Evaluation of electrical impedance tomography in the measurement of PEEP-induced changes in lung volume

STUDY OBJECTIVES: A new noninvasive practical technique called electrical impedance tomography (EIT) was examined for the measurement of alveolar recruitment. DESIGN: Prospective clinical study. SETTING: ICU of a general hospital. PATIENTS: Acute respiratory failure (ARF) patients. MEASUREMENTS: The ventilation-induced impedance changes (VICs) of the nondependent and the dependent part of the lung were determined by EIT as a measure of tidal volume distribution. By the use of an impedance ratio (IR), defined as the VIC of the nondependent part of the lung divided by the VIC of the dependent part of the lung, the ventilation performances in both parts of the lung were compared to each other. RESULTS: Between patients, the VIC of the nondependent part of the lung was significantly lower in the patients with a level of positive end-expiratory pressure (PEEP) of > 10 cm H2O than in patients with a PEEP of < 5 cm H2O (p < 0.05). A significantly lower IR (-/+ SD) was found in the group with PEEP of > 10 cm H2O than in the group with PEEP between 0 and 5 cm H2O (1.28+/-0.58 vs 2.99+/-1.24, respectively; p < 0.01). In individual patients, the VIC of the whole lung increased when the PEEP level was increased. The VICs of the nondependent part of the lung and of the dependent part of the lung showed significant increases at a PEEP of 10 cm H2O compared to a PEEP of 0 cm H2O (p < 0.05). Also the IR decreased in individual patients when the PEEP was increased; a significant decrease was found at 10 cm H2O compared to 0 cm H2O (1.67+/-1.24 vs 2.23+/-1.47, respectively; p < 0.05). CONCLUSIONS: The decrease in IR indicates an increase in VIC in the dependent part of the lung above the nondependent part of the lung. The increase in VIC can be regarded as an increase in lung volume, implying alveolar recruitment in the dependent part of the lung. The same results also have been shown in earlier reports by CT scan. Since EIT is far more practical than CT scanning and also is a bedside method, EIT might help in the adjustment of ventilator settings in ARF patients.     

Regional ventilation distribution determined by electrical impedance tomography: reproducibility and effects of posture and chest plane

Background and objective: Reliable assessment of regional lung ventilation and good reproducibility of electrical impedance tomography (EIT) data are the prerequisites for the future application of EIT in a clinical setting. The aims of our study were to determine (i) the reproducibility of repeated EIT measurements and (ii) the effect of the studied transverse chest plane on ventilation distribution in different postures. Methods: Ten healthy adult subjects were studied in three postures on two separate days. EIT and spirometric data were obtained during tidal breathing and slow vital capacity (VC) manoeuvres. EIT data were acquired in two chest planes at 13 scans/s. Reproducibility of EIT findings was assessed by Bland‐Altman analysis and Pearson correlation in 16 regions of interest in each plane. Regional ventilation distribution during tidal breathing and deep expiration was determined as fractional ventilation in four quadrants of the studied chest cross‐sections. Results: Our study showed a good reproducibility of EIT measurements repeated after an average time interval of 8 days. Global tidal volumes and VCs determined by spirometry on separate days were not significantly different. Regional ventilation in chest quadrants assessed by EIT was also unaffected. Posture exerted a significant effect on ventilation distribution among the chest quadrants during spontaneous breathing and deep expiration in both planes. The spatial distribution patterns in the two planes were not identical. Conclusions: We conclude that regional EIT ventilation findings are reproducible and recommend that the EIT examination location on the chest is carefully chosen especially during repeated measurements and follow‐up.     

A prospective study of lung water measurements during patient management in an intensive care unit

We prospectively evaluated a protocol that included extravascular thermal volume (ETV) as a measure of extravascular lung water (EVLW) instead of pulmonary artery wedge pressure (Ppaw) measurements to guide the hemodynamic management of 48 critically ill patients. Patients were randomized to either a protocol management (PM), or to a routine management (RM) group. In the RM group, EVLW measurements were unknown to the primary care physicians. The 2 groups were similar with respect to age, gender, and severity of illness. In patients with initially high EVLW, EVLW fell to a greater extent in PM than in RM patients (18 +/- 5 versus 4 +/- 8% decrease, p less than 0.05). This difference was even greater in patients with heart failure. No adverse effects on oxygenation or renal function occurred in following the protocol. Mortality for the groups as a whole was similar, but was significantly better (p less than 0.05) for PM patients with initially high EVLW and normal Ppaw (predominantly patients with sepsis or the adult respiratory distress syndrome). For both groups, patients with an initial EVLW greater than 14 ml/kg had a significantly greater mortality than did those with a lesser amount of EVLW: 13 of 15 (87%) versus 13 of 32 (41%), p less than 0.05. We conclude that management based on a protocol using EVLW measurements is safe, may hasten the resolution of pulmonary edema, and may lead to improved outcome in some critically ill patients.     

