation to improve the visual assessment of PCa in ADC maps. KEY POINTS: • Absolute ADC values are highly dependent on the choice of b values. • Absolute ADC thresholds should be used carefully to predict tumour aggressiveness. • Subjective ratings of ADC maps involving b = 0 s/mm ( 2 ) are poor to fair. • Minimum b value greater than 0 s/mm ( 2 ) is recommended for ADC calculation.

Extrapolation in the analysis of lung aeration by computed tomography: a validation study.

INTRODUCTION: Computed tomography (CT) is considered the gold standard for quantification of global or regional lung aeration and lung mass. Quantitative CT, however, involves the exposure to ionizing radiation and requires manual image processing. We recently evaluated an extrapolation method which calculates quantitative CT parameters characterizing the entire lung from only 10 reference CT-slices thereby reducing radiation exposure and analysis time. We hypothesized that this extrapolation method could be further validated using CT-data from pigs and sheep, which have a different thoracic anatomy. METHODS: We quantified volume and mass of the total lung and differently aerated lung compartments in 168 ovine and 55 porcine whole-lung CTs covering lung conditions from normal to gross deaeration. Extrapolated volume and mass parameters were compared to the respective values obtained by whole-lung analysis. We also tested the accuracy of extrapolation for all possible numbers of CT slices between 15 and 5. Bias and limits of agreement (LOA) were analyzed by the Bland-Altman method. RESULTS: For extrapolation from 10 reference slices, bias (LOA) for the total lung volume and mass of sheep were 18.4 (-57.2 to 94.0) ml and 4.2 (-21.8 to 30.2) grams, respectively. The corresponding bias (LOA) values for pigs were 5.1 (-55.2 to 65.3) ml and 1.6 (-32.9 to 36.2) grams, respectively. All bias values for differently aerated lung compartments were below 1% of the total lung volume or mass and the LOA never exceeded ± 2.5%. Bias values diverged from zero and the LOA became considerably wider when less than 10 reference slices were used. CONCLUSIONS: The extrapolation method appears robust against variations in thoracic anatomy, which further supports its accuracy and potential usefulness for clinical and experimental application of quantitative CT.

A patient with a large recurrent pheochromocytoma demonstrating the pitfalls of diagnosis.

BACKGROUND: A 59-year-old man presented for a follow-up, 6 years after surgery for a large pheochromocytoma. He had suffered from diabetes mellitus, hypertension and abdominal pain in the right flank region. Previous postoperative follow-up did not reveal tumor recurrence. INVESTIGATION: Measurement of plasma free metanephrine and normetanephrine by high-performance liquid chromatography and radioimmunoassay; 123I-metaiodobenzylguanidine (MIBG) scintigraphy; hybrid 123I-MIBG single-photon emission CT (SPECT)-CT; MRI; testing for plasma norepinephrine and epinephrine; intraoperative ultrasonography; histological staining for chromogranin A and synaptophysin; and postoperative 18F-dihydroxyphenylalanine (DOPA) PET scan. DIAGNOSIS: Recurrent pheochromocytoma. MANAGEMENT: Laparotomy with tumor resection. Reduction of antihypertensive medications. Further follow-up by MRI, hybrid 123I-MIBG SPECT-CT and testing for plasma catecholamines and free metanephrines.

Computed tomographic assessment of lung weights in trauma patients with early posttraumatic lung dysfunction.

