Correction: Nitrogen washout/washin, helium dilution and computed tomography in the assessment of end expiratory lung volume

INTRODUCTION: End expiratory lung volume (EELV) measurement in the clinical setting is routinely performed using the helium dilution technique. A ventilator that implements a simplified version of the nitrogen washout/washin technique is now available. We compared the EELV measured by spiral computed tomography (CT) taken as gold standard with the lung volume measured with the modified nitrogen washout/washin and with the helium dilution technique. METHODS: Patients admitted to the general intensive care unit of Ospedale Maggiore Policlinico Mangiagalli Regina Elena requiring ventilatory support and, for clinical reasons, thoracic CT scanning were enrolled in this study. We performed two EELV measurements with the modified nitrogen washout/washin technique (increasing and decreasing inspired oxygen fraction (FiO2) by 10%), one EELV measurement with the helium dilution technique and a CT scan. All measurements were taken at 5 cmH2O airway pressure. Each CT scan slice was manually delineated and gas volume was computed with custom-made software. RESULTS: Thirty patients were enrolled (age = 66 +/- 10 years, body mass index = 26 +/- 18 Kg/m2, male/female ratio = 21/9, partial arterial pressure of carbon dioxide (PaO2)/FiO2 = 190 +/- 71). The EELV measured with the modified nitrogen washout/washin technique showed a very good correlation (r2 = 0.89) with the data computed from the CT with a bias of 94 +/- 143 ml (15 +/- 18%, p = 0.001), within the limits of accuracy declared by the manufacturer (20%). The bias was shown to be highly reproducible, either decreasing or increasing the FiO2 being 117+/-170 and 70+/-160 ml (p = 0.27), respectively. The EELV measured with the helium dilution method showed a good correlation with the CT scan data (r2 = 0.91) with a negative bias of 136 +/- 133 ml, and appeared to be more correct at low lung volumes. CONCLUSIONS: The EELV measurement with the helium dilution technique (at low volumes) and modified nitrogen washout/washin technique (at all lung volumes) correlates well with CT scanning and may be easily used in clinical practice. TRIAL REGISTRATION: Current Controlled Trials NCT00405002

Effects of thoraco-pelvic supports during prone position in patients with acute lung injury/acute respiratory distress syndrome: a physiological study

INTRODUCTION: This study sought to assess whether the use of thoraco-pelvic supports during prone positioning in patients with acute lung injury/acute respiratory distress syndrome (ALI/ARDS) improves, deteriorates or leaves unmodified gas exchange, hemodynamics and respiratory mechanics. METHODS: We studied 11 patients with ALI/ARDS, sedated and paralyzed, mechanically ventilated in volume control ventilation. Prone positioning with or without thoraco-pelvic supports was applied in a random sequence and maintained for a 1-hour period without changing the ventilation setting. In four healthy subjects the pressures between the body and the contact surface were measured with and without thoraco-pelvic supports. Oxygenation variables (arterial and central venous), physiologic dead space, end-expiratory lung volume (helium dilution technique) and respiratory mechanics (partitioned between lung and chest wall) were measured after 60 minutes in each condition. RESULTS: With thoraco-pelvic supports, the contact pressures almost doubled in comparison with those measured without supports (19.1 ± 15.2 versus 10.8 ± 7.0 cmH(2)O, p ≤ 0.05; means ± SD). The oxygenation-related variables were not different in the prone position, with or without thoraco-pelvic supports; neither were the CO(2)-related variables. The lung volumes were similar in the prone position with and without thoraco-pelvic supports. The use of thoraco-pelvic supports, however, did lead to a significant decrease in chest wall compliance from 158.1 ± 77.8 to 102.5 ± 38.0 ml/cmH(2)O and a significantly increased pleural pressure from 4.3 ± 1.9 to 6.1 ± 1.8 cmH(2)O, in comparison with the prone position without supports. Moreover, when thoraco-pelvic supports were added, heart rate increased significantly from 82.1 ± 17.9 to 86.7 ± 16.7 beats/minute and stroke volume index decreased significantly from 37.8 ± 6.8 to 34.9 ± 5.4 ml/m(2). The increase in pleural pressure change was associated with a significant increase in heart rate (p = 0.0003) and decrease in stroke volume index (p = 0.0241). CONCLUSION: The application of thoraco-pelvic supports decreases chest wall compliance, increases pleural pressure and slightly deteriorates hemodynamics without any advantage in gas exchange. Consequently, we stopped their use in clinical practice

