Regional and overall ventilation inhomogeneities in preterm and term-born infants

Objectives  We compared ventilation inhomogeneity assessed by electrical impedance tomography (EIT) and multiple breath washout (MBW) in preterm and term-born infants. We hypothesised that EIT measurements in spontaneously breathing infants are repeatable and that differences in regional ventilation distribution measured by EIT can distinguish between preterm and term-born infants. Design  Cross-sectional group comparison study. Setting  Lung function laboratory at a University Children’s Hospital. Participants  Seventeen healthy term-born and 15 preterm infants at a matched postmenstrual age of 44 weeks. Measurements and results  We concurrently measured ventilation inhomogeneity by EIT, ventilation inhomogeneity (LCI) and functional residual capacity (FRC) by MBW and tidal breathing variables during unsedated quiet sleep. EIT measurements were highly repeatable (coefficient of variation 3.6%). Preterm infants showed significantly more ventilation of the independent parts of the lungs compared to healthy term-born infants assessed by EIT (mean difference 5.0, 95 CI 1.3–8%). Whereas the two groups showed no differences in lung volumes or ventilation inhomogeneities assessed by MBW, EIT discriminated better between term and preterm infants. (FRC/kg: mean difference 1.1 mL, 95% CI −1.4–3.8 mL; LCI: mean difference 0.03, 95% CI −0.32–0.25). Conclusions  EIT shows distinct differences in ventilation distribution between preterm and term-born infants, which cannot be detected by MBW. Although preterm infants are capable of dynamically maintaining overall functional residual volume and ventilation distribution, they show some spatial differences from fullterm infants.     

Assessment of regional lung recruitment and derecruitment during a PEEP trial based on electrical impedance tomography

Objective To investigate whether electrical impedance tomography (EIT) is capable of monitoring regional lung recruitment and lung collapse during a positive end-expiratory pressure (PEEP) trial. Design Experimental animal study of acute lung injury. Subject Six pigs with saline-lavage-induced acute lung injury. Interventions An incremental and decremental PEEP trial at ten pressure levels was performed. Ventilatory, gas exchange, and hemodynamic parameters were automatically recorded. EIT and computed tomography (CT) scans of the same slice were simultaneously taken at each PEEP level. Measurements and results A significant correlation between EIT and CT analyses of end-expiratory gas volumes (r = 0.98 up to 0.99) and tidal volumes (r = 0.55 up to r = 0.88) could be demonstrated. Changes in global and regional tidal volumes and arterial oxygenation (PaO₂/FiO₂) demonstrated recruitment/derecruitment during the trial, but at different onsets. During the decremental trial, derecruitment first occurred in dependent lung areas. This was indicated by lowered regional tidal volumes measured in this area and by a decrease of PaO₂/FiO₂. At the same time, the global tidal volume still continued to increase, because the increase of ventilation of the non-dependent areas was higher than the loss in the dependent areas. This indicates that opposing regional changes might cancel each other out when combined in a global parameter. Conclusions EIT is suitable for monitoring the dynamic effects of PEEP variations on the regional change of tidal volume. It is superior to global ventilation parameters in assessing the beginning of alveolar recruitment and lung collapse.     

The value of electrical impedance tomography in assessing the effect of body position and positive airway pressures on regional lung ventilation in spontaneously breathing subjects

