Changes In Distribution Of Ventilation Research Articles

Electrical Impedance Tomography as a monitoring tool during weaning from mechanical ventilation: an observational study during the spontaneous breathing trial

BackgroundProlonged weaning from mechanical ventilation is associated with poor clinical outcome. Therefore, choosing the right moment for weaning and extubation is essential. Electrical Impedance Tomography (EIT) is a promising innovative lung monitoring technique, but its role in supporting weaning decisions is yet uncertain. We aimed to evaluate physiological trends during a T-piece spontaneous breathing trail (SBT) as measured with EIT and the relation between EIT parameters and SBT success or failure.MethodsThis is an observational study in which twenty-four adult patients receiving mechanical ventilation performed an SBT. EIT monitoring was performed around the SBT. Multiple EIT parameters including the end-expiratory lung impedance (EELI), delta Tidal Impedance (ΔZ), Global Inhomogeneity index (GI), Rapid Shallow Breathing Index (RSBIEIT), Respiratory Rate (RREIT) and Minute Ventilation (MVEIT) were computed on a breath-by-breath basis from stable tidal breathing periods.ResultsEELI values dropped after the start of the SBT (p < 0.001) and did not recover to baseline after restarting mechanical ventilation. The ΔZ dropped (p < 0.001) but restored to baseline within seconds after restarting mechanical ventilation. Five patients failed the SBT, the GI (p = 0.01) and transcutaneous CO2 (p < 0.001) values significantly increased during the SBT in patients who failed the SBT compared to patients with a successful SBT.ConclusionEIT has the potential to assess changes in ventilation distribution and quantify the inhomogeneity of the lungs during the SBT. High lung inhomogeneity was found during SBT failure. Insight into physiological trends for the individual patient can be obtained with EIT during weaning from mechanical ventilation, but its role in predicting weaning failure requires further study.

Validation of three-dimensional thoracic electrical impedance tomography of horses during normal and increased tidal volumes

Objective. Data from two-plane electrical impedance tomography (EIT) can be reconstructed into various slices of functional lung images, allowing for more complete visualisation and assessment of lung physiology in health and disease. The aim of this study was to confirm the ability of 3D EIT to visualise normal lung anatomy and physiology at rest and during increased ventilation (represented by rebreathing). Approach. Two-plane EIT data, using two electrode planes 20 cm apart, were collected in 20 standing sedate horses at baseline (resting) conditions, and during rebreathing. EIT data were reconstructed into 3D EIT whereby tidal impedance variation (TIV), ventilated area, and right-left and ventral-dorsal centres of ventilation (CoVRL and CoVVD, respectively) were calculated in cranial, middle and caudal slices of lung, from data collected using the two planes of electrodes. Main results. There was a significant interaction of time and slice for TIV (p < 0.0001) with TIV increasing during rebreathing in both caudal and middle slices. The ratio of right to left ventilated area was higher in the cranial slice, in comparison to the caudal slice (p = 0.0002). There were significant effects of time and slice on CoVVD whereby the cranial slice was more ventrally distributed than the caudal slice (p < 0.0009 for the interaction). Significance. The distribution of ventilation in the three slices corresponds with topographical anatomy of the equine lung. This study confirms that 3D EIT can accurately represent lung anatomy and changes in ventilation distribution during rebreathing in standing sedate horses.

Impact of Supine Versus Semirecumbent Body Posture on the Distribution of Ventilation in Acute Respiratory Distress Syndrome.

In some patients with acute respiratory distress syndrome (ARDS), a paradoxical improvement in respiratory system compliance (CRS) has been observed when assuming a supine (head of bed [HOB] 0°) compared with semirecumbent (HOB 35-40°) posture. We sought to test the hypothesis that mechanically ventilated patients with ARDS would have improved CRS, due to changes in ventilation distribution, when moving from the semirecumbent to supine position. We conducted a prospective, observational ICU study including 14 mechanically ventilated patients with ARDS. For each patient, ventilation distribution (assessed by electrical impedance tomography) and pulmonary mechanics were compared in supine versus semirecumbent postures. Compared with semirecumbent, in the supine posture CRS increased (33 ± 21 vs. 26 ± 14 mL/cm H2O, p = 0.005), driving pressure was reduced (14 ± 6 vs. 17 ± 7 cm H2O, p < 0.001), and dorsal fraction of ventilation was decreased (48.5 ± 14.1% vs. 54.5 ± 12.0%, p = 0.003). Posture change from semirecumbent to supine resulted in a favorable physiologic response in terms of improved CRS and reduced driving pressure-with a corresponding increase in ventral ventilation, possibly related to reduced ventral overdistension.