Regional ventilation by electrical impedance tomography: a comparison with ventilation scintigraphy in pigs

STUDY OBJECTIVE: The validation of electrical impedance tomography (EIT) for measuring regional ventilation distribution by comparing it with single photon emission CT (SPECT) scanning. DESIGN: Randomized, prospective animal study. SETTINGS: Animal laboratories and nuclear medicine laboratories at a university hospital. PARTICIPANTS: Twelve anesthetized and mechanically ventilated pigs. INTERVENTIONS: Lung injury was induced by central venous injection of oleic acid. Then pigs were randomized to pressure-controlled mechanical ventilation, airway pressure-release ventilation, or spontaneous breathing. Measurements and results: Ventilation distribution was assessed by EIT using cross-sectional electrotomographic measurements of the thorax, and simultaneously by single SPECT scanning with the inhalation of (99m)Tc-labeled carbon particles. For both methods, the evaluation of ventilation distribution was performed in the same transverse slice that was approximately 4 cm in thickness. The transverse slice then was divided into 20 coronal segments (going from the sternum to the spine). We compared the percentage of ventilation in each segment, normalized to the entire ventilation in the observed slice. Our data showed an excellent linear correlation between the ventilation distribution measured by SPECT scanning and EIT according to the following equation: y = 0.82x + 0.7 (R(2) = 0.92; range, 0.86 to 0.97). CONCLUSION: Based on these data, EIT seems to allow, at least in comparable states of lung injury, real-time monitoring of regional ventilation distribution at the bedside.     

Pulmonary vascular responses to hypoxia and hyperoxia in healthy volunteers and COPD patients measured by electrical impedance tomography

BACKGROUND: Electrical impedance tomography (EIT) is a noninvasive imaging technique using impedance to visualize and measure blood volume changes. STUDY OBJECTIVE: To examine the validity of EIT in the measurement of hypoxic pulmonary vasoconstriction (HPV) and hyperoxic pulmonary vasodilation in healthy volunteers and COPD patients. PARTICIPANTS: Group 1 consisted of seven healthy volunteers (mean age, 46 years; age range, 36 to 53 years). Group 2 comprised six clinically stable COPD patients (mean age, 65 years; age range, 50 to 74 years). INTERVENTIONS: EIT measurements were performed in healthy subjects while they were breathing room air, 14% oxygen (ie, hypoxia), and 100% oxygen (ie, hyperoxia) through a mouthpiece. Maximal impedance change during systole (DeltaZsys) was used as a measure of pulmonary perfusion-related impedance changes. Stroke volume (SV) was measured by means of MRI. In the COPD group, EIT and SV also were determined, but only in room air and under hyperoxic conditions. RESULTS: The data were statistically compared to data for the room air baseline condition. In the volunteers, the mean (+/- SD) DeltaZsys for the group was 352 +/- 53 arbitrary units (AU) while breathing room air, 309 +/- 75 AU in hypoxia (p < 0.05), and 341 +/- 69 AU in hyperoxia (not significant [NS]). The mean MRI-measured SV was 83 +/- 21 mL while breathing room air, 90 +/- 29) mL in hypoxia (NS), and 94 +/- 19 mL in hyperoxia (p < 0.05). In the COPD patients, the mean DeltaZsys for this group was 222 +/- 84 AU while breathing room air and 255 +/- 83 AU in hyperoxia (p < 0.05). In this group, the SV was 59 +/- 16 mL while breathing room air and 61 +/- 13 mL in hyperoxia (NS). Thus, the volunteer EIT response to hypoxia is not caused by decreased SV, because SV did not show a significant decrease. Similarly, in COPD patients the EIT response to hyperoxia is not caused by increased SV, because SV showed only a minor change. CONCLUSION: EIT can detect blood volume changes due to HPV noninvasively in healthy subjects and hyperoxic vasodilation in COPD patients.     