Objective Functional electrical impedance tomography (EIT) measures relative impedance changes in lung tissue during tidal breathing and creates images of local ventilation distribution. A novel approach to analyse the effect of body position and positive pressure ventilation on intrapulmonary tidal volume distribution was evaluated in healthy adult subjects.Design and setting Prospective experimental study in healthy adult subjects in the intensive care unit at university hospital.Subjects Ten healthy male adults.Interventions Change in body position from supine to prone, left and right lateral during spontaneous breathing and positive pressure support ventilation.Measurements and results EIT measurements and multiple-breath sulphur hexafluoride (SF₆) washout were performed. Profiles of average relative impedance change in regional lung areas were calculated. Relative impedance time course analysis and Lissajous figure loop analysis were used to calculate phase angles between dependent or independent lung and total lung (). EIT data were compared to SF₆ data washout measuring the lung clearance index (LCI). Proposed EIT profiles allowed inter-individual comparison of EIT data and identified areas with reduced regional tidal volume using pressure support ventilation. Phase angle of dependent lung in supine position was 11.7±1.4°, in prone 5.3±0.5°, in right lateral 11.0±1.3° and in left lateral position 10.8±1.0°. LCI increased in supine position from 5.63±0.43 to 7.13±0.64 in prone position. Measured showed inverse relationship to LCI in the four different body positions.Conclusions EIT profiles and of functional EIT are new methods to describe regional ventilation distribution with EIT allowing inter-individual comparison.This article refers to the editorial The study was supported by the Preston James Foundation and SensorMedics, The Netherlands     

Electrical impedance tomography: a method for monitoring regional lung aeration and tidal volume distribution?

Objective To demonstrate the monitoring capacity of modern electrical impedance tomography (EIT) as an indicator of regional lung aeration and tidal volume distribution.Design and setting Short-term ventilation experiment in an animal research laboratory.Patients and participants One newborn piglet (body weight: 2 kg).Interventions Surfactant depletion by repeated bronchoalveolar lavage, surfactant administration.Measurements and results EIT scanning was performed at an acquisition rate of 13 images/s during two ventilatory manoeuvres performed before and after surfactant administration. During the scanning periods of 120 s the piglet was ventilated with a tidal volume of 10 ml/kg at positive end-expiratory pressures (PEEP) in the range of 0–30 cmH₂O, increasing and decreasing in 5 cmH₂O steps. Local changes in aeration and ventilation with PEEP were visualised by EIT scans showing the regional shifts in end-expiratory lung volume and distribution of tidal volume, respectively. In selected regions of interest EIT clearly identified the changes in local aeration and tidal volume distribution over time and after surfactant treatment as well as the differences between stepwise inflation and deflation.Conclusions Our data indicate that modern EIT devices provide an assessment of regional lung aeration and tidal volume and allow evaluation of immediate effects of a change in ventilation or other therapeutic intervention. Future use of EIT in a clinical setting is expected to optimise the selection of appropriate ventilation strategies.     

Distribution of lung ventilation in spontaneously breathing neonates lying in different body positions

Objective

The aim of our study was to determine the effect of the irregular spontaneous breathing pattern and posture on the spatial distribution of ventilation in neonates free from respiratory disease by the non-invasive imaging method of electrical impedance tomography (EIT). Scanning of spontaneously breathing neonates is the prerequisite for later routine application of EIT in babies with lung pathology undergoing ventilator therapy.

Design

Prospective study.

Setting

Neonatal intensive care unit at a university hospital.

Patients

Twelve pre-term and term neonates (mean age: 23 days; mean body weight: 2,465 g; mean gestational age: 34 weeks; mean birth weight: 2,040 g).

Interventions

Change in body position in the sequence: supine, right lateral, prone, supine.

Measurements and results

EIT measurements were performed using the Göttingen GoeMF I system. EIT scans of regional lung ventilation showing the distribution of respired air in the chest cross-section were generated during phases of rapid tidal breathing and deep breaths. During tidal breathing, 54.5±8.3%, 55.2±10.5%, 59.9±8.4% and 54.2±8.5% of inspired air (mean values ± SD) were directed into the right lung in the supine, right lateral, prone and repeated supine postures respectively. During deep inspirations, the right lung ventilation accounted for 52.6±7.9%, 68.5±8.5%, 55.4±8.2% and 50.5±6.6% of total ventilation respectively.

Conclusion

The study identified the significant effect of breathing pattern and posture on the spatial distribution of lung ventilation in spontaneously breathing neonates. The results demonstrate that changes in regional ventilation can easily be determined by EIT and bode well for the future use of this method in paediatric intensive care.