Effect of routine suction on lung aeration in critically ill neonates and young infants measured with electrical impedance tomography

Endotracheal suctioning is a widely used procedure to remove secretions from the airways of ventilated patients. Despite its prevalence, regional effects of this maneuver have seldom been studied. In this study, we explore its effects on regional lung aeration in neonates and young infants using electrical impedance tomography (EIT) as part of the large EU-funded multicenter observational study CRADL. 200 neonates and young infants in intensive care units were monitored with EIT for up to 72 h. EIT parameters were calculated to detect changes in ventilation distribution, ventilation inhomogeneity and ventilation quantity on a breath-by-breath level 5–10 min before and after suctioning. The intratidal change in aeration over time was investigated by means of regional expiratory time constants calculated from all respiratory cycles using an innovative procedure and visualized by 2D maps of the thoracic cross-section. 344 tracheal suctioning events from 51 patients could be analyzed. They showed no or very small changes of EIT parameters, with a dorsal shift of the center of ventilation by 0.5% of the chest diameter and a 7% decrease of tidal impedance variation after suctioning. Regional time constants did not change significantly. Routine suctioning led to EIT-detectable but merely small changes of the ventilation distribution in this study population. While still a measure requiring further study, the time constant maps may help clinicians interpret ventilation mechanics in specific cases.

Changes in ventilation distribution during general anesthesia measured with EIT in mechanically ventilated small children

BackgroundAtelectasis during general anesthesia is a risk for perioperative complications. EIT measurements were performed in mechanically ventilated healthy children during elective surgery to demonstrate the changes in ventilation distribution during general anesthesia. The ventilation distribution was quantified by calculating the Global Inhomogeneity index (GI).MethodsEIT measurements were performed in 23 children (9 weeks—10 years) without lung disease to detect changes in regional ventilation during elective surgery. Three previously defined time points were marked during the measurement: after intubation and start of pressure-controlled ventilation (PCV), change to pressure support ventilation (PSV), and after extubation (spontaneous breathing—SB). Ventilation distribution based on regions of interest (ROI) and changes in end-expiratory volume (∆EELV) were collected at these time points and compared. The Global Inhomogeneity index was calculated at the beginning of pressure-controlled ventilation (PCV).ResultsWith increasing spontaneous breathing, dorsal recruitment of atelectasis occurred. The dorsal ventilation fraction increased over the time of general anesthesia with increasing spontaneous breathing, whereas the ventral fraction decreased relatively (Difference ± 5.5 percentage points respectively; 95% CI; 3.5—7.4; p < 0.001). With the onset of spontaneous breathing, there was a significant reduction in end-expiratory volume (Difference: 105 ml; 95% CI, 75–135; p < 0.001). The GI of the lung-healthy ventilated children is 47% (SD ± 4%).ConclusionControlled ventilation of healthy children resulted in increased ventilation of the ventral and collapse of the dorsal lung areas. Restart of spontaneous breathing after cessation of surgery resulted in an increase in ventilation in the dorsal with decrease in the ventral lung areas. By calculating the GI, representing the ratio of more to less ventilated lung areas, revealed the presumed homogeneous distribution of ventilation.Trial registrationClinicalTrials.gov Registration ID: NCT04873999. First registration: 05/05/2021.

Wearable pulmonary monitoring system with integrated functional lung imaging and chest sound recording: a clinical investigation in healthy subjects