Assessment of regional lung ventilation by electrical impedance tomography in a patient with unilateral bronchial stenosis and a history of tuberculosis

Bronchial stenosis can impair regional lung ventilation by causing abnormal, asymmetric airflow limitation. Electrical impedance tomography (EIT) is an imaging technique that allows the assessment of regional lung ventilation and therefore complements the functional assessment of the lungs. We report the case of a patient with left unilateral bronchial stenosis and a history of tuberculosis, in whom regional lung ventilation was assessed by EIT. The EIT results were compared with those obtained by ventilation/perfusion radionuclide imaging. The patient was using nasal continuous positive airway pressure (CPAP) for the treatment of obstructive sleep apnea syndrome. Therefore, we studied the effects of postural changes and of the use of nasal CPAP. The EIT revealed heterogeneous distribution of regional lung ventilation, the ventilation being higher in the right lung, and this distribution was influenced by postural changes and CPAP use. The EIT assessment of regional lung ventilation produced results similar to those obtained with the radionuclide imaging technique and had the advantage of providing a dynamic evaluation without radiation exposure.     

Pulmonary artery wedge pressure and extravascular lung water in patients with acute cardiogenic pulmonary edema requiring mechanical ventilation

This study describe the values of pulmonary artery wedge pressure (PAWP) and the extravascular lung water (EVLW) index in patients with acute cardiogenic pulmonary edema who require mechanical ventilation. Ten consecutive patients with acute cardiogenic pulmonary edema who required mechanical ventilation were studied. Cardiac index was determined with thermodilution. Central venous pressure and PAWP were measured with a pulmonary artery catheter. EVLW index was determined with the thermal dye dilution technique, using a commercially available computer system. Measurements were made at regular preset intervals after the initiation of mechanical ventilation. PAWP was normal at baseline (11.6+/-0.9 mm Hg, range 8 to 17) and did not change. EVLW index was elevated at baseline (13.7+/-1.5 ml/ kg) and decreased to a normal value after 24 hours (8.6+/-1.2 ml/kg, p = 0.02). Concomitantly cardiac index increased from 2.61+/-0.24 to 3.61+/-0.14 L/min/m2 (p = 0.05). There was no correlation between PAWP and EVLW index. Fluid balance was +1,221+/-908 ml after 24 hours and there was a weight gain of 0.88+/-1.06 kg after 24 hours. Thus, patients with acute cardiogenic pulmonary edema requiring mechanical ventilation may have a normal PAWP after mechanical ventilation has been initiated. In a hemodynamic unstable situation, these patients may require fluid challenges to improve cardiac output, despite the presence of pulmonary edema. The pulmonary edema, measured as EVLW index, resolves rapidly when cardiac performance improves, despite positive fluid balances and weight gain in the first 24 hours.     

Improved outcome based on fluid management in critically ill patients requiring pulmonary artery catheterization.

We performed a randomized, prospective trial to evaluate whether fluid management that emphasized diuresis and fluid restriction in patients with pulmonary edema could affect the development or resolution of extravascular lung water (EVLW), as well as time on mechanical ventilation and time in the intensive care unit (ICU), in critically ill patients requiring pulmonary artery catheterization (PAC). PAC was performed on 101 patients. A total of 52 patients were randomized to an EVLW management group using a protocol based on bedside indicator-dilution measurements of EVLW. The other 49 patients were randomized to a wedge pressure (WP) management group in whom fluid management decisions were guided by WP measurements. A total of 89 patients had pulmonary edema (defined as EVLW greater than 7 ml/kg ideal body weight). Except for a clinically unimportant difference in mean age, the two groups were entirely comparable at baseline. The study groups were managed differently, as evidenced by cumulative input-output of 2,239 +/- 3,695 ml (median = 1,600 ml) in the WP group versus 142 +/- 3,632 ml (median = 754 ml) in the EVLW group (p = 0.001). EVLW decreased significantly, and ventilator-days and ICU days were significantly shorter only in patients from the EVLW group. No clinically significant adverse effect occurred as a result of following the EVLW group algorithm. Thus, a lower positive fluid balance, especially in patients with pulmonary edema regardless of cause, is associated with reduced EVLW, ventilator-days, and ICU days.     