     

No change in the regional distribution of tidal volume during lateral posture in mechanically ventilated patients assessed by electrical impedance tomography

We assessed the distribution of regional lung ventilation during moderate and steep lateral posture using electrical impedance tomography (EIT) in mechanically ventilated patients. Seven patients were placed on a kinetic treatment table. An elastic belt containing 16 electrodes was placed around the chest and was connected to the EIT device. Patients were moved to left and right lateral positions in a stepwise (10°) mode up to 60°. EIT images [arbitrary units (AU)] were generated and scanned for assessment of relative ventilation distribution changes [tidal volume (V_T)]. A calibration procedure of arbitrary units (AUs) versus ventilator‐derived V_T performed in all patients during three predefined positions (supine, 60°‐left dependent and 60°‐right‐dependent) showed a significant correlation between V_T in supine, left and right lateral positions with the corresponding AUs (r² = 0·356, P<0·05). Changes in V_T were calculated and compared to supine position, and specific regions of interest (ROIs) were analysed. In our study, in contrast to recent findings, a change in lateral positions did not induce a significant change in regional tidal volume distribution. In right lateral positions, a broader variation of V_T with a trend towards an increase in the dependently positioned lung was observed in comparison with supine. Lateral positioning promotes the redistribution of ventilation to the ventral regions of the lung. The use of EIT technology might become a helpful tool for understanding and guiding posture therapy in mechanically ventilated patients.     

Electrical impedance tomography in monitoring experimental lung injury

Objective: To apply electrical impedance tomography (EIT) and the new evaluation approach (the functional EIT) in monitoring the development of artificial lung injury. Design: Acute experimental trial. Setting: Operating room for animal experimental studies at a university hospital. Subjects: Five pigs (41.3 ± 4.1 kg, mean body weight ± SD). Interventions: The animals were anaesthetised and mechanically ventilated. Sixteen electrodes were attached on the thoracic circumference and used for electrical current injection and surface voltage measurement. Oleic acid was applied sequentially (total dose 0.05 ml/kg body weight) into the left pulmonary artery to produce selective unilateral lung injury. Measurements and results: The presence of lung injury was documented by significant changes of PaCO₂ (40.1 mmHg vs control 37.1 mmHg), PaO₂ (112.3 mmHg vs 187.5 mmHg), pH (7.35 vs 7.42), mean pulmonary arterial pressure (29.2 mmHg vs 20.8 mmHg) and chest radiography. EIT detected 1) a regional decrease in mean impedance variation over the affected left lung (–41.4 % vs control) and an increase over the intact right lung ( + 20.4 % vs control) indicating reduced ventilation of the affected, and a compensatory augmented ventilation of the unaffected lung and 2) a pronounced fall in local baseline electrical impedance over the injured lung (–20.6 % vs control) with a moderate fall over the intact lung (–10.0 % vs control) indicating the development of lung oedema in the injured lung with a probable atelectasis formation in the contralateral one. Conclusion: The development of the local impairment of pulmonary ventilation and the formation of lung oedema could be followed by EIT in an experimental model of lung injury. This technique may become a useful tool for monitoring local pulmonary ventilation in intensive care patients suffering from pulmonary disorders associated with regionally reduced ventilation, fluid accumulation and/or cell membrane changes. Received: 22 December 1997 Accepted: 7 April 1998     

Alveolar edema dispersion and alveolar protein permeability during high volume ventilation: effect of positive end-expiratory pressure