Objective. Current wearable respiratory monitoring devices provide a basic assessment of the breathing pattern of the examined subjects. More complex monitoring is needed for healthcare applications in patients with lung diseases. A multi-sensor vest allowing continuous lung imaging by electrical impedance tomography (EIT) and auscultation at six chest locations was developed for such advanced application. The aims of our study were to determine the vest’s capacity to record the intended bio-signals, its safety and the comfort of wearing in a first clinical investigation in healthy adult subjects. Approach. Twenty subjects (age range: 23–65 years) were studied while wearing the vests during a 14-step study protocol comprising phases of quiet and deep breathing, slow and forced full expiration manoeuvres, coughing, breath-holding in seated and three horizontal postures. EIT, chest sound and accelerometer signals were streamed to a tablet using a dedicated application and uploaded to a back-end server. The subjects filled in a questionnaire on the vest properties using a Likert scale. Main results. All subjects completed the full protocol. Good to excellent EIT waveforms and functional EIT images were obtained in 89% of the subjects. Breathing pattern and posture dependent changes in ventilation distribution were properly detected by EIT. Chest sounds were recorded in all subjects. Detection of audible heart sounds was feasible in 44%–67% of the subjects, depending on the sensor location. Accelerometry correctly identified the posture in all subjects. The vests were safe and their properties positively rated, thermal and tactile properties achieved the highest scores. Significance. The functionality and safety of the studied wearable multi-sensor vest and the high level of its acceptance by the study participants were confirmed. Availability of personalized vests might further advance its performance by improving the sensor-skin contact.

Changes in ventilation distribution in children with neuromuscular disease using the insufflator/exsufflator technique: an observational study

Patients with neuromuscular disease often suffer from weak and ineffective cough resulting in mucus retention and increased risk for chest infections. Different airway clearance techniques have been proposed, one of them being the insufflator/exsufflator technique. So far, the immediate physiological effects of the insufflator/exsufflator technique on ventilation distribution and lung volumes are not known. We aimed to describe the immediate effects of the insufflator/exsufflator technique on different lung volumes, forced flows and ventilation distribution. Eight subjects (age 5.8–15.2 years) performed lung function tests including spirometry, multiple breath washout and electrical impedance tomography before and after a regular a chest physiotherapy session with an insufflator/exsufflator device. Forced lung volumes and flows as well as parameters of ventilation distribution derived from multiple breath washout and electrical impedance tomography were compared to assess the short-term effect of the therapy. In this small group of stable paediatric subjects with neuromuscular disease we could not demonstrate any short-term effects of insufflation/exsufflation manoeuvres on lung volumes, expiratory flows and ventilation distribution. With the currently used protocol of the insufflation/exsufflation manoeuvre, we cannot demonstrate any immediate changes in lung function.

Prolonged Continuous Monitoring of Regional Lung Function in Infants with Respiratory Failure.

Rationale: Electrical impedance tomography (EIT) allows instantaneous and continuous visualization of regional ventilation and changes in end-expiratory lung volume at the bedside. There is particular interest in using EIT for monitoring in critically ill neonates and young children with respiratory failure. Previous studies have focused only on short-term monitoring in small populations. The feasibility and safety of prolonged monitoring with EIT in neonates and young children have not been demonstrated yet. Objectives: To evaluate the feasibility and safety of long-term EIT monitoring in a routine clinical setting and to describe changes in ventilation distribution and homogeneity over time and with positioning in a multicenter cohort of neonates and young children with respiratory failure. Methods: At four European University hospitals, we conducted an observational study (NCT02962505) on 200 patients with postmenstrual ages (PMA) between 25 weeks and 36 months, at risk for or suffering from respiratory failure. Continuous EIT data were obtained using a novel textile 32-electrode interface and recorded at 48 images/s for up to 72 hours. Clinicians were blinded to EIT images during the recording. EIT parameters and the effects of body position on ventilation distribution were analyzed offline. Results: The average duration of EIT measurements was 53 ± 20 hours. Skin contact impedance was sufficient to allow image reconstruction for valid ventilation analysis during a median of 92% (interquartile range, 77-98%) of examination time. EIT examinations were well tolerated, with minor skin irritations (temporary redness or imprint) occurring in 10% of patients and no moderate or severe adverse events. Higher ventilation amplitude was found in the dorsal and right lung areas when compared with the ventral and left regions, respectively. Prone positioning resulted in an increase in the ventilation-related EIT signal in the dorsal hemithorax, indicating increased ventilation of the dorsal lung areas. Lateral positioning led to a redistribution of ventilation toward the dependent lung in preterm infants and to the nondependent lung in patients with PMA > 37 weeks. Conclusions: EIT allows continuous long-term monitoring of regional lung function in neonates and young children for up to 72 hours with minimal adverse effects. Our study confirmed the presence of posture-dependent changes in ventilation distribution and their dependency on PMA in a large patient cohort. Clinical trial registered with www.clinicaltrials.gov (NCT02962505).