Assessment of the pulmonary volume pulse in idiopathic pulmonary arterial hypertension by means of electrical impedance tomography

BACKGROUND: Electrical impedance tomography (EIT) is a non-invasive imaging technique which can be used to measure the blood volume changes in the pulmonary vascular bed during the cardiac cycle. STUDY OBJECTIVES: This study was performed to evaluate the differences in the EIT signal of the pulmonary vascular bed between healthy subjects and patients with idiopathic pulmonary arterial hypertension (IPAH), who are known to have a remodelled pulmonary vascular bed. PATIENTS AND METHODS: Twenty-one patients (17 females, 4 males) with IPAH and 30 healthy controls (5 females, 25 males) were measured. EIT measurements were performed in duplicate, on the same day as right heart catheterization to obtain haemodynamic data. The maximal impedance change during systole (Delta Z(sys)) was used as a measure of the pulmonary volume pulse and expressed in arbitrary units (AU). Total lung capacity, spirometric values and diffusion capacity for carbon monoxide were measured as well. RESULTS: Mean Delta Z(sys) was 215 +/- 58 x 10(-2) AU (95% CI 193 x 10(-2) to 236 x 10(-2)) in the healthy subjects and 78 +/- 27 x 10(-2) AU (95% CI 66 x 10(-2) to 91 x 10(-2)) in the IPAH patient group (p < 0.0001). No significant correlation was found between Delta Z(sys) and any of the haemodynamic or lung function data. CONCLUSION: The impedance pulsation of the pulmonary vascular bed is reduced in IPAH in comparison with controls, indicating a reduced volume pulse. This might represent the reduced cross section area, as well as the reduced compliance and number of the pulmonary vessels in these patients.     

Electrical impedance tomography is able to track changes in respiratory function in endotoxin-challenged rodents

Background and objective:   In order to assess and optimize the effect of new therapies for acute lung injury (ALI) in rodent models, a monitoring technique that continuously assesses the functional state of the lung is mandatory. Electrical impedance tomography (EIT) has been suggested as a technique for quantifying lung inflammation in ALI. However, EIT has not been evaluated in a rodent model of ALI.
Methods:   EIT measurements were compared in ventilated Sprague–Dawley rats ( n  = 14), randomly subjected to intratracheal administration of endotoxin (LPS) or saline (control). Lung mechanics, lung weight wet/dry ratio and inflammatory markers in bronchoalveolar lavage fluid were also evaluated.
Results:   LPS caused a significant decrease in lung compliance and TLC as compared with control (−42.0%, P  = 0.04, and −27.9%, P  = 0.02, respectively). These changes were paralleled by differences in mean impedance changes as detected by EIT (Spearman's rank correlation coefficient: ρ = 0.66 and 0.73, respectively, P  < 0.01). LPS increased the lung weight wet/dry ratio (6.35 ± 0.42 vs 5.15 ± 0.07, P  = 0.003), and the bronchoalveolar lavage total WCC (8.96 ± 1.87 vs 1.16 ± 0.10 × 10⁹/L, P  = 0.002) as compared with control. The lung weight wet/dry ratio was inversely related to the mean impedance change (ρ = −0.76, P  < 0.01).
Conclusions:   This study has demonstrated for the first time that eight-electrode EIT readily tracks the inflammatory response of lung tissue in a rodent model of ALI. EIT may thus provide a promising, non-invasive technique for monitoring the time-course of ALI in rodent models, and for testing novel pharmacological strategies to counter it.     

Impact of acute respiratory failure on survival of COPD patients managed with long-term non-invasive ventilation and oxygen therapy

Our study aimed to assess the impact of acute respiratory failure (ARF) on survival of patients with chronic obstructive pulmonary disease (COPD) receiving long-term oxygen therapy (LTOT) plus nasal intermittent positive pressure ventilation (NIPPV). Survival was analysed retrospectively in 24 patients with severe COPD initiated to NIPPV in addition to LTOT. Fourteen patients were established on NIPPV following exacerbation of acute respiratory failure which has required mechanical ventilation (group 1). Ten patients (group 2) have never been hospitalized for ARF. Comparison of clinical details at baseline, 6 months, 1, 2, and 3 years for the two groups failed to reveal any difference with the exception of prior episodes of ARF. The probability of survival at 3 years was 65% (95% confidence interval [CI] 43-86) for the overall population, 46% (95% CI 15-77) in group 1, and 74% (95% CI 42-105) in group 2. The difference between the two groups was statistically significant. We show that ARF requiring mechanical ventilation appears to be a factor that is negatively correlated with survival for patients treated by LTOT plus NIPPV. This data suggests that NIPPV should be tried before ARF arising in COPD patients who present a deterioration in chronic respiratory failure with hypercapnia.     