Objectives To evaluate whether PEEP affects intrapulmonary alveolar edema liquid movement and alveolar permeability to proteins during high volume ventilation. Design and setting Experimental study in an animal research laboratory. Subjects 46 male Wistar rats. Interventions A ^99mTc-labeled albumin solution was instilled in a distal airway to produce a zone of alveolar flooding. Conventional ventilation (CV) was applied for 30 min followed by various ventilation strategies for 3 h: CV, spontaneous breathing, and high volume ventilation with different PEEP levels (0, 6, and 8 cmH₂O) and different tidal volumes. Dispersion of the instilled liquid and systemic leakage of ^99mTc-albumin from the lungs were studied by scintigraphy. Measurements and results The instillation protocol produced a zone of alveolar flooding that stayed localized during CV or spontaneous breathing. High volume ventilation dispersed alveolar liquid in the lungs. This dispersion was prevented by PEEP even when tidal volume was the same and thus end-inspiratory pressure higher. High volume ventilation resulted in the leakage of instilled ^99mTc-albumin from the lungs. This increase in alveolar albumin permeability was reduced by PEEP. Albumin permeability was more affected by the amplitude of tidal excursions than by overall lung distension. Conclusions PEEP prevents the dispersion of alveolar edema liquid in the lungs and lessens the increase in alveolar albumin permeability due to high volume ventilation. This research was supported by a grant from the French Académie Nationale de Médecine     

Non-invasive radiation-free monitoring of regional lung ventilation in critically ill infants

OBJECTIVE: Established techniques used to examine lung function in critically ill infants cannot continuously follow regional aspects of lung ventilation although this information would be beneficial for proper therapy planning. We have studied the applicability and clinical relevance of a relatively new non-invasive radiation-free imaging method, electrical impedance tomography (EIT), in monitoring regional lung function in paediatric intensive care patients. DESIGN: Prospective study. SETTING: Neonatal and paediatric intensive care unit (ICU) at a university hospital. PATIENTS: Eight infants (1 day-7 years old) suffering from miscellaneous diseases requiring intensive care therapy. INTERVENTIONS: Adjustment of ventilator settings, surfactant administration, and postural changes. MEASUREMENTS AND RESULTS: Repeated EIT measurements were performed with the intention to monitor regional lung ventilation in mechanically ventilated and spontaneously breathing infants. The follow-up time ranged between 1 and 11 days. During individual EIT measurements of 100-s duration electrical voltages resulting from repetitive injection of small electrical currents were continuously measured on the thoracic circumference using conventional surface electrodes. Acquired data were used to generate functional cross-sectional thoracic images of regional lung ventilation. A total of 638 EIT measurements were performed. The redistribution of lung ventilation and changes in regional ventilation magnitude resulting from adjusted positive end-expiratory pressure, peak inspiratory pressure, inspiration-expiration ratio, surfactant instillation, and prone or supine positioning were identified. CONCLUSIONS: Provided that EIT hardware and software are further developed to guarantee stable and undisturbed measurements in the ICU and that practical handling is improved, this non-invasive method may become a useful bedside monitoring tool of regional lung ventilation in critically ill infants.     

PEEP has beneficial effects on inflammation in the injured and no deleterious effects on the noninjured lung after unilateral lung acid instillation

Objective In clinical lung injury areas of inflammation and structural alveolar alteration are unevenly distributed and interspaced between healthy or less injured lung areas. Positive end-expiratory pressure (PEEP) applied with mechanical ventilation (MV) may affect injured and healthy lung areas differently. We compared the effects of PEEP on the inflammatory response in injured and noninjured regions of the lung in an animal model of unilateral lung acid instillation.Subjects Anesthetized, paralyzed, and ventilated rats.Interventions Rats underwent left-endobronchial instillation with either hydrochloric acid or isotonic saline and were randomized 24 h later to MV using constant tidal volume (16 ml/kg) with either ZEEP, PEEP at 5 mmHg, or PEEP at 10 mmHg. After 4 h of MV the animals (n = 9 or 10 per group) were killed and inflammatory markers assessed in left- and right-lung lavage fluid samples. In four additional animals per group differential lung perfusion was assessed.Results Unilateral acid injury alone worsened oxygenation, decreased left-lung perfusion, and increased left-lung lavage neutrophil and macrophage counts and cytokine levels. MV with ZEEP further impaired oxygenation and further decreased left-lung perfusion in acid-injured animals. MV with high PEEP preserved oxygenation and significantly decreased left-lung lavage protein content and cell counts in acid-injured animals and had no deleterious effect on the right (noninjured) lung.Conclusion In this model of unilateral lung acid injury high PEEP attenuates the inflammatory cell response in the acid-injured lung, preserved oxygenation and has no deleterious effects in the opposite lung.Electronic supplementary material The electronic reference of this article is . The online full-text version of this article includes electronic supplementary material. This material is available to authorised users and can be accessed by means of the ESM button beneath the abstract or in the structured full-text article. To cite or link to this article you can use the above reference.     