Dynamic lung behavior under high G acceleration monitored with electrical impedance tomography

Objective. During launch and atmospheric re-entry in suborbital space flights, astronauts are exposed to high G-acceleration. These acceleration levels influence gas exchange inside the lung and can potentially lead to hypoxaemia. The distribution of air inside the lung can be monitored by electrical impedance tomography. This imaging technique might reveal how high gravitational forces affect the dynamic behavior of ventilation and impair gas exchange resulting in hypoxaemia. Approach. We performed a trial in a long-arm centrifuge with ten participants lying supine while being exposed to +2, +4 and +6 G x (chest-to-back acceleration) to study the magnitude of accelerations experienced during suborbital spaceflight. Main results. First, the tomographic images revealed that the dorsal region of the lung emptied faster than the ventral region. Second, the ventilated area shifted from dorsal to ventral. Consequently, alveolar pressure in the dorsal area reached the pressure of the upper airways before the ventral area emptied completely. Finally, the upper airways collapsed and the end-expiratory volume increased. This resulted in ventral gas trapping with restricted gas exchange. Significance. At +4 G x , changes in ventilation distribution varied considerably between subjects, potentially due to variation in individual physical conditions. However, at +6 G x all participants were affected similarly and the influence of high gravitational conditions was pronounced.

Lung ventilation distribution in patients after traditional full sternotomy and minimally invasive thoracotomy: An observational study.

The aim of the study was to examine the post-operative ventilation distribution changes in cardiac surgical patients after traditional full sternotomy (FS) or minimally invasive thoracotomy (MIT). A total of 40 patients scheduled for FS with two-lung ventilation or MIT with one-lung ventilation were included. Ventilation distribution was measured with electrical impedance tomography (EIT) at T1, before surgery; T2, after surgery in ICU before weaning; T3, 24hours after extubation. EIT-based parameters were calculated to assess the ventilation distribution, including the left-to-right lung ratio, ventral-to-dorsal ratio, and the global inhomogeneity index. The global inhomogeneity index increased at T2 and T3 compared to T1 in all patients but only statistically significant in patients with MIT (FS, P=.06; MIT, P<.01). Notable decrease in the dorsal regions (FS) or in the non-ventilated side (MIT) was observed at T2. Ventilation distribution was partially improved at T3 but huge variations of recovery progresses were found in all patients regardless of the surgery types. Subgroup analysis indicated that operation duration was significantly lower in the MIT group (240±40 in FS vs 205±90minutes in MIT, median±interquartile range, P<.05) but the incidence of atrial fibrillation/flutter was significantly higher (5% in FS vs 50% in MIT, P<.01). Other exploratory outcomes showed no statistical differences. Ventilation distribution was impaired after cardiac surgery. The recovery process of ventilation homogeneity was strongly depending on individuals so that MIT was not always superior in this aspect. EIT may help to identify the patients requiring further care after surgery.

NOVEL X-RAY VELOCIMETRY-BASED QUANTITATIVE REGIONAL LUNG FUNCTION ANALYSIS TO ASSESS RISK OF RADIATION-INDUCED PNEUMONITIS AND PULMONARY FIBROSIS