Monitoring patients with left ventricular failure by electrical impedance tomography

Acute left ventricular failure (LVF) is a common medical emergency but detection and monitoring of pulmonary oedema remains problematic. Fluid is an important determinant of tissue impedance. Electrical impedance tomography (EIT) is a non-invasive technique allowing localisation of impedance changes within tissue. We have investigated the relationship between LVF and the electrical impedance of lung tissue. Twenty patients with a clinical diagnosis of acute left ventricular failure were compared with 30 normal subjects. Patients were monitored using serial chest radiographs and electrical impedance tomography measurements of lung impedance during hospital admission. Radiographs were graded according to the severity of pulmonary oedema by two independent radiologists. Lung impedance was significantly (P<0.0001) lower than normal in patients with left ventricular failure. Values returned towards the normal range as LVF resolved. There was a similar improvement in the score of the chest radiographs. The electrical impedance of the lung is low in left ventricular failure and increases following treatment.     

Imbalances in regional lung ventilation: a validation study on electrical impedance tomography

Imbalances in regional lung ventilation, with gravity-dependent collapse and overdistention of nondependent zones, are likely associated to ventilator-induced lung injury. Electric impedance tomography is a new imaging technique that is potentially capable of monitoring those imbalances. The aim of this study was to validate electrical impedance tomography measurements of ventilation distribution, by comparison with dynamic computerized tomography in a heterogeneous population of critically ill patients under mechanical ventilation. Multiple scans with both devices were collected during slow-inflation breaths. Six repeated breaths were monitored by impedance tomography, showing acceptable reproducibility. We observed acceptable agreement between both technologies in detecting right-left ventilation imbalances (bias = 0% and limits of agreement = -10 to +10%). Relative distribution of ventilation into regions or layers representing one-fourth of the thoracic section could also be assessed with good precision. Depending on electrode positioning, impedance tomography slightly overestimated ventilation imbalances along gravitational axis. Ventilation was gravitationally dependent in all patients, with some transient blockages in dependent regions synchronously detected by both scanning techniques. Among variables derived from computerized tomography, changes in absolute air content best explained the integral of impedance changes inside regions of interest (r(2) > or = 0.92). Impedance tomography can reliably assess ventilation distribution during mechanical ventilation.     

Assessment of lung injury in the adult respiratory distress syndrome using multiple indicator dilution curves

To assess its usefulness as an index of lung injury in critically ill patients with respiratory failure, the lung microvascular permeability surface area product for urea (14C-PSu) was measured using a multiple radioisotopic indicator dilution technique in 10 patients with the adult respiratory distress syndrome (ARDS) and in a control population of 5 patients without ARDS. The mean values for 14C-PSu and for extravascular lung water (EVLW) were both significantly elevated in patients with ARDS compared with those in control patients (14C-PSu: 18.7 +/- 4.4 versus 7.6 +/- 0.7, p less than 0.05; EVLW: 676 +/- 55 versus 269 +/- 53, p less than 0.001); 14C-PSu and EVLW were significantly correlated (R = 0.52, p less than 0.001). In the patients with ARDS, 14C-PSu and oxygenation, assessed as the alveolar-arterial oxygen difference, did not appear to be correlated. Repeated measurements of 14C-PSu were variable in the 3 control patients in whom 4 or more measurements were obtained (SD = 50, 57, and 54% of the mean values, respectively); 14C-PSu did not predict clinical outcome assessed by survival of individual patients with ARDS. These data suggest that measurement of 14C-PSu in critically ill patients is a clinically applicable parameter that reflects the degree of microvascular injury in groups of patients. However, our study did not indicate a clear advantage of 14C-PSu over EVLW in assessing lung injury in this patient population. The variability in 14C-PSu control patients also suggests that directional changes in 14C-PSu, as a measure of changes in the degree of lung microvascular dysfunction, should be interpreted with caution.     