Electrical Impedance Tomography's Correlation to Lung Volume is Not Influenced by Anthropometric Parameters

Study objectives. Electrical impedance tomography (EIT) is able to reflect physiological parameters such as real-time changes in global and regional lung volume. EIT can aid in the assessment of lung recruitment, and its use has been validated in preliminary studies monitoring mechanical ventilation at the bedside. ICU patients vary widely in their body habitus, and obesity is becoming more prevalent. Our primary research purpose was to establish whether anthropometric parameters influence EIT's reliability. Our secondary question was whether body position alters its correlation to spirometric measurements. { Subjects.} 22 healthy adult volunteers (12 male, 10 female) with broadly variable anthropometric parameters. { Interventions.} Simultaneous measurements of changes in lung volume using EIT imaging and a pneumotachograph were obtained with two breathing patterns (quiet and deep breathing) and in four body positions (standing, sitting, semi-reclining and supine). { Measurements and results.} Correlation between measurements of changes in lung volume using EIT imaging and a pneumotachograph was excellent. Variations attributable to anthropometric measurements accounted for at most a 1.3% difference. { Conclusions.} Anthropometric variability and body position do not adversely influence the EIT estimation of changes in lung volume. These data suggest EIT could be used to monitor critically ill mechanically ventilated adults with variable body habitus regardless of position. Marquis F, Coulombe N, Costa R, Gagnon H, Guardo R, Skrobik Y. Electrical impedance tomography's correlation to lung volume is not influenced by anthropometric parameters.     

Respiratory load compensation during mechanical ventilation—proportional assist ventilation with load-adjustable gain factors versus pressure support

Rationale In mechanically ventilated patients respiratory system impedance may vary from time to time, resulting, with pressure modalities of ventilator support, in changes in the level of assistance. Recently, implementation of a closed-loop adjustment to continuously adapt the level of assistance to changes in respiratory mechanics has been designed to operate with proportional assist ventilation (PAV+).Objectives The aim of this study was to assess, in critically ill patients, the short-term steady-state response of respiratory motor output to added mechanical respiratory load during PAV+ and during pressure support (PS).Patients and interventions In 10 patients respiratory workload was increased and the pattern of respiratory load compensation was examined during both modes of support.Measurements and results Airway and transdiaphragmatic pressures, volume and flow were measured breath by breath. Without load, both modes provided an equal support as indicated by a similar pressure–time product of the diaphragm per breath, per minute and per litre of ventilation. With load, these values were significantly lower (p < 0.05) with PAV+ than those with PS (5.1 ± 3.7 vs 6.1 ± 3.4 cmH₂O.s, 120.9 ± 77.6 vs 165.6 ± 77.5 cmH₂O.s/min, and 18.7 ± 15.1 vs 24.4 ± 16.4 cmH₂O.s/l, respectively). Contrary to PS, with PAV+ the ratio of tidal volume (V_T) to pressure–time product of the diaphragm per breath (an index of neuroventilatory coupling) remained relatively independent of load. With PAV+ the magnitude of load-induced V_T reduction and breathing frequency increase was significantly smaller than that during PS.Conclusion In critically ill patients the short-term respiratory load compensation is more efficient during proportional assist ventilation with adjustable gain factors than during pressure support.Electronic supplementary material The electronic reference of this article is . The online full-text version of this article includes electronic supplementary material. This material is available to authorised users and can be accessed by means of the ESM button beneath the abstract or in the structured full-text article. To cite or link to this article you can use the above reference.     