SESSION TITLE: Late Breaking Pulmonary Fibrosis SESSION TYPE: Original Investigations PRESENTED ON: 10/22/2019 08:45 AM - 09:45 AM PURPOSE: Quantification of small changes in lung function is necessary for early diagnosis and intervention in chronic lung diseases. Pneumonitis is a frequent complication of lung radiation that currently has no known therapy and can only be diagnosed late when it manifests changes in the pulmonary function tests (PFT). Unlike existing PFT, X-ray Velocimetry (XV) technology uniquely measures 4D lung motion to quantify regional lung function with high resolution and accuracy providing a novel diagnostic tool for early assessment of risk of radiation induced pneumonitis and/or pulmonary fibrosis. METHODS: This study was primarily designed to assess the performance of XV technology in comparison to other clinically available measures (spirometry, CT) in diagnosing radiation pneumonitis. Patients with a predicted risk for pneumonitis of 25% (V20 Gy>20%) were consented and enrolled in this study. In order to test the capacity of XV to detect changes in lung function over time, XV-scans were acquired pre-treatment, weekly on treatment and at 4-months and 12-months following treatment in combination with PFTs, and/or 4DCT or CT. RESULTS: Compared to PFT, the tidal volume and ventilation (Heterogeneity Index, HI% and Ventilation Defect Percentage, VDP) data from XV scans obtained 1 week apart showed excellent reproducibility in preliminary analysis. Moreover, derived global metrics such as ventilation heterogeneity and VDP varied by less than 2% for each patient analyzed. In the case of normal lung function (as indicated by PFT), XV scan results were consistent over multiple days, despite variability in imaging conditions. In the next case, XV and PFT measurements at 4-months and 12-months post-treatment were validated. At 4-months this subject’s FEV1 was >100% of expected levels for normal lung function, and the FEV1/FVC ratio was 1.07. By 12-months, FEV1s had decreased to 81% of expected, with FEV1/FVC = 0.89. Similarly, XV indicates a moderate change in lung function over this period, with an increase in HI from 56.2% to 66.1% and an increase in VDP from 7.1% to 11.6%. Moreover, contour maps of specific ventilation highlight changes in the regional distribution of ventilation. The lower region of the right lung was substantially less ventilated at twelve months post-treatment, with compensation occurring in other regions, showing the potential of XV in capturing regional lung function changes not available from PFT. CONCLUSIONS: This ongoing trial demonstrate that XV is repeatable and sensitive, detecting modest regional changes in lung function, such as the location of abnormally ventilated regions that may be an early indicator for lung fibrosis. CLINICAL IMPLICATIONS: XV analysis using existing fluoroscopes, has significantly lower radiation-exposure (compared to CT), and huge potential for early detection and treatment of a variety of lung diseases. DISCLOSURES: Employee relationship with 4Dx Limited Please note: $20001 - $100000 Added 06/20/2019 by Richard Carnibella, source=Web Response, value=Salary No relevant relationships by John DeMarco, source=Web Response Employee <br Employee relationship with 4Dx Inc Please note: >$100000 Added 06/16/2019 by Jonathan Dusting, source=Web Response, value=Salary Owner/Founder relationship with 4Dx Please note: >$100000 Added 06/21/2019 by Andreas Fouras, source=Web Response, value=Ownership interest Owner/Founder relationship with 4Dx Please note: >$100000 Added 06/21/2019 by Andreas Fouras, source=Web Response, value=Ownership interest Employee relationship with 4Dx Please note: >$100000 Added 06/20/2019 by Robert Jamison, source=Web Response, value=Salary Owner/Founder relationship with 4Dx Please note: >$100000 Added 06/20/2019 by Robert Jamison, source=Web Response, value=Ownership interest No relevant relationships by Cynthia Martin, source=Admin input Employee relationship with 4Dx Please note: $20001 - $100000 Added 06/20/2019 by Punit Shah, source=Web Response, value=Salary No relevant relationships by Stephen Shiao, source=Web Response Employee relationship with 4Dx Limited Please note: >$100000 Added 06/20/2019 by Neeraj Vij, source=Web Response, value=Salary Employee relationship with 4Dx Please note: $20001 - $100000 Added 06/20/2019 by David Wenger, source=Web Response, value=Salary Employee relationship with 4Dx Limited Please note: $20001 - $100000 Added 06/20/2019 by Alex Winnett, source=Web Response, value=Salary

Assessment of Ventilation Distribution during Laparoscopic Bariatric Surgery: An Electrical Impedance Tomography Study.