Noninvasive vs conventional mechanical ventilation in acute respiratory failure: a multicenter, randomized controlled trial

STUDY OBJECTIVE: Noninvasive mechanical ventilation (NIMV) is beneficial for patients with acute respiratory failure (ARF) when added to medical treatment. However, its role as an alternative to conventional mechanical ventilation (CMV) remains controversial. Our aim was to compare the efficacy and resource consumption of NIMV against CMV in patients with ARF. DESIGN: A randomized, multicenter, controlled trial. SETTING: Seven multipurpose ICUs. PATIENTS: Sixty-four patients with ARF from various causes who fulfilled criteria for mechanical ventilation. INTERVENTION: The noninvasive group received ventilation through a face mask in pressure-support mode plus positive end-expiratory pressure; the conventional group received ventilation through a tracheal tube. MEASUREMENTS AND RESULTS: Avoidance of intubation, mortality, and consumption of resources were the outcome variables. Thirty-one patients were assigned to the noninvasive group, and 33 were assigned to the conventional group. In the noninvasive group, 58% patients were intubated, vs 100% in the conventional group (relative risk reduction, 43%; p < 0.001). Stratification by type of ARF gave similar results. In the ICU, death occurred in 23% and 39% (p = 0.09) and complications occurred in 52% and 70% (p = 0.07) in the noninvasive and conventional groups, respectively. There were no differences in length of stay. The Therapeutic Intervention Score System-28, but not the direct nursing activity time, was lower in the noninvasive group during the first 3 days. CONCLUSIONS: NIMV reduces the need for intubation and therapeutic intervention in patients with ARF from different causes. There is a nonsignificant trend of reduction in ICUs and hospital mortality together with fewer complications during ICU stay.     

Granulocyte colony-stimulating factor-induced capillary leak syndrome confirmed by extravascular lung water measurements

The study purpose was to report the first case of granulocyte colony-stimulating factor (G-CSF)-induced capillary leak syndrome (CLS) in which serial extravascular lung water (EVLW) measurements were performed and to compare this case with previously reported cases. To identify previously reported cases, we performed a literature search, using PubMed with the following search terms: CLS, EVLW, G-CSF, granulocyte-macrophage colony-stimulating factor (GM-CSF) and stem cell transplantation and the references in the bibliographies of the papers retrieved. To obtain additional information about these cases, we contacted the authors by e-mail. We describe the case of a 68-year-old woman who developed severe CLS during G-CSF treatment after autologous haematological stem cell transplantation. CLS is caused by damage to the endothelial cells, resulting in extravasation of plasma proteins and fluid from the capillaries into the extravascular space. This is illustrated by high values of EVLW and pulmonary vascular permeability, necessitating mechanical ventilation. We found five other case reports in the literature. The white blood cell count at the onset of the CLS varied from very low (zero) to very high (90,500/l). The symptoms began on day 5–9 of the G-CSF treatment. All patients had fever. Three patients were mechanically ventilated and four received renal replacement therapy. Two patients died. Treatment with G-CSF can induce fatal CLS. Monitoring of EVLW in patients with severe CLS may be useful to guide fluid therapy and improve oxygenation.     

有创呼吸支持技术的进展与挑战

有创呼吸支持技术作为挽救危重症患者生命的重要生命支持手段之一,临床上通过动态观察反映肺应力的驱动压和跨肺压指标,评价肺的应变。并应用新的监测手段,如重症超声、电阻抗等,建立个体化动态评价有创呼吸支持的临床解决方案,指导肺保护性通气、呼气末正压(PEEP)滴定、肺复张、俯卧位通气、体外膜肺氧合等呼吸支持技术,在有效改善危重症患者有效氧合的同时尽量减少有创通气的副作用。     

Effect of crystalloid resuscitation and inhalation injury on extravascular lung water: clinical implications