INTRODUCTION: Quantitative computed tomography (qCT)-based assessment of total lung weight (Mlung) has the potential to differentiate atelectasis from consolidation and could thus provide valuable information for managing trauma patients fulfilling commonly used criteria for acute lung injury (ALI). We hypothesized that qCT would identify atelectasis as a frequent mimic of early posttraumatic ALI. METHODS: In this prospective observational study, Mlung was calculated by qCT in 78 mechanically ventilated trauma patients fulfilling the ALI criteria at admission. A reference interval for Mlung was derived from 74 trauma patients with morphologically and functionally normal lungs (reference). Results are given as medians with interquartile ranges. RESULTS: The ratio of arterial partial pressure of oxygen to the fraction of inspired oxygen was 560 (506 to 616) mmHg in reference patients and 169 (95 to 240) mmHg in ALI patients. The median reference Mlung value was 885 (771 to 973) g, and the reference interval for Mlung was 584 to 1164 g, which matched that of previous reports. Despite the significantly greater median Mlung value (1088 (862 to 1,342) g) in the ALI group, 46 (59%) ALI patients had Mlung values within the reference interval and thus most likely had atelectasis. In only 17 patients (22%), Mlung was increased to the range previously reported for ALI patients and compatible with lung consolidation. Statistically significant differences between atelectasis and consolidation patients were found for age, Lung Injury Score, Glasgow Coma Scale score, total lung volume, mass of the nonaerated lung compartment, ventilator-free days and intensive care unit-free days. CONCLUSIONS: Atelectasis is a frequent cause of early posttraumatic lung dysfunction. Differentiation between atelectasis and consolidation from other causes of lung damage by using qCT may help to identify patients who could benefit from management strategies such as damage control surgery and lung-protective mechanical ventilation that focus on the prevention of pulmonary complications.

Image reconstruction affects computer tomographic assessment of lung hyperinflation.

OBJECTIVES: Lung hyperinflation may be assessed by computed tomography (CT). As shown for patients with emphysema, however, CT image reconstruction affects quantification of hyperinflation. We studied the impact of reconstruction parameters on hyperinflation measurements in mechanically ventilated (MV) patients. DESIGN: Observational analysis. SETTING: A University hospital-affiliated research Unit. PATIENTS: The patients were MV patients with injured (n = 5) or normal lungs (n = 6), and spontaneously breathing patients (n = 5). INTERVENTIONS: None. MEASUREMENTS AND RESULTS: Eight image series involving 3, 5, 7, and 10 mm slices and standard and sharp filters were reconstructed from identical CT raw data. Hyperinflated (V(hyper)), normally (V(normal)), poorly (V(poor)), and nonaerated (V(non)) volumes were calculated by densitometry as percentage of total lung volume (V(total)). V(hyper) obtained with the sharp filter systematically exceeded that with the standard filter showing a median (interquartile range) increment of 138 (62-272) ml corresponding to approximately 4% of V(total). In contrast, sharp filtering minimally affected the other subvolumes (V(normal), V(poor), V(non), and V(total)). Decreasing slice thickness also increased V(hyper) significantly. When changing from 10 to 3 mm thickness, V(hyper) increased by a median value of 107 (49-252) ml in parallel with a small and inconsistent increment in V(non) of 12 (7-16) ml. CONCLUSIONS: Reconstruction parameters significantly affect quantitative CT assessment of V(hyper) in MV patients. Our observations suggest that sharp filters are inappropriate for this purpose. Thin slices combined with standard filters and more appropriate thresholds (e.g., -950 HU in normal lungs) might improve the detection of V(hyper). Different studies on V(hyper) can only be compared if identical reconstruction parameters were used.

In vivo glenohumeral analysis using 3D MRI models and a flexible software tool: feasibility and precision.

PURPOSE: To implement a PC-based morphometric analysis platform and to evaluate the feasibility and precision of MRI measurements of glenohumeral translation. MATERIALS AND METHODS: Using a vertically open 0.5T MRI scanner, the shoulders of 10 healthy subjects were scanned in apprehension (AP) and in neutral position (NP), respectively. Surface models of the humeral head (HH) and the glenoid cavity (GC) were created from segmented MR images by three readers. Glenohumeral translation was determined by the projection point of the manually fitted HH center on the GC plane defined by the two main principal axes of the GC model. RESULTS: Positional precision, given as mean (extreme value at 95% confidence level), was 0.9 (1.8) mm for the HH center and 0.7 (1.6) mm for the GC centroid; angular GC precision was 1.3 degrees (2.3 degrees ) for the normal and about 4 degrees (7 degrees ) for the anterior and superior coordinate axes. The two-dimensional (2D) precision of the HH projection point was 1.1 (2.2) mm. A significant HH translation between AP and NP was found. CONCLUSION: Despite a limited quality of the underlying model data, our PC-based analysis platform allows a precise morphometric analysis of the glenohumeral joint. The software is easily extendable and may potentially be used for an objective evaluation of therapeutical measures.