Introduction. The aim of the study was to assess changes of regional ventilation distribution at the level of the 3rd intercostal space in the lungs of morbidly obese patients as a result of general anaesthesia and laparoscopic surgery as well as the relation of these changes to lung mechanics. We also wanted to determine if positive end-expiratory pressure of 10 cm H2O prevents the expected atelectasis in the morbidly obese patients during general anaesthesia. Materials and Methods. 49 patients completed the examination and were randomized to 2 groups: ventilated without positive end-expiratory pressure (PEEP 0) and with PEEP of 10 cm H2O (PEEP 10) preceded by a recruitment maneuver with peak inspiratory pressure of 40 cm H2O. Impedance Ratio (IR) was utilized to examine ventilation distribution changes as a result of anaesthesia, pneumoperitoneum, and change of body position. We also analyzed intraoperative respiratory mechanics and pulse oximetry values. Results. In both groups general anaesthesia caused a ventilation shift towards the nondependent lungs which was not further intensified after pneumoperitoneum. Reverse Trendelenburg position promoted homogeneous ventilation distribution. Respiratory system compliance was reduced after insufflation and improved after exsufflation of pneumoperitoneum. There were no statistically significant differences in ventilation distribution between the examined groups. Respiratory system compliance, plateau pressure, and pulse oximetry values were higher in PEEP 10. Conclusions. Changes of ventilation distribution in the obese do occur at cranial lung regions. During pneumoperitoneum alterations of ventilation distribution may not follow the direction of the changes of lung mechanics. In the obese patients PEEP level of 10 cm H2O preceded by a recruitment maneuver improves respiratory compliance and oxygenation but does not eliminate atelectasis induced by general anaesthesia.

Challenging a paradigm: Positional changes in ventilation distribution are highly variable in healthy infants and children

Current understanding is that infants and children preferentially ventilate non-dependent lungs, a reversal of that of adults, based on studies using krypton-81m ventilation scanning. Participants in these studies had lung disease and were either sedated or ventilated. There is little understanding of the distribution of ventilation in spontaneous breathing healthy infants and children. This study aimed to determine the effects of side lying on the distribution of ventilation in healthy, spontaneously breathing infants and children between the ages of 6 months and 9 years. Measurements were taken using electrical impedance tomography (EIT) in supine, left and right side lying. Distribution of ventilation was described using end-expiratory to end-inspiratory relative impedance change. Fifty-six (31, 55% male) participants were studied. Nineteen (35%) participants consistently showed greater ventilation in the non-dependent lung, eight (15%) consistently showed greater ventilation in the dependent lung and 28 (51%) showed a varied pattern between left and right side lying. Overall, left side lying resulted in significantly better mean ventilation of the right (non-dependent) lung (P < 0.01). Distribution of ventilation in right side lying was relatively equal between left and right lungs. This study demonstrates that the distribution of ventilation in spontaneously breathing infants and children is not as straightforward as previously described. The distribution of ventilation was variably affected by body position with no clear reversal of the adult pattern evident.

Distribution of ventilation in pregnant Shetland ponies measured by Electrical Impedance Tomography

The regional distribution of ventilation in conscious standing pregnant Shetland pony mares was investigated by Electrical Impedance Tomography (EIT). Six ponies were repeatedly examined a minimum of four weeks prior to (antepartum, AP) until three weeks after parturition (postpartum, PP). From the cross-sectional ventilation image the ventral to dorsal (V/D), left to right (L/R) ventilation distribution ratio and the relative ventilation in four horizontal regions of interest (ROI) placed symmetrically in the chest was analyzed. Antepartum V/D was 0.74 ± 0.09 on day -28 ± 3 (AP28) and decreased to 0.68 ± 0.10 on day -3 ± 2 (AP3). Postpartum V/D increased significantly (p<0.05) to 0.96 ± 0.08 on day 7 ± 2 (PP7). The L/R ventilation distribution remains unaffected. Ventilation in the most ventral ROI was significantly lower on days AP28 and AP3 compared to PP7. These results suggest that in Shetland ponies late pregnancy compromises the ventilation in ventral (dependent) lung regions. We demonstrated the feasibility of a repeated EIT measurement in standing conscious ponies.

Electrical impedance tomography measured at two thoracic levels can visualize the ventilation distribution changes at the bedside during a decremental positive end-expiratory lung pressure trial

IntroductionComputed tomography of the lung has shown that ventilation shifts from dependent to nondependent lung regions. In this study, we investigated whether, at the bedside, electrical impedance tomography (EIT) at the cranial and caudal thoracic levels can be used to visualize changes in ventilation distribution during a decremental positive end-expiratory pressure (PEEP) trial and the relation of these changes to global compliance in mechanically ventilated patients.MethodsVentilation distribution was calculated on the basis of EIT results from 12 mechanically ventilated patients after cardiac surgery at a cardiothoracic ICU. Measurements were taken at four PEEP levels (15, 10, 5 and 0 cm H2O) at both the cranial and caudal lung levels, which were divided into four ventral-to-dorsal regions. Regional compliance was calculated using impedance and driving pressure data.ResultsWe found that tidal impedance variation divided by tidal volume significantly decreased on caudal EIT slices, whereas this measurement increased on the cranial EIT slices. The dorsal-to-ventral impedance distribution, expressed according to the center of gravity index, decreased during the decremental PEEP trial at both EIT levels. Optimal regional compliance differed at different PEEP levels: 10 and 5 cm H2O at the cranial level and 15 and 10 cm H2O at the caudal level for the dependent and nondependent lung regions, respectively.ConclusionsAt the bedside, EIT measured at two thoracic levels showed different behavior between the caudal and cranial lung levels during a decremental PEEP trial. These results indicate that there is probably no single optimal PEEP level for all lung regions.