Effect of a heated humidifier during continuous positive airway pressure delivered by a helmet

INTRODUCTION: The helmet may be an effective interface for the delivery of noninvasive positive pressure ventilation. The high internal gas volume of the helmet can act as a 'mixing chamber', in which the humidity of the patient's expired alveolar gases increases the humidity of the dry medical gases, thus avoiding the need for active humidification. We evaluated the temperature and humidity of respiratory gases inside the helmet, with and without a heated humidifier, during continuous positive airway pressure (CPAP) delivered with a helmet. METHODS: Nine patients with acute respiratory failure (arterial oxygen tension/fractional inspired oxygen ratio 209 +/- 52 mmHg) and 10 healthy individuals were subjected to CPAP. The CPAP was delivered either through a mechanical ventilator or by continuous low (40 l/min) or high flow (80 l/min). Humidity was measured inside the helmet using a capacitive hygrometer. The level of patient comfort was evaluated using a continuous scale. RESULTS: In patients with acute respiratory failure, the heated humidifier significantly increased the absolute humidity from 18.4 +/- 5.5 mgH2O/l to 34.1 +/- 2.8 mgH2O/l during ventilator CPAP, from 11.4 +/- 4.8 mgH2O/l to 33.9 +/- 1.9 mgH2O/l during continuous low-flow CPAP, and from 6.4 +/- 1.8 mgH2O/l to 24.2 +/- 5.4 mgH2O/l during continuous high-flow CPAP. Without the heated humidifier, the absolute humidity was significantly higher with ventilator CPAP than with continuous low-flow and high-flow CPAP. The level of comfort was similar for all the three modes of ventilation and with or without the heated humidifier. The findings in healthy individuals were similar to those in the patients with acute respiratory failure. CONCLUSION: The fresh gas flowing through the helmet with continuous flow CPAP systems limited the possibility to increase the humidity. We suggest that a heated humidifier should be employed with continuous flow CPAP systems

Mechanisms of oxygenation responses to proning and recruitment in COVID-19 pneumonia

Purpose This study aimed at investigating the mechanisms underlying the oxygenation response to proning and recruitment maneuvers in coronavirus disease 2019 (COVID-19) pneumonia. Methods Twenty-five patients with COVID-19 pneumonia, at variable times since admission (from 1 to 3 weeks), underwent computed tomography (CT) lung scans, gas-exchange and lung-mechanics measurement in supine and prone positions at 5 cmH(2)O and during recruiting maneuver (supine, 35 cmH(2)O). Within the non-aerated tissue, we differentiated the atelectatic and consolidated tissue (recruitable and non-recruitable at 35 cmH(2)O of airway pressure). Positive/negative response to proning/recruitment was defined as increase/decrease of PaO2/FiO(2). Apparent perfusion ratio was computed as venous admixture/non aerated tissue fraction. Results The average values of venous admixture and PaO2/FiO(2) ratio were similar in supine-5 and prone-5. However, the PaO2/FiO(2) changes (increasing in 65% of the patients and decreasing in 35%, from supine to prone) correlated with the balance between resolution of dorsal atelectasis and formation of ventral atelectasis (p = 0.002). Dorsal consolidated tissue determined this balance, being inversely related with dorsal recruitment (p = 0.012). From supine-5 to supine-35, the apparent perfusion ratio increased from 1.38 +/- 0.71 to 2.15 +/- 1.15 (p = 0.004) while PaO2/FiO(2) ratio increased in 52% and decreased in 48% of patients. Non-responders had consolidated tissue fraction of 0.27 +/- 0.1 vs. 0.18 +/- 0.1 in the responding cohort (p = 0.04). Consolidated tissue, PaCO2 and respiratory system elastance were higher in patients assessed late (all p < 0.05), suggesting, all together, "fibrotic-like" changes of the lung over time. Conclusion The amount of consolidated tissue was higher in patients assessed during the third week and determined the oxygenation responses following pronation and recruitment maneuvers