STUDY OBJECTIVE: Arterial thermal dilution with an integrated fiberoptic monitoring system (COLD Z-021; Pulsion Medical Systems; Munich, Germany) allows measurement of extravascular lung water (EVLW) and pulmonary permeability index (PPI). The aim of this study was to evaluate the widespread clinical assumption that early respiratory failure following burn and inhalation injury is due to interstitial fluid accumulation in the lung. DESIGN: Clinical, prospective study. SETTING: ICU of a university referral center of burn care. PATIENTS: Thirty-five severely burned adults (> 20% of body surface area). INTERVENTIONS: Resuscitation therapy was guided by the results of hemodynamic monitoring using the intrathoracic blood volume (ITBV) as a cardiac preload indicator. The resuscitation goals included a normalization of preload (ITBV > 850 mL/m(2)) and cardiac index (> 3.5 L/min/m(2)) within 24 h after ICU admission. Fluid loading was implemented to reach these goals. MEASUREMENTS AND RESULTS: One hundred forty lung water measurements were performed at 0 h, 12 h, 24 h, and 48 h after admission to the ICU. Significant elevation of EVLW and PPI was found in three measurements (2%) at 48 h after ICU admission, and was in one patient associated with inhalation injury. EVLW and PPI were not significantly different between patients with and without inhalation injury. No correlation was found between resuscitation volume and EVLW (r(2) = 0.02) or between the alveolar-arterial oxygen pressure difference and EVLW (r(2) = 0.017). Chest radiograph abnormalities were found in 2 of 22 patients with inhalation injury; these were not associated with increased values of EVLW. CONCLUSION: Early fluid accumulation in the lung in burned patients is very uncommon, even in the presence of inhalation injury. There is no evidence that thermal injury causes an increase in pulmonary capillary membrane permeability.     

Lung function tests in neonates and infants with chronic lung disease: global and regional ventilation inhomogeneity

This review considers measurement of global and regional ventilation inhomogeneity (VI) in infants and young children with acute neonatal respiratory disorders and chronic lung disease of infancy (CLDI). We focus primarily on multiple-breath inert gas washout (MBW) and electrical impedance tomography (EIT). The literature is critically reviewed and the relevant methods, equipment, and studies are summarized, including the limitations and strengths of individual techniques, together with the availability and appropriateness of any reference data. There has been a recent resurgence of interest in using MBW to monitor lung function within individuals and between different groups. In the mechanically ventilated, sedated, and paralyzed patient, VI indices can identify serial changes occurring following exogenous surfactant. Similarly, global VI indices appear to be increased in infants with CLDI and to differentiate between infants without lung disease and those with mild, moderate, and severe lung disease following preterm birth. While EIT is a relatively new technique, recent studies suggest that it is feasible in newborn infants, and can quantitatively identify changes in regional lung ventilation following alterations to ventilator settings, positive end expiratory pressure (PEEP), and administration of treatments such as surfactant. As such, EIT represents one of the more exciting prospects for continuous bedside pulmonary monitoring. For both techniques, there is an urgent need to establish guidelines regarding data collection, analysis, and interpretation in infants both with and without CLDI.     

Noninvasive Assessment of Gastric Acid Secretion in Man (Application of Electrical Impedance Tomography (EIT))

Electrical impedance tomography (EIT) is atubeless technique that generates tomographic images ofgastric resistivity. We investigated the application ofEIT to measure gastric acid secretion. Nineteen normal subjects underwent a standard intubationtest. Basal acid output (BAO) and stimulated acid output(SAO) (millimoles per hour) were measured before andafter pentagastrin, respectively. On a different day, EIT was performed before (basal) and afterpentagastrin (stimulated). The changes in impedance overtime were measured and the area under the curve (AUC)was calculated. Both the tests were repeated in 13 subjects after omeprazole treatment. Asin the intubation test, there was the expected increasein AUC value after pentagastrin (basal vs stimulated;1.2 ± 2.8 vs 731 ± 297, P < 0.0001). Asignificant fall in acid output and AUC following omeprazolepretreatment was observed (without vs with omeprazole;20.5 ± 5.7 vs 0.03 ± 0.06, P < 0.0001for intubation test and 731 ± 297 vs 44 ±172, P < 0.0001 for EIT). There was a significant correlation between SAO and theAUC with (r = 0.65 P < 0.001) or without (r =0.95, P < 0.001) omeprazole and in all theexperiments (r = 0.87, P < 0.001). This studydemonstrates the predictable change of gastric impedance and may be useful as anoninvasive test for measuring gastric acidsecretion.