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 (VT)]. A calibration procedure of arbitrary units (AUs) versus ventilator-derived VT performed in all patients during three predefined positions (supine, 60°-left dependent and 60°-right-dependent) showed a significant correlation between VT in supine, left and right lateral positions with the corresponding AUs (r2 = 0·356, P<0·05). Changes in VT 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 VT 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.

Effects of restricted thoracic movement on the regional distribution of ventilation

Restricted thoracic movement is often encountered in patients, necessitating mechanical ventilation during surgery or intensive care treatment. High intraabdominal pressure, obesity or thorax rigidity and deformity reduce the chest distensibility and deteriorate the lung function. They render the selection of proper ventilator settings difficult and complicate the weaning process. Electrical impedance tomography (EIT) is currently being proposed as a bedside imaging method for monitoring regional lung ventilation. The objective of our study was to establish whether the effects of decreased chest compliance on regional lung ventilation can be determined by EIT. Ten healthy male volunteers were studied in our pilot study under three conditions: (1) unrestricted breathing and (2) restricted breathing by abdominal and (3) lower rib cage strapping. The subjects were followed during spontaneous tidal breathing in five postures (sitting, supine, prone, left and right side). EIT and spirometry data were acquired in each condition. The distribution of ventilation in subjects with unrestricted breathing corresponded with the physiologically expected values. In the left and right lateral postures, abdominal and thoracic cage restrictions reduced the ventilation in the dependent lung areas; the non-dependent areas were unaffected. In the prone position, the ventilation of the dependent and non-dependent areas was reduced. The effects of strapping were least pronounced in the supine posture. We conclude that EIT is able to measure changes in the regional distribution of ventilation induced by restricted chest movement and has the potential for optimising artificial ventilation in patients with limited chest compliance of different origins.

Prone equals prone? – impact of different techniques of body positioning on functional residual capacity and ventilation distribution in anaesthetised, paralysed preschool children

Introduction: In children undergoing anesthesia or sedation, optimizing functional residual capacity (FRC) is of special importance, because they have smaller elastic retraction forces compared with adults and a lower relaxation volume that makes them more prone to airway collapse. Moreover, children are particularly vulnerable to hypoxaemia because of their higher oxygen demand per kilo body weight. Although the prone position is effectively used to improve oxygenation, its impact on FRC is controversial. Thus, additional confounding factors such as changes in ventilation distribution or differences in positioning techniques might be of importance. In fact, positioning techniques such as flat versus augmented prone position could exert different degrees of pressure on the abdominal contents and thus differences in the cephalic displacement of the diaphragm. The aim of this study was to determine the impact of two different prone positioning techniques on FRC and ventilation distribution in anesthetized, paralyzed preschool‐aged children. We hypothesized that augmented prone positioning improves FRC and ventilation distribution compared with the supine or flat prone position.Methods: Following local Ethics Committee approval, 30 preschool children without cardiopulmonary disease undergoing elective surgery were studied. FRC and lung clearance index (LCI), a measure of ventilation distribution, were calculated using a sulfur‐hexafluoride gas (SF6) multibreath washout technique. After intubation, the measurements were taken in the supine position and in random order in the flat prone and augmented prone position (gel pads supporting the pelvis and the upper thorax to ensure free movement of the abdomen). The position of the arms was kept constant and the head was turned to the side for all assessments. Measurements were taken 5 min after each positioning. Results: Mean (range) age was 48.5 (24–80) months, weight = 17.2 (10.5–26.9) kg. FRC (mean ± SD) was 22.9 ± 6.2 ml·kg‐1 in the supine position and 23.3 ± 5.6 ml·kg‐1 in the flat prone position while LCI was 8.1 ± 2.3 vs 7.9 ± 2.3 in these two positions, respectively. In contrast, FRC increased to 27.6 ± 6.5 ml·kg‐1 (P &lt; 0.001) in the augmented prone position while at the same time the LCI decreased to 6.7 ± 0.9 (P &lt; 0.001).Conclusions: FRC and ventilation distribution were similar in the supine and flat prone positions, while these parameters improved significantly in the augmented prone position suggesting that the technique of prone positioning could have a major impact on respiratory function in anaesthetized, mechanically ventilated preschool children.Acknowledgement: The study was funded by the Department of Anaesthesia, University of Basel, Switzerland.