Outcome of assisted ventilation for acute respiratory failure in cystic fibrosis

Objectives To assess outcome of assisted ventilation in cystic fibrosis (CF) patients with acute respiratory failure (ARF), to identify risk factors associated with poor outcome and to compare long-term outcome of CF children who were mechanically ventilated for ARF with unventilated CF controls.Design Retrospective cohort study.Setting Two large CF centres in the Netherlands.Patients CF patients who required assisted ventilation for ARF and unventilated CF controls.Interventions None.Measurements and results Thirty-one CF patients required assisted ventilation for ARF between January 1990 and March 2005. All five children (under 2 years of age) and seven adults (27%) survived. In the total population, age was a statistically significant risk factor for poor outcome (p = 0.02). In adult CF patients who required invasive mechanical ventilation, acute on chronic respiratory failure was associated with poor outcome. In children who required mechanical ventilation for ARF, lung function and CF related complications 5 years later were not significantly different compared with controls matched for age, gender and genotype.Conclusions CF patients younger than 2 years old, who are ventilated because of ARF, have a good prognosis and their long-term outcome seems identical to unventilated CF controls. ARF in adult CF patients still is associated with high mortality, especially among patients with acute on chronic respiratory failure.Electronic supplementary material The electronic reference of this article is . The online full-text version of this article includes electronic supplementary material. This material is available to authorised users and can be accessed by means of the ESM button beneath the abstract or in the structured full-text article. To cite or link to this article you can use the above reference.     

High-frequency oscillatory ventilation reduces lung inflammation: a large-animal 24-h model of respiratory distress

Objective High-frequency oscillatory ventilation (HFOV) may reduce ventilator-induced lung injury in experimental neonatal respiratory distress. However, these data permit no conclusions for large animals or adult patients with acute respiratory distress syndrome (ARDS), because in neonates higher frequencies and lower amplitudes can be used, resulting in lower tidal volumes (VT) and airway pressures. The aim of this study was to compare gas exchange, lung histopathology and inflammatory cytokine expression during lung-protective pressure-controlled ventilation (PCV) and HFOV in a long-term large-animal model of ARDS. Design Prospective, randomized, controlled pilot study. Setting University animal laboratory. Subjects Sixteen female pigs (55.3 ± 3.9 kg). Interventions After induction of ARDS by repeated lavage, the animals were randomly assigned to PCV (VT = 6 ml/kg) and HFOV (6 Hz). After lung injury, a standardised lung recruitment was performed in both groups, and ventilation was continued for 24 h. Measurements and results: After lung recruitment sustained improvements in the oxygenation index were observed in both groups. The mean airway pressure (mPaw) was significantly lower in the HFOV group during the experiment ( p < 0.01). Histologically, lung inflammation was significantly ameliorated in the HFOV group ( p < 0.05). The messenger RNA expression of IL-1-β in lung tissue was significantly lower in the HFOV-treated animals ( p < 0.01). Conclusions These data suggest that HFOV compared with conventional lung-protective ventilation can reduce lung inflammation in a large-animal 24-h model of ARDS. Furthermore, it was shown that lung recruitment leads to sustained improvements in gas exchange with a significantly lower mPaw when HFOV is used. This article is discussed in the editorial available at: .     

Effects of mechanical ventilation on the extracellular matrix

The extracellular matrix (ECM) plays an important role in the biomechanical behaviour of the lung parenchyma. The ECM is composed of a three-dimensional fibre mesh filled with different macromolecules, including the glycosaminoglycans and the proteoglycans, which have important functions in many lung pathophysiological processes: (1) regulating the hydration and water homeostasis, (2) maintaining the structure and function, (3) modulating the inflammatory response, and (4) influencing tissue repair and remodelling. Ventilator-induced lung injury is the result of a complex interplay among various mechanical forces acting on lung structures such as the epithelial and endothelial cells, the extracellular matrix, and the peripheral airways during mechanical ventilation. Although excellent reviews have synthesized our current knowledge of the role of repeated cyclic stretch and high tidal volume ventilation on alveolar and endothelial cells, few have addressed the effects of mechanical ventilation on the ECM. The present review focused on the organization of the ECM, mechanotransduction and ECM interactions, and the effects of mechanical ventilation on the ECM. The study of the ECM may be useful to improve our understanding of the pathophysiology of lung damage induced by mechanical ventilation. This article is discussed in the editorial available at: .     