Early recovery from post-traumatic acute respiratory distress syndrome.

BACKGROUND: To present and discuss the rationale and possible benefits of timely alveolar recruitment in early post-traumatic acute respiratory distress syndrome. METHODS: A 17-year-old patient who had sustained blunt thoracic trauma presented with severe hypoxaemia on admission and whole body computed tomography showed pulmonary contusion and substantial bilateral atelectasis. Oxygenation and lung mechanics did not improve with low tidal volume ventilation using high positive end-expiratory pressures (PEEPs). Therefore we applied an alveolar recruitment manoeuvre 7 h after admission. After alveolar recruitment, PEEP was titrated to the lowest level which prevented alveolar derecruitment. RESULTS: Oxygenation and lung compliance improved rapidly and aeration of the entire lung was confirmed by computed tomography 27 h after the recruitment manoeuvre. The patient recovered completely and was discharged after 17 days. CONCLUSION: Although robust evidence is still lacking, several lines of evidence suggest potential benefits of timely alveolar recruitment. Patients with early post-traumatic respiratory failure seem to most readily respond to alveolar recruitment manoeuvres and could thus benefit from the gain in functional lung volume and oxygenation. Moreover the probability of ventilator associated complications may be reduced.

Alveolar recruitment in combination with sufficient positive end-expiratory pressure increases oxygenation and lung aeration in patients with severe chest trauma.

OBJECTIVE: Investigation of oxygenation and lung aeration during mechanical ventilation according to the open lung concept in patients with acute lung injury or acute respiratory distress syndrome. DESIGN: Retrospective analysis. SETTING: Surgical intensive care unit of a university hospital. PATIENTS: We retrospectively identified 17 patients with acute lung injury/acute respiratory distress syndrome due to pulmonary contusion who had thoracic helical computed tomography scans before and after ventilation with the open lung concept. INTERVENTIONS: Baseline ventilation consisted of low tidal volumes (< or =6 mL/kg) and positive end-expiratory pressure (PEEP; 5-17 cm H2O). We briefly applied high inspiratory pressures for opening up collapsed alveoli. External PEEP and intrinsic PEEP were combined to keep recruited lung units open. We generated intrinsic PEEP by pressure-cycled high-frequency inverse ratio ventilation (80 min, inspiratory/expiratory ratio 2:1) and maintained our ventilatory strategy for 24 hrs. Then, after reducing total PEEP by decreasing respiratory rate, Pao2/Fio2 ratio was reevaluated. If it remained >300 mm Hg, weaning was started. If not, previous ventilator settings were resumed for another 24 hrs after recruiting the lungs once again. MEASUREMENTS AND MAIN RESULTS: Physiologic variables and ventilator settings were obtained from routine charts. Data from computed tomography before and after the open lung concept were analyzed for volumetric quantification of lung aeration and collapse. All results are presented as median and range. During baseline ventilation, PEEP was 10 (range, 5-17) cm H2O and after recruitment 21 (range, 18-26) cm H2O. Opening pressures were 65 (range, 50-80) cm H2O. After recruitment, Pao2/Fio2 ratio was higher in all patients. Total lung volume increased from 2915 (range, 1952-4941) to 4247 (range, 2285-6355) mL and normally aerated volume from 1742 (range, 774-2941) to 2971 (range, 1270-5232) mL. Atelectasis decreased significantly from 604 (range, 147-1538) to 106 (range, 0-736) mL. Hyperinflation increased significantly from 5 (range, 0-188) to 62 (range, 1-424) mL, whereas poor aeration did not change substantially from 649 (range, 302-1292) to 757 (range, 350-1613) mL. No hemodynamic problems occurred. CONCLUSIONS: Lung recruitment increased arterial oxygenation, normally aerated lung volume, and total lung volume while decreasing the amount of collapsed tissue. These results indicate that the open lung concept is a reasonable mode of ventilation for patients with severe chest trauma.