Therapeutic Hypercapnia and Ventilation-Perfusion Matching in Acute Lung Injury: Low Minute Ventilation vs Inspired CO2

Hypercapnic acidosis has antiinflammatory effects in animal models of acute lung injury (ALI) and improves ventilation-perfusion (V/Q) matching in normal lungs. The effect of hypercapnia on V/Q matching in ALI is conflicting. Hypercapnic acidosis produced by reduced tidal volumes (Vts) was associated with an increased shunt fraction (QS/QT) in patients with ALI compared with control subjects. Vt differences between groups make the assessment of hypercapnic acidosis on V/Q matching difficult. Adding CO2 to the inhaled gas allows the comparison of gas exchange under identical Vt conditions. We hypothesized the presence of hypercapnic acidosis from inspired carbon dioxide (ICD) would improve gas exchange in ALI and would be superior to that of low minute ventilation (LVe) produced by reduced respiratory rate, rather than Vt.University laboratory study of anesthetized New Zealand White rabbits.Assessment of V/Q relationships using the multiple inert gas elimination technique was performed in 10 saline solution-lavaged animals, which were ventilated with 6 mL/kg Vts and a positive end-expiratory pressure of 8 cm H2O. Each rabbit was studied while it was in eucapnia, followed by hypercapnia (Pa(CO2), 95 to 100 mm Hg) induced by LVe from decreased respiratory rate and by 10% ICD, in random order.The Pa(O2) was greater in ICD and LVe compared to eucapnia, but no significant differences in alveolar-arterial oxygen pressure difference or Pa(O2)/fraction of inspired oxygen ratio occurred. LVe statistically reduced the mean V/Q distributions compared with ICD and eucapnia. Log SDs of ventilation and combined retention and excretion curves of the dispersion index were both increased during LVe, indicating the presence of unfavorable changes in ventilation distribution. Neither LVe nor ICD altered the QS/QT.LVe slightly impairs overall gas exchange and ventilation distribution, but does not increase QS/QT compared with eucapnia and ICD. While ICD does not significantly improve gas exchange, it may be superior to LVe in achieving the antiinflammatory effects of "therapeutic" hypercapnia, since it does not adversely alter gas exchange and has the potential to make the lung more uniformly acidotic.

Changes in distribution of ventilation with lung growth.

We systematically studied the effects of varying preinspiratory lung volumes and expiratory flow rates on the alveolar plateau of the single-breath oxygen test in children and adults. With inhalations of oxygen beginning at functional residual capacity (FRC) compared with residual volume (RV), the slope of phase III increased in 52 of 54 children and 6 of 6 adults (mean increase 29.2%, P less than 0.001) but then decreased at preinspiratory volumes greater than FRC. With maximal expiratory flows, the slopes were smaller than slopes from conventional maneuvers in 14 of 15 children by a mean 24.1%, P less than 0.001. These data suggest that apex-to-base differences in regional lung volume are a major determinant of the slope. Slopes (FRC maneuver) decreased as a function of the height of the children (r = -0.73, P less than 0.001), but differences in nitrogen concentration over the alveolar plateau increased with height (r = 0.70, P less than 0.001). This indicates that the apex-to-base differences in regional lung volume increase with lung size. An estimate of mixing efficiency between resident and inspired gas derived from the alveolar plateau increased with height for both RV (r = 0.40, P less than 0.005) and FRC maneuvers (r = 0.45, p less than 0.005) and was greater for FRC than RV (P less than 0.001). These increases in mixing efficiency are consistent with previously demonstrated decreases in closing volume with growth.