Virus infection in exacerbations of chronic obstructive pulmonary disease requiring ventilation

Objectives We aimed to characterise and quantify the incidence of common infectious agents in acute exacerbations of chronic obstructive pulmonary disease (COPD) requiring ventilation, with a focus on respiratory viruses.Design An epidemiological study conducted over 3 years.Setting A 12-bed intensive care unit (ICU).Participants ICU patients over 45 years of age with a primary diagnosis of COPD exacerbation requiring non-invasive ventilation (NIV) or ventilation via endotracheal tube (ETT).Materials and methods Nasopharyngeal aspirates (NPA) and posterior pharyngeal swabs (PS) were tested for viruses with immunofluorescence assay (IFA), virus culture (VC) and polymerase chain reaction (PCR). Paired virus and atypical pneumonia serology assays were taken. Blood, sputum and endotracheal aspirates were cultured for bacteria.Results 107 episodes in 105 patients were recorded. Twenty-three (21%) died within 28 days. A probable infectious aetiology was found in 69 patient episodes (64%). A virus was identified in 46 cases (43%), being the sole organism in 35 cases (33%) and part of a mixed infection in 11 cases (10%). A probable bacterial aetiology was found in 25 cases (23%). There was no statistically significant difference in clinical characteristics or outcomes between the group with virus infections and that without.Conclusion Forty-six (43%) of the patients with COPD exacerbation requiring mechanical ventilation had a probable viral pathogen. Prodromal, clinical and outcome parameters did not distinguish virus from non-virus illness. PCR was the most sensitive whilst virus culture was the least of virus assays.Electronic supplementary material The electronic reference of this article is . The online full-text version of this article includes electronic supplementary material. This material is available to authorised users and can be accessed by means of the ESM button beneath the abstract or in the structured full-text article. To cite or link to this article you can use the above reference.The study was self-funded by internal grants from the Central Coast Health Services Research Fund and the Hunter Area Pathology Service. There was no funding from pharmaceutical or other commercial organisations or agencies.There was no conflict of interest.This article is discussed in the editorial available at:     

The effect of breathing exercises with body positioning on regional lung ventilation

This review discusses the distribution of ventilation in the normal adult lung and includes the influence of quiet and deep breathing on regional ventilation. The effects of breathing at low lung volumes; inspiratory flow rate; posture; age; and body weight on ventilation are also described. A selection of breathing exercises are examined with regard to their ability to influence regional ventilation. There is no evidence that breathing control (diaphragmatic breathing exercises) improves regional ventilation to the dependent zones of the lungs. Limited evidence does suggest that thoracic expansion exercises, whereby respiratory muscles are voluntarily contracted to alter regional chest wall expansion, can improve underlying ventilation. However, there remains a paucity of evidence regarding the effects of breathing exercises on regional ventilation.     

Measurement of functional residual capacity by helium dilution during partial support ventilation: in vitro accuracy and in vivo precision of the method