Ventilator-Induced Lung injury: a preliminary morphological study

In this study we aimed at characterizing by morphological methods the effect of ventilator-induced lung injury (VILI) on lung structure, and we analyzed collagen and elastin content to understand the possible role of the main components of lung connective tissue in the development of VILI. For this purpose four female piglets (21.7±4.5 kg) were sedated, intubated and mechanically ventilated with high pressure to induce VILI. After death, lungs were excised inflated; each lung was divided in four regions, and lung fragments were obtained from each region of both lungs: three samples from subpleural regions, one sample from the medial portion of the lung. Lung fragments were immediately fixed in 4% formalin in 0.1M phosphate buffered saline (PBS), pH 7.4, routinely dehydrated, paraffin embedded, and serially cut (thickness 5 μm). Lung structure was analyzed in haematoxylin-eosin stained sections using a semiquantitative grading scale to assess the injury grade. To study collagen and elastin content, sections were stained by Sirius red and Weigert’s resorcin-fuchsin, respectively, and analyzed by a specific software. Collagen and elastin content were expressed as a percent of the stained area relative to the lung tissue. Light microscopy analysis of hematoxylin-eosin stained sections revealed that VILI induced several lung injuries such as hyaline membranes, interstitial and septal infiltrate, vascular congestion and intra-alveolar hemorraging, alveoli rupturing and basophilic material deposition. These lesions were diffuse and involved the whole lung parenchyma without any preferential localization. Image analysis of Sirius red and Weigert’s resorcin-fuchsin stained sections showed that lung injury was more evident where elastin was less abundant, but was also evident where elastin content was high and collagen was concomitantly less abundant. These preliminary data suggest that lung extracellular matrix could influence the response to damaging ventilation, and that bot

Additional file 1: of Airway driving pressure and lung stress in ARDS patients

Expanded results with additional tables and figures. (PDF 2454 kb

Decreasing pulmonary ventilation through bicarbonate ultrafiltration: An experimental study

OBJECTIVE: To demonstrate the technical feasibility of CO2 removal with a commercial hemofilter and a replacement solution containing sodium hydroxide to replace bicarbonate. DESIGN: Prospective animal experiment in sheep. SUBJECTS: Seven mixed-breed female sheep. INTERVENTIONS: Blood ultrafiltrate containing half of the metabolic production of CO2 was removed with a commercial hemofilter and a replacement solution containing sodium hydroxide was given as replacement. Minute ventilation was lowered to less than half of its baseline value. Ultrafiltration was stopped at 18 hrs, and Paco2 was allowed to increase for about 1 hr; at this time, the sheep were electively killed. MEASUREMENTS AND MAIN RESULTS: Every 6 hrs, blood was sampled from the carotid artery, the pulmonary artery, and from the extracorporeal perfusion circuit (before the hemofilter, immediately after the hemofilter, and after mixing with the replacement solution). To maintain normocapnia, minute ventilation was reduced from 3.8 \uc2\ub1 0.1 L/min to 1.9 \uc2\ub1 0.7 L/min; Paco2 remained near constant during the study. The average blood pH, after mixing with the replacement solution, was 7.64 \uc2\ub1 0.12. One hour after the ultrafiltration had stopped, Paco2 had increased from 36.7 \uc2\ub1 4.2 torr (4.9 \uc2\ub1 0.6 kPa) to 59.6 \uc2\ub1 9 torr (7.9 \uc2\ub1 1.2 kPa) (p &lt; .01) and blood pH had decreased from 7.317 \uc2\ub1 0.041 to 7.151 \uc2\ub1 0.051 (p &lt; .01). CONCLUSION: CO2 removal with bicarbonate ultrafiltration may be an effective treatment for patients with respiratory failure. \uc2\ua9 2009 Lippincott Williams &amp; Wilkins, Inc