Objective Measurement of functional residual capacity (FRC) during controlled and especially during assisted ventilation remains a challenge in the physiological evaluation of ventilated patients. To validate a bag-in-box closed helium dilution technique allowing measurements both during pressure-controlled (PCV) and pressure-support ventilation (PSV). Design and setting Experimental study on lung models containing different volumes, and measurements in patients in the intensive care unit of a university hospital. In patients measurements were performed in duplicate during controlled and assisted ventilation. Patients Thirty-three patients (aged 57 ± 17 years) mechanically ventilated with PCV and PSV. Measurements and results In the lung model assessment of accuracy showed an overall mean difference between FRC measurements and lung model volume of 0.5% (2 SD 5.7%). In patients assessment of repeatability showed a bias between duplicate FRC measurements of −1 ± 70 ml (95% CI −141 to +139 ml). The coefficient of variation was of 3.2% for all measurements with a comparable repeatability in PSV and PCV mode (coefficient of variation of 3.4 and 3.2%, respectively). During the rebreathing period a small reduction in tidal volume (−8.5 ± 5.4%) and mean airway pressure (−2.3 ± 4.7%) was observed with only a 0.3 cmH₂O mean increase in PEEP and no change in respiratory rate and I/E ratio. Conclusions This specifically designed closed helium dilution bag-in-box technique allows accurate FRC measurement with good repeatability during both partial PSV and PVC without exposing patients to disconnection and changes in PEEP. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The mechanics of breathing in children with acute severe croup

Rationale The assessment of the severity of croup and response to therapy has remained a clinical one. Despite recognition of the importance of a reproducible and easily applicable method for objectively measuring severity, currently, no such technique exists. Objectives We postulated that measurements of air flow and intrathoracic pressure changes in patients with severe croup would provide detailed information about the mechanics of breathing and the potential for the development of continuous bedside methods for objective monitoring of upper airway obstruction. Methods Twenty out of 21 eligible infants and children with severe upper airway obstruction from croup, and 5 control participants, were studied under light sedation utilizing face masks and nasogastric feeding tubes for flow and esophageal pressure measurements. Measurements and main results Children with croup had lower tidal volumes, but breathed faster, thus maintaining similar minute volumes to the controls. During inspiration, all but 2 croup patients (but no controls) displayed flow limitation. Area within the flow–volume curve was significantly decreased and minute ventilation for effort expended was nearly 4.5 times higher in croup patients than in controls. Peak-to-trough pleural pressure swings, pressure–rate product and pressure–time integral were also significantly higher than in controls (p < 0.001) and returned to the normal range in the 9 patients who were subsequently intubated (p < 0.001). Conclusions Patients with severe croup maintain minute ventilation by means of huge increases in intrathoracic pressure changes. Inspiratory flow limitation is present. In future outcome studies, measurements of respiratory function that do not include intrathoracic pressure changes are unlikely to be effective measures of the severity of croup. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Declaration: The authors are neither supported by, nor maintain any financial interest in, any commercial activity associated with the topic of this article.     

Constant flow insufflation of oxygen as the sole mode of ventilation during out-of-hospital cardiac arrest

Background Constant flow insufflation of oxygen (CFIO) through a Boussignac multichannel endotracheal tube has been reported to be an efficient ventilatory method during chest massage for cardiac arrest.Methods Patients resuscitated for out-of-hospital cardiac arrest were randomly assigned to standard endotracheal intubation and mechanical ventilation (MV; n = 457) or use of CFIO at a flow rate of 15 l/min (n = 487). Continuous chest compressions were similar in the two groups. Pulse oximetry level was recorded every 5 min. Outcome of initial resuscitation, hospital admission, complications, and discharge from the intensive care unit (ICU) were analyzed. The randomization scheme was changed during the study, but the in-depth analysis was performed only on the first cohort of 341 patients with CFIO and 355 with MV, because of randomization problems in the second part.Results No difference in outcome was noted regarding return to spontaneous circulation (CFIO 21%, MV 20%), hospital admission (CFIO 17%, MV 16%), or ICU discharge (CFIO 2.4%, MV 2.3%). The level of detectable pulse saturation and the proportion of patients with saturation above 70% were higher with CFIO. Ten patients with MV but only one with CFIO had rib fractures.Conclusions CFIO is a simplified alternative to MV, with favorable effects regarding oxygenation and fewer complications, as observed in this group of patients with desperate prognosis.Electronic supplementary material The electronic reference of this article is . The online full-text version of this article includes electronic supplementary material. This material is available to authorised users and can be accessed by means of the ESM button beneath the abstract or in the structured full-text article. To cite or link to this article you can use the above reference.